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The Aley carbonatite complex Mäder, Urs Karl 1986

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THE ALEY CARBONATITE COMPLEX by URS KARL MADER Dipl. Natw. ETH, Zurich, Switzerland THESIS SUBMITTED IN PARTIAL FULFILMENT THE REQUIREMENTS FOR THE DECREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Geological Sciencies We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October 1986 © Urs Karl Ma der, 1986 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of CicOLOCnICRL SciElVCItS The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date OcTOBfjZ. f± ) Abstract The Aley carbonatite complex, a property belonging to Cominco Ltd., is 140 km north-northeast of Mackenzie, British Columbia at latitude 56°27' N, longitude 123°45' W. The complex intruded Cambrian rocks 345 ma ago near the shelf / off-shelf boundary of ancient North America and is now contained in an imbricate thrust sheet of the Northern Rocky Mountains. The circular complex is 3 km in diameter, cylindrical with respect to the third dimension and little affected by structures of the Rocky Mountains. The relationship of nearby lamprophyric dikes and the lamproitic Ospika diatreme, closely related in time, is unclear. The Aley carbonatite complex consists of an older, outer "syenite" ring (33% of the area) and a younger dolomite carbonatite core with minor calcite carbonatite "sweats". Rare-earth rich ferro-carbonatite dikes intruded the contact aureole. The contact aureole is composed of recrystallized rocks characterized by brownish weathering, but is little affected by metasomatism and shows no indication of high temperature contact metamorphism. The mineralogy and mineral chemistry were studied in detail. Over forty mineral species are described, including rare-earth carbonates (burbankite, ancylite, cordylite, huanghoite etc.), niobium oxides (pyrochlore, fersmite, columbite) and alkali-rich silicates (arfvedsonite, aegirine, richterite). Dolomite carbonatite contains apatite, pyrite and fersmite pseudomorphs after pyrochlore. Calcite carbonatite is composed of apatite, magnetite, biotite, pyrochlore, pyrite, ± richterite. The inner part of the contact aureole forms an annular, cylindrical ductile shearzone suggesting that doming was the major mechanism of emplacement. This is consistent with the circular structural trends in the carbonatite core. Temperatures deduced from field observations and mineralogy (250°C-400°C) disagree with temperatures calculated for a cooling igneous body based on a simple heat conduction model (500°C-600°C) further supporting the view that the complex was ii emplaced at subsolidus temperatures. Oxygen and carbon isotope ratios (5iaO = 7.7-15.4, 513 C = -4.7 - -6.1) and some initial Sr isotope ratios (^Sr/^Sr = 0.7034-0.7036) are indicative of a mantle source of carbonatite and syenite. Ceochemically, the carbonatites are enriched in the incompatible elements LREE, Th, U, Nb, Ta, Zr. The rare-earth carbonatite dikes represent a residual liquid extremely enriched in Fe, S, LREE, Sr and Ba. The "syenite" is not a .typical alkali-syenite, bearing quartz instead of felspathoids. A strong metasomatic overprint is marked by secondary aegirine and metamorphic textures. Processes by which the rocks of the Aley may be related genetically are discussed in the light of petrography, geochemistry and experimental studies. iii Table of Contents Abstract ii Table of Contents v List of Tables viList of Figures ix Acknowledgements . xi Introduction xi1. Geology, Age and Stratigraphy 1 1.1 Location and Access1.2 Regional Geology '. 1 1.3 Age •. ...2 1.4 Stratigraphy 4 1.4.1 Kechika Formation (Cambrian) 4 1.4.2 Skoki Formation (Ordovician) 6 1.4.3 Road River Group (Ordocician - Silurian) 9 1.5 Local Geology 10 2. Structure 2 2.1 Ductile Versus Brittle Deformation 12.2 Ductile Shearing Related to Doming 2 2.3 Stress Field around a Doming Intrusion - Dike Emplacement 18 2.4 Structures within the Intrusive Complex 19 2.5 Structures and Shear Zones Related to the Fold and Thrust Belt 23 2.6 Cross Sections 28 2.7 Regional Tectonic Setting 22.8 A Possible Sequence of Tectonic Events 30 3. Mineralogy and Mineral Chemistry 33 3.1 Introduction 33.2 Carbonates • 35 iv 3.3 Phosphates 41 3.4 Oxides 2 3.5 Silicates 8 3.6 Sulfates 55 3.7 Sulfides .". 55 4. Petrography 7 4.1 Dolomite Carbonatite 54.2 Calcite Carbonatite 60 4.3 Rare - Earth Carbonatite Dikes 61 4.3.1 Rare-Earth Carbonatite Dikes of the North Ridge 62 4.3.2 Rare-Earth Carbonatite Dikes of the Northwest Ridge .....63 4.4 "Syenite" ' 64 4.5 Contact Aureole . 67 5. Geochemistry 69 5.1 Rocks of the Carbonatite Complex 65.1.1 Dolomite Carbonatite 69 5.1.2 Calcite Carbonatite5.1.3 Rare-Earth Carbonatite Dikes 71 5.1.4 "Syenite" 75.2 Rocks of the Contact Aureole 71 5.3 Isotope Geochemistry 76 5.3.1 Strontium and Rubidium 75.3.2 Oxygen and Carbon Isotope Ratios 77 6. Aspects of Petrogenesis 80 6.1 Evidence on Sequence of Emplacement 86.2 Temperature Distribution around the Carbonatite Complex 81 6.3 Sequence of Crystallization in Carbonatite Magmas 88 v 6.4 Genetic Relationships 91 6.5 Physical Properties of Carbonatite Magmas 93 6.6 Hypothetical Processes in Carbonatite Magma Chambers 94 7. Conclusions 96 BIBLIOGRAPHY 8 APPENDIX A: MINERALOGY AND MINERAL CHEMISTRY 105 APPENDIX B: X-RAY FLUORESCENCE ANALYSES 146 APPENDIX C: TRANSIENT TEMPERATURE DISTRIBUTIONS CALCULATED FOR THE MARGIN OF A COOLING ICNEOUS BODY 160 vi LIST OF TABLES Table Page 1 : List of minerals identified in the Aley carbonatite complex 33 2 : Geochemistry of calcite and dolomite carbonatite 70 3 : Geochemistry of REE-carbonatite dikes 72 4 : Geochemistry of syenite 73 5 : Trace element geochemistry of the contact aureole 75 6 : Locations of samples used in tab 5 77 : Rubidium and strontium isotope data 6 8 : 813C and 5180 ratios for carbonatite 78 9 : Composition of calcite used for geothrmometry 82 10: References on experimental topics related to carbonatites 90 11: Standard sets used for EMS-analysis 106 12: Composition of standards for EMS-analyses 107 13: EMS analyses of dolomite 108 14: EMS-analyses of ankerite 9 15: EMS-analyses of calcite 110 16: EMS-analyses of albite 1 17: EMS-analyses of arfvedsonite 112 18: EMS analyses of arfvedsonite 3 19: EMS-analyses of aegirine 114 20: List of possible XRF peak overlaps 148 21: List of samples processed for XRF analyses 150 22: Machine settings for XRF analyses 1523: Mass attenuation coefficiants 1 24: Major element concentrations of standards 152 25: Mass attenuation coefficients for standards 153 26: Mass attenuation coefficients for standards 154 27: Mass attenuation coefficients of unknowns 155 vii 28: Mass attenuation coefficients of unknowns 156 29: Major element concentrations of unknowns 157 30: Normalized major element concentrations of unknowns 158 31: Trace element concentrations of unknowns 159 viii LIST OF FIGURES Figure Page 1 : Regional map .1 2 : Geological map 3 3 : Stratigraphic column ...5 4 : Gastropods from the Skoki Dolomite 6 5 : Stratigraphy of the Skoki Volcanic Unit , 7 6 : "Chocolate-tablet" boudinage 14 7 : Shear folds 15 8 : Strained limestone 6 9 : Sheath folds ...17 10: Stressfield around an updoming intrusion 19 11: Relaxation stress field 112: Magnetite layering 21 13: Structural map of mineral layering 214: Ruptured syenite with carbonatite veins 4 15: Anticline along the west-side of the complex 25 16: Detail of anticline in figure 15 26 17: Deformed limestone 27 18: Geological cross sections 9 19: Possible sequence of tectonic events 31 20: Xenoliths in "syenite" 66 21: Age versus 87 Sr/86 Sr diagram 77 22: 513C versus 6ieO diagram 9 23: P-T diagram of the system CaO-MgO-Si02-COz 83 24: T-XCo2 diagram of the system CaO-MgO-Si02-H20-C02 84 25: t-T-x diagram for a syenite intrusion ..87 26: Back-scattered electron image - REE carbonates 115 27: Back-scattered electron image - REE carbonates 116 ix 28: Back-scattered electron image - REE carbonates 117 29: Back-scattered electron image - REE carbonates 118 30: Photomicrograph of REE-carbonates 119 31: Photograph of burbankite in rare-earth dike 1132: Back-scattered electron image of dolomite with rutile lamellae 120 33: Photomicrograph of twinned baddeleyite 1234: Habit of pyrochlore 121 35: Back-scattered electron image of pyrochlore 1236: Photomicrograph of pyrochlore 122 37: Autoradiograph of zoned pyrochlore 1238: Habit of primary fersmite 123 39: Back-scatterd electron image of fersmite pseudomorph 124 40: Detail of figure 39 1241: Photomicrograph of syenite xenolith 125 42: Composition space for sodic amphiboles 126 43: Block diagram of arfvedsonite 1244: Composition space for sodic-calcic amphiboles 127 45: Block diagram for richterite 1246: Block diagram for aegirine .128 47: Photomicrograph of syenite with aegirine 1248: Coordinate system during solidification ....162 49: Coordinate system after solidification 1650: Model parameter X 167 51: Solidification time as a function of X 168 52: Contact temperature as a function of X 9 53: t-T-x diagram for a carbonatite dike 170 x Acknowledgements Dr. H.J. Greenwood provided academic, financial and moral support whenever needed. Cominco Ltd. made this project possible with generous financial and logistic support. Valuable discussions and guidance in the field by K.R. Pride, P.C. LeCouteur and B.H. Mower (all of Cominco Ltd.) formed a sound basis for mapping and petrographic analysis. J.M. Hamilton of Cominco Ltd. greatly improved the manuscript by critical reciews. Drs. j.K. Russell, E.P.Meagher, J. Pell and D.C. Murphy devoted time and interest for critical discussions. Skillfull technical assistance was provided by Stanya Horsky, Krista Scott, Ed Montgomery, Rob Berman, John Knight, Yvonne Douma and by Dr. E.D. Ghent and John Machacek (both at the University of Calgary). Ursula, with a lot of care and understanding, supported me through the hardships of life. The Geology Grad Group contributed much to my extra curricular education and Canadianization by dragging me out to the hockey rink and by patiently trying to explain the rules of baseball (although I still think Swiss non-sparkling cider, fondue with Kirsch and Swiss chocolate have yet to be surpassed by other cultures). xi Introduction The brown-weathering carbonatite rocks and the dark coloured amphibole-syenite were first mapped by Thompson (1978) on a reconnaissance scale as part of the Ordovician volcanic section. During an exploration campaign in 1980 by Cominco Ltd. "strange looking rocks" were collected by K.R. Pride, leading subsequently to the recognition of the largest known alkaline-carbonatite complex in British Columbia. The Aley turned out to be one of the best exposed and preserved carbonatite complexes in the world. Staking of the claims was completed in October 1982 (Pride, 1983) followed by mapping, trenching and soil sampling during the field seasons thereafter. The first diamond-drilling project started in 1985 and was continued in 1986. Economic interest focuses on the niobium-bearing mineral assamblages within the carbonatite rocks with an academic interest in some rare-earth concentrations. The exotic mineralogy, the unusual chemistry of these igneous carbonate rocks and the lack of understanding of many of the processes leading to alkaline-carbonatite magmatism has been a challenging project and the combination of academia and industry has been most productive. xii 1. GEOLOGY, AGE AND STRATIGRAPHY 1.1 LOCATION AND ACCESS The Aley property (Pride, 1983) is located approximately 140 kilometers north-northwest of Mackenzie and east of Williston Lake at latitude 56° 27' N, longitude 123° 45' W on NTS map sheet 94B/5 (figure 1). The property may be reached by fixed wing aircraft to Davis airstrip on the east side of Williston Lake and then about 50 kilometers east by helicopter. 125* ll20' ^ \ AI rr\/ FOnT \\ \ ALfcY ST.JOHN J s,\.V \\ MACKENZIE I "AV • \j L— i f * PRINCE /^-^ 1 GEORGE ( \, 10 0km I X7-Figure 1: Regional map of the Williston Lake area 1.2 REGIONAL GEOLOGY The Aley carbonatite complex crops out within an imbricate thrust sheet of the Northern Rocky Mountains fold and thrust belt (Rocky Mountains structural subprovince of Thompson 1978, 1985) in the southwest corner of the Halfway River map area (94B). The complex is nearly circular, about three kilometers in diameter, mid-Paleozoic in age (see section 1.3) and little affected by the Rocky Mountains structures (figure 2). The stratigraphy, structure and tectonic evolution of the map 1 2 area is presented by Thompson (1978, 1979, 1982, 1985) based on field work (1975, 1976) and on previous studies (Irish, 1970; Taylor & Stott, 1973, 1979; Taylor, 1979, 1983). The Rocky Mountains structural subprovince consists of eastward-transported imbricate thrust sheets comprising Hadrinian to Devonian sedimentary rocks of the continental margin of ancient North America (Thompson 1978). In contrast to the Southern Rocky Mountains, folding contributes significantly to the overall shortening of the fold and thrust belt in the Northern Rocky Mountains (Thompson, 1979). Paleogeographically, the alkaline-carbonatite complex intruded the miogeoclina! sedimentary wedge near the carbonate - shale boundary of early to mid-Paleozoic time. This boundary corresponds to the shelf off-shelf boundary of the continental margin (Thompson, 1978). The simple shape of this boundary further to the north is obscured in the area of interest by the Ospika Embayment (eastward closing) and its southern border the Peace River Arch (Thompson, 1985). In a larger context, the Aley complex is part of widespread alkaline activity along the ancient continental margin represented along both sides of the Rocky Mountain Trench (Pell, 1985, 1986; Currie, 1976). The Aley is similar in size and structural setting to the Ice River alkaline complex (Currie, 1975). 1.3 ACE At present, three K-Ar ages on biotite are available: 339i12 ma and 349i12 ma from carbonatite samples (LeCouteur, pers. com., 1986) and 334 ma (Armstrong, pers. com., 1986) on the nearby Ospika diatreme (figure 2). A first attempt to date zircons failed because of the very low lead content of the sample (Parrish, pers. com., 1986). Further studies on U-Pb systematics of pyrochlore and possibly monazite and badelleyite are in progress (Parrish, pers. com., 1986). 3 Ok . ALEY Sil Ord-Sil Ord Ord I j ROAD RIVER GR (dol) contours ] ROAD RIVER GR (sst.sh) I ROAD RIVER GR (sh) I SKOKI FM (dol.volcanics) 1 km ALKALI-SYENITE Oev CARBONATITE RARE-EARTH CARB. DIKES Camb ?[ : j KECHIKA FM (1st,marl.silt) D 9 DIATREME (OSPIKA PIPE) U. MADER Figure 2: Geological map 4 1.4 STRATIGRAPHY The stratigraphy of the Halfway River map area has been established with enough detail by Thompson (1985) to correlate mappable lithologlcal units with established formation names. Ages of the sedimentary rocks in the Aley area are not well constrained paleontologically. Only a few locations have provided graptolites. A Cambrian limestone unit, the Ordovician Skoki (dolomite) Formation with its volcanic succession and an upper Ordovician graded sandstone sequence provide excellent marker horizons for field mapping. Figure 3 is a stratigraphic column for the area mapped, with subdivisions based on lithologies. Due to faulting and folding there is no complete reference cross section available in the area. Locations of type localities for individual lithologies are referred to in their respective paragraphs. The thicknesses of the units in figure 3 represent the maximum sections of a particular unit within the area mapped. The thicknesses of shaley units must be considered as minimum values due to tectonic thinning. The stratigraphic column before the Columbian orogeny might therefore have been considerably thicker than presented below. 1.4.1 KECHIKA FORMATION (CAMBRIAN) The reference cross section is located within the contact aureole extending from the intrusive contact (12750N, 10200E) along the ridge northwestwards. The upper part of the Cambrian Kechika Formation present in the area may be subdivided into four lithologies, starting with the oldest unit: Cream Dolomite Unit (>80 m): This unit occurs only within the contact aureole of the carbonatite complex and is recrystallized to a cream weathering, bedded (5-40 cm), clean dolomite marble with minor units of calcite marble. Characteristic are 1 to 10 mm thick interbedded marly horizons. The base is not i ' I I I I I lj_ l_l _L ±_ i i i I , White Dolomite Unit Laminated Siltstone-Shale Unit Upper Dolomite-Shale Unit Sandstone Unit Lower Dolomite-Shale Unit Black Shale Unit Upper Dolomite Unit Skoki Volcanic Unit Lower Dolomite Unit Parallel Laminated Unit Grey Limestone Unit Thin Bedded Limestone Unit Cream Dolomite Unit SRRd SRRsh ORRq ORRqz ORRq ORRsh 0SKd2 OSKv OSKdl 6 0KI € OKc € OKp € 9Kd Figure 3: Stratigraphic column for the area mapped 6 exposed in the map-area. The top is marked by a sharp lithologic change. Thin Bedded Limestone Unit (100 - 200 m): This unit consists of evenly alternating beds of grey, impure calcareous limstone (2-5 cm) and dark marls (1-3 cm). Characteristic is the abundance of minor folds. Within the contact aureole of the complex, the limestone beds (marbles) weather recessively with respect to the recrystallized marly layers. The upper contact is gradational over a few meters. Grey Limestone Unit (100 - 150 m): Laminated grey limestones and bedded limestones (10-50 cm) are interbedded with orange-brown siltstones and shales. Some sections resemble the unit below. The top is marked by the absence (or scarcity) of thicker limestone beds. Parallel Laminated Unit (>700 m): This unit consists of buff-brown and grey weathering thinly laminated limestones and minor nodular limestones interbedded with silty and shaley laminated layers. The uppermost part of the unit is marked by the occurrance of massive (5-50 cm) grey dolomite beds typical of the Skoki Formation. The top is defined by the onset of bedded to massive dolomite. The Kechika Formation is generally in fault contact with the Skoki Formation. 1.4.2 SKOKI FORMATION (ORDOVICIAN) This cliff-forming dolomite formation is divided by a volcanic sequence into a lower and an upper dolomite unit. Up to two additional volcanic horizons may be present in the northwestern pert of the map-area in the lower and the upper dolomite units. Locations of reference sections are shown in figure 5. Lower Dolomite Unit (200 • 300 m): This unit is medium to thick bedded, massive, dark grey weathering dolomite with rare large (5 cm) gastropods (Maclurites, identification by Cominco Ltd.) , crinoids and minor chert lenses. At point 13070N, 8070E, 10 meters below the main volcanic sequence, two beds contain abundant well preserved gastropods (figure 4). Near 14350N, 9700E a 10 to 7 20 meter thick volcanic layer is present consisting of ash mixed with dolomite. The top of the unit is a sharp or gradational (1-5 m) contact with fine-grained volcaniclastic rocks. Figure 4: Gastropods from the Lower Dolomite Unit (13070N, 8070E) Skoki Volcanic Unit (50 • 100 m): (Figure 4) The lower part of the unit consists dominantly of cream, buff-brown, brown-green and purple laminated to bedded very fine-grained marine tuffs and crystal tuffs, ln the middle and upper part amygdaloidal basalt flows (10-100 cm) may be present. Near the middle part one or several breaks in volcaniclastic supply occurred marked by normal Skoki dolomite sedimentation (,1 - 5 m). A curled nautiloide was found at point 8400N, 9730E. A shaley, brown-green weathering sheared sequence may be present in the middle part of the section. Near the top thick (1-5 m) conglomerate beds occur containing angular to subangular unsorted fragments of amygdaloidal flows and tuffaceous material ranging in size from mm to 1 m. The top is marked by a sharp or gradational change from fine volcaniclastic to normal dolomite sedimentation. Texturally well preserved pillow basalts occur in a subcrop in a creek at point 11870N, 8480E but have not been observed in outcrop. 4 cm 8 Upper Dolomite Unit (250 • 400 m): This unit typically is thick bedded to very massive with minor black chert. Black chert lenses become more abundant towards the top. A fine tuffaceous 20 m thick section is present in the western part of the map-area (13340N, 8120E). The top is marked by the first appearance of black shale. m 90 10 0 i i - r -i-i SECTION 1 8 400N/9 5S0E 10 SECTION 2 9 830N/12 6006 [i-^LJdolomite with chert | | marine tuff ggg| ahaley-tuMaceous section |- • • '| amygdoidal basalt flows | r [massive basalt flows [v.'.| volcaniclastic conglomerates m SO 10 e * •» — * p w SECTION 3 13 BOON/7 800E 45 10 0 El DTTTL Jd3 SECTION 4 14 OOON/10 I20E Figure 5: Stratigraphy of the Skoki Volcanic Unit 9 1.4.3 ROAD RIVER CROUP (ORDOCICIAN - SILURIAN) Reference sections are exposed along the ridges from points 12430N, 8600E and 12400N, 12250E as well as 11630N, 13070E. The lower part of the Road River Group present in the area mapped is divided into six units: Black Shale Unit (>100 m): The unit consists of dark grey, calcareous, planar laminated, fissile, graptolitic (Glossograptus, identification by Cominco Ltd) shale. The contact with the underlying Skoki Formation is locally unconformable. The top is marked by the first appearance of grey dolomite beds. Lower Dolomite - Shale Unit (250 - 300 m): The unit is characterized by abundant, well bedded dolomite horizons (5 cm - 3 m) between laminated, calcareous and dolomitic shale. Slump textures and intrabed breccias are common, ln the upper part the dolomite beds are fossiliferous (rugosa corals, crinoids) and chert layers (2 - 10 cm, generally fossiliferous) are abundant. The top of the unit is defined by the appearance of graded sandstone. Sandstone Unit (5 • 15 m): This marker unit consists of well bedded (5-80 cm), medium grained, mature, graded sandstones with minor laminated calcareous layers. The top and bottom of the unit are sharply defined. Upper Dolomite - Shale Unit (100 - 200 m): The upper unit is similar to the lower dolomite-shale unit but with far less abundant dolomite and additional siitstones. Dicellograptus Morrosi (mid-Ordovician, identification by Cominco Ltd.) may occur in this part of the section. The top of the unit is not well defined, gradually becoming more silty and dolomite banks becoming scarce. Laminated Siltstone Unit (>200 m): This unit consists of laminated to fine-bedded siitstones, silty shale and minor light-grey weathering dolomite beds (cm - dm). Monograptus Spiralus (identification by Cominco Ltd.) occurs occasionally in the shaley lower part of this section indicating a Silurian age. The top is sharply defined by the first appearance of massive, white dolomite. 10 White Dolomite Unit (>100 m): This massive dolomite weathers a distinctive light grey colour. The top of the unit was not examined. 1.5 LOCAL GEOLOGY Two brief references about the Aley give an introduction to the geology (Pride, 1983; Pell, 1986b). The nearby Ospika diatreme is mentionend in Pell, 1986a. The alkaline-carbonatite complex is ovoid in outline, 3 to 3.5 km in diameter and occupies an area of about seven square km (figure 2). Outcrop is scarce near the bottom of the major valley (1300-1350 m altitude), abundant above tree line (around 1600 m) and continous along the high ridges (1800-2200 m). The body is cylindrical with respect to the third dimension with a westward plunging, nearly vertical axis and has probably been but little tilted compared to its original orientation. The two major rock types of the intrusion form a ring complex with a "syenite" rim and a carbonatite core. Two rare-earth element rich ferrocarbonatite dike swarms intruded rocks of the Kechika formation parallel to the northwest side and the northeast side of the intrusion. The carbonatite complex and its contact aureole are part of an imbricate thrust sheet bounded to the west by a high angle thrust fault juxtaposing Cambrian rocks against Silurian. The Silurian rocks form part of a tectonically thinned eastern limb of a tight anticline with a Cambrian core to the west. This structural element is disected by faults striking at high angles to the Rocky Mountain trend (NNW-SSE). Along the eastern side of the complex a tectonically thinned reversed stratigraphic section with a set of subparallel lower-angle thrust faults is thrusted onto an imbricate sheet containing Silurian rocks (to the east of the area mapped; Thompson, 1978). Tectonic movements within the reversed section occurred along the Kechika-Skoki and the Skoki-Road River unconformable contacts. 11 Lamprophyres occur within the Kechika Formation and the Road River Croup. A small lamproitic diatreme (Ospika pipe; Pell, 1986a) intruded dolomite of the Skoki Formation 250 meters west of the complex (10850N, 9450E). 2. STRUCTURE The Aley carbonatite complex provides an excellent opportunity to study relationships between intrusion and tectonics. Its convenient size, lack of disruption and good exposure make it particularly suitable for study, and its setting in an unmetamorphosed fold and thrust belt allows to distinguish between deformation related to the emplacement of the body and that related to the formation of the fold and thrust belt. 2.1 DUCTILE VERSUS BRITTLE DEFORMATION The deformation related to the intrusion of the complex affected contact metamorphic rocks (marbles, recrystallized marls and shales) at elevated temperatures (cf. section 6.2) and will therefore be under a ductile regime. Note also that marls are structurally incompetent with respect to limestone when unmetamorphosed but competent when metamorphosed. Minor folds, for example, can thus be related by their geometry unequivocally to deformation under contact metamorphic conditions versus deformation under unmetamorphic conditions (Brack, 1981). The deformation related to the formation of the fold and thrust belt affected unmetamorphosed sedimentary rocks (and cooled rocks of the complex and its aureole) and these may have behaved as brittle materials. Structures close to the outer margin of the contact aureole may not be related easily to one of the two distinct events. 2.2 DUCTILE SHEARING RELATED TO DOMING The complex intrudes into a similar stratigraphic level all the way around the intrusion. The Cambrian Cream. Dolomite marble, for example, borders the intrusive contact for nearly half of the circumference of the complex in the northern part. 12 13 Bedding of the host rocks near the intrusion is subvertical and parallels the syenite (carbonatite) - host rock contact. Radial shortening within the first few hundred meters adjacent to the igneous contact is extreme. Extension took place within a vertical curved surface parallel to the contact and subparallel to bedding. Horizontal and vertical components resulted in "chocolate-tablet" boudinage of recrystallized marly layers within the Cream Dolomite Unit (figure 6). Measurements of extension (Al / l0) in both directions give minimum values for extension between 200 and 400 %. An average value of 300 % applied uniformly within the plane of extension will result in shortening perpendicular to the plane by a factor of 16 assuming constant volume. In the Thin Bedded Limestone Unit abundant shear folds, shear bands and some sheath folds are indicative of high strain (figures 7, 8, 9). The trends of the sheath axes of folds (at point 12130N, 9570E, adjacent to the syenite contact, figure 9) are nearly vertical and suggest a strong vertical shear component. A horizontal shear component resulted in en echelon boudinage of competent beds and early veins (figure 8). The inner part of the contact aureole is therefore interpreted to be an annular, cylindrical ductile shear zone developed during emplacement of the complex. Doming must have played an important role as an intrusion mechanism at the exposed structural level. Extreme radial shortening can account for a major part of the lateral room problem created by the emplacement of the igneous body. Evidence for sidestoping and overhead stoping is lacking, strongly suggesting an intrusion mechanism different from many granitoid plutons. 14 Figure 6: "Chocolate-tablet" boudinage in the Cream Dolomite Unit (Kechika Formation). (12500N, 11780E) 15 Figure 7: Shear folds, Kechika Formation. (11550N, 12250E) 16 Figure 8: Highly strained Thin Bedded Limestone Unit, Kechika Formation. B = bedding, V = en echelon boudinaged carbonate vein, S = shear band. (12780N, 10100E) 17 Figure 9: Sheath folds, Thin Bedded Limestone Unit, Kechika Formation. (12130N, 9570E) 18 2.3 STRESS FIELD AROUND A DOMING INTRUSION - DIKE EMPLACEMENT Physical models to explain stress distributions around intrusions have been derived successfully by analysis of dike patterns surounding plutons (Anderson, 1936; Billings, 1945; Currie, 1956; v. Eckermann, 1958; Gussow, 1968; Kresten, 1980). Intrusion of a major mass of igneous or salt material will cause updoming of the overlying country rock. Radial dikes may form, following directions perpendicular to maximum stress. The stress field created by the upward movement may give rise to two sets of joints: tension joints and shear joints (figure 10). The former are believed to be responsible for the intrusion of cone sheets (Anderson, 1936). Upon cooling and degassing of the magma chamber (and injection of dikes) the pressure is expected to decrease. If the pressure becomes lower than that exerted by the overlying rocks, a new stress distribution will cause subsidence of the wallrock. Subvertical shear joints may result in the formation of ring dikes (Anderson, 1936; Reynolds, 1956; figure 11). Following this line of reasoning, the nearly vertical rare-earth carbonatite dikes that parallel the intrusion contact could not have been emplaced synchronously with the intrusion (cf. figure 10). The dikes must have intruded either as sills before intrusion of the complex took place or as late stage ring dikes during a relaxation stress field. If the dikes were pre-intrusive they should be as intensly deformed as the "chocolate-tablet" marls. The minor boudinage observed at the dike swarm along the northeastern margin, however, might be due to the brittle Rocky Mountain deformation related to the thrust zone along the east side of the complex, but generally, evidence for such strain is lacking. For petrologic reasons (cf. section 6.4) it is regarded as most reasonable to classify the carbonatite dikes as late stage ring dikes rather than pre-intrusive sills, although the field observations are somewhat ambiguous. 19 Figure 10: Updoming intrusion with distribution of shear joints (S) and tension joints (T) Figure 11: Distribution of shear joints (S) and tension joints (T) in a relaxation stress field 2.4 STRUCTURES WITHIN THE INTRUSIVE COMPLEX The carbonatite complex with its immediate aureole must have behaved as a rigid body during the formation of the Rocky Mountains in order to be as well preserved as indicated by the exposure in the northern part of the body. No major fault zones are exposed which dissect the complex, perhaps with the exception of the southwest comer, which may have been sliced off by a poorly exposed high angle fault or shear zone. This fortunate tectonic setting together with the very low grade of regional metamorphism offers the opportunity to find primary magmatic textures preserved. 20 Mineral layering: Mineral banding or layering, often emphasized by a well developed parallel cleavage or foliation, is very common throughout the complex, particularly towards its margins. In dolomite carbonatite the parallel texture is commonly formed by disk-shaped flattened apatite aggregates up to 1.5 cm in diameter paralleled by a weakly or strongly developed cleavage. In mineralized zones magnetite, pyrochlore, fersmite, biotite and amphibole enhance this parallel texture to various degrees by mineral banding and compositional zoning (figure 12). The oxides are mostly euhedral to subhedral with magnetite grains commonly broken apart whereas amphiboles form very fine bluegreen needles aligned parallel to the fabric. Field measurements show the planar texture to dip steeply with the strike directions roughly parallel to the margin of the complex (figure 13). There is a slight tendency towards steep western dips along the west side as well as along the east side. Near the center of the body attitudes vary more at random. Cross-sections based on drill core to a depth of 200 m show that the plunge of the fabric does not vary much with depth. The mineral layering is interpreted to be vertical flow banding, and thus to be a primary magmatic texture. Approximately circular stressfields, possibly late magmatic and subsolidus, enhanced the flowbanding by the overprint of a planar fabric. This regime of compressional and shear stress might well relate to the doming of the intrusion. More intensly developed fabrics towards the margin and especially close to the syenite-carbonatite contact may be explained in the same way. Near vertical orientation of mineral zoning is observed in many other alkaline - carbonatite complexes: Oka (Cold, 1967), Magnet Cove (Erickson & Blade, 1963). 21 Figure 12: Magnetite layering in calcite carbonatite (MR-301H; float; 12800N, 10200E) Breccia zones and fracture zones: Drill cores near the margin of the carbonatite body display a variety of narrow (5-50 cm) shear zones, fracture zones and brecciated zones marked by intense weathering and abundant oxidized pyrite. Displacement along these trends, which often parallel the fabric outlined by mineral layering, appears to be minor and is more likely associated with a more recent event, possibly with the formation of the Rocky Mountains fold and thrust belt. Figure 13: Structural map of cleavage and mineral layering outlined by apatite, magnetite, pyrochlore, amphibole (structural data by K.R. Pride, P.C. LeCouteur (Cominco Ltd.) and U.K. Ma der) 23 Along the southeastern margin breccia zones and shear zones are quite abundant. One type of shear zone is characterized by abundant chlorite, pyrochlore, magnetite, zircon and relatively high radioactivity. The proximity of the brittle shear zone along the east side may be partly responsible for the more intense deformation in this part of the complex. The mineralization of some of the breccia and fracture zones, however, required hydrothermal activity which could have occurred during a late stage magmatic activity. Breccia zones at the syenite - carbonatite contact are quite spectacular due to their size and the contrasting colours of the two igneous rocks (figure 14). ln detail most of the mega-breccias can be recognized as having formed by rupture of the syenite with carbonatite veins filling the gaps. Major vertical or horizontal relative displacements could not be confirmed. Small scale compositional layering in the veining carbonatite (commonly calcite carbonatite) resembles magmatic flowbanding and would thus suggest that these breccias formed synchronously with the intrusion with injected liquids cementing the vugs. 2.5 STRUCTURES AND SHEAR ZONES RELATED TO THE FOLD AND THRUST BELT The key outcrop to interpreting the structure along the western side of the carbonatite complex is a north facing cliff striking perpendicular to the structural trends which exposes Cambrian rocks in the core of a tight anticline (figure 15). A penetrative axial planar shistosity is developed (figure 16). Within the steeply dipping limbs to the west and east shearing resulted in greatly reduced stratigraphic thicknesses and produced schistosities parallel to bedding. The Skoki Dolomite is missing in the eastern limb in this section due to the presence of a high angle forelimb thrust which juxtaposes the Cambrian core against rocks of the Road River Formation (upper Lower Dolomite Shale Unit ?). This entire anticlinal package was moved along a high angle thrust fault onto Cambrian rocks of the contact metamorphic aureole (figures 18, 19). Small and large scale boudinage indicate shortening perpendicular to the structural trends (figure 17). Extension joints are 24 Figure 14: Ruptured syenite with carbonatite veins forming a mega-breccia (11680N, 9730E) 25 frequently developed in the competent layers within a plane subperpendicular to the fold axis (figure 16). Similar structures can be identified along ridges to the north and to the south, but stratigraphic sections, however, may vary considerably in detail. Along the ridge immediately to the north, for example, the eastern limb of the anticline is stratigraphically complete whereas the western limb is cut off by a thrust fault. The anticlinal structure must therefore be segmented by faults. These faults strike at high angles to the Rocky Mountain trend and may be interpreted as wrench faults due to differential thrusting resulting in the lateral disection of the hanging wall. Figure 15: Cambrian core (Kechika Formation) of the anticline along the west-side of the complex. Arrow indicates location of figure 16 (11500N, 8800E) Along the eastern margin of the complex numerous subparallel thrust faults form an extensive brittle shear zone within a reduced, westward dipping, reversed stratigraphic section. Large scale boudinage of competent rock packages is common. Shaly and marly sections have a strong schistosity developed parallel to bedding. Extension joints are common in competent layers with some large quartz-filled Figure 16: Core of anticline (figure 15) showing axial planar schistosity (A), bedding (B) and extension joints (E). (11450N, 8750E) 27 Figure 17: Thinned limestone (Lower Dolomite Shale Unit, Road River Croup) showing bedding (B), schistosity (S), boudinaged limestone bed (L) with calcite filled necks (C) and a deformed carbonate vein (V). (1200N, 8900E) 28 sigmoid shaped extension joints developed in the Sandstone Unit of the Road River Formation. A major fault contact must be located between the contact-metamorphosed Cambrian Kechika rocks and a very reduced package of Skoki Dolomite. Some parts of the Skoki Dolomite however were affected by the intrusion resulting in locally elevated radioactivity. Furthermore an isolated slab of basalt from the Skoki Volcanic Unit (13080N, 11600E) was clearly part of the contact aureole. The stratigraphic section from the carbonatite contact to the Road River Group was therefore fairly continuous at the time of intrusion with significant but not large scale displacements during the Columbian Orogeny. The major displacements within the shear zone took place within the Kechika Formation, at the boundary to the Skoki Formation and within the overlaying shales of the Road River Group. The width of the reversed section towards the east is not known but may well exceed one kilometer. 2.6 CROSS SECTIONS Two geological cross sections are shown in figure 18. Both are drawn across the carbonatite complex and the sourrounding structures at high angles to the Rocky Mountain structural trends and are located as shown on the geological map. An important consequence of attempting to extrapolate the structure to depth is the likelihood that the complex may be cut by the eastern shear zone at relatively shallow depths. The two sections project the fault contact underneath the center of the complex to elevations between 800 meters (A - A') and 200 meters (B - B'). The shear zone may however steepen with depth or deflect at the host rock - carbonatite discontinuity. 2.7 REGIONAL TECTONIC SETTING Thompson's (1978) regional mapping shows the area of the Aley complex as a large anticlinal structure between two branches of the Burden Thrust. The carbonatite itself is shown as part of the Skoki Dolomite Unit and the syenite ring 29 Figure 18: Geological cross sections through the Aley carbonatite complex (for abbreviations cf. figure 3) 30 as thickened parts of the Skoki Volcanic section. The general nature of the structure presented in this study is similar to that reported by Thompson (1978), essentially consisting of a steep westward dipping normal stratigraphic section along the western side of the complex and a westward dipping reversed section along the eastern side of the complex with the complication of a tight anticline along the western side of the complex. The "core" of the large scale anticline shown by Thompson is formed by the carbonatite complex. The thrust sheet hosting the Aley complex may be part of a duplex structure encompassed by the Burden Thrust. 2.8 A POSSIBLE SEQUENCE OF TECTONIC EVENTS Combining the material presented in this chapter a tentative simplified sequence of events is suggested and depicted diagrammatically in figure 19. a) The emplacment and updoming of the intrusion into a layer-cake stratigraphy created a ring-shaped ductile shear zone. b) Traces of future thrust faults related to the formation of the Rocky Mountains outline a duplex structure. c) A blind thrust (1), locked at point L, gave rise to the anticline along the western margin of the complex. d) Thrusting continued along faults 2 and 3 causing uplift of the western anticlinal package and a footwall shear zone along the eastern margin of the complex. An interesting consequence of the inferred duplex structure is the likelihood that considerable parts of the complex were cut above and below the presently exposed level. The cut off parts of the complex have been transported as members of different thrust packages further east or left behind to the west along the trajectory of overall eastward thrusting. A detailed knowledge of the regional structural pattern as well as relative amounts of displacement along individual faults may prove to be a valuable exploration tool in the search for other parts of the Figure 19: Possible sequence of events. For explanation see text. 32 complex. Amounts of shortening and displacement may be reconstructed from balanced cross sections with techniques already applied successfully in various parts of the Rocky Mountains (Thompson, 1979, 1986; Brown et al, 1986; Murphy, in press). 3. MINERALOGY AND MINERAL CHEMISTRY 3.1 INTRODUCTION . Carbonatites and related alkaline rocks are well known for their complex mineralogy (Heinrich, 1966; Vlasov, 1966; Turtle & Gittins, 1966; Kapustin, 1980) and are still a source of new mineral discoveries. The number of rock-forming minerals in carbonatites is small, but the list of rare minerals is endless. A knowledge of the mineralogy and mineral chemistry and their variations is one of the keys towards understanding the geochemistry of these rocks. Typically, the mineralogy varies spatially within the same rock type and often the chemistry of a mineral species displays a large compositional range. In the rocks of the Aley complex nearly fifty mineral species were identified or characterized within only four major rock types (table 1). The list of minerals is by no means complete with the number of new discoveries being largely a function of patience and magnification. The minerals are grouped below into mineral classes with no particular ordering scheme. Analysis, energy dispersive spectra, microphotographs, back scattered electron images and crystal optical schemes are arranged in appendix A. Mineral Mineral Class Occurrence dolomite - ankerite calcite strontianite (?) alstonite (barytocalcite) (?) BaCa(C03)2 aragonite - strontianite ss (?) Sr-Ca-Ba carbonate (?) burbankite (Na,Ca,Sr,Ba,LREE)6(CO3)5 ancylite LREE(Ca,Sr)(CO3)2(OH) • H 2O cordylite Ba(LREE,Ca,Sr)2(CO3)3F2 huanghoite BaLREE(C03)2F2 Ce-Ba-La-Ca carbonate (?) Ca-La-Nd carbonate (parisite) (?) carbonate carbonate carbonate carbonate carbonate carbonate carbonate carbonate carbonate carbonate carbonate carbonate cd,re1,re2,au cc,au,sy re1,cd re1 re1,sy re1 re1 re1,sy re1,cd re,cd re1 re2 33 34 LREE carbonate (calkinsite, lanthanite) (?) carbonate au Ca-Sr-Ba-Ce carbonate (?) carbonate re1,cc apatite phosphate cd,cc,re1,sy monazite (LREE,Th,Ca)P04 phosphate cd cheralite (Th,Ca,LREE)PO» phosphate cd rutile oxide cd hematite oxide cd,cc,au magnetite oxide cc baddeleyite Zr02 oxide cc thorianite Th02 oxide cd pyrochlore (Na,Ca)2 Nb206(OH,F) oxide cc fersmite (Ca,Na)(NbJaJi)2(0,OH,F)6 oxide cd,(cc) columbite Fe(Nb,Ta)2Os oxide cd ( zirkelite (?) (Ca,Th)Zr(Ti,Nb)207 oxide cc Ta-Ca zirconate-niobate oxide cd quartz silicate sy,cc,cd,re2 albite silicate sy,cd potassium feldspar silicate sy,re1 chlorite silicate cd,cc,di,la biotite silicate cc,di,la muscovite silicate au magnesio-arfvedsonite Na3 (Mg,Fe) „ Fe 3+ Si 8Oa(OH,F)2 silicate sy richterite Na2 Ca(Mg,Fe 2* ,Fe 34 ) 5 Si 8 O: a<OH,F)2 silicate cc aegirine (Na,Ca)(Fe 34 ,Mg,Fe 2* ,Ti)Si 2 O 6 silicate sy lorenzenite Na2Ti2Si209 silicate sy zircon silicate cd thorite (huttonite) silicate cd cerite (?) silicate au diopside silicate di augite silicate di Mg silicate silicate ce barite sulfate re1,re2 pyrite sulfide cd,re1,re2,cc galena sulfide re1 Table 1 : List of minerals identified in the Aley carbonatite complex. LREE = light rare-earth element (La,Ce,Nd,Pr); ss = solid solution; cd = dolomite carbonatite; cc = calcite carbonatite; re1 = rare-earth element carbonatite dikes (north ridge); re2 = barite rich rare-earth element carbonatite dikes (northwest ridge); sy = syenite; au = metamorphic rocks of the contact aureole; di = diatreme; la = lamprophyric dikes 35 3.2 CARBONATES , Dolomite Ca(Mg/Fe/Mn)[C03]2 trigonal Properties: light brown to chocolate-brown weathering; mostly untwinned; lamellar twinning abundant in marbles of the cantact aureole Chemistry: dolomite - ankerite - kutnahorite solid solution ranging from 4.6 mol% CaFe(C03)2 0.5 mol% CaMn(C03)2 (in dolomite carbonatite) to Mn-ankerite compositions (10.7 moI% CaFe(C03)2, 5.1 moI% CaMn(C03)2) in REE carbonatite dikes SrC03 values range from 0.02 moI% (dolomite carbonatite) to 0.25 mol% (REE carbonatite dikes) Occurrence: major constituent of dolomite carbonatite, often as euhedral to subhedral phenocrysts (mm - 2 cm) in a finer-grained dolomite matrix; as rhombohedral crystals (mm) in fine-grained calcite matrix near calcite carbonatite - dolomite carbonatite contacts; ankerite is the major constituent in REE dikes; also forms dolomite marbles of the contact aureole Alteration: minute grains of Fe-oxide/hydroxide (often hematite) cause a dusty appearance; Fe-oxide/hydroxide may concentrate along the rhombohedral cleavage and along grain boundaries; in various samples rutile forms thin (2 -10 u) sagenite figures along the rhombohedral cleavage leading to soft, fine, granular, metallic-looking aggregates (mm - cm); chlorite may also replace dolomite forming irregular or rhombohedral aggregates of fine, greenish black flakey aggregates (mm - cm) often mixed with sagenitic rutile, phosphates and Nb - oxides Appendix A: tab 13, tab 14, figure 32, EDS-271, EDS-100 Calcite (Ca,Mg,Fe,Mn)[C03 ] trigonal Properties: grey to grey-brown weathering; mostly fine-grained, anhedral Chemistry: Ca-Mg-Fe-Mn-Sr solid solution with composition near calcite Ca(0.973) Mg(0.014) Fe(0.002) Mn(0.003) Sr(0.008) C03 in calcite carbonatite; 36 manganese calcite in some syenite samples Occurrence: major constituent of calcite carbonatite, either uniformly fine-grained (<1 mm) or forming ovoid phenocrysts (1 - 7 mm) in a fine-grained calcite matrix; often intense parallel twinning; manganese calcite associated with aegirine and albite in syenite; forms calcite marbles of the contact aureole Alteration: calcite carbonatite appears to be more resistant towards weathering forming fresh, hard outcrops and clean drillcore Appendix A: tab 15, EDS-228 Strontianite (Sr,Ba,Ca)[C03] orthorhombic Properties: distinguishable only under the SEM-EDS Chemistry: always with significant Ba and Ca substitution Occurrence: in REE-carbonatite dikes (north ridge) and REE-rich dolomite carbonatite "sweats" associated with REE-carbonates; forms small, irregular grains (20 - 50 u.); it may be a (hydrothermal) alteration product References: Kapustin, 1980; Heinrich, 1967; Tuttle & Gittins, 1967 Appendix A: figure 26, EDS-24 Alstonite (or Barytocalcite) (?) BaCa[(C03)2] triclinic (monoclinic) Properties: distinguishable only under the SEM-EDS Chemistry: always with minor Sr substitution Occurrence: as irregular grains (<100 u) associated with the REE-carbonates in REE-carbonatite dikes (north ridge); alstonite and barytocalcite are reported to be low-temperature hyddrothermal alteration pruducts (Kapustin, 1980) Appendix A: figure 27, figure 28, EDS-136 37 Aragonite • Strontianite Solid Solution (?) Ca(Sr,Ba)[C03]2 orthorhombic Properties: distinguishable only under the SEM-EDS; sometimes forming fibrous aggregates Chemistry: composition close to CaSr(C03)2 with minor Ba substitution; such a phase is not known to occurr naturally, but was synthesized (Cuichard & Wyast, 1943; Faivre, 1944) Occurrence: forms irregular patches up to 0.2 mm in size associated with REE-carbonates in REE-carbonatite dikes (north ridge); in carbonate rich syenite as fibrous, irregular aggregates Appendix A: figure 27, EDS-131 Sr-Ca-Ba Carbonate (?) Properties: distinguishable only under the SEM-EDS Chemistry: about similar amounts of Sr, Ca and Ba; it might be a solid solution of the isomorphous minerals aragonite - strontianite - witherite Occurrence: as a minor phase in the REE-carbonate assemblage of REE-carbonatite dikes (north ridge); it may be an alteration product (cf. textures) although the aragonite-group minerals have high dissociation temperatures (800 - 900°C) Appendix A: figure 28, EDS-112 Burbankite (LREE,Sr,Ca,Ba,Na)6[C03]2 hexagonal Properties: colour, orange; transparent with a vitreous lustre under the binocular; no good cleavage (prismatic); uniaxial negative; low birefringence: A = 0.012; high relief; no euhedral crystals observed; heating curve shows first endothermic inflection around 670° C (Vlasov, 1966) Chemistry: an anhydrous Ca-Ba-Sr-Na-LREE carbonate; Ce is more abundant 38 than La; minor Pr, Nd Occurrence: burbankite forms with ancylite the bulk of the REE-carbonate assemblage in the REE-carbonatite dikes (north ridge); forms irregular grains up to 0.5 mm but always with inclusions of other carbonates, phosphates and barite; it is thought to be the major primary magmatic phase of the REE-carbonate assemblage References: Pecora & Kerr, 1953; Vlasov, 1966; Kapustin, 1980 Appendix A: figure 26, figure 27, EDS-21, figure 29 Ancylite LREE(Ca,Sr)[(OH)/(C03)2]. H20 orthorhombic Properties: colour, greenish - ochre; transparent with vitreous lustre under the binocular; imperfect cleavage; optical properties are carbonate - like; decomposes at 480 °C (Vlasov, 1966) Chemistry: a Sr-LREE carbonate with various amounts of Ca (cf. calcioancylite, Fleischer, 1980); the chemical formula as written above (Vlasov, 1966; Fleischer, 1980) is also written as (LREE),(Ca,Sr)3 [(OH)0/(CO)3)7] • 3H 20 (Rosier, 1980); Ce is the dominant LREE followed by La; Occurrence: it is a major constituent of the REE-carbonate assemblage in the REE-carbonatite dikes (north ridge) forming irregular grains and aggregates (<400 n); it is a (hydrothermal) alteration product, possibly replacing burbankite and other anhydrous carbonates or fluorcarbonates References: Kapustin, 1980; Vlasov, 1966; Heinrich, 1967 Appendix A: figure 26, figure 27, figure 28, EDS-139 Cordylite F3a(LREE,Ca,Sr)2[F2/(C03)3] hexagonal Properties: colour, ochre to wax-yellow Chemistry: a Ba fluorcarbonate with minor Ca and Sr; Ce is the major REE, 39 followed by La Occurrence: a minor phase in the REE-carbonate assemblage of the REE-carbonatite dikes (north ridge) forming irregular patches (<100 n) showing alteration (or exsolution) patterns (slight differences in Ca - Sr ratios); also associated with huanghoite as small grains in REE-rich dolomite carbonatite sweats; cordylite may be a primary magmatic fluorcarbonate References: Vlasov, 1966; Kapustin, 1980 Appendix A: figure 28, EDS-115 Huanghoite Ba(LREE)[F/(C03)2] hexagonal (?) Properties: colour, greenish yellow; clear with vitreous lustre under the binocular; distinct lamellar cleavage; lamellar, fan-shaped twinning common; always slightly biaxial negative due to deformation; relief and birefringence similar to dolomite; the heating curve shows a small endothermic inflection around 500 °C, decarbonatisation occurs around 680 °C (Vlasov, 1966) Chemistry: a Ba-LREE fluorcarbonate with apparently strong selective Ce incorporation; the mineral discribed as Ce-Ba-La-Ca carbonate might be related to huanghoite Occurrence: forms irregular interstitial aggregates up to cm-size in REE-rich dolomite carbonatite sweats; associated with minor cordylite, barite and phosphates; this is probably the first occurrence of huanghoite in North America References; Semenov & P'ei - Shan, 1963; Vlasov, 1966; Kapustin, 1980 note: huanghoite was originally named huanchite (cf. Vlasov, 1966) Appendix A: EDS-312 40 Ce-Ba-La-Ca Carbonate (?) Properties: distinguishable only under the SEM-EDS Chemistry: Ce > Ba > LA > Ca, LREE; similar to huanghoite, but with a higher LREE / Ba ratio and minor Ca substitution Occurrence: as a minor phase within the REE-carbonate assemblage of the REE-carbonatite dikes of the north ridge Appendix A; EDS-123 Ca-La-Nd Carbonate (?) (Parisite ?) Properties: distinguishable only under the SEM-EDS Chemistry; Ca, Ce > Nd > La > Pr; probably parisite CaLREE 2 [F 2 /(CO 3) 3 ] (hexagonal) or synchysite CaLREE[F/(C03)2] (hexagonal) Occurrence: forming interstitial aggregates (up to 0.5 mm) with barite in the barite-rich REE-carbonatite dikes (northwest ridge) References: Makasimocic & Panto, 1979; Vlasov, 1966; Kapustin, 1980 Appendix A: EDS-212 LREE Carbonate (?) Properties: distinguishable only under the SEM-EDS Chemistry: Ce >- La, Nd > Pr > Ca; it is probably one of the hydrous LREE carbonates calkinsite LREE2 [(C03 )3] • 4HzO (orthorhombic) or lanthanite LREE2[(C03)3]«8H20 (orthorhombic) Occurrence: as prismatic crystals (10 n) replacing parisite (?) in the Ba-rich REE-carbonatite dikes (northwest ridge); reported to be a weathering product of burbankite (Kapustin, 1980) References: Pecora & Kerr, 1953; Vlasov, 1966; Kapustin, 1980 41 Appendix A: EDS-242 Ca-Sr-Ba-Ce Carbonate (?) Properties: distinguishable only under the SEM-EDS Chemistry: Ca > > Sr > Ba, Ce > La; may be similar to carbocernite (Ca,LREE,Na,Sr)[C03] (orthorhombic) in composition Occurrence: minor phase in the REE-carbonate assemblage of the REE-carbonatite dikes (north ridge); as minute grains (10 n) in a drillcore sample of calcite carbonatite Appendix A: figure 26, figure 28, EDS-238 3.3 PHOSPHATES Apatite Ca5[(OH,F)/(P04)3] hexagonal Properties: easily visible on weathered surfaces as white grains against recessive weathering grey or brown carbonatite; hard tc identify on fresh rock Chemistry: usually contains no SEM-EDS-detectable substitution, except Fe in a few samples of calcite carbonatite; in REE-carbonatite dikes minor LREE (Ce > La, Nd) contents are characteristic Occurrence: abundant in dolomite carbonatite and calcite carbonatite as prismatic crystals, rounded prisms (in calcite carbonatite) or ovoid, radiating aggregates; small, rounded or irregular grains (50 - 100 u) in REE-carbonatite dikes and syenite; accessory mineral in sedimentary marbles of the contact aureole Appendix A: EDS-19, EDS-227 42 Monazite (LREE,Th,Ca)[PO(,] monoclinic Properties: mostly small anhedral inclusions and distinguishable only under the SEM-EDS; rarely euhedral, long prismatic (parallel c); high relief; birefringence: A =« 0.05; biaxial positive; small 2Vz; extinction angle X < c =* 16° Chemistry: most SEM-EDS patterns show detectable Th and Ca substitution; Ce is always the dominant REE followed by La, Nd and Pr Occurrence: in dolomite carbonatite where it is frequently associated with fersmite pseudomorphs after pyrochlore, forming euhedral crystals or small inclusions (10 - 50 u) Appendix A: EDS-79, EDS-2 Cheralite (?) (Th,Ca,LREE)[PO,l monoclinic Properties: distinguishable only under the SEM-EDS Chemistry: high Th-content (none or minor U), about similar amounts of Ca and total LREE (Nd, Ce > > La, Pr) Occurrence: was observed only in one dolomite carbonatite sample as minute inclusions in columbite Appendix A: EDS-15 3.4 OXIDES Rutile (Ti,Nb,Fe)02 tetragonal Properties: distinguishable only under the SEM - EDS Chemistry: always with substitution of Nb an Fe for Ti (ilmenorutiie is reported to contain up to 32 wt% Nb2Os, Palache et al, 1944); rutile from carbonatites are reported with up to 18 wt% Nb2Os (Kapustin, 1980) 43 Occurrence: as thin (5 - 10 n) sagenite lamellae (striation, 120° knee-shaped twinning) along the rhombohedral cleavage of dolomite forming dark, metallic, fine granular aggregates (mm - cm) nucleating from columbite-fersmite aggregates (after pyrochlore ?); also in chlorite aggregates (with Nb-oxides) probably replacing dolomite and pyrochlore in dolomite carbonatite; as small (10 - 50 u) accessory grains in dolomite carbonatite; as irregular inclusions (2 - 15 u, exsolution ?) in Iorenzenite References: Kapustin, 1980 Appendix A: figure 32, EDS-12 Hematite Fe203 hexagonal Occurrence: abundant in weathered dolomite carbonatite forming small inclusions in dolomite, often accumulated along the rhombohedral cleavage and grain boundaries; as small hexagonal platlets or aggregates of plates; as irregular grains and hexagonal plates in some pseudomorph assemblages replacing pyrochlore in dolomite carbonatite Magnetite Fe304 cubic Properties: frequently displaying cubic habit; also subhedral, large (1 - 2 cm) crystals (some with trapezohedral faces); exsolution lamellae of ilmenite are occasionally developed Chemistry: most analyses (SEM-EDS) show titaniferous magnetite Occurrence: typical constituent in calcite carbonatite, often forming bands sorted according to crystal size; may accumulate in areas as big as 100 m2 in calcite carbonatite with 10 - 30 % magnetite; inclusions of apatite, carbonate and biotite are common; larger grains are often fractured or broken apart; not observed in dolomite carbonatite or REE carbonatite dikes 44 References: Kapustin, 1980; Ramdohr, 1955 Appendix A: EDS-180, EDS-172 Baddeleyite Zr02 monoclinic Properties: fonns prismatic or tabular, rarely equant brown crystals with a vitreous lustre; cleavage, {001} good, {010} poor to distinct; very high relief; very high birefringence: A > 0.1; biaxial negative; 2Vx 20 - 30°; r > v; pleochroism: light yellow (Z, Y) to brownish yellow (X); absorption: X > Y > Z; always twinned: on {110} and polisynthetic on {100}; thermally stable to very high temperatures with two phase transitions reported (Kapustin, 1980) Chemistry: no SEM-EDS detectable impurities (small amounts of Fe203 and Hf02 are reported: Palache et al, 1944; Kapustin, 1980) Occurrence: was observed only in one sample of fine grained magnetite -apatite calcite carbonatite as abundant, small (0.2 - 0.6 mm) crystals; associated and partially replaced by niobian zirkelite (?) References: Kapustin, 1980; Palache et al, 1944 Appendix A: figure 33, EDS-165 Thorianite (?) (Th,U)02 cubic Properties: distinguishable only under the SEM-EDS Chemistry: Th with minor U; no clean EDS - signal was obtained due to the grainsize (2 M) Occurrence: as minute inclusions (2 n) in fersmite pseudomorphs after pyrochlore in dolomite carbonatite References: Vlasov, 1966; d'Arcy, 1949; Kapustin, 1980 45 Pyrochlore (Ca,Fe * ,Na,Th,U)3.m(Nb,Ti,Ta/Fe)2 Os (0,OH,F) ,.n • pH 2 O cubic Properties: colour: black, dark brown, honey-brown, straw-brown, tan, reddish brown, brownish pink; habit: octahedral, sometimes modified by the dodecahedron {110} and cube {100} (figure 34); 0.1 - 4 mm in size, some calcite carbonatites with irregular crystals up to 2 cm; fracture, conchoidal or splintery; vitreous to sub-metallic lustre; very high relief; isotropic or slightly anisotropic; intense body colour: dark brown, straw-brown, yellow-brown, red-brown; often zonal structures visible; grey, non - pleochroic under reflected light, similar to magnetite but with a slightly lower reflectivity; usually not metamict with a fairly sharp X-ray diffraction pattern Chemistry: a complex oxide of the A2B2OFI - type with a wide range of composition; the samples analyzed (SEM-EDS, EMS) are all close to the Nb-endmember with various amounts of Ca, Ti, Fe, Na, Ta, Th, U; compositional zoning may or may not be present and is mostly simple, rarely multiple; zoned crystals show a rim with a higher average atomic number than the core with Th being one of the elements enriched in the rim (figure 37) Occurrence: typical mineral in banded calcite carbonatite associated with apatite, magnetite, +biotite, lamphibole; may form relict crystals in fersmite-columbite pseudomrphs in altered, chlorite-rich dolomite carbonatite; often substantially • concentrated in narrow bands and sweats in calcite carbonatite; often with inclusions of carbonate, apatite and biotite; zoning frequently macroscopically visible Alteration: pseudomorphs of fersmite after pyrochlore are abundant in dolomite carbonatite; pyrochlore may show several stages of alteration (ie. secondary growth of fersmite in fersmite pseudomorphs after pyrochlore, columbitization of fersmite pseudomorphs after pyrochlore) References: Hogarth, 1961; Hogarth, 1977; Palache et al, 1944; Kapustin, 1980 Appendix A: figure 34, figure 35, fig 36, figure 37, EDS-224, 225, 277, 278 46 Fersmite (Ca,NaJh,U)(Nb,Ti,Fe,Ta,Zr)2(0,OH,F)6 orthorhombic Properties: habit: pseodomorph after octahedral pyrochlore, secondary growth of small prismatic crystals; primary equant crystals (several mm) with prism {110}, pinacoid {010} and orthorhombic dipyramid {111} developed (figure 38); colour, honey-brown to black-brown; resinous lustre if well crystallized (weathered crystal surfaces often dull); zonation often macroscopically visible; no good cleavage, concoidal fracture; very high relief; very high birefringence; colour, brown to grey-brown; often metamict (broad X-ray reflections) Chemistry: an oxide of the type AB2(0,OH,F)6 with a complex chemistry (Nb, Ca, Na, Fe, Ti, Ta, Th, U, Zr) similar to pyrochlore, but with a higher Nb content Occurrence: most common Nb-phase in dolomite carbonatite, almost always pseudomorph after pyrochlore; rarely as a primary phase in dolomite carbonatite; may replace pyrochlore in altered, chlorite-rich calcite carbonatite; associated with other Nb-oxides, phosphates, carbonate and hematite in pseudomorphs after pyrochlore (cf. pyrochlore: alteration) Alteration: often partially metamict as fine grained aggregates replacing pyrochlore; sometimes partially replaced by columbite References: Bohnstedt - Kupletskaya & Burova, 1947; Vlasov, 1966; Kapustin, 1980 Appendix A: figure 38, figure 39, figure 40, EDS-267, 70 Columbite (Fe,Mg)(Nb,Ti,Ta)2Os orthorhombic Properties: colour, black; lustre, sub-metallic; irregular grains (aggregates); high relief; opaque; grey under reflected light, reflectivity distinctive lower than pyrochlore (and magnetite); may show reddish brown internal reflections Chemistry: reported as a complex oxide near (Fe,Mn,Mg)(Nb,Ta)2Os, isostructural with brookite; the samples examined (SEM-EDS) show considerable 47 Ti substitution (Ti has been ascribed to impurities [Palache et al, 1944] which was not observed in the samples studied); Mg, Mn and Ta are above the SEM-EDS detection limit Occurrence: forms irregular, granular aggregates in a dolomite carbonatite sample with chlorite-rutile aggregates, carbonate-rutile aggregates and fersmite pseudomorphs after pyrochlore; some vaguely preserved octahedral forms suggest that columbite forms after pyrochlore; also as acicular, radiating aggregates forming in fersmite pseudomorphs after pyrochlore References: Palache et al, 1944; Vlasov, 1966; Kapustin, 1980 Appendix A: EDS-7 Zirkelite (?) (Ca,Th)Zr(Ti,Nb)207 monoclinic Properties: colour, black to dark brown; prismatic crystals (without distinct terminal faces) growing parallel or at 45° angels (0.05 - 0.2 mm); very high relief; isotropic or anisotropic; very strong dark reddish brown body colour; Chemistry: an A2B207 oxide consisting of Ti, Zr, Ca, Fe, Th, Nb, and possibly U; Ti / Zr ratio appears to be variable Occurrence: always intimately associated with baddeleyite and partially replacing it by forming an (epitaxial ?) overgrowth References: Borodin et al, 1957; Palache et al, 1944; Vlasov, 1966; Kapustin, 1980 note: the old names zirconolite and niobozirconolite are replaced by zirkelite (Hogarth, 1977) Appendix A: EDS-151 Ta-Ca Zirconate • Niobate Properties: probably a metamict, granular mass 48 Chemistry: Ta-rich Nb-phase with Ca, Th, U, Ti and minor Fe (may not be a pure SEM-EDS signal) Occurrence: together with fersmite replacing pyrochlore in a dolomite carbonatite sample Appenddix A: EDS-72 3.5 SILICATES Quartz Si02 trigonal Occurrence: accessory mineral in barite-rich REE-carbonatite dikes (northwest ridge) where it forms irregular aggregates with slightly undulous extinction; rare in altered dolomite carbonatite and calcite carbonatite; as coarse, irregular crystals of milky quartz (2-15 mm) accumulated in a dolomite carbonatite sample (float); constituent in syenite in variable abundancies Albite Na[AlSi308] triclinic Properties: as irregular grains, often untwinned; subhedral to euhedral crystals with frequent carlsbad and albite twinning Chemistry: almost pure NaAlSi308 with minor KzO (< 0.2 wt%) and FeO (0.4 wt%) Occurrence: major constituent in syenite-xenoliths in alkali syenite as subhedral to euhedral grains (0.1-2 mm); irregular grains in syenite; accessory mineral in some impure marbles; accessory mineral in a few samples of dolomite carbonatite Appendix A: table 16, figure 41, EDS-50 49 Potassic Feldspar K[AlSi308] monoclinic, triclinic Chemistry: almost pure potassium feldspar with 0.7 wt% Na20 and traces of Fe Occurrence: small, irregular grains as accessory mineral in REE-carbonatite dikes (north ridge); minor constituent in syenite; in marbles of the contact aureole; not observed in calcite carbonatite or dolomite carbonatite Appendix A: EDS-259 Chlorite (Mg,Al,Fe) 12 [(OH) 1s/(SLAl)8C>2o] monoclinic Properties: colour, dark green; colourless in thin section, brownish if weathered; uniaxial positive; negative elongation; occasionally with anomalous violet interference colours (and positive elongation) Chemistry: variable Mg / Fe ratio, but always substantial Fe; ranging from grochauite to aphrosiderite in composition Occurrence: common as a secondary mineral in dolomite carbonatite; subordinate in altered calcite carbonatite; in some chloritized zones it may form up to 50 % of the rock as ovoid crystals (0.5 - 5 mm); it may form fine grained aggregates with minor rutile in dolomite carbonatite Appendix A: EDS-81 Muscovite • Phengite K2Al2(AL,Mg,Fe)2[(OH,F)A/(Al,Si)2Si6O20] monoclinic Occurrence: as metamorphic mineral in impure marbles and metamorphic marls of the contact aureole 50 Biotite - Phlogopite K2(Mg,Fe)6j,(Fe,Al,Ti)0.2[(OH,F)a/Si6.5Al2.302o] monoclinic Properties: colour, light brown to dark brown or reddish brown; often forming hexagonal prismatic crystals or large flakes; variable pleochroism with reversed pleochroic scheme in calcite carbonatite: X > Y Z (cf. tetraferriphlogopite of Rimskaya - Korsakova & Sokolova, 1964; mentioned in Kapustin, 1980), X = brown, Y = Z = very pale brown; X = brown, Y = Z = pale greenish brown; X = pale brown, Y = Z = pale green, absorption X =* Y s* Z; X = deep bordeaux-red, Y = Z = pale brown; sometimes zoned with core (X = pale brown, Y = Z = pale green) and rim (X = green, Y = Z = green, absorption X < Y = Z); also with normal pleochroic scheme in lamproites: X = pale brown to colourless, Y = Z = dark red-brown to brown, absorption X < < Y = Z Chemistry: Mg-rich; some varieties (often the rim in zoned crystals) have SEM-EDS detectable Ti; biotite from the diatreme is Ti-rich and contains minor Cr. Occurrence: constituent in most calcite carbonatites (reversed pleochroic scheme), where it forms equant crystals (up to 5 mm); often enhancing banding together with pyrochlore, apatite and magnetite; constituent in the diatreme and lamprophyric dikes (groundmass and flakes up to 5 cm, with normal pleochroic scheme); as inclusions in magnetite (with apatite) forms also biotite rich zones at some syenite-calcite carbonatite contacts (very fine grained or coarse, with reversed pleochroic scheme) References: Kapustin,1980 Appendix A: EDS-77, 222, 223 51 Magnesio - Arfvedsonite (Na/Ca/K)3(Mg,Fe2*,Mn),(Fe3+,Ti)[(OH,F)2/Si8022] monoclinic Properties: colour, greenish black; vitreous lustre; perfect prismatic cleavage {110}; subhedral prismatic crystals (<0.5 mm) with {110} and subordinate {010}; often somewhat poikiloblastic; biaxial negative; 2Vx a* 70-80°; v > r very strong; extinction angle Z < c ^ 30°; birefringence: A =* 0.015; pleochroism: X = light greyish yellow-green, Y = light greenish grey, Z = pale greenish grey, absorption X Y Z; optic axial plane parallel (010); twinning uncommon, parallel (100); anomalous extinction: anomalous brown-violet to anomalous blue Chemistry: average composition: Si02(54.7 wt%), TiO2(0.2 %), Al2O3(0.1 %), FeO(11.0 %), MnO(0.9 %), MgO(16.3 %), CaO(2.5 %), Na20(8.3 %), K20(1.8 %), F(2.5 %); near magnesio-arfvedsonite with solid solution towards richterite and magnesio-riebeckite and K substitution; Ca values vary coupled with Fe and Mg Occurrence: abundant in syenite and micro-syenite xenoliths in syenite References: Kapustin, 1980; Troger, 1979; Veblen, 1981 Appendix A: table 17, table 18, figure 42, figure 43, EDS54, 95 Richterite (Na,K)2Ca(Mg,Fe,Mn)5[(OH,F)2/Si8022] monoclinic Properties: green to black-green; prismatic to acicular with {110}, {100} and {010}; perfect prismatic cleavage {110}; twinning common parallel (100); biaxial (negative ?); large 2V 75-105°; birefringence: A 0.02; extinction angle Z < c 20°; elongation positive; colourless or weak pleochroic: X = Y = pale greenish, Y = pale brown-orange; optic axial plane parallel (010) Chemistry: Al-poor sodic Mg-Ca pyroxene with variable Fe and Ca contents and always minor K Occurrence: rare to abundant in calcite carbonatite near syenite; oriented 52 parralel to planar fabric; sometimes forming almost monomineralic bands with comb-layering texture Appendix A: fig 44, fig 45, EDS-11 Aegirine (N^CaXFe3*^Fe^TMSijOs] Properties: colour, dark green; vitreous lustre; poor prismatic cleavage {110}; acicular, small crystals (< 0.4 mm); square cross sections common; birefringence: A = 0.04; 2V at 40-70°; stright extinction; pleochroism: X = Y = light yellow-green, Z = green, absorption Z > X » Y Chemistry: average composition: SiOz(52.7 wt%), Ti02(5.8 %), Al2O3(0.5 %), Fe203(23.2 %), MnO(0.4 %), MgO(2.6 %), CaO(1.3 %), Na20(13.5 %), K2 O(0.1 %); near 70 mol% acmite, but with additional Na (1.0 Na sites per 6 oxygens), minor Ca and substantial Ti substitution Occurrence: abundant in syenite as acicular or prismatic crystals; forming inwardly-pointing acicular crystals in small spherulites with albite and manganese calcite in syenite; less abundant in micro-syenite xenoliths in syenite References: Kapustin, 1980; Troger, 1979; Reviews in Mineralogy, vol. 7 Appendix A: table 19, figure 46, figure 47, EDS-68, 88 Zircon Zr[Si04] tetragonal Properties: colour, light honey-brown; diamond lustre; pale yellow-brown in thin section Chemistry: no other elements detectable under the SEM-EDS; apperently very low U-Pb contents (Parrish, pers. com., 1986) Occurrence: accessory mineral in dolomite carbonatite, usually rare, but enriched in some zones with abundant short prismatic dipyramidal crystals (1 -5 mm); as small grains (10 ju) associated with fersmite in fersmite 53 pseudomorphs after pyrochlore in dolomite carbonatite Lorenzenite Na2Ti2 [03/Si206] orthorhombic Properties: dark brown; vitreous lustre on broken surface; striated, long-prismatic crystals; pale lilac-brown in thin section; non-pleochroic; very high relief; very high birefringence: A > 0.1; good cleavage parallel c {001}, {110} poor; twinning parallel c frequent; often slightly undulous extinction; biaxial positive with a small 2V Chemistry: always shows some Nb substitution and rarely SEM-EDS detectable Fe Occurrence: as an accessory mineral in syenite as prismatic or irregular crystals; forms monomineralic veinlets in syenite References: Sakama, 1947; Kapustin, 1980 Appendix A: EDS-255 Thorite (Huttonite) (Th,U)[SiOa ] tetragonal (monoclinic) Properties: distinguishable only under the SEM-EDS Chemistry: close to Th(Si04) with minor U substitution Occurrence: small, irregular inclusions (5 - 20 ix) in fersmite pseudomorphs after pyrochlore and in columbite replacing pyrochlore in dolomite carbonatite References: d'Arcy, 1949; Kapustin, 1980 Appendix A: EDS-78 Cerite (?) (LREE,Ca)9(Mg,Fe)[Si7(0/OH,F)28] trigonal properties: distinguishable only under the SEM-EDS Chemistry: similar amounts of Si, Ca and LREE; Ce more abundant than La, 54 Nd, Pr; considerable confusion about the chemical formula: Ca2(LREE)8[Si04]7.3H20 (Rosier, 1980), (LREE,Ca)2[Si(0,OH)5] (Dana, 1896) Occurrence: small grains in a dolomite marble of the contact aureole References: Rosier, 1980; Fleischer, 1980; Dana, 1896; Glass et al, 1958; Kapustin, 1980; Vlasov, 1966 Appendix A: EDS-201 Diopside (Ca,Mg,Fe2+,Fe3*,Cr)2[(Si,Al)2Os] monoclinic Properties: pistacio green crystals;. vitreous lustre; excellent prismatic cleavage Chemistry: Ca-Si-Mg-Fe pyroxene with minor Al and Cr Occurrence: very rare as small, ovoid xenocrysts (mm) in the lamproitic diatreme Appendix A: EDS-3 Augite (Ca,Mg,Fe2+,Fe3+,Al,Ti)2[(Si,Al)2Osl monoclinic Properties: black crystals; vitreous lustre; good prismatic cleavage Occurrence: fairly abundant ovoid xenocrysts in the lamproitic diatreme Appendix A: EDS-4 Mg - Silicate Properties: weathering resistent dirty olive-green, roundish crystals (0.5 - 7 mm) with ochre encrustations; dark grey-green on fresh surfaces; vitreous lustre when fresh; clear X-ray diffraction pattern Chemistry: Mg-silicate with minor Ca Occurrence: in one sample (float) of calcite carbonatite associated with magnetite and minor pyrite and biotite 55 3.6 SULFATES Barite Baf.SO„l orthorhombic Properties: visible often only under the SEM-EDS; larger crystals are colourless, show undulous extinction and two good cleavages {100}, {010} Chemistry: no other elements above SEM-EDS detection limit Occurrence: accessory mineral in REE-carbonatite dikes of the north ridge forming small grains (10 p.) associated with the REE-carbonate assemblage; abunant in the REE-carbonatite dikes of the West ridge forming interstitial crystals (1 - 5 mm) within euhedral ankeritic dolomite; accessory mineral in alkali - syenite forming small irregular grains (10 - 50 u) References: Kapustin, 1980 Appendix A: figure 27, figure 26, EDS-211 3.7 SULFIDES Pyrite FeS2 cubic Occurrence: typical accessory mineral of dolomite carbonatite and calcite carbonatite; mostly idiomorphic (cube), sometimes irregular; often replaced by Fe-oxides/hydroxides; may be locally concentrated; typical in REE-carbonatite dikes (north ridge) as cubes (0.5 - 5 mm) Pyrrhotite Fe^xS monoclinic or hexagonal Occurrence: only observed in a drillcore sample of calcite carbonatite where it forms schlieren with euhedral magnetite, biotite and minor pyrite (exsolution in pyrrhotite ?) 56 Galena PbS cubic Occurrence: observed in one sample of a REE-carbonatite dike as a tiny grain (5 n); appears to be absent in all rock types of the complex 4. PETROGRAPHY The igneous rocks of the Aley carbonatite complex may be divided into four major types: dolomite carbonatite, calcite carbonatite, rare-earth carbonatite dikes and "syenite". In spite of this apparent simplicity the variety of textures, fabrics and mineral modes is puzzling. Thus, the reader should keep in mind, that "representative" sampling and petrographic analysis is likely to be biased. The following petrographic characterization of the major rock types is an attempt to synthesize the relevant observations and is thus a simplification. 4.1 DOLOMITE CARBONATITE Petrographic name: Fersmite- and pyrite-bearing dolomite-apatite-carbonatite Physical Properties: Dolomite carbonatite weathers a distinctive reddish brown colour and is white or brownish on fresh surfaces. Radioactivity is spatially variable, generally low, but distinctly higher than in the "syenite" ring and generally lower than in calcite carbonatite. Magnetic susceptibility is low. Density is close to 3.0 X103 kg/m3, calculated from dolomite compositions presented in section 3.2. Mineral mode: Modal abundances of constituents in dolomite carbonatite range from almost pure dolomite (^1 % apatite) to apatite-rich varieties ( = 10%). Accessory fersmite is always present and may be enriched in diffusely defined zones, but probably not exceeding 1 % modal concentration. Pyrite is a common accessory mineral, locally enriched (1-2 %) and commonly concentrated in fracture and shear zones (up to 5 %, almost always oxidized). Other accessory minerals include zircon, albite, quartz, rutile, columbite, monazite and strontianite. Alteration products include chlorite (up to 60 %), rutile, columbite and fersmite pseudomorphs after pyrochlore. 57 58 Textures: Different degrees of deformation and alteration result in a variety of textures. The transition between primary magmatic crystallization and recrystallization is probably diffuse such that primary and secondary carbonate textures are commonly ambiguous. Carbonatite dolomite textures do, however, look quite different from dolomite marbles. A typical, fresh dolomite carbonatite has a large range of grain sizes (0.1-4 mm) with a granoblastic interlocking texture with straight grain boundaries, abundant reentrant angles, unequal angle triple-joints and is almost idiotropic in some parts. Characteristic are small rhombohedral "inclusions" or subgrains of dolomite with a different crystallographic orientation than the dolomite host grain. Apatite occurs as prismatic (parallel c-axis), rounded crystals (0.1-2 mm) aligned subparallel to the planar fabric without a clear linear trend. Apatite may also form radiating bunches forming disk-like flattened aggregates up to 2 cm in size oriented parallel to the fabric. Narrow zones of higher strain are marked by abundant twinning of dolomite with conjugate glide-twin systems developed. Narrow fracture zones show much finer grain sizes and a granoblastic - polygonal texture. In these zones veinlets of secondary quartz might occur replacing dolomite but without forming any calc-silicate phases. Fersmite forms fibrous to fine-grained aggregates within perfect octahedrons, thus replacing pyrochlore (appendix A: figures 39, 40). Primary fersmite (orthorhombic) is rare (appendix A: figure 36). Columbite might replace fersmite which is observed commonly in chloritized zones. Relict cores of pyrochlore are rarely preserved. Fersmite pseudomorphs normally have inclusions of apatite, monazite and albite. Secondary overgrowth of small, prismatic, pyramidal fersmite crystals is common. 59 Alteration: Metallic black, fine granular aggregates (0.5-15 mm) which may be mistaken for columbite or fersmite are of widespread occurrence and consist mainly of thin sagenitic niobian rutile plates grown along the rhombohedral cleavage of dolomite (figure 32). These aggregates form brownish, dirty patches in thin section commonly associated with fine granular magnetite and minor Nb-oxides, apatite, monazite, chlorite and minute grains of Th-phases (thorite, thorianite, cheralite). Dolomite carbonatite rich in these aggregates shows a higher level of radioactivity. In some samples these aggregates seem to nucleate from altered pyrochlore cores, but this is the exception. A second type of black aggregate (1-15 mm) consists of fine grained chlorite with sagenitic rutile and is probably an alteration of dolomite-rutile aggregates. Rectangular grain shapes are indicative of pseudomorphism, although no relicts of the primary phase were observed. Heavily chloritized dolomite carbonatite zones (0.5-2 m wide) occur along the southeastern margin of the core - complex. They consist of up to 60 % chlorite, 30-35 % dolomite, 2-3 % apatite, 2-4 % quartz and commonly abundant (2-20 %) fine grained (0.1-0.5 mm) fersmite pseudomorphs after pyrochlore with frequently preserved pyrochlore cores. Equant, flaky chlorite (0.2-5 mm) replaces dolomite and quartz. Quartz commonly shows mosaic substructures similar to growth structures observed in vein quartz and is interpreted to be secondary quartz. Colourless, aluminous chlorite with normal interference colours develops anomalous blue fringes in contact with fersmite due to increased Fe-substitution. It is not clear whether the concentration of fersmite pseudomorphs is of primary magmatic origin or due to hydrothermal activity in fracture and breccia zones. The presence of silicification and chloritisation would favour the latter explanation. 60 4.2 CALCITE CARBONATITE Petrographic name: Magnetite, biotite, pyrochlore, amphibole-bearing calcite-apatite- carbonatite Physical properties: Calcite carbonatite weathers a distinctive grey to brownish grey colour, distinguishable easily from dolomite carbonatite. Density is about 2.8 to 3.0 XlO3 kg/m3 depending on the amount of metal oxides present. Magnetic susceptibility is high due to the presence of magnetite. Radioactivity is generally higher than in dolomite carbonatite due to the overall higher pyrochlore concentrations in calcite carbonatite. Mineral mode: Typically, calcite carbonatite displays a highly variable mineral content due to mineral layering and differences in the mineral content of individual calcite carbonatite "sweats". Mineral modes vary between: calcite (40-95 %), magnetite (0-40 %), apatite (2-10 %), biotite (0-5 %), pyrochlore (0-2 %), amphibole (0-5 %), pyrite (0-0.5 %) and traces of hematite, baddeleyite, zirkelite, quartz and chlorite. Textures: Calcite carbonatite typically has a strong parallel fabric marked by a cleavage and mineral layering (appendix A: figure 12). Calcite forms a granoblastic - polygonal texture and is much finer grained (0.05-0.2 mm) than dolomite carbonatite. Conjugate systems of glide-twins are well developed. Some calcite carbonatites have ovoid calcite "phenocrysts" (1-5 mm) in a fine grained matrix. Apatite forms prismatic, rounded crystals or disk-like flattened aggregates aligned parallel to the fabric. These aggregates are composed of radially textured, long prismatic crystals. The distribution of apatite is inhomogeneous due to the pronounced layering (cm-dm scale). Biotite forms hexagonal, prismatic, equant crystals (0.1-5 mm) enriched in bands where it is associated commonly with magnetite and/or pyrochlore. 61 Pyrochlore displays its octahedral habit with grain sizes ranging from 0.1 to 4 mm (appendix A: figure 34). It is isotropic, rarely slightly anisotropic (metamict ?). Pyrochlore is enriched in narrow bands following apatite-rich zones associated with or without biotite and magnetite. Inclusions of biotite, apatite and calcite are common. Zoned crystals are the rule with a marked break between the core and a narrow rim of higher mean atomic number (appendix A: figures 35, 36, 37). Amphibole of richterite composition is fibrous to acicular (5-200 u in width) aligned parallel to the fabric. Fibrous amphibole forms in fine grained zones of high strain, commonly marked by a brownish dirty colour in thin section due to preferential weathering. Amphibole is more abundant in calcite carbonatites immediately adjacent to "syenite" suggesting a metasomatic origin of most of the amphibole with the "syenite" being the source of silica and alkalies. Accessory minerals include pyrite cubes (0.05-0.3 mm) and baddeleyite associated with zirkelite (only in one sample observed). Alteration: Calcite carbonatite appears to be more resistant to weathering than dolomite carbonatite (cf. stable isotope data, section 5.3.2). Small amounts of chlorite amd secondary quartz may form in zones of higher strain and more intense weathering. Hematite as an oxidation product of magnetite occurs as minute grains in minor amounts. 4.3 RARE - EARTH CARBONATITE DIKES Two dike swarms occur in the contact aureole of the complex (cf. fig. 2): one across the north ridge, characterized by orange, ovoid rare-earth carbonate aggregates and one across the northwest ridge, characterized by abundant barite, quartz and dispersed rare-earth carbonates. Work was focussed on the dikes of the north ridge. 62 4.3.1 RARE-EARTH CARBONATITE DIKES OF THE NORTH RIDGE Petrographic name: Rare-earth carbonate and pyrite-bearing ankerite-carbonatite Physical properties: The rare-earth dikes weather a distinctive dark chocolate-brown colour. The dikes are resistant to weathering, off-white coloured on fresh surfaces with orange to greenish, granular, porous, ovoid rare-earth carbonate aggregates (appendix A: figure 31). Typical are black haloes around partially oxidized pyrite cubes. Density is about 3.2 X103 kg/m3 due to the ankeritic bulk composition. Magnetic susceptibility and radioactivity are very low. Mineral mode: The carbonatite dikes consist of 95 to 97 % manganese ankerite, 3 to 5 % rare-earth carbonates and 0.1 to 0.5 % pyrite. Apatite, barite, potassium feldspar, strontianite and alstonite (?) occur in trace amounts. Textures: Coarse-grained ankerite (1-4 mm) forms an irregular granular texture with commonly sutured grain boundaries. Intergranular mortar zones are abundant. Ankerite shows wavy extinction, but no twinning. Subgrains are locally developed. The rare-earth carbonate assemblages form ovoid or irregular aggregates (2-20 mm) (appendix A: figure 31). Characteristic are replacement textures and porosity due to weathering and defects from polishing. Burbankite is the major primary rare-earth carbonate forming grains up to 2 mm in size. Burbankite shows various stages of alteration: coherent grains with a web of thin veinlets of alteration products (appendix A: figure 30) to fine grained aggregates completely replacing burbankite. Most secondary rare-earth carbonates and other Ca-Ba-Sr carbonates are not distinguishable in thin section due to the small grain size and similar carbonate-like optical properties. One of the replacement minerals forms fibrous, fan-shaped aggregates, but could not be assigned to one of the many phases identified by 63 X-ray or SEM-EDS techniques. 4.3.2 RARE-EARTH CARBONATITE DIKES OF THE NORTHWEST RIDGE Petrographic name: quartz, barite, rare-earth carbonate-bearing ankerite-carbonatite Physical properties: The rare-earth dikes weather a distinctive dark chocolate-brown colour, have a brown tint on fresh surfaces and do not show macroscopically visible rare-earth minerals. Density is approximately 3.2 X103 kg/m3. Magnetic susceptibility is low, but the radioactivity is significantly higher than most carbonatite types due to abundant minute Th-rich phases. Mineral mode; The dikes consist of 85 to 90 % manganese ankerite, 2 to 3 % barite, 3 to 5 % quartz and dispersed, fine grained rare-earth carbonates (3 to 6 %). Textures: Ankerite forms irregular grains, 0.05 to 4 mm in size, with irregular grain boundaries. Mortar zones are common in between larger grains. Abundant parallel twinning is developed. Rare-earth carbonates can not be recognized in thin section due to the carbonate-like optical properties. Barite occurs in the interstices of ankerite bounded by straight, rational ankerite grain boundaries. Barite always shows undulatory to wavey extinction. Quartz with undulatory extinction forms irregular, interstitial aggregates rarely bounded by straight ankerite grain boundaries. Quartz appears to replace ankerite and to a minor extent barite marked by globular carbonate relicts within quartz and sutured grain boundaries. 64 4.4 "SYENITE" Petrographic name: Varies between aegirine- and arfvedsonite-bearing albite-quartz-rock and quartz-bearing albite-aegirine-arfvedsonite-rock. The term "syenite" is used to indicate its magmatic origin and petrographic nature before the metasomatic overprint. Physical properties: The "syenite" is greyish green to dark green and is resistant towards weathering, jointed and extremely hard. Density is approximately 2.8X103 kg/m3. Radioactivity and magnetic susceptibility are near background values. Mineral mode: The mineral content is extremely variable: 30 to 60 % albite, 5 to 50 % quartz, 1 to 10 % arfvedsonite, 3 to 30 % aegirine and accessory calcite, apatite, lorenzenite and rare-earth carbonates. Textures: A great variety of textures is displayed by the different types of "syenite". Although clearly of magmatic origin (cf. section 6.1), igneous textures are not commonly preserved, but are obscured by extensive metasomatism resulting in metamorphic fabrics. Primary igneous textures: Some preserved relict fabrics indicate an equigranular - hypidiomorphic micro-syenite texture with interstitial quartz, short-prismatic magnesio-arfvedsonite and accessory apatite. Lenticular albite shows abundant carlsbad and albite twinning. This primary texture is obscured by extensive overgrowth of fine, prismatic aegirine replacing albite, quartz and partially arfvedsonite. Quartz may recrystallize to form larger, granoblastic grains whereas albite breakes down to fine granular aggregates. Secondary textures: Strongly altered parts of the original syenite are characteristically enriched in quartz relative to albite and show extensive overgrowth of fine aegirine. Quartz is recrystallized and may form a granoblastic texture with fine, prismatic aegirine, 65 granular albite and relict arfvedsonite in zones of extreme quartz enrichment. A possible source for quartz may be the assimilation of quartzite xenoliths as indicated further below. Narrow, monomineralic veinlets of lorenzenite or arfvedsonite may occur crosscutting parts of the "syenite". Globular texture: In one sample abundant ovoid, small globules (0.2 mm) occur (figure 47). They consist of a well defined envelope, when fresh, and inwardly pointing acicular aegirine nucleating at the periphery. Albite and manganese calcite fill the interior volume. The globules appear to be compositionaily uniform. The matrix consists of granoblastic albite and quartz with patchy arfvedsonite, fine, prismatic aegirine and accessory apatite. Compositionaily, the matrix is high in silica and alumina and the globules are low in silica, alumina but high in alkalies, carbonate, iron and manganese. Approximate mineral modes: matrix (80 % albite, 5 % arfvedsonite, 10 % aegirine, 5 % quartz, 0.5 % apatite); globules (45 % aegirine, 40 % calcite, 15 % albite). These globules do certainly not represent any type of secondary vesicle-fillings. They might represent a liquid immiscibility texture between an alkali -carbonate rich liquid and a silica - alumina rich liquid. Whether this is a primary texture or a secondary, metasomatically induced texture (anatexis ?) is uncertain. Xenoliths: In some parts of the "syenite" abundant rounded xenoliths are characteristic and may form as much as 30 % of the rock (figure 20). Two major types of xenoliths occur: sedimentary xenoliths with quartzite being by far the most abundant type and igneous xenoliths, mostly consisting of micro-syenites and some albitites. 66 Figure 20: Quartzite and syenite xenoliths in "syenite" Quartzite Xenoliths: The well rounded inclusions range from millimeters to about 30 centimeters in size and may accumulate in rather large zones of the "syenite" ring, but without a systematic pattern of occurrence. They consist largely of pure, recrystallized quartzites and some feldspathic varieties which contain secondary aegirine. Reaction rims sourround the xenoliths, commonly consisting of a dense, fine grained aegirine-rich layer. Small inclusions of relict quartzite show all stages of absorption. Other types of sedimentary xenoliths, some banded, metamorphosed marls and shales are rare. The quartzite xenoliths were part of the massive basal qurtzites (late Proterozoic - early Cambrian ?) that crop out further to the west towards the Rocky Mountain Trench (Thompson, 1978, 1985). The stratigraphic position of the 67 quartzites is at least 1 km below the Cambrian rocks exposed at the Aley. Igneous xenoliths: Micro-syenite xenoliths are more than 50 times less abundant than quartzite xenoliths and of smaller size (1-8 cm). Reaction rims are well developed and consist of relict xenolithic albite grains and patchy arfvedsonite overgrown by a dense, acicular aegirine web. Fine grained calcite may be accumulated in these narrow rims (1-10 mm). The micro-syenite xenoliths display a well preserved igneous equigranular-hypidiomorphic texture formed by lenticular albite with abundant carlsbad-albite twinning. Interstitial secondary calcite and minor quartz is common. Magnesio - arfvedsonite forms short prismatic, somewhat patchy crystals with frayed edges. Aegirine is rare or absent. Apatite and lorenzenite are common accessory minerals. 4.5 CONTACT AUREOLE Physical properties: The physical properties are variable due to strong, bedding-parallel compositional heterogeneities. The sediments weather a distinctive ochre to brown colour. The pure dolomite and calcite marbles adjacent to the contact weather a cream colour (Cream Dolomite Unit). Radioactivity may range from background readings to highly anomalous intensities. A good correlation exists between radioactivity and apparently strongly affected strata of the sediments. Densities range from 2.6 to 2.8X103 kg/m3 Textures: Sediments within the first 300-600 m are completely recrystallized. Rocks near the intrusion-contact are highly strained, marked by an intense planar fabric and abundant glide-twinning in calcite and dolomite marbles. 68 Metamorphic mineral assemblage: White mica and potassiC feldspar are the only common metamorphic mineral observed in impure marbles, marls and silts. All the samples examined along the northwest ridge profile (out to a distance of 550 m from the contact) showed miner metamorphic white mica. Talc and calc-silicates were sought but not found. Alteration: Immediately adjacent to the contact (10-40 cm) in the Cream Dolomite Unit silicification and growth of (richteritic ?) green amphibole are common. Other signs of mass transfer connected with the intrusion are restricted to the distinct weathering colour of the sediments and minor, narrow carbonate veinlets and the occasional fluorite grain. Carbonate veinlets are restricted to the inner part of the contact aureole (0-100 m). 5. GEOCHEMISTRY The unusual chemical compositions of carbonatites in comparison with average silicate rocks presents analytical problems that are unique to carbonatite rock analysis. Problems related to XRF-analysis together with some solutions and suggestions are addressed in detail in appendix B. 5.1 ROCKS OF THE CARBONATITE COMPLEX 5.1.1 DOLOMITE CARBONATITE Dolomite carbonatite covers about two thirds of the area of the carbonatite complex and is thus the major igneous rock type exposed. The major element composition of dolomite carbonatite from the Aley is characterized by essentially no silica, no alumina, low alkali, but abundant phosphorous. The trace element geochemistry (table 2) may be described as follows: enriched in the incompatible elements LREE, Th, U, Nb, Ta, Zr but with low Ti, Rb, K, Pb; concentrations of siderophile metals (Co, Ni, Mo) that are close to the detection limit; low in sulfur and nearly undetectable chalcophile metals (Cu, Ag, Zn, As, Sb, Bi). A peculiarity in comparison with more common rocks is the extremely high carbon dioxide content of carbonatites, 40 to 43 wt% for "average" dolomite carbonatite (pure dolomite contains 47.73 wt% C02), but no water except traces in pyrochlore and fersmite. 5.1.2 CALCITE CARBONATITE Three analyses from drill core composites (data provided by COMINCO Ltd.) were chosen to represent "average" calcite carbonatite. Compared with dolomite carbonatite the calcite carbonatites are higher in silica, iron, phosphorous and sodium (if amphibole is present). The trace geochemistry (table 2) is similar to dolomite carbonatite (LREE, Y, Zr, Sr, Ba, Rb). 69 70 Dolomite Carbonatite Calcite Carbonatite wt% MR-550 MR-553 MR-552 MR-554 A85-4 A85-5 A85-8 Si02 0.50 0.28 0.52 1.08 3.84 2.17 3.53 Al203 0.26- 0.14 0.16 0.72 0.03 0.02 0.51 Ti02 <0.01 <0.01 0.01 0.12 0.10 0.04 0.08 FeO(tot) 2.95 1.08 1.92 0.76 Fe2Oa 2.24 1.32 13.17 FeO 2.10 0.97 0.51 MnO 0.26 0.87 0.77 0.25 , nd nd nd MgO 17.34 16.68 14.79 18.02 7.71 5.85 2.92 CaO 32.89 34.82 34.29 33.71 41.47 45.69 41.34 Na20 0.63 0.08 bd bd 0.46 0.48 0.18 K20 0.02 0.01 0.02 0.01 0.13 0.05 0.03 p2o5 1.74 1.36 8.69 3.15 5.03 4.60 7.73 S <0.01 0.01 0.01 0.01 0.35 0.21 0.01 LOI 43.52 42.00 40.16 41.96 36.06 38.72 30.20 total 100.0 100.0 100.0 . 100.0 (total) 95.70 93.04 100.25 95.87 99.2 99.9 100.3 ppm Nb (2.9) 490 168 1796 1384 4610 3290 5030 Zr (2.6) 66 465 499 497 559 604 308 Y (3.0) 41 14 69 122 93 97 122 Sr (2.7) 359 4377 4449 457 4630 5281 686 U (8.9) bd 223 19 74 <20 <20 26 Rb (2.6) 4 35 5 2 <20 <20 25 Th (7.3) 128 bd 21 184 106 65 464 Ta (7.8) 18 nd 17 166 <20 <20 59 Ba (13.4) 39 1225 85 33 248 314 308 La (9.6) 307 142 322 355 360 314 669 Ce (16.0) 746 224 909 856 823 708 1318 Nd (6.5) 237 59 310 297 nd nd nd Ce/La 2.4 1.6 2.8 2.4 2.3 2.3 2.0 Ce/Nd 3.2 3.8 2.9 2.9 Table 2: Major element and trace element concentrations of dolomite carbonatite and calcite carbonatite. Analyses of calcite carbonatite by Cominco Ltd. (composites from drill cores, XRF-analyses, major elements on fused disks). Numbers in parentheses are average detection limits for dolomite carbonatite analyses. LOI = loss on ignition, bd = below detection limit, nd = not determined, (total) = measured total including LOI, total = normalized total. For details of analysis see appendix B. 71 5.1.3 RARE-EARTH CARBONATITE DIKES Two geochemically different types of ankeritic rare-earth rich dikes exist: the barium-rich, siliceous dikes of the northwest ridge and the low-silica, barium-poor rare-earth dikes of the north ridge. Compared to dolomite carbonatite they have high concentrations of ferrous iron, manganese and sulfur, but low phosphorous values (table 3). Strontium, barium and total light rare-earth elements may reach major element concentrations. They are depleted in the incompatible elements niobium and tantalum. Cerium is the dominant LREE, followed by neodymium (northwest ridge) or lanthanum (north ridge) and praseodymium. 5.1.4 "SYENITE" Although clearly of igneous origin (cf. section 6.1), the silicate phase of the carbonatite complex displays a variety of textures and its chemistry appears to vary erratically. Four analyses of syenite are presented in table 4. Note that the high alkali content would permit classification of this rock as an alkali-syenite, but the absence of nepheline and presence of modal quartz instead require classifying it as a syenite or quartz-syenite. Its trace element geochemistry is of "diluted" carbonatite character, but with undetectable uranium and thorium contents and higher titanium. 5.2 ROCKS OF THE CONTACT AUREOLE The trace element geochemistry and measurement of radioactivity are the only quantitative indicators of the metasomatic processes that accompanied the intrusion. There is little visible evidence of metasomatism except the odd fluorite grain or minute particle of metal oxide. Yet the characteristic brown to ochre weathering colours of the aureole rocks leave no doubt that metasomatic fluids affected the rocks. The trace element abundances are highly variable as might be expected from the bedding-parallel banded weathering pattern of the rocks and primary 72 Northwest ridge North ridge North ridge wt% MR-503 MR-570 COM Si02 7.30 0.65 0.56 Al203 0.67 0.21 0.49 Ti02 0.04 0.01 0.02 FeO (tot) 10.49 8.41 Fe203 (tot) 5.82 MnO 3.30 4.11 1.58 MgO 7.91 11.29 13.48 CaO 24.59 28.14 27.73 Na20 0.79 1.13 0.10 K20 0.06 0.04 0.02 P2Os 0.09 0.14 0.34 S 1.11 0.06 nd F nd nd 0.88 LOI 33.31 42.55 nd BaO 7.74 0.69 1.37 La203 0.27 0.31 nd Ce2Oa 0.84 0.56 nd Nd203 0.42 0.12 nd total 98.74 98.77 42.39C) ppm Nb (4.8) 29 bd 10 Zr (4.3) 96 583 nd Y (5.0) 96 13 nd Sr (4.5) 699 5546 nd U (10.3) bd 21 nd Rb (3.8) bd bd nd Th (12.6) 839 28 293 La (15.0) 2291 2668 nd Ce (22.1) 7213 4757 nd Nd (9.0) 3584 1020 nd Ce/La 3.1 1.8 Ce/Nd 2.0 4.7 Table 3: Major element and trace element concentrations of rare-earth carbonatite dikes. Analysis of sample COM by Cominco Ltd. (XRF-analysis, major elements on fused disks). LOI = loss on ignition, bd = below detection limit, nd = not determined, (*) = total withot LOI. Numbers in parentheses are detection limits for sample MR-503. For details of analysis see appendix B. 73 wt% MR-316 MR-551 COM-a COM-b Si02 66.36 75.15 53.00 60.17 Al203 4.28 8.30 1.33 6.39 Ti02 0.68 0.41 0.35 1.31 FeO (tot) 12.00 3.88 Fe203 12.91 10.98 MnO 0.27 0.14 0.35 0.45 MgO 2.55 0.87 16.00 3.61 CaO 4.05 2.28 3.50 3.98 NazO 7.79 3.85 7.71 8.72 K20 0.24 3.68 1.15 0.20 P2O5 0.70 0.20 0.68 0.60 S 0.02 0.01 nd nd F nd nd 0.90 0.30 LOI 0.84 1.16 nd nd total 100.0 100.0 (total) 98.86 106.20 97.88 96.71 ppm Nb (3) 71 72 280 10 Zr (3) 267 887 387 nd Y (3) 6 18 21 nd Sr (3) 302 141 671 nd U (9) bd bd <20 nd Rb (3) bd 35 <20 nd Th (7) bd bd <20 12 Ba (13) 1343 184 537 461 La (10) 63 60 234 nd Ce (16) 168 143 110 nd Nd (7) 56 46 nd nd Ce/La 2.7 2.4 2.1 Ce/Nd 3.0 3.1 Table 4: Major element and minor element concentrations of syenite samples. Analyses COM-a and COM-b by Cominco Ltd. (XRF-analyses, major elements on fused disks). Numbers in parentheses are average detection limits for MR-sampI es. LOI = loss on ignition, bd = below detection limit, nd = not determined, (total) = measured total including LOI, total = normalized total. For details of alyses see a ppendix B. 74 compositional differences. Generally, the amount of material metasomatically introduced appears to decrease with distance from the contact (cf. KR-samples, table 5), but the heterogeneity of the sedimentary rocks causes large heterogeneities in their apparent intensity of alteration (cf. MR-samples, table 5). Trace elements noticeably enriched in strongly altered parts of the contact aureole (MR-511, MR-523) include Nb, REE, Th and F (chlorine was not determined). The extent of major element mass transfer is difficult to estimate because of the primary heterogeneity of the rocks. The recrystallized carbonate-rich sedimentary rocks do not provide simple replacement textures, except within 0.5 meters of the syenite. Dolomite marbles (Cream Dolomite Unit) adjacent to the syenite show secondary alkali-amphiboles (richterite ?) and are commonly silicified. The reader may have noticed that the term "fenite" has not been used. Fenite should be reserved for country rock that was affected by alkali-metasomatism (Heinrich, 1966). While there is no doubt that the rocks of the Aley aureole have been affected by metasomatic fluids, the changes are so subtle, and the major element proportions are so little affected, that the name "fenite" may be misleading. 75 Northwest Ridge West Ridge ppm MR-505 MR-506 MR-511 MR-523 KR-18a KR-19 KR-24a KR-27b KR-27c KR-28e Nb 144 183 19 24 <20 <20 193 380 126 379 Zr 50 70 115 41 134 94 42 98 48 242 Y 60 59 29 26 nd nd nd nd nd nd Sr 379 257 115 41 nd nd nd nd nd nd U bd bd bd 10 nd nd nd nd nd nd Rb bd 7 10 8 nd nd nd nd nd nd Th 109 58 bd 9 <20 <20 46 65 39 <20 Ba 41690 2420 503 345 224 299 794 23 74 473 La 13 38 64 36 <20 <20 <20 137 801 317 Ce 73 103 90 bd <20 <20 45 304 1455 638 Nd bd 64 34 bd nd nd nd nd nd nd F nd nd nd nd 160 120 205 960 310 4300 Table 5: Trace elements of selected sedimentary rocks from the contact aureole. KR-sample data from Cominco Ltd. (XRF-analyses on powder pellets), nd = not determined, bd = below detection limit. See text for sample locations and appendix B for details of XRF-analyses. Sample No Unit Distance Sample weight from contact [kg] [m] MR-505 Grey Limestone Unit 367 3.7 MR-506 Grey Limestone Unit 361 4.5 MR-511 Thin Bedded Limestone Unit 215 2.6 MR-523 Cream Dolomite Unit 52 2.4 KR-18a Grey Limestone Unit ca 200 KR-19 Grey Limestone Unit ca 180 KR-24a Thin Bedded Limestone Unit ca 100 KR-27b Thin Bedded Limestone Unit ca 80 KR-27c Thin Bedded Limestone Unit ca 80 KR-28e Cream Dolomite Unit ca 50 Table 6: List of samples and sample locations used in table 5. 76 5.3 ISOTOPE GEOCHEMISTRY 5.3.1 STRONTIUM AND RUBIDIUM Three samples were examined as a quick reconnaissance project. The analyses were done by Krista Scott using the facilities of R.L. Armstrong at the University of British Columbia. Results are summarized in table 7. Sample No. Rock type Sr (ppm) Rb (ppm) Rb/Sr 87Sr/B6Sr MR-550 dol. carb. 362 0.6 0.002 0.70344(4) MR-554 dol. carb. 419 0.9 0.002 0.70482(7) MR-316 syenite 545 0.0 0.000 0.70364(4) Table 7 : Strontium isotope analyses of carbonatite and syenite samples. No in situ decay corrections are necessary due to the negligible rubidium concentrations, dol. carb. = dolomite carbonatite. The variation of 87Sr/86Sr ratios from 0.7035 (MR-316, MR-550) to 0.7048 (MR-554) is far too large to be accounted for by original variations in the magma and reflects effects of alteration or assimilation. A greater sample density is required to constrain observed trends. The interpretation of strontium isotope data would be more rigorous if stable isotope values (oxygen, carbon) were used as an "alteration filter". The low 87Sr/86Sr ratios (0.7035) compare well with data from other carbonatite complexes (Bell & Powell, 1970; Pineau & Allegre, 1972; Bell et al, 1982; Griinenfelder et al, 1986). These authors interpret such low ratios as being indicative of a mantle source depleted in large ion lithophile (LIL) elements in comparison with the bulk earth. On a graph of age versus ^Sr/^Sr two values for 77 the Aley plot between the bulk earth trend and the three billion year old depleted mantle source trend proposed by Bell et al (1982) for some alkaline rocks of Northern Ontario (figure 21). One dolomite carbonatite sample plots above the bulk earth trend and may represent effects of deuteric alteration or analytical difficulties. Note, that in contrast with lead isotope systematics, the 87 Sr/86 Sr ratios are not a sensitive measure of minor crustal contamination beacause of high strontium concentrations (Grunenfelder, 1986). 11 e7Sr/MSr AGE 4.0 3.0 20 1.0 (Qa) 0.0 Figure 21: Age versus 87Sr/8SSr diagram modified after Bell et al (1982) with data points from the Aley carbonatite complex. 5.3.2 OXYGEN AND CARBON ISOTOPE RATIOS Eight samples were analysed by Dr. Karlis Muehlenbachs at the University of Alberta. One sample (MR-552) did not yield enough carbon dioxide for analysis. Table 8 and figure 22 summarise the analytical results. All the 613 C ratios show values typical of primary igneous carbonatites of mantle origin (Taylor et al, 1967; Pineau et al, 1973). The 51BO values are variable, a feature commonly observed in carbonate minerals. An elevated 5180 signature in 78 Sample No. Rock type Mineral analysed 613C 6180 (PDB%o) (SMOW%0) MR-550 dol. carb. dolomite -5.0 15.4 MR-553 dol. carb. dolomite -5.1 7.7 MR-85-5-1 dol. carb. dolomite -4.9 15.1 MR-85-2-J calc. carb. calcite -6.1 8.0 MR-85-5-D calc. carb. calcite -5.9 7.7 MR-570 REE-dike ankerite -4.7 12.0 MR-572 REE-dike ankerite -4.8 10.9 Table 8: 813 C and 618 O ratios for carbonate minerals of some carbonatite samples. PDB = Pee Dee Formation belemnite, SMOW = standard mean ocean water, dol. carb = dolomite carbonatite, calc. carb. = calcite carbonatite, REE-dike = rare-earth carbonatite dike. comparison with mantle values is usually taken to be indicative of post-magmatic recrystallization and deuteric alteration (Taylor et al, 1967). Both processes preferentially affect carbonate minerals (rather than silicates) and oxygen isotope ratios rather than carbon isotope ratios. The extremely fresh samples of calcite carbonatite from drill-cores are not affected at all by alteration. Dolomite carbonatite, almost always with a brownish tint due to weathering, shows 518 O values typical of mantle origin and elevated 618 O values due to recrystallisation and deuteric alteration. Ankerite from carbonatite dikes rich in rare-earths shows somewhat elevated 5180 signatures, but 813C values of mantle character. 79 A 5,3C .a.. -5 • CALCITE o DOLOMITE • ANKERITE 5180 10 12 14 16 Figure 22: 613 C versus 518 O diagram of data listed in table 8. Box outlines the general range of primary igneous carbonatites unaffected by weathering or deuteric and hydrothermal alteration (Taylor et al, 1967). 6. ASPECTS OF PETROCENIES1S An hypothesis for the mode of emplacement should explain the field observations, be consistent with the principles of physics and be the simplest possible solution. Such an hypothesis would describe a possible process but not necessarily the actual sequence of events as they occurred during emplacement of the carbonatite complex. 6.1 EVIDENCE ON SEQUENCE OF EMPLACEMENT Syenite • carbonatite core: The carbonatite core clearly intruded the syenite ring. Extensive veining on all scales of calcite carbonatite and dolomite carbonatite occurs along the entire inner circumference of the syenite ring. Calcite carbonatite - dolomite carbonatite: The field relationship between dolomite carbonatite and calcite carbonatite is ambiguous at some outcrops. Most commonly, however, calcite carbonatite veins are observed within dolomite carbonatite. Dolomite carbonatite veins within calcite carbonatite do occur as well as the occasional diffuse contact. The emplacement of calcite carbonatite dikes and "sweats" might thus be related in time very closely to the dolomite carbonatite emplacement and solidification, but appears to postdate dolomite carbonatite generally. Rare-earth carbonatite dikes: The relative position of the rare-earth carbonatite dikes with respect to syenite and the carbonatite core cannot be deduced from field observations due to the lack of crosscutting relationships. Structural considerations (cf. section 2.3) would be consistent with the dike emplacement either predating or postdating the emplacement of the complex. Petrologic (section 6.4) and geochemical (section 5.1.3) considerations indicate that the dikes are residual differentiates and thus suggest late-stage emplacement of the dikes in a manner similar to mafic dikes associated with many granitoid systems. The relationship of the carbonatite dikes to the timing of wall-rock alteration is not clear: the dikes of the north ridge appear to be unaffected but the dikes of the 80 81 northwest ridge show silicification which might or might not be related to the formation of the contact aureole. Lamprophyric dikes: The lamprophyric dikes within the contact aureole are clearly affected by the fluids that formed the aureole. Crosscutting relationships with the carbonatite complex or the syenite ring were not observed. The youngest sedimentary unit crosscut by lamprophyres is the Lower Dolomite-Shale Unit (Road River Croup, late Ordovician ?). Ospika Pipe: There are no crosscutting relationships between the diatreme and rocks of the carbonatite complex. The Ospika Pipe is similar in age to the carbonatite (cf. section 1.3). It is not clear whether the pipe is affected by the formation of the contact aureole. The massive host unit (Skoki Dolomite) is not very susceptible to fluids and thus betrays commonly no evidence of penetrating fluids. 6.2 TEMPERATURE DISTRIBUTION AROUND THE CARBONATITE COMPLEX Three different approaches were taken in order to deduce temperature distributions within the contact aureole: calcite-dolomite thermometry, comparison of metamorphic phase assemblages with calculated phase diagrams and calculated temperature distributions around a cooling intrusion based on a simple model. None of the methods by themseleves give satisfactory answers but the three methods combined allow some important conclusions. Calcite-dolomite thermometry: Microprobe analyses of coexisting calcite and dolomite in samples at various distances from the contact show very low and variable solid solution of MgC03 in calcite (table 9). Temperatures calculated with the geothermometer formula of Rice (1977) range from 241°C to 345°C with no apparent dependence on the distance from the intrusion contact. 82 Sample No EMS-No Distance from contact MgO FeO MnO xMgC03 T°C MR-513 PROF-3 149m 1.15 1.21 1.41 0.0115 345 MR-10 PROF-1 40m 0.88 0.10 0.06 0.0088 320 MR-10 PROF-2 40m 0.32 0.10 0.12 0.0032 241 MR-10 PROF-2 40m 0.59 0.18 0.18 0.0059 286 MR-10 PROF-2 40m 0.89 0.20 0.18 0.0089 321 Table 9: Composition of calcite (mol%) coexisting with dolomite and calculated temperatures based on the formula by Rice (1977): LogK>XMgC03 = -1690-T[°K] + 0.795 The extrapolation towards lower temperatures than experimentally constrained (Harker & Turtle, 1955; Graf & Goldsmith, 1955, 1858; Goldsmith & Newton, 1969) may result in large errors. The heterogeneity of the MgC03 content of calcite within the same probe section reflects the difficulty of attaining equilibrium at low temperatures. Corrections that account for FeC03 and MnC03 contents compared to the the pure system are expected to be in the order of 20 to 50 6C (Bickle & Powell, 1977). Metamorphic phase assemblages and calculated phase diagrams: The contact aureole consists of metamorphic carbonate rocks but lacks talc and calc-silicates such as tremolite, diopside and forsterite. The only metamorphic mineral besides potassium feldspar is phlogopite that occurs in impure marbles, metamorphosed marls and siitstones as an accessory mineral. Phlogopite formed in rocks next to the carbonatite complex as well as in sediments up to a distance of at least 500 meters along the northwest ridge. A pressure - temperature and a temperature - fluid composition diagram were calculated with the program package "PT-SYSTEM" (UBC). The pressure at the 83 TEMPERATURE (DEG C) Figure 23: Pressure - temperature diagram of the system CaO - MgO - Si02 -COz. Do = dolomite, Cc = calcite, Qz = quartz, Di = diopside, Fo = forsterite, Wo = wollastonite, Pe = periclase time of emplacement may be estimated from the approximate sedimentary overburden. Thompson's (1985) stratigraphic compilation suggests an overlying stratigraphic section of 5 to 8 km which would have produced pressures between 1.5 and 2.5 kbar. The large uncertanity is a result of the position of the Aley complex near the Paleozoic shelf/off-shelf boundary. Two extreme cases are represented by the calculated phase diagrams: the P-T-diagram represents metamorphism with pure excess C02 present, whereas the T-X-diagram assumes the fluid pressure to be equal to the total pressure. 84 Figure 23 shows the phase relationships in the presence of pure, dry COa. Caic-silicates, in this case, are not expected to form below 500°C at a pressure of 2 kbar. Note, however, that the occurrence of phlogopite indicates the presence of at least some steam or a H20-C02 fluid. Figure 24 shows the phase relationships as a function of fluid composition (Xco2)- ,n tne presence of CO 2-rich fluids talc and calc-silicates may not form at temperatures below 500°C. At a high H20 partial pressure, however, talc may form at temperatures below 400°C, if the fluid composition is not buffered along the phlogopite producing reaction boundary towards higher Xrjo2 compositions. Note that the indifferent crossover of the phlogopite-forming reaction with the tremolite-forming reaction may not be demonstrable in the rocks due to the increased stability of phlogopite of natural compositions. These compositional effects will shift the equilibrium towards lower temperatures. Deduced temperatures of around 500°C are consistent with the observed phase assemblages only if one assumes unreasonable water-poor fluids. Temperatures around 400°C or below seem most consistent with predicted phase relationships. 85 X (C02) AT P = 2000.00 Equilibria calculated: I Do + 2Qz = Di + 2COz 3 Di + 3Do = 2Fo + 4Cc + 2C02 4 6Do + 2Ksp + 2HzO = Phi + 6Cc + 6C02 6 Do + Qz + H20 =Tc +3Cc + 3Co2 7 8Qz + 5Do + H20 = Tr + 3Cc + 7C02 8 Tr + 3Cc + 2Qz = 5Di + 3COz + H20 9 Tr + 3Cc = 4Di + Do + COz + H2 II Tr + 11Do = Fo + 5Cc + 5COz 12 5Tc + 6Cc + 4Qz = 3Tr + 6C02 + 2H20 13 2Tc + 3Cc = Tr + Do + COz + H2 14 3Tr + 5Cc = 11Di + 2Fo + 5C02 + 3HzO Figure 24: Temperature - fluid composition diagram of the system CaO - MgO -Si02 - HzO - C02. Cc = calcite, Do = dolomite, Tr = tremolite, Tc = talc, Qz = quartz, Di = diopside, Fo = forsterite, Phi = phlogopite, Ksp = potassium feldspar 86 Calculated transient temperature distributions around a cooling igneous body A simple conductive cooling model of an igneous body (cf. appendix C) allows the calculation of transient temperature distributions for the margins of an igneous body. Field observations conf inn a two-stage intrusive event (cf. section 6.1.1) with an earlier syenite emplacement and a later concentric carbonatite intrusion. The temperature effect of the carbonatite on the contact aureole is thus screened by the syenite ring. The model is therefore applied to a syenite body of the dimensions of the Aley complex. Figure 25 is a t-T-x section (time - temperature - distance) calculated with physical properties of syenite (Turcotte & Schubert, 1982; Best, 1981) (cf. appendix C for boundary conditions). The calculated maximum temperature at the contact is 524°C. The same model applied to a carbonatite dike (rock data from Treiman & Schedl, 1983; Le Bas, 1981, Turcotte & Schubert, 1982) predicts a temperature at the contact of about 400°C. This much lower temperature is a combined effect of the lower solidification temperature and the lower heat of fusion compared to silicate melts. If the model were capable of accounting for convective heat transfer wilhin the magma chamber, the faster cooling rate would result in higher temperatures within the wallrock. Convective heat transfer within the wallrock would result in a higher rate of heating of distal portions of the aureole and thus lower the temperatures at the contact. Calculated temperature distributions around a syenite intrusion are predicted to be high enough to expect calc-silicate assemblages in impure marbles. The discrepancies in the predicted temperature distributions and the temperatures inferred from field observations must be explained by a different mode of emplacement than one on which the thermal model is based. 87 Figure 25: t-T-x diagram for a syenite intrusion 88 6.3 SEQUENCE OF CRYSTALLIZATION IN CARBONATITE MAGMAS Textural evidence: Dolomite carbonatite: Apatite appears to have crystallized early, on the basis of its euhedral habit in undeformed parts of dolomite carbonatite. Pyrochlore that was replaced by fersmite at a later stage is believed to be an early phase on the liquidus, on the basis of flowbanding textures and its idiomorphic habit. Dolomite crystallization is difficult to unravel due to the ease with which carbonates recrystallize. If zonation patterns could be successfully studied by cathode luminescence, Nomarski contrast interferometry or laser interferometry some insight might be gained into phenocryst - matrix relationships. Calcite carbonatite: Flow banding textures indicate that pyrochlore, apatite, magnetite and biotite appeared relatively early on the liquidus. Some samples that appear to contain calcite-phenocrysts in a fine-grained calcite matrix may indicate a large temperature (time) interval of calcite crystallization. The role of the sodic-calcic amphiboles is unclear. Fibrous amphibole in zones of higher strain appear to have formed metasomatically at a late stage. Fresh, prismatic crystals could represent primary magmatic amphibole. Rare-earth carbonatite dikes: The interstitial occurrence of rare-earth carbonates and barite indicate that these phases have crystallized late. Quartz in the dikes of the northwest ridge is probably a replacement mineral (cf.section 4.4.2). Constraints from experimental studies: Simplified carbonatite systems have been investigated experimentally since the late fifties. Table 10 lists experimental studies in carbonatite systems. References on liquid immiscibility, fluid inclusions, physical properties of carbonatite magmas and some studies on related silicate systems are included. 89 System / Topic Author Year CaC03-H20 Wyllie & Tuttle 1959 CaO-C02-H20 Wyllie & Tuttle 1960 Wyllie & Boettcher 1969 Koster van Croos 1982 CaC03-MgC03 Irving & Wyllie 1975 Byrnes & Wyllie 1981 CaC03-Ca(OH)2-CaS Helz & Wyllie 1979 CaO-MgO-C02-H20 Wyllie & Biggar 1966 Wyllie 1985 Fanelli et al i.p. Na2-K2-CaC03 Cooper et al 1975 Ca(OH) 2 -CaCO 3 -Ca 3 (PO 4) 2 -H 2 O Biggar 1969 CaO-CaF 2 -P2 O 5 -CO 2 -H 2 O Wyllie & Biggar 1966 BaS04-CaC03-CaF2 Kuellmer et al 1966 CaF2-Ca(OH)2-CaC03 Cittins & Tuttle 1964 Rare-earth carbonatite systems Chai 1978 Kutty et al 1978 Jones & Wyllie 1983a Jones & Wyllie 1983b Jones & Wyllie 1986 Summary papers Tuttle & Cittins 1966 Bowen 1945 Koster van Croos 1975 Le Bas 1977 Le Bas 1981 - Wyllie & Jones 1985 Si02-H20-C02 Boettcher 1984 CaO-MgO-Si02-C02 Wyllie & Huang 1975 Wyllie & Huang 1976 NaAlSi 3 O 8 -CaCO 3 -Ca(OH) 2-H20 Watkinson & Wyllie 1969 MgSi04-Si02-H20-C02 Eggler 1975 CaSi03-H20 Buckner et al 1960 Na 2 O-CaO-Al 2 O 3 -MgO-SiO 2 -CO 2 Eggler 1978 NaAlSi 3 O 8 -NaAlSiO ft -NaFeSi 2 O 6 Nolan 1966 CO 2 in melts Mysen et al 1976 Eggler 1978 Eggler & Rosenhauer 1978 Boettcher 1984 Physical properties Treiman & Schedl 1983 Fluid inclusions. Romanchev 1972 Rankin & Le Bas 1974 Rankin 1975 Nesbitt & Kelly 1977 90 Liquid immiscibility Creig Koster van Croos & Wyllie Koster van Groos & Wyllie Philpotts & Hodgson Koster van Groos & Wyllie Gittins Koster van Groos Wendlandt & Harrison Hamilton et al Freestone & Hamilton Bogoch & Magaritz 1928 1966 1968a 1968 1973 1973 1975 1979 1979 1980 1983 Table 10: List of references on experimental topics related to carbonatites The studies in simplified carbonatite systems provide insight into the possible sequence of crystallization and approximate solidus and liquidus temperatures of various peritectic and eutectic phase assemblages. Phases that appear early on the liquidus surface in the experimental systems include calcite, dolomite, apatite and periclase. Late crystallizing phases include portlandite, barite and rare-earth carbonates. Earlier experiments indicated the omnipresence of a calcite - portlandite eutectic which has never been corroborated by field observations. More recent experiments (Fanelli et al, in press; Wyllie & Jones, 1985) demonstrate the possibility of precipitation of calcite or dolomite or both over a large range of temperatures without ending in a eutectic with portlandite. The experiments also indicate the possibility that carbonatite melts may persist to low temperatures compared to silicate systems. These indications include: coprecipitation of calcite, dolomite and periclase from melts at 650°C at 2 kbar (Fanelli et al, in press; Wyllie & Jones, 1985); a eutectic in the system CaC03 -Ca(OH)2 - CaF2 - Ca3(POa)2 at 575°C at 1 kbar was reported (Wyllie & Biggar, 1966; Wyllie & Jones, 1985); addition of La(OH)3 to the eutectic composition of the preceding system resulted in a minimum of the solidus at 18% La(OH)3 and 91 543°C at 1 kbar. 6.4 GENETIC RELATIONSHIPS Although "true" carbonatites do show geochemical signatures indicative of mantle origin, they are thought by many to be derivative magrnas and not primary melts from the mantle (Tuttle & Cittins, 1966; Wyllie & Huang, 1975; Le Bas, 1977; Wyllie & Jones, 1985). Experimental phase equilibrium studies demonstrate possible differentiation paths from high temperature silicate melts to low temperature carbonatite melts (cf. references in table 10 under silicate systems; Le Bas, 1977, 1981; Wyllie & Jones, 1985). Liquid immiscibility might occur in more alkali-rich melts (cf. references in table 10) to produce carbonatite melts. At the present stage, geochemical data on the Aley complex and thermo-chemical data on carbonatite-alkaline systems do not allow quantitative modeling of systems closely related to carbonatite magma genesis. The following points are made in an attempt to relate the rocks of the Aley complex to each other. This will at the most contribute towards understanding of possible processes towards the end of magma ascent and will not have any bearing on processes occurring in the mantle source region. One of the major problems is the unknown quantity and composition of fluid phases present at various stages of magma diversification. Dolomite carbonatite • rare-earth carbonatite dikes: Major element and trace element geochemistry suggest a possible relationship by fractional crystallization of a dolomite carbonatite-iike parent magma towards a small amount of residual melt represented by the rare-earth carbonatite dikes. Fractionation of apatite, magnetite, dolomite and pyrochlore is consistent with the expected crystallization of phases appearing early on the liquidus. By this process the residual melt will be depleted in phosphate, magnesium, niobium and tantalum and enriched in iron (ankerite), sulfur and other incompatible elements (Sr, Ba, Mn). 92 Enrichment of rare-earth elements will occur if the amount of apatite crystallization is not capable of depleting the parent melt. Note, that the mineral-melt partition coefficient for REE in apatite is in favour of apatite only at low concentrations of REE in the melt. Thorium would generally be expected to be removed from the melt with pyrochlore and phosphate fractionation. The high thorium contents of the dikes of the northwest ridge appears to be unusual. The difference in concentration and state of occurrence of sulfur in the two type of dikes might be explained by a difference in oxygen fugacities: the presence of barite (sulfate) in the dikes of the northwest ridge suggest a higher oxygen fugacity than the sulfide-bearing dikes of the north ridge. This might also explain the two different rare-earth assemblages: if barium crystallizes in sulfate-form, bastnaesite-group carbonates (barium-free, northwest ridge) are more likely to form instead of burbankite and other barian rare-earth carbonates (north ridge). Quantitative testing of the "residual melt" hypothesis would involve mass balance calculation as a first step. The major difficulty would arise in the adequate modelling of the composition of fractionating a dolomite - ankerite - kutnahorite solid solution as a function of composition. Crystal-liquid partition coefficients are not yet known well enough to further constrain the hypothesis. Thermodynamic constraints appear to be even further in the future. Dolomite carbonatite - calcite carbonatite: Field evidence indicates that dolomite carbonatite and calcite carbonatite magma must have been physically separate liquids emplaced at different times (cf. section 6.1.1). The exposed relative proportions of dolomite carbonatite and calcite carbonatite (97 % and 2-3 % respectively) generally do not necessarily reflect the relative proportions of the respective magmas. The apparently later injecting calcite carbonatite sweats do not have the geochemical characteristics of a residual carbonatite melt and thus, are not an equivalent to pegmatites in granitoid systems. The large proportion of dolomite 93 carbonatite compared to calcite carbonatite is unusual compared to most carbonatite complexes (Heinrich, 1966; Le Bas, 1977): commonly calcite carbonatite forms the bulk of the core carbonatite followed by dolomitic, ankeritic or sideritic and finally rare-earth rich carbonatites. If vertical zonation is assumed (Le Bas, 1977, 1981) the relative proportions of carbonatite types is merely an effect of the level exposed. It is difficult to relate dolomite carbonatite and calcite carbonatite by fractionation, because calcite carbonatite would have to be produced as an early fractionating phase (Wyllie, 1985; Le Bas, 1981; Fanelli et al, in press). The major reason is that the calcite-magnetite dominated crystallization has to change rather abruptly to dolomite crystallization, while such a path is not supported by experimental data (Wyllie & Jones, 1985; Fanelli et al, in press). Better knowledge of the liquidus surfaces in the relevant system would greatly improve our ability to interpret field observations. Calcite carbonatite and dolomite carbonatite in the Aley complex cannot easily be related by a parent-daughter relationship. They probably had a common magma source, but followed different paths of diversification. Carbonatite -. Syenite: Field relationships, trace element geochemistry and initial ^Sr/^Sr ratios suggest a genetic relationship between syenite and carbonatite. Geochemical and experimental data are too scarce to delineate a specific differentiation path, possibly from a high temperature silicate melt to a low temperature carbonatite melt or, possibly a relationship by liquid immiscibility (Le Bas, 1977, 1981; Hamilton & Freestone, 1980; Wyllie & Jones, 1985). 6.5 PHYSICAL PROPERTIES OF CARBONATITE MAGMAS Carbonatite liquids are nearly unpolymerized ionic liquids with physical and thermal properties that are entirely different from those of silicate melts. Data on the physical properties of carbonatite liquids is limited (summarized in Treiman & 94 Schedl, 1983). Compared to polymerized silicate melts, carbonatite magmas have very low viscosities (=5«10~6 kg/m/s), low heats of fusion ( = 50-150»103 J/kg) and very high thermal diffusivities ( = 4«10~5 J/m/s/K) (Treiman & Schedl, 1983). Heats of fusion for calcite calculated from liquidus relationships in binary systems vary between 15* 103 and 30*103 J/mol (Flood et al, 1949; Bradly, 1962). 6.6 HYPOTHETICAL PROCESSES IN CARBONATITE MAGMA CHAMBERS On the basis of many assumptions and on analogies with studies in systems with comparable geometries, Treiman & Schedl (1983) deduced characteristic parameters (Prandtl number, Rayleigh. number, Reynolds number etc.) for a carbonatite magma chamber of cylindrical geometry and 1 km diameter. They arrive at the following conclusions: rapid crystal settling velocities are to be expected even for small grains (0.2-0.9 m/s for a grain of 1 mm diameter); convection driven by horizontal temperature gradients is expected to be turbulent because of the high Rayleigh numbers predicted dO^-IO20); estimated growth rates onto the walls of the magma chamber are in the order of cm per year and allow considerable thickness of carbonatite growth in situ. The likelihood of turbulent magma motion has some further important consequences: crystals may stay in suspension even if the net upward magma velocities are much smaller than calculated crystal settling velocities turbulence is characterized by high rates of heat, mass and momentum transfer that will enhance the reactivity of a carbonatite magma with silicate rocks although driven largely by temperature gradients, turbulence does not imply rapid equilibration of a magma chamber. The large range of scales at which turbulence operates will result in a large range of scale of transient heterogeneities within a magma chamber laterally persistent horizontal stratification due to crystal settling is not to be expected 95 irregularities of the walls of a magma chamber will act as "back-eddies" and may cause irregularly shaped volumes of crystal accumulation. 7. CONCLUSIONS Stable isotope data and initial strontium isotope ratios suggest a mantle origin for the rocks of the Aley carbonatite complex. The lack of knowledge of the parent magma composition makes it difficult to gain insight into processes in the mantle source region. Similarly, available data do not yet allow discrimination between a process of progressive differentiation and a process of liquid immiscibility, both leading from an alkali carbonatite magma to a low temperature carbonatite melt. Field observations suggest the following order of emplacement: syenite / dolomite carbonatite / calcite carbonatite / rare-earth carbonatite dikes. The lamprophyric dikes and the Ospika diatreme appear to be closely related in time. Their petrogenetic relationship was not studied. The petrogenetic relationship among the rocks of the complex is not established. The rare-earth dikes appear to be residual liquids (enriched in Sr, Ba, LREE, sulfide or sulfate) of a dolomite carbonatite-like parent magma. The syenite is geochemically and texturally extremely heterogeneous but it clearly is an igneous rock as indicated by field relationships and relict micro-syenite textures. The primary alkali-rich phases are magnesio-arfvedsonite and possibly aegirine. The strong metasomatic overprint marked by metamorphic textures and the extensive growth of aegirine indicate interaction with large volumes of an alkali-rich fluid phase The contact aureole is characterized by the presence of brownish alteration colours, locally elevated radioactivity and the absence of calc-silicates. It is possible that a highly mobile fluid phase penetrated the rocks of the contact aureole along bedding. The fluids that altered the syenite and those that altered the host rocks might be of the same parentage and the syenite may have acted as a "filter" or chemical trap for alkalies. 96 97 Temperatures in the wallrock probably did not exceed 400°C and are not consistent with temperatures predicted by a cooling model of a solidifying magma body. The formation of an annular, cylindrical ductile shear zone around the complex and the fabrics within the carbonatite core suggest doming as the major mechanism of emplacment at the level exposed. Simple gravitational diapirism in the solid state is physically not possible because of the higher density of the carbonatite rocks compared to the host rocks. Solid syenite in a plastic condition intruded by carbonatite as a driving force may have been a possible mechanism for doming. Quartzite xenoliths from stratigraphic levels not much more than 1 km below the host rocks indicate intrusion of syenite into a high crustal level. 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(1975) Peridotite, kimberlite, and carbonatite explained in the system CaO-MgO-Si02-C02, Geology, 3, 621-624. WYLLIE P.J., and HUANG W.L. . (1976) Carbonatite and melting reactions in the system CaO-MgO-Si02-C02 at mantle pressures with geophysical and petrological applications, Contrib. Mineral. Petrol., 54, 79-107. APPENDIX A: MINERALOGY AND MINERAL CHEMISTRY Appendix A contains electron microprobe analyses of minerals, back-scattered electron images (SEM-EDS), photo micrographs, autoradiographs, block diagrams with optical properties, composition diagrams and energy-dispersive patterns (SEM-EDS) for most minerals studied. The tables are listed in numerical order at the beginning of appendix A followed by the figures. The EDS-patterns are appended and structured in the same sequence as in chapter 3. 105 106 Electron Microprobe Analyses All the electron microprobe analyses were done using the ARL-SEMQ in the Department of Geology at the University of Calgary. The instrument was run at 15 keV and 0.15 nA measured on brass. The electron beam was focused for silicate analyses. A split beam was used for carbonate analyses. Data reduction was done off-line using ZAF correction procedures. Compositions of standards used are listed in table 11. The standard sets used for individual mineral groups are shown in table 12. Mineral group analysed Standard set used Carbonates 283,94,113,86,267,120,119 Amphiboles / Pyroxenes 48,296,22,23 Feldspars 58,90,113,83,181,91 Table 11: Standard sets used for electron microprobe analysis. For number codes of standards see legend of table 12 Composition of Standards used for Electron Microprobe Analysis No. Si02 Ti02 Al 203 FeO MnO MgO CaO Na20 K20 BaQ SrO Cr203 H20 F C02 22 23 48 58 83 55.74 49.01 40.45 55.60 49.42 0.05 4.90 0.32 14.50 28.30 23.57 7.09 44.99 10.96 14.73 0.37 0.10 18.55 3. 17 12.78 1.04 0.08 10.36 10.40 0.08 0.04 2.56 5.70 0.02 0. 32 0. 28 2.04 0 . 86 1 .00 2 .04 0.29 1 .67 6.23 18 .43 86 90 91 64.39 53.94 O. 26 18.58 0.66 0.30 0.03 2.93 61.11 0.04 1 . 14 14 . 92 0.82 0.07 16.93 24.55 0.24 0.01 0.01 0.21 0.03 94 113 119 68.80 19.40 0.02 0.02 21.86 3.97 0.04 30.41 1 1 .80 65.28 0.02 120 181 186 267 283 42.14 56.88 39.68 0.94 . 12.09 8.82 33.65 58.81 19.05 2.86 0.63 0.20 8.67 12.10 11 .56 16.83 24.65 56.03 1.63 5.37 0.93 2 . 36 296 40.30 1 . 32 14 . 30 1 .68 0.03 26.40 0.07 0.43 10. 10 3 . 10 38 . 50 30. 75 47.73 38.08 43.97 22 Mn - Cummingtonite 23 Grunerite 48 Hornblende 58 An(50) Glass 83 Hyalophane 86 Rhodochrosite 90 Orthoclase 91 Clino - Pyroxene 94 Strontianite 113 Albite 119 Dolomite 120 Siderite 181 Amphibole 186 Diopside - Jadeite 267 Tanzanite 283 Iceland - Spar 296 Phlogopite Table 12: Composition of standards used for electron microprobe analysis given in weight percent. Standard numbers refer to the University of Calgary electron microprobe standard catalogue. o ^4 EMS ANALYSES OF DOLOMITE FROM CARBONATITE MR-85-5-I WEIGHT PERCENT No. 5-1-1 5-1-2 5-1-3 5-1-4 5-1-5 5-1-6 5-1-7 5-1-8 5-1-9 5-1-10 5-1-11 average CaO 31.61 31.95 32.10 32.06 32.12 32.29 31.92 31.14 32.77 32.92 32.31 32.11 SrO 0.0 0.0 0.0 0.0 0.01 0.0 0.0 0.0 0.0 0.0 0.0 0.00 MnO 0.34 0.35 0.35 0.34 0.31 0.30 0.31 0.35 0.32 0.33 0.35 0.33 FeO 3.59 3.67 3.69 3.51 3.54 3.44 3.24 3.35 3.37 3.60 3.48 3.50 MgO 16.91 17.26 17.30 17.21 17.18 16.87 17.26 17.72 16.52 16.35 16.79 17.03 C02 *) 45.68 46.38 46.56 46.31 46.34 46.04 46.07 46.04 46.01 46.09 46.04 46.14 total 98.12 99.61 100.00 99.42 99.51 98.93 98.79 98.59 98.99 99.29 98.97 99.11 MOLAR PROPORTIONS CaC03 54.30 54.06 54.10 54.33 54.40 55.03 54.37 53.07 55.90 56.04 55.08 54.61 SrC03 0.0 0.0 0.0 0.0 0.01 0.0 0.0 0.0 O.O 0.0 0.0 0.00 MnC03 0.46 0.46 0.47 0.45 0.41 0.40 0.42 0.47 0.43 0.44 0.46 0.44 FeC03 4.81 4.85- 4.85 4.64 4.68 4.58 4.31 4.45 4.49 4.78 4.63 4.64 MgC03 40.43 40.62 40.58 40.58 40.49 39.99 40.90 42.01 39.19 38.74 39.82 40.31 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00' 100.00 100.00 100.00 100.00 100.00 Table 13: EMS-analyses of dolomite from dolomite carbonatite MR-85-5-I. *) = C02 calculated EMS ANALYSES OF ANKERITE FROM REE-DIKE MR-572A WEIGHT PERCENT No. 572A-1 572A-2 572A-3 572A-4 572A-5 572A-6 572A-7 572A-8 average CaO 28.80 29.10 29.22 29.13 28.93 28.83 28.89 28.92 28.98 SrO 0.37 0.16 0.26 0.20 0.18 0.26 0.25 0.28 0.24 MnO 3.64 3.82 3.81 3.45 3.57 3.65 3.78 3.52 3.66 FeO 7.74 6.24 5.31 7.68 7.64 8.04 8.59 7.13 7.29 MgO 13.40 14.68 15.26 13.94 14.04 13.77 13.53 14.34 14.12 C02 •) 44.39 45.12 45.31 45.00 45.00 44.96 45.16 45.02 45.00 total 98.33 99.11 99.17 99.40 99.36 99.52 100.21 99.21 99.29 MOLAR PROPORTIONS CaC03 50.92 50.61 50.61 50.79 50.45 50.33 50.21 50.41 50.54 SrC03 0.35 0.15 0.24 0.19 0.17 0.24 0.24 0.27 0.23 MnC03 5.08 5.25 5.22 4.76 4.93 5.04 5.19 4.86 5.04 FeC03 10.68 8.47 7.18 10.45 10.40 10.95 11.65 9.70 9.93 MgC03 32.96 35.52 36.76 33.81 34.05 33.44 32.72 34.77 34.26 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.OO 100.00 Table 14: EMS-analyses of ankerite from rare-earth carbonatite dike MR-572A. *) = C02 calculated SEM ANALYSES OF CALCITE FROM CARBONATITE MR-85-2-J WEIGHT PERCENT No. d-1 J-2 d-3 d-4 J-5 J-6 J-7 J-8 J-9 d-10 J-11 J-12 average CaO 52.71 52.64 53.36 53.86 54.36 52.98 52.88 52.84 53.26 52.92 53.08 53.02 53.16 SrO 0.75 0.83 0.72 0.82 0.87 0.88 . 0.84 0.84 0.75 0.72 0.86 0.69 0.80 MnO 0.19 0.20 0.18 0.26 0.20 0.21 0.20 0.24 0.16 0.18 0.24 0.21 0.21 FeO 0.13 0.11 0.16 0.16 0.11 0.15 0.13 0.18 0.12 0.12 0.15 0.12 0.14 MgO 0.55 0.59 0.69 0.65 0.42 0.63. 0.58 0.59 0.44 0.50 0.46 0.50 0.55 C02 *) 42.48 42.51 43.15 43.59 43.67 42.86 42.70 42.72 42.77 42.58 42.76 42.65 42.87 total 96.81 96.89 98.27 99.34 99.63 97.71 97.33 97.40 97.49 97.02 97.55 97.19 97.72 MOLAR PROPORTIONS CaC03 97.37 97.18 97.05 96.97 97.68 97.01 97.20 97.06 97.73 97.55 97.42 97.57 97.32 SrC03 0.74 0.83 0.71 0.80 0.85 0.87 0.84 0.83 0.74 0.72 0.86 0.69 0.79 MnC03 0.28 0.30 0.26 0.37 0.28 0.31 0.29 0.35 0.23 0.26 0.35 0.31 0.30 FeC03 0.19 0.16 0.23 0.23 0.16 0.21 0.18 0.26 0.18 0.17 0.21 0.17 0.20 MgC03 1.41 1.53 1.75 1.63 1.04 1.60 1.49 1.50 1.12 1.29 1.17 1.27 1.40 total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.OO 100.00 100.00 100.00 Table 15: EMS-analyses of calcite from calcite carbonatite MR-85-2-J. *) = C02 calculated EMS ANALYSES OF ALBITE FROM SYENITE MR-533 WEIGHT PERCENT No. 533-1 533-2 533-3 533-4 533-5 533-6 533-7 533-8 533-9 533-10 533-11 533-12 average CaO 0.0 0.19 0.08 0.02 0.23 0.03 0.01 0.01 0.02 0.01 0.0 0.00 0.05 K20 0.05 0.14 0.05 0.05 0.05 0.05 0.07 0.08 0.06 0.06 0.05 0.05 0.06 Na20 11.67 11.28 11.28 11.63 11.83 11.60 11.58 10.80 11.61 11.65 11.54 11.66 11.51 BaO 0.06 0.09 0.03 0.0 0.02 0.0 0.02 0.0 0.0 0.0 0.0 0.0 0.02 Si02 69.24 68.27 68.23 68.47 68.79 68.77 67.76 68.91 68.34 68.50 68.01 68.01 68.44 A1203 19.00 18.90 19.36 18.98 19.11 19.51 19.25 19.14 19.40 19.23 19.04 19.17 19.17 FeO 0.26 0.14 0.05 0.25 0.22 0.15 0.33 0.27 0.21 0.29 0.41 0.28 0.24 MgO 0.0 0.30 0.0 0.01 0.0 0.0 0.0 0.0 0.0 0.0 0.0 O.O 0.03 total 100.29 99.32 99.08 99.40 100.25 100.11 99.03 99.21 99.63 99.74 99.04 99.17 99.52 MOLAR PROPORTIONS NORMALIZED TO 8.0 OXYGENS Ca 0.0 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.0 0.00 0.00 K 0.00 0.01 0.00 0.00 0.00 0.00 0.00 O.OO 0.00 0.00 O.OO 0.00 0.00 Na 0.99 0.96 0.96 0.99 1.00 0.98 0.99 0.92 0.99 0.99 0.99 1.00 0.98 Ba 0.00 0.00 0.00 0.0 0.00 0.0 0.00 0.0 0.0 0.0 0.0 0.0 0.00 Si 3.02 3.00 3.00 3.01 3.00 3.00 2.99 3.02 3.00 3.00 3.00 3.00 3.00 Al 0.98 0.98 1.00 0.98 0.98 1.00 1.00 0.99 1.00 0.99 0.99 1.00 0.99 Fe 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 Mg 0.0 0.02 0.0 0.00 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.00 0 8 . 00 8 . OO 8 .00 8 . 00 8 . OO 8 . OO 8 . 00 8 . OO 8 : OO 8 . OO 8 . 00 8 . OO 8 . OO total 100.00 100.00 100.00 100.00 100.00 100.00 100.OO 100.00 100.00 100.OO 100.00 100.00 100.00 Table 16: EMS-analyses of albite from syenite MR-533 EMS ANALYSES OF ARFVEDSONITE FROM SYENITE MR-551 WEIGHT PERCENT No . 551 - 1 551 I-2 551 -3 551 I-4 551-5 551 I-6 533-7 551-8 551 I-9 551 I- 10 551-1 1 551-12 average Si02 54 . 78 55. 01 54. 73 54 . 82 54 .62 55. 14 54 . ,42 54 . 60 54 . 43 54 . 39 54. 37 54. 66 54. .66 Ti02 0. 19 0. 19 0. 21 0. 18 0 . 19 0. 23 0. 20 0. 23 0. 21 0. 23 0. .21 0. 21 0 .21 A 1203 0. 1 1 0. 08 0. 07 0. 09 0 . 10 0. 11 0. .21 0. 23 0. 15 0. 15 0. . 1 1 0. 13 0. , 13 FeO 10. 63 10. 79 10. 73 9. 75 9 .20 10. 33 12. .00 12 . 64 12 . 09 1 1 . 85 10. 96 1 1 . 00 1 1 , .00 MnO 0. 95 0. 98 0. 93 0. 85 0 95 0. 88 0. .92 0. 93 0. 96 0. 93 1 . 00 0. 94 0. .94 MgO 16. 82 16. 35 16. 59 16. 99 17 .55 17 . 06 15. .46 15. 26 15. 44 15. 69 16 . 22 16 . 31 16 . .31 CaO 2 . 87 2 . 45 2. 54 3. 24 3 .73 3 . 25 1 .63 1 . 23 1 . 65 1 . 89 2. 50 2. 45 2 .45 Na20 8. 22 8. 39 8 . 33 7 . 91 7 .86 7 . 81 8 .78 8. 77 8. 79 8 . 59 8. 29 8 . 34 8 . .34 K20 1 . 76 1 . 90 1 . 84 1 . 74 1 .70 1 . 66 1 . .80 1 . 94 1 . 87 1 . 73 1 . 69 1,. 78 1 . .78 BaO 0. 0 0. 01 0. 0 0. 0 0 .01 0. 01 0 .05 0. 0 0. 00 0. 0 0. 03 0. 01 0. .01 F 2 . 55 2 . 59 2 . 41 2 . 42 2 .45 2 . 19 2. . 36 2 . 45 2 . 36 2 . 41 2 . 74 2 . 45 2 .45 H20 * ) 0. 70 0. 70 0. 70 0. 70 0 .70 0. 70 0 . 70 0. 70 0. 70 0. 70 0. 70 0. 74 0. , 70 total 99 . 57 99 . 44 99 . 08 98 . 70 99 .07 99. 38 98 .54 98. 98 98 . 67 98 . 58 98 . .81 99. 02 98 . 99 MOLAR PROPORTIONS NORMALIZED i TO 24 .0 OXYGENS (O.OH, F) Si 8 . 05 8 . 10 8. 08 8. 09 8 .03 8 . 09 8. . 12 8 . 12 8 . 12 8 . 10 8 . .06 8 . 08 8 .09 Ti 0. 02 0. 02 0. 02 0. 02 0 .02 0. 03 0 .02 0. 03 0. 02 0. 03 0. 02 0. 02 0 .02 Al 0. 02 0. 01 0. 01 0. 02 0 .02 0. 02 0 .04 • 0. 04 0. 03 0. 03 0. 02 0. 02 0. .02 Fe 1 . 31 1 . 33 1 . 32 1 . 20 1 . 13 1 . 27 1 . .50 1 . 57 1 . 51 1 . 48 1 . 36 1 . 36 1 . .36 Mn 0. 12 0. 12 0. 12 0. 1 1 0 . 12 0. 1 1 0. . 12 0. 12 O. 12 0. 12 0. 13 0. 12 0. . 12 Mg 3 . 68 3 . 59 3 . 65 3 . 74 3 .85 3 . 73 3. 44 3 . 38 3. 43 3. 48 3 . 58 3 . 59 3 . .60 Ca 0. 45 0. 39 0. 40 0. 51 0 .59 0. 51 0. .26 0. 20 0. 26 0. 30 0. 40 0. 39 0. . 39 Na 2 . 34 2 . 39 2 . 38 2 . 26 2 .24 2 . 22 2 . .54 2 . 53 2 . 54 2 . 48 2 . 38 2 . 39 2 . 39 K 0. 33 0. 36 0. 35 0. 33 0 .32 0. 31 0. 34 0. 37 0. 35 0. 33 0. 32 0. 34 0, .34 Ba 0. 0 0. 00 0. 0 0. 0 0 .00 0. 00 0. 00 0. 0 0. 00 0. 0 0. 00 0. 00 0. .00 F 1 . 18 1 . 21 1 . 13 1 . 13 1 . 14 1 . 02 1 . 12 1 . 15 1 . 1 1 1 . 14 1 . 28 1 . 14 1 . 15 OH 0. 69 0. 69 0. 69 0. 69 0 .69 0. 69 0. 70 0. 69 0. 70 0. 70 0. 69 0. 73 0. .69 0 22 . 13 22 . 1 1 22 . 18 22 . 18 22 . 17 22 . 30 22 . 19 22. 15 22 . 19 22 . 17 22 . 02 22. 13 22 . 16 Table 17: EMS-analyses of magnesio-arfvedsonite from syenite MR-551 *) = estimated amount of water added for data reduction . EMS ANALYSES OF ARFVEDSONITE FROM SYENITE MR-533 WEIGHT PERCENT No. 533-1 533-2 533-3 533-4 533-5 533-6 533-7 533-8 average Si02 53 . 54 54. .63 54. 51 54 . .35 53 .68 55 .49 54 . 50 54. . 39 54 . . 39 Ti02 1 . 28 0. .75 1 . 52 0. .77 0 .76 1 , .09 . 1 .54 1 , , 10 1 . . 10 A1203 1 . 60 0. ,43 0. 56 0. .72 1 .53 1 . . 59 0, .22 0. .95 0. .95 FeO 9 . 57 12. ,04 1 1 . 79 1 1 . .50 10 . 19 1 1 . .25 12 .87 1 1 . .32 1 1 .32 MnO 0. .54 0. .65 0. 76 0. . 37 0 .75 0. .64 0 . 75 0. .64 0. .64 MgO 16. 68 14, .90 15. ,07 15. .44 16 .32 14, .38 14 . 13 15. .27 15. .27 CaO 2 . 84 0. ,69 0. 77 0. . 72 3 .76 0 .57 0 .40 1 , . 39 1 . 39 Na20 8 . 77 9 .53 9 . .50 9 .35- 8 .43 9 .72 9 .28 9. . 22 9. . 22 K20 1 . .03 1 .74 1 . 76 1 . .85 0 .83 1 .62 1 .88 1 , , 53 1 . 53 BaO 0. 04 0. .00 0. 06 O. .03 0 .03 0, .0 0. .01 0. .02 0. .02 F 2 . 36 2 . 14 2. 26 2. .25 2 .04 1 , , 78 1 . 74 2. .08 2 . 08 H20 * ) 1 • 00 1 .00 1 , ,00 1 .00 1 .00 1 .00 1 .00 1 . .00 1 . .00 total 99 . . 26 98 .50 99 , 55 98. .35 99 . 32 99, . 12 98 . 33 98 . .92 98 92 MOLAR PROPORTIONS NORMALIZED i TO 24 .0 OXYGENS (O.OH.F) Si 7 . .81 8 . 10 8. 01 8. .05 7 .86 8. . 12 8 . 13 8 . .01 8 . .01 Ti 0. 14 0 .08 0. 17 0. .09 0 .08 0 . 12 0. . 17 0. 12 O. 12 Al 0 28 0 .07 0. 10 0. . 13 0 .26 0. 27 0 .04 O. . 16 0. 16 Fe 1 . . 17 1 .49 1 . 45 1 , ,42 1 .25 1 . . 38 1 . .61 1 . . 39 1 . 39 Mn 0. .07 0 .08 0. 09 0. 05 0 .09 0, .08 0. .09 0. 08 0. 08 Mg 3. 63 3. ,30 3. 30 3. 41 3 .56 3. 14 3. 14 3. 35 3 . 35 Ca 0. . 44 0 . 1 1 0, 12 0, , 1 1 O .59 0. .09 0 .06 0. .22 0. 22 Na 2 . 48 2 . 74 2 , 7 1 2 . .68 2 .39 2 . 76 2 .68 2 . 63 2 . 63 K 0. 19 0 .33 0. 33 0. .35 0 . 16 0 .30 0. . 36 0. .29 0. 29 Ba 0. 00 0 .00 0. 00 0. 00 0 .00 0. .0 0. .00 0. .00 0. 00 F 1. 09 1 .00 1 . 05 1 . 06 0 .94 d. .82 0 .82 0. .97 0. .97 OH 0. 97 0 .99 0. 98 0. .99 0 .98 0. 98 1 .00 0. .98 0. 98 0 21 . 94 22 .01 21 . 97 21 . .96 22 .08 22. .20 22. . 18 22. 05 22 . 05 Table 18: EMS-analyses of magnesio-arfvedsonite from syenite MR-551 *) = estimated amount of water added for data reduction EMS ANALYSES OF AEGIRINE FROM SYENITE MR-533 WEIGHT PERCENT No. 533-10 533-11 533-12 533-13 533-14 533-15 533-16 533-17 533-18 533-19 533-20 average Si02 53 . 00 52 . 64 53. 04 52. 68 52 , ,77 52 . .49 51 . ,83 52. .51 52 . .65 52 . .92 53 . , 34 52 . .71 T102 3 . 99 7 . 14 7 . 92 6. 42 5, ,47 4 . . 13 4 . .33 5. 48 6 . . 19 6 .51 6 . . 38 5 . .82 A1203 0. 78 0. 38 0. 41 0. 48 0. .65 0. 82 0. 52 0. .43 0. .42 0. .40 0. 43 0 . 52 Fe203 24 . .71 21 . .75 20. 67 22. ,73 24, .30 25 .05 23. . 76 23. .92 23 .24 22 .82 22 . 69 23 . 24 MnO 0 .42 0. .42 0. 60 0. .42 0 . 19 0 .22 0. 40 0, . 2 1 0 39 0 .42 0 39 0 . 37 MgO 2. .45 2. 84 2 . 80 2 ,50 2 .23 2 .31 2. .52 2 . 35 2 .58 2 . 73 2 . 73 2 .55 CaO 2. .62 1 . .05 0. ,90 1 , ,26 1 .77 2 .00 1 . .70 0 . 50 0 .69 O .64 0. 61 1 . 25 Na20 12 . .50 13. ,75 13. .76 13. .61 13 . 1 1 12 .94 13 .52 14 . .08 13 . .71 13 . . 74 13 . 83 13 .51 K20 0, ,00 0. ,01 0. .0 0. ,00 0 .00 0 .01 0, .01 0. .01 0. .00 0. .00 0. 01 0. 01 BaO 0 .00 0. .02 0. .02 0. .00 0 .06 0 .01 0, .00 0. .08 O. .04 O. .05 0. 03 0. 03 F 0. .0 0. .02 0. .0 0. ,0 0 .04 0, .0 0 .0 0. .03 0. .00 0. 04 0. 0 0. 01 total 100 .48 100. .03 100. . 12 100, . 12 100 .60 99, .97 98 . .59 99 . .60 99 . .92 100. . 27 100. 43 100. 01 MOLAR PROPORTIONS NORMALIZED TO 6 .0 OXYGENS Si 1 . .98 1 . .97 1 . 98 1 , .97 1 .97 1 .98 1 . 98 1 . .98 1 . .98 1. .98 1 . 99 1 . .98 Ti 0. . 1 1 0. .20 0, .22 0, . 18 0 . 15 0, . 12 0. . 12 0. . 16 0. . 17 0. . 18 0. . 18 0. . 16 Al 0. .03 0 .02 0. .02 0, .02 0 .03 0, .04 o. .02 0, .02. 0. .02 0. .02 0. .02 0. 02 Fe 0, .70 0. .61 0. 58 0, .64 0 68 0, .71 0. 68 0, 68 0. .66 0. .64 0. .64 0. .66 Mn 0 .01 0. .01 0. .02 0. .01 0, .01 0, .01 0. .01 0, .01 0. .01 o. .01 O. .01 0. 01 Mg 0 . 14 0, . 16 0. . 16 0. 14 0, . 12 0, . 13 0. . 14 0. . 13 0. . 14 0. . 15 O. 15 0. 14 Ca 0 . 1 1 0. .04 0. 04 0. 05 0, .07 0. .08 0. .07 0, .02 0. .03 0. .03 0. .02 0. 05 Na 0. .91 1. .00 0. .99 0. 99 0 .95 0. .95 1. OO 1 . .03 1 . .00 1. OO 1 00 0. 98 K 0 .00 0 .00 0. .0 0, OO 0 .00 O .00 0. OO O. OO 0 .00 0 OO 0 OO 0 OO Ba 0, .00 0 .00 0. .00 0. OO 0 .00 0 .00 0. .00 0 .00 0 .00 0 .00 0 .00 0. .00 F 0 .0 0 .00 0. 0 0. .0 0 .00 0 .0 0. .0 0, .00 0 .00 0 .01 O 0 0 .00 0 6 .00 6 .00 6. .00 6. .00 6. .00 6. ,00 6 . .00 6 .00 6 .00 5 .99 6. .00 6. .00 Table 19: EMS analyses of aegirine from syenite MR-533. All Fe treated as ferrous iron 115 Figure 26: Back scattered electron image of REE-carbonate assemblage (MR-143B). anc = ancylite; apa = apatite; bar = barite; bur = burbankite; gal = galena; ? = Ca> >Sr>Ba,Ce,La; black areas = holes 116 Figure 27: Back scattered electron image of REE-carbonate assemblage (MR-143B). anc = ancylite; apa = apatite; ank = ankerite; bur = burbankite; str = strontianite; black areas = holes 117 Figure 28: Back scattered electron image of REE-carbonate assemblage (MR-572A). anc = ancylite; als = alstonite; ank = ankerite; ar-st = aragonite -strontianite solid solution; bar = barite; black areas = holes 118 Figure 29: Back scattered electron image of REE-carbonate assemblage (MR-572A). anc = ancylite; als = alstonite; ank = ankerite; cor = cordylite; ? = Ca>>Sr>Ba,Ce,La; ?? = Sr,Ca,Ba; black areas = holes 119 Figure 31: Photograph of rare-earth aggregates (predominantly burbankite) in rare-earth carbonatite dike of the north ridge. 120 Figure 32: Back-scattered electron image of dolomite (dark) with rutile lamellae (bright needles). Medium grey phase is apatite. Very bright spots are monazite and thorianite (MR-710) Figure 33: Photomicrograph of twinned baddeleyite 121 Figure 35: Back-scattered electron image of zoned pyrochlore grain (MR-85-5-D) 122 Figure 37: Autoradiograph of zoned pyrochlore. 123 Figure 38: Habit of primary fersmite (after P.C. LeCouteur, Cominco Ltd.) 124 Figure 39: Back-scattered electron image of fersmite (bright phase) replacing euhedral pyrochlore Figure 40: Detail of figure 39. Radiating textured phase is a Nb-oxide (possibly fersmite with a different composition) 125 Figure 41: Photomicrograph of micro-syenite xenolith with anomalous blue arfvedsonite (crossed nicols) (MR-301I) 126 glaucophane eckermannHe magnesio-arfvedsonlte ferro-glaucophane riebeckHe F6L,Mg arfvedsonite Na Na, FeJ Fe* SI, OM (OH) 2 Figure 42: Composition space for sodic amphiboles (classification after Hawthorne (1981)) pale i greenish grey\ /£ >/<!> Figure 43: Block diagram with optical properties for magnesio 533) - arfvedsonite (MR 127 ferrl-winchite richterite magneslo-arfvedaontte ferro-ferri-winchite riebeckite Fef.Mg arfvedsonite Na Na2 Fe* Fe' Si, Q22 (OH)t Figure 44: Composition space for sodic-calcic amphiboles (classification after Hawthorne (1981)) colourless to light green colourless to 1 i light brown-orange a X colourless to light green -Y=b Figure 45: Block diagram with optical properties for richterite (MR-398) 128 Figure 47: Photomicrograph (plane polarized light) of syenite with globular texture. Globule contains acicular aegirine (green), albite and calcite (high relief) EDS-271 (MR-85-5-I) dolomite dolomite carbonatite CA MG FE i < 8.32KEU XES 18.56KEU> EDS-100 (MR-572A) dolomite rare-earth carb. dike FE UN < 8.64KEU XES 18.88KEU> EDS-228 (MR-85-5-J) calcite calcite carbonatite CA 130 EDS-24 (MR-143B) strontianite rare-earth carb. dike SR BA CA SR < 8.32KEU XES 29.88KEV> EDS-136 (MR-572A) alstonite rare-eart carb. dike < t.28KEUXbS 6.48KEU> EDS-131 (MR-572A) aragonite-strontianite ss rare-earth carb. dike CA SR BA 131 EDS-112 (MR-572A) Sr-Ca-Ba Carbonate rare-earth carb. dike < 1.28KEU XES 6.48KEU> EDS-21 (MR-143B) burbankite rare-earth carb. dike < 8.64KEU XES 21.12KEU> EDS-139 (MR-572A) ancylite rare-earth carb. dike |REE < 888KEUXES29.48KEU> EDS-115 (MR-572A) cordylite EDS-8 (MR-312) huanghoite BA,LA,CE EDS-123 (MR-572A) Ce-Ba-La-Ca carbonate 132 rare-earth carb. dike rare-earth dolomite carb. rare-earth carb. dike EDS-212 (MR-503) Ca-La-Nd carbonate rare-earth carb. dike < 8.32KEU XE3 18.56KEM> EDS-242 (MR-500) LREE carbonate contact aureole CE PR NO CA llllilllilHl < 2 56KEV XES LA mi IBL1Q MM ? . 68KEU> EDS-238 (MR-85-2-J) Ca-Sr-Ba-Ce carbonate calcite carbonatite < 1.44KEU XE8 S.56KEU> 134 EDS-19 (MR-143B) apatite rare-earth carb. dike CA REE < 8.64KEU XES 18.88KEV> . l.-MKE. ..E„ o.56KEU> EDS-227 (MR-85-2-J) apatite calcite carbonatite CA < 8.64KE',' XES t*.*8KEU> EDS-79 (MR-417) monazite dolomite carbonatite CE P LA CA EDS-2 (MR-710) monazite dolomite carbonatite < 8.64KEU XES 18.88KE'J> EDS-15 (MR-710) cheralite dolomite carbonatite < 8.43KEU XES18.72KEU> EDS-12 (MR-395II) rutile dolomite carbonatite TI 1 L: NB CA I, FE < 8.&9KEU XES 18.24KE'J> 136 EDS-180 (MR-365) magnetite calcite carbonatite FE < 8.64KEU XE3 18.88KEv> EDS-172 (MR-317) magnetite calcite carbonatite FE < 9.64KEU XES 1B.88KEU> EDS-165 (MR-310) baddeleyite calcite carbonatite ZR 137 EDS-224 (MR-85-2-J) pyrochlore (rim) calcite carbonatite NB A < 8.64KEU XES 21.12KEV> < 9.64KEU XES 18 . 88KEU> EDS-225 (MR-85-2-J) pyrochlore (core) calcite carbonatite EDS-278 (MR-85-5-D) pyrochlore (rim) calcite carbonatite NB CA 138 EDS-277 (MR-85-5-d) pyrochlore (core) calcite carbonatite EDS-267 (MR-85-5-1) fersmite dolomite carbonatite NB CA TH | TI < 8.32KEU XES 18.56KEU> EDS-70 (MR-417) fersmite dolomite carbonatite 139 EDS-7 (MR-710) columbite dolomite carbonatite NB FE < 8.64KEU XES NB NB 21 . 12KEU> < 9.64KEU XES EDS-151 (MR-310) zirkelite calcite carbonatite < 1.44KEU XES 21.92KEU> < 1.44KEU XES 6.56KEV> EDS-72 (MR-417) Ta-Ca zirconate-niobate dolomite carbonatite TA K9 NB ZR I TH 4B !R CA CA TI FE TA TH NB NB TA U ZR ZR TI FE TA TA TA EDS-50 (MR-5331) albite SI NA < 9.32KEU XES 5.44KEU> EDS-259 (MR-3011) alkali feldspar < 8.32KEU XES 18.56KEU> EDS-81 (MR-417) chlorite I SI FE I syenite syenite dolomite carbonatite 141 EDS-77 (MR-412E) biotite Ospika diatreme < 8-32KEU XES18.56KEU> EDS-223 (MR-85-2-J) biotite (rim) calcite carbonatite < 8.64KEU XES 10 . 83KE'J> EDS-222 (MR-85-2-J) biotite calcite carbonatite .SI IK AL i MG FE 142 EDS-54 (MR-533) magnesio-arfvedsonite syenite FE SI < 8.32KEU XES 18 . 56KE'U> EDS-95 (MR-316) magnesio-arfvedsonite syenite FE SI 1 CA HA K TI MH j < 8 64KEU XES 18.88KEU> EDS-11 (MR-535) richterite calcite carbonatite CA AL I MG HA FE EDS-68 (MR-533) aegirine syenite MG NA SI CA TI FE < 8.32KEU XES 18.56KEU> EDS-88 (MR-316) aegirine syenite FE 31 CA NA | TI < 8 . 64KEU' ^XES*^^" 18.88KEU> EDS-255 (MR-301I) lorenzenite syenite SI TI NA bi 9.32KE'J XES 18 . 56KEU> EDS-78 (MR-417) thorite dolomite carbonatite I TH U TA NB | TH < 8.96KEU XES TH 21 . 44KEV> EDS-201 (MR-524) cerite contact aureole < 8.32KE" XEi 1* 5*KEU> EDS-3 (MR-412H) Cr-diopside Ospika diatreme SI CA AL HG FE CR 145 EDS-4 (MR-412B) augite Ospika diatreme EDS-211 (MR-503) barite rare-earth carb. dike APPENDIX B: X-RAY FLUORESCENCE ANALYSES CAUTIONARY NOTES There are more pitfalls in the XRF-analyses of carbonatites than one might expect. The unusual chemical composition and physical properties of carbonatite samples produce a number of unavoidable problems which make X-ray analysis tedious: Carbonatite samples are tough to mill, produce a large amount of dust and stick tenaciously to the walls of any mill. One should start with plenty of sample to produce fused disks because the loss on ignition may be as high as 45 wt%. The various metal oxides commonly present in carbonatites do not fuse easily and any slag may disturb the surface being analysed. Non-silicate glasses tend to crack upon cooling. Some "major" elements (Si, Al, K) may be minor elements in carbonatites and vice versa (P, Ba, Sr, REE) which can lead to unnoticed overlap of fluorescence peaks if "standard" procedures are followed. Available standards are directed towards the analysis of silicate rocks and cover too small a range of concentrations (major elements and trace elements). Existing data reduction programs may not be flexible enough to handle carbonatite compositions. FLUORESCENCE PEAK OVERLAPS Table 20 lists all the possible overlaps pertinent to carbonatite rock analysis. It is necessary to scan the 20-range of interest in order to decide whether corrections must be performed. On automated equipment correction pellets should 146 147 be run in any case, or correction factors might be used during data reduction instead. CONSIDERATIONS FOR CARBONATITE ROCK ANALYSIS The following considerations must be included in setting up routine procedures for carbonatite rock analysis. 1. Spiked standards based on a carbonate matrix (Ca, Mg, Fe, P) must be prepared for a wide range of compositions. 2. Correction pellets are needed to resolve the possible peak overlaps (cf. table 20). 3. The major elements of low atomic number (Al and lighter) are best analyzed on fused disks. 4. Carbonatite samples need long fusion times in a furnace and disks must be cooled very slowly on a heated casting dish to avoid cracking. 5. Data reduction programs for major elements for calculation of mass attenuation coefficients must be flexible to handle different sets of major elements, ie. a subset of Si, Al, Ti, Fe, Mn, Mg, Ca, Na, K, P, S, Sr, Ba, REE, Nb, C, H, O. 6. Peak positions for background readings must be determined carefully. 7. Well-characterized standards of natural carbonatite would be desirable. SAMPLE PREPARATION In this study, samples were cleaned, crushed and split in the field camp using a standard jaw crusher to obtain grain sizes smaller than 10 mm in two subsequent runs. Splits were further processed at the University of British Columbia using a tungsten-carbide mill with grinding times betwen 40 and 200 seconds. 148 Element Line Order Intensity 26 Comments P K<* 1 , 2 1 150 89.56° Ca K01,3 2 15 89.96° discrimination possible Mg Ka1,2 1 150 45.17° Ca Ka1f2 3 3 46.08° discrimination possible Ti Ka,r2 1 150 86.14° Ba La, 1 100 87.17° only if Ba high and Ti low Pr La! 1 100 75.42° La L0, 1 50 75.28° correction pellet Ba La, 1 100 87.17° Pr Ll 1 2 87.49° only if Ba low and LREE high Ti Ka!f2 1 150 86.14° discrimination possible V (Cr) Ka1,2 1 150 76.94° Ti 20 77.27° correction pellets Ba L03 1 6 77.36° Cr-V not possible if Ba high Nb Ka1,2 1 150 21.40° Y K/3, 1 16 21.20° only if Y high U L<32 1 20 21.60° only if U high Zr Ka,, 2 1 150 22.55° Sr K01 1 16 22.42° correction pellets Sr K03 1 8 22.44° correction pellets Th L0a 1 4 22.70° only if Th high Th L/3, 1 20 22.73° only if Th high Y Ka1f2 1 150 23.80° Rb Kj31 1 16 23.75° only if Rb low Rb Ka, f2 1 150 26.62° U La 2 1 10 26.49° only if U high and Rb present Table 20: List of possible Peak overlaps. Elements to be analyzed are printed bold, interfering elements are in light print. Intensities are comparative within the same line series only. Samples were split repeatedly to fill 50 ml glass vials. The final grinding was done in an automated agate mortar under acetone. Powder pellets were prepared using 5 g of sample with polyvinyl alcohol as a binder mantled by boric acid. Boric acid might react with carbonate samples if they contain too much binding liquid. 149 Table 21 lists all the samples processed with the bulk sample mass and the masses of splits during grinding stages. X-RAY FLUORESCENCE ANALYSIS The analyses were done with a Phillips PW 1410 X-ray spectrometer. Warm up time was determined to be approximately 2 hours and samples were run in one batch for the individual groups of elements to be measured with a particular X-ray tube. Standards were run before and after the unknowns and sometimes in between. Standard sample "G-2" (Abbey, 1980) was run as a monitor with every group of four samples for major element analysis. Peak positions were checked periodically and adjusted. Systematically drifting conditions were always observed, probably due to temperature dependent changes in the geometry of the equipement and some analyzing crystals (ie. PDP crystal). Table 22 lists machine settings, peak and background positions of the elements measured. DATA REDUCTION Existing data reduction programs did not allow convenient changes to handle some carbonatite compositions. Therefore FORTRAN-77 routines were developed to calculate mass attenuation coefficients (MAC) and concentrations of unknowns. Counting and regression statistics were neglected (except detection limits) because regressions could often be based only on very few standards. The need for interpolation and extrapolation required a close and careful control of data handling. Regression lines defined by the standards were plotted and forced through the origin of the "corrected counts" and "concentration" axis. The slopes of these regression lines were used by the routines to calculate major and minor element concentrations. Mass attenuation coefficients for the unknowns were calculated iteratively with an average MAC as a starting value until convergence was achieved (4 to 5 iterations). 150 Sample No. Rock type Bulk sample [kg] Crushed split Ground split MR-550 dol. carb. 10.3 1/16 1/4 MR-552 dol. carb. 4.5 1/8 1/4 MR-553 dol. carb. 12.1 1/16 1/4 MR-554 dol. carb. 5.4 1/16 1/2 MR-570 REE-dike 3.2 1/8 1/2 MR-503 REE-dike 4.5 1/8 1/4 MR-551 Syenite 6.0 1/16 1/2 MR-316 Syenite 10.6 1/8 1/8 MR-505 Sediment 3.7 1/8 1/4 MR-506 Sediment 4.5 1/8 1/4 MR-511 Sediment 2.6 1/8 1/2 MR-523 sedimrnt 2.4 1/4 1/4 Table 21: List of samples processed, dol. carb. = dolomite carbonatite. Element Target 20 peak 20 back Counting Analysing Counters Colli kV/mA measured position ground position time (peak / crystal mator background) Nb Mo 21.39° -2.99° 20/20 LiF(200) F + S fine 50/40 Zr Mo 22.54° 20/20 LiF(200) F + S fine 50/40 Y Mo 23.79° + 0.61° 20/20 LiF(200) F + S fine 50/40 Sr Mo 25.16° 20/20 LiF(200) F + S fine 50/40 U Mo 26.17° 20/20 LiF(200) F + S fine 50/40 Rb Mo 26.63° 20/20 LiF(200) F + S fine 50/40 Th Mo 27.49° + 1.31° 20/20 LiF(200) F + S fine 50/40 Ce Mo 71.66° -0.73° 100/100 LiF(200) F+S fine 60/50 Nd Mo 72.14° 100/100 LiF(200) F + S fine 60/50 Pr Mo 75.37° -1.17° 100/100 LiF(200) F + S fine 60/50 La Mo 82.95° + 1.55° 100/100 LiF(200) F + S fine 60/50 Ba Mo 87.22° + 5.00° 20/20 LiF(200) F fine 60/40 Ti Mo 86.20° 20/20 LiF(200) F fine 60/40 Cr Mo 69.43° -0.98° 100/40 LiF(200) F + S fine 60/40 Table 22: List of machine settings for XRF analysis for minor and major elements. MASS ATTENUATUIN COEFFICIENTS ABSORBER c 0 NA MG AL SI P S K CA TI CR MN FE SR ZR BA CE ND LA B NA 1918. 4033. 539. 804. 1054 . 1363. 1768. 2178 . 3843. 4657. 6218. 7935. 8931 . 9986 . 3559. 4370. 5560. 6344 . 6344. 6344. 1054 MG 1 153. 2424 . 5520. 475. 625. 811. 1055. 1303 . 2312. 2801 . 3741 . 4774. 5372. 6007 . 2194 . 2693 . 5657 . 5945 . 5945. 5945. 600. AL 724 . 1522 . 3466. 4340. 388. 504. 658 . 814 . 1453. 1760. 2351 . 3000. 3376. 3775 . 1409 . 1730. 5867 . 6562 . 6562 . 6562. 358 . SI 471 . 990. 2255. 2824. 3473. 325. 425. 528. 946. 1 146. 1531 . 1953. 2198. 2458 . 937 . 1 150. 3899. 4361 . 4361 . 4361 . 222. P 302 . 663. 1510. 1890. 2325. 2815 . 283. 352. 634 . 768 . 1025. 1308 . 1472 . 1647 . 3685 . 785. 2662 . 2977 . 2977 . 2977. 143. S 199. 458 . 1042 . 1305. 1604 . 1943 . 2322 . 242. 438. 530. 708. 903. 1017. 1137 . 3467 . 3030. 1871 . 2093. 2093. 2093. 94 .6 K 65.0 157 . 388. 486. 597. 723. 864 . 1021 . 163. 198 . 264 . 337. 379. 802. 1292. 1506. 731 . 818. 818. 818. 31.6 CA 46.5 113. 289. 361 . 444 . 538. 643 . 760. 1 185. 147 . 196 . 251 . 282. 316. 962. 1121. 552. 617 . 617. 617. 22 .8 TI 25.0 61 .4 166 . 209. 257 . 311. 372 . 439 . 685 . 782 . 114 . 145 . 163 . 183. 557 . 649. 328. 367 . 367 . 367 . 12.4 V 18 . 7 46 . 3 126. 162. 199. 241 . 288 . 340. 530. 606. 88.2 112. 127 . 142 . 432 . 503 . 257 . 288. 288. 288. 9 . 36 CR 14 . 2 35 . 3 96.4 127 . 156. 189. 226. 267 . 416. 175 . 607. 882 . 99.2 111. 338 . 394 . 676. 228 . 228. 228. 7. 15 MN 10.9 27 . 2 74 . 7 100. 123. 150. 179. 211. 329 . 376 . 481 . 69.8 78.6 87 .9 268. 312 . 718. 608 . 608. 608. 5.51 FE 8.47 21.2 58 . 5 80.2 94.5 117. 143. 169. 263. 300. 384 . 481 . 62 .8 70.2 214. 249. 632. 640. 640. 640. 4 . 30 RB 0.94 2 . 25 6 . 49 8 . 66 10.7 13.4 16.6 20.2 34 . 1 40.0 51 .O 63 . 7 70.7 78.2 28.6 33 . 3 89.5 98 . 7 98.7 98.7 O. 53 SR 0.83 1 .90 5.49 7 .34 9.09 11.4 14 . 1 17.2 29 . 1 34 . 1 43.5 54.3 60.3 66.7 24.6 28.6 77.2 85. 1 85. 1 85. 1 0.46 Y 0.74 1.61 4.67 6.25 7.74 9.72 12.0 14.7 24.8 29.2 37.3 46.5 51.7 57 . 1 21.2 24.7 66.9 73.7 73.7 73.7 0.40 ZR 0.66 1 . 37 3.99 5.34 6.62 8 . 32 10. 3 12.6 21.3 25. 1 32.0 40.0 44.4 49 . 1 18 . 3 21 .4 58 . 1 64 .0 64 .0 64 .0 0. 38 NB 0. 59 1 . 17 3.42 4.58 5.68 7 . 14 8.84 10.8 18.4 21.7 27.6 34.5 38.3 42.3 1 12. 18.5 50.7 55 .8 55.8 55.8 0.36 BA 25 . 7 63 . 2 171 . 214. 263. 319. 381 . 451 . 702 . 802. 117. 149. 167 . 187 . 571 . 665. 336. 376. 376. 376. 12.8 LA 22 . 7 55 . 9 151 . 192 . 236. 286 . 342 . 403. 629. 718. 104 . 133. 150. 168 . 511. 596. 302. 338 . 338. 338. 11.3 CE 20. 1 50.0 134 . 172. 212. 256 . 306 . 362 . 564 . 644 . 93.7 120. 135. 150. 459. 535. 273. 305. 305 . 305. 10.0 PR 17.8 43.9 120. 155 . 190. 230. 275 . 325 . 507 . 578. 740. 107 . 121 . 135. 412. 480. 246. 275. 275. 275. 8.89 ND 15.8 39. 1 107 . 139 . 171 . 207 . 248 . 293. 456 . 521 . 667 . 96.8 109. 122 . 371 . 433 . 223. 249. 249. 249. 7 .92 TA 4.01 10. 2 28.5 37.7 46.4 57.7 70.8 85.8 136. 155 . 199. 249. 276. 306 . 111. 129. 333. 367. 367 . 367 . 2 .07 TH 0.95 2.47 7.11 9.50 11.7 14 . 7 18.2 22 . 1 37.3 43.5 55.7 69.6 77.2 85.4 31.1 36 . 3 97.2 107 . 107. 107. 0.57 U 0.90 2.13 6.15 8.22 10. 2 12.8 15.8 19 . 2 32.4 38.0 48 . 5 60.6 67.2 74.3 27.3 33.9 85.4 94 . 2 94.2 94.2 0.50 Table 23: Mass attenuation coefficients for various wavelengths and absorbing elements (Leroux & Tinh, 1977) MAJOR ELEMENT CONCENTRATIONS OF STANDARDS (wt %) SI02 TI02 AL203 FE203 MNO MGO CAO NA20 K20 H20 C02 P205 F S CR203 SRO ZR02 CE203 AGV1 59.61 1.06 17.19 6.78 0.10 1.52 4.94 4.32 2.92 0.78 0.02 0.51 0.04 0.01 0. 0. 0. 0. G2 69.22 0.48 15.40 2.69 0.03 0.75 1.96 4.06 4.46 0.50 0.08 0.13 0.12 0.01 0. 0. O. 0. GSP 1 67.32 0.66 15.28 4.30 0.04 0.97 2.03 2.81 5.41 0.58 0.12 0.28 0.37 0.03 O. O. 0. O. BCR1 54.53 2.26 13.72 13.41 0.18 3.48 6.97 3.30 1.70 0.67 0.02 0.36 0.05 0.04 0. 0. 0. 0. SY3 59.68 0.15 11.80 6.42 0.32 2.67 8.26 4.15 4.20 0.42 0.38 0.54 0.66 0.05 0. 0. 0. 1.0 W1 52.72 1.07 15.02 11.11 0.17 6.63 10.98 2.15 0.64 0.53 0.06 0.14 0.03 0.01 0. 0. 0. O. MIFE 34.55 2.51 19.58 25.76 0.35 4.57 0.43 0.30 8.79 2.92 0.19 0.45 1.59 O. O. 0. O. 0. MIMG 38.42 1.64 15.25 9.49 0.26 20.46 0.08 0.12 10.03 2.10 0.15 0.01 2.86 0. 0. 0. 0. 0. JB1 52.60 1.34 14,62 9.01 0.15 7.76 9.35 2.79 1.42 1.01 0.18 0.26 0.04 0. 0. 0. 0. 0. JG1 72.36 0.27 14.20 2.16 0.06 0.76 2.17 3.39 3.96 0.54 0.08 0.09 0.05 O. 0. 0. 0. 0: NIMD 38.96 0.02 0.30 16.96 0.22 43.51 0.28 0.04 0.01 0.30 0.40 0.02 0.01 0.02 0. 0. O. 0. NI MG 75.70 0.09 12.08 2.02 0.02 0.06 0.78 3.36 4.99 0.49 0.10 0.01 0.42 0.01 0. 0. O. O. NI ML 52.40 0.48 13.64 9.96 0.77 0.28 3.22 8.37 5.51 2.31 0.17 0.06 0.44 0.65 0. 0.5 1.5 O. NIMN 52.64 0.20 16.50 8.91 0.18 7.50 11.50 2.46 0.25 0.33 0.10 0.03 0.03 0.01 0. O. O. O. NIMP 51.10 0.20 4.18 12.76 0.22 25.33 2.66 0.37 0.09 0.26 0.08 0.02 0.02 0.02 3.5 0. 0. 0. NIMS 63.63 0.04 17.34 1.40 0.01 0.46 0.68 0.43 15.35 0.22 0.09 0.12 0.01 0.01 O. O. O. O. GA 69.96 0.38 14.51 2.77 0.09 0.95 2.45 3.55 4.03 0.87 0.11 0.12 0.05 O. O. O. 0. O. URS1 0.00 0.00 0.00 0.00 0.00 21.47 30.83 0.00 0.00 0.23 41.95 5.51 O.OO 0.00 0.00 O.OO 0.00 0.00 Table 24: Major element concentration of standards used (Abbey, 1980) MASS ATTENUATION COEFFICIENTS FOR STANDARDS WAVELENGTH NA MG AL SI P S K CA TI V CR MN FE AGV1 3183. , 25~ 2077 . .35 1339 .86 1 164 .55 1505. .04 1043 .69 400 .20 308. .46 201 . 14 155. . 16 113 .91 98 .23 77 .04 G2 2922 . . 16 1909 . .83 1215 .55 1052 .66 1546, , 24 1068 .60 398 . 38 328 . .70 197 . .89 152 . ,61 1 16 .46 95 . 18 74 .52 GSP 1 3045 . , 22 1935 . . 37 1236 .99 1063. .81 1528 , . 10 1057 .47 398 .69 334. 06 201 . , 33 155 , . 30 1 19 .03 97 , .34 76 .29 BCR 1 3601 , ,51 2288 . .76 1520 . 14 1220 .69 1475, .02 1021 , , 57 409 .76 291 . ,87 201 . .47 155 .47 1 13 . 75 101 , .48 79, .79 SY3 3215. .09 2088 .73 1374 .69 1093 .38 1451 , .76 1007 . 16 386 .01 309. .75 218 . 12 168 33 1 14 . 34 104 . 10 81 .85 W1 3486 .90 2175 . 19 1524 . 20 1243 .93 1465 . 15 1012 .71 400 .00 279, .88 214 .08 165 . 27 109 .22 104 . 54 82 .25 MI FE 4279. ,43 2582 . 17 1730 .01 1452 .66 1384, . 18 959 .66 418 .21 335, 98 194 . .72 150 .28 124 .39 98 .85 77 .91 MIMG 3318 . 14 1996 . . 33 1747 . 16 1394 .04 1395, .89 963 .79 377 .52 348 . .40 200. . 10 154 , .42 125 . 70 99, .25 78 .29 JB 1 3355 . , 79 2121 . .40 1518 .94 1235. .52 1462 , .63 1012 .09 394: .29 286. .45 210. . 17 162, 21 111 .01 103, , 32 81 28 JG1 2899 , .75 1870. . 16 1 190 .79 1015 .54 1557 , .79 1076 , 20 399 .63 326. . 17 197 .43 152, . 26 115 .07 94 .45 73, .93 NIMD 34 1 1 .64 2049 .03 2335 .98 1524 . 57 1488, .87 1028 . 14 421 . 50 278, .94 161 . .04 124 . 27 96 .43 76 .41 60 .37 NIMG 2889 .56 1862 .82 1 169 .09 965 . 18 1564 . . 23 1079 .92 400 .66 336, 28 196. .33 151 , .40 1 16 .80 93 .46 73 . 14 NIML 3376. .81 2350 ,23 1481 . 78 1 195 .68 1448, ,34 1031 .82 414 .54 335. .77 208. .34 160, .68 120 .04 100, .09 78 .68 NI MN 3339 .21 2098 . 59 1498 .06 1253 .51 1474 , 47 1018, . 13 396, .38 277 . 94 215 . .85 166 . ,63 106 . 26 103, . 17 81 . . 12 NIMP 3475 ,98 2100 58 1930 .69 1326. . 29 1503. 51 1038, , 19 414 , .09 282 . 24 174 . .61 134 . 73 119 .00 83. ,42 75. .78 NIMS 2978 . 27 1803 . 76 1142 .04 1038 .34 1469 , 52 1015 .57 375 .55 410, .75 239. .06 184 . 54 142 .95 114. .00 89 . .66 GA 294 1 . 36 1901 . 76 1215 . 38 1037 . 48 1545, 50 1068, ,00 398 .24 324. .64 197 , .98 152 . 69 115 . 15 94, .99 74 . . 38 Table 25: Mass attenuation coefficients for standards used at wavelengths of interest. MASS ATTENUATION COEFFICIENTS FOR STANDARDS (cont.) WAVELENGTH FE RB SR Y ZR NB BA LA CE PR ND TA TH U AGV1 77 . .04 12 . .44 10 .59 9. .04 7 .75 6 .67 206. .33 184 . .54 165 .25 152 . .11 136 , .72 51 . 38 13, .61 1 1 , .84 G2 74 . .52 10 .01 8 .52 7 .26 6 .22 5 .35 203 .02 181 . .57 162 .58 147 . .42 132 , .46 42 . 12 10, .96 9, .53 GSP 1 76 . . 29 1 1 . .05 9 .40 8 . .02 6 .87 5 .91 206, . 52 184 . . 74 165 .43 150. .70 135, .42 46, . 1 1 12. .09 10. . 52 BCR 1 79 . . 79 16. .09 13 .70 1 1 . . 70 10 .04 8 .64 206. .63 184 .84 165 .51 157 . .03 141 , . 20 65, . 36 17 . .58 15. . 30 SY3 81 . .85 13 .03 1 1 .09 9. . 47 8 . 12 6 .99 223, .75 200. . 14 179, .24 161 . . 10 144 . 82 53 .54 14 . .25 12. .40 W1 82 . . 25 15 . 27 13 .01 1 1 . . 1 1 9 . 53 8 .21 219. .56 196. .43 175 .94 161 . .71 145 .42 62 . 14 16. .69 14. , 53 MIFE 77 .91 21 . 79 18 .57 15 .87 13 .63 11 .73 199. .58 178. .64 159 .98 152 . ,99 137 , .58 87 .45 23 .82 20. .71 MIMG 78 . .29 13 .95 1 1 .88. 10 . 14 8 .70 7 .48 205. . 16 183. .60 164 .47 153. . 75 138, . 14 57 .21 15. ,27 13, ,27 JB1 81 . .28 14 . 14 12 .04 10. .28 8 .82 7 .59 215, .56 192 . .83 172, .71 159 . . 90 143, .76 57 . 77 15. .45 13 . .45 JG1 73. .93 9 .68 8 .23 7 . .02 6 .01 5 . 17 202. .56 181 . . 16 162 .22 146. .26 131 , .42 40 .84 10. .60 9 .22 NIMD 60. . 37 15 .06 12 .82 10. .95 9 .39 8 .08 165, .09 147 . .76 132 .24 1 18. .59 106, .48 61 .47 16. .47 14 . .31 NIMG 73 . 14 9 .47 8 .06 6 . 87 5 .88 5 .05 201 .43 180. . 16 161 . 30 144 . 74 130 .04 40 .09 10. .38 9 .02 NIML 78 .68 14 .57 12 .41 10. .60 9 .09 8 .23 213, .71 191 , . 10 171 . 1 1 155 . 10 139, .40 59 .55 15. .93 13, 88 NIMN 81 . 12 14 .08 1 1 .99 10. . 24 8 .78 7 .56 221 . 39 198, .06 177 .40 159 .64 143 .54 57 , .53 15. .39 13, .39 NIMP 75 . 78 15 . 16 12 .90 11 . .02 9 .46 8 . 14 179 .07 160, .22 143 .45 129 . 25 1 16 . 13 61 , .84 16. .58 14, .42 NIMS 89 .66 1 1 .40 9 .71 8. .27 7 .09 6 . 10 245, . 17 219. .42 196 .58 176. .29 158, .44 47, ,60 12. .49 10, ,85 GA 74 . 38 10 .07 8 .56 7 . . 30 6 .26 5 .38 203. . 12 181 . ,66 162, .67 147 . . 10 132 , . 18 42. .31 1 1 . 02 9. , 59 Table 26 Mass attenuation coefficients for standards used at wavelengths of interest. MASS ATTENUATION COEFFICIENTS OF UNKNOWNS FOR WAVELENGTHS OF MAJOR ELEMENTS SI AL TI FE MG CA NA K P S SR BA ND CE MN MR -503 1318, .98 1999 . 15 233 . 10 129 .06 2564 .68 191 . 15 3907 . 10 258 .29 978 . 13 678 .73 16 .09 239 . 15 154 .77 191 .86 154 .88 MR -570 1 174 .75 1798 .07 226 .08 91 .40 2369 .36 149 .42 3823 . 34 203 .44 811 .09 565 .94 1 1 . . 77 231 .97 149 .59 185 .85 113 .31 MR -550 1 154 . 4 1 1767 . . 47 238 .77 90 .71 2162 .82 144 . 75 3556 .49 197 .49 778 .40 552 .21 9 . ,93 244 .96 157 .97 196 . 25 113 . 82 MR -553 1 165 65 1787 . .85 247 . 79 93 .94 2158 .45 148. . 58 3584 .96 202 .69 796 .70 565 . 32 10, , 54 254 .21 164 .03 203 .71 117. .97 MR -552 1 124 .99 1724 .69 259 . 26 98 .83 2170. .63 162 .60 3607 . 15 221 . 35 77 1 . 54 614 .92 1 1 .04 265 .96 171 .74 213 . 15 123, .93 MR -554 1 162 .49 1768 .17 247 .83 94 .52 2132 .34 150 .98 3544 , .51 205 .90 790 .96 573 .85 10, 35 254 .25 164 .47 203 .73 118 .57 MR -316 953 . 12 1353. . 22 176 . 70 67 .60 2051 . .80 274 , . 28 2908 , .40 368 .50 1451 .94 1009, . 26 6. 79 181 , .38 1 18. 88 145 .02 86. . 14 MR -551 914 , 86 1 187 81 194 .47 73. .31 1858. ,78 320. . 14 2846. 70 388. .70 1536. .54 1062. , 76 7. 31 199. .56 129. .93 159. 76 93. .56 MR -51 1 1022 . 47 1505 . .92 299 . 14 113. .64 2332. .06 161 . . 1 1 3692 . 46 214 , . 22 858. .73 594 . .87 12 . 49 306 . .91 198. .51 245. .96 143. .01 MR -506 1033 99 1356. 23 267 . . 26 102 . . 84 2 122 . 10 217. 92 3490. 63 271 , ,31 1082 . 34 748 . 05 1 1 . 21 274 . 18 178. 68 219. . 77 129. .75 MR -523 1022 . 47 1505. . 92 299. . 14 113 .64 2332 . 06 . 161. 1 1 3692 . 46 214, . 22 858. .73 594 . 87 12 . 49 306. .91 198. 51 245. .96 143. .01 MR -505 1033 . .99 1356 . 23 267 26 102 . .84 2122 . 10 217 . 92 3490. 63 271 , ,31 1082 . . 34 748. .05 1 1 . 21 274 . 18 178 . 68 219 . .77 129. 75 Table 27: Mass attenuation coefficients of unknowns calculated for wavelengths of major elements. MASS ATTENUATION COEFFICIENTS OF UNKNOWNS FOR WAVELENGTHS OF MINOR ELEMENTS NB ZR Y SR U RB TH TA TI BA CE ND PR LA MN S MR -503 10 .41 1 1 .93 13 .84 16 .09 17 .89 18 .80 20 .46 73 . 10 233 . 10 239 . 15 191 .86 154 . 77 171 .95 213 .85 154 .88 678 .73 MR -570 8. .03 8 .67 10 .09 1 1 , . 77 13 . 12 13 .81 15. ,03 54 .59 226 .08 231 .97 185 .85 149 . 59 166. , 33 207 .31 1 13 .31 565 .94 MR -550 6 . 33 7 .30 8 . 50 9 .93 1 1 .08 1 1 .67 12 .70 46 .52 238 .77 244 .96 196 . 25 157 .97 175 . 65 218 .95 1 13 .82 552 .21 MR -553 7 . . 14 7 . 74 9. .02 10, . 54 1 1 . 75 12 . 37 13. ,47 49, .26 247 . 79 254 .21 203 .71 164 .03 182 , . 37 227 . 25 117 .97 565 .32 MR -552 7 . .42 8 . 1 1 9 .45 1 1 .04 12 .31 12 .96 14 . , 12 51 , .65 259 . 26 265 .96 213 . 15 171 . 74 190. .89 237 .80 123. .93 614 .92 MR -554 6 .60 7 .60 8 .85 10 .35 1 1 .54 12 . 15 13. , 23 48 .44 247 .83 254 .25 203 . 73 164 .47 182 . 84 227. . 29 1 18. . 57 573 .85 MR -316 4 . 26 4 .93 5 . 75 6 . 75 7 . 56 7 .94 8 . .69 33 .75 175 .64 180 .29 144 . 15 1 18 . 15 131 . 57 161 . .06 85. .60 10O3 .98 MR -551 4 .56 5 .29 6 . 18 7 .25 8 . 12 8 .53 9. 34 36 , .29 192 , .91 197 . .96 158 , .47 128 .86 143. 44 177 . .00 92. . 79 1055 . 38 MR -51 1 7 .98 9 . 18 10 .69 12, .49 13, .94 14 .67 15. ,97 58. . 17 299, . 14 306 . .91 245. .96 198 .51 220. 57 274 .40 143. .01 594 . .87 MR -506 7 . 12 8 . 22 9 . 58 1 1 . .21 12 , .51 13 . 16 14 . 35 52. .94 267 . . 26 274 , . 18 219 . . 77 178 , .68 198. 60 245, . 20 129 . .75 748 . .05 MR -523 7 .98 9 . 18 10. ,69 12. .49 13, .94 14 . .67 15. 97 58. . 17 299, . 14 306, .91 245. .96 198. ,51 220. 57 274, .40 143. 01 594 . ,87 MR -505 7 12 8 . 22 9 58 1 1 . .21 12 .51 13 . 16 14 . 35 52 . 94 267 , . 26 274 . 18 219 . .77 178 . .68 198 . 60 245 , , 20 129. 75 748. 05 Table 28: Mass attenuation coefficients of unknowns calculated for wavelengths of minor elements. MAJOR ELEMENT CONCENTRATIONS OF UNKNOWNS (wt %) SI02 AL20 TI02 FEO MGO CAO NA20 K20 P205 S SRO BAO ND20 CE20 MNO LOI TOTAL MR -503 7 .30 0. .67 0. .04 10. .49 7 .91 24 .59 0 .79 0 .06 0 .09 1 . 1 1 0. .08 7. . 74 0 .42 0 .84 3 .30 33 .31 98 .74 MR -570 0 .65 0. 21 0 .01 8. .41 1 1 .29 28 . 14 1 . 13 0 .04 0. . 14 0 .06 0, .66 0. .69 0 . 12 0 .56 4 . 1 1 42 . 55 98 .77 MR -550 0 .46 0. 24 0. .00 2 . .71 15 .94 30 .23 0 .58 0. .02 1 . .60 0 .00 0. .04 0. .00 0 .03 0. .09 0. .24 43. .52 95 .70 MR -553 0 .25 0. 12 0. .00 0. .95 16 .44 30 .65 0 .07 0. .01 1 . .20 0 .01 0. .52 0. .01 0 .01 0. .03 0. . 77 42 , 93 .04 MR -552 0 .52 0. 16 0. 01 1 , .92 15. .03 34 .43 0 .0 0. .02 8. .73 0 .01 0, . 53 0. .01 0 .04 0. 1 1 0. . 77 40. . 16 100, , 25 MR -554 1 .00 0. 67 0. 1 1 0. .71 16 . 74 31 . 32 0 .0 0. .01 2 . .93 0 .01 0. .05 0. .00 0 .03 0. 10 0. .23 41 . .96 95. .87 MR -316 65. .60 4 . 23 0. 67 1 1 . 86 2 . . 52 4 .00 7 . . 70 0. 24 0. 69 0 .02 O. 04 0. 15 0. .01 0. 02 O. .27 0. .84 98 . 86 MR -551 79 88 8. 82 0. 44 4 . 12 0. .93 2 . .41 4 . .09 3. 91 0. 21 0. .01 0. 02 0. 02 0. .01 0. 02 0. 14 1 . 16 106. .20 MR -51 1 15 . 06 2 . 64 0. 08 0. 73 1 . . 74 44 . .05 3 . .05 0. 46 0. 27 0. .0 0. 07 0. 06 0. 00 0. 01 0. 08 37 . 15 105. 45 MR -.506 35 . 48 9 . 84 0. 51 5 . 12 0. 86 31 . 80 0. 57 2 . 27 0. 13 0. 0 0. 03 0. 27 0. 01 0. 01 0. 43 23 . 19 1 10. 52 Table 29: XRF-analyses of major elements on powder pellets. Calculations are based on mass attenuation coefficients (table 23) and regression slopes determined from standards (table 24; Abbey, 1980). MAJOR ELEMENT CONCENTRATIONS NORMALIZED TO 100 wt% SI02 AL20 TI02 FEO MGO CAO NA20 K20 P205 S SRO BAD ND20 CE20 MNO LOI TOTAL MR-503 7 . . 44 0. 68 0. .04 10 .67 8 .06 25 .06 0 .81 0 .06 0. .09 1 . 13 0 .08 7 .83 0. .43 0 .86 3 . . 36 33, .31 100 .OO MR-570 0, .66 0. .25 0. .01 8 .60 1 1 .45 28 . 76 1 . 16 0 .04 0. . 14 0 .06 0 .68 0. .74 0 . 12 0. .57 4 . . 20 42 , .55 100, .00 MR-550 0. .50 0. . 26 0 0 2 .95 17 . 34 32 .89 0 .63 0 .02 1 . 74 0 .0 0 .04 0 .0 0. .03 0. . 10 0. . 26 43 .52 100 .00 MR-553 0 . 34 0. . 16 0. 0 1 . 30 22 .42 4 1 . 8 1 0 . 10 0 .01 1 . .64 0 .01 0. .71 0 .01 0 .01 0. .04 1 . .05 42 .00 100, .00 MR-552 0 .52 0, , 16 0. 01 1 .92 14 . 79 34 .29 0 .0 0 .02 8 . 69 0 .01 0, .53 0. .01 0 .04 0. .11 0. .77 40 . 16 100. .00 MR-554 1 .08 0. . 72 0. 12 0 . 76 18 .02 33 .71 0. .0 0 .01 3 , . 15 0 .01 0. .05 0. .0 0 03 0. . 10 0. . 25 41 .96 100, .00 MR-3 16 66 . . 36 4 . 28 0. 68 12 . .00 2 . 55 4 .05 7 , . 79 0. .24 0. 70 0. .02 0. .04 0. . 15 0. .01 0. .02 0. 27 0, .84 100, .00 MR-551 75 . . 15 8. 30 0. 41 3, 88 0. .87 2 . .28 3 . .85 3 . .68 0. 20 0. .01 0. 02 0. 02 0. .01 0. 02 0. 14 1 . . 16 100. ,00 MR-51 1 13 . .86 2 . 43 0. 07 0. .67 1 . .60 40 . 53 2 . 81 0. 42 0. 25 0. 0 0. 06 0. 06 0. .0 0. 01 0. 07 37 . 15 100. .00 MR-506 3 1 . 20 8 . 65 0. 45 4 . 50 0. 76 28 .00 0. 50 2 . 00 0. 1 1 0. 0 0. 03 O. 24 0. 01 0. 01 0. 37 23 . 19 100. 00 Table 30: Normalized major element concentrations from table 29. Ln 00 TRACE ELEMENT CONCENTRATIONS OF UNKNOWNS (ppm) NB ZR Y SR U RB TH TA TI02(%) BA CE ND PR LA MNO(%) S MR-503 29. 96. 96. 699. 0. 0. 839. nd 0 .01 69395. 7213 . 3584 . nd 2291 . 3 .29 10868. MR-570 3. 583. 13. 5546. 21 . 3. 28. nd 0 .01 6169. 4757 . 1020. nd 2668 . 4 . 1 1 nd MR-550 490. 66. 41 . 359 . 4 . 4. 128 . 18. 0 .00 39 . 746 . 237. nd 307. 0. .26 nd MR-553 168. 465. 14 . 4377 . 223 . 35. 1 . 0. 0 .OO 1225. 224 . 59. nd 142. 0 .77 59. MR-552 1796. 499. 69. 4449 . 19. 5. 21 . 17 . 0 .01 85. 909 . 310. nd 322. 0 .76 59. MR-554 1384 . 497 . 122 . 457 . 74 . 2. 184 . 166. 0 . 1 1 33 . 856 . 297 . nd 355. 0, .23 90. MR-316 7 1 . 267 . 6. 302 . 1 . 2. 4 . nd 0. .62 1343 . 168 . 56 . nd 63 . 0. . 26 183. MR-551 72 : 887 . 18 . 141 . 3 . 35. 4 . nd 0. .40 184 . ' 143 . 46 . nd 60. 0. . 14 62. MR-51 1 19 . 1 15. . 29. 622 . 5. 10. 6 . nd 0. .08 503 . 90. 34 . nd 64 . 0. 08 nd MR-506 183. 70. 59 . 257 . 7 . 43. 58 . nd 0. 47 2422 . 103 . 64 . nd 38 . 0. 43 nd MR-523 24 . 41 . 26. 292. 10. 8. 9 . nd 0. .06 345. 0. 0. nd 36. 0. 04 nd MR-505 144 . 50. 60. 379. 0. 25. 109. nd 0. ,29 41691. 73 . 0. nd 13. 0. 55 nd Table 31: XRF-analyses of trace elements. Calculations are based on mass attenuation coefficients (tab. 29) and regression slopes derived from concentrations of standards (Abbey, 1980). nd * not determined. APPENDIX C: TRANSIENT TEMPERATURE DISTRIBUTIONS CALCULATED FOR THE  MARGIN OF A COOLING IGNEOUS BODY The Model The theory of heat conduction is well understood and a great number of exact solutions for various problems and geometries are described in the literature (lngersoll et al,1954; Carslaw & Jaeger,1959; Ozisik,1980; Turcotte & Schubert, 1982). Exact solutions to geological problems involving the heat of crystallization are restricted to simple geometries (Jaeger,1957; Carslaw & Jaeger,1959; Turcotte & Schuberr.,1982). For models directed towards understanding the cooling of igneous bodies the heat of crystallization must be taken into account. To maintain a simple solution a more tractable geometry of the igneous body was chosen to be that of an infinite, parallel sheet. Compared with the more appropriate cylindrical geometry of the "Aley" complex the results will represent maximum temperature distributions. The differences are believed to be within the limits of the accuracy of the physical data set (lngersoll et al,1954; ]aeger,1957). Assumptions An infinite slab of magma at the melting temperature (Tm) intrudes instantaneously into country rock initially at a uniform temperature (To). Solidification occurs at the melting temperature and proceeds parallel to the contact walls towards the center releasing the heat of crystallization (L). The solidified magma and the country rock are isotropic and have the same constant heat capacities (cp) and thermal diffusivities (K). The model requires estimates of physical properies of the solid igneous rock (heat capacity, thermal diffusivity), the melting temperature and the heat of crystallization. 160 Symbols and units Tm Melting temperature [K] To Temperature before intrusion [K] Tc Temperature at contact [K] T Temperature [K] K Thermal diffusivity [s/m ] L Heat of crystallization [J/kg] cp Heat capacity [)/kg/K] p Specific density of solid [kg/m ] k Thermal conductivity [J/kg/m/s] X Distance from centre of coordinate system fm] xm Position of solidification front [m] t Time after intrusion [s] ts Solidification time [s] b Halfwidth of dike [m] X Model parameter erf Error Function erf c Complementary Error Function 2/Ut) V Characteristic thermal diffusion distance [m] A Dimensionless similarity variable 2y/Kt T-To 0= Dimensionless time Tm-To Coordinate System PART A Figure 48: Coordinate system during solidification Figure 49: Coordinate system after solidification 163 Mathematics Cooling during solidification Equations: I One dimensional transient heat conduction equation for a homogenious, isotropic solid: (1) |f = K 3t 3x2 Boundary conditions: T(xm,t)=Tm T(o=,t)=To Initial condition: T(x,0)=To Note: There is no temperature gradient in the liquid phase and thus no heat will be conducted in the liquid. Heat balance equation at solidification front: rate of heat liberated during solidification (2) p-L -j— xm(t) = -k dt heat flux in x-direction through the solid phase 3T " 3x x=xm Heat conduction equation in dimensionless parameters (compare table on page 4 for parameter transformation): (3) -r, ae Boundary conditions: 1 d20 2 dt?2 0(oo)=O 0(O)=1 164 Solution Compare Carslaw & Jaeger,1959; Turcotte & Schubert,1982 (4) 0(T?) = erfc ( TJ) 1+erf(X) with (5) X = -xm( t) 2-/U-t) or (6) T(x,t) = To+(Tm-To)-erfc 1 2»i/U«t)-l 1+erf(X) The parameter X can be evaluated numerically from the transcendental function resulting from equation (2) after substitution of (5) into (2) and subsequent differentiation: (7) WU) exp(-X2) cp.(Tm-To) X-[1+erf(X)] The solidification time is calculated from (5) b2 (8) ts = 4-K-X2 The contact temperature is a constant during solidification, depending on X only: (9) Tc = To+(Tm-To) — j-p— 1 +erf (X) calculated from (4) with 77 = 0 From equation (7) it is obvious that the parameter X is dependent upon the ratio L/cp/(Tm-To), with L and Tm being the parameters with the strongest dependency on magma composition. 165 Cooling after Solidification This is a cooling problem of an infinite solid with a given initial temperature distribution (Carslaw & Jaeger,1959; lngersoll et al,1954; Ozisik,1982). A coordinate transformation, shifting the origin of the x-axis to -b is applied for symmetry reasons (compare figure 42). Equations: 3T 32T Heat conduction equation: — = * 3t 3x2 Initial Condition : T(x,0) = f(x) = To+(Tm-To) «erfc [ ]• L2V(K-ts)-l 1+erf(X) Solution: +00 1 r (X-U)2 -, T(x,t) = ; f(u).exp - .du — CD The integral has to be evaluated numerically. General Applications For this purpose three graphs are provided which enable a quick graphical evaluation of the solidification time (TS) and the contact temperature (TC) for any physical properties and any dimension. The following properties of the intrusive body have to be known: latent heat of fusion (L) heat capacity of solid (CP) diffusivity of solid (K) halfwidth of intrusive body (B) melting temperature of intrusive body (TM) 166 temperature of wallrock before intrusion (TO) Note: The diffusivity can be calculated from the thermal conductivity (k), heat capacity (CP) and specific density (p) : K = k/(CP-p) How to use the graphs: calculate L*/TT/[CP • (TM-TO)] evaluate LAMBDA from figure 50 evaluate TS/B2 from figure 51 and calculate TS evaluate (TC-TOV(TM-TO) from figure 52 and calculate TC 167 o.o 0 15 0.3 0 45 0.6 0.75 LRMBOfi 0 9 1 .05 1 .2 1 .35 1 .5 Figure 50: Model parameter X 168 L9MB0R Figure 51: Solidification time as a function of X 0.0 0.15 0.3 0.45 —1 0.6 0.75 LflMBOA 0.9 1 .05 1 .2 I .35 Figure 52: Dimensionless contact temperature as a function of X 170 Sample calculations Two time-temperature-distance (t-T-x) sections were calculated: one with syenite data (section 6.2: figure 25) and one for a carbonatite dike with a halfwidth of one meter (figure 53). Figure 53: t-T-x diagram for a carbonatite dike 171 Program "COOLING" A FORTRAN-77 program to calculate the transient temperature distribution around a cooling igneous body. The program is self explaining with an interactive input. All units are metric. The program may be called via the UBC-network (MTS) with the following command: $R URSM:COOLING.O The plotroutine URSM:COOLPLOT.O will produce a t-T-x plot. 172 1 Q ********************************************* 2 C * * 3 C * PROGRAM COOLING : SOLIDIFICATION OF A DIKE OR SILL * 4 C *5 Q ************************************************************* 6 C 7 C LIST OF VARIABLES: 8 C 9 C B HALFWIDTH OF DIKE [m] 10 C D THERMAL DIFFUSIVITY OF COUNTRY ROCK [m*m/s] 11 C K THERMAL CONDUCTIVITY OF COUNTRY ROCK [J/s/m/K] 12 C RO DENSITY OF MAGMA [kg/m/m/m] 13 C L LATENT HEAT OF FUSION [J/kg] 14 C CP HEAT CAPACITY OF COUNTRY ROCK [J/kg/K] 15 C T TEMPERATURE- [ K ] 16 C TM MELTING TEMPERATURE OF MAGMA [K] 17 C TO TEMPERATURE OF COUNTRY ROCK [K] 18 C TC TEMPERATURE AT THE CONTACT [K] 19 C TIME COOLING TIME [a] 20 C TIMS SOLIDIFICATION TIME [s] 21 C TIMSA SOLIDIFICATION TIME [a] 22 C 23 Q ************************************************************* 24 C 25 IMPLICIT REAL*8 (A-L,0-Z)-26 LOGICAL LO 27 EXTERNAL FN,DF 28 COMMON C1,C2,C3,C4,C6,Y,B,TO,TM 29 CALL FTNCMD('ASSIGN 1=-INPUT;') 30 CALL FTNCMD('ASSIGN 8=-PLOT;') 31 NSTEP=50 32 NLOOP=33 C 34 Q ****************** INTERACTIVE INPUT ************************ 35 C 36 WRITE(6,100) 37 100 FORMAT(1X,'THIS PROGRAM CALCULATES THE TEMPERATURE PROFILE') 38 WRITE(6,101) 39 101 FORMAT(IX,'DURING SOLIDIFICATION OF A DIKE AS A FUNCTION OF') 40 WRITE(6,102) 41 102 FORMAT(IX,'TIME, DIMENSION AND PHYSICAL PROPERTIES') 42 C 43 WRITE(6,103) 44 103 FORMAT(1X,//,'INPUT DATA AND OUTPUT SUMMARY IN FILE "-INPUT"' 45 WRITE(6,104) 46 104 FORMAT(1X,'TO OBTAIN A PLOT RUN "COOLPLOT.O"',//) 47 C 48 WRITE(6,110) 49 110 FORMAT(/,IX,'ENTER HALFWIDTH OF DIKE [m] :') 50 READ(5,111)B 51 111 FORMAT(D20.10) 52 WRITE(6,11453 114 FORMAT(/,1X,'ENTER HEAT CAPACITY OF COUNTRY ROCK [j/kg/K] :') 54 READ(5,111)CP 55 WRITE(6,112) 56 112 FORMAT(/,1X,'ENTER DIFFUSIVITY OF CONTRY ROCK [m*m/s] :') 57 READ(5,111)D 58 WRITE(6,113) 173 59 113 60 61 62 115 63 64 65 116 66 67 68 1 17 69 70 C 71 C .72 c 73 74 20 75 C 76 C 77 C 78 79 50 80 81 51 82 83 52 84 85 53 86 87 55 88 89 56 90 91 57 92 C 93 C 94 C 95 96 97 98 99 100 C 101 102 C 103 C302 104 C 105 C 106 C 107 108 109 1.10 1 1 1 C 1 12 1 1 3 1 1 4 C 1.15 116 200 FORMAT(/,1X,'ENTER LATENT HEAT OF FUSION [J/kg] :') READ(5,111)L WRITE(6,115) FORMAT(/,IX,'ENTER MELTING TEMPERATURE OF MAGMA [K] :') READ(5,111)TM WRITE ('6,"1 1-6) FORMAT(/,IX,'ENTER TEMPERATURE OF CONTRY ROCK [K] :') READ(5,111)TO WRITE(6,117) FORMAT(/,IX,'ENTER PROFILE LENGTH (MULTIPLES OF HALFWIDTH) :') READ(5,111)BMULT WRITE(8,20)T0,TM,BMULT,B FORMAT(1X,4E15. 5) ******************** INPUT DATA SUMMARY ********************* WRITE(1,50) FORMAT('INPUT FOR PROGRAM "COOLING"',/) WRITE(1,51)B FORMAT(1X,'HALFWIDTH ',E10.3,' [m]') WRITE(1,52)D FORMAT(IX,'DIFFUSIVITY ',E10.3,' [m*m/s]') WRITE(1,53)CP FORMAT(IX,'HEAT CAPACITY ',E10.3,' [J/kg/K]') WRITE(1,55)L FORMAT(IX,'HEAT OF FUSION ',E10.3,' [J/kg/K]') WRITE(1,56)TM FORMAT(1X,'MELTING TEMPERATURE ',F10.1,* [K]') WRITE(1,57)T0 FORMAT(1X,'T OF COUNTRY ROCK ',F10.1,* [K]') ******************* CALCULATION OF ts AND Tc *************** DPI=3.141592653589793D00 X1=0.01D00 X2=10.0D00 EI=1.0D-12 C1=L*DSQRT(DPI)/CP/(TM-T0) CALL ZERO1(X1,X2,FN,EI,LO) WRITE(6,302)X1,X2 FORMAT(1X,2E20.14) IF(LO.EQ..FALSE.)GO TO 999 TIMS=B*B/4.0/D/X1/X1 TIMSA=TIMS/3.1536D07 TIMSD=TIMSA*365.0 TIMSH=TIMSD*24.0 C4=1.0+DERF(X1) TC=T0+(TM-T0)/C4 WRITE(6,200)TIMSA FORMAT(/,1X,'SOLIDIFICATION TIME :',E18.10,* YEARS') 174 1 1 7 WRITE(6,90)TIMSD 118 90 FORMAT(1X,' ',E18.10,' DAYS') 119 WRITE(6,91)TIMSH 120 91 FORMAT(1X,' ',E18.10,' HOURS') 121 WRITE(6,201)TC FORMAT(/,1X,'CONTACT TEMPERATURE :',F8.2,' K') 122 201 123 C 124 C ********************** OUTPUT DATA SUMMARY ****************** 125 c 1 26 WRITE(1,60) 127 60 FORMAT(//,'OUTPUT SUMMARY :',/) 128 WRITE(1,61)TIMSA 129 61 FORMAT(1X,'SOLIDIFICATION TIME ',E10.3,' YEARS') WRITE(1,62)TC 1 30 131 62 FORMAT(IX,'CONTACT TEMPERATURE ' ,F10.1,* KELVIN *) 132 WRITE(1,63) FORMAT(//,*T-X PROFILES AFTER :',/) 133 63 134 C 135 C ****************** CALCULATION OF t-T-X'PROFILES *********** 136 C 137 399 WRITE(6,118) FORMAT(/,IX,'ENTER TIME AFTER INTRUSION [a] :') READ(5,111)TIME 138 118 139 1 40 C 141 WRITE(1,70)TIME 142 70 FORMAT(1X,E10.3,' YEARS') 143 C 1 44 C 145 NLOOP=NLOOP+1 146 CALL FTNCMD('ASSIGN 3=-3;') 147 WRITE(3,30)NLOOP 148 30 F0RMAT(1X,I3) 149 C 150 TIMES=TIME*3.1536D07 151 C2=4.0*D*TIMES 152 C3=DSQRT(C2) 153 IF(TIMES.GT.TIMS)GO TO 400 154 C 155 C ************* COOLING DURING SOLIDIFICATION **************** 156 C 157 YM=-X1*C3 158 WRITE(6,301)YM 159 301 FORMAT(1X,'SOLIDIFICATION FRONT AT ',E12.3,' METERS') 160 YPLOT=YM+B 161 WRITE(8,300)YPLOT,TM 162 300 FORMAT(1X,2F12.4) 163 C 164 STEP=(BMULT*B-YM)/NSTEP 165 DO 310 N=1,NSTEP 166 YM=YM+STEP 167 C5=1.0-DERF(YM/C3) 168 T=T0+(TM-T0)*C5/C4 169 YPLOT=YM+B 170 WRITE(8,300)YPLOT,T 171 310 CONTINUE 172 C 173 GO TO 399 174 c 175 175 C ***************** COOLING AFTER SOLIDIFICATION ************* 176 C 177 400 TIMES=TIMES-TIMS 178 C2=4.0*D*TIME179 C3=DSQRT(C2) 180 C6=DSQRT(4.0*D*TIMS) 181 Y=0.0D00 182 STEP=(BMULT+1.00)*B/NSTEP 183 DU=1.0D00 184 C 185 DO 405 N=1,50 186 ' FDU=DF(DU) 187 IF(FDU.LT.1.OD-50)GO TO 406 188 DU=DU*5.0 189 405 CONTINUE 190 C 191 406 DST=DU/500.0D00 192 C 193 DO 410 N=1,NSTEP+1 194 AREA=0.0D00 195 X=-DU 196 F1=DF(X) 197 C 198 DO 420 M=1,1000 199 X=X+DST 200 F2=DF(X) 201 DAREA=(F1+F2)/2.0*DST 202 AREA=AREA+DAREA 203 . F1=F2 204 420 CONTINUE 205 C 206 T=1.0D00/C3/DSQRT(DPI)*AREA 207 WRITE(8,300)Y,T 208 Y=Y+STEP 209 410 CONTINUE 210 C 211 GO TO 399 212 C 213 998 STOP 214 999 WRITE(6,900) 215 900 FORMAT(/,1X,'ZER01 FAILS') 216 STOP 21 7 END 218 C 219 C 220 C 221 FUNCTION FN(X1) 222 IMPLICIT REAL*8(A-L,0-Z) 223 COMMON C1,C2,C3,C4,C6,Y,B,TO,TM 224 FN=DEXP(-X1*X1)/X1/(1.0+DERF(X1))-C1 225 RETURN 226 END 227 C 228 FUNCTION DF(X) 229 IMPLICIT REAL*8(A-L,0-Z) 230 COMMON C1,C2,C3,C4,C6,Y,B,TO,TM 231 DF2=DEXP(-(Y-X)*(Y-X)/C2) 232 XPR=X 176 233 IF(X.LT.O.ODOO)XPR=-X 234 DF1=T0+(TM-T0)*DERFC((XPR-B)/C6)/C4 235 DF=DF1*DF2 236 RETURN 237 END 

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