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Examination of the mineralogical effects of biologically-assisted leaching of a mixed copper sulphide… Melluish, Julie Marguerite 1994

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EXAMINATION OF THE MINERALOGICAL EFFECTS OF BIOLOGICALLY-ASSISTEDLEACHING OF A MIXED COPPER SULPHIDE ORE FROM THE IVAN MINE, CHILEbyJULIE MARGUERITE MELLUISHB. Sc. (Honours), Queen’s University, Kingston, 1985A THESIS SUBMITTED iN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinTHE FACULTY OF GRADUATE STUDIES(Department of Geological Sciences)We accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAJuly, 1994© Julie M. Melluish, 1994In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature)Department of 7/(ZJ ‘l(11CC5The University of British ColumbiaVancouver, CanadaDate /DE-6 (2/88)11ABSTRACTA mineralogical and biohydrometallurgical study of a mixed copper-sulphide ore from the Ivan Mine nearAntofagasta in northern Chile was conducted by a multidisciplinary group at the University ofBritishColumbia. The purpose of the mineralogical study was to establish an understanding of current knowledgeregarding biologically-assisted leaching, especially as it relates to the solids involved, while supplyingmineralogical support for the metallurgical experiments. An extensive review of bioleaching, a briefdescription of the Ivan Mine, a summary of the metallurgical experiments, a discussion of results fromcomputer modeling of a column leach experiment, a report of the results from a detailed mineralogicalstudy of the solid residues from two of the column experiments, and suggestions for future studies areincluded in this work.Bacteria that utilize energy derived from oxidation of reduced iron and/or sulphur species play an importantrole in the leaching of copper suiphides by catalizing specific reactions. Although much is known about theleaching process current understanding of the interactions between these bacteria and the solids in thesystem is incomplete.The simulation of a colunm leach experiment using the computer program PATH supplied useful insightsinto the chemical processes occurring. Although the overall column reaction was studied here, a modelingprogram such as this is useful for examining possible reactions in microenvironments within the columns.Detailed mineralogical examination of the solid residues from two of the column experiments revealedseveral interesting features. The insoluble precipitates forming in the column are jarosite, a non-crystallineiron-phosphate (possibly strengite), and a non-crystalline iron oxide-sulphate (possibly schwertmannite).These precipitates generally occur in porous particle coatings scattered with silicate mineral grains. Theleached particles commonly exhibit an increase in the number of veins, voids, and regions of porous silicatealteration, predominantly in rims up to 500 ji.m thick. Larger veins and regions of porous silicate alterationexpose the interiors ofmany particles to the leach solution. Bornite and anilite appear to alter to covellitebefore solubilizing. Dissolution of covellite and large chalcopyrite grains (commonly aggregates) occursalong grain boundaries sometimes leaving a porous crust of elemental sulphur.111TABLE OF CONTENTSPageABSTRACT iiTable of Contents iiiList of Tables viiList of Figures xACKNOWLEDGEMENT xii1. INTRODUCTION 12. THE IVAN MINE: SITE OF PROPOSED HEAP LEACHING 22.1 Geologic Setting 52.2 The Orebody 52.3 Mineralogy of the Orebody 62.4 Proposed Project 63. REVIEW OF BIOHYDROMETALLURGICAL LEACHING OF COPPER-BEARING 8SULPHIDE ORES3.1 The Bacteria 93.1.1 General Description ofMetal Solubilizing Bacteria 113.1.2 Thiobacillusferrooxidans 143.1.3 Thiobacillus thiooxidans 153.1.4 Other Microorganisms Involved in Metal Suiphide Solubilization 173.2 Reactions Involved in Microbially Assisted Leaching 193.2.1 Microbially Catalyzed Reactions 193.2.2 Chemical Reactions 243.2.3 Galvanic Effects 273.3 Character of Typical Solid Residues 293.3.1 Alteration ofMetal Sulphides 31Chalcopyrite 31Pyrite 32Chaicocite 33Bornite 333.3.2 Alteration of Silicates in the Ore Matrix 34Feldspars 34Micas and Various Other Phyilosilicates 373.3.3 Precipitates 41Ferric Iron Species 42Water Soluble Secondary Suiphates 443.3.4 Geometry of Ore Particle Degredation 453.4 Bioleaching Experiments 483.4.1 Bacterial Requirements 493.4.2 Shake Flask Experiments 513.4.3 Column Experiments 52iv4. EXPERIMENTAL BIOHYDROMETALLURGICAL LEACHING OF 54IVAN MINE ORE4.1Shake Flask Experiments 544.1.1 Basic Experimental Procedure 544.1.2 The Original Bacterial Cultures 554.1.3 Variations in Leaching Conditions 564.1.4 Results of Leaches 564.1.5 The Banks 584.2 Column Leach Experiments 584.2. 1 Basic Experimental Procedure 584.2.2 Experimental Conditions 634.2.3 Results of Column Experiments 635. MODELLING OF COLUMN LEACHING USING THE COMPUTER 66PROGRAM PATH5.1 The Program 665.2 Conditions 685.2.1 Reactants 685.2.2 Aqueous Phase 715.2.3 Thermodynamic Data 725.3 Results 725.3.1 Change in the Mass of Solids 74Silicate Reactants 74Metallic Reactants 74Products 765.3.2 Change in the Activities of Aqueous Species 795.4 Discussion 825.4.1 The Precipitates 83Jarosite and Goethite 83Amorphous Quartz 84C½aicanthite 845.4.2 Program Limitations 84The Thermodynamic Database 84Reaction Kinetics 85Data Output 855.4.3 Final Note 866. TECHNIQUES USED FOR THE MINERALOGICAL EXAMINATION OF 88THE IVAN ORE SAMPLE AND THE SOLID LEACH RESIDUES6.1Sample Types, Sampling Methods, and Special Sample Preparation Techniques 886.1.1 Unleached Ivan Ore 886.1.2 Evaporites 906.1.3 Precipitates 916.1.4 Leached Ore Particles 91V6.2 Analytical Techniques 926.2.1 Optical Microscopy 926.2.2 Sieve Analysis 946.2.3 Powder X-ray Diffraction 946.2.4 Secondary Electron Microscopy with Energy Dispersive Spectrometry 946.2.5 Automated Image Analysis 966.2.7 Wet Chemical Analyses 967. DISCUSSION OF THE RESULTS FROM THE MINERALOGICAL 97EXAMINATION7.1 Unleached Ore 977.1.1 Mineralogy 97Silicates 100Apatite 103Oxides 103Suiphides 103Alteration of the Silicate Matrix 1117.1.2 The Crushed Sample 1117.2 Evaporites 1157.3 Precipitates 1227.3.1 Mineralogy 1247.3.2 Habit 1277.3.3 Distribution 1337.4 Leached Ore Particles 1397.4.1 Changes in the Silicate Matrix 139Veins and Open Voids 139Silicate Alteration Product 1467.4.2 Sulphide Mineral Degredation 1527.5 Bacteria 1597.6 Summary 1598. CONCLUSIONS AND RECOMMENDATIONS 1619. REFERENCES 166APPENDIX A List ofmicrobiological terms used in section 3.1 178APPENDIX B Flow charts illustrating the serial transfers performed in the shake flask 180experiments in order to test and adapt Type A, B, and C bacterial culturesAPPENDIX C Calculations of input data for the column 4 simulation and full equations 185established from resulting dataAPPENDIX D List of samples along with, where applicable, the sample preparation 191and mineralogical examination techniques usedAPPENDIX E Data collected using automated image analysis techniques 198viAPPENDIX F Electron probe microanalyses of albite, muscovite, chlorite, hematite, 201magnetite, chalcopvrite, bornite, anilite, and covelliteAPPENDIX G Descriptions of the precipitates observed in cross-sections of individual 215leached particles using reflected light microscopyAPPENDIX H Descriptions of the cross-sections of individual leached particles using 229reflected light microscopyviiLIST OF TABLESPage2.1 Average composition of the Upper and Lower Desesperado groundwaters 43.1 A list of the principle elements found in bacteria, their typical relative distribution, 11and their physiological functions3.2 Inhibitory levels of certain metals compared to maximum concentrations observed 15in bioleaching3.3 Bacterial species potentially involved, either directly or indirectly, in metal sulfide 17solubilization3.4 Reactions involved in the bioleaching of various copper-bearing suiphides and pyrite 193.5 Electrochernical series of some iron- and copper-bearing suiphide minerals in an 26H2S04solution with a pH of 2.53.6 Formulae for important minerals discussed in section 3.3 283.7 Several proposed culture media 484.1 List of shake flask tests and experimental conditions 574.2 Experimental conditions for the column leach experiments 635.1 Experimental conditions for the column 4 experiment 675.2 Inital conditions used for column 4 modelling 695.3 Minerals added or removed from the thermodynamic database 705.4 Highlights of the column 4 simulation 735.5 Mass change of silicate reactants during the simulation 756.1 Sample types, preparation methods, and analytical techniques used 896.2 Sieves used in size analysis of the -12.7 mm unleached ore 957.1 Typical compositions of the silicate minerals present in the unleached Ivan ore 1007.2 Typical compositions of oxide minerals present in the unleached Ivan ore 1027.3 Typical compositions of the suiphide minerals present in the unleached Ivan ore 1037.4 Ideal Cu:Fe and (Cu+Fe) :S ratios for copper and copper/iron sulphide minerals 1047.5 Size distribution of particles in the -12.7 mm crushed sample 1127.6 Chemical analyses of unleached Ivan ore including analyses of individual size fractions 112and calculated distribution in the whole sample7.7 List of evaporite minerals forming crusts on the exterior of the column experiments 115organized into groups with similar habits7.8 Minerals identified in the evaporite samples using powder x-ray diffraction techniques 1167.9 Distribution of precipitate morphologies based on mineralogical examination of polished 133particle cross-sections7.10 Summary of observations made of changes to the silicate matrix based on 139mineralogical examination of polished particle cross-sections7.11 Summary of observations with respect to sulphide mineral degredation based on 140mineralogical examination of polished particle cross-sectionsAppendix AA-i List ofmicrobiological terms used in section 3.1 179viiiAppendix CC-i Calculation of volume% and weight% estimates for initial conditions 186C-2 Calculation of reaction rates for the reactants 187C-3 Calculation of the theoretical solution chemistry due to addition of the 9K salts 188C-4 The theoretical composition of the column 4 leach solution on Day 0 of the experiment 189Appendix DD- 1 The unleached ore samples examined in the mineralogical study 192D-2 The evaporite samples examined in the mineralogical study 194D-3 The solid leach residues examined in the mineralogical study 195Appendix EE- 1 Distribution of minerals in each size fraction and in the whole sample (minus the 199-45 micron fraction which represents 0.78 weight% of the sample)E-2 Relative distribution ofminerals in the whole sample (minus the -45 micron fraction 199which represents 0.78 weight% of the sample)E-3 Grain size distribution versus shape factor (minimum diameter/maximum diameter) 200distribution for chalcopyriteE-4 Grain size distribution versus shape factor (minimum diameter/maximum diameter) 200distribution for the anilite/covellite/bornite groupAppendix FF-i Electron probe operating conditions for silicate and oxide minerals 202F-2 Electron probe operating conditions for suiphide minerals 203F-3 Electron probe microanalyses of feldspar 204F-4 Electron probe microanalyses ofmuscovite 207F-5 Electron probe microanalyses of chlorite 208F-6 Electron probe microanalyses of hematite 209F-7 Electron probe microanalyse ofmagnetite 211F-8 Electron probe microanalyses of chalcopyrite 211F-9 Electron probe microanalyses of bornite 212F- 10 Electron probe microanalyses of anilite 213F-il Electron probe microanalyses of covellite 214Appendix GG- 1 General description of the various precipitate types based on SEM/EDS examinations 216G-2 Descriptions of the precipitates observed in column 2, 15 cm (6 inches) below the top 217G-3 Descriptions of the precipitates observed in column 2, 45 cm (1’6”) below the top 218G-4 Descriptions of the precipitates observed in column 2, 75 cm (2’6”) below the top 219G-5 Descriptions of the precipitates observed in colunm 2, 105 cm (36”) below the top 220G-6 Descriptions of the precipitates observed in colunm 2, 135 cm (4’6”) below the top 221G-7 Descriptions of the precipitates observed in column 4, 15 cm (6 inches) below the top 222G-8 Descriptions of the precipitates observed in column 4, 45 cm (1’6”) below the top 223G-9 Descriptions of the precipitates observed in column 4, 75 cm (2’6”) below the top 224G-10 Descriptions of the precipitates observed in column 4, 105 cm (36”) below the top 226G-i 1 Descriptions of the precipitates observed in column 4, 135 cm (46”) below the top 227ixAppendix HH-i Description of the changes in the leached particles from column 2, 15 cm (6 inches) 230below the top.H-2 Description of the changes in the leached particles from column 2, 45 cm (1 ‘6”) 232below the top.H-3 Description of the changes in the leached particles from column 2, 75 cm (2’6”) 235below the top.H-4 Description of the changes in the leached particles from column 2, 105 cm (3’6”) 237below the top.H-5 Description of the changes in the leached particles from column 2, 135 cm (3’6”) 239below the top.H-6 Description of the changes in the leached particles from column 4, 15 cm (6 inches) 241below the top.H-7 Description of the changes in the leached particles from column 4, 45 cm (1’6”) 243below the top.H-8 Description of the changes in the leached particles from colunrn 4, 75 cm (2’6”) 245below the top.H-9 Description of the changes in the leached particles from column 4, 105 cm (3’6”) 247below the top.H- 10 Description of the changes in the leached particles from column 4, 135 cm (4’6”) 249below the top.xLIST OF FIGURESPage2.1 Site of the Ivan Mine project 33.1 Illustration of the galvanic mechanism using the pyrite/chalcopyrite system 263.2 Residual layer on the walls of an etch pit in albite 343.3 Illustration of a typical mica structure (muscovite) 373.4 Illustration of the possible morphology of ore particle degredation and suiphide mineral 45solubilization3.5 Characteristic bacterial population growth curve under laboratory conditions 514.1 Comparison of copper extraction curves for experiments using three culture types 594.2 Comparison of copper extraction curves for experiments using 9K and OK nutrients 594.3 Comparison of copper extraction curves for experiments using 4 and 8 g of ore 604.4 Schematic diagram illustrating the basic setup of the six column experiments 604.5 Copper extraction results for the six column experiments 634.6 Photograph of columns during a draining cycle 655.1 Change in mass of the metallic reactants during the simulation 755.2 Change in mass of products during the simulation 775.3 Detail of the above figure 775.4 Change in the activities of the dominant aqueous species 815.5 Change in the activities of other abundant aqueous species 816.1 Preparation of polished mounts 937.1 Mineral distribution in the unleached Ivan ore sample based on image analysis data 987.2 X-ray diffractogram of the bulk unleached Ivan ore sample 987.3 Grain size distribution of chalcopyrite in the unleached Ivan ore sample 1067.4 Grain size distribution of the anilite/covellite/bornite mineral group in the unleached 106Ivan ore sample7.5 Typical sulphide textures in the unleached ore 1077.6 Evidence of primary solution penetration in unleached ore 1107,7 Morphology of common evaporite minerals found at the tops and bottoms of the 117acrylic tubes, outside the columns of ore7.8 Evaporite sample taken before the addition of 9K salts 1197,9 The solid residues removed from columns 2 and 4 after termination of the 121leach experiments7.10 Detail of a typical XRD analysis of fines sampled from solid residues of a column 123leach test7.11 Typical non-crystalline iron-bearing precipitates observed in the two columns 1247.12 Typical jarosite textures 1267.13 Typical botryoidal mixtures of iron oxide-sulphate and iron phosphate 1287.14 Less common habits exhibited by the non-crystalline iron phases 1297.15 Sites where precipitates are typically found 1297.16 XRD analyses of fines from columns 2 and 4 1327.17 XRD analyses illustrating the change in fines after bioleaching 138xi7.18 Typical changes to the silicate matrix 1417.19 Typical chemistry and morphology of the silicate alteration product found in the 146leached particles7.20 Other interesting features exhibited by the silicate alteration product 1487.21 Alteration of anilite and initial dissolution of covellite 1527.22 Further dissolution in covellite grains 1547.23 Examples of chalcopyrite dissolution 1567.24 Unusual particles thought to be renmants of bacteria 158Appendix BB-i Illustration of the serial transfers done using the Type A bacterial culture from Bacon, 181Donaldson & Associates Ltd., CanadaB-2 Illustration of the serial transfers done using the Type B bacterial culture from Bacon, 182Donaldson & Associates Ltd., CanadaB-3 Details of the new Type B series 183B-4 Illustration of the serial transfers done using the Type C bacterial culture from Bacon, 184Donaldson & Associates Ltd., CanadaAppendix CC-i The full equations given as partial equations in the text of Chapter 5 190xiiACKNOWLEDGMENTSI would like to thank the many people involved in this project. I am grateful to my supervisor, Dr. LeeGroat, for supporting this foray into a new and exciting field and for helping me to spread the word. Iwould also like to thank the other members of the ‘Rayrock group’, Dr. Dave Dreisinger, Dr. RichardBranion, Dr. Lynton Gormely, Brenna Leong, Ralph Hack!, and the two people who diligently maintainedthe columns, Anita Lam and Harold Eng. Thanks go also to David Crombie and Rayrock YellowknifeResources Inc. for initiating and supporting the project. Funding was also provided by the Natural Scienceand Engineering Research Council (NSERC). I am also grateful to Dr. Rolando Lastra of CANMET(Department of Energy Mine and Resources) for allowing me to use the automated image analysis systemin Ottawa.Finally, I would like to thank my husband, Rory McIntosh, for helping me to keep things in perspective, forsupporting my academic endeavors, and, most of all, for his patience.11. INTRODUCTIONIn his presidential address to the Mineralogical Association of Canada (Hawthorne, 1993), Prof. F.C.Hawthorne stated that important areas for future research include biological/mineralogical interactions atsurfaces, mineralogical aspects of acid rock drainage, and process mineralogy. This study was conceivedas an introduction to these areas of research, which have been largely ignored by mineralogists.The study began when a multidisciplinary group of researchers from the University of British Columbiaformed a working group to investigate the opportunities available for research in the field of acid rockdrainage. The Ivan mine project was a result of adapting this interest to a hydrometallurgical problem.Minera Rayrock Ltd. wanted to assess the possibility of heap leaching the suiphide zone of a mine, the Ivanmine, located near Antofagasta, in northern Chile. One of the local water supplies is highly saline and thecompany wanted to determine if bacteria, which are necessary for efficient suiphide mineral extraction,could be adapted to saline conditions, and, if so, whether a heap leaching process that used these adaptedbacteria would be economical. Since many of the processes that occur under bioleaching conditions arevery similar to those occurring in acid mine drainage sites, this project gave the group an opportunity tobecome more familiar with the acid mine drainage problem while also collecting data important to theindustrial partner.The purpose of the mineralogical component of the Ivan mine project was to establish an understanding ofcurrent knowledge regarding bioleaching, especially as it relates to the solids involved, while supplyingmineralogical support for the metallurgical experiments. In order to achieve this several different studieswere undertaken. These include an extensive review of bioleaching , computer modeling of a column leachexperiment, and a detailed mineralogical study of unleached ore, soluble crusts, insoluble precipitates, andleached particles. All these studies are discussed in the following document. A brief description of the Ivanmine and a summary of the metallurgical experiments have also been included.It is hoped that this study will address some of Dr. Hawthorne’s suggestions and inspire further work in theoverlapping fields of biological/mineralogical interactions, acid rock drainage, and process mineralogy.22. THE IVAN MINE: SITE OF PROPOSED HEAP LEACHINGThe Ivan Mine, a volcanoclastic-hosted supergene-enriched copper oxide and suiphide deposit, is situatedin the Atacama desert of northern Chile, approximately 35 km northeast of the coastal city ofAntofagasta(Figure 2.1). The mine site is easily accessible by road. Furthermore, railroad and power lines passnearby.The area is extremely arid with an average annual precipitation of less than 3 mm. Rainfall occurs rarely;however, fog from the sea is common. Temperatures range from 15 to 25°C. Flora and fauna are virtuallynon-existent.Fresh water is piped into Antofagasta from the mountainous region to the east; however, groundwaterexploration in the Quebrada El Desesperado surface drainage area was undertaken by Errol L.Montgomery & Associates, Inc. (1990) to search for a more affordable water source for the mineoperations. Two aquifers, designated upper and lower Desesperado basins, were delineated duringexploration. The aquifers are located approximately 10 km west of the mine site (Figure 2.1) in basin filldeposits. It is believed that groundwater recharge does not occur in this region and that these aquiferscontain residual waters only. Both aquifers are very saline with average chloride-contents of 11 and 24 g/Lfor the upper and lower basins, respectively (Table 2.1). Results of pumping tests indicate that the twoaquifers contain adequate accessible water to meet the requirements of the proposed heap leachingoperation.To date, ore has been extracted from pits and underground workings by several small mining operations.Underground workings reach to a depth of about 135 m. Approximately 200,000 tonnes of oxide oregrading 2% copper was produced prior to 1984. A further 20,000 tonnes of suiphide ore grading 5.5%copper were removed from 1984 to 1987. Results of exploration by Minera Rayrock Ltda. indicates thatproven and probable copper reserves are currently over 2 million tonnes with an average copper-content of1.7% for oxides and 4.6% for sulphides (Kilbom Inc., 1991).3MEJILLONESpower substation)MINA IVANMANTOSB LAN C OSANTOFAGASTA(population 250,000) paved road- dirt road1111111111111 railroad—w---— power lineaquifers10 15 20kmFigure 2.1: Site of the Ivan Mine project. (After Hunt and Marquardt, 1987)4Table 2.1: Average composition of the Upper and Lower Desesperado groundwaters compared toseawater. Note the high chloride contents. Units are gIL. (After Errol L. Montgomery &Associates, Inc., 1990)Lower Basin Upper Basin Seawateracalcium 3.72 2.5 0.41magnesium 0.50 0.15 1.29sodium 10.59 4.55 10.76potassium 0.25 0.12 0.40silica 0.01 0,01 0,01bicarbonate (as CaCO3) 0.04 0.05 0.14chloride 23.64 10.95 19.00sulphate 1.68 1.33 2.70nitrate 0.21 0.06 <<0.01<<0.01 <<0.01 <<0.0147,52I 2156b 35.00orthophosphatetotal dissolved solidsafrom Goldberg et al. (1971)ban average of analyses given by Errol L. Montgomery & Associates, Inc. (1990). Any discrepencybetween these values and totals for the constituants reflects discrepencies in the data from Montgomery.5Information in this chapter has been reported previously by Vivanco (personal communication), KilbornInc. (1991), Micon International Limited (1990), Errol L. Montgomery & Associates, Inc. (1990), andHunt and Marquardt (1987).2.1 Geologic SettingThe mine is situated in the southern part of the locally-named El Desesperado Mining District which islocated in the coastal range of northern Chile. This is a very active and emergent continental margin.Numerous northeasterly and northerly trending faults have, in the past, deformed this region and continueto show movement today.The El Desesperado District is located in the southern part of a belt of andesite- and diorite-hosted copperdeposits extending from Tocopilla to Antofagasta. Other mines located in this 150 km long belt includeMantos Blancos, Carolina de Michilla, and Buena Esperanza. The mines lie in the “La Negra” formation,a section of continental andesitic rocks associated with basic intrusives (diorites and gabbros). These rocksare believed to be Jurassic in age. To the west of this formation lie older granites and schists. To the eastlie younger andesites.The El Desesperado District lies along the western and southern margin of a dioritic batholith 15 by 50 kmin size. The andesites in the district strike north to northeast and dip gently to the west. Coppermineralization occurs in a belt along the margin of a dioritic stock extending into the andesitic rocks for 1-2km. Copper mineralization has been observed along faults and in associated breccias.2.2 The OrebodyThe Ivan orebody is located near the top of a volcano-clastic andesite section. The andesitic rocks consistof flow breccias, mud flows, andesitic sandstones, and conglomerates. More massive and porphyriticandesite flows overly this section. Numerous faults along with small diorite and andesite intrusives arelocated near and within the deposit.6The orebody is tabular in form with a true width of from 20 to 40 ni. It strikes in a northwest-southeastdirection, dipping 70 degrees to the west. The tabular form appears to plunge steeply to the southeast to atleast 300 m below the surface.Partial oxidation and, possibly, leaching has occurred. Uneven secondary enrichment is present to depthsof 200 m. Suiphide minerals begin to appear at about 100 m below the surface.Associated walirock alterations are not well understood. Epidote and a pink mineral identified asmicrocline are present in the footwall of the orebody. A “pink alteration” of rock clasts found in high grademineralized breccias has been observed. It is believed that this alteration is some form of silicification withor without albitization andlor sericitization associated with fme-grained hematite.2.3 Mineralogy of the OrebodyThe copper mineralization occurs as veins, seams, pods, and disseminations in the fragmented andesiticrock. The iLjor copper-bearing minerals in the core of the orebody are secondary chalcocite and, to alesser extent, primary bornite. They occur as coarse grains in breccia matrix, in a stockwork texture, andas disseminated grains. Chalcopyrite-rich ore occurs in a narrow irregular shell around this core. Minor totrace covellite occurs locally throughout the orebody (Vivanco, personal communication). Pyrite is rarewithin the orebody but occurs as an irregular shell outside the chalcopyrite zone.The zone of oxidation generally extends to approximately 100 m below the surface: however, it does locallyextend to approximately 200 m at the outer edge of the orebody. The major copper-bearing oxides areatacamite and chrysocolla. Minor amounts of native copper, goethite, and hematite have also beenobserved. These minerals occur in stockwork and disseminated textures. Regions of primarilydisseminated and stockwork goethite and hematite only are also present in the periphery of the orebody.2.4 Proposed ProjectRayrock Minera Ltda. proposed to recover the copper from the Ivan Mine using heap leaching techniques.There are several advantages to using hydrometallurgical rather than pyrometallurgical techniques for7metal recovery (Lundgren et at., 1986). These include: (1) metal from low grade ores (as well as highgrade ores) can be recovered economically; (2) energy requirements are lower; (3) the resulting product ismore economically processed (cementation or electrowinning), producing a relatively pure metal; and (4)there are fewer and more controllable potential environmental hazards. Although the ore is not consideredlow grade (on average 4.6% Cu in the sulphide ore), the lower energy requirements for extraction andconcentration improve the economic viability of the mine. In particular, the production of a pure coppermetal rather than copper concentrate (the result of using conventional flotation techniques) allows Rayrockto avoid the currently difficult and expensive task of selling the product to a smelter. Furthermore,difficulties with processing both oxide and suiphide ore are overcome. Separate heap operations will beestablished for the two ores but the same equipment can be used to process the leach solution of bothoperations.Unfortunately, copper-bearing suiphides do not leach as readily as their oxide counterparts (Murr, 1980).Rayrock wished to investigate biologically assisted leaching to see if that would improve the recovery ratefrom their sulphide ore. There are numerous examples of successful commercial facilities usingbioleaching to recover copper from sulphide ores (Rossi, 1990); however, each ore reacts differently. Aseries of experiments to determine the amenability of the Ivan Mine ore to bioleaching were undertaken. Inaddition, experiments were done to determine the optimum conditions for bioleaching this ore. Numerousfactors that could effect the leaching were examined and will be discussed generally in Chapter 3 and inmore detail in Chapter 4.83. REVIEW OF BIOHYDROMETALLURGICAL LEACHING OF COPPER-BEARINGSULPHIDE ORESBiohydrometallurgy has been defined by Rossi (1990) as a “branch of biotechnology dealing with the studyand application of the economic potential of the interactions between the microbial world and the mineralkingdom”. It interests all those involved in mineral exploitation and environmental protection, includingmetallurgists, mining engineers, geologists, geochemists, hydrologists, chemists, and microbiologists. Inthis chapter applications to mineral exploitation, with particular emphasis on copper-bearing suiphides, willbe examined. However, it is worth noting that much of the theory is also relevant to environmentalprotection interests, especially those connected to the mining industry. Note also that a few of the termsused in this chapter may be unfamiliar to some. Many are defined in the text when first used; however,their definitions are also given in Appendix A.Hydrometallurgical copper recovery has its origins in ancient times. Writings by the Chinese king Liu-Anin the second century B .C. refer to the cementation of copper, that is converting iron to copper in a bluesolution (Dun Pu, 1982). In the first and second centuries A.D. there are references to fairly elaborate insitu leaching operations in Spain and Cyprus (C. Plinii Secundi, 1988; Koucky and Steinberg, 1982). Bythe eleventh century A.D. in situ copper leaching and recovery by cementation using iron had becomecommon practice in China (Dun Pu, 1982). In both Europe and China no new developments in thetechnology occurred during the Middle Ages, probably because more economic pyrometallurgicaltechniques were developed (Rossi, 1990). The first records of heap leaching were written in 1752,referring to the Rio Tinto mine in Spain (Gerbella, 1940). Heaps of crushed ore and cut wood lying onimpervious ground were set alight and then water was percolated through them. The solution was collectedat the base of the heaps and the copper removed. Roasting was discontinued at Rio Tinto in 1888 butleaching continued until the 1970’s (Taylor and Whalen, 1943/1942). Interestingly, during this time periodthe techniques used at Rio Tinto were not applied to other low grade copper deposits. It was felt that, asVan Arsdale (1953) stated, “the success of this process was supposed to be due to some obscure andmysterious quality either of the Rio Tinto ore or of the Spanish climate”.It wasn’t until the early 1950’s that this “mysterious quality” was discovered by Colmer, Temple, andHinkle (Colmer et at., 1950; Temple and Colmer, 1951). They isolated from coal drainage waters a9bacterium that derived its energy from oxidation of inorganic compounds and derived its carbon from CO2.Because of its ability to catalyze the oxidation of iron, the bacteria was later named Thiobacillusferrooxidans. As early as 1838 (Ehrlich, 1981) scientists were recognizing microorganisms that interacteddirectly with the lithosphere; however, it wasn until the discovery of this iron (and sulphur) oxidizingbacteria that interest in metal sulphide solubilization, and therefore metal extraction applications,developed. In 1963, RazelI and Trussell confirmed that these bacteria catalyzed the solubilization ofcopper from a sulphide ore. Since then a great deal of experimental work in the field of bioleaching hasbeen done. Not only has our understanding of the processes involved been clarified but othermicroorganisms involved in the solubilization of minerals, including metal suiphides, have been discovered.In the following sections the current understanding of various aspects of biohydrometallurgical leaching ofcopper sulphides will be discussed. The topics include a description of the bacteria, a discussion of thereactions involved in the leaching process, an examination of the current knowledge regarding the nature ofsolid leach residues, and a description of the methods used in bioleaching experimentation. A list of termsused in this chapter that may not be familiar to geologists is given in Appendix A along with definitions.All these terms are also defined within the text when they are first used.3.1 The BacteriaIt is generally accepted that the association between microorganisms and the Lithosphere is both complexand very intimate. Microorganism have played and still do play a role in geological and geochemicalprocesses such as rock weathering, soil formation, metal accumulation, and inorganic compound formation(and degradation). It is not surprising then that microorganisms are found in mineral deposits, both naturaland man-made, and associated aqueous systems. Many of these microorganisms interact with sulphurand/or various metals found in these environments. Because of the obvious economic interest, muchresearch has concentrated on bacteria involved in solubilization of base metal sulphides. Thiobacillusferrooxidans and, to a lesser extent, Thiobacillus thiooxidans are the main microorganisms believed to beinvolved in this process (Lizama and Suzuki, 1989; Ingledew, 1986; Norris and Kelly, 1982;). However,it has been recognized that environments in which suiphide mineral solubilization is occurring are generallymore microbiologically complex than this (Rossi, 1990; Norris and Kelly, 1982).103.1.1 General Description of Metal Solubilizing BacteriaBacteria are single-celled organisms classified as prokaryotes, one of the four basic groups ofmicroorganisms. Prokaryotes are characterized by the lack of a true nucleus, Bacteria are furtherclassified based on various cell characteristics including morphology, biochemical features, physiology,nutritional requirements, and genetics (Chapelle, 1993). In this section general physiological andnutritional characteristics ofmetal suiphide solubilizing bacteria will be discussed as these are features thatare most relevant to the Ivan Mine leach study.In order to survive and grow any bacterial population has certain requirements. These include: (1) water,(2) a source of energy for various metabolic functions, (3) a source of carbon for use in production ofvarious cell components, (4) a source of numerous other trace elements necessary for production of specificcomponents, and (5) favourable solution conditions including temperature and pH (Chapelle, 1993). T.ferrooxidans and T. thiooxidans, along with many other bacteria involved in metal suiphide solubilization,are classified as acidophilic chemolithoautotrophs. This means that they use inorganic compounds as theirsource ofmetabolic energy (chemolithotroph), CO2 as their source of carbon (autotroph), and they requirean environment with a pH of 3 or less for optimum growth (acidophile) (Chapelle, 1993; Rossi, 1990).Most of these bacteria also require oxygen and minor amounts of nutrients such as phosphorous andnitrogen (Rossi, 1990).For these chemolithotrophs energy for maintenance and growth of cells is derived from oxidation ofreduced sulphur compounds and/or metals (Chapelle, 1993). Thus, these bacteria must grow in the vicinityof an appropriate substrate such as ferrous sulphate, elemental sulphur, metallic sulphides, or sulphidebearing ore.Carbon is a basic component of organic cellular material (Table 3,1). In addition, it is used in energyaccumulation and storage processes within the cell. Many of the bacteria involved in sulphidesolubilization are obligate autotrophs, meaning they must use dissolved CO2 as their source of carbon(Rossi, 1990). In order to use the carbon in CO2 the bacteria must convert it to an organic form,11Table 3. 1: A list of the principle elements found in bacteria, their typical relative distribution , and theirphysiological functions (After Rossi, 1990 and Chapelle, 1993).Element Compositiona FunctionC 50% energy accumulation; formation of organic cell material0 20% energy exchange; formation of cellular water and organic cell material;electron acceptor in respiration of aerobes (as 02)N 8-14% energy accumulation; formation of proteins, nucleic acids, andcocnzymesH 8% energy exchange; formation of cellular water and organic cell materialP 1-3% energy accumulation; formation of nucleic acids, phospholipids, andcoenzymcsS 0.5-1% energy accumulation; formation of proteins, and coenzymesK 1% one of the priicipal inorganic cations in cells; cofactor for someenzymes; metabolism regulatorNa 2%Ca 0.5% metabolism regulator, important cellular cationMg 0.5% metabolism regulator, important cellular cationCl 0.5%Fe 0.2% redox regulator; formation of specific proteinsMnb -- metabolism regulator; inorganic cofactor for some enzymesCob -- probably redox regulator; formation ofB12 vitaminNib -- probably redox regulatorCu,Zn,Mob -- formation of special enzymesavalues are in weight%bcombined these elements comprise less than 0.3% of a typical cell’s dry mass12commonly carbohydrates. This is done in a very energy demanding process called the Calvin cycle(Chapelle, 1993). This process is regulated so that if there is no adequate source of energy carbohydratesare not formed and energy is conserved (Rossi 1990; Chapelle 1993).In addition to carbon, the bacteria require other elements for various purposes as outlined in Table 3.1.Oxygen, nitrogen, and hydrogen are also basic building blocks of the cell and are used in various metabolicfunctions. In addition, other elements such as phosphorous, sulphur, and potassium are present in smalleramounts but are necessary components contributing to metabolic processes. Finally, a few elements suchas copper and cobalt are present in very minor amounts and have very specific roles, often in specificenzymes. For the sulphide solubilizing bacteria these elements, called nutrients, are often readily availablefrom the substrate and solution they are growing in. However, in experimental environments (cultures)these nutrients must often be added. Numerous culture media have been established for growing thesebacteria and will be discussed in more detail in section 3.4.It is important to note that the role of oxygen is of particular importance to most metal sulphide solubilizingbacteria (Rossi, 1990). They produce energy for metabolic functions by removing electrons from reducedsulphur compounds and/or metals and transferring them to molecular oxygen. Most of these bacteria areclassified as obligate aerobes which means that they cannot substitute another electron acceptor such assulphate for the oxygen (Chapelle, 1993). Obviously, in the absence of oxygen these bacteria do notthrive.Although bacteria are capable of living in a wide range of pH conditions (Chapelle, 1993), most of themetal sulphide solubilizing bacteria cannot survive at a pH greater than 6 (Rossi, 1990). As Rossi (1990)notes, many of these species, including T. ferrooxidans and T. thiooxidans, exhibit optimum growth at pH2 to 3.5. This is not surprising since at least some, if not all, of their metabolic energy is derived fromoxidation of reduced sulphur which ultimately produces sulphuric acid. This will be discussed further insection 3.2.As with pH, bacteria are found in environments with a wide range of temperatures, from 0 to over 100°C(Chapelle, 1993). The metal sulphide solubilizing bacteria are principally mesophiles, meaning they grow13in the range of 10 to 40°C, although, there are a couple of notable species that thrive at much highertemperatures (Rossi, 1990) These bacteria are classified as thermophiles. Copper suiphide leaching tendsto be done at temperatures below 40°C; therefore, the mesophiles are of particular interest here.3.1.2 ThiobacillusferrooxidansThiobacillusferrooxidans is an extensively studied and, therefore, much described species of bacteria.Some more recent reviews of the current knowledge with regards to this species can be found in Rossi(1990), Norris (1990), and Norris and Kelly (1982).T ferrooxidans is a small (0.5 to 1.7 j.m long and 0.3 to 0.4 m in diameter), primarily rod-shaped, gram-negative species of bacteria that derives its metabolic energy from oxidation of reduced sulphurcompounds, elemental sulphur, iron, and possibly other metals. Of particular interest here is the ability ofthis species to oxidize various metal sulphide minerals including bornite [Cu5FeS4],chalcocite [Cu2S],chalcopyrite [CuFeS2],covellite [CuS], and pyrite [FeS2] (Ehrlich, 1990). The gram-negativeclassification refers to the bacteria’s inability to retain a purple dye (crystal violet) due to its cell wallcomposition (Chapelle, 1993). These bacteria may also exhibit ovoid or spherical morphology. Smallchains of 2 to 7 rod-shaped cells have been observed.This species is autotrophic, making CO2 essential for survival and growth. There is one reported incidenceof growth with organic carbon (Barros et al,, 1984); however, workers such as Norris (1990) and Rossi(1990) appear to disagree on its validity.T ferrooxidans can be found growing at temperatures from 10 to 40°C and is classified as a mesophile(Rossi, 1990). Most strains exhibit optimum growth at temperatures of 30 to 35°C; however, some strainshave been shown to have optimum temperatures as low as 20°C and others as high as 37°C (Norris, 1990).Generally the lower the optimum temperature the lower the maximum temperature for cell viability. Onemust be cautious, however, of comparing these types of reports as growth can be significantly effected byother factors such as pH.14T. ferrooxidans is acidophilic, growing in pH conditions of less than 1.4 to 6 (Rossi, 1990). The optimumpH is generally around 2; however, as with temperature, this can differ significantly from strain to strain(Norris 1990).Of particular interest to biohydrometallurgists is this species’ ability to resist concentrations ofmetal ions atsimilar levels to those found in hydrornetallurgical processes (Table 3.2). This is not the case for mostmicroorganisms. Of particular interest here is the tolerance to copper. Kuznetsov eta!. (1963) isolated astrain from mine waters that was naturally resistant to copper concentrations of 7.5 g/L. Resistance tocopper levels of up to 55 g/L have been observed in chalcopyrite concentrate leach tests (Rossi, 1990).As may be evident from the previous discussion, T. ferrooxidans is a species that exhibits very diversereactions to different environmental conditions. Not only can various strains react differently to suchconditions as pH and temperature but they can also react differently to a type of substrate or nutrientsupplement. Furthermore, their ability to adapt to a set of conditions can also vary. Obviously the morevigorous the culture, the more efficient it will be in sulphide mineral solubilization. This translates intomore efficient metal extraction for the biohydrometallurgist. Unfortunately, there is no standard substratethat can predict sulphide mineral solubilization rates for various ores. Testing with the particular ore ofinterest must be done. This will be discussed in more detail in section Thiobacillus thiooxidansThiobacilius thiooxidans is much less extensively studied than T. ferrooxidans, probably due to itsapparently subordinate role in metal suiphide solubilization. Two recent descriptions are given in Norris(1990), and Norris and Kelly (1982).T. thiooxidans is a small, rod-shaped, gram-negative species of bacteria very similar to T. ferrooxidans. Ittoo thrives in aerobic and acidic conditions and has an optimum temperature of 30°C. In fact, it is oftenfound growing with 1’. ferrooxidans. However, there is a major difference between the two species. T.thiooxidans derives its metabolic energy from oxidation of sulphur only. Pure cultures of this species do15Table 3.2: Inhibitory levels of certain metals compared to maximum concentrations observed inbioleaching (After Rossi, 1990).Metal Inhibitory Level Bioleaching Level(in g/L) (in g/L)Zn <10 15-72Ni >10 12-50Cu >10 12-50Co >10 12-50Mn >10 --Al >10 6.0U <7 0.2-0.5Ag <0.5 --As <2 1-2Se <1 --Te <1 --Mo <0.05 0.06-0.9016not affect the solubilization ofmany suiphide minerals. Two exceptions are zinc and cadmium suiphideswhose leaching depends on oxidation of elemental sulphur (Kelly et at. 1979).There is some evidence that T. thiooxidans can contribute to mineral degradation when mixed with iron-oxidizing bacteria such as T. ferrooxidans (Norris, 1990). In particular, it is thought that T. thiooxidanscontributes to chalcopyrite solubilization by oxidizing elemental sulphur layers that are believed to form onthe mineral surface during the oxidation process. Norris (1990) also suggests that a mixture with acommon iron oxidizing bacteria, Leptospirillumferrooxidans, may be beneficial.3.1.4 Other Microorganisms Involved in Metal Sulphide SolubilizationAlthough studies have concentrated on T. ferrooxidans and T. thiooxidans, many other bacterial speciesinvolved in the solubilization ofmetal sulphides have been discovered in various environments, Some ofthese species are listed in Table 3.3. Most of them grow best in a temperature range of 25 to 35°C andunder acidic conditions. Notice, however, that the optimum pH range does vary widely. The majority ofthe species listed oxidize sulphur in some form. Those species that oxidize both iron and sulphur aregenerally thermophilic, T. ferrooxidans being the exception. The natural variations in growth conditions ofthese species may be useful in future applications.One example of this potential is a bacterial species that oxidizes iron only, Leptospirillumferrooxidans. Ithas been studied more extensively than most of those listed, probably because it has been found in mixedcultures with T. ferrooxidans and 7’. thiooxidans. L. ferrooxidans was first described by Balashova et at.(1974). It exhibits a highly variable morphology: helix shapes with 2-5 spirals, curved rods , and v-shapedvibrios. The cells are 0.9 to 1,1 m long and 0.2 to 0.4 JIm in diameter and often form long chains. Asindicated in Table 3.3, L. ferrooxidans is an acidophilic chemolithoautotroph that grows best at pH 3.0 and30°C. Of possible interest is its higher tolerance to uranium, molybdate, and silver than that ofT.ferrooxidans (Rossi, 1990). Unfortunately, this species has a lower tolerance for copper. Furthermore, theability of pure cultures to grow on pyrite and chalcopyrite is uncertain. Nevertheless, Rossi (1990) did findthat mixed cultures ofL. ferrooxidans and T. ferrooxidans grow on pyrite and chalcopyrite, activelyoxidizing them.17Table 3.3: Bacterial species potentially involved, either directly or indirectly, in metal sulfidesolubilization. Most of them are aerobic chemolithoautotrophs. Some of the other relevantcharacteristics are included. (After Rossi, 1990)Species Source Oxidize pH Temperature (°C)S Fe range (opt.) growth (max.)T thiooxidans Soil x -- <0.5-6.0 (2.0-3.5) 10-37 50T. thioparus Canal water, mud, soil x -- 4.5-10 (6.6-7.2) 28-30T. neopolitanus Seawater corroded x -- 3.0-8.5 (6.2-7.0) 28concreteT. perornetabolis x -- 2.6-6.8 (6.9) 30T. denitrf1cans Canal, river, and salt x -- 5.0-7.0 30water; peat, compost,mudT. interniedius Mud x -- 1.9-7.0 (6,8) 30 40T. noveilus Soil x -- 5.0-9.2 (7.8-9.0) 30T. versutus x (8.0-9.0)T. concretivorus Corroding concrete x -- 0.5-6.0 -- -- --T. organoparus Suiphide mine waters x -- 1.5-5.0 (2.5-3.0) 27-30 37-40T. rubellus Mine waters x (5.0-7.0) 25-35 35T. delicatus Mine waters x -- -- (5.0-7.0) 25-35 40T. Icabobis Sulphur piles x -- 1,8-6.0 (3.0) 28T. albertis Sulphur stockpile x -- 2.0-4.5 (3.5-4.0) 28-30T. acidophilus Sulphide mine waters x 1.5-6.0 (3.0) 25-30 --T. ferrooxidans Sulphide mine waters x x 1.4-6,0 (2.35) 28-35 50Tprosperusa Heated sea water x x 1.0-6.5 (2.0) 23-41 37L. ferrooxidans Sulphide deposits -- x 1.5-4.5 (3.0) 30Metallogenium spp. Groundwater, mine -- x 3.5-6.8 (4.1)drainage watersSiderocapsa spp. Marine waters -- x -- -- --Gallionella spp. Natural waters, mine -- x 6.4-6.8 6 25springsLeptothrix spp. Natural waters, mud, -- x 5.8-7.8 5-40 40swampsCrenothrix spp. Natural waters -- x 5.5-6.2 -- 18-24 --Sulfolobus Thermal acid soils, x x 0.9-5.8 (2-3) 55-85 85acidocaldarius acid hot springsSulfobacillus Sulphide ore deposits x x 1.9-3.0 (1.9-2.4) 28-55 60thermosulfidooxidansAcidophilluin criptum Sulphide mine waters -- -- 2.0-6.0 mesophilicafrom Huber and Stetter (1989)18One final species that is of particular interest to the Ivan Mine study is Thiobacillus prosperus. It is anaerobic and acidophilic chemolithoautotroph that grows on suiphide ores and in solutions containing 0 to3.5 weight% NaC1 (Huber and Stetter, 1989). Since one of the objectives of the study is to determinewhether a mixed Thiobacilli culture can be adapted to relatively high chloride level, the existence of thisspecies is encouraging.3.2 Reactions Involved in Microbially Assisted LeachingMicrobially assisted leaching ofmetal sulphides is accomplished in an acidic solution by a mixture ofmicrobially catalyzed and pure chemical redox reactions. The bacteria are involved both directly andindirectly in the solubilization. Direct solubilization occurs when the bacteria attack the crystal lattice,rendering the metal suiphide soluble. Generally, chemical oxidants that solubilize metal sulphides are alsopresent in the leach solution either as products ofmicrobial activity (indirect involvement) or as addedsalts. Because most metal sulphides can conduct electrons both microbially catalyzed and pure chemicaloxidations can be considered to be corrosion systems with anodic and cathodic reactions occurring at themineral surface (Natarajan, 1990). Another mechanism, galvanic oxidation, occurs in mixed sulphide oreswhere different types ofmetal suiphides are in electrical contact.In this section the solubilization mechanisms mentioned above will be discussed in relation to the copper-bearing sulphides found in the Ivan Mine sulphide ore sample: chalcopyrite, bornite, chalcocite, andcovellite. The solubilization of pyrite will also be discussed despite its rarity in the Ivan ore samplebecause it is a very important component in many other ore leaching situations. The various reactionsinvolved are summarized in Table 3.4 and will be discussed in the following sections.3.2.1 Microbially Catalyzed ReactionsAs stated above, bacteria oxidize metal sulphides by directly attacking the crystalline lattice. It would seemobvious that in order to accomplish this the bacteria must be in intimate contact with the mineral surface.Numerous researchers including Berry and Murr (1976, 1978) have observed bacterial attachment usingTable3.4:Reactionsinvolvedinthebioleachingofvariouscopper-bearingsulphidesandpyrite.SolidPhaseReactionCommentspyrite2FeS+702+2H0—2FeSO4+2HS04(3.g)’e,fbacteriaFeS2+Fe2(S04)3-3FeS0+2S°(315)a,b,d,fchemicalchalcopyrite4CuFeS2+1702+2HS04-44CuSO+2Fe(S04)3+2H0(3.6)bacteria4CuFeS2+1702+10H20-44Cu+4Fe(OH)3+85042+8I-{(37)bbacteriaCuFeS2+2Fe(S04)3—CuSO4+2FeSO4+2S°(—5CuSO4+13FeSO4+S°(3.12)achemicalCu5FeS4+xFe2(S04)3+8.502—Cu5FeS4+xCuSO4+2xFeSO4(3.20)CchemicalchalcociteCu2S+0.502+H2S04-4CuSO4+CuS+H20(35)a,b,gbacteriaCu2S+Fe2(S04)3-2CuS0+2FeSO4+CuS(3.13)achemicalcovelliteCuS+202-4CuSO4(32)a,fbacteriaCuS+Fe2(S04)3—>CuS0+2FeSO4+S°(3.14)achemicalferroussulphate4FeSO+02+2HS04—+2Fe(S04)3+2H0(3.9)Sbacteriaelementalsulphur2S°+302+2H0-2HS04(3.4)abacteriaferricprecipitatesFe2(S04)3+6H20—*2Fe(OH)3+H2S04(3.16)’ferrichydroxideFe2(S04)3+4H20—2FeOOH+3H2S04(3.17)hloxyhydroxide(e.g.goethite)Fe2(S04)3+2H0—+2Fe(OH)S04+H2S04(3l8)b,C,ebasicferricsulphate3Fe2(S04)+12H20+2A—+2AFe3(S04)OH)6+5H2S04+2H(3.19)ijarositeA=K,Na,Ag,H30,NH4aMuff(1980);bEhrlich(1990);(1993);d5(1991);eTuovinen(1990);Lundgreneta!.(1986);(1990);hmffijfromvanBreeman(1982);‘modifiedfromRosseta!.(1982)20electron microscope techniques. There is some indication that attachment and leaching occur at specificsites, possibly where lattice imperfections such as dislocations occur (Ehrlich, 1990; Southwood andSouthwood, 1986; Berry and Murr, 1978; Murr and Berry, 1976). The details of the mechanism involvedin the direct attack are not yet understood; however, Ehrlich (1990) suggests that the bacteria acquiremetabolic energy by transferring electrons from cathodic regions of the mineral surface to oxygen in thesolution.The direct oxidation of simple metal suiphides can be expressed by the following general reaction:MS+2O2—MS4 (3.1)where M represents a divalent metal such as Cu2+ (Rossi, 1990). Covellite is oxidized in this manner.CuS + 202 —* CuSO4 (3.2)In this reaction only the sulphur is attacked by the bacteria since copper is in its most oxidized form.Ehrlich (1990) suggests that sulphur oxidation actually occurs in two steps as follows:CuS + 0,502 + 2H — Cu2”+ S° +H20 (3.3)S° + 1.50 +H20—*H2S04 (3.4)Direct oxidation of chalcocite produces covellite along with copper sulphate and water, which then furtheroxidizes as shown above.Cu2S + 0.5 02 +H2S04—4 CuSO + CuS +H20 (3.5)It has been suggested, because only divalent copper is observed in solution, that the monovalent copper inthe chalcocite lattice is oxidized before the sulphur, leaving behind divalent copper in the covellite lattice(Ehrlich, 1990 and Rossi, 1990). However, Tuovinen (1990) questions the validity of the evidence used toconfirm this. He suggests that researchers only observe divalent copper in solution because under the21leaching conditions being considered monovalent copper rapidly oxidizes and would not be detected even ifinitially present.Direct oxidation of chalcopyrite produces copper sulphate and a ferric iron species while producing orconsuming acid, depending on which iron species forms.4CuFeS2+ 1702 + 2HS04— 4CuSO +2Fe(S04)3+ 21120 (3.6)4CuFeS2+ 1702 + 101120 —> 4Cu + 4Fe(OH)3+ 8S042 + 8H (3.7)Once again there is some disagreement as to the details of this reaction. Ehrlich (1990) assumes that ironpresent in the mineral is divalent and that both sulphur and iron are oxidized by the bacteria. However,Rossi (1990) suggests that work by Yakhontova et al. (1980) and De Filippo et al. (1 988a) implies thatonly copper is oxidized, since iron in the solid is present in its most oxidized form (trivalent), copper in thesolid is monovalent, and copper in solution is divalent. Again, Tuovinen’s argument discussed above raisesquestions about this theory.Despite the disagreement on mechanisms most researchers seem to agree that leaching of chalcopyrite oftenproduces a layer of reaction product which may act as a diffusion barrier, retarding, if not stopping theleaching process. This layer will be discussed in more detail in section 3.3.1,Although Silverman and Ehrlich (1964) list bomite as one of the sulphides oxidized by T. ferrooxidans it isunclear whether this degradation is due to direct bacterial attack. Furthermore, reactions describing thedirect oxidation of bomite have not been proposed.Pyrite is directly oxidized to produce sulphuric acid and ferrous sulphate.2FeS + 702 + 2H0—* 2FeSO4+2HS04 (3.8)This reaction, which does occur in the absence of bacteria, is significantly catalyzed by bacteria such as T.ferrooxidans (Lundgren et al., 1986). Notice that only the sulphur is oxidized in this case. This reaction isof particular importance in many natural and industrial situations since pyrite is the most ubiquitous22sulphide mineral in the Earth’s crust and oxidation produces one mole of sulphuric acid for every mole ofpyrite,Many of the bacteria involved in metal suiphide leaching have the ability to oxidize other reduced ironand/or sulphur species (Rossi, 1990). Ferrous iron and elemental sulphur are two of these speciescommonly found in the leaching system being considered here. Both are products of the oxidation processas discussed above. The oxidation reactions shown below describe the conversion of ferrous iron to ferriciron and elemental sulphur to sulphate.4FeSO + 02 + 2HS04—*2Fe(5O4)3+2H0 (3.9)S°+1.50H0—*HS0 (3.4)These reactions can occur in the absence of bacteria but are so slow under efficient metal suiphide leachingconditions that they are insignificant. However, in the presence of bacteria the rate of oxidation increasessubstantially. In fact, Lacey and Lawson (1970) showed that the rate of ferrous iron oxidation couldincrease by 500,000 times at a pH of 2.2 and a temperature of 31°C when T. ferrooxidans was present.The full significance of these reactions will become clearer in the next section; however, it should be notedthat the catalyzed oxidation of elemental sulphur may play a more significant role in the direct oxidation ofthe copper-bearing suiphides as discussed above, especially for covellite and chalcopyrite.3.2.2 Chemical ReactionsFerric sulphate is a powerful oxidizing agent that is commonly used in the mining industry to leach metalsuiphides (Silverman and Ehrlich, 1964). It can be produced during microbially assisted leaching of ironbearing suiphides or added to the leach solution as salts. Oxidation ofmetal suiphides occurs at theexpense of the ferric iron according to the following general equation:MS + 2Fe3—M2+ 2Fe +S° (3.10)where M represents a divalent metal such as Cu2+ (Ehrlich, 1990). Reactions for the specific copper-23bearing minerals and pyrite are as follows:CuFeS2+2Fe(S04)3-4 CuSO + 2FeSO4+ 2S° (3.11)Cu5FeS4+6Fe2(S04)3—* 5CuSO4+ 13FeSO4+ S° (3.12)Cu2S +Fe2(S04)3— 2CuSO4 + 2FeSO4 +CuS (3.13)CuS +Fe2(S04)3—+ CuSO + 2FeSO4+ S° (3.14)FeS2 +Fe2(S04)3—> 3FeSO + 2S° (3.15)Notice that in all cases ferrous sulphate and elemental sulphur are generated. In bioleaching systemschemical oxidation of the metal sulphides usually occurs simultaneously with microbially assistedoxidation; thus, as discussed in the previous section, the ferrous sulphate and elemental sulphur producedare oxidized by bacteria to generate acid (3.4) and ferric sulphate (3.9). The solution pH is maintained andonce again ferric sulphate oxidizes the metal sulphides.This important cycle continues unless the activity of the bacterial population diminishes or iron is removedfrom the solution. The level of bacterial activity is controlled by the various environmental and nutritionalrequirements discussed in section 3.1. The level of iron in the solution is controlled by the composition ofthe metal sulphides being leached, the degree of ferric iron hydrolysis, and the solution pH. If the orecontains iron-bearing sulphides, iron is added to the solution as the mineral degradation progresses (3.6,3.7, 3.8, 3.11, 3.12, 3.15). However, ferric iron tends to hydrolyze under bioleaching conditions and maybe removed from solution by precipitation of various ferric hydroxides [Fe(OH)3],oxyhydroxides (goethite)[FeOOH], basic ferric sulphates [Fe(OH)S04],and/or jarosites [AFe3(S04)2OH)6](Hacki, 1993, vanBreeman, 1982) as follows:Fe2(S04)3+6H20-4 2Fe(OH)3+H2S04 (3.16)Fe2(S04)3+4H20-4 2FeOOH + 3H2S04 (3.17)Fe2(S04)3+ 21-120 -4 2Fe(OH)S0 +H2S04 (3.18)3Fe2(S04)+ 12H0+ 2A -4 2AFe3(S0)OH)6+5H2S04+ 2H (3.19)In equation 3.19 ‘A’ represents K, Na, Ag,H30, NH4. These reactions are acid generating and depend on24the solution pH - increased pH decreases ferric iron solubility. Hacki (1993) states that complete ferriciron precipitation occurs at a solution pH greater than 2.8. Jarosite is stable at lower pH values than theother hydrolyzed ferric species (Nordstrom, 1982) and may form diffusion barriers on mineral surfaces(Tuovinen, 1990; Ehrlich, 1990). Interestingly, although these coatings are believed to create problems inheaps no such situation has been produced in laboratory scale systems (Tuovinen, 1990).Although the overall reactions given in Table 3.4 for chemical leaching of chalcocite and bornite arestraightforward, there is some evidence that leaching of these minerals is more complex (Whiteside andGoble, 1986; Scott, 1991). These researchers showed that ferric iron leaching of chalcocite removescopper from the crystal lattice producing a series of copper suiphides as follows:Cu2S —* Cu1 97S —> Cu18S —> Cu1 75S —> Cu16S -4 Cu14S —> Cu1 12S —* CuSchalcocite djurleite digenite anilite geerite spionkopite yarrowite covelliteFurthermore, blue-remaining (blaubleibender) covellite, a mineral recognized for many years in oxidationzones of oxide ores, was found to be composed of spionkopite, yarrowite, and, very rarely, geerite. In 1988another copper sulphide mineral, roxbyite (Cu1 78S), was added to this series (Mumme et al., 1988) andfurther study of oxidized copper ore deposits may well increase this list.The reaction path for chemical leaching of bornite is also complex (Scott, 1991). Leaching rapidlyremoves up to approximately 10% of the copper to produce a copper deficient bomite according to thefollowing equation:Cu5FeS4+xFe2(S04)3+ 8.502 — Cu5 FeS4 + xCuSO4+ 2xFeSO4 (3.20)At this point the copper deficient phase destabilizes to slowly produce chalcopyrite and digenite while morerapidly producing a second copper-iron phase with a formula ofCu3FeS4,with y between 0 and 1.1. Inconcentrate leaching below 65°C the reaction continues until all the bornite is converted and approximately25% of the copper is solubilized. No elemental sulphur is formed. At temperatures above 65°C bornite iscompletely solubilized and elemental sulphur is produced. It is unclear how leaching of a bornite ore wouldV 25differ and how the presence of bacteria would effect the leaching.It should be noted here that ferric chloride [FeC13Jis also an effective copper sulphide oxidant andenhancement of copper extraction by concentrations of chloride ion (up to approximately 7 g/L) in acidicleach solutions has been shown to occur (Murr et al., 1979; Murr, 1980). Unfortunately, Tuovinen andKelly (1972) have shown that T. ferrooxidans exhibits 50 to 90% inhibition in systems containing 3 to 6g/L chloride. For this reason, ferric chloride has not been used in bioleaching processes.3.2.3 Galvanic EffectsIt has been shown by numerous researchers that chalcopyrite leaches more readily in the presence of pyrite(Dutrizac and MacDonald, 1973; Mehta and Murr, 1982; Ahonen et al., 1986). This is an example ofpreferential oxidation due to galvanic interactions. It is generally accepted that sulphide minerals, like puremetals, can conduct electrons and, therefore, can be arranged in an electrochemical series based on theirrest potentials. One such series is given in Table 3.5. Series such as this one should be used with cautionas the arrangement ofminerals can vary; each metal suiphide exhibits a range of rest potential valuesdepending on the specific mineral sample and the nature of the leach solution (Rossi, 1990; Natarajan,1990).Nevertheless, when two sulphide minerals with different potentials are in contact during leaching a galvaniccouple is formed. The mineral with the lower potential acts as the anode and will oxidize more readily thanthe mineral with the higher potential which acts as the inert cathode. Oxygen at the cathodic mineralsurface is reduced and water is produced according to the following half reaction:O2+2H+4e—*H (3.21)In the chalcopyrite/pyrite system, as illustrated in Figure 3.1, chalcopyrite behaves as the anode andoxidizes according to the following half reaction (Rossi, 1990):CuFeS2—* Cu2 + Fe2 + 25° + 4e (3.22)26Table 3.5: Electrochemical series of some iron- and copper-bearing sulphide minerals in anH2S04solution with a pH of 2.5. Open-circuit potential are measured against a saturated hydrogenelectrode. (After Yakhontova, 1985)Mineral Potential(mV)chalcocite Cu2S 350 reactivechalcopyrite CuFeS2 400 1’stannite CuFeSnS4 450 Ipyrrhotite FeS 450 Itetrahedrite Cu3SbS 450 .1’pyrite FeS2 550-600 nobleH Fe3H20 102 t H20\J/•\2,Cu2L\\zE;Jsilicate host rockFigure 3.1: Illustration of the galvanic mechanism using the pyrite/chalcopyrite system. Oxidationoccurs at the surface ofthe chalcopyrite grain, releasing electrons that travel to the surface ofthe pyrite grain. Reduction of oxygen and the formation ofwater occur at this surface.Notice that elemental sulphur and ferrous iron are produced at the chalcopyrite surface,along with copper. Bacteria, if present, further oxidize these species. \Vhether the bacteriapreferentially attach to the cathodic mineral surface (as shown) or not is unclear. (AfterRossi, 1990)2.27Notice that in Figure 3.1 bacteria have been placed on the surface of the corroding chalcopyrite. The rolethat iron and/or sulphur oxidizing bacteria play in this galvanic leaching mechanism is actually not wellunderstood; however, it has been shown that galvanic degradation ofmetal suiphides is enhanced in thepresence of bacteria such as T. ferrooxidans and T. thiooxidans (Rossi, 1990; Natarajan, 1990).Improvement may only be through general oxidation of the ferrous iron (3.9) and elemental sulphur (3.4)being produced; however, there is also some evidence that bacteria will preferentially attach to the lessnoble mineral in a galvanic couple, possibly further increasing the rate of preferential oxidation (Natarajanand Iwasaki, 1985).The contribution of this galvanic mechanism to the overall metal sulphide leaching process can varysignificantly depending on many factors. Some of the more important of these include: (1) the totalamount and duration of contact area between minerals of differing rest potentials, (2) the degree ofdifference between rest potentials, (3) the relative anode-cathode surface area, (4) the availability ofoxygen, and (5) probably, the viability and oxidation capability of the bacterial population (Natarajan,1990). Although interesting , this mechanism probably does not contribute significantly to the leaching ofmixed copper-bearing suiphide ores without pyrite because the most common of these sulphides have fairlysimilar rest potentials under commonly used bioleaching conditions (Table 3.5).3.3 Character of Typical Solid ResiduesDuring the bioleaching of a sulphide ore the character of the solid component is altered. Suiphide mineralgrains are degraded to varying degrees, leaving behind alteration products when removal is not complete.The rock matrix is also modified, generally to a lesser degree, and alteration products are common.Finally, due to the leaching of these solid components the concentration of numerous elements in the leachsolution increases and precipitation of various compounds may occur. In this section current knowledgeregarding the character of these various solid residues will be examined. In addition, the geometry of oreparticle degradation will be discussed briefly.A list of the minerals discussed in this section along with their chemical formulae are included for reference(Table 3.6).28Table 3.6: Formulae for minerals discussed in section 3.3.Group Mineral Formulasuiphides chalcopyrite CuFeS2bomite Cu5FeS4chalcocite Cu2Scovellite CuSpyrite FeS2pyrrhotite Fe1Ssphalerite ZnSpentlandite (Fe,Ni)98quartz Si02feldspars microcline KA1Si3O8albite NaA1Simicas muscovite KA12(A1Si10)(OH)margarite CaA1(A1Si3O0)(OH)2phengite K(Al,Fe,FeMg)25(AlSiO10)(OH)2aphiogopite KMg3(A1SiO10)(OH)2biotite K(Mg,Fe)(A1Si)(OFI)glauconite (K,Na)(Fe+,A1,Mg)Si,A140H)bother pyllosilicates illite ( ,0)(Al,Mg,Fe)2Si A1)0[(OH)2,HO]’kaolinite A1SiO5(OH)4montrnorillonite (A1,Mg)8Si0103(OH) 2HOnontronite Na03(Fej2Si,Al)10(OH)2.nH2Obvermiculite Mg(Si,Al)4OH .4.5H0[Mg]35suiphates jarosite KFe(S0)OH)6natrojarosite NaFe3(S02OH)ammoniojarosite 4Fe(S0OH)hydroniurnjarosite HOFe(S0)OH)6argentojarosite AgFe3(S02OH)plumbojarosite PbFe(S04OH)melanterite FeSO.7H20rozenite FeSO4.4H0°szmolnokite FeSO,H2OCsiderotil (Fe, Cu)S04.5HOdcopiapite e+Fe3(S0)6(OH)antlerite CuSO4(OHbrochantite CuSO(OH)6chalcanthite CuSO4.5H20gypsum CaSO.2Hoxides/hydroxides gibbsite Al(OH)3goethite cz-FeOOHferoxyhyte &FeOOHeakaganeite f3-FeOOWferric hydroxide Fe(OH)Weferrihydrite 5Fe2O3.9H20or Fe5HO8 .4H2Ohschwertmannite e80(OH)6S041from Bhatti et al. (1993); bRoberts et al. (1990); CNordstrom (1982); dScort (1991);eBrady eta!. (1983); Bigham eta!. (1990); gHackj (1993); hlJambor (1994); ‘Bigham (1994)293.3.1 Alteration ofMetal SulphidesDuring bioleaching metal suiphide grains are broken down by the leach solution and bacteria at the mineralsurface and along any structural weaknesses within the grains. As indicated in section 3.2, in many casesoxidation and subsequent solubilization is non-stoichiometric and a layer of partially altered material,commonly called a reaction zone, may form. Unfortunately, as recognized by Ahonen and Tuovinen(1993), the method of formation and the morphology of these zones in bioleaching environments are seldomdiscussed in the literature. Chalcopyrite and, to some extent, pyrite appear to be exceptions. Ahonen andTuovinen (1993) have also recently done a study to examine the alteration in a complex sulphide oreconsisting of a concentrated mixture of pyrite, pyrrhotite [Fe1..,S], chalcopyrite, sphalerite [ZnS], andpentlandite [(Fe,Ni)9S8]. Furthermore, despite the lack of direct observations, some predictions can bemade regarding the composition of alteration zones in covellite and bornite based on proposed leachreactions (section 3.2). These predictions are very tentative since they do not take into account reactionkinetics and, in the case of bomite, the presence of bacteria.Reaction zones in chalcopyrite, pyrite, chalcocite, and bornite will be discussed in more detail. There is noindication that covellite produces alteration products during the bioleaching process, although a layer ofelemental sulphur is formed under sterile conditions (Corrans et al., 1972).ChalcopyriteIt is commonly known that during both ferric iron and microbiologically-assisted leaching processeschalcopyrite exhibits unusual leaching kinetics believed to be connected to the formation of a reactionzone. Initial copper extraction is relatively fast; however, the leaching rate is reduced by severalhundred-fold at or before 50% copper recovery (Rossi, 1990). Regrinding of the leach residuetemporarily restores the fast leaching rate; however, further regrinds are often necessary to achieveadequate copper recovery (McElroy and Bruynesteyn, 1978). This problem has been studiedextensively because the regrinds of chalcopyrite, the most common copper-bearing sulphide mineral,are uneconomical in vat leaching systems and are not possible in dump, heap, and in situ processes(Rossi, 1990).30As stated above, it is generally agreed that these unusual leach kinetics are caused by the formation ofa reaction zone that hinders chalcopyrite dissolution; however, the nature of this reaction zone is asubject ofmuch controversy (Rossi, 1990). Basically there are two hypotheses as follows:(1) The reaction zone is a layer of elemental sulphur that acts as a diffusion barrier either to ferric ironor electrons and is formed according to equation 3.11 (Tuovinen, 1990; Miller and Portillo, 1979;Munoz eta!., 1979; Dutrizac eta!., 1969; Sullivan, 1933)(2) The reaction zone consists of a layer of copper-deficient sulphide which differs both chemicallyand structurally from chalcopyrite, overlain by a layer of very porous elemental sulphur (AnimouChokrum, 1977; Linge, 1976; Peters, 1973; Burkin, 1969). This copper-deficient layer,confirmed by De Filipo et a!. (198 8b) using x-ray photoelectron spectroscopy, is formed by nonstoichiometric solid state cation diffusion which is the rate-limiting process (Linge, 1976). Theelemental sulphur layer has no hindering effect and is readily oxidized in bioleaching regimes(Ermilov et a!., 1969).In both cases the success of regrinding leach residues is probably due to exposure of fresh chalcopyritesurfaces (Rossi, 1990).It should be noted that Ahonen and Tuovinen (1993) found no evidence of any sort of reaction layer onleached chalcopyrite in the mixed ore they were studying. They did observe loosely attached jarositelayers on some of the mineral grains; however, they did not feel that this layer formed a diffusionbarrier. A jarosite layer has been suggested as another possible cause of the chalcopyrite leachingproblem by Cooney et al. (1981), but no proof was supplied.PyriteAlthough bioleaching of pyrite does not appear to cause the formation of a reaction zone extensivepitting has been observed on grain surfaces (Ahonen and Tuovinen, 1993; Southwood and Southwood,1986; McKibben and Barnes, 1986; Hultunen eta!., 1981). Southwood and Southwood (1986)studied this phenomenon in some detail. The results of their experiments suggest that the tube-shaped31pits often found in leached pyrite grains are probably formed by preferential, direct bacterial leaching.In fact, attached bacteria have been observed within corrosion pits. Furthermore, the pits generallypropagate along planes parallel to the crystallographic axes, inferring structural control. The authorsargue that since structural weaknesses such as dislocations have been shown to predominantly occur inpyrite along planes parallel to the crystallographic axes, their results confirm the suggestions of Beimetand Tributsch (1978) and Berry and Murr (1978) that the corrosion pits are probably formed alongstructural defects by bacteria. It should be noted that Southwood and Southwood (1986) did observesparsely distributed and poorly formed tubular pits in sterile control samples. They caution that thereis still a possibility, if slight, that the pits are formed by some form of indirect leaching.JhalcociteWhiteside and Goble (1986) determined that under ferric sulphate leaching conditions chalcocite altersat varying rates to a series of copper suiphides ending with covellite (section 3.2). Other research hasshown that chalcocite quickly loses copper until a covellite-like residue is formed (Rossi, 1990). Thisresidue dissolves at a much slower rate, although the rate is significantly increased in the presence ofbacteria, One would expect a reaction zone, if present, to be composed of this covellite-like residue.No information about the morphology of this layer could be determined from the Whiteside and Goble(1986) study as identification of the alteration products was done using x-ray diffraction techniques.However, Rossi (1990) alludes to the more porous nature of this secondary covellite compared tonatural covellite.BorniteUnder ferric iron leach conditions bornite alters to a copper-poor bornite, then quickly to chalcopyriteand digenite, and, more slowly, to a second copper-poor bomite phase (section 3,2). One would expectthe reaction zone to be comprised of some combination of these species along with secondary covellite;however, this is very speculative since the effect of bacteria on bomite degradation does not currentlyappear to be known in any detail. Again, the morphology of this zone is not known.323.3.2 Alteration of Silicates in the Ore MatrixDuring bioleaching of a suiphide ore the minerals making up the rock matrix, generally silicates, are alsoattacked by the leach solution. Quartz [5i02] is relatively inert; however, micas and feldspars are prone toattack (Bhatti eta!., 1993). Dissolution of these minerals is accomplished by acid consuming hydrolysisreactions which can have an adverse effect on metal sulphide dissolution by inhibiting bacterial activityand/or removing ferric iron from solution by precipitation of insoluble ferric iron species (Nahon, 1991;Silverman and Ehrlich, 1964).Little research has been done on the details ofmica and feldspar dissolution in bioleaching systems;however, some useful information can be obtained from three studies, done by Bhatti et a!. (1993), Ross eta!. (1982), and Ivarson et a!. (1978), that investigate the role of silicate dissolution in these systems,generally as it relates to jarosite formation. They studied various silicate minerals including albite[NaA1Si3O8],microcline [KA1Si3O8],muscovite [KA12(AlSi3O10)(OH)2], illite, kaolinite[A125i0(OH)4],montmorillonite [(Al,Mg)g(5i4010)3(OH) 2HOJ, phlogopite[KMg3(A1Si10)(OH),and phengite. Observation from these studies along with some generalinformation on weathering of feldspars and micas will be discussed in the following section.FeldsparsNahon (1991) and Velbel (1 984a) have summarized the current ideas regarding weathering offeldspars. It is generally agreed that the higher the aluminum-content the more readily the feldsparweathers. This is the case because Al-O bonds, with a smaller covalent component, is weaker than theSi-O bond. However, there is some controversy regarding the details of feldspar dissolution kineticsand mechanisms. The controversy is derived primarily from two schools of thought regarding thepresence or absence of a residual layer, the presence indicating nonstoichiometric dissolution. Theresults of an early series of experiments done by Holdren and Berner (1979), Berner and Hoidren(1979, 1977), and Petrovic et a!. (1976) indicated that dissolution was stoichiornetric and occurredpreferentially in regions of excess energy which includes edges, corners, cracks, scratches, holes, pointdefects, boundaries, and dislocations. This has an interesting similarity to the work on bioleaching ofpyrite discussed in section 3.3.1. Examination of naturally weathered feldspars revealed similar33weathering patterns and no weathering residues (Velbel, l984a1b; Berner and Holdren, 1979; Wilson,1975). The results of the weathering studies further suggested that the dissolution kinetics arebasically linear and the dissolution reaction is dependent on the density of surface weaknesses. Notethat dissolution kinetics would be parabolic if diffusion through a residual layer was the rate limitingfactor (Velbel, 1984a).The results of a later series of experiments done by Hoidren and Speyer (1986,1985a1b) and Chou andWollast (1985, 1984) suggested that dissolution was nonstoichiornetric and strongly pH dependent. Analuminum- and alkali-poor residual layer tens of angstroms thick was observed at the mineral surface(Figure 3.2). Other researchers also found evidence of a residual layer as thick as 30-40 nm (300-400angstroms) but usually no thicker than 6 nm (60 angstroms) (Perry et at., 1983; Della Mea et at.,1983; Petrovic et al., 1976). Holdren and Speyer (1985b) considered the solution pH to be thedetermining factor in the degree of nonstoichiometric dissolution. Their studies had shown an increasein the degree of nonstoichiometric dissolution with a decrease in pH. However, Chou and Wollast(1985, 1984) felt that the degree of nonstoichiometric dissolution was connected to the residual layer.They suggested that the degree of nonstoichiometric dissolution is originally quite high but quicklydecreases to apparent stoichiometry as the rate of alteration of fresh feldspar, which is dependent ondiffusion through the residual layer, and the rate of dissolution of the residual layer at the outer surfacereach a steady state (Figure 3.2).Nahon (1991) and Schott and Petit (1987) suggest that a combination of the results from the two seriesof experiments explains the situation. A residual layer as described by Chou and Wollast (1984) formson the walls of the etch pits (Figure 3.2) that have been shown by Hoidren and Berner (1979) andBerner and Holdren (1979,1977) to preferentially form at places of excess energy. The rate ofdissolution is controlled by the density of these excess energy zones and therefore is linear as suggestedby the earlier series of experiments. Finally’ the overall dissolution reaction is stoichiometric due to thesteady-state conditions described above for the residual layer.Perhaps of mor} interest to this discussion, despite their lack of details, are the observations from thebioleaching studies mentioned in the introduction to this section. Bhatti et at. (1993) observed a partial34fresh albite removed materialmineral surface/__‘<-I‘<-1I etch pit‘<-Iresidual layeroriginal mineral surface35 A22 AFigure 3.2: Residual layer on the walls of an etch pit in albite. (After Schott and Petit, 1987; Chou andWollast, 1984)‘<H35dissolution of feldspar in bioleached material which did not occur in the sterile control samples. Rosset at. (1982) and Ivarson et at. (1978) studied this in more detail and determined that the dissolution isprobably stoichiometric although some loss of crystallinity did occur. These results must be viewedcautiously because they are primarily based on powder x-ray diffraction (XRD) analyses and not moredetailed examinations of leached surfaces. Generally, the detection limit of XRIJ techniques isapproximately 5% by volume (Mati Raudsepp, personal communication.). The bioleachingexperiments were done at a pH of approximately 2; so, according to the conclusions ofHoldren andSpeyer (1985b), dissolution of the feldspar samples would have been significantly non stoichiometric.Presumably, any residual layer produced would have been thick and possibly abundant enough to berecognizable in XRD patterns, As stated above some loss of crystallinity was indeed noted by Ross etat. (1982). Despite all this, the presence of a residual layer still cannot be ruled out since there is apossibility that the layer is amorphous (Ivarson et al., 1978) and, therefore, invisible to x-rays.Finally it is commonly accepted that feldspar weathering produces secondary minerals via a dissolvedaqueous stage (Velbel, 1984a). In fact, weathering products are observed at some distance from emptyetch pits, often in cracks in inert minerals such as quartz (Velbel, 1984a). The composition of theseproducts is dependent on the aqueous species within the solution they precipitate out of (Velbel,1984a). Obviously the source of these species is dissolving minerals although bacteria can alsocontribute as equations 3.4 and 3.9 illustrate. In natural weathering systems gibbsite [A1(OH)3],kaolinite, and 2:1 clays are the most commonly observed products (Velbel, 1984a). In bioleachingsystems the alkali cations generally precipitate out in jarosite or natrojarosite (Ross et al., 1993;Ivarson et at., 1978). Although no other precipitates were observed in the bioleaching experimentsbeing discussed in this section, Bhatti et al. (1993) noted that other phases may precipitate if levels ofaluminum and silicon reach saturation conditions.Micas and Various Other PhyltosilicatesThe current ideas regarding weathering ofmicas have also been summarized by Nahon (1991) andVelbel (1984a). Both authors concentrate on potassium-bearing micas because they are the mostabundant and studied of all the micas. This group of minerals has a distinctly layered structure and, as36illustrated in Figure 3.3, cations occur in three very different environments within the lattice (Velbel,1984a). The ideal mica structure contains two layers of silicon (often with some aluminum) tetrahedrathat share, within a plane, three of their four oxygens. Between these two layers is an octahedral sheet,usually containing aluminum, iron, and/or magnesium. Two-thirds of the octahedral corners are sharedwith the apical oxygens in the tetrahedral layers. The remaining corners are commonly hydroxyls butcan be fluorine ions. These three layer units are held together by interlayer cations, usually potassium,sodium, and/or calcium. Micas are arranged into two categories depending on the site occupancy in theoctahedral layer. Dioctahedral micas, which include muscovite and margarite[CaA12(A1Si3O10)(OH)],have two-thirds site occupancy (usually aluminum) and trioctahedral micas,which include phlogopite and biotite [K(Mg,Fe)3(AlSiO10)(OH)2] have full occupancy (usually ironand/or magnesium). It is important to understand the structure ofmicas since it has been shown thatweathering of this mineral group is non stoichiometric and the incongruent dissolution ortransformation is related to the different cation environments within the lattice (Velbel, 1984a).Velbel (1 984a) suggests that three processes are occurring at different rates during mica weathering.In the fastest process the interlayer cations, potassium in his examples, are being replaced by hydratedspecies or hydrogen ions. Numerous researchers have suggested that this process is controlled by theorientation of the hydroxyl ions in the octahedral layer (for example: Nahon, 1991; Fanning andKeramidas, 1977; Norrish, 1973; Bassett, 1960). If the octahedral sites are fully occupied, as fortrioctahedral micas, then the repulsion of the cation with the proton component of the hydroxl forcesthe hydroxyl radical to be oriented perpendicular to the layer, placing the proton close to the interlayercation where the repulsion is somewhat weaker. If the octahedral sites are only partially occupied, asfor the dioctahedral micas, then the cation-proton repulsion orients the hydroxyl radical toward theempty site and parallel to the layer structure. Because the proton component of the hydroxyl radical ispositioned relatively far from the interlayer cation, no repulsion occurs and the cation is more stronglybonded than in the trioctahedral micas. It has been shown by numerous researchers (Em andClemency, 1981 a; Hurd et al., 1979; Leonard and Weed, 1970) that trioctahedral micas are moresusceptible to weathering than dioctahedral micas.The octahedral cations are removed at a somewhat slower rate. Lin and Clemency (198 ib) showedthat the rate of dissolution in trioctahedral micas is directly dependent on the ratio of octahedral to37} tetrahedral layerinterlayer cations} tetrahedral layer}}octahedral layertetrahedral layerinterlayer cations} tetrahedral layer• OH, sometimes F K, Na, and/or CaFigure 3.3: Idealized diagram of a potassium-bearing mica based on the muscovite structure. Thetetrahedrons contain silicon (often with some aluminum), and the octahedrons containaluminum, iron, andlor magnesium. (Modified from Klein and Hurlbut, 1985)38tetrahedral sites. Lin and Clemency (1981 a) demonstrated that octahedral aluminum that is dissolvedimmediately precipitates as an insoluble amorphous aluminum hydroxide; however, a dissolutionbarrier is not formed. Iron and magnesium do not seem to reprecipitate after dissolution; however,iron may oxidize before being removed from the crystal lattice. In trioctahedral micas partial removalof octahedral cations and/or oxidation of the iron allows a reorientation of the hydroxyl radicals thatcreates regions with more stable potassium ions, hindering further dissolution (Velbel, 1 984a; Tarziand Protz, 1979).Velbel (1984a) suggests that the two processes discussed above result in the transformation of theoriginal micas to more silica-rich phyllosilicates such as hydrobiotite (interlayered muscovite andvermiculite), talc, and vermiculite[Mg3(Si,Al)4OH2.5HO[M ]035],possibly with clay or waterlayers. Further dissolution to achieve complete mineral removal requires intense and often prolongedweathering because of the stabilizing affect of the weathering-induced hydroxyl rotation and therecalcitrant nature of the silicon tetrahedra. Laboratory experiments done by Lin and Clemency(1981 a, b, and c) and Clemency and Lin (1981) suggest that dissolution of silica is the rate-limitingstep in complete mica dissolution. Because of this tendency to retain the silicate lattice until the end ofthe dissolution process, in common weathering situations the micas are generally not as extensivelyweathered as other silicates (Velbel, 1982).The weathering features discussed above are interesting; however, the conditions under which metalsulphide bioleaching is done are generally more extreme, at least with respect to pH (section 3.1). Aswith feldspar, Bhatti et al. (1993), Ross et al. (1982), and Ivarson et al. (1978) studied the effect ofbioleaching on several micas as well as montmorillonite, illite, and kaolinite. Unlike in the systemsdiscussed above, they found, using XRD techniques, that muscovite, montmorillonite, and illitedissolution was stoichiornetric although montmorillonite exhibited a slight loss of crystallinity and illiteshowed minor expansion. Glauconite and phiogopite did exhibit non stoichiometric dissolution withsignificant preferential potassium removal. Glauconite converted to nontronite and phlogopiteconverted to vermiculite or a mixed layer vermiculite-phlogopite. Kaolinite, the most common claymineral found in acid sulphate soils (similar conditions to bioleaching), exhibited no dissolution.39It should be noted that Bhatti et a!. (1993) suggest that iron-oxidizing bacteria play an indirect role inphiogopite alteration by producing ferric iron that leads to the formation ofjarosite which appears toenhance the removal of interlayer potassium.Based on their experiments Ross et a!. (1982) and Ivarson et al. (1978) suggested that glauconitedegrades faster than illite and muscovite which degrade faster than microcline. Although they alsosuggested that albite degraded faster than microcline they made no attempt to compare albite with thephyllosilicates also being studied. Still, this finding is interesting since it differs from observationsmade by Velbel (1982) and may indicate that dissolution at low pH levels does not proceed in the sameway as dissolution in common natural weathering environments.Finally, Bhatti et al. (1993) noted that formation of vermiculite or mixed layer vermiculite-phlogopitecould become a serious problem in leaching processes due to the ability of these minerals to expand inthe presence ofwater. When expanded, they could seriously reduce metal sulphide oxidation rates byreducing permeability and thus, solution flow and contact at all scales down to individual minerals(diffusion barriers).3.3.3 PrecipitatesUp to this point the discussion has concentrated on mineral degradation processes. The result of theseprocesses is an increase of various ionic species within the leach solution, in particular ferric iron andsulphate (equations 3.4 and 3.9). Often the solution reaches saturation with respect to ferric iron andprecipitation of insoluble minerals occurs (Lazaroff et al., 1985). Jarosites are generally present in theprecipitate (Bhatti et al., 1993); however, it has been difficult to identif,’ the other compounds oftenpresent because of their amorphous nature (Lazaroff et a!., 1985). In addition to these insoluble minerals,various highly soluble sulphate minerals have been observed in natural acid sulphate environments such asheap leaching operations and acid sulphate soils where drying has occurred (Nordstrom, 1982; Wagner eta!,, 1982). The presence of these precipitates is temporary since they readily dissolve with the return ofmoisture.40Ferric Iron SpeciesIt appears to be generally accepted that jarosite commonly precipitates according to equation 3.19during bioleaching ofmetal suiphide minerals in acidic environments (for example: Ahonen andTuovinen, 1993; Hacki, 1993; Lazaroff eta!., 1985/1982; van Breeman, 1982; Ivarson et a!.,1982). It has a yellow colour and is comprised of aggregates of small (1-4 across), generallyglobular to rhombohedral to pseudocubic crystals (Lazaroff et al., 1985; Wagner et a!., 1982).Tabular forms and hexagonal plates are also possible (Palache et al., 1951). As previously discussed(section 3.2.2), some researchers believe that jarosite precipitates form diffusion barriers on metalsulphide surfaces; however, no evidence of this has been found in laboratory experiments (Tuovinen,1990).Several species ofjarosite with the general formulaMFe3(SO4)2OH)6may form depending on thetype of univalent cation (Mj available (Lazaroffet cii., 1985; Ross et al., 1982; Ivarson et al.,1982/1978). The most common cations to be taken into the structure are K [jarosite], NH4[ammoniojarosite], Na [natrojarosite], andH3O [hydroniumjarosite] (Lazaroff et aL, 1985);however, other cations such as Ag [argentojarosite] and Pb2+ [plumbojarosite] have been observed(Dutrizak and Kaiman, 1976; Ivarson, 1973). Experiments by Lazaroff et a!. 1985 have shown thatthe relative order of formation of the common jarosite-group minerals is as follows:jarosite > ammoniojarosite > natrojarosite > hydroniumjarositeBioleaching studies by Bhatti et cii. (1993), Ross et a!. (1982), and Ivarson et al. (1978) demonstratedthat the necessary cations could be derived from common soil minerals, feldspars and variousphyllosilicates (section 3.3.2). They found that the presence of significant amounts ofNH4blockedthe release of potassium from various potassium-bearing minerals and formed ammoniojarosite. Theyalso found that natrojarosite would form only when potassium was eliminated from the leach solution.Furthermore, in addition to the exchange of cations, selenate (Se042)has been shown to substitute tosome extent for sulphate, despite being highly toxic to bacteria (Lazaroff et al., 1985). Lazaroff et al.(1985) also demonstrated that organic compounds such as methanol, ethanol, acetone, urea, and41amino acids interfere with the uptake of the cations and results in production of a cation-free ferric ironsulphate.The role of bacteria in jarosite formation appears to be indirect (by catalysis of ferric iron production)as no chemical or structural differences are apparent between jarosite produced chemically and in thepresence of bacteria (Tuovinen and Carlson, 1979).Many researchers recognize that a second amorphous dark red to reddish-brown compound is oftenpresent in precipitates formed during bioleaching ofmetal sulphides (for example: Bhatti et al., 1993;Lazaroffet al., 1985/1982; Nordstrom, 1982; van Breeman, 1982; Wagner eta!., 1982). Othershave observed the formation of an amorphous reddish-brown material when cations necessary forjarosite formation are not present in the solution (Lazaroff et al., 1985; Ivarson et al., 1978). Materialof this description is often identified as a mixture of goethite with or without ferrihydrite [5Fe2O3.9H0orFe5HO8.4H20]; however, these compounds appear to be the result ofjarosite transformation due toa rise in pH and dilution of the sulphate solution (Brady et a!., 1986; van Breeman, 1982; Nordstrom,1982; Wagner eta!.; 1982; Tuovinen and Carlson, 1979). Others have identified fresh samples of theamorphous material as ferrihydrite (Ferris eta!., 1989), feroxyhyte [6-FeOOH] (Crosby eta!., 1983),and jarosite (Filipek et al., 1989; Ivarson et al. 1982). Bigham (1994), Bigham et al. (1990) andLazaroff et a!. (1985) believe that a newly identified hydroxysulphate, schwertmannite[Fe8O(OH)6S04],dominates in poorly crystalline precipitates found in streams fed by acid minedrainage; however, it has a distinct yellow colour. Nevertheless, it appears to sometimes exhibit afilamentous or fibroporous morphology (Lazaroff et al., 1985) which is typical of reddish-brownprecipitates seen in many natural acid sulphate environments (Ferris et a!., 1989; Brady et al., 1986;Lazaroffet a!., 1982). Finally, Hackl (1993), Nordstrom (1982), and van Breeman (1982) suggestthat ferric hydroxides [Fe(OH)3]or oxyhydroxides such as goethite precipitate from solution with pHlevels above those common in bioleaching experiments (>3.0). Bigham (1994) agrees with this;however, Lazaroff et a!. (1985) feel that, although it has been seen in laboratory experiments this isunlikely to occur in natural systems.42Obviously, the mineral composition of ferric iron precipitates is complicated and still not clearlyunderstood, probably because of the poor crystallinity ofmuch of the material. In addition, the role ofbacteria in the formation of these ferric iron precipitates is unclear.Water Soluble Secondary SulphatesWilliams (1990) estimates that over 238 species of secondary sulphates, including those discussed inthe section above, are found in the oxidized zones of base metal sulphide deposits. Many of thesesuiphates are water soluble and are found as transient efflorescent crusts in acid sulphate environmentssuch as oxidized zones of sulphide deposits, soils, coal beds, mine tailings, and heap or dump leachsystems (Scott, 1991; Williams, 1990; Nordstrom, 1982; van Breeman, 1982; Wagner et at., 1982).These efflorescences generally form as a result of evaporation which causes capillary draw up ofsulphate-rich solutions to surfaces where further evaporation causes their precipitation (Scott, 1991;Nordstrom, 1982).Commonly green to blue melanterite [FeSO4.7H20]forms but with further evaporation it transforms tothe less hydrous white powdery rozenite [FeSO.4H0],white powdery szmolnokite [FeSO4.H201,orsiderotil [(Fe,Cu)S04.5H20]ifcopper is present (Scott, 1991; Nordstrom, 1982). Furthermore, if theenvironment is warm and somewhat moist these sulphates can partially oxidize to form yellowcopiapite[Fe2F3(SO4)6OH)](Nordstrom, 1982). Copiapite may also precipitate directly fromsolution but the only field evidence appears to be occurences of obvious copiapite overgrowths onmelanterite (colour Plate lB in Nordstrom, 1982). Other divalent or trivalent cations such asCu2,Mg2,Zn2,andAl3may substitute for iron in copiapite (Bayliss and Atencio, 1985;Nordstrom, 1982).The main copper sulphates generally found associated with oxidized copper-bearing ore are light todark green antlerite [Cu3SO4(OH)],light to dark green brochantite [Cu4SO(OH)6],and bluechalcanthite [CuSO45H2O](Scott, 1991). These three minerals interconvert readily depending on thesolution pH. Chalcanthite is stable at the lower end of the pH range, antlerite at the intermediate level,and brochantite at the highest level. The actual pH range in which these minerals are stable variesdepending on the activity of sulphate; however, at log a(S042jof -2 the stability boundaries are at pH43values of 3 and 4.5 and brochantite is stable up to 7.5 (Scott, 1991; Williams, 1990).Gypsum [CaSO42HO]is another sulphate that is observed in many dryer acid sulphate enviromnentswhere calcium is available (van Breeman, 1982; Wagner et al., 1982).For a considerably more extensive discussion of both hydrous and anhydrous secondary sulphateminerals read Williams (1990). He examines groups of suiphates, including copper, lead, zinc, ferriciron, and ferrous iron species, found in the oxidized zones of base metal sulphide deposits anddiscusses possible mineralizing processes using specific sulphate suites.3.3.4 Geometry of Ore Particle DegradationIn the above discussion the alteration of individual minerals has been examined extensively; however, inmost cases, even in concentrates, the particles being leached are composed of sulphide minerals intergrownwith relatively inert minerals having no economic value, often called gangue (Rossi, 1990). It should benoted that pyrite, which is common in the copper-bearing sulphide ores being discussed here, is generallyconsidered to be a gangue mineral with no direct economic value; however, in leaching operations it doeshave indirect value since its oxidation produces iron and acid conditions, both important in metal sulphidedissolution. Although the distribution of sulphides in copper-bearing ores varies greatly (Craig andVaughan, 1980), a general picture, suggested by Rossi (1990), of a small volume of relatively fine-grainedsuiphide particles disseminated throughout a matrix of gangue minerals as individual grains, aggregates,and/or veinlets will be used for this discussion.As inferred in section 3.2, suiphide dissolution requires direct contact of oxidants, ferric iron or bacteria, onthe mineral surface. Rossi (1990) suggests that theoretically this can be achieved in ore particles bycomplete mineral dissolution at the particle surface to gradually expose sulphide grains or by penetration ofthe oxidant-bearing solution through channels in the particle. In reality both occur but the latter appears tobe the dominant mechanism (Rossi, 1990; Braun et a!., 1974; Auk and Wadsworth, 1973).44The leach solution reaches the sulphide grain along two general paths, either directly to the mineralsurfaces unimpeded or through the unreacted or partially reacted gangue matrix (Ross, 1990). Obviouslydiffusion through the gangue matrix is the slower of the two routes. Ross (1990) recognizes that thecontribution from each leaching regime is dependent on the size of the suiphide grains in relation to the oreparticle. If the particle size is essentially the same as the sulphide grain size then leaching is primarilyunimpeded. When particles are larger than the sulphide grains but the grains are at least partially exposedat the surface, leaching is still dominantly unimpeded; however, there is some reduction in the leaching ratebecause portions of the sulphide grains must be accessed by diffusion of the leach solution through thegangue minerals. If the particle is much larger than the suiphide grains and some grains are not initiallyaccessible to the leach solution, the diffusion regime becomes more important. As the ratio of particle tosulphide grain size increases the rate of suiphide leaching is reduced and diffusion through the ganguematrix becomes the limiting factor.This last scenario is the most common for heap, dump, and in situ leaching operations and has beenexamined further by Rossi (1990), Braun et al. (1974), and Auck and Wadsworth (1973). As illustrated inFigure 3.4, they propose that the disseminated suiphide minerals are solubilized as the leach solutioncontacts them along channels within the gangue matrix. A zone of reaction in which the sulphide mineralsare actively degrading progresses through the particle toward its core. The authors suggest that the leadingedge of this zone is located at a distinct boundary between reacted and unreacted material and the secondboundary marks the point at which total sulphide solubilization has occurred. Braun et al. (1974)recognized that as leaching progresses this reaction boundary becomes rough due to preferential solutionpenetration along channels. In fact, they have shown that at late stages of leaching this roughening of theboundary can actually increase the active leaching surface to the point where leaching rates will increaseslightly. Bartlett (1973) suggests that the reaction zone is not this well defined. He proposes that a zone ofhigh oxidation activity which is surrounded on both sides by regions of gradually lower dissolution movesthrough the particle toward the core. In either case, as the active leaching progresses further from theparticles exterior the diffusion path of both reactants and products becomes longer and the metal extractionrate is reduced (Braun eta!., 1974; Auck and Wadsworth, 1973). This effect is probably diminishedsomewhat by enlargement of channels due to gangue mineral dissolution.45suiphide grainsFigure 3.4: Illustration of the possible morphology of ore particle degredation and sulphide mineralsolubilization. The reaction zone where sulphide minerals are actively being solubilizedmigrates from the particle’s outer surface to its core. Precipitates forming in the openchannels are porous and do not inhibit suiphide solubilization. In fact, dissolution at theexposed surface releases ferric iron that then migrates to the suiphide surface and aids inoxidation and results in solubilization of the mineral grain. (After Auck and Wadsworth,1973)unreacted core reaction zone reacted outer rim46Braun et a!. (1974) and Auck and Wadsworth (1973) also observed precipitates, identified by them asbasic iron suiphates, within the open channels in the reacted rim of particles; however, there was noindication that these precipitates effected the leaching rate in their experiments. They theorized thatprecipitate dissolution occurred at the mouth of these plugged channels resulting in increased ferric ironconcentration in the leach solution moving through the porous precipitate to the suiphide mineral surfacewhere oxidation could occur (Figure 3.4). They made no suggestions regarding driving forces for thismovement and did not consider the role of bacteria.Auck and Wadsworth (1973) observed suiphide grains apparently blocking channels and voiced concernthat these grains could effect leaching by impeding further channel development until complete grainsolubilization.It should be noted here that although Rossi (1990), Braun et al. (1974), and Auck and Wadsworth (1973)make no reference to how the channels through which the solution moves are formed their presence is notunlikely, especially in enriched copper ores. All rocks have some natural porosity (Domenico andSchwartz, 1990). Furthermore, the ore particles being leached, whether they are from experiments, dumps,heaps, or in situ operations, had to be reduced in size to some extent and this is likely to producemicrofractures. Finally, copper ores with secondary enrichment, as in the case of the Ivan Mine material,have previously had solutions flowing through them, In fact, it is these solutions that enrich the originalsuiphides and/or deposit additional copper suiphides. Also, bearing in mind the discussion in section 3.3.2,it is not difficult to visualize the opening of these channels indicated in Figure 3.4.As Braun et a!. (1974) suggest, it is evident from this discussion that physical features of the ore are animportant factor in leaching efficiency, possibly as important as the type of suiphide minerals involved.3.4 Bioleaching ExperimentsNumerous laboratory techniques have been developed to study different aspects of the biological leachingprocess. A good review of these is given in Rossi (1990). In this section only the techniques used in the47Ivan Mine study will be discussed. Certain bacterial requirements applicable to both experimentaltechniques will also be examined.3.4.1 Bacterial RequirementsAs was discussed in section 3.1, in order to maintain viability and/or grow, bacteria have certainrequirements. Since bioleaching systems need healthy bacterial populations to achieve efficient metalsulphide solubilization, these requirements must be met. Their metabolic energy source is supplied by themetal sulphides; however the bacteria require additional nutrients to meet elemental requirements of thecell and to aid in metabolism (Table 3.1).Culture media, in this case aqueous mixtures of compounds that meet all the elemental requirements of thecell and supply a metabolic energy source, have been and are still being developed for the bacteriacommonly used in bioleaching. Since T. ferrooxidans is extensively studied, culture media for mesophilicchemolithoautotrophs are generally designed for this species (Rossi, 1990). Table 3.7 lists severalproposed culture media. Those of Leathan et al. (1951) and Silverman and Lundgren (1959) weredeveloped early in the study of metal suiphide bioleaching but are still commonly used today, especially thelatter. Some more recently proposed culture media include added trace elements (Beck, 1967) orthiosulphate as the supplementary energy source (Bounds and Colmer, 1972). Furthermore, Tuovinen andKelly (1972) and Norris and Kelly (1983) proposed media with reduced amounts of ferrous sulphate and,in the former study, a pH of 1.3 to minimize the precipitation of ferric iron species (sections 3.2.2 and3.3.3).When developing a culture media for bioleaching experiments, Rossi (1990) suggests that modifications tothe published examples may be necessary. One must take into consideration the nutrient contribution fromthe ore and furthermore, a compromise may have to be made between acceptable sulphide oxidation ratesand insoluble ferric iron compound precipitation.Finally, certain concentrations of many organic compounds along with various cations and anions caninhibit bacterial growth (Rossi, 1990); therefore, they must either be avoided or their presence noted whenstudying bioleaching systems.48Table 3.7: Several proposed culture media. Values are in grams unless otherwise specified.(After Rossi, 1990)Components 1 2 4 5 6nutrients(N14)2S0 0.15 3.0 1.0 3.0 0.4 0.4KC1 0.05 0.10K2HPO4 0.05 0.50 0.4 0.4MgSO.7H0 0.5 0.50 0.2 0.5 0.4 0.4Ca(N03)2 0.01 0.01distilledH20 1000 700 1000 1000 1000 2000KH2PO4 0.5 3.0CaCL.2H0 0.25energy sourceFeSO4.7H20 lOmlof 300mlof 1.00 33.3 27.810% (wlv) 14.74% (wlv)solution solutionH2S04 1%(v/v) 0.1ONiN solution solutionsodium thiosulphate 5.0nil 1.3trace elementsH3B0 0.060(NH4)MoO.4H2 0.26CuSO.5H0 0.40MnCL2 0.008ZnC12 0.200H20 10001 Leathenetal. (1951)2 Silverman and Lundgren (1959)3 Beck (1967)4 Bounds and Colmer (1972)5 Tuovinen and Kelly (1972)6 Norris and Kelly (1983)a ratio of nutrients to energy source to trace elements mixtures is 79:20:1493.4.2 Shake Flask ExperimentsShake flask experiments are commonly used to study the amenability ofminerals and ores to bioleachingand to determine the effects of different bacterial strains or species on leaching kinetics (Rossi, 1990). Inaddition, the same procedures can be used, where possible, to adapt bacterial strains to different leachingconditions before inoculation into larger scale systems (Hacki, 1993).The apparatus commonly used is quite simple. The leaching takes place in Pyrex glass Erlenmeyer flasks,usually with a 250 ml capacity. The flasks may have small baffles on their bottom surfaces to ensurehomogeneous mixing of the contained slurry. Once charged these vessels are place in a sealed shaker,basically a platform with several clamps for the flasks and an attached drive mechanism to move theplatform. Commonly the shaking rate used is 250 to 300 strokes per minute. The shaker is usually in asealed unit to allow for temperature and atmosphere control.In recent years most tests use approximately 100 g of pulp consisting of 1 to 10 g of ore or mineralconcentrate commonly ground to less than 40 pm, the culture medium (section 3.4.1), and 1 g of inoculum(Rossi, 1990). The inoculum is either a sample concentrated from a natural ore or soil or one previouslycollected and cultured, The experimental temperature and gas flow rates (to control atmosphere) used aremuch more variable and depend on the objectives of the experiment (Rossi, 1990).Rossi (1990) describes the general procedure for an experiment. Once the slurry is assembled in theErlenmeyer flask, a pH reading and a small sample are taken to establish initial conditions. The flask isthen weighed and placed in the shaker. At fixed time intervals agitation is stopped. The flasks are weighedand any moisture loss is compensated for by addition of distilled water. The slurry is then allowed tounmix. Once the solids and liquid are separated the pH is measured and a small solution sample(approximately 1 cm3) is removed for chemical assay (Rossi, 1990). The flasks are then returned to theshaker. Once metal extraction slows or stops the experiment is terminated. Note that at least threeduplicates are commonly run for each experiment (Rossi, 1990).The results of an experiment are metal extraction and/or pH versus time curves. The shape of these curvesgenerally follows that of a laboratory growth curve for bacterial populations (Figure 3.5). Initially there is50a slow increase in the population (lag period) where the bacteria are adapting to their new environment(Chapelle, 1993). Once adapted there is a period of exponential growth where cells rapidly divide(Chapelle, 1993). It is the slope of the extraction curve at this stage that is considered to indicate thesolubilization rate (Rossi, 1990). Once the energy source is depleted growth slows (asymptotic stage) andeventually ceases (stationary stage) (Chapelle, 1993; Rossi, 1990). Finally the cells may die (death stage)(Chapelle, 1993).Often bacterial cultures need to be adapted to experimental leaching conditions such as a new ore ordifferent solution composition (Rossi, 1990; Elzeky and Attia, 1989). This is achieved by running a seriesof tests that, after the initial inoculation, use a small slurry sample (approximately 1 cm3) removed fromthe previous test during the late exponential or asymptotic growth stage (Figure 3.5) as the inoculum(Rossi, 1990). Solution chemistry may be slowly changed from one transfer to the next in order to avoidshocking and possibly killing the bacteria. If adaptation is successful duration of the lag stage should bereduced and, hopefully, the degree and rate of metal extraction should increase (Rossi, 1990). Thisprocedure can also be used to maintain a culture.It should be noted that shake flask experiments are very useful for quickly assessing the amenability of oresto bioleaching, for studying the effects of different leaching conditions on extraction rates, and foradaptation of bacteria to new conditions; however, the results of such experiments cannot be used todesign commercial scale leaching operations (Rossi, 1990). Because very fine grained ore is usedsolubilization rates are much higher than would be expected in a dump, heap, or in situ leaching operationwhere the ore particle sizes are significantly larger than 40 jim (Rossi, 1990). Furthermore, the very smallamounts of ore used may not be representative of the large volumes of ore leached in these commercialoperations. Finally, leach conditions in the shake flask tests are highly variable unlike those in thecontinuous systems of the large scale operations (Rossi, 1990).3.4.3 Column ExperimentsUnlike shake flask tests, column leaching experiments can be used to establish various design features ofcommercial scale operations since the amount and, in particular, the particle size distribution of the ore51U)0)C.)00).0ECFigure 3.5: Characteristic bacterial population growth under laboratory conditions. Growth is initiallyslow as bacteria adjust to new conditions (lag period). Once adapted the population growsexponentially due to rapid cell division (exponential growth). Once the energy source ornutrients are near depletion cells maintain themselves but the population does not grow(stationary period). Finally the nutrients or energy source are depleted and cells begin todie (death phase). If the culture is being maintained or adapted inoculum is transferred atthe late exponential or asymptotic growth stage. (After Chapelle, 1993)lag —t4-exponential 4 stationary period 4 death phaseperiod growthasymptotic stagewhere transfer donetime —+52samples used better resemble those in the large operations (Rossi, 1990). Furthermore, Rossi (1990)suggests that column experiments are more cost effective than both the very fast shake flask tests whichresult in relatively unreliable data and the more costly pilot scale heap tests which result in very similardata to that achieved with the column experiments. However, this is not universally accepted. Despiterecognizing the reliability of column test results such as acid consumption and metal solubilization, Hacki(1993) believes that pilot-scale heap or dump experiments are necessary to acquire the results needed forcommercial scale-up. Nonetheless, column leach tests are widely used (Rossi, 1990).The apparatus utilized in these experiments is generally simple but can vary in size significantly, oftenmaking comparisons difficult (Rossi, 1990). Central to the experiment is a colunm commonly of plastic orfibreglass that can range in height from 1 to 10 m (Rossi, 1990). The height is not critical since severalcolumns can be arranged in series to better represent commercial scale ore depth. The diameter of thecolumn generally varies from 3 to 30% of the height but, more importantly, in order to minimize walleffects it should be from 4-10 times larger than the diameter of the largest ore particles being used (Hackl,1993; Rossi, 1990; Rak and Shaw, 1989). The ore is supported in the column by a perforated plate oftencovered by material such as glass wool to prevent loss of fines (Hackl, 1993). The column is usually filledto within centimetres of the top(Rossi, 1990). The leach solution in column experiments using suiphide oreis commonly recirculated (Rak and Shaw, 1989); therefore, the bucket placed under the bottom opening ofthe upright column both collects the column discharge and supplies the leach solution. A peristaltic pumpis used to pump the solution to the upper opening of the column at a controlled rate, commonly about 10L/hr/m2or 0.17 L/minlm2(Hacki, 1993; Rossi, 1990; Rak and Shaw, 1989). The leach solution is evenlydistributed over the top surface of the ore using a spray nozzle or a layer ofmaterial such as burlap orglass wool and percolates through the ore by gravity (Rossi, 1990; Rak and Shaw, 1989). Thetemperature of the column may be controlled to allow for observations of internal temperature variations.This is done by wrapping the column with heating tape, or by controlling the temperature of the roomcontaining the column (Rossi, 1990).Although the experimental methods for column tests vary significantly there appears to be some generallyapplied procedures. Before the ore is loaded into the column it is often agglomerated and cured, aprocedure which cements the finer ore particles to coarser ones thus minimizing the possibility of local53permeability problems from migrating fines. This is achieved by mixing the ore and a small amount ofsulphuric acid on a rolling or blending cloth, loading the column with the resultant moist mixture (no morethan 12% moisture), and leaving it for at least 24 hours before beginning to put a weak acid solutionthrough the column (Rak and Shaw, 1989). Once the pH of the solution has been stabilized at the desiredlevel, commonly 2.0-2.5, nutrient salts at similar concentrations to those in culture media (section 3.4.1)are added and the column is inoculated (Hack!, 1993).Once the initial setup has been completed a monitoring routine is established. At fixed intervals a smallsolution sample is removed for chemical analysis, generally copper, iron, and sulphate for copper sulphideores, and the solution pH is determined (Hackl, 1993). The pH is maintained at the desired level byaddition of the appropriate amount of a weak sulphuric acid solution. This acid consumption is monitoredclosely. In addition volume losses due to evaporation are determined and corrected generally with distilledwater. Additional monitoring of such things as internal pH, oxygen-content, and ore particle alterationmay occur if the column has been set up with a series of ports along its length (Rossi, 1990).In some column experiments the solution is periodically treated to extract the metal of interest using solventextraction or electrowinning procedures (Hackl, 1993). This better simulates the procedures used in heap,dump, and in situ ope—ations.During this monitoring period metal extraction curves are calculated and maintained in order to watch theleaching progress and determine when to terminate the experiment (Rak and Shaw, 1989). Upontermination the column is often washed with distilled water in order to extract as much of the remainingmetal-bearing solution as possible (Rak and Shaw, 1989). Finally the solid residues are usually dried andsamples analyzed to determine the amount of metal remaining in the ore.Despite the controversy over the degree of usefulness for commercial scale-up the data collected fromcolumn leaching experiments are very useful and can result in a better understanding of numerous variablesincluding temperature variations, percolation rate, particle size effects, composition of the leach solution,pH and Eh profiles, and acid consumption of ore (Hack!, 1993).544. EXPERIMENTAL BIOHYDROMETALLURGICAL LEACHING OF IVAN MINE OREThe experimental work described in this chapter was performed by personnel in the Department of Metalsand Materials Engineering (MMAT) at the University of British Columbia (UBC) under the supervision ofDr. D.B. Dreisinger. Much of the work is described in Leong et a!. (1993). The objectives of theexperiments were: (1) to establish whether bacteria could be acclimatized to high chloride levels and, if thiswas successful, (2) to establish whether efficient copper extraction could be achieved with these bacteria.In order to meet these objectives a series of shake flask and colunrn leach tests were performed. Theexperimental procedures, the leaching conditions, and the results of these experiments will be discussed inthis chapter.4.1 Shake Flask ExperimentsThe shake flask experiments were run to acclimatize several bacterial cultures to the Ivan Mine ore andestablish whether any of these cultures could be adapted to high chloride levels. If these objectives could beachieved, the successful culture or cultures would be used in the colunrn leaching experiments.4. 1.1 Basic Experimental ProcedureExperiments were carried out in 250 ml, bottom-baffled Erlenmeyer flasks. The flasks were kept in anenvironmental shaker in order to maintain a constant temperature of 35°C and continuous agitation of 250rpm, In order to contain the slurry solutions but maintain exposure to the atmosphere foam stoppers wereplaced in the flasks.Small amounts, 4 or 8 g, of Ivan Mine ore ground to -212 p.m (-70 mesh) were used as the experimentalsubstrate. Nutrients were provided in a solution (referred to as 9K) at concentrations suggested bySilverman and Lundgren (1959) and presented in Table 3.7. In some experiments the iron was omittedfrom the solution (OK). Along with 70 ml of one of these solutions, 5 ml of inoculum from culture bankswere added to the shake flasks. Sterile control flasks were also maintained by initially adding 5 ml of 2 gIL55thymol in methanol instead of the inoculum and continually adding 1 ml of the thymol solution atapproximately 14 day intervals until the experiments were terminated.The flask experiments were monitored regularly. They were weighed daily and deionized water was addedto compensate for any evaporation. The pH was monitored and maintained below 2.8 by addition of 6MH2S04. Small solution samples were taken every two days to determine iron, copper, and sulphateconcentrations.In order to monitor the level of bacterial activity, the E1 of the suspended material in each flask wasmeasured daily using a platinum combination electrode. Once the bacteria reached late-exponential phase(Figure 3.5) 5 ml of slurry was transferred to another flask. Conditions in the new flask were modified ifthe bacterial culture was being adapted to, for example, higher chloride levels . The conditions were notaltered if the culture was being maintained. This was the case for the original cultures once they wereadapted to the Ivan ore.4.1.2 The Original Bacterial CulturesThe original bacterial cultures were obtained from Bacon, Donaldson and Associates Ltd. of Richmond,B.C., Canada. Mixed Thiobacilli cultures were chosen for the experiments. As stated in Chapter 3,Thiobacilli are widely considered to be the dominant genus involved in suiphide mineral degradation attemperatures below 40°C and pH below 6. For this reason, these bacteria are commonly used in suiphidemineral bioleaching work and were a good choice for this study.Three strains were chosen for the study. They were designated Type A, Type B, and Type C. The Type Aculture contained bacteria that had been grown on a copper concentrate substrate (grading 28.5% copper)that came from Gibralter Mines Ltd. of British Columbia, Canada. It was hoped that this strain wouldreadily adapt to the Ivan Mine ore that graded over 4% copper. The Type B culture contained bacteriagrown on a pyrite substrate in a solution containing 5 g/L chloride. It was felt that if this strain could beadapted to the Ivan copper ore, it might retain its resistance to high chloride concentrations. The thirdculture, Type C, had been grown on pyrite in the absence of chloride ions. This strain was chosen as amore general culture that might be better suited to adaption to two extreme conditions.564.1.3 Variations in Leaching ConditionsTwo parallel sets of shake flask experiments were run: one to compare leaching results under variousconditions (leaches) and the other to maintain banks of the strains used in the leach experiments (banks).Table 4.1 lists all the tests and briefly describes the experimental conditions they were run under.The leaches were run once the cultures acquired from Bacon, Donaldson and Associates had been adaptedto Ivan ore. The main purposes of the leaches were (1) to determine the importance of added iron, (2) tocompare performances in high and no chloride conditions, and later (3) to ascertain whether increasingslurry density would affect leaching. Reactions to increased slurry densities were of interest because higherslurry densities tend to produce more bacteria per volume, but can be a growth hindrance when too high. Ifthe density of bacteria in each flask could be increased fewer banks would need to be maintained forcolumn inoculations.Sterile leaches were also run under similar conditions to several of the bacterially assisted experiments.A number of strains showing promising results were maintained in banks until those to be used in thecolumn leach experiments were chosen. The high chloride Type B bank could not be maintained at 8 g/LC1 despite the success of initial experiments. The transferred cultures did not thrive; therefore, the bankwas reestablished with a fresh Type B culture from Bacon, Donaldson and Associates. The new bank wassuccessfully maintained at 5 g/L chloride.4.1.4 Results of LeachesThe most important results from the shake flask experiments were previously presented in Leong et al.(1993) and Melluish et a!. (1993). This section summarizes the results.All three cultures successfully adapted to Ivan ore (Figure 4.1). The initial flask experiments exhibitedrelatively fast leaching and achieved copper recoveries of 90 to 95%. Similar sterile experiments achievedcopper recoveries of only 35 to 40%.57Table 4.1: List of shake flask tests and experimental conditions.Type Bacterial Nutrient Chloride Ore Sample No. of Name CodeStrain Type Level Size Transfers (Appendix B)Sterile None 9K none 4 g 0 SCOControl 5 g/L 4 g 0 SC56g/L 4g 0 SC6Leaches A OK none 4 and 8 g n/a AO(4), AO(8)9K none 4 and 8 g n/a A9(4), A9(8)B OK 8g/L 4g n/a BO(4)9K 8g/L 4g n/aC OK none 4 and 8 g n/a C0(4), CO(8)9K none 4 and 8 g n/a C9(4), C9(8)Banks A 9K none 4 g 0 A-2(4)none 8g 15 A-2(8)toA-17(8)B 9K 8gIL 4g 1 B-2(4)8g/L 8g 1 B-2(8)toB-3(8)B(new) 9K 8000a 8g 5 Set#lto#68g 5 Set#1to610000b 8 and 16g 7 Set#lto#6,5gIL Banks (1-17),columns 2, 3, and 5C 9K none 4 g 0 C-2(4)none 8 and 16 g 17 C-2(8) to C-17(8), noC1 Banks (1-8),columns 4 and 6appm NaClbppm NaCl and eventually 5 g/L C158The presence of iron in the nutrient solution appeared to benefit the leaching. The adaptive lag time (Figure3.5) was either reduced or not affected and copper recoveries remained at the 90 to 95% level (Figure 4.2).The presence of chloride ions slowed down the leaching in the inoculated experiments; however, therecoveries were not affected. The Type A and Type C cultures reached maximum recoveries inapproximately 10 days; whereas, the Type B cultures reached maximum recoveries in 20 to 40 days(Figures 4.1 and 4.2). Interestingly, the results from the sterile leaches indicated that chloride ionsimproved the efficiency and, to some extent, the copper recovery of the purely chemical processes involved(Figure 4.1).Increases in slurry density (the weight of ground ore added was doubled) did not affect the leach resultssignificantly (Figure 4.3). Banks were therefore maintained at the higher slurry density. In fact, for banksproduced for inoculation of the columns 16 g of ground ore were used.4.1.5 The BanksAs stated previously, promising cultures were maintained in banks until a decision was made on whichstrains would be used for the column leach experiments. Based on the results described in the sectionabove, it was decided that the Type C strain grown on 8 g of ore in the 9K/no chloride solution and the newType B strain grown on 8 g of ore in the 9K/i 0,000 ppm NaCl solution would be used for the column tests(Table 4.1). The high chloride strain was transferred to flasks containing solutions with 5 gIL C1.4.2 Column Leach ExperimentsThe column leach experiments were run in order to investigate the effects of bacterial leaching on the Ivanore under conditions that more closely simulated those found in heap leaching regimes.4.2.1 Basic Experimental ProcedureThe basic setup for each column experiment is shown in Figure 4.4. Clear acrylic columns measuring 1.83m (6 ft.) in height with internal diameters of 15.3 cm (6 in.) were filled with approximately 40 kg of ore.590C)(Uxa,a,0.00C)Type A, 9K, no Cl.— Type B, 9K, 8 gIL CI—a.--- Type C, 9K, no Cl—)4(— sterile control, 0 g/L—X— sterile control, 5 gIL0 10 20 30 40 50 6010080o 60C)(Uxa)_______a, 40 x....>ç ><0.>< ><.XJ2:‘ I Itime (days)Figure 4.1: Comparison of copper extraction curves for shake flask experiments using the three culturetypes and experiments using sterile conditions. The bacteria successfully adapted to Ivanore, significantly improving leaching rates and recoveries. Notice that the presence ofchloride ions reduced the leaching rate for the Type B experiment.100806040200time (days)Figure 4.2: Comparison of copper extraction curves for shake flask experiments using the 9K and OKnutrient solutions. The leaching rates using the OK solution are significantly lower than thoseusing the 9K solution. Notice that the presence of chloride ions slows down the leachingprocess in both Type B experiments.0 10 20 30 40 50 60Figure 4.3: Comparison of copper extraction curves for shake flask experiments using 4 and 8 g ofground ore. Since there was no significant difference in the results of these experiments 8 gof ore were used in all subsequent tests. The increase in ore volume was believed to result inan increase in the number of bacteria per experiment. Thus fewer experiments would need tobe maintained for column inoculation.60C0C)(xa,a,0C)time (days)Ea15.3 cm•844solution circulation = 9.8LIm2Ihrglass wool40 kg of Ivan oreparticle size = -12.7 or-9.5 mmCu grade = 5.33 wt.%glass wool and perforated plexi-glass plate20 L of leach solutionpH 1.7to2.1Cu = <15g/LFigure 4.4: Schematic diagram illustrating the basic setup of the six column experiments.61The ore was supported by a layer of glass wool and a perforated acrylic plate held in position by twoplastic covered steel rods. The leach solution was semi-continuously circulated through the ore. It wascollected in a 20 L bucket at the bottom of each column and recirculated at a rate of 9.8 L/hr/m2to the topvia Tygon tubing using Masterfiex pumps. The solution drips were dissipated over the top surface of theore by another thin layer of glass wool. Each colunm structure was suspended on support bracketsattached to a wall using two steel rods.The ore, which had been crushed to -12.7 mm (-1/2 in.) or -9.5 mm (-3/8 in.), was agglomerated beforebeing loaded into the columns. As stated in section 3.4, agglomeration is often used as a means ofattaching fines to larger particles. In this case, 40 kg batches of ore were wetted to a 7% moisture levelusing anH2S04solution and then blended and rolled on a heavy plastic sheet until agglomerates formed.The agglomerated ore was left to cure for 24 hours before being loaded into the columns.Before the loaded columns could be inoculated they were prepared. Initially 20 L of appropriately mixedwater (Upper Desesperado and deionized water to the required chloride level) was acidified using 6MH2S04to a pH of 2 and circulated through the ore. Acid was regularly added to the leach solution in orderto maintain the low pH level. Once the solution stabilized at a pH value near 2 sufficient salts were addedto produce 9K nutrient solution conditions. The column was then drained overnight. The following day thecolumn was inoculated. Half a litre of supernatant from appropriate bacteria banks or thymol solution (forthe sterile control) was added to the top surface of the ore.Once the column was inoculated maintenance and observation routines were established. Eh and pH of theleach solution were measured every day and later every other day. The pH was maintained below 2.1 byaddition of 6MH2S04. Acid consumption was monitored. In addition, once a week solution samples weretaken to determine the copper- and iron-content of the leachate.At 7 day intervals the loss of water to evaporation was also monitored. Each column was drainedovernight and weighed the following day along with the solution bucket. These measurements werecompared to those taken when the column was first drained before inoculation and any loss ofweight wascorrected by adding the appropriate amount of deionized water.62The copper level in solution was also regulated in order to prevent precipitation of copper salts in thecolumns and mortality in bacterial populations. A routine bleeding of the system was established at a 7 to14 day interval to keep the copper concentration below 15 gIL. A volume of leach solution, from 5 to 10 L,was removed from the leach bucket and an equivalent volume of OK nutrient solution with an appropriatechloride-content was added. The bled leachate was stored.One fmal procedure was required for the sterile control column. At intervals of approximately 14 days 0.5L of a 2% thymol in methanol solution was added to prevent growth of bacteria.4.2.2 Experimental ConditionsSix column leaching experiments were run. They were designed to examine the effects of various solutionsalinities and particle sizes on the leaching process. Table 4.2 outlines the experimental conditions. Forcolumns 1, 2, 3, and 5 Upper Desesperado basin water was mixed with deionized water to achieve therequired chloride concentrations. Column 1, as indicated, was the sterile control experiment. Columns 2,3, and 5 were designed to examine leaching at high chloride levels and different particle sizes. Column 4was designed to be used as a comparison to the high chloride leaches. Column 6 was run to simulateleaching with the local fresh water source.Columns 2 and 4 were terminated to allow for detailed mineralogical examination on Day 294. Eachcolumn was drained of solution for several days. The solid residues were then removed to 5.5 foot longtroughs made of 12 inch PVC pipe cut in half lengthwise. The residues maintained good verticalpositioning throughout the procedure. They were air dried and samples were taken.4.2.3 Results of Colunrn ExperimentsCopper extraction results are given in Figure 4.5. Notice that columns 2 and 4 were terminated earlier thanthe other experiments. This was done to allow for detailed mineralogical examinations. At the time oftermination the leaching conditions of the other columns were altered slightly. The pH was reduced toapproximately 1.3 and maintained below 1.7 until the remaining experiments were terminated.Table 4.2: Experimental conditions for the column leach experiments. (After Leong et a!., 1993)63Test Conditions Column 1 Column 2 Column 3 Column 4 Column 5 Column 6Crush Size -12.7 -12.7 -12.7 -12.7 -9.5 -12.7(mm)Cl- concentration 5 5 7.5 0 5 0.35(g/L)Inoculum 2 g/L Bacteria in Bacteria in Bacteria in Bacteria in Bacteria inthymol in 5g/L Cl 5g/L Cl- no C1 5g/L C1 no/L C1methanol solution solution solution solution solutionTypea Sterile B B C B Ca see Table 4.1j1008060402000time (days)Figure 4.5: Copper extraction results for the six column experiments. The arrows indicate when the pHlevels for columns 1,3,5, and 6 were lowered to 1.3. (After Leong eta!., 1993)100 200 300 400 50064It is quite obvious that addition of bacteria does improve the rate of leaching and the subsequent copperrecovery of this ore. The sterile control, column 1, achieved a copper recovery of only 23% after 294 days,compared to a recovery of 63% in the same time period for column 2. The only difference in the leachingconditions used in these experiments was the presence of bacteria (Table 4.2).It is also apparent that the presence of chloride in the leach solution does not significantly inhibit leachingwhen chloride adapted bacteria are used. The rate of leaching and final recoveries achieved by columns 2,3, and 5 (high chloride tests), compare favourably to those achieved by columns 4 and 6 (low chloridetests). Column 3 did lag behind the other tests initially. This is probably due to the fact that the bacterialstrain.used in inoculation was adapted to 5 g/L chloride and required some time to adapt to the higher 7.5g/L concentration. Notice also that column 6 with 0.35 g/L chloride exhibited better leaching than column4 with no chloride. This agrees with the results from the shake flask tests (Figure 4.1).The particle sizes used in this series of experiments do not affect leaching significantly. The results fromcolumns 2 and 5 are almost identical. The only difference in the leaching conditions for these two tests wasthe initial particle size of the ore (Table 4.2).The formation of precipitates was also monitored visually and was found to occur in all the columns tovarying degrees (Figure 4.6). The identity, morphology, and distribution of the precipitates will bediscussed in much more detail in later chapters; however, for this discussion it is important to know thatthey were identified as various types of porous iron compounds. Because of their porous nature, it was feltthat these precipitates did not directly impede the leaching process. They did cause a dramatic decrease inthe amount of iron left in the leach solution which would adversely effect the indirect leaching processes.A reduction in the rate of leaching, which was attributed to the lack of iron in solution, was observedaround the 50% copper recovery stage for columns 2, 4, 5, and 6 (Figure 4.5). In order to rectify thesituation, the pH of experiments 1, 3, 5, and 6 was reduced to approximately 1.3 as discussed above. Theleaching rate increased and most of the precipitates were removed. At this stage in the experimentscolumns 2 and 4 were terminated and their pH levels were not altered.65Figure 4,6: Photograph of columns during a draining cycle. Notice the yellow and orange/red precipitateson the dark grey ore and the blue/green and yellow material at the tops and bottomi of thecolumns.665. MODELING OF COLUMN LEACHING USING USING THE COMPUTER PROGRAMPATHPATH, a computer program described by Helgeson et at. (1970) and Perkins (1980), was used to modelreactions occurring in the column 4 leach experiment (Table 5.1). The purpose of the modeling was toestablish a better understanding of possible chemical reactions within the column and to determine whatminerals might form during the leaching process.5.1 The ProgramPATH was developed to model geochemical processes that involve irreversible reactions between mineralsand an aqueous phase. It predicts the change in composition and the number ofmoles of both solid andaqueous phases by breaking the reaction down into small steps and assuming equilibrium at each step. Aseries ofmass balance and mass action equations are solved. The theory and subsequent program weredeveloped by Helgeson and others (Helgeson, 1968; Helgeson et at., 1970; and Perkins, 1980).The user describes an initial solution chemistry and inputs a list of reactants with user-defined reactionrates. Assuming constant temperature and pressure the program determines an initial distribution ofspecies in the aqueous phase and then adds, in steps, small amounts of the reactants according to thereaction rates. In each step the distribution of species in the aqueous solution and the irreversible masstransfer occurring between the various reactants and the solution are calculated. Thermodynamic data issupplied to the program through a file that can be altered by the user. Mineral saturation is also monitoredat each step and upon saturation the mineral begins forming.The system is described at all times by a set of independent components which include water (H20) andany saturated minerals. Electrical neutrality is established when necessary by slight alterations in thenumber of moles of a user designated ion present in abundance in the system. Data from user designatedsteps are saved in an ASCII file.Table 5.1: Experimental conditions for the column 4 experiment (detail of Table 4.2).67Test Conditions Column 4Crush Size -12.7(mm)C1 concentration 0(g/L)Inoculum Bacteria inno C1solutionTypeaa see Table 4.1C68The progress of the overall reaction is controlled by the progress variable, dE, which was defined byHelgeson (1968). In simple terms the reaction progress is the amount ofmolar change of any givenreactant with respect to its reaction rate and can be loosely equated to time.5.2 ConditionsSimulation of the column 4 experiment was run at standard temperature and pressure, 298.15 °K and 1.0atmosphere. It was decided that the modeling would attempt to simulate the leaching process after additionof the 9K salts (Chapter 4) and inoculation. Day 0 of the experiment was chosen as the starting point.Initial conditions for the reactants and aqueous phases (Table 5.2) and modifications to the thermodynamicdatabase (Table 5.3) are discussed in this section.5.2.1 ReactantsMost of the reactants were chosen based on initial mineralogical examination of the unleached Ivan oresample. The three non-mineral species also included in the list of reactants will be discussed later.Reaction rate coefficients for all but the last three minerals were calculated using volumetric distributionestimates (volume%) from AlA and XRD data, and rate constants suggested by Bladh (1978), who used anearlier version of the PATH program to simulate weathering of porphyry copper rocks and formation ofiron-bearing gossans. Weight% data were calculated using density values given in Klein and Hurlbut(1985). All calculations are given in Appendix C.As shown in Table 5.2 quartz and hematite were suppressed. Although both minerals arethermodynamically very stable, in the short time frame of the column experiments these minerals do notform. Quartz was replaced by amorphous silica that has a much higher solubility. Based on itsthermodynamic properties a solubility ten times that of quartz was used. Under sulphide mineralbioleaching conditions various iron phases including schwertmannite, ferrihydrite, goethite, and ferroxyhyteare observed to form, not hematite (section 3.3.3). Thermodynamic data was available for goethite (Bladh,1980); therefore it was used to represent the iron precipitates in the simulation.69Table 5.2: Inital conditions used for column 4 modelling. Values in bold type face were used as input forrun #1.REACTANTS AQUEOUS PHASEMineral Volume% Weight Rxn Rate Species Molality or Log Activity(estimate) (g) (niol//cm3) (estimated) (used)chalcocite 1.24 25.6 0.40covellite 0.96 16.4 0.31bornite 0.55 10.2 0.18chalcopyrite 0.02 0.3 0.006pyrite 0.16 2.9 0.05magnetite 0.20 3.8 0.06quartza 47.52 none suppressedalbite 41.89 401.1 0.002muscovite 2.05 21.1 0.005clinochlore 5.41 31.4 0.0073annite 26.9 0.0063anorthite 0.0 0.0 0.0hematiteb 0.0 none suppressedCu I.O1E-01 1.OE-01log [K] -1.75 to -2.1 -1.85S042 2.86E-01 2.9E-O1Fe2 1 .26E-0 1 6.0E-07’NH4 4.55E-02 4.6E-02Mg2 2.03E-03 2.OE-03Cl 1.34E-03 1.3E-03Ca2 3.38E-05 3.4E-04K 5.O1E-83 5.OE-03AI3 0.0 1.OE-15Na 0.0 1.OE-15HSi04 0.0 3.9E04dP04 3.67E-03 not includedelog [°2lgas -0.699 0.699Othersulphuric acidoxygenamorphoussilicanone400460.29999.0100.00.002aorphous silica replaced quartz. Thermodynamic data was estimated to give it a solubility ten times thatof quartz. The quartz reaction coefficient was used.bhematite was suppressed because it saturates during the simulation and there is evidence that inbioleaching systems it does not form.cFe2+was reduced because the solution was saturating with iron compounds before the simulation couldget started.derror— this value is for column 2 initial conditions. This was noticed much too late to rerun thesimulation. Presumably amorphous silica would saturate niuch later in the simulation if the correct valueof 1.OE-15 was used.ethe phosphate was assumed to be totally consumed by the bacteria in the column experiment (section 3.1).70Table 5.3: Minerals added or removed from the thermodynamic database.REMOVED ADDEDName’ FormulaHf Sourceakernianite ELEMENTAL SULPHUR S 0.0 Robie et al. (1978)andalusite H-SULFATE H2S04 -22200.0 trial and errorbandradite AMORPHOUS SILICA Si02 -917263.9 trial and erroreCa-Al pyroxene K-JAROSTTE KFe3(S04)OH)6 -3756893.1 Bladh (1980)clinoenstatite HYDRONIUM-JAROSITE (0)FeS0OH) -3758429.4 Bladh (1980)diopside NATROJAROSITE NaFe3(SO42OH)6 -3712479.7 Bladh (1980)enstatite GYPSUM CaSO.2H0 -2022628.0 Bladh (1980)epidote GOETHITE FeO(OH) -542987.0 Bladh (1980)fayalite MOXYGEN 02 -63871.9 trial and errordforsteritegrossularhigh sanidinejadeitekyaniteprotoenstatitesillirninitespinelaas seen in the database.bvalue determined so that H-SULFATE will never saturate.evalue determined so that solubilitv is I Ox higher than that for alpha-quartzdvalije determined so that the log activity of oxygen gas is -0.69971Several other features of the column 4 experiment required the addition of two non-mineral reactants,sulphuric acid and oxygen. During the column experiment the solution pH was monitored closely andmaintained in the range of 1.75 to 2.1 (section 4.2). Addition of sulphuric acid was necessary throughoutthe experiment due to acid consumption by reactions such as those involved in silicate dissolution. Duringthe simulation the pH also steadily increased. So, in order to reproduce the column conditions thesimulation was run in a series of steps each ending when the pH reached 2.1. At the beginning of all butthe first step the amount of sulphuric acid required to bring the pH back to 1.75 was rapidly added.The oxygen-content of the aqueous phase also had to be considered. During the experiment column 4 wasopen to the atmosphere at either end, as was the bucket containing the excess solution (Figure 4.4). Noinfoririation regarding the oxygen-content of the solution either outside or inside the column was available;therefore, for the simulation it was assumed that oxygen was saturated. This seemed to be a reasonableassumption since the overall column reaction was being simulated and oxygen depletion would probablyhave occurred at a local scale only, in the very middle of the column. Because many of the reactions in thesimulation required oxygen, saturation was established by an initial rapid addition and maintained bymaking excess oxygen available at all times. Once established this did not require monitoring as with pH.5.2.2 Aqueous PhaseAs stated above, the initial composition of the aqueous phase in this simulation is given in Table 5.2. Thevalues are based primarily on calculations of a theoretical composition (Appendix C) since only the pH,iron-content, and copper-content were known when the simulation was run (Leong, 1 992a). The amount ofiron was significantly reduced in the initial input file because various iron compounds saturated before themodeling could commence. Also, total iron was actually input as Fe3+ because this is the dominant ironspecies under the conditions being considered. P04-was not included in the initial solution compositionbecause the phosphorous was assumed to be totally consumed by the bacteria in the column experiment.The species in the aqueous phase were used as the initial set of independent components. Because thespecies had to be independent, NH4+was used to represent all nitrogen-bearing species added to the leachsolution. Furthermore, very small amounts ofA13+ and Na+ were included despite theoretically not being72present because aluminum and sodium were added to the solution in step I as muscovite, albite, andclinochlore.An error was made with regards to the amount of silica that theoretically should have been present. Theamount input was the value calculated for the column 2 experiment. The column 2 leach solution containedUpper Desesperado water that contains some silica. Theoretically, the column 4 solution should havecontained very little, if any, silica and the input value should have been the same as that for the sodium andaluminum. Presumably, aniorphous silica would have saturated later in the simulation if the correct valuehad been used.5.2.3 Thermodynamic DataThe thermodynamic data used for solids and aqueous species are from Helgeson et al. (1978) and Helgeson(1969), respectively. These relatively old data sets were used despite the availability ofmore recent datafor many of the solids (Bennan, 1988) because they are consistent. Several minerals in the standarddatabase were removed because they were not relevant to the system being modeled and made outputscumbersome (Table 5.3). Several minerals, both real and created, were added because it was felt that theycould be relevant or were necessary. Note that because in the program reactants have to be solids theimaginary solids H-SULFATE and MOXYGEN were created to represent sulphuric acid and oxygen,respectively. Table 5.3 lists the added minerals , their formulae, the thermodynamic data input, and thesource of the information.5.3 ResultsSix runs were executed during the simulation. Highlights of these runs are given in Table 5.4. As wasplanned, oxygen saturated almost immediately (run #1) and was maintained to the end of the simulation.Jarosite and amorphous silica saturated soon after. In run #4 goethite saturated and was followed byhydroniumjarosite in run #5. Hydroniumjarosite was suppressed because of a problem with the program.Run #5 was executed a second time without hydronium jarosite in the thermodynamic database. Bornite73Table 5.4: Highlights of the column 4 simulation.RUN pH COMMENTS STEP ()#1 1.85 01.85 -oxygen saturates 1 (3.800E-22)1.856 -k-jarosite saturates 13 (2.035E-04)2.07 -amorphous silica saturates 80 (9.518E-03)#2 2.101 -1.74g sulphuric acid added 89 (1.0681E-02)1.74 -sulphuric acid consumed 117 (1 .0682E-02)#3 2.097 -2.Og sulphuric acid added 290 (2.0155E-01)1.748 -sulphuric acid consumed 314 (2.0155E-01)#4 1.82 -run #3 stopped early so pH still low 387 (2,5779E-01)1.874 -goethite saturates 434 (2.8940E-01)#5 2.09 -2,5g sulphuric acid added 617 (4.6730E-01)1.843 -hvdroniumjarosite saturates 637 (4.6730E-01)-suppressed and step rerun because of problems with program1.75 -sulphuric acid consumed 645 (4.6730E-0 1)#6 2.095 -2,90 sulphuric acid added 928 (8.2826E-01)1.752 -sulphuric acid consumed 952 (8.2826E-01)1.897 -bornite consumed 1089 (1.0332)2.044 -chalcanthite saturated 1213 (1.2922)2.102 -stopped simulation 1217 (1.3906)-Cu over 20g/l (need to bleed 5L of solution - section 4.2)-note: when pH was allowed to pass 2.102 alunite saturated74was consumed in run #6. Soon after, chalcanthite saturation was reached. Run #6 was terminated at step1217 at the point where the pH reached 2.102 and the solution’s copper-content reached 2OglL. It wasdecided not to continue the simulation beyond this point; however, initially the program was allowed toexceed pH of 2.1 and alunite saturated soon after.During the simulation more than 1 Og of sulphuric acid were added to the system to maintain the pHbetween 1.75 and 2.10. The amount required in each step increased as the simulation progressed.The changes in the mass of solids and activities of aqueous species are presented in the following sections.Many of these data sets exhibit a relatively rapid increase or decrease at the beginning of the simulation(run #1). This is due to the fact that the reaction rates in run #1 are 10 times larger than in the subsequentruns. The rates were changed to accommodate the rapid input of sulphuric acid. Correction of the run #1reaction rates was overlooked.5.3.1 Change in the Mass of SolidsSilicate ReactantsDue to very small relative reaction rates (Table 5.2) the change in mass of the silicate reactants is verylow (Table 5.5). The total mass of amorphous silica actually increased slightly due to its earlysaturation. This increase would have been smaller if the correct theoretical silica-content had beenused.Metallic ReactantsThe change in mass of the metallic reactants (Figure 5.1) vary depending on their relative reaction rates(Table 5.2). The total mass of chalcocite and covellite decrease by over 4 g. Magnetite and pyritedecrease by 2 g or less. The total final mass of magnetite is actually lower than pyrite. Chalcopyrite isreduced by almost half to 0.136 g.All of the bomite (10.2 g) is consumed during the simulation despite its relative reaction rate beingabout half that of chalcocite (Table 5.2). This occurs because these reaction rates are based on molar75Table 5.5: Mass change of silicate reactants during the simulation. The values are in grams. Notice thatthe amount of amorphous silica increased due to saturation at Step 80.Minerals Step 0 Step 1217 Net Loss( = 3.81E-22) (E = 8.28E-01)amorphous silica 460.20 460.70 -0.50albite 401.10 400.00 1.10muscovite 21.10 20.81 0.29annite 31.40 30.95 0.45clinochlore 26.90 26.33 0.57runs#1 and #2 I4 wns#3and#4 U run #5—*— chalcocite25—.— cove lute—D— bornite-+- magnetite-— pyrite20 —0- chalcopyriteG) 10o ‘ 0.4 O.5 O7 0.9 1 11!2 : .4reaction progress (E)Figure 5.1: Change in mass of the metallic reactants during the simulation. Notice bomite is depleted.76quantities and not mass. Since one mole of bornite (502 g) is significantly heavier than one mole ofchalcocite (159 g), a larger mass of bornite is consumed at each step.ProductsThe products exhibit more complex mass changes than the reactants (Figure 5.2). Jarosite is the firstmineral to saturate. It rapidly forms almost 2.8 g at which point goethite saturates and the rate ofjarosite production decreases. The overall reaction occurring after these saturations is described in thefollowing two unbalanced equations:4OCu2S+ 31CuS + 1CuFeS2+ 18Cu5FeS4+ 5FeS2 + 6Fe304+ 35202 + 7511S04 +4Fe3+ 31H—*KFe3(50)O I)6+ 44Fe0(OH) + 202Cu + 224S04 + 3MgSO4+ 32H0 (5.1)0.2NaAlSi3O4+0.5KAI3SiO10(OH)2+0.6KFe3A1SiO10(OH)2+0.7Mg5Al2Si3O10(OH)8—>KFe3(S04)OH)6+ 6.OSiO2+ 2.9MgSO4+ 3.7Al + 0.2Na + 0.2K + 0.6Mg2 (5.2)Note that unbalanced equations are used in this section in order to emphasize the important componentsin the reactions being considered. Appendix C contains fully balanced equations for these partialreactions.Relatively small deviations in this overall reaction, related to the input of sulphuric acid, occur duringthe simulation (Figure 5.3). Before goethite saturation, jarosite becomes undersaturated with thedecrease in pH and a small amount ofjarosite is consumed according to the following unbalancedreaction:18KFe3(504)2OH)6+K504 + 9999H2S04+ 4023S0— 19K + 14082HS0 + 5808H + 109H2 (5.3)Table 5.6 lists the mole change of various other species involved in the reaction above. The activity ofiron species increases due to the input of iron from the jarosite. Notice that all of the aqueouscomplexes except the iron chlorides break down with the decrease in pH.reaction progress (E)Figure 5.2: Mass change of the products during the simulation. Notice the change in the rate ofproduction ofjarosite when goethite becomes saturated. The slight change in goethiteproduction rate just above 1.0 corresponds to the depletion of bornite.._______ ____________ ____________r,ntA_______________Figure 5.3: Detail of the above figure. The point ofjarosite saturation is more obvious here. The initialhigh production rate is due to the higher relative reaction rate used in run ft 1. Notice, also,the increase in jarosite corresponding to a decrease in goethite when sulphuric acid is added.Before goethite saturation jarosite is destroyed with the addition of sulphuric acid.runs#land#2 N4 runs#3and#4 144 run7700Ea)—A— goethite-*- sulphuric acid—.— chalcanthitexxe p1 ete dx jarosite satuates// : goete sat ateborn ite dchalcanthite saturatesx—:)x-x—xX-x x__ /____x-x >0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.414 runs#land#2 N run #5cz)U,U,Ea)0.0 0.1 0.2 0.3 0.4 0.5reaction progress ()78Table 5.6: The amount (in moles) of dominant minerals and aqueous species being consumed andproduced during addition of sulphuric acid at the beginning of run #3, before goethitesaturation. Jarosite [KFe3(S042OH)6]is dissolving at an increased rate as the pH decreases.The pH for steps 89 and 104 are 2.08 and 1.89, respectively. Notice that most complexes aredisassociating; however, iron chlorides are forming.Consumed ProducedMineral/Species Step 89 Step 104 Mineral/Species Step 89 Step 104CU2S(SOljd) 0.04 0.04 Si02(S) 0.55 0.55CUS(SOljd) 0.03 1 0.03 Cu2 0.56 0.76Cu5FeS4(Old) 0.018 1.018 HS04 14083.00 13801.00°2(oas) 0.35 0.35 18.90 29.50H2504 9999.00 9999.00 Fe3 47.70 78.60KFe3(SOOH)6SQld 17.18 29.50 FeCl2 6.04 y9.85KSO4- 1.06 0.04 FeCl2 <0.01 0.01S042 4027.00 3719.00 Mg2 23.30 23.00MgSO4 23.30 23.00 Ca2 0.28 0.27CaSO4 0.28 0.27 H 5808.00 6020.00H20 278.00 281.00 Al3 0.51 0.22C1 5.70 9.30CuCl 0.36 0.56H4SiO 0.55 0.55Al(OH)2 0.51 0.2279After the overall saturation of goethite it becomes undersaturated with the addition of sulphuric acid.A relatively small amount of goethite is consumed and jarosite production actually increases accordingto the following partial reaction:291FeO(OH) + 6KS04 + 42K + 9999H2504+ 5547S02 —48KFe3(S0)OH)6+ 15480HS0 + 3932H + 296H0 (5.4)Table 5.7 lists the relative mole change of various other species involved in this reaction. The activityof the iron species involved (not shown in reaction) increases substantially because jarosite formationdoes not consume all the iron released from goethite. The activity of the potassium species decreasessubstantially because of the uptake by jarosite. The other complexes present disassociate under thedecreasing pH conditions.Interestingly, only goethite exhibits a slight decrease in production rate at a c-value of 1.03, wherebornite becomes depleted (Figure 5.1). Jarosite is not effected by the loss of iron from the bornitedissolution.Finally, chalcanthite becomes saturated very close to the end of the simulation and forms rapidly. Over4 g of chalcanthite form in one tenth of the ‘time’ that approximately 3 g of goethite and jarosite form.5.3.2 Change in the Activities of Aqueous SpeciesDuring the simulation PATH considers the activity of 40 aqueous species. Most of these species have verylow activities and will not be discussed here.The most abundant species relevant to the simulation include Cu2,HS04,S042,H, K, and Fe3.Figure 5.4 illustrates the variation in activities of these ions. Cu2+ shows a steady but small increase inactivity with only a slight decrease at the point where chalcanthite saturates (Figure 5.2). Cu+, not shown,80Table 5.7: The amount (in moles) of dominant minerals and aqueous species being consumed andproduced during addition ofH-SULFATE at the beginning of run #6, after goethite saturation.Goethite [FeO(OH)] is dissolving at an increased rate and jarosite [KFe3(S04)2OH)]isforming at a decreased rate as the pH decreases. The pH for Steps 928 and 945 are 2.08 and1.86, respectively. Notice that most complexes are disassociating; however, iron chlorides areforming.Consumed ProducedMineral/Species Step 928 Step 945 Mineral/Species Step 928 Step 945Cu2S(SOld) 0.04 0.04 KFe3(SO4)2OH)6SOld 48.17 5.94CuS(SO1d) 0.03 1 0.03 SiO2(soljd) 0.48 0.48Cu5FeS4(SOld) 0.018 1.018 Cu2 1.41 3.59°2(gas) 0.35 0.35 H504 15480.00 14687.00H2S04 9999.00 9999.00 Fe3 130.85 391.14FeO(OH)(SOld) 291.45 453.32 FeCl2 16.13 44.41KS04 6.16 0.74 FeCl2 0.01 0.03K 42.01 5.19 Mg 23.91 22.84So42- 5547.00 4676.10 Ca2 0.18 0.17Mg504 23.91 22.84 Al3 1.03 0.36CaSO4 0.18 0.17H20 250.04 251.68H 3931.60 3986.20CuC1’ 1.21 3.38H4SiO 0.48 0.48M(OH)2 1.03 0.36-2Cl). -3>,>CuC)0-4-5-6runs#land#2 44 runs#3and#4 l40.0run #681Figure 5.4: Change in activities of the dominant aqueous species during the simulation. Fe2 and Cu (notshown here) exhibit similar patterns to Fe3 and Cu2 but at much lower activities. Notice thereduction in K activity and the increase in Fe3 activity when H-SULFATE is added to thesolution. The cause of the strange pattern for Fe between 0.2 and 0.3 is not known.C).i50>C.)CuC)0•1-2-3-4-5-60.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4reaction progress ()Figure 5.5: Change in the activities of other abundant aqueous species. K and H are included forreference. Notice that the activity ofmost of the other species remain virtually the same orincrease slightly. One exception is Ca2,which decreases while another species not shownhere, CaSO4.actually increases.0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4reaction progress ()runs #1 and #2 44 runs #3 and #4 N4 #682exhibits the same pattern but in a lower activity range. Unlike HS04 and SO42-that exhibit severalvirtually instantaneous increases in activity, neither copper species are effected by the input of sulphuricacid.The activities ofKand Fe3 are effected by the sulphuric acid. After goethite saturation the activity ofKrapidly and significantly decreases and the activity ofFe3 similarly increases. Fe2,FeCl2,and KS04(not shown) exhibit patterns in their activity changes similar to those of these more abundant species. Theactivity of the iron species increase due to dissolution of goethite (Figure 5.3). The decrease in activity ofthe potassium species occurs because jarosite production increases, as indicated by equation (5.4). Thecause of the strange pattern in Fe3 activity at of approximately 0.2 is unknown.Figure 5.5 illustrates the change in activities of various other abundant species. H+, and K+ are includedfor comparison. These species do not show any significant deviations due to the input of sulphuric acid;however, many of the complexes present do disassociate and very small, temporary increases in activitiesofMg2,A13, and Ca2 do occur (Tables 5.6 and 5.7). Al3 and Na show an overall increase in activitydue to the input primarily from albite and muscovite. Mg2exhibits a steady but smaller increase due tothe slower input of annite. The activity ofH4SiO,after an initial increase, does not change significantlybecause amorphous quartz becomes saturated. The activity ofCa2+decreases slowly but steadilycorresponding to a similar overall increase in CaSO4,not shown. N03 exhibits a similar steady decreasebut there is no corresponding increase of the activity of any other nitrogen-bearing species.5.4 DiscussionThe results from the column 4 simulation explain some of the processes occurring in the leach experiment.Of particular interest are the predictions of the types of precipitates that might form and their reactions tothe addition of acid. PATH has been very useful for predicting and explaining possible internal columnconditions; however, it does have some limitations which are also discussed in the following section.835.4.1 The PrecipitatesJarosite and GoethiteThe pattern ofjarosite and goethite formation is the most accurate prediction of the simulation. As willbe discussed in later chapters, in most of the column experiments (including 4) jarosite was the firstprecipitate to be observed. This was followed by formation of unidentified iron species that tended toaccumulate below the jarosite, at the bottom of the columns. The simulation predicted formation ofjarosite followed by goethite and in a moving system like the column experiments this would appear asa layer ofjarosite over a layer ofgoethite.It was also observed that with time the precipitates, especially jarosite, moved down the columns in aplug flow fashion. The simulation may indicate a reason for this phenomenon. It predicted thatlowering of the pH would cause solubilization ofjarosite where goethite is not saturated andsolubilization of goethite along with precipitation ofjarosite where the goethite had been saturated. Ifthis is correct one could visualize that a solution of increased acidity introduced to the top of a columnmight pick up iron and potassium from the solubilizing jarosite and transport it to the goethite zonewhere jarosite could precipitate and goethite solubilize. During this movement the pH of the solutionwould undoubtedly be increasing due to dilution with resident leachate and reaction with the silicateminerals that are present in abundance in the ore. At some point in the downward flow the pH of thesolution would increase to the point of goethite saturation and precipitation might occur. In this waythe precipitate zones would appear to migrate downward.One fmal point to consider with regards to these precipitates is the presence of a mixed precipitateregion observed at the boundary between the two zones in columns 2 and 4. The simulation predictsthat only small fractions of the precipitated material would solubilize. If this is true one would expectthat not all of the goethite would solubilize in the region where the jarosite was reforming. Thisscenario would result in a mixture of the two precipitates between the two zones.84Amorphous SilicaAmorphous silica saturates very early in the simulation. Unfortunately, no obvious occurrences of thisphase were observed in the leached material. Furthermore, dissolution of quartz in the ore particleswas not observed. The reaction rate used for this simulation may be too large.ChalcanthiteThe saturation of chalcanthite at copper levels near 20 g/L is another interesting prediction. In thecolumn 4 experiment the copper-content of the leach solution was kept below l5gfL (section 4.2) aftera decrease in copper was observed when the solution neared 20 g/L copper. Interestingly, it wasthought that a copper-bearing phase was precipitating out at this point. Unfortunately, no evidence ofthis phase was observed in the mineralogical examination of the leached material. If it was chalcanthitethe chances of preserving it during the experiment and sample preparation afterward would be slimsince it is highly water soluble.5,4.2 Program LimitationsThe results of this exercise must be used cautiously as the program does have limitations both in its basicsetup and execution, Some of the more important limitations will be discussed here.The Thermodynamic DatabaseThe database has limitations due to the lack of some pertinent mineral and aqueous species and thequality of some of the thermodynamic data. Many minerals and aqueous species have not beenincluded in the database due to lack of thermodynamic data. Other species have been included despitethe fact that their thermodynamic properties are not well known. This means that the simulation maynot predict all the products and reactions present in the experiment. However, it should be emphasizedthat the behavior of the major species involved have been modeled fairly accurately.85Reaction KineticsThe program assumes equilibrium conditions at small steps in the overall irreversible reaction; howeverthere is evidence that individual reaction kinetics are important elements in the progress of the leachingprocess being modeled (Nordstrom, 1978). The user-defined reaction rates of the reactants docompensate to some extent for the lack of kinetic information; nevertheless, they do not take intoaccount the presence of catalyzing bacteria, the possible formation of impeding coatings on reactants,and fluid flow. Furthermore, the reaction rates are only estimates based on relative volumes andproposed mineral dissolution kinetics. In the case of the copper-bearing sulphides some generallyagreed upon but as yet unquantified information was not included in the rate estimates. It is commonlyagreed among hydrometallurgists that covellite dissolves much faster than chalcocite and bornite muchfaster than chalcopyrite (Hacki, 1993). This probably wouldn’t effect the present simulationsubstantially but should be considered in future modeling.Indirectly the program actually has crudely taken into account the presence of bacteria. Severalimportant reactions that are catalyzed by bacteria (section 3.2) and probably are not rate limiting in thecolumn 4 experiment, are not progress limiting in the simulation because all reactions are considered tohave the same relative reaction rates.Finally, the fact that the program did not take into consideration the presence of reaction impedingcoatings and fluid flow may not be significant in this simulation. No impermeable coatings wereidentified in the column 4 solid residues (Chapter 7), and the fluid was recirculated almost continuallyduring the experiment, allowing frequent exposure to the same solution.Data OutputThe data output format for PATH is very cumbersome. Each run produced over 100 pages of outputof which only a very small portion was examined. It required several full days ofmanipulation toproduce the limited results discussed in this chapter. Although it can be important to examine parts ofthis output in detail, generally a summary containing data on mass changes, species activities, reactioncoefficients, and corresponding dE values would be sufficient. This would allow the user to run moresimulations to examine the effects of slight changes to the system. For this exercise several runs at86different pH ranges and copper values would have been useful for studying microenvironments thatmay occur in the column.5.4.3 Final NoteSince the simulation was run a chemical analysis of a bleed sample taken on Day 19 of the column 4experiment has been acquired. Table 5.8 compares these results to the theoretical solution chemistryused for the simulation. Except for the pH, iron, and copper values which were analyzed by the Metalsand Materials Engineering group at U.B.C. (see Chapter 4), all the elements or species were actuallypresent in higher amounts than calculated. Future simulations would incorporate this chemicalinformation into the input data.87Table 5.8: Comparison of colunm 4 theoretical and analyzed solution chemistry at Day 0 and Day 19,respectively. All values are in mol/kg8010 unless otherwise stated.Theoreticala AnalyzedbCu l.01E-01 LOIE-OlS042 2.86E-01 4.52E-01Fe2 1.26E-01 9.85E-02NH4 4.55E-02 n/aMg2 2.03E-03 2.02E-02Cl 1.34E-03 1.04E-02Ca2 3.38E-05 1.35E-02K 5.O1E-03 1.41E-03Al3 0.00 1.67E-02Na 0.00 3.48E-02H4SiO 0.00 7.69E-03P04 3.67E-03 <1.OOE-04log [H] -1.94 -1.94log [°2]gas -0.699 n/aasee Table 5.2banalyses done by Chernex Labs Ltd., NorthVancouver, Canada using inductively coupledplasma (ICP) techniques.886. TECHNIQUES USED FOR THE MINERALOGICAL EXAMINATION OF THEIVAN ORE SAMPLE AND THE SOLID LEACH RESIDUESA variety of samples and analytical techniques were used in the mineralogical study thus requiring anumber of different preparation methods. The samples were collected from unleached Ivan ore and thesolid residues of the column leach experiments. Material from shake flask experiments were not examined.The analytical techniques used include optical microscopy (stereoscopic, transmitted light, and reflectedlight), sieve analysis, powder x-ray diffraction (XRD), secondary electron microscopy with energydispersive spectrometry (SEM/EDS), automated image analysis (AlA), and electron probe microanalysis(EPMA). Generally, standard sample preparation methods were used; however, a couple of innovativetechniques were developed and will be discussed in some detail. A complete list of samples along with thepreparation methods and analytical techniques used is given in Appendix D and summarized in Table Sample Types, Sampling Methods, and Special Sample Preparation TechniquesThe samples that were examined include unleached Ivan ore, evaporites from the column rims, precipitatesfrom the exterior of the leached particles, and the leached particles themselves. Various sample preparationmethods were applied depending on what analytical techniques were used (Table 6.1). Only non standardpreparation methods are described in this section. Standard preparation methods are discussed in theanalytical techniques section that follows,6.1.1 Unleached Ivan OreTwo large samples of Ivan ore were received from Rayrock Minera Ltda. The first sample consisted ofapproximately 40 kg of broken ore ranging in size from less than 1 mm to over 5 cm in diameter. It wasdivided into 3 equal portions using a modified coning and quartering method (Jones, 1987). One portionwas retained for mineralogical study; another portion was stored for later use; and the last portion wasground to -75 p.m for use in the initial shake flask experiments. A small amount of this ground ore wasretained for XRD analysis.89Table 6.1: Sample types, preparation methods, and analytical techniques used in the mineralogical studyof the Ivan ore and solid residues from column leach tests.Sample Type Preparation Methods Analytical TechniquesIvan ore (unleached) crushed to -12.7mm optical microscopyground XRDcut in half (and polished) SEMJEDSsized (sieve analysis) AlAmounted and polished EPMAwet chemistryEvaporites ground optical microscopymounted on stubs XRDSEM/EDSPrecipitates ground optical microscopymounted on stubs XRDSEMJEDSwet chemistryLeached Particles ground optical microscopycut in half (and polished) XRDmounted on stubs SEM/EDSmounted and polished EPMAwet chemistry90The second sample consisted of 750 kg of broken ore ranging in size from less than 1 mm to over 30 cm indiameter. This material was manually homogenized and separated into 26 approximately equal portions.Roughly 240 kg of this ore (about eight 20 L buckets) were crushed to -12.7 mm using a small bench jawcrusher. An additional 50 kg sample was crushed to -9.5 mm using the same equipment. In order tominimize the fines produced the ore was crushed in a series of steps in which the crusher aperture wasdecreased. In each step the -12.7 mm or -9.5 mm material was removed by manual sieving.Approximately 40 kg of the -12.7 mm material was retained for mineralogical study, size analysis, andchemical analysis. Ten kilograms of the -9.5 mm material were ground to -75 .tm for use in the shake flasktests. A small amount of this material was also retained for XRD analysis. The remaining crushedmaterial was used in the column experiments as described in Chapter 3. The remaining uncrushed ore wasstored for later use.The analytical techniques used to study these unleached ore samples include optical microscopy, XRD,SEMJEDS, AlA, and EPMA (Table 6.1). The samples examined using SEMIEDS techniques were handpicked from both mineralogical samples. They were chosen as representatives of the different textures inthe ore. The particles were cut in half using a Raytech Jem Saw with a 6 inch blade. Some of the cutsurfaces were polished using standard polishing techniques (Jones, 1987; Craig and Vaughan, 1980). Thesamples examined using EPMA techniques were also hand picked as textural representatives; howeverthese particles came from the second sample only, the -12.7 mm crushed ore. Material used for XRD andAlA examination were randomly separated from larger samples using the riffling method (Jones, 1987).Generally, standard sample preparation procedures, as described in later sections, were used; however, anunusual sample mounting method was utilized to prepare some of the particles for examination usingEPMA techniques. This technique is described in section EvaporitesDue to evaporation of a portion of the recirculating leach solution, salts formed on the top and bottom rimsof the columns. Samples of this material (evaporites) were removed from the columns for analysis. Theevaporites were air dried and a portion of each sample was ground using a mortar and pestle in preparation91for XRD analysis. The remaining material was mounted on aluminum stubs using sticky tabs inpreparation for SEM/EDS analysis. Experiments using more conductive carbon paint (colloidal carbon inethanol) were unsuccessful as the salts, which are highly soluble, reacted with the ethanol in the carbonpaint.6.1.3 PrecipitatesSignificant amounts of precipitate were produced during the column experiments (Figure 4.6). Before theexperiments were tenninated, rock particles were removed from the tops of the columns and the precipitatesthat had formed on the surfaces were examined optically. After drying, these precipitates were initiallyexamined in situ using SEM/EDS techniques. Following the preliminary examination samples of theprecipitates were isolated and again examined using SEM/EDS techniques. In both cases standard samplepreparation techniques were used.Once columns 2 and 4 were terminated and the ore removed from the acrylic tubes and dried largerprecipitate samples could be collected. Bulk samples of leached particles and precipitates were removedfrom the columns at 15 cm (6 inch) intervals. After closer examination approximately half of thesesamples were chosen for detailed study. In order to collect larger samples of the precipitates 1/4 of eachbulk sample was washed several times in distilled water using an ultrasonic bath. Suspended material wasdecanted and filtered after each wash. Once dried the decanted solids were prepared for XRD analysisusing standard techniques. It should be noted that this method not only removes the precipitates from theparticle surfaces but also concentrates the fine silicates that are present.6.1.4 Leached Ore ParticlesAs stated above, rock particles were removed from the tops of the columns before the termination of theexperiments. Several of these particles were cut in half using a Raytech Jem Saw and examined usingoptical microscopy and SEM/EDS techniques. Standard methods were used in preparing the samples.92A large number of particles from the terminated columns 2 and 4 experiments were also examined. Theparticles were selected randomly from unused portions of the same bulk samp1es discussed in the previoussection. They were prepared for examination by optical microscopy and SEM/EDS techniques.These samples, along with some of the unleached particles, were prepared using an unusual variation ofstandard methods (Figure 6.1). The rock particles were mounted in clear acrylic tubes using Buehler’sEPO THIN low viscosity epoxy (Figure 6. la). These tubes are 2.8 cm long with an outer diameter of 2.5cm and a 0.3 cm thick wall. To prevent epoxy leakage, the tubes were sealed to a layer of aluminum foilon plate glass using petroleum jelly. As soon as the epoxy had been poured, the mounts were placed in adesiccator that was attached to a 120 volt/6.8 amp Precision Scientific Co. vacuum pump, model #25(Figure 6. ib). The desiccator was evacuated in order to remove as much trapped air as possible from theparticles. The pump was turned off when the epoxy began to froth. After one minute the desiccator wasslowly brought back to atmospheric pressure. The mounts were removed and allowed to harden overnight.Once hardened, the mounts were cut in half (Figure using an Avco Selker Corp. rock saw with a 12inch blade. One of the halves was then ground and polished by hand using standard materials andequipment (Jones, 1987; Craig and Vaughan, 1981).6.2 Analytical TechniquesDue to the large variety of samples to be examined, numerous different analytical techniques were used.To reiterate, these techniques include: optical microscopy (stereoscopic, transmitted light, and reflectedlight), sieve analysis, XRD, SEM/EDS, AlA, and EPMA.6.2.1 Optical MicroscopyAll rough samples were examined using either a Nikon or Wild Leitz stereoscopic microscope. No specificsample preparation was required.b93Figure 6.1: Preparation of polished mounts exposing the interior of both unleached and leached oreparticles. (a) Large ore particles (longest dimension 12.7 mm) were mounted in clear acrylictubes with 2.5 cm diameters using Epo-Thin low viscosity epoxy. Once cured, the mountswere cut in half; thus exposing the interior of the particles. One of the halves was manuallypolished using standard equipment. (b) Trapped air was removed from the mounts using avacuum pump attached to a dessicator. Notice that mounts were prepared on a sheet ofaluminum foil stabilized by a glass plate.94Standard polished thin sections, polished rock particles, and polished particle mounts (section 6.1.4) wereexamined using either a Carl Zeiss Ultraphot or Leitz Laborlux II polarizing microscope. The microscopeswere used for both transmitted and reflected light examinations. A Hitachi colour video camera and a Sonyblack and white video printer connected to the Leitz microscope were useful for initial documention ofcomplex textural features found in the leached ore particles.6.2.2 Sieve AnalysisA sample of the -12.7 micron unleached Ivan ore was analyzed to determine the size distribution of thematerial. Using 20 cm brass screens as listed in Table 6.2 and a mechanical shaker, the sample wasseparated into 10 logarithmically equal size fractions. An eleventh size fraction included all the materialsmaller than the last sieve’s aperture size (45 jim).6.2.3 Powder X-ray DiffractionSamples that were dried and ground, either manually or using a 12 inch ring mill, were analyzed using aSiemens D5000 powder X-ray diffractometer with a graphite monochromator. Using CuKct radiation, avoltage of 40 kV, and current of 30 mA, the samples were generally analyzed from30 to 60°20 in steps of0.02 degrees 20 for 1.0 second per step (1.2 degrees 20 per minute).6.2.4 Secondary Electron Microscopy with Energy Dispersive SpectrometrySamples were mounted on aluminum stubs using carbon paint (colloidal carbon in ethanol), and sputtercoated with carbon. Examinations were initially accomplished using a Nanolab 7 scanning electronmicroscope with a KEVEX Unispec System 7000 energy dispersive spectrometer; however, much of thestudy was done using a Philips XL3O scanning electron microscope with a Princeton Gamma-Tech energydispersive spectrometer. An accelerating voltage of 15 keV and a working distance of 10-20 jim wereused.95Table 6.2: Sieves used in size analysis of the -12.7 mm unleached ore.Opening Size (mm) Opening Size (inch) Sieve Type0.045 0.0017 T0.147 0.0058 Ta0.250 0.0098 Eb0.425 0,0165 T0.707 0.0278 T1.19 0.0469 E2,00 0.0787 E3.35 0.132 T5.6 0.22 T8.0 0.32 T12.7 0.50 Ea Canadian Metric Sieve SeriesThe W.S. Tyler Company of Canada, Ltd.b Endecotts (Test Sieves) LimitedLondon, England966.2.5 Automated Image AnalysisA representative sample of unleached ore was analyzed using AlA techniques in order to obtain semi-quantitative mineral distribution and grain size data. The sample was separated into 5 size fractions:-12.5,+3.35 nmi; -3.35,+0.710 mm; -710,+150; -150,+45 .tm; and -45 Several polished thinsection were prepared for all the size fraction, except the -451.trn, using standard techniques (Jones, 1987).Polished sections were analyzed using a Kontron image analyzer interfaced with a JEOL 733 electronprobe microanalyzer using backscattered electron images. Due to limitations in discriminating betweenvarious copper sulphides chalcocite, covellite and bornite were grouped together as one phase.Chalcopyrite, pyrite/iron-titanium oxides, and gangue are the other phases that were analyzed. Thecollected data are based on surface area measurements not frequency as this gives a better estimate ofvolume percent (Petruk, 1978). Grain size values are calculated diameters of circles with surface areasequivalent to measured surface areas.The -45 fraction was not analyzed using AlA techniques because preparation and analysis of arepresentative polished section would be very difficult. Furthermore, the sample represents only 0.8 weightpercent of the whole sample and contains less than 2% of the copper (section 7.1.2).6.2.6 Electron Probe MicroanalysesPolished thin sections and polished mounts prepared using techniques described in section 6.1.4 wereexamined using a CAMECA SX-50 electron probe microanalyzer. Various techniques including x-raymapping, EDS, WDS, and secondaryfbackscattered electron imaging (SEIIBSE) were applied. Generallyan accelerating voltage of 15 keV was used.977. DISCUSSION OF THE RESULTS FROM THE MINERALOGICAL EXAMINATIONThe objective of the mineralogical examination discussed here was to gain some understanding of theprocesses involved in biologically assisted acid leaching as they relate to the solids in the system. In orderto achieve this the material received from Rayrock Minera Ltda. was treated as a single sample. Noattempt was made to connect this sample with the Ivan orebody.Unleached ore, evaporites, the precipitates that formed in the columns, and the leached ore particles werestudied. The unleached ore was examined to establish the nature of the material that was to be leached,allowing for comparisons to be made. The evaporites were examined so that any evaporites forming on theleached material when it was dried could be recognized as such. This study concentrated on the mineralsthat formed on the ore during the experiments, not after removal from the acrylic tubes. The precipitateswere studied in order to establish their composition and morphology. Finally, the leached ore particles,both exteriors and interiors, were examined to determine the state of the silicate matrix and the nature of thetransitional suiphide phases. Attention was paid to changes in the nature of both the precipitates and theleached particles along the vertical length of the columns and between columns.7.1 Unleached Ore7.1.1 MineralogyThe ore sample used in this study is from the suiphide zone of the Ivan Mine. Although the sample as awhole is composed primarily of feldspar, quartz, fine-grained muscovite, and chlorite with small amountsof apatite, various iron and titanium oxides (no copper oxides were observed), pyrite, and copper-bearingsulphides, it exhibits considerable local heterogeneity with respect to both mineralogy and textural features.The oxides and suiphides comprise approximately 3% by volume of the sample (Figure 7.1). This variessignificantly on a local scale. Anilite, covellite and bornite are the most common of the metallic phases(88%), with pyrite and the oxides representing approximately 11% and chalcopyrite approximately 1%.suiphides and oxidesFigure 7.1: Mineral distribution in the unleached Ivan ore sample based on image analysis data(Appendix E). The suiphides and oxides comprise approximately 3% by volume of thesample. Of this 3% the majority (88%) is composed of a mixture of anilite, covellite, andbornite. Chalcopyrite comprises only 1%. The pyrite and oxides make up 11%.10 20 30 40Figure 7.2: X-ray diffractogram of the bulk unleached Ivan ore sample (RR16). Notice that albite andquartz are the most abundant minerals in this sample.98volume%a ni lite/covellite/born itesilicates and apatiteall minerals0(U0(UC)0tC)E aq a/rn/cdegrees 2-theta99No quantitative distribution data is available for the non-metallic minerals; however, XRD analysisindicates that quartz and albite are the most abundant minerals present (Figure 7.2).The original andesitic host rock has been altered (albitized, sericitized, and silicified) to varying degrees(section 2.2); thus, the sample exhibits a range of textures from distinctly porphyritic to finely granular.Evidence of brecciation which is related to the mineralization (section 2.3) has also been observed. Theoriginal bomite and chalcopyrite mineralization has been altered to varying degrees by supergeneenrichment and in the sample as a whole anilite and covellite are the most abundant sulphides.SilicatesPlagioclase feldspar, which is present in much of the sample, occurs as large phenocrysts up to severalmillimetres in size and as small laths or granular material in the fine-grained porphyry matrix. Bothtypes of crystals exhibit alteration to muscovite which varies greatly from minor to complete. All ofthe plagioclase feldspar is compositionally very close to pure albite (Table 7.1).Potassium feldspar, probably orthoclase, is also present. According to XRD analyses it is significantlyless abundant than quartz and albite but more abundant than chlorite and muscovite (Figure 7.2). Itsgeneral habit is unknown as it is not recognizable in thin section; however; examination usingSEM/EDS techniques suggests that it occurs as granular grains in the porphyry matrix, oftenintergrown with muscovite and albite.Quartz occurs as large irregular crystals similar in size to the albite phenocrysts and as very finegrained material (crystals much less than 10 tm in diameter) in the groundmass. The large crystalsexhibit a granular texture and generally occur in small clumps of 5 or 6 individual grains or as veinfillings.Fine-grained muscovite is present both in the albite crystals as mentioned above and in the groundmass.Analyses of several coarser grains reveal a slight depletion in the interlayer cation (K, Ca, Na) contentcompared to a typical muscovite analysis (Deer et al., 1966). According to Speer (1984) it has beenshown that this site often exhibits much less than full occupancy in secondary muscovites of100Table 7.1: Typical compositions of the silicate minerals present in the unleached Ivan ore. A completeset of silicate analyses are given in Appendix F.Feldspar Chlorite MuscoviteD22B D21OA D26BSi02 68.290 Si02 28.930 48.710A1203 20.220 Al203 17.770 33.830FeO 0.090 Ti02 0.050 0.010MgO -- FeO 23.390 1.160CaO 0.610 MnO 0.760 0.100Na20 11.470 MgO 16.580 0.450K20 0.070 Cr203 -- 0.030SrO -- CaO 0,320 0.060BaO -- Na20 0.090 0.150_________1(20 0.060 10.090Total 100.750 F 0.400 0.180Cl 0.030 --H20a 11.350 4.430O=F -0.170 -0.080O=Cl -0.010 --Total 99.550 99. 120Number of ions on the basis of:8 (0) 36 (O,OH,F,Cl) 24 (0,OH,F,Cl)Si 2.966 4.00 Si 6.012 8.00 6.469 8.00Al 1.035) Al 1.988) 1.53 1 )Fe2 0.003 Al 2.364 3.764 “Mg-- I Ti 0.008 I 0.001 ICa 0.028 I Fe2’ 4.065 I 0.129 I 4.00Na 0.966 I 1.00 Mn 0.134 I 0.011 IK 0.004 I Mg 5.136 I 11.83 0.089 ISr -- I Cr -- I 0.003)Ba-- ) Ca 0.07 1 I 0.009Na 0.036 I 0.039 I 1.76‘ M 2.8 K 0.016) 1.710)Mole %‘ Abb 96,8 F- 0.263 0.076) Orb 0.4 Cl- 0.011 16.00 -- I 4.0015.727) 3.924)0 20.00 20.00Fe/Mg+Fe 0.44 n/aaDeteined by stoichiometry assuming:(i) 4(F,Cl,OH) for muscovite(ii) 16(F,Cl,OH) for chloritebCalculations based on relative molar abundance of Ca, Na, and K, respectively.101igneous rocks due, possibly, to substitution ofK byH20plus a vacancy. Furthermore, this depletionmay at least in part be due to the presence of barium (not analyzed) and the accompanying vacancies(Guidotti, 1984).Chlorite is not as pervasive as the other silicate minerals. It usually occurs in a distinctly greenporphyry that shows much less alteration than the rest of the sample. The chlorite is present as clumpsof fine-grained crystals with iron (± titanium) oxide inclusions. These clumps are thought to representaltered mafic phenocrysts. Much less frequently, the chlorite occurs with quartz and muscovite in thefine-grained porphyry groundmass or along veins with or without copper-bearing sulphides. The iron-content of the large clumps of chlorite (Table 7.1) is that of a pycnochlorite (Deer et al. 1966).ApatiteApatite is not a common constituent of the Ivan ore sample. It occurs locally in relatively coarse veins,sometimes exhibiting the typical hexagonal cross-section.OxidesAs with the chlorite, the oxides are predominantly found in the green porphyry. Large subhedralcrystals occur in the coarse chlorite clumps. Smaller anhedral grains (generally <20 jim) aredisseminated throughout the sample; however, they are most common in the green porphyry. The largecrystals tend to be subhedral magnetite grains that exhibit varying degrees of alteration to hematiteand/or an ulvospinel (Table 7.2). Notice that the ulvospinel analysis has a low total (91.67%); this isprobably due to its somewhat porous nature. The smaller anhedral grains found throughout the sampleare predominantly hematite although very small grains (<1 jim) of an unknown titanium oxide mineralalso occur.SuiphidesThe sulphide minerals identified in the sample optically include chalcocite, covellite, bornite, minorchalcopyrite, and minor pyrite. Electron probe microanalyses of the copper sulphides indicate that theidentifications were correct for all but the chalcocite (Tables 7.3 and 7.4). The mineral identified as102Table 7.2: Typical compositions of oxide minerals present in the unleached Ivan ore. A complete set ofanalyses is given in Appendix F.Total 100.000 101.010 9 1.670Number of ions on the basis of:3 anions (0) and2 cations32 anions (0) and24 cationsSiTiAlCrFe3Fe2+(a)MnMgZnCaNi00.0010.0090.0011.9780.0080.001 I0,001 I0.001,)0.254I 15.7515.491 )8.2250.0418.596 I0.04514.506 I 23.340.0560.0420.051 I0.003,)Hematite Magnetite Ulvospinel(D211F) (2C-1) (D33C)Si02 0.040 0.130Ti02 0.460 2.270 36.130A1203 0.020 0.120Cr203 0.020Fe203 99.000 64.980 --FeO 0.340 33.320 54.830MnO 0.020 0.210MgO 0.090ZnO 0.040CaO 0.030 0.150NiO 0.030 0.010I 2.003.00 32.00 32.00(a) calculated by valence balancing.Table 7.3: Typical compositions of the sulphide minerals present in the unleached Ivan ore. Thecomplete results from the sulphide analyses are given in Appendix F.anilite bornite covellite chalcopyrite(D3 2A) (D3 6B) (D3 4A) (D3 8A)Cu 77.491 62.249 66.171 34.354Fe 0.017 10.991 0.002 30.336Pb n/aZn n/aAu -- 0.019 0.029 n/aAs 0.006 -- 0.001 n/aHg n/aMn 0.011 n/aCo n/aNi -- 0.010 -- n/aSb 0.011 0.017 -- n/aS 22.412 25.365 33.451 34.886Total 99.948 98.65 1 99.654 99,576Number of atoms on the basis of a total of 100 cations plus anionsCu 63.544 49.781 49.951 24.894Fe 0.016 10.001 0.001 25.011Pb n/aZn -- -- n/aAu 0.005 0.007 n/a=As 0.004 n/aHg n/aMn 0.010 n/aCo — -- -- n/aNi -- 0.009 -- n/aSb 0.005 0.007 -- n/aS 36.420 40.197 50.040 50.095Cu+Fe/S 1.75 1.49 1.00 1.00Cu/Fe >>6 4.98 >>6 1.00103104Table 7.4: Ideal Cu:Fe and (Cu+Fe):S ratios for copper and copper/iron suiphide minerals.Mineral Formula (Cu+Fe)/S Cu/Fechalcocite Cu2S 2 n/acovellite CuS 1 n/aanilite Cu7S4 1.75 n/adigenite Cu9S5 1.8 n/adjurleite Cu31S16 1.94 n/ageerite Cu8S5 1.6 n/aspionkopite Cu39S28 1.39 n/ayarrowite Cu9S8 1.125 n/achalcopyrite CuFeS2 1 1bornite Cu5FeS4 1.5 5cuba’-’ite CuFe2S3 1 0.5fukuchilite Cu3FeS8 0.5 3haycockite Cu4Fe5S 1.125 0.8idaite Cu3FeS? 1 3rnooihoekite Cu9FeS16 1.125 1nukundamite (Cu,Fe)4? 1105chalcocite is actually a more oxidized form of copper suiphide called anilite, Cu7S4. It has a Cu:Sratio of approximately 1.75, much lower than for chalcocite (Table 7.4).As stated above, the distribution of the various sulphide minerals is extremely variable due to theheterogeneity of the supergene alterations; however some textural generalizations can be made on thefairly local scale of the -12.5 mm crushed particles.Pyrite, when present, occurs as small (<50 .tm), rounded, equant grains disseminated throughout thegroundniass, often in clumps of 5 or 10 grains. Rare cases of pyrite inclusions in chalcopyrite havealso been observed.Chalcopyrite occurs as irregular grains varying in size from less than 10 to several millimetres indiameter. At least 50% (by volume) of these grains are greater than 20 .irn in diameter (Figure 7.3).There are two common occurrences of this mineral: (1) large and small grains disseminated throughoutthe rock, sometimes with pyrite inclusions as described above; and (2) very small grains (<10 rim)either included in large bornite grains or dissenainated throughout regions with minimal suiphidealteration (Figures 7.5a and b). Large chalcopyrite grains in the former occurrence may have irregularrims of covellite.Bornite, when it is present, occurs as irregular to equant grains disseminated throughout the silicatematrix. It can also occur as vein fillings (Figure 7.5b). The grains vary in size from severalmillimetres to less than 10 .tm. The larger grains (>50 p.m) often exhibit alteration rims of anilite(Figure 7. 5b) often with covellite on the outer surface (Figure 7. 5a). The degree of alteration is highlyvariable and can be complete. Smaller grains (<50 tim) generally show little or no alteration.A.nilite fornas irregular to subequent grains that range in size from less than 10 tm to severalmillimetres. As for chalcopyrite, there are two common occurrences of this mineral: (1) irregulardissenainated grains of anilite with or without varying amounts of covellite (Figure 7.5c); and (2) asdescribed above, rims of varying thickness on large bornite (± chalcopyrite) grains, generally withcovellite outer rims (Figure 7.5a).a,a,0.a,ED0>1008060402004.1 6.8 11106Figure 7.3: Grain size distribution of chalcopyrite in the unleached Ivan ore sample. The bars representthe distribution by size range and the curve represents the cumulative distribution. Dataindicate that there is a bimodal arrangement. Approximately 50% of the grains are greaterthan 20 jim in diameter. Note that the data is erratic due to the small population measured(Appendix E).Ca)a,a,E1008060402004.1 6.8 11 19 32 53 90 150 250 425 710 1180size fractions (microns)Figure 7.4: Grain size distribution of the anilite/covellite/bornite mineral group in the unleached Ivanore sample. The bars represent the distribution by size range and the curve represents thecumulative distribution. Data indicate that there is a slightly bimodal arrangement.Approximately 50% of the grains are greater than 50 p.m in diameter. See Appendix E fordata in tabular formH19 32 53 90 150 250 425 710 1180size fractions (microns)I jIfliflIflIflIflIfliflifli107Figure 7.5: Typical suiphide textures in the unleached ore. (photomicrographs, scale bars are 200 jim)(a) A typical large bomite (pink) grain partially altered to anilite (pale blue) and covellite(dark blue). Notice the tiny chalcopyrite (yellow) inclusions near the grain rim.(b) Somewhat smaller bornite (pink) grains as vein filling and interstitial material. Minoralteration to anilite (light blue) has occurred, Notice the very small chalcopyrite grains(arrows) along with small bornite, anilite, and covellite (dark blue) grains in the silicatematrix.(c) Typical anilite-only texture.(d) Typical bladed texture of covellite-only grains (blue). Some very small bornite (pink)grains are also present.109Covellite occurs as irregular masses ofmatted blades. It can occur on its own (Figure 7.5d) but, morecommonly, it forms alteration rims on the other copper suiphides, especially anilite. The masses rangein size from less than 10 jim to several hundreds ofmicrons. In the larger grains there is often a smallremnant of anilite and/or bomite present in the core (Figure 7.5a).Grain size distribution data was collected for bomite, anilite, and covellite as a group (Figure 7.4).These minerals exhibit a bimodal distribution with 50% by volume greater than 50 jim in diameter.Although many of these large grains are actually a mixture of two or more of the three coppersulphides, mono-mineralic grains do tend to be larger than the chalcopyrite grains.Alteration ofthe Silicate MatrixDuring formation of the Ivan Mine ore fluids have infiltrated the rock at least twice, once to emplacethe bornite, chalcopyrite, and pyrite, and a second time to emplace the supergene copper sulphideminerals (anilite and covellite). During these processes the silicate matrix has been altered to someextent. One would expect fine channels connecting the sulphide minerals to be present; however, onlya few larger veins (>25 jim across) are visible. These veins are usually filled by chlorite with orwithout copper-bearing sulphides and quartz (Figures 7.6a and b). In addition to the veins, a non-crystalline aluminum silicate with minor iron believed to be an alteration product of the silicate matrixoccurs in veins and around altered suiphide grains (Figures 7.6c and d). It is a porous material with avariable chemistry. The Si:Al ratio ranges from approximately 1:1 through to 2: The Crushed SampleAs discussed in Chapters 4 and 6, portions of the ore sample were crushed for use in the column leachexperiments. Since the column containing the -9.6 mm material was not examined, only the -12.5 mmmaterial will be discussed here. Particle size distribution for this sample is given in Table 7.5. The attemptto minimize production of fine material during crushing was fairly successful as less than 30 weight% ofthe sample contains particles below 3 mm in diameter.110Figure 7.6: Evidence of primary solution penetration in unleached ore.(a) A large vein filled with chlorite. This vein is the only one present in the ore particle.(photomicrograph, bar is 200 .im)(b) A large vein filled with chlorite and covellite. Notice the small open veins associated withthis vein. (backscattered electron image)(c) Anilite (white) partially altered to covellite (blue) and surrounded by the porous silicatealteration product (grey). (photomicrograph, bar is 200 Backscattered electron image of (c) illustrating the porosity in the silicate alterationproduct (dark grey). Notice that the covellite/anilite mixture (white) does not exhibit apartially dissolved,tbroken’ texture. The small medium grey grains are composed of theunknown titanium oxide.I414—1—112Table 7.5: Size distribution of particles in the -12.7 mm crushed sample.Table 7.6: Chemical analyses of unleached Ivan ore including analyses of individual size fractions andcalculated distribution in the whole sample. A head sample assay and a calculated head sampledistribution are also given. Copper, iron, and total sulphur were the only elements analysed for.(After Leong, 1 992b)Size Fraction Assays(%) Distribution (g/l OOg ore)a Distribution (%)(mm) Cu Fe S0i Cu Fe Stotai Cu Fe S0i-0.045 7.67 2.16 2.82 0.06 0.02 0.02 1.2 0.7 1.2“-0.045,+0.150’ 7.92 2.22 2.81 0.06 0.02 0.02 1.3 0,8 1.3“+0.150,-0.250” 7.01 2.42 2.54 0.04 0.01 0.01 0.8 0.6 0.8“+O.250,-0.425” 6.52 2.35 2.32 0.05 0.02 0.02 0.9 0.8 1.0“+O.425,-0.710’ 6.31 2.07 2.24 0.08 0.03 0.03 1.5 1.1 1.5“+0n710,-1.18” 5.82 2.07 2.07 0.12 0.04 0.04 2.3 1.8 2.3“+1.18,-2.00” 5.59 1.95 1.98 0.22 0.08 0.08 4.4 3.4 4.5“+2.00,-3.35” 5.46 2.20 1.80 0.44 0.18 0.14 8.7 7.8 8.2“+3.35,-5.60” 5.23 2.18 1.77 0.73 0.31 0.25 14.5 13.5 14.1“+5.60,-8.00” 4.96 2.17 1.74 1.07 0.47 0.38 21.1 20.7 21.3“+8.00,-12.5” 4.75 2.38 1.66 2.20 1.10 0.77 43.4 48.7 43.7Calculated Head 5.07 2.26 1.76Head Sample (RRO2) 5.33 2.50 1.77Size Fraction Weight Weight% Cumulative(mm) (g) Weight%-0.045 77 0.8 0.8-0.45,+0,150 81 0.8 1.6+0.150,-0.250 54 0.5 2.1+0.250,-0.425 72 0.7 2.9+0.425,-0.710 120 1.2 4.1+0.710,-1.18 196 2.0 6.1+1.18,-2.00 392 4.0 10.0+2.00,-3.35 795 8.1 18.1+3.35,-5.60 1383 14.0 32.1+5.60, -8.00 2130 21.6 53.7+8.00,-12.7 4573 46.3 100.0acalculated using the weight% distribution of size fractions from Table 7.5.113Results ofwet chemical analyses for copper, iron, and total sulphur that were carried out on the 11 sizefractions are given in Table 7.6. Both the copper- and sulphur-content of the size fractions increase withdecreasing particle size. The iron-content remains fairly constant. These data indicate that there is anincrease in covellite- and/or anilite-content with the decrease in particle size. This would be expected sincethe hardness of these copper suiphides is lower than that of chalcopyrite and bornite. The total copper-,iron-, and sulphur-contents of the sample were calculated to be 5.07, 2.26, and 1.76% (by weight),respectively. These values compare favourably with the measured values of 5.33, 2.50, and 1.77%.Table 7.6 also includes relative distribution data for copper, iron, and sulphur. A decision to concentratedetailed examinations on large particles (>—6 mm) was made based on the relative distribution of copper inthe size fractions. Notice that particles smaller than 5.6 mm contain 40 weight% of the copper andparticles smaller than 3.35 mm contain only 20%. When the experiments were terminated both columnshad copper extractions of over 50%. It was assumed that the majority of the copper in the -3.35 mmfraction of the ore sample had been completely removed. Furthermore, it was felt that copper leaching hadprobably progressed too far in the -5 .60,+3 .35 fraction to leave evidence of the alteration process. A largerproportion of the remaining 30% extracted copper would have come from the -5.60 mm particles comparedto the +5.60 mm particles because of their larger surface area to volume ratio. In other words, a largerproportion of the copper in the -5.60 mm particles (compared to that in the +5.60 mm particles) would havebeen exposed to leaching at the particle surfaces. Therefore, it was thought that the larger particles wouldcontain more information regarding the leaching process.7.2 EvaporitesDuring the column experiments water soluble crusts very similar to the efflorescence sample pictured inNordstrom (1982) continually formed from the evaporating leach solution at the tops and bottoms of theacrylic tubes, outside the columns of ore (Figure 4.6). They have been characterized to aid futurerecognition of minerals formed due to evaporation of residual leach solution. This study concentrated onthe minerals that formed on the ore during the experiments, not after removal from the acrylic tubes.114Table 7.7 lists the evaporite minerals identified in the samples according to habit and colour. Table 7.8lists the minerals identified in each sample using x-ray diffraction techniques. They are given in descendingorder of approximate relative abundance. All but one of the samples examined is composed of a blue togreen granular base with varying amounts of a yellow, often bulbous, coating (Figure 7.7a). Theblue/green crystalline base is generally composed of tabular chalcanthite [CuSO4.5H20](Figure 7.7b) withor without tschermigite [NH4AI(S0)2.12H0j (Figure 7.7c) and/or melanterite [FeSO4.7H20](Figure7.7d). In one sample the crystalline base is made up ofmohrite [(NH42Fe(S0.60]and melanteritewith minor tschermigite and chalcanthite. The yellow coatings are actually made up of small balls ofradiating plates (Figure 7.7d). The dominant mineral exhibiting this habit is ferrocopiapite[Fe467(S0)OH)2.20H0]; however, alunogen [A12(S04)3.17H20], halotrichite[Al2Fe(S04).22H0],and an unidentified jarosite species [XFe3(SO4)2OH)6]are also locally present in these coatings.Acicular to tabular gypsum [CaSO4.2H0Joften occurs embedded in the yellow balls (Figure 7.7b).One sample (RRO3) was taken from column 1 before addition of the 9K salts to the leach solution (Table7.8). This sample contains dendritic eriochalcite [CuCl2.2H0]with interstitial halite [NaC1] (Figure 7.8),and gypsum.Note that these evaporite samples can give some indication of the chemistry of the leach solutions if it isassumed that the process of evaporation is so fast that as water is removed from the system there is nochange in the aqueous species present. The observations made must be very general since the smallevaporite samples examined may not represent the composition of all evaporites forming at the time ofsampling.There is a dramatic change in the mineralogy of the colunm 1 evaporites when the 9K salts are added(Table 7.8). Before addition of the salts copper and sodium chloride appear to be the dominant species inthe leach solution, since eriochalcite and halite are the dominant evaporite minerals. The sulphate, added assulphuric acid (section 4.2.1), forms gypsum. Note that water from the Chilean aquifers (Table 2.1) usedin the experiments is the source for calcium, not the ore. Once the salts are added copper, iron andammonium/aluminurn sulphates form, indicating that aqueous chloride complexes are no longer dominantin the leach solution. Copper suiphates become more abundant as the leaching progresses.115Table 7.7: List of evaporite minerals forming crusts on the exterior of the column experiments organizedinto groups with similar habits. Identifications were made by comparing observations usingSEMi’EDS techniques to mineral descriptions in Roberts, et aL (1990) and SEM/EDS data inWelton (1984).Habit Colour Mineral Formulabballs ofminute plates yellow ferricopiapite Fe3467(S0)60H)2.2OHalunogen A1(S017H20jarositea KFe(S00H)white/green halotrichite Al2F(S04).22Htabular crystals blue chalcanthite CuSO4.5H20clear/white gypsum CaSO.2Hoctahedral crystals clear/white tscherrnigite NH4AI(S04)2.12H0cubic crystals clear/white halite NaC1dendritic strands blue eriochalcite CuCl2.2H0balls of rhombic crystals ? unidentified Cu-sulphate (from EDS)unknown (base material) blue/green melanterite Fe2SO4.7H0green mohrite (NH)eS0.6roemerite Fe23(S04).14H20apossibly jarosite, jarosite (hydronian), hydroniurn jarosite, or ammoniojarosite. The variety could not beidentified because this mineral was only recognized in the XRD patterns and the peaks were too small tomake a definite identification.bfomiulae from JCPDS powder diffraction files (1991), Alpers et aL (1994), and Roberts et aL (1990).116Table 7.8: Minerals identified in the evaporite samples using powder x-ray diffraction techniques. Theyare listed in estimated descending abundance from top to bottom. Estimates are based on peakheights in the XRD analyses.(modified from Melluish et a!., 1993)Mineralseriochalcitehalitegypsum1 (bottom) RRO9 42 chalcanthitetschermigiteferricopiapitehalotrichitegypsum1 (top) RRO6 34 mohritemelanteritegypsumtschermigitechalcanthitejarositehalotrichite2 (top) RR26 126 chalcanthitejarositetschermigitegypsumferricopiapite3 (top) RR27 131 chalcanthitejarositetschermigitegypsumferricopiapite4 (bottom) RR1 0 35 chalcanthitegypsumroemerite5 (top) RR28 131 chalcanthiteferricopiapitehalotrichitetschermigitegypsumjarosite6 (bottom) RRO8 14 chalcanthitemelanteritehalotrichitetschermigitejarositeferricopiapitegypsumColumn (location)1 (bottom)Sample No.RRO3Day of Sampling.3aaTest days are numbered such that Day 0 is the day that the 9K salts wereadded. The column underwent treatment before this, hence the negative day.117Figure 7.7: Morphology of common evaporite minerals found at the tops and bottoms of the acrylictubes, outside the columns of ore.(a) Photomicrograph of a typical evaporite sample. It is made up of a blue-green crystallinebase covered by spherical yellow growths. The sample measures approximately 1cmacross.(b) Backscattered electron image of rhombohedral chalcanthite [CuSO4.5H20]crystals.Notice small gypsum needles with ferricopiapite plates at the left edge of the image. (baris 200 p.m)(c) Backscattered electron image of octahedral tschermigite [NH4A1(S0)2.12H01 crystals.(bar is 100 Backscattered electron image of tabular melanterite [FeSO4.7H20]crystals and balls offerricopiapite [Fe467(S0)OH)2.20H0}plates. (bar is 20 jim)I41—119Figure 7.8: Evaporite sample taken before the addition of 9K salts. It is composed of dendritic bluegreen eriochalcite [CuC12.2H0]and interstitial small equant halite [NaCI} crystals.(a) Photomicrograph of a portion of the sample that is 1.5 cm across.(b) Backscattered electron image showing clearly the dendritic eriochalcite and interstitialhalite. (bar is 40 tim)120Ferrous iron suiphates form due to the presence of ferrous iron from the 9K salt solution As theexperiment continues a ferric iron sulphate also forms. The source of the ferric iron is unclear sincecolumn 1 is sterile and the oxidation of ferrous iron should be extremely slow (Nicholson, 1994).Tschermigite, the aluminum/anmionium sulphate, forms due to the presence of ammonium from the 9Ksalts and aluminum thought to be from the albite and muscovite in the ore.The samples taken from the other columns generally have the same mineralogical composition,predominantly chalcanthite with similar relative amounts of tschermigite and gypsum and no chlorides,indicating that the solution chemistry is fairly consistent. Only the iron sulphates vary to some extent.Ferrous iron sulphates (melanterite, halotrichite, and roernerite) are dominant early in the experiments(samples RRO8 and RR1 0) and ferric iron sulphates (ferricopiapite and jarosite) are dominantapproximately 100 days later (samples RR26, RR27, and RR28). Since bacterial oxidation of ferrous ironcontrols the ferric iron-content of the leach solution (section 3.2) this change in mineral composition mayreflect the adaption of the bacterial population to the leaching conditions and consequent populationgrowth.7.3 PrecipitatesDuring the column leach experiments yellow and orange/red precipitates were observed through the clearacrylic columns (Figure 4.6). These precipitates exhibited a zoned distribution with a region dominated byyellow precipitate overlying one dominated by orange/red precipitates. Over time they increased in volumeand migrated down the column in an apparent plug flow movement thus maintaining the zonation. As canbe seen in Figure 7.9, when columns 2 and 4 were terminated these precipitates were quite abundant. Theywere examined in some detail using reflected light microscopic and SEM/EDS techniques. Of particularinterest was the possibility that these precipitates had inhibited copper extraction by forming barriers onmineral grains (Tuovinen, 1990; Ehrlich, 1990), and/or by removing important ions such as iron fromsolution (section 3.2.2).Figure7.9:Thesolidresiduesremovedfromcolumns2and4afterterminationoftheleachexperiments.Noticethattheyellowjarositeisdominantinthetop50cm(1.5feet)ofbothcolumns.Theorange/rednon-crystallineironphasesaredominant belowthis, tothebottomincolumn4andtoapproximately75cm(2.5feet)belowthetopincolumn2.Furthermore,theprecipitates,especiallythenon-crystallineironphases,appeartobesignificantlymoreabundantincolumn4.1227.3.1 MineralogyThe yellow precipitate most common at the top of the two columns (Figure 7.9) is jarosite[(K)Fe3(S04)2OH)6].Results from XRD analyses suggest that this jarosite may contain a minorhydronium [H3O] component (Figure 7.10).The orange/red material more common in the bottom half of the columns is not a hydrated iron oxide as iscommonly expected (section 3.3) but is composed of at least two non-crystalline iron phases, a phosphateand an oxide-sulphate (Figure 7.11). Judging by the cracks observed in polished mounts, these phases areprobably hydrated. As illustrated in the EDS analyses in Figure 7.11, minor components often appear tobe present in the two phases. It is not clear, because of the finely intergrown nature of the material,whether the small amounts of sulphate in the phosphate and phosphate in the oxide-sulphate are part of thephase or contaminants. It is also unclear whether the small amounts of silicon and aluminum, which arenot always present and when present vary significantly, are part of the amorphous material or contaminantsfrom surrounding silicates. In rare cases the non-crystalline iron phases contain more minor aluminum thansilicon, which is never seen in the silicate phases identified in the ore. This suggests that rarely aluminumoccurs as a minor component of the precipitate or as an aluminum oxide or sulphate finely intergrown withthe iron-bearing precipitates. Finally, the small amount of copper in both phases, also variable, is generallypresent whether sulphides are in the vicinity or not and may be a true component.These non-crystalline iron species are very interesting, especially the iron phosphate, since they do not seemto have been previously described in bioleaching experiments. Nevertheless, the iron oxide-sulphate maybe the poorly crystalline mineral schwertmannite described from mine drainage ochres by Bigham et al.(1990) and Bigham (1994). The iron phosphate species may be poorly crystalline vivianite[Fe32(PO4.8HO]or, more likely considering the probable chemistry of the solution (section 3.2),strengite[Fe3+(P04).2H0J. Both these mineral are relatively common and can occur in oxidized zones ofsuiphide deposits as well as weathered zones in tailings and waste rock piles (Alpers et al., 1994).Unfortunately, more precise identification could not be achieved here since these phases are amorphous tox-rays, are very fine grained, and generally finely intergrown. Obviously, more detailed study, if possible,is necessary to properly identify these phases.12328.40 29.40Figure 7.10: Detail of a typical XRD analysis of fines sampled from solid residues of a columnleach test. The jarosite that forms in the columns may have an hydronium [H30+]component. Very small amounts of ammoniojarosite may also be present butnatrojarosite and hydroniumjarosite are not.28.60 28.80 29.00 29.20degrees 2-thetaFigure7.11:Typicalnon-crystallineiron-bearingprecipitatesobservedincolumns2and4.(a)Backscatteredelectronimageofcompactfinelylayeredironoxide-sulphate(lightgrey)andironphosphate(mediumgrey).(b)EDSspectrumoftheironoxide-sulphate.Minoraluminum,silicon,phosphorus,andcoppermaybecontaminantsfromsurroundingmaterial.(c)EDSspectrumoftheironphosphate.Minoraluminum,silicon,sulphur,andcoppermaybecontaminantsfromsurroundingmaterial.10.0_0.05.010.0keV0.05.0keV1257.3.2 HabitJarosite generally occurs as tabular crystals less than 4 im across or semi-rounded equant flakes from 6 to25 microns across. There is some indication that the flakes may actually be clumps of the smaller crystals(Figure 7. 12a). Commonly the flakes and/or crystals occur in porous unconsolidated layers interspersedwith silicate grains and, less commonly, sulphide grains of varying size (Figures 7. 12a, b, and c). Asindicated in Figures 7. 12b and c, the ratio ofjarosite to silicate grains can vary from less than 5% to morethan 80%. Furthermore, this unconsolidated material may be overlain by a semi-porous layer of denselypacked jarosite crystals or flakes (Figure 7.1 2b).Jarosite can also occur with the non-crystalline iron phases, generally a consolidated layer overlying semi-porous material containing the other iron compounds and silicate grains (Figure 7.1 2d) or as flakesinterspersed with the non-crystalline iron compounds and silicate grains in porous layers (Figure 7. 14b). Inaddition, jarosite occurs rarely with or instead of the amorphous iron oxide-sulphate in typical botryoidaltextures exhibited by the non-crystalline precipitates (Figure 7.13).Jarosite very rarely occurs in the porous material as small rods similar in size and shape to Thiobaccilli,approximately 2 .tm long and less than 0.5 m thick (Figure 7.1 3aTh and 7.1 4b). However, it is not clearwhether these are jarosite coated bacteria since larger rods can also be present.The non-crystalline material generally occurs as fine layered intergrowths of the iron-phosphate and ironoxide-sulphate (Figure 7.11). This finely intergrown material primarily exhibits a more botryoidal habitthan seen in Figure 7.11, either in fairly thick (>50 jim) semi-porous layers or somewhat thinner (<50 jim)relatively compact layers (Figures 7.1 3a, b, and c). Furthermore, the amorphous material often formscoatings on silicate and, rarely, suiphide grains. The relative distribution of the iron oxide-sulphate to theiron phosphate varies from virtually 100% oxide-sulphate to 100% phosphate but is most commonlysomewhere in between. Typically pure iron oxide-sulphate or iron phosphate occurs as thin (<10 jim)compact layers (Figure 7. 14a). Iron phosphate (± iron oxide-sulphate) also occurs with jarosite either ascompact botryoidal intergrowths or as a porous mixture with silicate grains (Figure 7. 14b).126Figure 7.12: Typical jarosite textures. In the figures jarosite is light grey, silicates medium to dark grey,and the mounting epoxy black. (backscattered electron images).(a) Porous material composed predominantly ofjarosite crystals (approximately 80%) withsome silicate grains interspersed. The jarosite crystals may have a hexagonal crosssection. Furthermore, clumps of crystals on the left hand side of the figure may representthe jarosite flakes seen elsewhere.(b) A porous mixture ofjarosite flakes and crystals (<5%) and silicate grains overlain by adense semi-porous jarosite layer.(c) Jarosite flakes and some silicate grains in a porous mixture partially overlain by a morecompact jarosite layer. Notice the semi-porous layered material below this material. Itis composed of silicon-aluminum oxide phases with varying aluminum-contents thatappear to be the result of silicate alteration. The dark grey material in the upper rightcorner is also composed of this material.(d) A compact semi-porous layer ofjarosite flakes overlays a more porous mixture of ironphosphate, iron oxide-sulphate, very minor jarosite, and silicate grains. Note that theiron phases are a slightly darker grey than the jarosite.74‘N127:—fr. ‘S.. .,‘.1•h••‘. .1 rfr ,.çI. —.I.•.,,‘..4.1-‘II4.-..•:‘:‘.:.--Figure7.13:Typicalbotryoidalmixturesofironoxide-sulphate(lightgrey)andironphosphate(mediumgrey).Silicatesaredarkgreyandmountingepoxyisblack.Noticethecrackingthatmaybeduetodehydration.(backscatteredelectronimages)(a)Asemi-porousmixtureintergrownwithafewsilicategrains.Rodshapedparticles(—.2imlongand<0.5p.mwide)maybejarositecoveredThiobaccilli.Theyalsooccurinporousmaterialnearby.(b)Thinlayersformedaroundsilicategrainscementingthemtothelargeparticleontheright.(c)Athickersilicate-freebotryoidalgrowthonthewallsofalargevein.Theprecipitatecoatingisintermittentandneartheveinmouth.129Figure 7.14: Less common habits exhibited by the amorphous iron phases. (backscattered electron images)(a) A very thin layer (<10 tm) of iron phosphate (medium grey) on the outer surface of arock particle. This precipitate coats semi-porous, irregularly layered silicon aluminumoxide material that is probably the product of silicate (slightly lighter grey) alteration.Notice that the covellite (white) in contact with the porous material exhibits a somewhatbroken habit due to partial dissolution.(b) Porous material that is a mixture ofjarosite flakes (light grey), iron phosphate (mediumgrey), and silicates (dark grey). Notice the rod shaped particles on right side of theporous layer defined by a light grey outline (jarosite?). Many are the same size as butothers are much too large.Figure 7.15: Sites where precipitates are typically found.(a) The precipitates most commonly occur on the outer surface of the rock particles. Wherethey are abundant they often loosely cement smaller particles to the large ones. Here theprecipitate layer is made up of the semi-porous botryoidal mixture of iron phosphate andiron oxide-sulphate in Figure 7.1 3a. (photomicrograph, view is 1 mm or 1000 im wide)(b) Less commonly the precipitates, especially the amorphous iron phases, occur on veinwalls and as vein fillings in smaller veins. Here a large vein cutting through semi-poroussilicon aluminum oxide is coated by botryoidal iron phosphate and iron oxide-sulphate.Notice that the precipitates have infiltrated the semi-porous material filling small veins.Notice also that this semi-porous material is devoid of sulphides that are very commonelsewhere in the particle. (backscattered electron image)—Hr.fJ.-bI-ft..,/-—,,,131The precipitates generally occur on the outer surface of the particles. It is interesting to note that wherethey are abundant they commonly loosely cement small and large particles together (Figure 7. 15a). Thecompact forms of the precipitates, generally the non-crystalline iron phases, may also occur in veins withinthe particles, either as coatings on vein walls or as fillings (Figures 7.1 3c and 7.1 5b).7.3.3 DistributionAs stated above, visual observations of the columns once the experiments were terminated indicate thatboth contain substantial amounts of the precipitates (Figure 7.9). The yellow jarosite is dominant in the top45 cm (1.5 feet) of both columns. The orange/red non-crystalline iron phases are dominant below this, tothe bottom in column 4 and to approximately 75 cm (2.5 feet) below the top in column 2. Furthermore, theprecipitates, especially the non-crystalline iron phases, appear to be significantly more abundant in column4 than column 2. XRD analysis of the fines from various positions along the columns indicates that forjarosite (the other precipitates are amorphous to x-rays) the visual observations are accurate (Figure 7.16).Assuming that the quantity of quartz in the fines is constant, the relative abundance ofjarosite is higherthroughout colunm 4. Notice that small amounts ofjarosite persist to the bottom of both columns.More detailed examination of particles sampled from the same positions as the x-rayed fines (Figure 7.16)reveals several interesting trends. The observations made from reflected light microscope and SEM/EDSexaminations of polished particle cross-sections are summarized in Table 7.9. More detailed descriptionsare given in Appendix G. It should be noted that the observations made here are qualitative only since theyare based on visual estimates from a small number of grains (9-14).Total precipitate abundance, based on estimates of particle surface coverage, is relatively constant over thewhole length of column 4; however, in column 2 the abundance decreases from approximately the sameamount as in column 4 at the top to virtually zero at the bottom.Column 2 contains various amounts of porous, semi-porous, and compact precipitates throughout itslength. The porous material, composed of scattered jarosite flakes and silicates with or without irregularpieces or coatings of iron phosphate and/or iron oxide-sulphate, is the most abundant particle covering15cm6”45cm1’6”75cm2’6”105cm3’6”135cm46”IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII104030degrees2-thetaFigure7.16:XRDanalysesoffinesfromcolumns2and4.Assumingtheamountofquartzisconstantthroughbothcolumns, therelativeabundanceofjarositeishigheratthetopsofbothcolumns.Jarositeisalsomorecommonincolunm4thancolumn2.Noticethatjarositepersiststhroughoutbothcolumns.Noticealsothatincolumn2therealtiveabundanceofalbiteandclinochioreislowertowardthetopofthecolumn.Thisdoesnotappeartobethecaseincolumn4althoughtherelativeabundanceofalbitedoesvaiy.Column2bot2030om102040Table7.9:Distributionaofprecipitatemorphologiesbasedonmineralogicalexaminationofpolishedparticlecross-sections.Indescriptionsphasesinbracketsmaybepresentinminortotraceamounts.Column2Column43?!45U6flJI2P6U4Htotalnumberofparticlesexamined9111011111010101014averagecoverageb37%31%26%10%5%40%30%38%28%47%rangeofcoverageb15-7510-60<5-80<5-20<<5-1020-6010-6015-8010-70<10-75poroussilicates(Fephosphate±Fesulphate-oxide)--—9(0)9(1)10(1)——------porousjarosite+silicates7(1)8(2)--2(5)--9(1)8(2)6(2)d7()d4(2)porousjarosite+Fephosphate+silicates5(4)C--—--8(2)6(2)6(3)d10d7(7)fporousFephosphate/Fesulphate-oxide(jarosite)+5(3)----—-------_----silicatesporousFephosphate(±Feoxide-sulphate)+silicates----1(6)(6)C----------semi-porousFephosphate(Feoxide-sulphate)+----(7)1(1)--(1)(1)(1)(l)C2(1)gsilicatessemi-porousFeoxide-sulphate(Fephosphate)+1(4)--(5)----2(1)1(1)(4)e3(6)silicatessemi-porousFephosphate+Feoxide-sulphate+------(2)(6)3(5)1(2)2(3)--(2)silicatessemi-porousdenselypackedjarositeflakes(2)--------3(5)2(1)------compactFephosphate(Feoxide-sulphate)±silicates--(1)(4)(3)----1(0)(2)--1(1)compactFeoxide-sulphate(Fephosphate)±silicates--(1)--(4)------2(5)1(5)7(2)compactFephosphate+Feoxide-sulphate±silicates(2)----(2)(1)1(4)3(2)2(3)1(1)1(2)compactdenselypackedjarositeflakes--—--——1(1)2(2)1(3)----avaluesnotinbracketsindicatethenumberofparticleswherethemorphologyisdominant,,inbracketsthenumberoftimespresent butnotdominantbbasedonvisualestimatesCsometimesclumpsofjarositeinsteadofFephosphatedamountofprecipitatesareminorwithrespecttotheamountofsilicategrainsrarelyminorjarositealsopresent‘Fephosphateisveryminorcomponent;gbothphasesareabundantinthemixturealthoughoneismorecommon134throughout. In the bottom 90 cm (3 feet) of the column the precipitates in this porous mixture are muchless abundant than in the top 60 cm (2 feet). Semi-porous material is also present throughout but is muchless common than the porous material. It is composed ofmore densely packed jarosite flakes or finelybotryoidal to more densely packed pieces of iron-phosphate and iron oxide-sulphate, all including varyingamounts of silicate grains. The semi-porous jarosite layers are present in the top 60 cm (2 feet) of thecolumn only, often above the porous material. The semi-porous material containing the non-crystallinephases occurs throughout the column with the ratio of iron oxide-sulphate to iron phosphate varyinggreatly. Finally, compact coatings, generally thin (<30 jim) coarse botryoidal layers of iron phosphate andiron oxide-sulphate sometimes with silicate grains, are also present along the column’s entire length but arerare. These thin layers occur either on particle surfaces or in veins coating the walls or completely fillingthe channels.The coatings in column 4 are generally the same texturally as those in column 2; however, their relativeabundances differ somewhat. As in column 2, the porous material is a major component of the particlecoatings along the whole length of the column. Again, jarosite is more common in the top half of thecolumn and iron-phosphate in the bottom half. Unlike in column 2, the iron oxide-sulphate phase does notoccur in the porous material and only in the centre of the column are the precipitates a very minorcomponent in the porous mixture. At the top and bottom of the column the precipitates represent up to80% of the scattered particles.The semi-porous coatings in column 4 are much more common throughout and for many particles are amajor component of the coatings. As for column 2, the semi-porous densely packed jarosite layers arecommon in the top 60 cm (2 feet) but are not present in the bottom 90 cm (3 feet) of the column. Thevarious mixtures of iron phosphate and iron oxide-sulphate along with some silicates are again presentthroughout; however, they are present in much larger amounts than in column 2 and sometimes containsmall amounts ofjarosite.As for the semi-porous material, the compact coatings are consistently more abundant than in column 2. Asignificant amount of compact jarosite is present in the top 90 cm (3 feet) of the column but not below that.The iron oxide sulphate and iron phosphate mixtures are also present in significant amounts. Unlike in135column 2, they are somewhat more abundant than the same semi-porous mixture. Notice that ironphosphate dominated mixtures are more conimon in the top 90 cm (3 feet) of the column and iron oxide-sulphate dominated mixtures are more common below that. In fact, the iron oxide-sulphate dominatedmixtures, both semi-porous and compact, are most common at the bottom of column 4.These more detailed examinations of the precipitates confirms the visually apparent zonation of theprecipitates which is seen more clearly in column 4 than in column 2. The dominance ofjarosite in theupper part of the columns and the mixture of iron oxide sulphate and phosphate in the lower parts mustreflect a change in solution chemistry since all other conditions such as temperature and ore type were thesame along the entire length of both columns. The ions necessary for formation of the precipitatespredominantly come from the 9K nutrient solution or the acid solution used to maintain the pH. Thedissolving sulphides supplied additional iron and sulphate and the degrading silicates (potassium feldspar,muscovite, and clinochlore) supplied some additional potassium along with other cations.During the leaching experiments small amounts of solution from the large reservoir (more than 15 L) wereslowly added to the top of the column. Once the solution had moved through some of the ore, solubilizingsilicates along with the sulphides as it went, the solution chemistry would have changed. The pH wouldhave increased since the silicate dissolution reactions are acid consuming and the copper-bearing sulphidedissolution reactions generally do not produce acid (section 3.2). Since jarosite forms very near the topsurface of the column (although not in the solution reservoir) conditions would have become favourable forjarosite formation almost immediately. The solution pH would have continued to increase as the solutionflowed downward. Furthermore, some iron and most of the potassium would presumably have beenremoved to the jarosite. Replacement of potassium through silicate mineral dissolution is unlikely sinceeven in the PATH simulation where silicate reaction rates are probably high the potassium is quicklydepleted when only jarosite is precipitating (Figure 5.4). Either the higher pH, the lack of potassium, or acombination of both would have eventually made conditions favourable for precipitation of the ironphosphate and iron oxide-sulphate. Interestingly, results from the PATH simulation suggests that anincrease in pH may be the important factor.136In this manner a coarse zonation could be produced. It is thought that as later solutions passed through thispartially leached ore the pH increased a bit more slowly (somewhat fewer oxidizeable silicate surfacesexposed) and the precipitates formed somewhat lower down. Some of the previously fonned precipitatesprobably dissolved and reprecipitated farther down the column; although some must have remained tomaintain the precipitates that occur at the top of the column. In this way the zones might appear to beflowing downward. As this process progressed down the column the supply of oxygen may have becomerestricted. This may be why iron phosphates are more common in the centre of column 4 and the ironoxide-sulphate is more common close to the open bottom.This model tries to explain the coarse patterns seen in the columns, especially coluni.n 4; however, in detailthe precipitates are actually mixed together throughout. It should be remembered that the colunrn of ore isnot saturated with solution; therefore, different portions of the solution follow different paths through theore column. Thus solutions in different localized areas, microenvironments, could have very differentchemistries, for example some with very high and others with very low pH’s. If this is the case thenenvironments favourable to precipitation of all the precipitates could occur at the same level in a column.For instance, jarosite could form at the bottom of a column where Fe oxide-sulphate is the generallyfavoured precipitate. Notice that combinations of the precipitates are either porous to semi-porousaccumulations of precipitate pieces or layered botryoidal intergrowths. None of these textures requiresimultaneous formation of different precipitate species.Finally, it is very obvious that precipitates are much more abundant in colunrn 4 than in column 2. Theonly difference between the 2 leach experiments is the presence of 5 gIL of chloride in column 2. Onelikely explanation for this substantial difference is that there is less iron available for precipitate formationin colunm 2 due to the presence of chloride. It is apparent from the PATH simulation that under theseleaching conditions iron chloride complexes are stable. This alone may make some of the iron inaccessible,slowing down precipitate formation. However, when this condition is combined with the often weeklysolution bleeds, much of the iron in solution is removed thus reducing the amount of precipitates that canform.1377.4 Leached Ore ParticlesThe impact of the leaching process is less obvious in the ore particles than for the precipitates. XRDanalyses of the washed fines do show a decrease in albite and clinochlore but no difference in quartz,orthoclase, and muscovite (Figure 7.17), probably reflecting the greater susceptibility of albite andclinochiore to degradation. Furthermore, copper recoveries that reached at least 50% for both columnsindicate that a portion of the suiphide minerals have been solubilized (Figure 4.5). Nevertheless, in order tobetter study the effects of leaching the polished cross-sections of particles examined for precipitates werefurther examined using reflected light microscopy and SEM/EDS techniques. Again, the data from thisstudy are qualitative only since they are based on visual estimates from a small number of ore particles. Inaddition, individual particle changes are not always clear since their original state is not known. In thisstudy only trends are recognized.A summary of the observations dealing with the silicate matrix is given in Table 7.10 and one for sulphidedissolution observations is given in Table 7.11. More detailed descriptions are given in Appendix H.7.4.1 Changes in the Silicate MatrixIt is difficult, and sometimes impossible, to conclusively differentiate between primary alteration of thesilicate matrix and alteration due to the leaching experiments; however, the number of veins and openvoids and the abundance of the silicate alteration product seen in the unleached ore (Figure 7.6d) appear tohave increased. Furthermore, the increase is somewhat greater for column 2 compared to column 4. Thisis not surprising since copper extraction at experiment termination was higher in column 2 than in column 4(Figure 4.5).Veins and Open VoidsVeins and open voids are most commonly seen in rims around the particles and are obviously formedby leach solution degradation. Concentrations of open voids, interpreted to be cross sections of veinsand/or the holes left by dissolved sulphides, form rims up to 500 !.Lm thick (Figure 7.1 8a). In someFigure 7.17: XRD analyses illustrating the change in the mineralogical composition of the finematerial after bioleaching. In both columns the amount of albite and clinochloredecreases toward the top of the column and the amount of orthoclase and muscoviteis virtually unchanged. This is thought to reflect the greater susceptibility of albiteand clinochlore to weathering (section 3.3.2).Column 2138Emtop of columnbottom of columnunleached finesI I I I I I I I i i I I I10 20 30 40degrees 2-thetaColumn 40Ebottom of columnunleached finesI I I I I I I I I I I I I I I I I I I I I I10 20 30degrees 2-theta40Table7.10:Summaryofobservationsmadeofchangestothesilicatematrixbasedonamineralogicalexaminationofpolishedparticlecross-sections.2”6”3HColumn2totalnumberofparticlesa810999distributionofveinabundance<100100310-2035422Column46”3H88992054564averagenumberofveinsb2222242719range1’10-397-4312-5111-406-33distributionofveinsizecaveragenumberoflarge76575averagenumberofsmallb1515192013111225555232211517156-334-261-293-28total45 4 16 24 230-’,.,6 16 28 Li 17 18200-500100-500I3536736317importantfeaturesdopenvoidsareminor(ofteninrim)openvoidsareverycommonveinsparalleltosurfacecommonrimsexhibitsuiphidedissOlutioflerangeofrimthickness(.tm)obviousmajorparticlebreakupsomeveinsareopenSiAloxideassociatedwithcovellitelargeregionsofSiA1oxide645431513111094 4 2 3100-5006 5 37 2 5 47 3 6 5100-5008 7 34’6”total124661132031512162-301-30 4 11931315614117100-200100-400165264332144 5 3 5100-2008 8 56 3 1 1100-2009 9 34 4 3 5100-4001 6 8 26 2 1 5100-2003 8 46 3 3 4200-3004 7 6 26 3 1 3100-2005 7 4aobservationsfromthegreenporphyryparticleswerenotincludedinthedatabecausethedegreeoffluidpenetrationinthesegrainsisgenerallyminimalandnotimportant tothediscussionsincetheydonotcontainsulphides.However,itshouldbenotedxthatthegreenporphyrygrainsincolumn2tendtocontainmoreveinsthanincolumn4.bareminimumvaluessinceinmostcasessomeveinsareill-defmedandcouldnotbecountedClargeveinsareconsideredtobethosethatpenetrateadistanceofmorethan1/4oftheparticlediameter.Smallveinsarethosethatpenetratenomorethan1/4ofthediameterandcommonlymuchless.Alltheveins,especiallythesmallones,usuallyoriginateattheparticlesurface.dfrequencyobserved:generallydefinedbymanyvoidsandfew,ifany,suiphides-rarelybyaconcentrationofcovellitenotseenelsewhereintheparticle.Table7.11:Summaryofobservationswithrespect tosuiphidemineraldegredationbasedonmineralogicalexaminationofpolishedparticlecross-sections.Column2totalnumberofparticlesa810999abundanceofcovelliteb<33%1(30)1(20)2(13)1(30)4(18)33%,<66%1(60)3(52)2(53)--2(43)66%6(85)6(87)5(93)8(91)3(97)Column41’6”3U88991290%33353abundanceofothersulphides°anilite1(5)1(3)0(1)0(2)1(1)bornite0(2)1(2)1(2)1(2)3(1)chalcopyrite--1(2)2(1)0(1)1(2)--3(20)3(13)2(0)5(24)6(49)1(35)3(50)--3(47)2(95)4(86)3(88)7(78)4(84)212116”1’6”2”6”3’6”4’6”total459208(5D28(89)173(12)6(9)4(6)321232151--43418100-500200-500100-50057363317importantfeaturesdcovellitebrokentextureminorcovellitebrokentexturecommonsulphuraftercovellitechalcopyritedissolvingdirectlyrimsexhibitsuiphidedissolutionerangeofrimthickness(jim)SiAloxideassociatedwithcovellitelargeregionsofSiA1oxide1(3)1(3)3(4)0(4)3(4)1(1)1(2)0(1)0(3)3(3)2(0)1(1)2(0)2(1)1(1)2 3 1 3 5100-5007 33 5 1 1 5100-2008 52 2 1 1 1100-2009 3--2223221——1—————1——15543100-400100-200200-300100-200886724241 1 1..100-2004 2agreenporphyryparticleswerenotusedinthedatacompilationbecausetheycontainnosuiphidesbwithrespecttototalsulphidesintheparticle.Valuesarethenumberofparticlesintheabundancerangeand,inbrackets,theaverageabundance(%)Cnumberofparticlesinwhichthemineralisthemajorsulphideand,inbrackets, thenumberinwhichthemineralisnotdominant butatleast10%ofthetotalsulphidesdnumberofparticlesinwhichthefeatureispresent.generallydefinedbymanyvoidsandfewifanysulphides-rarelybyaconcentrationofcovellitenotseenelsewhereintheparticle.141Figure 7.18: Typical changes to the silicate matrix.(a) Open voids that are interpreted to be vein cross-sections and/or the holes left by dissolvedsuiphides concentrated at the particle surface. (photomicrograph, bar is 200 jim)(b) Partial dissolution of covellite grains at the particle surface. (photomicrograph, bar is200 jim)(c) A small vein that is semi-parallel to the particle surface is causing small-scale break up ofthe particle. (photomicrograph, bar is 200 jim)(d) A concentration of semi-parallel veins causing extreme breakup of the particle surface.(photomicrograph, bar is 200 jim)(e) A less magnified view of (d). The concentration of semi-parallel veins appears as aleached rim (arrow) on the particle. (photograph, circular mount is 1 inch across)(f) A large precipitate-lined vein is causing this particle (arrow) to break apart.(photograph, circular mount is 1 inch across)kLii-d A d.•.‘ b,•J •‘ •A wS• . ‘...- —. I— St1• .,•.. I. S •.•a- 2’ 4r’ IA. LSt•‘\.f$I’I.¶£tIa144particles this dissolution of suiphides is not complete and voids containing cores of sulphide mineralsand/or their dissolution products are also observed (Figure 7.1 8b). The veins concentrating at theparticle surface are generally small and often run semi-parallel to the surface (Figures 7.1 8c and d). Itis not difficult to see that these veins cause the break up of particle surfaces which may account forsome of the changes in fines composition indicated by XRD data (Figure 7.17). This breakup can beminor as in Figure 7.18c or quite extensive as in Figures 7.18d and 7.18e depending on the abundanceand concentration of the veins. Note that only two particles with surface break up as extensively as inFigure 7.1 8d were observed.Larger veins and open voids in the centres of the particles are less commonly seen (Table 7.10). It isnot clear whether any of the larger veins are formed by the leach solution; however, since they areopen and often contain precipitates (Figures 7.1 3c and 7.1 5b) it is likely that the solution flows intothem exposing more rock surface and often sulphide minerals to degradation. In fact, several particleswere observed to be breaking apart along large precipitate lined veins (Table 7.10) (Figure 7.180.Obviously, the leach solution either created the veins or weakened original veins to the point where theparticle pieces could separate when mounted. If the weakness had been there originally the roughhandling that occurred during transport of the crushed ore and loading of the columns would havebroken the particle before leaching began. Since the particles were handled as intact pieces when beingmounted in epoxy this could not have been the case. It is interesting to note that the precipitates inthese veins did hold the particles together until the epoxy infiltrated, allowing the pieces to separatesomewhat.Open voids, when present throughout a particle are accompanied by numerous large veins and/or largepatches of the silicate alteration product that will be discussed in the next section. Again they areinterpreted to be cross sections of veins and/or the holes left by dissolved sulphides. Remnants ofsulphide minerals are sometimes present.Silicate Alteration ProductPorous aluminum silicate material with the same morphology (Figure 7.6d) and chemistry as that in theunleached ore is found in much greater abundance in the leached particles. It occurs in most of the145particles examined and in some of these it forms large patches representing up to a third of the particlevolume (Table 7.10). This material appears to be the product of silicate matrix alteration and theincreased abundance is presumably due to further alteration of this matrix. As in the unleached ore, itis composed primarily of silicon, generally less aluminum, oxygen, minor iron, and a variety ofminorelements (S, P. K, Mg, and Cu) that vary and may represent contamination from the leach solution orsurrounding minerals (Figure 7.1 9a). The ratio of silicon to aluminum varies from 1:1 through toapproximately 5:2. The oxygen- and iron-content can vary slightly as well. There does not seem to beany pattern to the compositional variations; however, a more extensive study may delineate one. Basedon the EDS analyses the material with a ratio of approximately 1:1 may be kaolinite [A14SiO10(OH)8Jorhalloysite[Al2O3SiO4H](Welton, 1984) but this cannot be confirmed without an XRDanalysis which was not obtained due to sampling difficulty. This material is fine grained and finelyintergrown with other minerals. Furthermore, if this material is the same as that in the unleached ore itis amorphous to x-rays and probably not a mineral. The extensive compositional variation anddistinctly non-crystalline porous morphology (Figures 7.1 9b/c and 7.20b) would also suggest that thisis the case.As with the veins and open voids, it can be difficult to differentiate between the primary silicatealteration product and that formed by the leach solution. Nevertheless, there are some cases where thealteration is obviously secondary. For example, many particles contain veins that are surrounded bysilicate alteration that decreases in abundance from the particle surface to the interior (Figure 7. 19b).Also obviously secondary are thin (commonly <25 urn) rims of the alteration product that oftenencircle leached particles (Figures 7. 12c and 7. 14a).Somewhat less obviously secondary are the large regions of alteration product that occur in particleinteriors and at particle surfaces (Figures 7.1 8c and d). The dimensions of these regions aresubstantially larger than those for the occurrences discussed above and would suggest a much longerexposure to leaching solutions or similar exposure to stronger solutions. Furthermore, these regionsare not concentrated at particle surfaces as would be expected if the degradation was due to theexperimental leach solutions. Despite this, it is difficult to imagine that no secondary alteration hasoccurred since the alteration product is always very porous (Figures 7.1 8c and d). Indeed, proof of146Figure 7.19: Typical chemistry and morphology of the silicate alteration product found in the leachedparticles.(a) Three EDS spectrum illustrating the variation in Si:Al ratio in the silicate alterationproduct. Notice that iron is always present but the other minor components (S, P. K, andMg) vary. The bottom scales are in keV.(b) A vein surrounded by porous silicate alteration (darkest grey). Notice that the alterationdecreases in abundance from the particle surface toward the interior. (backscatteredelectron image)(c) A portion of a large region of silicate alteration product (darkest grey) located in theparticle interior and connected to the particle surface by several large veins. Notice thatthis region is very porous and devoid of sulphides (white). Silicate minerals surroundingthe alteration product are a mixture of albite. orthoclase, and muscovite. (backscatteredelectron image)(d) Photomicrograph of a typical large region of silicate alteration product located at theparticle surface. Notice that it contains many covellite grains and some voids at theexposed surface. (bar is 200 tim)a-1SiSiSi AlaAA00L0. 7.20: Other interesting features exhibited by the silicate alteration product.(a) A large region of silicate alteration product with voids containing remnants of covellitegrains and elemental sulphur (arrows). The precipitate that coats and partially infiltratesthis region is a semi-porous mixture of iron oxide-sulphate and iron phosphate.(backscattered electron image)(b) Large veins surrounded by the silicate alteration product infiltrates the particle muchfurther than 500 j.i.m. Notice that the alteration product is basically devoid of suiphides(white). Furthermore, the suiphides adjacent to this region are partially dissolved (notvisible at this magnification). (backscattered electron image)(c) A thin (<25 tm), somewhat stratified and compact layer of material with the samecomposition as the silicate alteration product. Layers like this are often present onparticle surfaces. They appear to be exposed vein fillings such as that seen in this figure.Notice how the light and dark grey layers are symmetrical around a central point in thematerial. (backscattered electron image)(d) Another example of the thin compact layer of aluminum silicate. The material on theparticle surface is obviously an exposed portion of vein filling. photomicrograph, bar is200 p.m)•,;....•A150solution penetration can be seen in Figure 7.1 5b and 7.20a where precipitates infiltrate regions of thismaterial. In addition, open voids within the silicate alteration material in Figure 7.20a containremnants of dissolved covellite which are never seen in the unleached ore. It is important to note thatbecause of the porous nature of these large regions suiphide mineral surfaces and rock matrix occurringdeeper in the particles than the commonly observed alteration rims penetrate (>500 are exposed todegradation by the leach solution. Figure 7.20b, which contains much alteration product and a largeopen vein, is a good example of this. Because of this patchy increase in infiltration the total surfacearea exposed to the leach solution is larger than the total surface area of the particles. This is animportant feature to consider when deciding what particle size to use in a commercial scale operation.One unusual occurrence of the silicate alteration product appears to be primary, thin (<25 gm),somewhat stratified and compact layers often present intermittently on particle surfaces (Figures7.20c). This material usually has a Si:Al ratio of 2:1 and has been observed as vein filling in someparticles (Figure 7.20d). Judging by its morphology it is probably original and is certainly not aprecipitate as was originally thought.As stated above, the silicate alteration product occurs in most of the particles. There does not appearto be a pattern to its distribution or chemistry, neither along the lengths of the columns nor between thecolumns (Table 7.10). Again, a more detailed examination may delineate one.7.4.3 Sulphide Mineral DegradationCovellite appears to be more common in the leached ore particles than in the unleached ore. It comprisesmore than 33% of the sulphides in most of the particles examined (Table 7.11). Notice that covellite-richparticles (abundance >66% of total sulphides) are more common in column 2 than in column 4. Anilite,bomite, and chalcopyrite are much less abundant in both columns. They comprise less than 10% of thesulphides in most of the particles examined (Table 7.11). Furthermore, none of the large grains withbornite cores commonly seen in the unleached ore were observed.151This significant relative increase in covellite would suggest that the other copper-bearing sulphides arealtering to covellite before solubilizing. In fact, direct dissolution of suiphide minerals was observed inmany covellite grains and in rare large chalcopyrite grains but not in anilite and bomite. Apparently, assuggested by Whiteside & Goble (1986), Rossi (1990), and Scott (1991), anilite and bornite grains exposedto the leach solution are altering to covellite which is then dissolving.The dissolution of the covellite begins along grain boundaries in the typically matted mass of blades formedduring alteration (Figure 7.2 lb and d), giving covellite the ‘broken’ texture noted in some particles (Table7.11). This broken texture is probably more common than indicated in Table 7.11 since it is difficult to seein the microscope when it is at its initial stage. As dissolution continues a rim of elemental sulphur (S°)may form (Figures 7.20a and 7.22a). Many of the larger masses dissolve from the centre out leavingelemental sulphur in their cores (Table 7.11) and covellite blades at their rims (Figure 7.22b). In othergrains (masses ofmatted blades) the covellite dissolves leaving no elemental sulphur (Figures 7.22c and d).In both cases the dissolution continues eventually leaving empty voids where the covellite was (Figure7.18a).In several particles chalcopyrite dissolution was also observed (Table 7.11). Varying degrees ofdissolution were seen in large chalcopyrite grains, actually compact agglomerates of small crystals,surrounded by covellite (Figures 7.23a, b, and c). As with covellite, dissolution appears to begin alonggrain boundaries giving the large agglomerates a granular ‘broken’ texture. Again, elemental sulphur is leftbehind once all the copper and iron is removed. The copper deficient layer suggested by Arnmou-Chokrum(1977), Linge (1976), Peters (1973), and Burken (1969) and seen by Rossi (1990) was not observed;however; the layer may have been too small to be seen with the equipment used in this study. Notice thatthe surrounding covellite also dissolves to leave a coating of elemental sulphur; however, this coating has amore streaky texture than the sulphur remaining after chalcopyrite dissolution (Figure 7.23b).As with open voids and small veins, the sulphide alteration and dissolution described above is oftenconcentrated along rims around the leached particles. These rims commonly range in thickness from 100 to500 .tm (Table 7.11). In addition, significant covellite dissolution occurs along veins and within large152Figure 7.21: Alteration of anilite and initial dissolution of covellite.(a) Large grains of anilite (white) exhibiting almost complete alteration to covellite (blue).These grains are located inside an ore particle but are connected to the outer surface by anetwork of veins that are locally surrounded by silicate alteration product.(photomicrograph, bar is 200 A more detailed view of the anilite/covellite grains (white) showing that covellitedissolution along grain boundaries has begun. Porous silicate alteration product (darkestgrey) surrounds these grains. (backscattered electron image)(c) Alteration of anilite (light blue) to covellite (darker blue blades) along open veins (grey).The yellow mineral is covellite. (photomicrograph, bar is 200 tm)(d) A large covellite grain with a greater degree of dissolution along grain boundaries than in(b). This ‘broken’ texture is common in the leached particles. Black material iscomposed of silicate minerals and epoxy. (backscattered electron image)Ed—i_7//pp:\ -154Figure 7.22: Further dissolution in covellite grains. (backscattered electron images)(a) Partially dissolved covellite grains(white) in silicate alteration material (dark grey) at thusurface of a leached particle. Notice that the upper grain is surrounded by a porous layerof elemental sulphur (darkest grey) and a patchy coating of iron oxide-sulphate (lightgrey). The thin layer ofmaterial at the particle surface (medium grey) is iron phosphate.(b) A large mass of covellite blades located at the particle surface appears to have dissolvedfrom the inside outward leaving behind a small coating of elemental sulphur (mediumgrey) surrounded ry covellite (white). The very dark grey and black materials are silicateminerals and epoxy, respectively.(c) A partially dissolved covellite grain (white) with no associated elemental sulphur.(d) Another partially dissolved covellite grain with no associated elemental sulphur.Dissolution has obviously occurred along blade boundaries.-__,Figure7.23:Examplesofchalcopyritedissolution.(a)Alargechalcopyriteaggregatesurroundedbycovellite.Boththechalcopyriteandcovellitearepartiallydissolvedalongcrystalboundaries.Noticethatthechalcopyritehasamoregranulartexture.DarkregionsaroundthismaterialcontainsS°.(backscatteredelectronimage,bar200p.m)(b)Asimilarmixedchalcopyriteandcovellitegrainthatisalmost completelyremoved.Minoramountsofcovellite(white)remainattherimandS°(mediumgrey)occursinthecentre.NoticethattheS°resultingfromcovellitedissolutionismorestreakythanthatfromchalcopyrite.(backscatteredelectronimage)(c)Photomicrographof(b)showingthepseudo-metallicS°.Thefigureisrotatedclockwise90°.(baris200tim)UiC’157regions of the silicate alteration product both of which are often present in the leached particles (Table7.10). There does not seem to be any pattern to suiphide degradation along the columns; however, aswould be expected based on copper extraction levels (Figure 4.5), column 2 exhibits greater suiphidedegradation than column 4.7.5 BacteriaNo Thiobaccilli cells were recognized during examination of the leached ore particles; however, numeroussmall flattened ovoid particles approximately 4 p.m across were observed on feldspar and quartz crystals inseveral voids in a leached particle sampled from the top of column 2. These may be the mineralizedremains of bacterial cells either from the mixed culture added to the column or from the ore itself (Figure7.24). The morphology of these spheres suggest a biological origin; however, nitrogen, a necessarycomponent of all biological material, does not appear to be present (Figure 7.24). Nevertheless,microorganisms are known to form apatite (Lucas and Prévôt, 1985) and the composition of these particlesis that of a calcium-bearing phosphate. Furthermore, light rare earth elements not present in the ore andpresent only in very low concentrations in the leach solution appear to have been concentrated in thespheres and bacteria are known to concentrate elements such as gold and uranium in their cell walls(Rennie, 1992). In order to determine the origin of this unusual material, if possible, more detailedexamination is required.7.6 SummaryResults of the mineralogical examination of the solid residues from the columns 2 and 4 leach experimentshave implications both for commercial scale leaching of the Ivan ore and for the more generalunderstanding of copper sulphide degradation in acid sulphate environments containing iron and sulphuroxidizing bacteria.A major concern in bioleaching operations is the formation of precipitates that inhibit sulphide mineraldegradation. In the experiments with the Ivan ore sample much precipitation of relatively insoluble iron-bearing phases has occurred (Figure 7.9). Nonetheless, the precipitates are predominantly porous in1580.0 10.0keVFigure 7.24: Unusual particles thought to be the remnants of bacteria.(a) Backscattered electron image of the unusual particles. The substrate is predominantlyfeldspar. (bar is 20 micrometres)(b) An EDS analysis of the particles. They appear to be made up of a calciumphosphate with significant amounts of light rare earth elements.5.0159nature, suggesting that inhibition of copper extraction by formation of diffusion barriers on the ore particlesand/or the suiphide mineral grains is minimal if present at all. The precipitates also occur as less porous tocompact layers which might be expected to create solution infiltration barriers; however these occurrencesare much less common than the porous coatings and are very localized. The higher rate of copperextraction exhibited by column 2 is probably due to the presence of ferric chloride, a strong oxidant(section 3.2.2), and not to the lower abundance of precipitates compared to column 4.Probably more significant to sulphide mineral solubilization is the indirect inhibition of sulphide mineraldegradation by the removal from solution of iron and, to a lesser extent, phosphate and sulphate byprecipitation of these insoluble phases. As has been explained in section 3.2, iron is an importantcomponent in the sulphide mineral solubilization process. Its removal from solution reduces the rate offerric iron degradation of suiphide minerals and thus reduces the copper extraction rate. Furthermore,removal of iron, phosphate, and, sulphate may inhibit growth of the bacterial population which wouldresult in further reduction of suiphide mineral solubilization. The degree of inhibition produced by theremoval of iron, phosphate, and sulphate cannot be determined here; however, it should be noted that adecrease in pH in colunrns 1, 3, 5, and 6 (not examined in this study) did cause solubilization of much ofthe precipitates in those columns and resulted in an increase in the rate of copper extraction (Figure 4.5).The degree of sulphide mineral surface exposure is also a factor that affects the rate of sulphide mineraldegradation and thus copper extraction. The presence of large veins and/or regions of porous silicatealteration observed in most of the leached particles examined indicates that the total surface area of oreexposed to solution is greater than the total surface area of the ore particles. It appears that the totalsurface area of sulphide minerals is also increased by the presence of these features. This suggests thatusing an ore particle size less than 12.7 mm (1/2 inch) probably would not increase the copper extractionrate significantly. In fact, one of the six leach experiments run, column 5, contained -9.6 mm (-3/4 inch)ore particles and had a virtually identical copper extraction rate to column 2 (Figure 4.5), the experiment itmost closely resembled. These results suggest that a larger particle size may not significantly reducecopper extraction rates. Obviously a leach experiment run under similar conditions to columns 2 and 5 isnecessary to confirm this.160Finally, the various stages of suiphide mineral degradation observed in the residues of the two columnexperiments are of interest as they confirm and/or enhance observations made by other researchers(Chapter 3). As suggested by Whiteside & Goble (1986), Rossi (1990), and Scott (1991), anilite andbomite do appear to alter to covellite before dissolution. Furthermore, covellite grains are actually massesofmatted blades and dissolution occurs along the blade boundaries not just at the grain surfaces. Assuggested by Ehrlich (1990), a porous crust of elemental sulphur is often left after removal of copper fromthe covellite; however, this study could not ascertain whether the elemental sulphur layers inhibit furthersulphide mineral dissolution as suggested by many researchers. Interestingly, in other dissolving covellitegrains, commonly at or near particle surfaces, elemental sulphur is not present. The absence of thismaterial may imply the presence of bacteria which have oxidized the sulphur to sulphate (Ehrlich, 1990);however, covellite grains with elemental sulphur crusts are also observed near particle surfaces.Although much of the chalcopyrite in these experiments shows no evidence of dissolution, a few largerchalcopyrite grains, unlike anilite and bornite, appear to solubilize directly. This direct dissolution occursalong grain boundaries as in covellite, the large grains actually being aggregates ofmany small ones. And,as for covellite, a crust of elemental sulphur is left after removal of the copper and iron. It is unclearwhether this crust represents the inhibitory reaction zone suggested by Tuovinen (1990), Miller and Portillo(1979), Munoz et al. (1979), Dutrizac et al. (1969), and Sullivan (1933) to explain the strange kineticsseen in chaleopyrite concentrate leaching experiments. Furthermore, it was not possible to ascertainwhether the copper deficient layer suggested to be the inhibitory zone by Arnmou-Chokrum (1977), Linge(1976), Peters (1973), Burken (1969), and Rossi (1990) was present.It should be emphasized that the elemental sulphur crusts sometimes left after covellite and chalcopyritesolubilization do not appear to inhibit total suiphide removal. Evidence of virtually complete removal hasbeen observed in both cases.Finally, if the ovoid particles observed in leached material from column 2 are indeed the remains of bacteriathat have concentrated light rare earth elements from solution, commercial applications may be possible.However, more study is required to understand this phenomenon before applications can be considered.1618. CONCLUSIONS AND RECOMMENDATIONSA major objective of this study was to compile information about and contribute to the understanding ofacid sulphate environments containing iron and/or sulphur oxidizing bacteria, more specificallybioleaching. During this process suggestions for improving the current study of leaching and for areaswhere further study is needed have become apparent.The compilation of the current understanding of bioleaching processes given in Chapter 3 introduces thegeologist, and more specifically the mineralogist, to the complexities of acid sulphate environmentscontaining iron and sulphur oxidizing bacteria and the processes that effect the solid components of thesesystems. Although written in terms of hydrometallurgical bioleaching much of the information is valid forother acid sulphate environments such as acid sulphate soils, tailings heaps, and areas exposed to acid minedrainage. Obviously bacteria play an important role in controlling the chemistry of these environments;however, the current understanding of the interaction between the iron and/or sulphur oxidizing bacteriaand the minerals they come in contact with is incomplete. Several issues remain unresolved:(a) The biological mechanisms involved in direct bacterial attack of metal sulphides are not wellunderstood.(b) It is not clear how the lattices of the various copper-bearing sulphides and pyrite break down, whichelements or sites are oxidized and in what order. Of particular interest is the question of whethercopper is directly oxidized by the bacteria.(c) The presence and composition of diffusion barriers, especially on chalcopyrite grains, remain in dispute.(d) The poorly crystalline to non-crystalline iron-bearing precipitates often produced in the acid sulphateenvironment are not yet well characterized.(e) The role of bacteria in silicate mineral degradation is unclear; however, there is some indication that thedegradation does not follow the same paths as those seen under normal geological weatheringconditions (Bhatti et al., 1993; Ross et al., 1982; Ivarson et al., 1978)162Hopefully, by using new technologies that enable one to view these interaction in great detail, either directly(scanning tunneling electron microscopy) or indirectly (x-ray photon spectroscopy), these issues can beresolved. A better understanding of the processes involved in individual mineral degradation should help toimprove our understanding of the more complex multirnineralic systems commonly seen in sulphidemineral-bearing materials such as exposed ore and tailings.Modeling of the column 2 leach experiment done using PATH was relatively useful in helping to establishpossible reactions occurring in the columns. Most significantly, the results suggested a mechanism for theproduction of the distinct zoning seen in the precipitate formation. Basically, as the solution flows throughthe column its pH increases due to silicate mineral dissolution and the two phases which precipitate atdifferent pH’s form at different vertical positions in the colunrn, creating the zonation. Also of interest isthe suggestion that iron-chloride complexes remain relatively abundant and stable over the pH range seen inthe column experiments. This stability is thought to be the factor that causes fewer precipitates to form inthe high chloride experiments, especially column 2. The complexes make some of the necessary ironunavailable and cause more iron to be removed during the bleed processes that were used to maintain thecopper level below 15 gIL. Finally, the simulation suggested that chalcanthite, a copper sulphate, mightform at copper levels near 20g/L. Indeed, initially copper levels were observed to fall somewhat when thesolution concentration neared 20 g/L and quickly increase after a bleed brought the concentration down toapproximately 5 g/L. It was thought at the time that a relatively soluble copper phase was forming and forthis reason the copper level was later maintained below 15 g/L.Despite the obviously useful insights supplied by the simulation, the program does have some seriouslimitations which include a limited thermodynamic database, no kinetic component, and very cumbersomeoutputs. Because the simulation was useful it would be worth improving the PATH program and/orinvestigating the usefulness (applicability) of other geochemical modeling programs. If a more completethermodynamic database and improved data output could be achieved it would be worthwhile to runnumerous simulations to study the possible effects of different system variables such as solution chemistryand reactant composition. The simulation done in this study looked at the overall column reaction;however, because solution flow is not saturated the colunms contain many microenvironments that arepotentially very different.163The mineralogical study of the solid residues from the column 2 and 4 leach experiments produced insightsinto the effects of bioleaching on the solid component of the leaching system. The insoluble precipitatesthat formed in the columns include commonly observed jarosite and two non-crystalline phases that do notappear to have been identified in previous bioleaching experiments, an iron phosphate and an iron oxide-sulphate. Based on studies of other acid sulphate environments, these phases may be poorly crystallinevivianite or strengite and schwertmannite, receptively. Because these precipitates are relatively abundantthere was some concern that they might have inhibited copper extraction either by forming diffusionbarriers on the particle and/or sulphide mineral surfaces or by removing iron, phosphate, and sulphate fromthe leach solution. Results from the mineralogical examination suggest that inhibition by diffusion barriersis minimal if present at all since the majority of the precipitates occur in porous mixtures of scatteredprecipitate and silicate grains. The removal of iron and possibly phosphate and sulphate from solution isthought to be more significant. Dissolution of a large portion of these precipitates in columns 3, 5, and 6,achieved by a decrease in solution pH, did result in an increase in the copper extraction rate.The leached particles examined in the mineralogical study commonly exhibit an increase in the number ofveins, voids, and regions of porous silicate alteration product. This increase is more extreme in the column2 particles which was expected since the total copper extraction in column 2 was greater than that forcolumn 4. The presence of these features is thought to be indicative of fluid infiltration and degradation.Much of the infiltration appears to be along rims no more than approximately 500 tm deep; however, theless common larger veins and regions of silicate alteration product do expose the interiors ofmany particlesto the leach solution. This property should be considered when a crush size for the commercial heapoperation is decided upon. Copper extraction from particles greater than the 12.7 .im (1/2 inch) may notbe significantly different than that from smaller ones.Examination of the sulphide minerals in the leached particles suggested that bomite and anilite alter tocovellite before solubilizing. Dissolution of covellite and large chalcopyrite grains, both commonlyaggregates of small crystals, occurs along grain boundaries often leaving a crust of elemental sulphurbehind. This crust is not always present in dissolving covellite grains, possibly indicating the presence of164bacteria that readily oxidize the sulphur to sulphate. Furthermore, there was no indication that thiselemental sulphur forms diffusion barriers on the suiphide mineral grains.As has been discussed, the results from the mineralogical study of the solid residues have indicated sometrends in the distribution of the three precipitates, their morphologies, ore particle alteration, and suiphidemineral degradation; however, none of these results are quantitative. Now that a better understanding ofthe nature of the precipitates and leached particle alterations has been established, future studies should bedesigned to collect more quantitative information, either using point counting or image analysis techniques.This more quantitative data may reveal zoning in the distributions of some of these features which could beimportant when designing a conmiercial heap operation. In addition , the more quantitative data may aid inour understanding of the processes occurring in the columns.In this study no differentiation could be made between the effects of bacterial leaching and chemicalleaching since a sterile control column was not available for comparison. One was established along withthe other leaching experiments but it could not be terminated at the same time as columns 2 and 4 and inthe last part of the experiment the solution pH was changed from 2 as in columns 2 and 4 to approximately1.5. Unfortunately, any comparison would be useless. Obviously, a study of the residues from a sterileand a biologically assisted leach experiment would be very interesting as it would shed more light on therole of bacteria in the leaching process.Another variable that was not considered in this study is time. Oniy qualitative observations regarding theprogress of the leaching process could be made. Examination of the process at various stages may revealmore about the progress of leaching through individual particles and the entire column of ore. To achievethis a series of identical column experiments run for different periods of time should be examined.Finally, despite the fact that the bacteria present in the column experiments were not closely examined, anew bacteria (the ivoid particles) with unusual light rare earth element concentrating capabilities may havebeen discovered. More detailed monitoring of the bacterial populations in leach experiments may wellreveal other unusual and potentially useful microorganisms. In addition this monitoring could increase ourknowledge of population dynamics within the columns.In conclusion, this study has highlighted the importance ofmineralogy to research in the fields ofbiological/mineralogical interactions, acid rock drainage, and process engineering (specifically processmineralogy). 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Hossner, eds.), SoilScience Society of America Special Publication Number 10, Madison, Wisconson, pp. 37-56.Welton, J.E. (1984): SElviPetrology Atlas, The American Association of Petroleum Geologists, Tulsa,237 pages.Whiteside, L.S., and Goble, R.J. (1986): Structural and compositional changes in copper suiphides duringleaching and dissolution, Canadian Mineralogist, v. 24, pp. 247-25 8.Williams, P.A. (1990): Oxide Zone Geochemistry, Ellis Horwood, London, pp. 141-173177Wilson, M.J. (1975): Chemical weathering of some primary rock-forming minerals, Soil Science, v. 119,pp. 349-355.Yakhontova, L.K. (1985) :The role of sulphide constitution in the process of their bacterial leaching. InBiogeotechnology ofMetals (G.I. Daravaiko and S.N. Groudev, eds.), Centre of International Projects,G.K.N.T., Moscow, p. 216.Yakhontova, L.K., Nesterovich, L.G., Grudev,A.P, and Suchantzeva, V. S. (1980): Ob okislenii Sulfidofmcdi v sviasi s problemoi bakterialnova viscelachnivania rud, Izvestiia Vysshikh Uchebnykh Zavedenil- Geologiia i Razvedka., no. 1, p.52. (also see Rossi, 1990)178APPENDIX AList of microbiological terms used in section 3.1.179Table A-i: List of microbiological terms used in section 3.1.Term Definition Referencechemotrophic deriving metabolic energy from chemical energy - oxidation of organic Chapelle (1993)or inorganic compounds. TrUper (1984)lithotrophic using inorganic electron donors such as ferrous iron. Chapelle (1993)TrUper (1984)organotrophic using organic electron doners. Truper (1984)obligate aerobe bacteria that require oxygen as the electron acceptor during metabolic Chapelle (1993)processes.autotrophic using carbon dioxide as the carbon source for biosynthesis of cell Truper (1984)material.heterotrophic using organic carbon compounds as the carbon source for TrUper (1984)biosynthesis of cell material.acidophilic able to grow optimally in media with a pH equal to or less than 3. Harrison (1984)gram negative a procaryotic cell with a multilayered wall. ‘Negative’ refers to the Rossi (1990)cell’s inability to retain retain a purple dye (crystal violet). Chapelle (1993)gram positive a procaryotic cell with a single layered wall. ‘Positive’ refers to the Rossi (1990)cell’s ability to retain a purple dye (crystal violet). Chapelle (1993)procaryotic cell a cell with no true nucleus to house chromosomes. A single, naked Rossi (1990)DNA molecule contains all genetic information. Bacteria are typical Chapelle (1993)procaryotic organisms.mesophile an acidophilic organism that dominates at temperatures oenerally Chapelle (1993)below 40°C.thermophile an acidophilic organism that dominates at temperatures generally Norris & Kellyabove 40°C. This catagory is further broken down into moderate and (1982)extreme thermophiles that are generally dominant at temperaturesabove and below 50°C.vibrio a v-shaped cell. Note that ‘bacillus’ refers to a rod-shaped cell and Chapelle (1993)‘spirillum’ refers to a helical rod-shaped cell.proteins three-dimensional biological polymers constructed from a set of 20 Campbell (1990)different amino acids.nucleic acid biological molecules that allow organisms to reproduce. Campbell (1990)enzymes proteins that catalyze chemical reactions in cells. Chapelle (1993)coenzymes a nonprotein component required by many enzymes for initiation of Chapelle (1993)activity.cofactors inorganic ions required by some enzymes. Chapelle (1993)phospholipids a component of biological membranes. They have a polar hydrophilic Campbell (1990)head and a nonpolar hydrophobic head.180APPENDIX BFlow charts illustrating the serial transfers performed in the shake flaskexperiments in order to test and adapt Type A, B, and C bacterial cultures.The source of inoculants for the colunm experiments are indicated.+[ AO(4)A9(4)• AO(8)A9(8)Figure B-i:181Illustration of the serial transfers done using the Type A bacterial culture from Bacon,Donaldson & Associates Ltd., Canada, The original culture was grown on a copperconcentrate grading 28.5% copper. The solution contained no chloride. The resultingcultures were not used in the column leach tests. Note that values in brackets represent theamount of ground ore, in grams, used for that step. For the leaches the other numbersrepresent the type of nutrient solution used, 9K or OK. For the banks the unbracketed valueis the number of transfers done to that point.BkA-2(4).Figure B-2:182Illustration of the serial transfers done using the Type B bacterial culture from Bacon,Donaldson & Associates Ltd., Canada. The original culture was grown on pyrite in asolution containing 8,000 ppm Na Cl. The culture eventually died and another series wasstarted from a new sample of type B. See Figure B-3 for details not shown here. Note thatvalues in brackets represent the amount of ground ore, in grams, used for that step. For theleaches the other numbers represent the type of nutrient solution used, 9K or OK. For thebanks the unbracketed value is the number of transfers done to that point../\Leaches,BO(4)B9(4)I BUIC IIBU2d IIBU3e Ia8,000 ppm NaCIb10,000 ppm NaCIC25:75 fresh:U. Desesperado waterd50:50 fresh:U. Desesperado water ie0:100 fresh:U. Desesperado waterf5g1Lc1-183Figure B-3: Details of the new Type B series. Resultant cultures were used in the columns 2, 3, and 5column experiments.B-O (new)BD,cpy, 8000ppm NaCI4j 10,000 ppm5gIL Banks’#1 to#5#6 to #9#lOto#14#15#16#17#3rI gIL CI-Set #18000ppm9000ppmI 0000ppmSet #2toSet #6/#25 gIL CI-#55 gIL CI-184Illustration of the serial transfers done using the Type C bacterial culture from Bacon,Donaldson & Associates Ltd., Canada. The original culture was grown on pyrite in asolution containing no chloride. The resultant culture was used in the column 4 and 6experiments. Note that values in brackets represent the amount ofground ore, in grams, usedfor that step. For the leaches the other numbers represent the type of nutrient solution used,9K or OK. For the banks the unbracketed value is the number of transfers done to that point.Figure B-4:/ /Leaches.1 CO(4)1 C9(4)‘ CO(8)C9(8) I/185APPENDIX CCalculations of input data for the column 4 simulation and full equations established from resulting data.Table C-i: Calculation of volurne% and weight% estimates for initial conditions.Table C-2: Calculation of reaction rates for the reactants.Table C-3: Calculation of the theoretical solution chemistry due to addition of the 9K salts.Table C-4: The theoretical composition of the column 4 leach solution on Day 0 of the experiment.Figure C-i: Full equations given as partial equations in the text of Chapter 5.TableC-i:Calculationofvolume%andweight%estimatesforinitialconditions.MineralAlADataEstimateVolume%DensityeWeightWeight%(volume%)(recalculated)g/cm3g/100cm3chalcocite(j45b1.245.657.012.56covelliteI2.75035b0.964.684.491.64bomite)0.555.072.791.02chalcopyrite0.‘0.36(0.16c0.165.020.800.29magnetite)0.20c0.,respectively)wasaquiredfromanaverageelectronprobemicroanalysis.Densitywasassumedtobethesameforbothminerals;therefore,volume%datawerealsodeterminedusingthemicroprobedata.brelatjvedistributionfromavisualestimateinpercent.Cdistributjon(notrelative)fromavisualestimateinpercent.dpeakintensitiesfromapowderx-raydiffractionanalysisoftheIvanoresampledoneinSpring,1992.Valuesinthebracketsaretherelativedistributions(in%)basedonthepeakintensities.efromHurlbetandKlein(1985).00187Table C-2: Calculation of reaction rates for the reactants.Mineral Volume%’ Reaction Coefficientb Reaction Rate(k)chalcocite 1.24 0.40covellite 0.96 I sum 0.31bomite 0.55 of 0.18chalcopyrite 0.02 1 0.006pyrite 0.16 I 0.05magnetite 0.20 ) 0.06quartz 47.52 4.50E-05 0.002albite 41.89 4.50E-05 0.002muscovite 2.05 2.50E-03 0.005clinochlore 2.50 2.50E-03 0.006annite 2.91 2.50E-03 0.007afrom Table C-i.breaction coefficients modified those used by Bladh (1978) which are as follows:quartz 4.50E-05k-feldspar 4.50E-05mica (plus other clays) 2.50E-03sulphides sum to IModifications used in this simulation include addition of magnetite to the suiphide group and equatingalbite to k-feldspar.188Table C-3: Calculation of the theoretical solution chemistry due to addition of the 9K salts. Theconcentrations of salts used are given in Silverman and Lundgren (1959).Salts Calculations(NH4)2S0 3 g/L= (3 gIL) / [{(2)(14.007) + (8)(1.008) + (32.064) + (4)(15.9994)) g/mol] / (1 kgIL)= 0.0227 molal (m)KH2PO4 0.5gIL= (0.5 gIL) / [{(39. 102) + (2)(1.008) + (30.974) + (4)(15.9994)} glmol] / (1 kg/L)= 0.00367 molal (rn)MgSO4.7H20 0.5 gIL= (0.5 g/L) / [{(24.312) + (32.064) + (l1)(15.9994) + (14)(1.008)} g/mol] / (1 kg/L)= 0.00203 molal (rn)KC1 0.lgIL= (0.1 g/L) / [{(39.102) + (35.453)) glrnol] / (1 kgIL)=0.OOl34molal (m)Ca(N03)2.4H0 0.01 g/L(0.01 g/L) / [{(40.08) + (2)(14.007) + (14)(15.9994) + (4)(l.008)} g/mol] 1(1 kg/L)= 0.0000338 molal (m)FeSO4.7H20 9 g/L Fe2= (9 g/L) I [(55.847) g/mol] 1(1 kgIL)=0.l6lmolal (m)189Table C-4: The theoretical composition of the column 4 leach solution on Day 0 of the experiment.Calculations, where given, are based on the assumption that the solution has a density oflgJmI.Species Compositionlog [Hj -1.94 (range of log [Hj is -1.84 to -2.10)log [°2]gas -0.699 (assume oxygen saturation, P02 = 0.20)Cuto1 6.41 gILa= {(6.4lgIL) 1(63.54 glmol)} 1(1 LIkg)= 0.101 mFet0i 7.05 g/L a= {(7.05 g/L) / 55.847 glmol)} / (iL/kg)0.126mSO42- = {0.10002 mH2S04}b+ {0.0227 rn (NH4)2SO}’+ {0.00203 mMgSO4.7H2O}’+ {0.161 mFeSO.7H0}c= 0.286 m= (2){0.0227 m (NH4)2S0}c+ (2){0.0000338 mCaNO)2.4HO}c0.0455 mCl- =0.00134mcMg2 =0.00203 mcCa2 =0.0000338 mcK+ {0.00367 mKH2PO4}°+ {0.00134 m KC1}’= 0.00501 mP04 Leong (1992).bfrom data given in Leong (1992) it was determined that 333.4 ml of 6MH2S04solution was added tocolumn 4 by Day 0. This converts to: (0.3334 L) x (6 mol/L) /(20kg of solution) = 0.10002 mcfrom Table C-3.FigureC-5:ThefullequationsgivenaspartialequationsinthetextofChapter5.Speciesinboldcomprisethepartialequations.Fullequationforpartialeqations5.1and5.2:40.OOCu2S(S)+31.OOCuS(S)+O.6OCuFeS2()+18.OOCu5FeS4()+5.OOFeS2()+6.OOFe3O4(S)+O.2ONaA1S134(S)+O.5OKAI3Si1(OH)2(S)+O.6OKFe3AISi1(OH)2(S)+O.7OMg5Al2Si31o(OH)8()+3517502(aq)+75.13HSO4(aq)+3.51Fe(aq)+0.38FeClj’(a+3O.66H(aq)-*1.O8KFe3(S04)2OH)6S)+44.O5FeO(OH)(S)+6.OOSiO2(s)+2O1.52CU(aq)+224.25S04(aq)+2.9ZMgSO4(q)+3.7OAl(aq)+O.2ONa(aq)+O.O2K(aq)+O.58Mg2(+0.3lCl(aq)+0.07CuC1(aq)+31.53H20)Fullequationforpartialequation5.3:0.40Cu2S(S)+0.31CuS(S)+0.OO6CuFeS2(S)+0.18Cu5FeS+O.05Fe52(S)+O.O6Fe34()+O.OO2NaAlSi34()+0.O05KAl3SiOlo(OH)2()+0.OO6KFe3A1SiO1(OH)2(S)+0.007Mg5Al2Si3O1o(OH)8()+178.92KFe3(S04)2OH)6S)+3•5202(g)+9999O.OOH2SO4(aq)+40226.00S042(aq)+lO.6OKSO4(aq)+232.99MgSO4(q)+2.79CaSO4(aq)+3.55CuCt(aq)+56.99Cl(aq)+5.O9Al(OH)2(aq)+5.46H4SO(aq)+lO.55KSO4(aq)5.52SiO2(S)+l4082.71HSO4(aq)+189.48K(aq)+233.02Mg(aq)+2.79Ca(aq)+5.57Cu2(aq)+5.13Al3(aq)+O.0O2Na(aq)+476.27Fe3(aq)+6O.44FeCl2(aq)+O.O5FeCl2+58O77.21H(aq)+1090.80H20()Fullequationforpartialequation5.4:0.4OCu2S(8)+0.31CuS(S)+0.006CuFeS2()+0.18Cu5FCS4(S)+0.O5FeS2(S)+O.06Fe34(S)+0.OO2NaAlSi3O4(S)+0.OO5KAI3SiO1(OH)2(S)+0.006KFe3AlSiOlo(OH)2()+0.007Mg5Al2Si3O1o(OH)8()+2914.48FeO(OH)(S)+35202(g)+61.56KS04(aq)+42O.13K(aq)+999O.OOH2SO4(aq)+55469.30S042(aq)+239.I5MgSO4(aq)+1.81CaSO4(aq)+12.08CuCl(aq)+149.3lClaq)+4.84H4S1O4(aq)-481.68KFe3(SO)2OH)6S)+4.90SiO2(S)+154800.7OHSO4(aq)+239.18Mg2(aq)+1 .81Ca2(a+14. 10CU2(aq)+10.35M3(aq)+0.002Na(aq)+1308.03Fe3(aq)+161.29FeCL2(aq)+0.11FeCl2(aq)+39318.O7H(aq)+2960.10H0)191APPENDIX DList of samples along with, where applicable, the sample preparation andmineralogical examination techniques used. Samples are separated intounleached ore, evaporites, and solid leach residues.TableD-1:Theunleachedoresamplesexaminedinthemineralogicalstudy.Includedarethesamplepreparationandexaminationtechniquesused.Sample#DescriptionPreparationExaminationRRO1Ainitialmetallurgicalsamplegroundto-75j.tmMMAT,smallamountanalyzedusingXRDRROlBinitialmetallurgicalsample-crushedto-1.18mm-petrographicmicroscopeexamination-minus0.710mmfractionremoved-SEMJEDS-polishedthinsection(TS)madeRRO1Cinitialmetallurgicalsample-groundto-75im-powderXRDRRO2A-Qinitialmetallurgicalsample-handpickedsamples•petrographicmicroscopeexaminationofTS-polishedTSmadefromsamplesA,B,C, G,K,N,O,P,QRRO4A-Jlargemetallurgicalsample-10kgcrushedto-12.7mm-onesetchemicallyanalyzed-sievedinto9logarithmicallyequalsize-onesetrecombined(seeRRO5)fractionsplusa-0.150mmfraction-eachsizefractionseparatedinto3equalpartsafterbeingweighedRRO5A-EonethirdofRRO4A-J-recombinedaccordingtosieveanalysistogive-chemicalanalysisof44j.tmfraction4samples-petrographicmicroscopeexaminationofTS-minus44imfractionremoved-EPMAofsulphides,micas,feldspars, and-+3.35,-12.5mmfractioncrushedmanuallytospinelsinRRO5DTSapprox.-3.35mmbeforeTSpreparation-AlAexaminationofB,C,D,E-polishedTSmadeof+44imsizefractionsRR16--750goflargemetallurgicalsample-crushedto-12.7mm(beforeseparation) portionforwetchemicalanalysis-remainderusedassubstrateinshakeflaskexperiments(seeChapter4)RR3Opinkquartz-richparticlefrom-12.7mmcrushedoresampleRR31granite-likeparticlefrom-12.7mmcrushedoresampleRR32non-pinkquartz-richparticlefrom-12.7mmcrushedoresampleTableD-1(unleachedore)continued.Sample#DescriptionPreparationExaminationP.R33porphyry-typeparticlefrom-12.7namcrushedoresample2Bpalepink/lowgradeparticlesfromlarge-1polishedmount-polishedmountexaminedusingpetrographicmetallurgicalsamplecrushedto-12.7mmmicroscopeandSEM,BSE,EDS,andEPMAtechniques2Cgreenporphyryparticlesfromlarge-1polishedmount-polishedmountexaminedusingpetrographicmetallurgicalsamplecrushedtomicroscopeandSEM,BSE,EDS,andEPMA-12.7mmtechniques2Dred/pinkparticlesfromlarge-1polishedmount-polishedmountexaminedusingpetrographicmetallurgicalsamplecrushedtomicroscopeandSEM,BSE,EDS,andEPMA-12.7mmtechniques2E1-3grey,coarse-grainedhighgradeparticles-3polishedmounts-polishedmountexaminedusingpetrographicfromlargemetallurgicalsamplecrushedmicroscopeandSEM,BSE,EDS,andEPMAto-12.7mmtechniques2F1/2red,coarse-grainedhighgradeparticles-2polishedmount-polishedmountexaminedusingpetrographicfromlargemetallurgicalsamplecrushedmicroscopeandSEM,BSE,EDS,andEPMAto-12.7mmtechniques2FGgrey,coarse-grainedhighgradeparticle-1polishedmount-polishedmountexaminedusingpetrographicandgrey,fine-grainedparticlefromlargemicroscopeandSEM,BSE,EDS,andEPMAmetallurgicalsamplecrushedto-12.7mmtechniques2Ggrey,fine-grainedparticlesfromlarge-1polishedmount-polishedmountexaminedusingpetrographicmetallurgicalsamplecrushedto-12.7mmmicroscopeandSEM,BSE,EDS,andEPMAtechniques2H1-3light,medium-grainedhighgrade-3polishedmounts-polishedmountexaminedusingpetrographicparticlesfromlargemetallurgicalsamplemicroscopeandSEM,BSE,EDS,andEPMAcrushedto-12.7mmtechniquesU)TableD-2:Theevaporitesamplesexaminedinthemineralogicalstudy.Includedarethesamplepreparationandexaminationtechniquesused.Sample#DescriptionPreparationExaminationRRO3crustfrombottomcolumn1-portionmountedonstub-SEMJEDS-portiongroundwithmortarandpestle-powderXRDRRO6crustfromtopcolumn1(outside)-portionmountedonstub-SEM/EDS-portiongroundwithmortarandpestle-powderXRDRRO7crustfromtopcolumnI(inside)-portionmountedonstub-SEMJEDS-portiongroundwithmortarandpestle-powderXRDRRO8crustfrombottomcolumn6-portionmountedonstub-SEM/EDS-portiongroundwithmortarandpestle-powderXRDRRO9crustfrombottomcolumn1-portionmountedonstub-SEM/EDS-portiongroundwithmortarandpestle-powderXRDRR1Ocrustfrombottomcolumn4-portionmountedonstub-SEMJEDS-portiongroundwithmortarandpestle-powderXRDRR11blackmaterialongreensubstratefrom-driedandstored(turnedbrownondiying)bottomcolumn1RR12browncrustfrombottomcolumn6-destroyedbeforeanalysispossibleRR14yellow/bluecrustfromtopcolumn6-driedandstoredRRI5yellow/greencrust-topofcolumn2-driedandstoredRR2Obrownfrombottomofcolumn5-portionmountedonstub-SEMJEDS-portiongroundwithmortarandpestle-powderXRDRR26yellowandgreencrustfromtopcolumn-portionmountedonstub-SEMIEDS2-portiongroundwithmortarandpestle-powderXRDRR27yellowandgreencrustfromtopcolumn-portionmountedonstub-SEMJEDS3-portiongroundwithmortarandpestle-powderXRDRR28yellowandgreencrustfromtopcolumn-portionmountedonstub-SEMIEDS5-portiongroundwithmortarandpestle-powderXR])RR8Ocrustfromtopcolumn2(afterstop)-storedTableD-3:Thesolidleachresiduesexaminedinthemineralogicalstudy.Includedarethesamplepreparationandexaminationtechniquesused.Pleasenotethatallverticalpositionsaremeasuredfromthetopofthecolumns.Sample#DescriptionPreparationExaminationRR13A-Eparticlesfromtopofcolumn6during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,24/07/92E-groundusingmortarandpestle(fines)-fines(E)analyzedusingXRDRR21particlesfromtopofcolumn1during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,16/10/92RR22particlesfromtopofcolumn2during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,16/10/92RR23particlesfromtopofcolumn3during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,16/10/92RR24particlesfromtopofcolumn4during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,16/10/92RR25particlesfromtopofcolumn6during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,16/10/92RR41particlesfromtopofcolumn1during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,‘1/12/92RR42particlesfromtopofcolumn2during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,‘1/12/92RR43particlesfromtopofcolumn3during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,‘1/12/92RR44particlesfromtopofcolumn4during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,‘1/12/92RR45particlesfromtopofcolumn5during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,‘1/12/92RR46particlesfromtopofcolumn6during-particleorpartsofmountedonstub-microscopy,SEM,EDSanalysisleachexperiment,‘1/12/92(-‘ITableD-3(solidleachresidues)continued.Sample#DescriptionPreparationExaminationRR52glasswoolfrombottomofcolumn4-storedinsealedbag-mountedmaterialexaminedusingSEMfor-smallportionmountedonSEMtabandcarbonevidenceofbacteriacoatedRR53glasswoolfromtopofcolumn4-storedinsealedbagRR54fineclay-likematerial-2”,column4-finesgroundwithmortarandpestle-analyzedusingXRDRR55largeconsolidatedblock-2”,column4-storedRR56Afineclays+pptes.-column4,2’-2’ 1”-finesgroundwithmortarandpestle-analyzedusingXRDRR57fineclays+pptes.-column4,3’-3’2”-storedRR58A/Bsolidresidues-column4,5’A-stored-finesanalyzedusingXRDB-finesremovedusingdistilledwaterandanultrasonicbathRR59A-Gsolidresidues-column4,4’6”A-—5Ogsamplegroundto-75tm-‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,AISDEPMARR6OAsolidresidues-column4,4’-storedRR61A-Gsolidresidues-column4,3’6”A-—‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,ANDEPMARR62Asolidresidues-column4,3’-stored--RR63A-Gsolidresidues-column4,2’6”A--5Ogsamplegroundto-75tm-‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,ANDEPMARR64solidresidues-column4,2’-stored--TableD-3(solidleachresidues)continued.Sample#DescriptionPreparationExaminationRR65A-Gsolidresidues-column4,1’6”A-—‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,ANDEPMARR66A-Gsolidresidues-column4,6”A-—50gsamplegroundto-75i.m-‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,ANDEPMARR67Asolidresidues-column4,0’-storedRR81glasswoolfromtopofcolumn2-storedinsealedbagRR82glasswoolfrombottomofcolumn2•storedinsealedbag-mountedmaterialexaminedusingSEMforsmallportionmountedonSEMtabandcarbonevidenceofbacteriacoatedRR83A/Bsolidresidues-column2,0”A-stored-finesanalyzedusingXRDB-finesremovedusingdistilledwaterandanultrasonicbathRR84A-Gsolidresidues-column2,6”A-‘-50gsamplegroundto-75tm-‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,ANDEPMARR85solidresidues-column2,1’-stored--RR86A-Gsolidresidues-column2,1’6”A--50gsamplegroundto-75jtm-‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,ANDEPMARR87A-Gsolidresidues-column2,2’-stored--RR88A-Gsolidresidues-column2,2’6”A-—50gsamplegroundto-75p.m-‘A’materialanalyzedusingwetchemistryB-finesremovedusingdistilledwaterandan-finesanalyzedusingXRDultrasonicbath-C-Gexaminedusingpetrographicmicroscopy,C-G-largeparticlesinpolishedmountsSEM,BSE,EDS,ANDEPMA198APPENDIX EData collected using automated image analysis techniques.TableE-1:Distributionofmineralsineachsizefractionandinthewholesample(minusthe-45micronfractionwhichrepresents0.78weight%ofthesample).Individualsizefractiondatawerecombinedtogivethewholesampledistributionusingthemodifiedsieveanalysisdatagivenincolumn6.Allvaluesareestimatesofvolume%.Thedensitiesofthesizefractionswereassumedtobethesame,allowingthesieveanalysisdata(weight%)tobeusedasvolumedistributiondata.SizeFractionDistributionbySizeFractionSieveAnalysisDistributionofMineralsinWholeSample(micron)ChalcopyriteAN/CV/BNaHematite/PyriteGangue(no-45micron)ChalcopyriteAN/CV/BNaHematite/PyriteGangue-45n/an/an/an/an/an/an/an/an/a+45,-1500.153.770.4595.640.830.,-7100.162.740.4196.752.420.,-33500.042.940.1596.8614.210.010.420.0213.77+3350,-125000.012.700.3996.9782.540.012.230.3279.98Totaln/an/an/an/aTotal0.022.740.3696.88MetallicsDist’n”18811n/aaAN/CWBN:anilite,covellite,bornitebrelativedistributionofsulphidesandoxides(notgangue)whichcomprise3%byvolumeofthewholesample.TableE-2:Relativedistributionofmineralsinthewholesample(minusthe-45micronfractionwhichrepresents0.78weight%ofthesample).Allvaluesareestimatesofvolume%.Thedensitiesofthesizefractionswereassumedtobethesame,allowingthesieveanalysisdataweight%)tobeusedasvolumedistributiondata.SizeFractionRelativeDistributionofEachMineralinWholeSample(micron)ChalcopyriteAN/CVIBNaHematite/PyriteGangue-45n/an/an/an/a+45,-iSO6.,-71019.642.422.782.42+710,-335026.2315.235.8014.2+3350,-1250048.0681.2190.3882.57Total100.00100.00100.00100.00aAN/CV/BN.anilite,covellite,borniteTableE-3:Grainsizedistributionversusshapefactor(minimumdiameter/maximumdiameter)distributionforchalcopyrite.DatafromtheindividualsizefractionswerecombinedusingrelativeabundancevaluesfromTableE-2.GrainSizeShapeFactorTotalArea(microns)0to0.10.1to0.20.2to0.30.3to0.40.4to-0.50.5to0.60.6to0.70.7to0.80.8to0.90.9to1.0(percent)+4.1,-,8,-,-,-320.000.450.002.651.961.582.443.881.540.1814.69+32-,530.,900.,1500.,2500.,4250.,7100.,11800.,-,-,-,-320.,-530.000.030.381.022.243.353.432.391.260.0414.14+53,-900.000.000.331.593.023.834.543.151.500.1718.14+90,-iSO0.,-2500.000.000.800.191.512.832.581.690.550.0010.17+250,-4250.,-7100.,-11800. FElectron probe microanalyses of albite, muscovite, chlorite, hematite, magnetite, chalcopyrite,bomite, anilite, and covellite. The electron probe operating conditions are also included.202Table F-i: Electron probe operating conditions for silicate and oxide minerals.Mineral Type EPMA Code Element Line Standard Name Crystal Time (sec)Feldspar BAFELD Na KcL Albite TAP 20(albite) K Kc4 Orthoclase PET 20Al Koc Anorthite TAP 20Acc. Volt. (kV): i5 Fe Kc Aegirine LW 20Beam Current (MA): 20 Ca Kx Anorthite PET 20Beam Size (.tm): 10 Si Kc Orthoclase TAP 20Mg Kc4 Diopside TAP 20Phyllosilicates BIOTITE Na KcL Hornblende TAP 20(chlorite and muscovite) K Kc F-phlogopite PET 20Si Kc Muscovite TAP 20Acc. Volt. (kV): 15 Fe KcL Biotite LIF 20Beam Current (NA): 20 F Kc F-phlogopite TAP 20Beam Size (.tm): iO Cl Kc Halite PET 20Mg ICc F-phlogopite TAP 20Mn Kc Spessartine LW 20Al Kcs Muscovite TAP 20Ti Kx Rutile PET 20Cr K Chromite LIF 20Ca K Hornblende PET 20Oxides SPINEL Si K Fayalite TAP 20(hematite, ulvospinel) Ti Kc Rutile PET 20Al Kc Spinel TAP 20Acc. Volt. (kV): 20 Cr Kc Chromite LIF 20Beam Current(1A): 30 Fe Kc4 Fayalite LW 20Beam Size (jim): 2 Mn Kc Spessartine LW 20Mg Kx Spinel TAP 20Zn Kc Sphalerite LW 20Ca KcL Diopside PET 20Ni Kcc Ni-olivine LW 20(magnetite) Ji HEMATITE Fe Kx T104 LIF 20Acc. Volt. (kV): 15 Ti Kc S442 PET 20Beam Current (-qA): 20Beam Size (jim): 1203Table F-2: Electron probe operating conditions for suiphide minerals.Mineral Type EPMA Code Element Line Standard Name Crysta Time (sec)Suiphides SULPHJDE Cu Kcc Covellite LIF 30(bornite, anilite, covellite) S Kc Pyrrhotite PET 30Fe KcL Pyrrhotite LW 30Acc. Volt. (kV): 20 Pb Mcc Galena PET 30Beam Current (i1A): 30 Zn Kc Sphalerite LIF 30Beam Size (gm): 2 Au Moc Au PET 30As KcL Tetrahedrite LW 30Hg Mci. HgTe PET 30Mn J(ci. Mn LIF 30Co Kci. Co LIF 30Ni Koc Ni LW 30Sb Loc Tetrahedrite PET 30Ag La. Ag 30( plus chalcopyrite) CUPRIC Cu Kcc Covellite LIF 30Acc. Volt. (kV): 20 S Kci. Pyrrhotite PET 30Beam Current (i1A): 30 Fe Koc Pyrrhotite LIF 30Beam Size (tm): 2204Table F-3: Electron probe microanalyses of feldspar.D24A D24B D25A D25B D25CSi02 66.590 65.730 65,970 67.300 67.150A1203 20.140 21.460 20.270 19.850 20.230FeO -- 0.080 0.030 0.010 0.020MgO 0.010 0.040 -- 0.010 --CaO 0.280 0.430 0.540 0.080 0.390Na20 11.700 10.640 11.550 11.800 11.480K20 0.050 0.770 0.050 0.030 O.0’70SrOBaO 0.020 0.030Total 98.770 99. 170 98.410 99.110 99.340Number of ions on the basis of 8 anions (0)Si 2.952 4.00 2.908 ‘ 4.03 2.938 ‘ 4.01 2.970 4.00 2.957 4.01Al 1.052) 1.119) 1.064) 1.032) 1.050)Fe2 -- 0.003 0.001 -- 0.001Mg 0.001 I 0.003 I -- I 0.001 I -- ICa 0.013 I 0.020 I 0,026 I 0.004 I 0.018 INa 1.006 I 1.02 0.913 I 0.98 0.997 I 1.03 1.010 I 1.02 0.980 I 1.00K 0.003 I 0.043 I 0.003 I 0.002 I 0.004 ISr -- I -- I -- I -- I -- IBa -- ) -- ) -- ) o.ooi) -- )l Ana 1.3 2.1 2.5 0.4 1.8Mole% Aba 98.4 93.5 97.2 99.4 97.8) ora 0.3 4.4 0.3 0,2 0.4aCalculations based on relative molar abundance of Ca, Na, and K, respectively.205Table F-3 (contd)D212D D23A D23B D228 D211BSi02 67.360 68. 160 68.290 68.290 65.950A1203 20.190 19.840 19.760 20.220 20.120FeO 0.010 0.030 0.010 0.090 0.240MgO -- -- 0.010 --CaO 0.520 0.040 0.120 0.610 0.310Na20 11.440 11.710 11.660 11.470 11.630K20 0.060 0.020 0.010 0.070 0.050SiO -- -- -- -- —BaO 0.030 0.050 0.020 -- 0.020Total 99.610 99.850 99.880 100.750 98.320Number of ions on the basis of 8 anions (0)Si 2.959 4.00 2.982 ‘1 4.01 2.986 “ 4.00 2.966 ‘ 4.00 2.942 4.00Ai 1.045) 1.023) 1.018) 1.035) 1.058)Fe2 -- 0.00 1 “ -- 0.003 0.009 “Mg -- I -- I o.ooil -- -- ICa 0.024 I 0.002 I 0.006 I 0.028 I 0.015 INa 0.974 I 1.00 0.993 I 1.00 0.988 I 1.00 0.966 I 1.00 1.006 I 1.09K 0.003 I 0.001 0.001 0.004 I 0.003 ISr -- I -- I -- -- I — IBa 0.001 ) 0.001 ) -- ) -- ) — )2.4 0.2 0.6 2.8 1.5Mole % Aba 97.3 99.7 99.3 96.8 98.2) Ora 0.3 0.1 0.1 0.4 0.3aCalculations based on relative molar abundance of Ca, Na, and K, respectively.206Table F-3 (cont’d)D29A D29B D29DS102 66.710 66.420 66.560AL203 20.200 20.400 20.370F’EO 0.010 0.070 0.170MGO -- -- 0.020CAO 0.610 0,930 0.720NA2O 11.400 11.150 11.230K20 0.060 0.070 0.270SRO -- -- --BAO -- 0.010 0.020TOTAL 98.990 99.050 99.360Number of ions on the basis of 8 anions (0)Si 2.950 4.00 2.939 4.00 2.940 ‘ 4.00Al 1.053) 1.064) 1.060)Fe2 -- 0.003 0.006Mg -- I -- I 0.0011Ca 0.029 I 0.044 I 0.034 INa 0.978 1.00 0,956 I 1.01 0.962 I 1.02K 0.003 0.004 I 0.015 ISr -- I -- I -- IBa -- ) -- ) -- )‘j Afla 2.9 4,4 3.4Mole% Aba 96.8 95.2 95.2) Ora 0.3 0.4 1.5aCcu1ations based on relative molar abundance of Ca, Na, and K, respectively.207Table F-4: Electron probe microanalyses ofmuscovite.Sample D21A D21B D22A D26B D26CSi02 49.290 51.410 51.360 48.710 51.310A1203 29.560 28.530 27.680 33.830 29.530Ti02 0.030 0.040 0.0 10 0.0 10 0.060FeO 2.740 3.200 3.140 1.160 2.740MnO 0.050 0.050 0.020 0.100 0.020MgO 1.620 2.080 2.060 0.450 1.430Cr203 0.020 0.010 -- 0.030 0.020CaO 0.160 0.140 0.140 0.060 0.150Na20 0.100 0.130 0.090 0.150 0.870K20 7.870 9.320 9.300 10.090 8.990F 0.160 0.200 0.200 0.180 0.160Cl 0.020 0.020 0.100 -- 0.060H20 * 4.310 4.410 4.340 4.430 4.440O=F -0.070 -0.080 -0.080 -0.080 -0,070O=Cl -- -0.020 -- -0.010Total 95.850 99.450 98.330 99. 120 99.700Number of ions on the basis of 24 (O,OH,F,C1)Si 6.738 8.00 6,839 8.00 6.909 8.00 6.469 8.00 6.795 ‘1 8.00Al 1.262) 1.161) 1.091) 1.531) 1.205)Al 3.500” 3.312 3,297” 3.764” 3.404’Ti 0.003 I 0.004 I 0.00 1 0,00 1 I 0.006Fe2 0.313 I 4.15 0.356 4.09 0.353 4.07 0.129 I 4.00 0.303 4.00Mn 0.006 I 0,006 0.002 I 0.011 0.002Mg 0.330 I 0.413 I 0.413 I 0.089 0.282 ICr 0.002) 0.00 1 ) -- ) 0.003 ) 0.002)Ca 0.023 0.020 “ 0.020 “ 0,009 ‘ 0.02 1Na 0.027 I 1.42 0.034 I 1.64 0.023 I 1.64 0.039 I 1,76 0.223 11.76K 1.372 ) 1.582) 1.596 ) 1.710 ) 1.519)F- 0.069 ‘ 0.084 “ 0.085 0.076 0.067 ‘Cl- 0.005 I 4.00 0.005 I 4.00 0.023 I 4.00 - I 4.00 0.013 4.00OH 3.926) 3.911) 3.892) 3.924) 3.920)0 20.00 20.00 20.00 20.00 20.00aDetcined by stoichiometry assuming 4(F,C1,OH)208Table F-5: Electron probe microanalyses of chlorite.Sample D21OA D21OB D21OC D211D D28ASi02 28.930 29.170 28.440 27.750 28.280A1203 17.770 17.770 19.390 19.890 18.740Ti02 0.050 0.060 0.010 0.020 --FeO 23.390 23.780 21.740 23.430 19.900MnO 0.760 0.750 0.620 0.620 0.490MgO 16.580 15.950 16.950 14.840 20.030Cr203 0.010 0.010CaO 0.320 0.300 0.170 0.240 0.010Na20 0.090 0.070 0.050 0.070 0.010K20 0.060 0.050 0.020 0.020 --F 0.400 0.270 0.180 0.140 0.160CL 0.030 0.050 0.040 0.050 0.020H20 11.350 11.390 11.500 11.340 11.6200=F -0.170 -0.110 -0.080 -0.060 -0.0700=C1 -0.010 -0.010 -0.010 -0.010 0.000TOTAL 99.550 99.480 99.030 98.350 99.200Number of ions on the basis of 36 (0,OH,F,CL)Si 6.012 8.00 6.070 8.00 5.882 8.00 5.830 ‘ 8.00 5.795 8.00Al 1.988) 1.930) 2.118) 2.170) 2.205)Al 2.364 ‘ 2.428 ‘ 2.602 ‘ 2.755 ‘ 2.321Ti 0.008 I 0.009 I 0.002 0.003 I -- IFe2 4.065 I 4.138 I 3.760 4.116 I 3.410 IMn 0.134 0.132 I 0.109 I 0.110 0.085Mg 5.136 11.83 4.948 111.76 5.226 111.76 4.648 111.72 6.119 11.94Cr -- I - I -- I 0.002 I 0.002 ICa2+ 0.071 I 0.067 I 0.038 I 0.054 I 0.002 INa 0.036 I 0.028 I 0.020 I 0.029 I 0.004 IK 0.016) 0.013 J 0.005) 0.005) -_ )F 0.263 “i 0.178 0.118 ‘ 0.093 0.104 “Cl 0.011 116.00 0.018 116.00 0.014 116.00 0.018 116.00 0.007 116.00OHa 15.727) 15.805) 15.868) 15.889) 15.889)0 20.00 20.00 20.00 20.00 20.00Fe / Fe+Mg 0.44 0.46 0.42 0.47 0.36aDetened by stoichiometry assuming 16.00 (OH,F,Cl)209Table F-6: Electron probe microanalyses of hematite.Sample D211F D211G D33A D33B D33D5i02 0.040 0.080 0.090 0.090 0.390Ti02 0.460 0.670 1.740 1.210 1.040A1203 0.020 0.080 0.040 0.030 0.290Cr203 0.020 0.000 0.0 10 0.020 0.0 10Fe2O3(’) 99.000 99. 150 96.540 97.220 96.440FeO(a) 0.340 0.570 1.570 1.100 0.900MnO 0.020 0.050 0.040 0.020 0.020MgO 0.010 0.240ZnO 0.040 -- 0.020 -- --CaO 0.030 0.020 0.010 0.040 0.030NiO 0.030 0.050 0.030 0.0 10 0.020Total 100.000 100.680 100.090 99.750 99.380Number of ions on the basis of 3 anions (0) and 2 cationsSi 0.00 1 0.002 ‘ 0.002 ‘ 0.002 ‘ 0.0 10Ti 0.009 I 0.013 I 0.035 I 0.024 I 0.021 IAl 0.001 I 0.002 I 0.001 0.001 I 0.009 ICr -- I -- I -- I -- I -- IFe3 1.978 I 1.967 I 1.924 I 1.945 I 1.928 IFe2 0.008 I 2.00 0.013 I 2.00 0.035 I 2.00 0.024 I 2.00 0.020 I 2.00Mn -- I 0.001 I 0.001 I -- I -- IMg -- I -- I -- -- I 0.0101Zn o.ooil -- I -- I -- I -- ICa 0.001 I 0.001 I -- 0.001 I 0.001 INi 0.001) 0.001 ) 0.001 ) -- ) -- )0 3.00 3.00 3.00 3.00 3.00aDetemlined by valence balance. Iron-content measured as Fe3h210Table F-6 (cont’d)Sample D37A D37BSi02 0.060 0.370Ti02 1.790 1.690A1203 0.470 0.3 10Cr203 0.050 0.030Fe(a) 95.300 95.830FeO(a) 1.620 1.560MnO 0.0 10 0.0 10MgO -- 0.200ZnO 0.020 0.010CaONiO 0.030 0.030Total 99.360 100.040Number of ions on the basis of 3 anions (0) and 2 cationsSi 0.002 0,010Ti 0.036 I 0.034 IAl 0.015 I 0.010 ICr 0.001 I 0.001 IFe3 1.909 I 1.903 IFe2 0.036 I 2.000 0.034 I 2.001Mn --I --IMg -- I 0.0081Zn -- I -- ICa -- I -- INi 0.001) 0.0010 3.000 3.000aDetemined by valence balance. Iron-content measured as Fe3+.211Table F-7: Electron probe microanalyse of magnetite.Sample 2C-1 2C-2 2C-3 2C-4Ti02 2.270 1.390 1,600 1.110Fe03(a) 64.980 66.210 66.600 67.520FeO(a) 33.320 32.290 32.840 32.370Total 101,010 100.560 99.890 101.040Number of ions on the basis of 32 (0) and 24 cationsTi 0.254 “i 15,75 0,522 ‘ 15.48 0.322 15.68 0.367 15.63Fe3 15.491) 14.956) 15.356) 15.267)Fe2 8.26 8.52 8.32 8.370 32.00 32.00 32.00 32.00aDeteined by valence balance. Iron-content measured as Fe3+.Table F-8: Electron probe microanalyses of chalcopyrite.D38A D38B D38DCu 34.354 34.284 34.236Fe 30.336 29.827 30.312S 34.886 34.749 34.691Total 99.576 98.860 99.239Number of atoms on the basis of a total of 100 cations plus anionsCu 24.894 25.010 24.904Fe 25.011 24.756 25.087S 50.095 50.234 50.008Cu+Fe/S 1.00 0.99 1.00Cu/Fe 1.00 1.01 0.99212Table F-9: Electron probe microanalyses of bornite.Total 98.769 98.651 100.413 100.242 99.356Table F-9 (cont’d)5.01 5.0099.233 100.427 99.634D36B D35A D3 5E D3-6B D3 6C D3 5A D3 SISample D36ACu 62.431 6Ot19 63.435 63.200 62.694 62.280 63.231 62.695Fe 11.208 10.991 11.285 11.346 10.998 10.954 11.279 11.113Pb -- -- -- -- n/a n/a n/a n/aZn -- -- -- -- n/a n/a n/a n/aAu -- 0.0 19 -- -- n/a n/a n/a n/aAs -- -- 0.065 0.00 1 n/a n/a n/a n/aHg -- -- -- 0.003 n/a n/a n/a n/aMn 0.014 -- 0.002 -- n/a n/a n/a n/aCo -- -- 0.003 -- n/a n/a n/a n/aNi -- 0.010 0.003 -- n/a n/a n/a n/aSb -- 0.017 -- -- n/a n/a n/a n/aS 25.116 25.365 25.620 25.692 25.664 25.999 25.917 25.826Number of atoms on the basis of a total of 100 cations plus anionsCu 49.956 49.781 49.906 49.755 49.732 49.325 49.624 49.555Fe 10.204 10.001 10.101 10.163 9.926 9.870 10.071 9.993Pb -- -- -- -- n/a n/a n/a n/aZn -- -- -- -- n/a n/a n/a n/aAu -- 0.005 -- -- n/a n/a n/a n/aAs -- -- 0.043 0.00 1 n/a n/a n/a n/aHg -- -- -- 0.00 1 n/a n/a n/a n/aMn 0.0 13 -- 0.002 -- n/a n/a n/a n/aCo -- -- 0.002 -- ala n/a n/a n/aNi -- 0.009 0.003 -- n/a n/a n/a n/aSb -- 0.007 -- -- n/a n/a n/a n/a5 39.827 40.197 39.943 40.081 40.343 40.805 40.306 40.452Cu+Fe/S 1.51 1.49 1.50 1.49 1.48 1.45 1.48 1.47Cu/Fe 4.90 4.98 4.94 4.90 5.01 5.00 4.93 4.96arepeated in second set of analysesSample D3-6B D3 6C D3 5A D3 SICu 62.694 62.280 63.231 62.695Fe 10.998 10.954 11.279 11.113S 25.664 25.999 25.917 25.826Total 99.356 99.233 100.427 99.634Number of atoms on the basis of a total of 100 cations plus anionsCu 49.732 49.325 49.624 49.555Fe 9.926 9.870 10.071 9.993S 40.343 40.805 40.306 40.452Cu+Fe/S 1.48 1.45 1.48 1.47Cu/Fe 4.93 4.96213Table F- 10: Electron probe microanalyses of anilite.D35Ba D3 5Ga D3 2Aa D3 2B D3 1A D3 1BCu 77.512 77.632 77.491 77.792 77.175 77.128Fe 0.216 0.052 0.017 0.010 0.084 0.101Pb -- -- -- -- -- --Zn -- -- -- -- -- --Au 0.026 -- -- -- 0.042 --As 0.079 -- 0.006 0.058 0.018 --Hg 0.032 0.014 -- -- 0.065 --Mn 0.005 -- 0.011 -- 0.007 --Co -- -- -- -- -- --Ni 0.014 -- -- 0.011 -- --Sb -- -- 0.011 0.026 -- --S 22.544 22.586 22.412 22.533 22.516 22.460Total 100.428 100.284 99.948 100.430 99.907 99.689Number of atoms on the basis of a total of 100 cations plus anionsCu 63.255 63.398 63.544 63.488 63.285 63.349Fe 0.201 0.048 0.016 0.009 0.079 0.094Pb -- -- -- -- -- --Zn -- -- -- -- -- --Au 0.007 -- -- -- 0.011 --As 0.054 -- 0.004 0,040 0.013 --Hg 0.008 0.004 -- -- 0.017 --Mn 0.005 -- 0.010 -- 0.006 --Co -- -- -- -- -- --Ni 0.012 -- -- 0,010 -- --Sb -- -- 0.005 0.011 -- --S 36.457 36.551 36.420 36.442 36.589 36.557Cu+Fe/S 1.74 1.74 1.75 1.74 1.73 1.74Cu/Fe 314.70 1320.79 3971.50 7054.22 801.08 673.93aRepeated in the second set of analyses.Table F- 10 (cont’d)Sample D3 5G D3 2A D3 2B D3 lBCu 77.836 77.382 77.900 76.535Fe 0.007 0.000 0.000 0.163S 22.616 22.647 22.586 22.310Total 100.459 100.029 100.486 99.008Number of atoms on the basis of a total of 100 cations plus anionsCu 63.457 63.292 63.510 63.287Fe 0.006 0.000 0.000 0.154S 36.537 36.708 36.490 36.559Cu+Fe/S 1.74 1.72 1.74 1.74Cu/Fe 10576.2 n/a n/a 410.95214Table F-il: Electron probe microanalyses of covelliteSample D3 5D D3 4Aa D3 5H D3 5J D3 2C D3 2D2 D3 4A D3 4BCu 66.095 66.171 67.095 67.777 66.233 66.877 66.631 67.040Fe 0.049 0.002 0.048 0.055 0.003 0.085 0.009 0.021Pb -- -- n/a n/a n/a n/a n/a n/aZn -- -- n/a n/a n/a n/a n/a n/aAu -- 0.029 n/a n/a n/a n/a n/a n/aAs 0.034 0.001 n/a n/a n/a n/a n/a n/aHg -- -- n/a n/a n/a n/a n/a n/aIvIn -- -- n/a n/a n/a n/a n/a n/aCo 0.0 10 -- n/a n/a n/a n/a n/a n/aNi -- -- n/a n/a n/a n/a n/a n/aSb 0.00 1 -- n/a n/a n/a n/a n/a n/aS 33.351 33.451 31.134 31.156 33.628 33.352 33.323 33.224Total 99.540 99.654 98.277 98.988 99.864 100.31 99.963 100.28____ ____ ____ ____ ____4____5Number of atoms on the basis of a total of 100 cations plus anionsCu 49.965 49.951 50.359 52.305 49.845 50.259 50.221 50.443Fe 0.042 0.001 0.051 0.048 0.003 0.073 0.008 0.018Pb -- -- n/a n/a n/a n/a n/a n/aZn -- -- n/a n/a n/a n/a n/a n/aAu -- 0.007 n/a n/a n/a n/a n/a n/aAs 0.022 -- n/a n/a n/a n/a n/a n/aHg n/a n/a n/a n/a n/a n/aMn -- n/a n/a n/a n/a n/a n/aCo 0.008 n/a n/a n/a n/a n/a n/aNi n/a n/a n/a n/a n/a n/aSb. -- -- n/a n/a n/a n/a n/a n/aS 49.962 50.040 49,589 47.647 50.152 49.669 49.771 49.539Cu+Fe/S 1,00 1.00 1.02 1.10 0.99 1.01 1.01 1.02Cu/Fe 1189.6 49951. 987.43 1089.6 16615, 688.48 6277.6 2802.34 09 0____3 9aRepeated in second set of analyses.215APPENDIX GDescriptions of the precipitates observed in cross-sections of individual leached particles usingreflected light microscopy. Where used the short forms cpy and cv refer to chalcopyrite andcovellite, respectively. In addition, coating thicknesses are given in micrometres.Note: The precipitates cannot be well differentiated under the microscope unless presentas coarse intergrowths. The more concentrated less coarse grained precipitates are,the lighter they appear. Hence finely scattered porous material appears dark and theless scattered the precipitates in this material the lighter they appear. Furthermore,the more silicates present in any mixture the darker the precipitates appear.Because of this, lists of the compositions of the various types of precipitatecoatings, based on the SEM/EDS examinations, are also included.216Table 0-7: General description of the various precipitate types based on SEMJEDS examinations.Type DescriptionColumn 2porous dark -a scattered mixture of silicate grains with minor to trace amounts ofiron phosphate with or without iron oxide-sulphate or jarosite-silicate grains dominate the materialprous dark/light -a scattered mixture of iron phosphate, often minor iron oxide-sulphate,silicate grains, and rarely jarosite-the silicate grains are less abundant than in the porous dark materialsemi-porous light and/or -finely botryoidal mixtures or somewhat packed pieces of ironvery light phosphate and iron oxide-sulphate commonly with minor silicates-light material is dominated by iron phosphate and very light material isdominated by iron oxide-sulphatecompact light and/or very -coarsely botryoidal layers of iron phosphate and iron oxide-sulphatelight locally with trace amounts of silicate grains-these layers are generally thin than the semi-orous material and muchrarer-light material is dominated by iron phosphate and very light material isdominated by iron oxide-sulphate-thin layers of iron phosphate (only) occurcompact dark (yellow tint) -actually layers of primary silicate alteration product-thought to have been vein fillingsColumn 4porous dark -a scattered mixture ofjarosite crystals or flakes with silicate grains-the relative distribution ofjarosite to silicates varyprous dark/light -a scattered mixture ofjarosite crystals or flakes with iron-phosphatepieces and silicate grains-the relative distribution of components varysemi-porous light and/or -finely botryoidal mixtures of iron phosphate and iron oxide-sulphatevery light commonly with minor silicates-light material is dominated by iron phosphate and very light material isdominated by iron oxide-sulphatecompact light and/or very -coarsely botryoidal layers of iron phosphate and iron oxide-sulphatelight locally with trace amounts of silicate grains-these layers are generally thiimer than the semi-porous material-light material is dominated by iron phosphate and very light material isdominated by iron oxide-sulphate-thin layers of iron phosphate (only) occurcompact dark (yellow tint) -actually layers of primary silicate alteration product-thought to have been vein fillingsTableG-2:Descriptionsoftheprecipitatesobservedincolumn2,15cm(6inches)belowthetop.Notethatlocallytheporousdarkmaterialiscomposedofjarositeandsilicategrains.Also,semi-porousverylightmaterialisgenerallydenselypackedjarositeflakesratherthanmixturesofthenon-crystallineironspecies.Thesedensejarositelayersoftenoverlaytheporousmaterial.SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedarklightv.lightlayeredmixedincls.(average)RR84B-1yellowtodark75%XXtraceXcpy,<10-50-predominantlyporousdarkordark/lightlayersorangerocks(30)-verylocalizedsemi-porousverylightandcompactdark-muchrock,cv,cpyparticlesmixedwithprecipitatesRR84B-2yellowand40%X*XXrocks,<10-100-predominantlyporousdarklayersbutsomeporousdark/lightlayersdarkorangecpy(10-20)RR84B-3yelloworange50%XXtraceXXrocks,<10-300-commonlycompactdarkorporousdark/lightCpy,cv(50-80)-locallycompactdark/verylightmixtures-locallyporousverylightlayeroverlayscompactdarkorporousdark/lightlayers-lighthasslightorangetintRR84C-1yellowand20%XXXXXrock<10-600-predominantlyporousdarklayerminordarkcpy(20-30)-someporouslightordark/lightlayersalsoorange-locallysemi-porousverylightlayeroverlaysporouslightordark/lightlayers-verylighthasred/orangetintRR84C-2yellowand15%XXX<10-500-predominantlyporousdarklayersminororange(50)-lesscommonareporousdark/lightlayers-semi-porousverylightmaterialoverlaysporousdark/lightlocallyRR84C-3yellowtodark15%X*XXXXrock<10-800-porousdarkordark/lightlayerspredominateorange(80-100)-locallysemi-porousverylightlayeroverlaysporousdark/light-verylocalthinsemi-porousverylightlayerRR84D-1yelloworange40%X*XtraceXXrock<10-500-predominantlyporousdarkordark/lightmaterialcpy(50-100)-locallyoverlainbysemi-porouslightorverylightlayersRR84D-2yelloworange25%XtraceX<10-100-generallycompactverythinlayersofdark(10)-compactlightandporousdarklayersareveryrareRRB4D-3yellowtodark50%XXXXXn/a<10-900-actuallyagroupofgrainslooselyboundbyprecipitatesorange-predominantlyporousdarkmaterialinthemiddlewhichgradesintoporousdark/lightandfinallyaporoustosemi-porousverylightlayer-precipitatescementgrainstogetherTableG-3:Descriptionsoftheprecipitatesobservedincolumn2,45cm(1’6”)belowthetop.Notethatporousdarkisoftencomposedofsilicategrainswithminorjarositeflakesandtraceiron-phosphate.Theporousdark/lightmaterial oftencontainslargeclumpsofjarosite.SampleMegascopicViewMineralogyHabitThicknessCommentsj[colourcoveragedarklightv.lightlayeredmixedincls.(average)RR86B-1orange40%XXXrocks600-<10-predominantlyporousdarkmaterial(50-60)-locallysemi-poroustocompactlightoverlaysthis-verylocallythincompactlightlayeronlyRR86B-2yellowto50%X*XXXXrocks300-<l0iim-predominantlyporousdark/lightmaterialorange(50)-locallysemi-porousverylightlayeroverlaysthis-someporousdarkalsopresent-rarelyporousdark/verylightoccurs-somethincompactverylightlayersalsopresentRR86B-3yellowto20%X*XtraceXrocks200-<1Oiim-generallyporousorcompactdarkmaterial(50:50)orange(30)-locallycompactdarkoverlainbysemi-porousverylight-porouslight/darkmaterialisrareRR86C-1yellowto60%X*XXXXrock<10-400-predominantlyporousdarkorverylightmaterialorangecpy,cv(50-80)-locallyporousdark/verylightordark/lightlayerspresentRR86C-2yellowto25%XXXrock<10-400-predominantlyporousdark/lightmixtureorange(80-100)-localizedporousdarkalsooccursRR86D-1orange60%X*XXXXrock<10-600-generallyporousdarkmaterialcpy(80-100)-semi-porousverylightmaterial(redtint)lesscommon-porousdark/lightmixtureisrareRR86D-2orange20%X*XXXXrock<10-500-predominantlyporousdarkmaterialcpy,cv(30-50)-semi-porousverylightmaterial(redtint)islesscommonRR86D-3yellowto35%XXminorXXrock<10-600-mostlyporousdark,dark/light,ordark/verylightlayersorangecpy,cv-locallythinsemi-porousverylightlayersoverlaytheporousdark/lightmixture-lightandverylighthasaredtintRR86F-1yellowto10%X*XX<10-200-mostlyporousdarkordark/light,dark/verylightmaterialorange(10)-verylocalizedthinsemi-porousverylightlayerpresentRR86F-2yellowto15%XXXXXcv,cpy<10-400-precipitatesareveryrareorangerock(20)-generallyporousdark/lightordark/verylightmixture-locallyverylightlayeroverlaystheporousdark/verylightmaterialRR86F-3yellowand10%X*XX?XXrock<10-200-veryrareprecipitatesaremostlyporousdarkmaterialdarkorangecv(20)-somelocalsemi-porousverylightlayers(withredtint)-rareporousdark/lightmaterialalsopresent00TableG-4:Descriptionsoftheprecipitatesobservedincolumn2,75cm(2’6”)belowthetop.Notethatporouslightanddark/light containminoriron-phosphateandironoxid-sulphate.Theporousdarkmaterial containssilicatesgramsonly.SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedarklightv.lightlayered[mixedincls.((average)RR88B-1darkorange<5%X*traceXXrock<10-100-precipitatesarerareandintermixedwithmuchrockandyellowcpy,cv(10)-mostlysemi-porousmaterial-veryraresmall(—20jim)blebsoflightobservedindarkRR88B-2yellowand10%X*XminorXrock<10-300-predominantlysemi-porouslightwithmuchrockdarkorangecv,cpy(20)-porousdark/lightmixtureoverlainbysemi-porousverylightlayerobservedlocallyRR88B-3yellowand20%X*XXXXrock<10-100-predominantlyporousdarkverylocallymixedwithlightdarkorangecpy(25)-localizedsemi-porousverylightlayersalsoobserved-onesmallregionofcompactlight/verylightmaterialRR88C-1yelloworange20%X*XminorXXrock<10-300-predominantlyporousdarkmaterialwithlesscommonporousdark/lightcvmixturesandmuchassociateddebris-oneoccuranceofdarkwithbluetint-semi-porousverylightlayerspresentinsmallamountsRR88C-2orange&60%X*XXXrock<10-200-porousdarkordark/lightmaterialdominatesyellow(30-40)-minorsemi-porousverylightandlight/verylightpresentRR88C-3yellow&25%X*XXX*Xrock<10-200-generallyporousdarkordark/lightmaterialorangecvcpy(20)-porousandcompactverylightmaterialisrare-atveinmouthporousdarkoversemi-porousverylightRR88D-1orangeand15%X*XminorXXrock<10-200-predominantlyporousdarkorlightmaterialyellowcv(20-40)-porousandsemi-porousverylightislesscommon-compactlight/verylightisevenrarerRR88D-2orangeand15%XXminorXrock<10-400-predominantlyporousdarkmaterialwithsomewhatlesscommonporousyellowcv,cpy(20)lightanddark/light-onethickregionofporousdark/lightisoverlainbyasemi-porousverylightlayer-anotheroccuranceofsemi-porousverylight(orangetint)atveinmouthoverlainbyaporousdarklayerRR88D-3yellowand10%X*XminorXrock<10-300-generallyporousdarkmaterialorangecv,cpy(20-30)-somecompacttosemi-porousverylightmaterialalsoRR88D-4orangeand80%X*XXXX<10-300-sparseprecipitatesmostlyporousdark/lightordark/verylightmaterialyellow(20-30)-someporousverylightandlocalthincompactdarklayeralsopresent-oneareaofporousdark/lightmixtureisoverlainbyasemi-porousvery_______lightlayertJTableG-5:Descriptionsoftheprecipitatesobservedincolumn2,105cm(3’6”)belowthetop.Notethattheporousmaterialveryrarelycontainsjarositeandalwaysinverysmall amounts.Thesemi-porousmaterialismorecommonlyafinebotryoidalmixtureratherthanpackedpieces.Commonlythincompactlightlayerscontainironphosphateonly.SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedarklightv.lightlayeredmixed[incls.(average)RR9OB-1yellowand20%X*XXXXrock<10-500-predominantlyporousdarklocallywithlarge(-.20llm)blebsoflightorangeandcv,cpy(30-50)-elsewhereporousdark/lightandcompactlight/verylightcommondarkred-locallyporousdarkanddark/lightlayersareoverlainbycompacttosemi-porousverylightRR9OB-2yellowand10%X*minorXXXrock<10-300-predominantlyporousdarkbutalsoporousdark/light/verylightoftenorangecpy(20-30)overlainbyasemi-porousverylightlayer-somesemi-poroustocompactverylightorlight/verylightRR9OC-1yellowand15%X*XXXrock<10-300-mostlyporousorcompact(yellowtint)darkdarkorangecv(20-30)-alsosomelocalizedporousdark/lightorlight/verylight-compactdarklocallyoverlainbysemi-porouslightorporousdarkRR9OC-2yellowand5%X*minorXXrock<10-200-predominantlysemi-porouslightwhichappearstoinfiltrateparticleorange(10)-porousdark/lightoccursverylocallyRR9OC-3yellowand20%XXXXXrock<10-200-generallyporoustosemi-porousdarkorangecpy(30-40)-porousdark/lightoccursverylocally-semi-poroustocompactverylightregionsalsopresentsometimesoverlayingporousdarkordark/lightRR9OD-1yellowand5%XXXXXrock<10-400-mostlyporousdarkinoneareaoverlainbysemi-poroustocompactveryorangecpy,cv(30-50)light-locallycompactlightorverylightlayersoccuraloneRR9OD-2yellowand10%XXtraceXXrock<10-500-predominantlyporousdark,dark/light,orthincompactlightorangecv,cpy(50)-rarelyverylightlayeroverlaysporousdarkllightmixture-muchdarkinfiltratestheparticleRR9OD-3darkorange<5%XminorXX*rock<10-150-mostlyporousorcompactdarkandyellowcpy,cv(10-20)-semi-porousandcompactverylightobservedrarelyRR9OD-4orangeand15%XXminorXrock<10-200-predominantlysemi-porousdark/lightorlightyellowcv,cpy(50-80)-semi-porousverylightalsooccursbutisrareRR9OF-1yellowand<5%XXminorXrock<10-300-generallyporousdarkwithraresemi-porousverylightveryminorcpy(50-80)orangeRR9OF-2orangeand5%X*XXrock<10-150-predominantlythinlayersofcompactdarkyellowcv,cpy(10)-semi-porousverylightandporousdarkarelesscommonandoftenpy?overlaythecompactdark-I’-)t’JTableG-6:Descriptionsoftheprecipitatesobservedincolumn2,135cm(4’6”)belowthetop.Notethatveryrarelyporousdarkcontainsjarositeandsilicategrainsonly, elsewherenojarositeoccursintheismaterial.SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedark[lightv.lightlayered[mixedincls.(average)RR92B-1yellowand10%XXminorXX*rock<10-300-mostlyporousdarkwithlesscommonporousdark/lightorangecpy,cv(20-50)-someareasareoverlainbysemi-porouslightandverylightRR92B-2orangeand<5%X’XXrock<10-100-sparseprecipitatespredominantlyporousdarkyellow(10)-locallysem-porouslightandverylightlayerspresentRR92B-3yellow5%X*minorXXXrock<10-400-predominantlyporousdark(yellowtint)verylocallyoverlainbysemicv(50)porousverylight-porousdark/lightmixtureoccursrarelyRR92B-4yellowand<5%X*XXrock<10-100-sparseprecipitatesaregenerallyporousdarkmaterialorangecv(10)-isverylocallyoverlainbysemi-porouslightRR92E-1yellowand5%X*minorXXrocks<10-150-predominantlyporousorcompactdarkthatisusuallyoverlainbyporousorange(50)darkordark/lightmixture-verylocalporousdark/lightlayeronlycv-compactdarkdoesntappeartohinderinfiltrationRR92E-2yellowand5%X’minorXX<10-150-sparseprecipitatesaremostlyporousorcompactdarkorange(30-50)-localoizedsemi-porouslightalsopresentRR92E-3yellow,todark5%XminorminorXrock<10-100-predominantlyporousdarkorangecv,cpy(10)-locallysomesemi-porouslightorverylightRR92E-4yellowand10%X’XXXXrock<10-30-generallyporousdarkbutsomecompactdarkpresentdarkorangecv,cpy(10-20)-rarelysemi-porousverylightoverlayscompactdark-localizedporoustosemi-porousdark/lightpresentalsoRR92F-1yellowand<<5%X’minorminorXXrock<10-150-sparseprecipitatesaremostlyporousorcompactdarkorangecv(10)-thin(<5i.Lm)compactlayerscover—1/3ofparticlesurfaceandappearstobeassociatedwithveins-oftenoverlainbythickerporousdarklayer-verylocalsemi-porouslightorverylightlayersalsoRR92F-2orangeand<5%X*XXXXrock<10-100-predominantlythin(<—75%ofsurface)and/oryellowcv,cpy(10)porousdark(oftenovercompact)-somesemi-poroustocompactlight/verylightandsemi-porousverylight,elsewhereminorporousdark/light-notecompactassociatedwithorcoatsveinsbutdoesn’t appeartostopsolutioninfiltrationRR92F-3yellowand5%XtraceXrock<10-100-precipitatesaresparseandgenerallyporousdarkorsemi-porouslightorangecpy(20-40)-compactdarkalongoneedgeTableG-7:Descriptionsoftheprecipitatesobservedincolumn4,15cm(6inches)belowthetop.Notethatlocallytheporousdarkmaterialisdominatedbyironphosphateandironoxide-sulphatepieces.Also,semi-porousverylightmaterialisoftendenselypackedjarositeflakesratherthanmixturesofthenon-crystallineironspecies.Thesedensejarositelayersoftenoverlaytheporousmaterial.SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedarklightv.lightlayeredmixedincls.(average)RR66C-1yellowto20%X*XXXXrock<10-700-v.porousdarkordark/lightcommonorangecpy(20-30)-rarelyoverlainbycompactv.lightlayercv-lesscommonissemi-porousv.lightandv.light/light-rarecompactdark(withyellowtint)overlainbycompactv.lightwith2veinsRR66C-2yellowtodark25%X*XXXX’rock<10-100-generallysemi-poroustoporouslayersofdark,dark/light,orv.lightorange(30-50)-minorv.lightlayeroverlainbydark/lightlayerRR66D-1yellowto20%X*XtraceXX*rock<10-150-generallyv.porousdark,light,ordark/lightlayersorange(10)-rarecompactdark/light(400x50tm)-veryraresemi-porousv.lightatouteredgeofthicklightRR66D-2orangetodark40%X*XXXrocks<10-150-generallyv.porousdarkordark/lightlayersorange(10)-approximately1/5ofsurfacecoveredbya—80limthickcompactlayerofdark(withyellowtint)-locallycoveredbyv.porousdark-semi-porousv.lightlayerscommon(<100urnthick)RR66D-3yellowto30%X*minorXXXrock<10-150-compacttosemi-porousv.lightlayercommonorange(30)-elswherev.porousdarkordark/lightlocallyoverlainbysemi-porousv.lightlayerRR66E-1orangetodark65%X*XXXXrock<10-300-v.porousdarkordark/lightcommonredcpy(20)-veryrarethin(<<10tm)compactv.lightlayercv-elsewheresemi-porouslightorlightlviightlayers-sometimesoverv.porousdarklayer(>200timlayer)RR66E-2yellowto30%XXXXXrock<10-200-v.porousdarkordark/light commonorangecv(20-30)-orsemi-poroustocompactv.lightorv.lightllightlayerscpy-veinsobservedcuttingcompactlayersRR66F-1yellowwith60%XXXXX*rock<10-300-approximately80%coveragelocalred(<10)-generallyv.porousdarkorrarelydark/lightandsemi-porousv.lightorv.light/light-minorcompactv.lightRR66F-2yellowto50%X*XXXX*rock<10-300-v.porousdarkordark/lightcommonorange(50)-oftenoverlainbycompacttosemi-porousv.light-elsewherethincompactv.lightorlight/v.lightlayersRR66F-3yellowtodark60%XXXXX*<10-100-generallyv.porousdarkordark/lightandv.poroustosemi-porousv.lightorange(20)orlight/v.light layers-locallyrarecompactv.light/lightmixtureTableG-8:Descriptionsoftheprecipitatesobservedincolumn4,45cm(1’6”)belowthetop.Notethatintheporousdarkmaterialironphosphateisalwaysminorandjarositerodsoccurlocally.Also,semi-poroustocompactverylightmaterial canbedenselypackedjarositeflakesratherthanmixturesofnon-crystallineironspecies.Veryminoramountsofjarositecanalsooccurwiththemixturesofnon-crystallineironphases.SampleMegascopicViewMineralogyHabit}ThicknessCommentscolourcoveragedarklightv.lightlayered]mixedincls.(average)RR65B-1orangetodark50%XXXXXrock<10-150-lessthan50%coverageredcv(20)-porousdarkorsemi-porousv.lightorv.light/Iight-light&verylightprecipitatesoftenonoutersurfaceRR658-2darkorange40%XXXXXrock<10-300-bothsemi-porousandporousdarklayerscommoncv(20)-overlaincommonlybyporouslightundercompactv.light(someminorintermixingofporouslayer)RR65B-3yellowtodark25%XXtraceXX*rock<10-500-approximately90%coverageorangecpy,cv(50)-approximately1/3compactviightorv.light/light-approx.1/3porousdark,dark/lightordark/v.light-approximately1/3semi-porousv.light-compactlayersarethinner(<75jim)thanporousv.EightRR65D-1yellowand10%XXXXXrock<10-500-approximately80%coveragedarkorangecv(50)-approximately1/4ofparticlesurfaceiscoveredbycompactv.lightorcpyviight/light-lesscommonisporouslight/v.lightlayer-porousdarkordark/lightcommonalsoRR65D-2yellowtodark60%minorXX”XXrockcpy,<10-200-predominantlycompactv.tight,light,orlight/v.lightlayersvaryingfromredcv(20)<lOto100jimthick-minorthick(>50jim)semi-porouslightorV.lightlayers-porousdarkanddark/lightveryrareRR65D-3yellowtodark30%XXXXXrock<10-400-porousdark,light,dark/light,orv.lightondarkorangecv,cpy(50-80)-onesmallregionofcompactdark(withyellowtint)RR65E-1yellowand30%X*XXXXrock<10-200-approximately80%coverageorangecv(30-50)->1/2surfaceiscoveredbycompact10-60jimthickdarklayer(withyellowtint),locallywithlight-muchlesscommonisporousdark,dark/light(>60jimthick)-veryrarecompactv.lightIlightRR65E-2orangeand25%XtraceXrock<10-80-lessthan50%coverageyellow(<10)-predominantlyporousdark,dark/fight-somecoveredbyporouslayerRR65E-3yellow10%XXXrock<10-300-lessthan25%coveragecv,cpy(10)-allissparseporousdarkordark/lightlayerRR65C-1yellowand20%XXXXX*rock<10-400-lessthan50%coverageorangewithcv,cpy(20-30)-generallyporousdarkordark/lightlayerlocaldarkred-rarecompactdark(withyellowtint)andv.lightllightTableG-9:Descriptionsoftheprecipitatesobservedincolumn4,75cm(2’6”)belowthetop.Notethatonlyironphosphatewasobservedintheporousdark/lightmixtures(noironoxide-sulphate).Semi-porousverylightmaterialsometimesalsocontainsveryminoramountsofjarosite.SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedarklightv.llghtlayered[mixedincls.(average)RR63B-1yellowtodark30%XXXX’Xrocks<10-400-approximately11401particlesurfacecoveredbycompactdarklayerorangecpy(<10)(<10-50tmthick)cv-oftenhasv.light±lightlayeronouteredge-approximately1/401surfacecoveredbyporousdark/light±v.lightlayers(usuallyquitethick->50tm)-minorthincompactv.lightlayerslocallycutbyveinRR63B-2orangeto80%XminorXXX<10-100-approximately2/3ofparticlesurfacecoveredbythin(<10iim)compactbrown(10)v.lightandlocallylightlayer-wherev.lightisthicker(>400lIm)issemi-porous-lesscommonporousdark/light±v.lightRR63B-3yellowtodark55%X*XXXXrocks<10-400—1/4ofparticlesurfacecoveredbycompactdark(yellowtint)orangecpy(10)-locallywithsemi-porousv.lightand/orlightcoatingcv-approximately1/3ofsurfaceiscoveredbyporousdarkordark/light(locallyroughlylayered)-locallyveinscutthroughthislayer-verylighthasredtintwhereconcentratedRR63C-1yellowtodark55%X*XXXrock<10-100-approximately85%coverageorangecpy(20-10)-approximately1/3ofparticlesurfaceiscoveredbycompactdark(50-100iimthick)(withyellowtint)-sometimesoverlainbysemi-porouslightorcompactv.light-elsewherepredominantlyporousdarkordark/light-veryminorcompactv.lightandrarelight10-75.tmthickRR63C-2orange40%XXtraceXrock<10-200-precipitatesnotabundant(20-30)-semi-porouslightlv.lightlayercommon-elswhereporousdark,dark/lightordark/v.lightRR63C-3yellowto20%XXtraceXrock<10-100-muchporousdarkanddark/lightorangecv(10)-elsewheresemi-porousIight/v.lightlayeroftenoverporousdarkRR63C-4orange20%XXXX<10-50-lessthan20%coverage(<10)-predominantlyv.lightandv.light/lightinsemi-poroustocompactlayers(smallpieces)-elsewhereporousdarkinembaymentsTableG-9(cont’d)SampleMegascopicViewMineralogyHabitThickness“Commentscolourcoveragedarklightv.lightlayered[mixedincls.(average)RR63D-1yellow15%XtrtrXrock<10-100-verythick(100-400JIm)porousdarkordark/ugh±v.lightiscommoncpy(<10)-muchlesscommonisthinner(<20-100tm)compacttosemi-porouslayersofv.lightorv.Iight/lightRR63D-2orange50%X*XXX*Xrock<10-500-porousdarkanddark/lightcommon(20-30)-lesscommonbutsignificantiscompactv.lightoverporousdarklayer(minorintermixing)-verylightprecipitatehasredtingeRR63D-3orange15%X*XXXX<10-50-generallyporousdarkorminordark/light±v.light(20)-lesscommonisporouslightorv.lightonlyc,ITableG-10:Descriptionsoftheprecipitatesobservedincolunm4,105cm(3’6”)belowthetop.Notethatonlyironphosphatewasobservedintheporousdark/lightmixtures(noironoxide-sulphate).Semi-porousverylightmaterialrarelyalsocontainsveryminoramountsofjarosite.Commonlythincompactlightlayerscontainironphosphateonlyandthincompactverylightcontainsironoxide-sulphateonly.SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedarklightv.lightlayered]mixedincls.(average)RR61D-1yellowto10%XXXXrock<10-100-somelocalcompactdarklayers(withyellowtint)orange(10)-generallyporousdarkwithporouslightonouteredgewithminormixingoflightanddarkRR61D-2yellow15%XXminorXX<10-50-generallyporouslayersofdark/light ±v.light(<10)-veryminorcompactv.lightRR61D-3yellowand35%XXXXX*rock<10-500-approximately1/6ofparticlesurfacecoveredbythin(10-20lim)darkredcpy(20-30)compactv.lightlayerwithlightcores-someveinscutthislayer-mostisporousdarkordark/lightmixture-locallythick(>50tim)semi-porousv.lightlayerRR61E-1orangeto15%XXminorXXrock,<10-100-approximately75%coveragedarkredcpy,cv(10-20)-semi-porouslayerofdarkordark/light/v.lightmixturegenerally-rarelysemi-porouscompactv.Iightlayerwithveins-lightandverylightprecipitatesoftenmoreabundantontheoutersurfaceRR61E-2orange20%XXXrock<10-50-minorcoveragecv(<10)-porousmixtureofdark/lightRR61E-3yelloworange20%X*XXXX*<10-100-generallyporousmixtureofdark/light(20)-minorcompacttosemi-porousv.lightlayersalsoRR61E-4orange70%X*XminorXX*rock<10-200-generallyporousdark/lightmixture(20-30)-minorsemi-porouslightorviightonporousdarkRR61F-Iyellowtodark25%X*XXXXcv<10-200-predominantlyporousdarkordark/light±v.lightorange(20-30)-veryminorsemi-porouslightandv.light-rarecompactv.lightwithveinscuttingRR61F-2darkorange45%XXminorXX*rock<10-200-someregionsofcompactdark(withyellowtint)cpy(30-50)-elsewhereporousdark/lightordark/v.light-minorcompactv.lightlayerssometimesonporousdarkRR61F-3orangeto25%XXXXXrock<10-150-approximately1/3ofparticlesurfacecoveredbythin(<10tim)compactdarkorange(<10)v.lightorv.lightllightlayers-elsewhereporousdarkordark/light-minorcompactdark(withyellowtint)withcompactv.IightonouteredgeTableG-l1:Descriptionsoftheprecipitatesobservedincolumn4,135cm(4’6”)belowthetop.Notethatonlyironphosphatewasobservedintheporousdark/lightmixtures(noironoxide-sulphate).SampleMegascopicViewMineralogyHabitThicknessI Commentscolourcoveragedarklightv.lightlayeredmixedincls.(average)RR59B-1minoryellow75%X*XX”XXrock<10-800-v.light generallycompactevenwhenmixedwithlightonoutersurfaceswithdarkcpy(50)-locallysomeveinsthroughv.lightlayersorangetoredcv-oneverysmallareasomeporousdarkoverv.lighttoblack-oneregionofsemi-porousv.lightatthemouthofalargevein-darkanddarkllightmixturesareporouswherepresentRR59B-2orangetodark50%X*XXXXrock<10-300-v.light compactwherenotmixedwithdarkred(10-20)-dark,light,anddark/lightmixtureareallporous-minorporousv.light/darkmixtureRR59B-3darkorangeto35%X*XminorXXrock<10-200-generallyporousmixturesredcv(10-20)-veryminorcoverageRR59C-1darkred35%XXXXXcpy<10-200-dark,dark/lightmixtureareporous(20-30)-compactlight,v.light,anddarkarecommonalso-compactdarkactuallylayersinporousdark-semi-porousv.lightlayersarepresentbutnotcommon-lightandv.lightcommonlymoreabundantonouteredgeRR59C-2yellowto50%X*XXXrock<10-500-v.compactdarklayer(withyellowtint)commonbyselfandunderorangecv(30-50)porousdark/light±v.lightlayer-porousdark/light ±v.lightlayerscommonelsewheretoo-somecompactv.lightwithcoreoflight-veinsoccurthroughthislayer-lightandv.lightcommonlyonouteredgeRR59C-3orangetodark30%X*XXXXrock10-300-generallyporousmixturesofdark/light ±v.lightred(50-100)-verylocalthin(<<10lIm)compactlayersofv.lightRR59D-1orangeand<10%X*XX<10-100-mixturesofdark/light±rarev.lightareporousblue(?)(30)-layersoflightorv.light(minor)aresemi-porous-somedarkexhibitsabluetintandlargeholes(soft??)RR59D-2yellowto60%X*XtraceXrocks<10-250-generallyaporousmixtureofdark/lightorange(10-20)-onelocalstretchofcompactdark(withyellowtint)RR59D-3darkorangeto60%XXX”X’Xrocks<10-900-atleasthalfofparticlesurfaceiscoveredbycompacttosemi-porousredcv,cpy(10-20)v.light-v.lightiscompactwherethelayeristhin(<10jim)-minormixturesofdarkanddark/lightoccurasporouslayers-v.lightoftenmoreabundantonoutersurfaceTableG-11(cont’d)SampleMegascopicViewMineralogyHabitThicknessCommentscolourcoveragedarklightv.lightlayeredmixedincls.(average)RR59D-4yellowtodark60%XXXXXrocks<10-100-covers—95%ofsurfaceincrosssectionredcpy,cv(10-20)-approximatelyhalfofsurfacecoveredbymostlythin(<10m)compactv.lightlayer-locallyblobsoflightwithv.lightrimsontheselayers-elsewhererareporousdarkanddark/lightlayersandsemi-porousv.lightandv.light/lightlayers-v.light oftenmoreabundantonoutsideofv.light/lightRR59E-1yellowtodark40%X*XXXXrocks,<10-200-approximately1/3ofparticlecoveredbythin(<10tm)compactv.lightorangecpy,cv(10-20)andlocallylightlayer-elsewherethick(*XXXX<10-300-approximately50%coverageorange(20-30)-approximately1/401particlecoveredbycompact,generallythin(<±v.lightorsemi-porousV.lightinthickerlayerthanwherecompactRR59E-3yellowtodark75%X*XXXX<10-500-v.lightaslayeraloneorontopofotherprecipitatesisgenerallysemi-red(30)porous-locallythin(<10lIm)layersarecompact-onelargeareaofcompactdark(withyellowtint)-elsewhereminorporousdark/lightmixture-verythicklayerofprecipitatesoftenRR59E-4yellowtodark25%X*XXXXrocks<10-200-approximately70%coverageorange(50-10)-approx.1/3ofparticlesurfacecoveredbycompactdark(withyellowtint)-elsewheresemi-porouslightorv.lightlayers-lesscommonisalayerofporousdark/lightmixture00229APPENDIX HDescriptions of the cross-sections of individual leached particles using reflected light microscopy. Note thefollowing definitions that apply to all of the Tables:(1) Penetration categories (1/4, 1/3, .)- fractions of particle diameters(the values given are frequencies)(2) Pptes - precipitates observed in veins(3) Sulphide Contents - the relative distribution of the sulphideminerals in each particle(4) cpy - chalcopyrite; bn - bornite; cv - covellite; an - anilite(5) SAP - porous silicate alteration product(6) S° - elemental sulphur(7) tr - traceTableH-i:Descriptionofthechangesintheleachedparticlesfromcolumn2,15cm(6inches)belowthetop.SampleFluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/22/33/41cpybncvan([rimsRR84B-112931light-smallonesill-definedsomay134605bn=an/cv-primary/secondary?openbemorean=cv-primary/secondary?-largeonewideandopencv=,holesXX-secondary-oftennearsurfaceRR84B-2541-smallonesto—1/16-nosulfides(greenporphyry)penetrationandgenerallyintoplagioclasephenocrystsatsurface.RR84B-327+20+412light-smallonesoftenparallelto8020ancv-primary/secondaryopensurfaceand1/8penetration-largestonehascvcorewithcv=holesXX-secondarySAP-mostcommonalong200-400jimrim-oftencvstillincentreofvoids-somebrokentexturealongrimRR84C-123+12+5213open-probablymoreveinssinceill-tr3070an=cvXX-secondarydefinedcpy=cv-onelargegrain(secondary?)cv=holesXX-secondary-rimofalterationvariesfrom400-500jim -rimsomewhatdevoidofanysulfidesI00-200jimfewvoidsorcvgrainsintheinteriorRR84C-210+10+-veinsilldefinedbut judgingtr28018an=cv-primary/secondary?bysulfidealteration,muchbn=an/cv-primary/secondary?fluidpenetrationcv±holes-quitecommon/secondary±S-manyvoidsespeciallyalong—100-200+SAPjimrim-somecvatrimhasbrokentextureTableH-i(cont’d)SampleFluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentMineralsHabitofveins1/41/31/22/33/41cpy1bncvan(!(difficult tocount288010cpy=cv-primarybecauseinterconnected)bn=an/cv-primary/secondary?-someopen-afewopenvoidstooancv-primary/secondarycv=holesXX-secondary+SAP-cvhasvariousdegreesofbrokentextureRR84D-125+1-smallveinsareill-defined-trtr9010-cpyandbn?tiny(40jim)probablymanymorebutnotdisseminatedroundedgrainsbeyond—1/8penetration(200ancv-primary/secondary?jim)-manyopenvoidsalong500jicv+SAP-withsomelargergrainsmthickrim-secondary/twolargegrainsalteredtocv=S°S-andthroughoutparticlecv=hofesXX-secondary-manyopenvoidsthroughoutbutconcentratedat—500jimrim-someholeshuge(>400jim)°XX-secondary/common±holes-inseveralareasmostofcvhasbeenpartiallyremovedwithsmallamountofS°-coarsebrokentextureinremainingcv-jsomelargegrains(50-100jim)ofhematiteRR84D-3open-numerousveinsofallsizesintrtr9010ancv-secondarymostofthegrains>0.25cmcv=holes-aseriesofsmallparticleswithmuchacrosssulphidedissolution-cvhasbrokentexturet-.)TableH-2:Descriptionofthechangesintheleachedparticlesfromcolumn2,45cm(1’6”)belowthetop.SampleFluidPenetrationCommentsSuiphideAlterationCommentstotalno.1PenetrationPptesContentAlteration[HabitofveinsII4Il31pylbnan(eg.bncv)[veinsnmsRR86B-119+16+13open-highlyalteredgrain105805cpycv-primary?Iunalteredcpyatparticle-probablymoreveinsbutverysurfaceill-definedbn/an=cvXX-secondary?-inonearea—200-300gm-noalterationwherelittleevidenceofthickrimdisintegratingfluidpenetrationcv=holesXX-secondary+SAP-SAPencircleslargegrains-cvhasbrokentextureRR866-218+15+111open-manysmalloneshave1/8110881bn=an-primary?penetrationonlycv=holes-secondary±S0-twoexamplesofS°butnotcomplete+SAPRR86B-37511open-manysmallonesactuallythin5552020bn=an/cvX-primary/secondaryembayments-alterationcompleteatrimcv=holes-someholesalongrimtooRR86C-126+11+54114open-highlyalteredtr5050an=cvXX-secondary?-manyveinsill-definedcvholesX-secondary-severalsmallerveinsare-rim200-400imthickhaslesssulfidesparalleltosurfaceandandnumerousholesseparatingmaterialoff-manylargerveinspartiallycv+SAPX-secondaryopen-muchSAPassociatedwithsome-someveinsprimarywithlargeveinspartialsecondaryinfiltration-nearlargeveinscvtakesonbrokentexturenotseenelsewhereinsectionRR86C-221+16+23-manyoftheveinsareparallel6040cpycvX-secondary?tothesurface-somealterationinsideparticlealsocv=holesX-secondary-rims.-200-SOOiimthickwithvirtuallynocpyandlesscv(holesmorecommon)-notethathavedisseminatedgrainswithfairlyseparateregionsofcvandcpy-littleintermixingTableH-2(cont’d)SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/2[2/3]ilbncvan(eg.bncv)vnsnmsRR86D-11091open-manyparalleltosurfacetrtr8020cpy=hole-secondary?-coceoflargecvgraingoneancv-secondary?cv=holesX-secondary-rim1 00-200l.tmthicklesscvandmoreholescv+SAP-severaloccurancesofSAPnearmissingcpygrainRR86D-238+25+23512open-highlyalteredparticletrtr955?ancv-secondary?-varyinthicknesscpycvprimary/secondary?-someparalleltosurface-ononeedgeveinofcvwithcpycore-wholeregionsofSAPmostlymissingcv=hoIes-secondary+SAP-holesmorecommoninalteredSAPregions(manyveins)bnandcpyaretiny(<1Otim)disseminatedgrainsRR86D-3151221open-maybemoreveinsbutareill-151065bn=cvX-secondarydefined-regionsofcpy+bn?arebasically-largeveinispartiallyopenunalteredbutonlucvelsewherecv+SAP-localcv=holesXX-secondary-holesmuchmorecommonalongrims100-500imthick-n2tsomehematite?present-notalteredevenatsurfacewherecvalmostgoneRR86F-1221921open-manysmallveinsmorelike-nosulphides(greenporphyry)1/8penetration-largeveinhasopencoreandSAPcoatingTableH-2(cont’d)SampleFluidPenetrationCommentsSulphideAlterationCommentstota’no.PenetrationJPptesContentAlterationHabitofveins1/41/31/22/33/4iicpybn[cvan(±S-cvvariesfromfairlyintacttovery+SAPbrokentovirtuallygone-SAPcommonlyassociatedwithbrokencv-goodexampleofS0aroundavoidRR86F-319151111-somelargeveinsthought totrtr9010bn=cv-minor/secondary?beprimarywithsecondary-cpy/bnarecommonlysmall(<20im)infiltrationdisseminatedunalteredgrainsancv-secondary?cvcommonatsurfacecv=holesXX-secondary+SAP-morebrokentexturealongrimandveinst)TableH-3:Descriptionofthechangesintheleachedparticlesfromcolumn2,75cm(2’6”)belowthetop.SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/3[1/2cpy[bncvan([nmsRR88B-12824121open-manysmallonesareparallel55tr405cpycv..primarytosurfaceand1/8bnan-primarypenetrationcv+SAP-fairlycommoncv=hoIes-secondaryRR88B-2?many-wholesectors—50%oftr30655bn=cvXX-rare/secondaryparticleriddledwithopenancv-secondary?veinsandassociatedSAP-inalteredsectorcv=holes-secondary+SAP-goodexampleofinitialbreakupofcv(surroundedbySAP)alongbladeboundaries-holescommontooRR88B-351+30+105114open-highlyalteredtrtr955bn=an-?primarylight-severallargeveinsactuallycv=S-secondarycausingparticletobreakup+SAP-cvexhibitsvariableamountsofbrokentexture-locallysmallamountofS°cv=holesXX-secondary-morevoidsin200-100imrimRR88C-121201open-mostaremore1/87525cpy=S°-secondarypenetration-surroundedbydissoMngcv-notverywelldefinedcvholesXX-secondary?+SAP-somevoidsandcvwithbrokentexturenearrimRR88C-23?12-probablymanymoreveins-100tr’?cv=holes-secondaryactuallymorelikesectorsof+SAP-cvexhibitsbrokentextureSAP(withyellowtint)-voidsassociatedprimarilywith-plusmanyopenvoidsregionsofSAPRR88C-3121011open-verylittlealteration85tr?15bn=cvX-secondary-smallveinsare1/8penetrationbnan-primary?TableH-3(cont’d)SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/22/33/41cpybncvan(—200j.tmrim-covellitecommonlyhasbrokentexture-notehematite?commonwithbn?RR88D-218162open-manyofthesmallveinshavetrtr100trbnan-?primary1/8penetrationcv+SAP-fairlycommon-zonesofSAPandcv+holescommon(1/3penetration)cvholesXX-secondary-largeveinsopen-cvhasbrokentexture-holesmorecommonin1 00-200iimrimRR88D-31914113open-alsoseveralzonesofSAP10tr855cpycv-primary-manylargerveinsopen-somesmall(<1Ohm)disseminatedcpymaybepyriteancv-secondary?cv+SAP-commoncv=holes-secondaryXX-mostcommoninalterationzonesandatrim-cvgenerallyhasbrokentextureRR88D-455open-verysmall-i/8penetration-nosulphides(greenporphyry)-generallyparalleltosurfaceTableH-4:Descriptionofthechangesintheleachedparticlesfromcolumn2,105cm(3’6”)belowthetop.SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentMineralsHabitofveins1/41/31/22/3[3/41cpy’bncvan(<50imscaleRR9OC-128+20+3221open-mostsmallveinsaremore10107010cpycv-primary?like1/8penetration-cpyexhibitsabrokentexture-holescommoninrimbn=cvX-secondaryprimarily-manydeep/wide(50-1OOlim)embaymentsancvXX-secondary-largeembaymentswithSAPcv±holesXX-secondaryandcv+SAP-cvexhibitsabitmoreofabrokentextureat—100-200imrimalongwithsomeholesRR9OC-2?-nowell-definedveinshoweveitr100cvholes-secondarypresenceofmuchSAPand+SAP-SAPthroughoutparticlemanyholesindicates-numerousholesthroughoutinfiltrationinmostoftheparticleRR9OC-330212323open-largeveinsareactuallya11971bn=cvX-rare/secondarylightnetworkofveinsthatconnectcpy=cv-primary?throughparticlein—500iim±s°-secondary?-cpybreakingupasseenthickzoneelsewhereincentreoflargecvmass-onehascausedseparationofapieceofrockfromthe-secondary/commonparticlecvholesXX+SAPTableH-4(cont’d)SampleFluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/22/33/41cpybncvan( toparticlesurfacecountcv=holesX-secondary?+SAP-SAPnot common-gcpydoesnotexhibitabrokentextureRR9OD-27?61-halfoftheparticleistr595bn=cv-possiblybothprimaryandsecondarycomposedofcvandSAP-secondary-appearstobetotalcv=holes-cvhasbrokentexturepenetrationinthatregion+SAPRR9OD-312912-allareverythin(<10tm)tr7030bncvX?-possiblybothprimaryandsecondary-verylittlealteration-secondary/veryrarecv=holesX+SAPRR9OD-4?open-individualveinsill-definedbuttr199bn=cv-primary?—80%ofparticlecoveredbycv=holes-secondaryanetworkofveins+SAP-cvstartingtoexhibitbrokentexture-nodepletionobservedatrimRR9OF-139+26+33214open-probablymorebutisavery570-py25%complexnetworkofveins-pyritethroughoutunalteredeveninorthroughparticlenearveinscpy=cv-?primary-oneinstanceofcvallgonebutcpyleftincentrecvholesXX-secondary±S-cvveryfinegrainedandhasbroken+SAPtexturewithmanyholes-oneoccurenceofS°atthemouthofaveinRR9OF-2532open-halfareparalleltoparticle-nosulphides(greenporphyry)surface00TableH-5:Descriptionofthechangesintheleachedparticlesfromcolumn2,135cm(4’6”)belowthetop.SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/4f1/31/22/33/41lt)t1]an(’?subparallelveinsofvariouscv=holesXX*-secondarysizesallparalleltoparticle+SAP-becomemorecommonnearparticlesurface-almostcompletelysurfacearoundrim-cvmorebrokennearsurface-couplegointointerior-jcpyandbnsmall(<10im)disseminatedgrainsRR92B-27421open-veryfewveinsandmostly255025trbn=cv/an?X-primary?butnearsurfaceparalleltosurfacecv=holesXX-secondary-commonatsurface-nosulfidesnearveinseitherRR92B-326183113-largeveinsarealltr4060an=cvXX-secondaryinterconnectedatcentrecv=holesXX-secondary-manysmallareparallelto+SAP-alongveinsdonthavetotalanilitesurfaceandonly1/8alterationbutrim500-300iimthickpenetrationalmostcompletealterationRR92B-4191031113open-allverynarrow982cpy=cvX-veryrare/secondary-somelargeinaconnectedcpy+SAP-verylittlecpyalterationevenatrimnetworkactually———RR92E-1159213open-largeareactuallywidetr5)95?bn=cv-probablyprimaryandsecondaryregionsofopenvein-visibleinregionswithmuchlower(-.50%ofparticle)apparentinfiltrationcv=holes-secondary+SAP-muchSAP-many!holesinlargealteredregionsoftenwithsomecvincentreRR92E-277-allareparalleltothesurfacetrtr100trcv+SAPXX-verycommon-strangelackofvisibleveinscv=holesXX-secondary?andverycommonsincetherearemanyopen-holesabitmorecommonalongrimvoidsandotherevidenceof200limthickinfiltration-flcvgenerallyhasbrokentextureTableH-5(cont’d)SampleFluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/22/33/41cpybncvan(eg.bncv)veinsrimsRR92E-3-none-nosulphides(greenporphyry)RR92E-4651-smallonesallparallel to575155bnan-primarysinceanincentreofgrainssurfacebn=cv-notcommon/secondary?cvholesX-secondary+SAPRR92F-125184111open-allveinsareverynarrow205030?bn=cvXX-secondary?-mostsmallareactually1/8cv=holes-secondarypenetrationandmanysmall+SAP-cvhassomewhatbrokentextureparalleltosurface-veinscommonincv--notewherecvoccursisaregionthatrich/sulfide-richareaismoresulfideandveinrichRR92F-218332—4open-allverythin(oneexception)454510bnan/cvXX-primary/secondary?light-probablybothascvmostcommonalongrimandveinscvholesXX*-secondarybutnotcommonexceptat+SAP200iimthickrim-cvexhibitsmorebrokentextureatrimRR92F-3541open-allparalleltosurface-nosulphides(greenporphyry)-surfaceappearslocallytobebrokento<100imdepth(rocksandprecipitate)TableH-6:Descriptionofthechangesintheleachedparticlesfromcolumn4,15cm(6inches)belowthetop.SampleFluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/4jh/V2TTTcpylbncvan(—RR66C-128+25+21open-manyveinsill-defined4060an=cvXX-secondary-manyofthesmallestveins-rimI 00-200iImthickhasnosulfideshave1/8penetration-unalteredanilitewherenoveins-severalincentreofparticlecv=holes-secondaryareopen+SAP-holescommonlywithSAP-cvhasabrokentexture-noteunalteredanilitegrainshaveamottledcolourlocallyRR66C-266-alllessthan1/8penetrationtrtr6535ancv-secondary?-poorlydefinedcvholes-secondary+SAP-alterationnotdominantbutisseenthroughouttheparticle-smallSAPregionsarealsopresent-cvhasbrokentexture————-onelargecvgrainincentreofvoidRR66D-11410211open-smallveinsparalleltosurfacetr5545bn=cvXX-secondary-manyofthesmallveinsand-predominantlycvatrimsall ofthelargeonesarebn+SAPX-secondarythoughttobeprimarywith-bnwithverylittleifanycvobviouslypartialsecondaryinfiltrationbreakingupcvholesXX-secondary+SAP-holesverycommon-cvhasbrokentextureRR66D-224192111open-smalloftenparallel tosurfacetr306010bn=an-primary?-largeveinappearstobebn=cv-secondary?butnotobviouslyremovingwedgeofmaterialassociatedwiththerimorveins-maybemoreveinsbut ill--manybn-onlygrainsstillpresentdefined-alterationvisibleancvXX-secondary(notalwaysobvious)megascopicallycv=holesXX-secondary!+SAP-SApandholesverycommonalong——————rim(100-300llm)TableH-6(contd)SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabit1Ticpybncvan(eg.bncv)veinsnmsofveinsRR66D-31911521open-highlyalteredparticle6040cpycvX-primaryandsecondary?-manysmallveinsparallelto-alongveinsbutseecpycommonlyatsurfacerimcv=holesXX-secondary+SAP-SAPnotcommon-holeson—400imrimonlywherecvisprevalentRR66E-125+10.34323open-veinsvisiblemegascopically5545cpy=cvX-notclearbutprobablymostlyprimary-largerveinsactuallyasinceunalteredsmallcpygrainsincomplexnetworkofveinswithpartiallyalteredbiggerinterconnectedveinsparallelgrainstoeachotherinonecornerofcv=holesXX-secondarytheparticle±SAP-alongveinsandrims,especiallythe-severalarepartiallyopenhighlyalteredSAPregion-nobrokentextureincvevidentRR66E-233+20.22216light-highlyalteredparticletrtr100tr?cpy/>1.5mmacross)—200jimthickrimRR66F-1-noveins-nosulphides(greenporphyry)-locallysomesmall———embayments—————RR66F-2-noveins-nosuiphides(greenporphyry)-obviouslocalbreakupofphenocrystsatsurface—————RR66F-321+20+1light-highlyalteredtr9010ancvXX-secondaryopen-manymoreveinsbutisacvholes-common/secondarycomplexnetworkofveins+SAP-holesmostcommonatrim(200-400ji-openvoidscommonm)especiallyin200-400jimrim-largepatchesofSAPthroughoutparticleTableH-7:Descriptionofthechangesintheleachedparticlesfromcolumn4,45cm(1’6”)belowthetop.SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContent[Alteration[HabitofveinsV42/33/4(1cpybncvmsRR65B-11915211light-smallonesgenerally1/810tr7515bn=cv-rare/secondary?openpenetrationancv-secondary?-largestoneprimarywith-mostaniliteseenininterior-notatsecondarypenetrationedgecv=holes-secondary+SAP-SAPlesscommonthanholesbutgoodexampleatedge-voidsassociatedwithcvaremuchmoreprevalentatrim-gcpysmall(<lOjim)disseminatedgrainsRR65B-2?-highlyalteredparticletrtr8515an=cv-secondary?-mostofsectioninvadedbycvholes-manyvoidsassociatedwithcvSAP(—1/2ofparticle)+SAP-nopatterntovoids-manyvoidsthroughoutwith-cvexhibitssomebrokentextureseveralverylargeones(50--manylargeSAPareaswithsmall200iimacross)grainsofsulphides(almosthalfof-veinsnotwelldefinedparticle)-notesomeanilitehasmottledcolourRR65B-319+13+123light-veryalteredparticle8515ancvX-secondary?-lightprecipitateinmouthsof-cvmorecommonatrimlargeveins-secondary-verylargeveinispartiallytocv=holes-holesmoreprevalentin—200imrimalmostcompletelyopenand÷SAPandalongveins50-100jimwide-cvexhibitsbrokentexturelocally(near-small veinsoftennotwell-rimsgenerally)defined-SAPverycommonthroughoutRR65D-119+13+411light-verylargeveinisopenat3070ancvXX-predominantlysecondarycentreandhasrimoflight-sulfidedepletionin—1 50l.tmrim-somesmallerveinshavelight-cvatrimexhibitsabrokentexturecorecv+SAP-wholeregionsofSAP(withyellowtint)-manysmallestveinsareill-withlittlesulphides(unlikeelsewhere)definedand1/8penetrationassociatedwithlargeveinsandrim-largeregionsofSAPwithlittlesulphidesassociatedwithlargeveinsandrim——————TableH-7(cont’d)SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/3[1/2[icpybncvan(±SAP-SAPassociatedlocallydefinedcv=holesXX-notcommon/secondary+SAP-generally—100-200j.tmrimnosuiphidesandmoreholesRR65E-2431-onelargeregion3030355bn=>cvXX-secondarypredominantlySAP(—1/5of-alsoassociatedwithvoidsparticle)withmanyopencpy=cvX-notapparentthatisalterationbutvoids±holesareasareassociatedandcpyexhibitsbrokentexturecvholes-secondary50-mostcommoninhighlyaltered+SAPregions50onlyinthisregionandverycommonRR65E-311open—-nosulphides(greenporphyry)RR65C-11815111open-mostsmallveinshave1/8955cpycvXX-butmuchcpyisunalteredalongveinspenetrationandrim-manyareparalleltosurface-anysecondarycomponentisunclear-2largestveinsareprimary-muchcvwithminorcpycoresalongwithpossiblesecondaryoneedgeinfiltration-secondary/rarecvholesX-SAPwithcvonedge(mentioned+SAPabove)TableH-8:Descriptionofthechangesintheleachedparticlesfromcolumn4,75cm(2’6”)belowthetop.SampleII FluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveinsV21cpybnvan(>cv-secondary?lightsecondaryinfiltrationcvholes-secondary-corealteredtocv+SAP-cvgrains(+SAPoften)generally-obviousbreakupofrockexhibitabrokentexture-muchSAPpresentalongoneedge——————(—500jimrim)RR63C-118153open-generallyparalleltosurfacetrtr9010ancv-secondary?-smallveinscommonly1/8cv=holesXX-secondarypenetration+SAP-moreholesthanSAP-covellitehasbrokentexture-isdepletedin—200jimrim-notemuchhematiteassociatedwith————sulphides(upto50jimindiameter)RR63C-211100trcpycvX-veryrare!!—atrimwheresome————-depletionofcpyRR63C-312+8+22open-veinspoorly-definednetwork5104045bnanX-probablyprimary-surfaceappearscrumbly-ancv-partiallysecondaryrockheldtogetherbySAP-covellitedominantinrim-manylargeregionsofSAPinsideparticlecvSAP-manyholesandSAParoundcv/an±holesgrains-cvhasminorbrokentextureatrimRR63C-42116221open-veinscommonlyparallelto5tr8510an/bn=cvX-secondary?surfacecv=holesXX-commonlyalong—200-300jimrim-oftenpartiallyopen±SAP-SAPalterationisveryrare-numerousemptyorpartially-verylittlecvhasbrokentextureemptydeepvoidsalongrimandininteriorLI’TableH-8(cont’d)SampleII FluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/22133/41cpy]bncvan( remaininganiliteisbasically“brokenupunaltered-manyopenvoidsespeciallycv=tiotesxX-secondaryalongrim±SAP-SAPquiterare-smallveinsarecommonly1/8penetrationRR63D-227+17+2413-onelargeveinactuallytotallytr56035an=cvXX-secondaryopenandbreaksparticlesbn=an=cv-secondary-smallbornitegrains(50--someprimaryquartzveins1 OOiim)thatarentusuallyalteredalsopresent withpartialfluidpenetrationandopenvoidscv=holesXX-secondary+SAPmanyprimaryquartzveinswithaniliteusuallypartiallyalteredtocvRR63D-329+18+533open-largerveinsoftenhave2080ancvXX-secondaryv.lightorangetinge-someveinsprimaryandalterationonly-manyactuallyfineveinshalfwayalong(<<10im)interconnectedin-muchanilitenotalteredatallacomplexnetwork-notesomeanilitehasamottledcolour-manyvoidsalongveins-plusaprimaryquartzveinwithmostcv!anmissingTableH-9:Descriptionofthechangesintheleachedparticlesfromcolumn4,105cm(3’6”)belowthetop.SampleFluidPenetrationCommentsSuiphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/22/33/41cpybncvanl(—————-nosulfides(greenprophyry)RR61D-21010light-probablynomorethan1/8100-noalterationvisiblepenetration-severallargeopenvoidsininteriorRR61D-322143311open-openvoidsoftenassociated105805bn=cvX-notextensive/secondarylightwithlargerveinscpy=cv-?pnmary-appearstobebreakingupbutissomeunalteredatsurfaceancvX-secondarycv=holesXX-secondary+SAPRR61E-1281634113open-largeveinsaretr25705bn=anXX-ornearvoids(secondary)holesinterconnectednetworkancvXX-secondary-oftenpartiallyopencv=holesXX-secondary-approximatelyhalfofsmall+SAP-cvandholesprimarilyatrimandveinsareactually1/8alongveinspenetration-covellitealongoneedgeshowssomeevidenceofdissolutionwithholesin——————centreofgrainsRR61E-2321open-smallparalleltosurface75-pyfiLe25%-alsomany50-100irmdeep-bothseenatparticlesurfacewithnoby30imembayments—————signofalterationRR61E-3981-generallyparalleltosurface7030ancvXX-secondary--lookslikeatypicalan-(evenlargeone)onlytexturebeingaltered-voidsoccuralongsomeveins-grainsgenerallyassociatedwithholesshowalterationcv=holesXX-secondary+SAP-cvonlygrainsorholesareprevalentatrims-someareasofSAPonlyTableH-9(cont’d)SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/22/3[3/41cpybncvan(!9010ancv-secondary?-aroundlargeveinsmanycv=holes-secondarysmallpoorlydefinedveins±SAP-generallyholesbutsomeminorSAP-verylargeveinopenatcentre-manyholesstillhavecvonedge-muchverylightprecipitate-2largecvgrainsobviouslyalmostlining2largestveins(darkcompletelyalteredorange/red)-manypatchesofSAPwithvoidsmakeupapprox.halfofparticle———00TableH-10:Descriptionofthechangesintheleachedparticlesfromcolumn4,135cm(4’6”)belowthetop.SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentAlterationHabitofveins1/41/31/212/313/41cpyI bncvI an(—————RR59B-22217131open-smallveinsgenerallyparallel5106520bn=cv±an-primary?tosurfaceandonly1/8ancv-probablysecondaryandprimarypenetration-appearsleachedcv=holes-rare/secondarymegascopically—————RR59B-34211-unclearwhethersmallveins5503510bn=cvX-veryminoratgrainedgesaresecondaryorprimary-notclearwhethersecondary-largeisprimarywithpartialbn=an-primary?secondaryinfiltrationan=cv-secondary?cv=holes-inlocalizedpatchesbutnoobviousconnectiontoparticleexteriorRR59C-1211light-veinsparalleltosurface———-nosulfides(greenporphyry)RR59C-220+12+224open-manyveinsconcentrated57520bn=>cv-localizedandhardtotellifprimaryorlightalong—1mmrimsecondary-manyveinsparalleltothecvholesX-probablysecondarysurface-locallyline-grainedcv(<—————beapolishingartifactRR59D-1151311light-manysmallveinsonlyl/8324055bn/cpy=an-primary?openpenetrationcv-fivelargewedgescontainingancvXX-probablyprimaryandsecondarybutSAPandfewsulphidesalsosecondaryseldomcompletepenetrateupto1/3ofparticlediametercvholesX-minor/secondary+SAP-seenaroundbn/cpy/cvgrain-jgthataniliteappearstobemottled——————(oxidation?)TableH-10(cont’d)SampleFluidPenetrationCommentsSulphideAlterationCommentstotalno.PenetrationPptesContentMineralsHabitofveins1/41/31/22/33/41cpybncvan(>holes-manyholesthroughoutgrain+SAP-SAPveryrare-noteaniliteoftenmottledRR59D-47911light-notclearallsmallaretr108010bn=cv-generallyminor/primary?opensecondaryan=cv-probablysecondarybutnotclear-2largeveinshavesomecovellitemissingCV+SAPX-rarecv=holesX-secondary-oftenclosetoparticlesurfaceRR59E-1none-nosulfides(greenporphyry)RR59E-21010321open-manysmallveinsare1/8tr3070bn=cv-primary/secondary?lightpenetrationorparalleltocv=holesXX-secondarysurface-somecvshowingstartofbroken-manyareopenpartiallytexture-largeveincutsthroughcvandcutawedgefromrockRR59E-330+??8light-highlyalteredparticle8515ancv-probablysecondaryv.light-obvious(megascopic)cv+SAPXX-commonalterationatsurface-locallySAPwithsmallscattered-manysmallveinsbutill-grainsofcvdefined-actuallycomplexnetwork-someveinspartiallyopen-manyopenvoidsalsoRR59E-46411light-manyparalleltosurface304030bn=cv-secondary?-nearveinsandtheparticlesurface-gmanyopenvoidsnear(wherealterationnotcomplete)surfacemaybeveinscv=holesXX-secondary-cvoccursatrimsandalongveinswithverybrokentexturecM


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