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UBC Theses and Dissertations

Geologic setting, mineralization, and aspects of zoning at the Berg porphyry copper-molybdenum deposit,… Panteleyev, Andrejs 1976

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GEOLOGIC SETTING, MINERALIZATION, AND ASPECTS OF ZONING AT THE BERG PORPHYRY COPPER-MOLYBDENUM DEPOSIT, CENTRAL BRITISH COLUMBIA by Andrejs Panteleyev B . S c , 1964, M.Sc , 1969, University of British Columbia A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Geological Sciences We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1976 fc^ Andrejs Panteleyev In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r re ference and study. I f u r t h e r agree t h a t permiss ion for e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed without my w r i t ten pe rm i ss i on . Department of The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date &&M£ 10 (97b ABSTRACT i Berg copper-molybdenum deposit i s i n mountainous terrain of the Tahtsa Range in west-central B r i t i s h Columbia. It is a type example of Lowell and Guilbert's (1970) model of porphyry copper deposits. The deposit i s i n thermally metamorphosed and hydrothermally altered Middle Jurassic volcanic rocks and Tertiary quartz d i o r i t e adjacent to a weakly mineralized Eocene stock. The stock i s about 2,100 feet in diameter and consists of four major quartz monzonitic phases. Unmineralized volcanic and sedimentary strata of the Cretaceous Skeena Group crop out east of the deposit. Hydrothermal alteration and sulphide minerals are arranged i n concentric, annular zones around the composite stock. From the inte r i o r outward pervasive alteration zones are potassic, p h y l l i c , and p r o p y l i t i c . A r g i l l i c alteration i s rare. A b i o t i t i c alteration zone that surrounds the stock i s largely a thermal aureole but i s also p a r t i a l l y of hydro-thermal origin. A multistage vein stockwork i s superimposed on the pervasively altered rocks. Early veins, many with alteration envelopes, were deposited from saline fluids at temperatures in excess of 400 degrees centigrade. Later veins were deposited from cooler, less saline fluids and commonly have retrograde alteration margins. A gypsum-filled sub-horizontal fracture cleavage cuts a l l alteration minerals and veins. The molybdenite zone follows closely the intrusive contact where a quartz stockwork i s well developed. Chalcopyrite i s most abundant in the b i o t i t i c alteration zone. Pyrite forms a broad halo that extends outward for at least 2,000 feet from the stock. Minor elements In pyrite are concentrated i n disseminated pyrite from well-mineralized copper zones. Leaching and supergene mineralization cause pronounced v e r t i c a l zoning i n the deposit. In the leached capping copper has been removed to a depth of 125 feet but molybdenum remains and i s loca l l y concentrated i n limonite. In the supergene zone,which overlies the entire deposit and i s up to 300 feet thick, copper i s enriched by a factor of 1.25 times primary grade. Supergene mineralization i s a contemporary ongoing process that was initiated after Pleistocene glaciation. i i i • TABLE OF CONTENTS Page ABSTRACT 1 CHAPTER I - INTRODUCTION GENERAL STATEMENT 1 SCOPE AND PURPOSE OF THE STUDY . 2 LOCATION AND ACCESS 2 WEATHER A HISTORY OF EXPLORATION . . . . 5 PHYSIOGRAPHY 8 GLACIATION 9 CHAPTER II - GEOLOGY REGIONAL GEOLOGY OF TAHTSA RANGE INTRODUCTION 11 BEDDED ROCKS 14 Stratigraphic Relationships i 14 Hazelton Group (Middle Jurassic: Map 1, Unit 1) 15 Skeena-Group (Lower Cretaceous and ? Younger: Units 2 to 4) 16 INTRUSIVE BODIES 20 Quartz Diorite 20 Quartz Monzonite Porphyry 22 Minor Intrusions 23 STRUCTURE 24 GEOLOGY OF BERG DEPOSIT INTRODUCTION 26 iv Page CHAPTER II - GEOLOGY (continued) GEOLOGY OF BERG DEPOSIT (continued) BEDDED ROCKS 31 INTRUSIVE ROCKS 35 Quartz Diorite (Map 2, Unit 2) 38 Quartz Monzonite Stock and Dykes (Map 2, Units 3 to 5) 39 Quartz Monzonite Porphyry Phase (QPM, Unit 3) . . . 39 Sericitized Quartz Plagioclase Porphyry Phase (QPP; Map 2, Unit 4) 42 Plagioclase Biotite Quartz Porphyry (PBQP; Map 2, Unit 5) 43 Quartz Monzonite-Granodiorite or Quartz-Bearing Monzodiorite Dyke (hornblende quartz feldspar porphyry, hbde QFP; Map 3, Unit 6) 44 Basic Dykes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Chemical Composition 50 Distribution and Geometry (Map 2) 50 Age of Intrusions .• 56 BRECCIAS .'• 58 Intrusive Pebble Breccia Pipe 59 Other Breccias (Observed Only in Diamond-Drill Core) . 60 Breccia 1 60 Breccia 2 61 Breccia 3 62 Breccia 4 62 STRUCTURE 63 V '-. Page CHAPTER III - HYDROTHERMAL ALTERATION INTRODUCTION 68 DEFINITION OF ALTERATION FACIES AND ZONES 70 POTASSIC ALTERATION . . 70 PHYLLIC ALTERATION 71 PROPYLITIC ALTERATION 72 ARGILLIC ALTERATION 74 BIOTTTIC ALTERATION 74 VEINS ; 81 ORIGIN OF HYPOGENE ALTERATION AND ZONING 85 PRINCIPLES . . . 85 HYDROTHERMAL PROCESSES IN THE FORMATION OF BERG DEPOSIT . . . 90 CHAPTER IV - MINERALIZATION INTRODUCTION 99 PRIMARY MINERALIZATION AND LATERAL ZONING 100 SECONDARY MINERALIZATION AND VERTICAL ZONING 108 INTRODUCTION 108 EXTENT OF LEACHING AND SUPERGENE ENRICHMENT . 112 MINERALOGY AND PROCESSES OF FORMATION 117 Zone of Oxidation and Sulphide Leaching 117 Zone of Supergene Enrichment 125 CHAPTER V - MINOR ELEMENTS IN PYRITE INTRODUCTION 134 UNIVARIATE ANALYSIS 140 v i Page CHAPTER V - MINOR ELEMENTS IN PYRITE (continued) BIVARIATE ANALYSIS 156 MULTIVARIATE ANALYSIS 164 MINOR ELEMENT ZONING IN THE DEPOSIT 170 INTRODUCTION 170 UNIVARIATE MINOR ELEMENT ZONING 174 ZONING OF FACTORS (MULTIVARIATE ANALYSIS) 181 CHAPTER VI - SUMMARY AND CONCLUSIONS 186 BIBLIOGRAPHY . . . 199 LIST OF APPENDICES A CHEMICAL ANALYSES OF QUARTZ MONZONITE PORPHYRIES . . 211 B ALTERATION: CATALOGUING OF CORE AND ESTIMATION OF ALTERATION INTENSITY 212 C CLAY SEPARATION TECHNIQUE 214 D FLUID INCLUSION DATA 216 E MINOR ELEMENTS IN PYRITE: SAMPLE VARIABILITY 218 F ELEMENTS DETECTED IN BERG PYRITE 220 G ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) 224 H DATA PARAMETERS AND COMPUTED CHI SQUARE VALUES 233 I VARIMAX FACTOR MATRIX, DISSEMINATED PYRITE 234 J VARIMAX FACTOR MATRIX, VEIN PYRITE 235 v i l "'• Page LIST OF TABLES 1 Mineralogical Composition of Intrusive Rocks, Berg Deposit 51 2 Chemical Compositions and Norms 52 3 Potassium-Argon Ages, Berg Deposit . 57 4 Partial Analyses of Iron Ores and Berg Ferricrete 120 5 Analytical Precision (For Logged Data) 138 6 Comparison of Spectrographs and Atomic Absorption Analyses of Pyrite Concentrates (All Analyses In PPM) 139 7 Summary - Means and Standard Deviations of A l l Analyses 145 8 Calculated t and F Probability of Vein Pyrite Versus Disseminated Pyrite (Based on L o g V a l u e s of A l l Available Data) . . . . . . 148 9 F and t Tests - Ni In Pyrite 149 10 Summary of t and F Tests For A l l Elements (Significance of Host Rock Type) 151 11 Correlation of Paired Variables 158 2 12 R and F Ratios For A l l Data of A l l Pairs of Variables Having Significant Correlation 160 13 Characteristic Co and Ni Concentrations In PPM 163 14 Successive Q-Mode Varimax Factor Components - Disseminated Pyrite . 166 15 Q-Mode Varimax Factor Scores - Disseminated Pyrite 167 16 Successive Q-Mode Varimax Factor Components - Vein Pyrite 168 17 Vertical Variation of Minor Elements in Pyrite 173 18 Spectrographs Analysis of Pyrite - Elements For Which Concentrations Were Determined . . . . 221 19 Minor Element Content of Chalcopyrite (In PPM) 222 v i i i Page LIST OF FIGURES 1 Berg Property location map 3 2 Geology of Tahtsa Range . 12 3 Air photo interpretation of fracture trends. Measurement of 87 most prominent photo linears in bedrock in Berg map-area. . 25 4 Geology - Berg Deposit 29 5 Geologic cross sections (view looking northerly) 30 6 Subdivision of Hazelton Group volcanic succession at Berg Deposit 33 7 Mineralogical composition of intrusive rocks, Berg Deposit 53 8 Generalized alteration zones, Berg Deposit 77 9 Mineral assemblages in thermally metamorphosed andesitic, quartz diorite, and quartz monzonite. Average rock compositions from Nockolds, 1954 93 10 Primary minerals - pyrite 103 11 Pyrite-chalcopyrite ratio 104 12 Primary minerals - Cu 105 13 Primary minerals - Mo 106 14 Primary Cu and MoS2 grade in relation to distance from main intrusive contact 109 15 Vertical zoning of Cu and KoS^ grades in diamond-drill cores . . . 111 16 Trend surface elevation marking start of gypsum in fractures . . . 114 17 Trend surface isopach map, strongly oxidized rocks (Cu leached). 115 18 Trend surface isopach map, supergene Cu mineralization 116 19 Mineral stability fields at 25° C, 1 ATM. A. Cu-Fe-S-O-H modified from Garrels (1960); B. Mo-Fe-S-O-H after Barakso and Bradshaw (1971); C. Fe-S-O-H in presence of K +, after Brown (1971). Field of weathering after Sato (1960) 126 20 Stability fields in Cu-H 0-C0 2 -0 2 -S system (including chalco-pyrite) at 25° C and 1 ATM 127 i x 'V. Page LIST OF FIGURES (continued) 21 Mineral compositions showing possible phase relationships 130 22 Primary and supergene copper minerals. Zones underlain by >.4% Cu. 132 23 Ni and Zn content of pyrite. Normal curve fitted to L°gjg data. 142 24 Pb and Ag content of pyrite 143 25 Frequency distributions of As, Co, and Ti 144 26 BImodal distribution containing vein and disseminated pyrite populations (Normal curves fitted to the data) 147 27 Distribution of Ni in pyrite. Data grouped according to host rock. A, C, D are fitted normal curves. 150 28 Cumulative probability. Minor elements in disseminated pyrite.. 155 29 Linear least squares regression line Y = a + bX for Co:Ni (A) and Pb:Zn (B) 157 30 Cobalt-nickel scatter diagram showing pyrite according to source 161 31 Co-NI ratios of pyrite 162 32 Zoning of minor elements in pyrite (As, B i , Ti) 175 33 Zoning of minor elements in pyrite (Co, Ni , Co + Ni, Co/Ni) . . . . 176 34 Zoning of minor elements in pyrite (Pb, Zn, Ag, Mn) 177 35 Composite of maximum minor element values > X + SD 179 36 Contoured plan of Q-mode factor values 182 37 Composite of factors 1 to 4 184 38 Berg Deposit - idealized geological sections 192 LIST OF PLATES FRONTISPIECE: Berg deposit, view looking northerly 1 8,103 peak with unconformity between Hazelton Group volcanic rocks (MJ, Map 1, Unit 1) and overlying Skeena Group volcanic rocks (LK, Map 1, Unit 4) 18 X Page LIST OF PLATES (continued) 2 Skeena Group rocks about 2 miles east of 8,103 peak 18 3 Panoramic view of Berg prospect, view to north and east . . . 28 4 and 5 Embayed skeletal myrmekitic quartz phenocrysts containing oligoclase inclusions in quartz monzonite porphyry . . . 40 6 and 7 Quartz monzonite porphyry (QMP; Map 2, Unit 3) 46 8 Quartz monzonite porphyry (QMP; Map 2, Unit 3) 47 9 Quartz monzonite porphyry dyke (part of QMP; Map 2, Unit 3) 47 10 Sericitized quartz plagioclase porphyry (QPP; Map 2, Unit 4) 48 11 Typical sericitized quartz plagioclase porphyry (QPP;. Map 2, Unit 4) 48 12 Plagioclase biotite quartz porphyry (PBQP; Map 2, Unit 5) . 49 v 13 Hornblende quartz feldspar porphyry (hbde QFP; Map 2, Unit 6) 49 14 Potassic alteration in quartz monzonite porphyry (DDH.6) . . 78 15 Phyllic (quartz-sericite-pyrite) alteration of quartz monzonite porphyry (DDH 25) 78 16 Potassic alteration of biot i t ic volcanic rocks (DDH 43) (quartz-orthoclase veined biotite hornfels) 79 17 Propylitic alteration of biot it ic volcanic rocks (DDH 16) . 79 18 Potassic alteration of biotit ic volcanic rock (DDH 43) . . . . 80 19 Propylitic alteration-in l a p i l l i tuff (DDH 68) with ~-bleached fracture margins 80 20 Subhorizontal gypsum-bearing fracture cleavage crosscutting pyrite and chalcopyrite grains (DDH 28) 84 21, 22, Electron microprobe beam scan of Berg limonite ('Berg X') and 23 showing Mo concentration in rim 124 xi ACKNOWLEDGMENT Fieldwork for this study was done while the writer was employed by Kennco Explorations, (Western) Limited. The late Dr. J . A. Gower stimu-lated the writer's interest in the deposit and suggested many research possibil it ies. George 0. M. Stewart and other Kennco field geologists familiarized the writer with geology of the deposit. The most beneficial contribution to this study was the supervision in the f ie ld , enthusiasm, and sustained interest by the late Charles S. Ney. Dr. A. D. Drummond has kindly kept the writer informed of results from recent exploration at the deposit. At the University of British Columbia research was supervised by the late Drs. W. H. White and J . A. Gower. Preparation of this dissertation began under the direction of Dr. A. E. Soregaroli and was later assumed by Dr. A. J . Sinclair." -The writer"is indebtedto Dr. Sinclair for in i t ia l ly supervising the investigation of pyrite geochemistry and later undertaking the role of thesis supervisor. Dr. C. I. Godwin made many suggestions for improvement of earlier manuscripts. At Queen's University, Kingston, Ontario, where the writer spent one academic session, Dr. W. D. McCartney acted as graduate advisor and Mr. Leo Mes provided invaluable instruction and assistance in the spectro-chemical laboratory. Mr. Harley Goddard of Kennco Explorations, (Western) Limited analysed a number of rock and pyrite specimens and Messrs. N. Colvin and P. Ralph of the British Columbia Department of Mines and Petroleum Resources provided some mineral identifications and analyses. x i i Assistance with computerized statist ical analyses was given by Messrs. A.L.C. Fox and D. G. Cargil l at the University of British Columbia and trend surfaces were generated by Mr. A. F. Bowman of the British Columbia Department of Mines and Petroleum Resources. Mr. A. Bentzen assembled equipment and instructed the writer in use of the microscopic heating apparatus. Preparation of this thesis was greatly facilitated by the efforts of the following members of the British Columbia Department of Mines and Petroleum Resources: photography by Mr. R. E. Player; drafting by Messrs. M. Calloway and J . Armitage; and typing by Ms. L. Mott. The final manu-script was typed by Mrs. Rosalyn J . Moir. The writer gratefully acknowledges a National Research Council of Canada Studentship for 1967/68; a National Research Council of Canada Postgraduate Scholarship for 1968-70; and financial assistance from Kennco Explorations, (Western) Limited during the winter of 1970/71. Expenses for spectrographs analyses at Queen's University were defrayed by National Research Council of Canada Grant A-4240 to W. D. McCartney. Finally I extend my gratitude to the members of ray family who patiently endured my long studentship and without whose optimism and encouragement I might never have completed this project. LEAF x i i i OMITTED IN PAGE NUMBERING. FRONTISPIECE: Berg deposit, view looking n o r t h e r l y . Pale coloured ridge i n centre of photo i s quartz monzonite porphyry stock. The mineralized zone i s defined by d r i l l access roads. East-ward dipping Hazelton Group p y r o c l a s t i c rocks form ridges on the north. Berg camp at el e v a t i o n of 5,100 feet i s at lower l e f t o f photograph. (Photo: T. Schroeter, September, 1974) xiv GEOLOGIC SETTING, MINERALIZATION, AND ASPECTS OF ZONING AT THE BERG PORPHYRY COPPER-MOLYBDENUM DEPOSIT, CENTRAL BRITISH COLUMBIA CHAPTER I INTRODUCTION GENERAL STATEMENT Berg prospect Is a copper-molybdenum deposit in the Canadian Cordillera that closely resembles the 'typical' porphyry copper deposit described in the idealized model of Lowell and Guilbert (1970) and the statist ical composite model of De Geoffroy and Wignall (1973). Copper and molybdenum sulphides are associated with a small Tertiary quartz monzonite porphyry stock that intrudes Mesozoic volcanic rocks. The stock has a number of intrusive phases and associated breccia bodies. Hypogene mineralization Is present as (1) fracture-controlled and disseminated pyrite and chalcopyrite; (2) a quartz stockwork with pyrite, molybdenite, and chalcopyrite; and, less commonly, (3) quartz and quartz-carbonate veins containing pyrite, sphalerite, galena, chalcopyrite, and sulphosalts. Sulphide zoning is evident within a broad annulus of hydrothermally altered rocks about a weakly mineralized intrusive core. Weathering has produced a leached capping underlain by a laterally extensive supergene copper zone. Hypogene copper and molybdenum sulphides below the supergene zone are locally of ore grade. Geological reserves are In the order of 400 million tonnes containing 0.3 per cent copper and .05 per cent molybdenite at a 0.25 per cent copper cutoff grade. 2 SCOPE AND PURPOSE OF THE STUDY This study describes regional setting, detailed geology, and style of mineralization at Berg deposit. Documentation of the type and abundance of ore and alteration minerals, as well as an investigation of minor element content of pyrites, were undertaken with emphasis placed on defining distributions and systematic variations (zoning) in the area of economic interest. Interpretation of mineralogical and minor element distribution patterns might aid in defining and understanding processes of ore formation in porphyry copper environments, as well as refining existing porphyry copper models and thus improving their potential for practical applications. LOCATION AND ACCESS Berg deposit is in Omineca Mining Division in west-central British Columbia at latitude 53 degrees 49 minutes north, longitude 127 degrees 25.5 minutes west (Figures 1 and 2). It l ies in Tahtsa Range approximately midway between Tahtsa, Nanika, and Kidprice Lakes in the northwestern corner of Whitesail map-area (NTS 93E/14W). Except for some habitation at Kemano to the southwest and Ootsa Lake to the east, the closest centres of commerce are Houston, 53 air miles to the northeast and Smithers, 68 miles to the north. The property is about 365 air miles north of Vancouver. The area of economic interest is on moderate to steep, south and west-facing slopes in generally rugged, mountainous terrain. The claims group containing Berg deposit l ies between elevations of 4,500 and 6,800 feet, mostly to the north of the east fork of Bergeland Creek. Figure 1 BERG PROPERTY LOCATION M A P 4 Access by personnel during much of the early exploration phase was by helicopter from bases at Smithers and Houston, but later a 26-mile bulldozer road was built to the camp from Twinkle Lake on the Tahtsa Lake Forest Access road. The access road trends along the northern flank of Sibola Peak and then follows Kidprice Creek to its headwaters where i t crosses a 5,700-foot pass and descends to camp at an elevation of 5,100 feet. During the early stages of exploration most d r i l l equipment and supplies were brought to the property on sleds with a bulldozer but work on the access road has upgraded i t to the point where, since 1970, i t is almost always possible during summer months to reach the property with a four-wheel-drive vehicle and occasionally with a two-wheel-drive vehicle. Access for about six winter months is restricted to vehicles capable of travel in snow, but winter travel requires prudence because of avalanche hazards. Spring thaw and resulting breakup render the property inaccessible by road for up to one month. Alternate access routes from the north and west may be feasible If mining development continues. WEATHER The weather, typical of mountainous terrain along the east flank of the Coast Mountains, is unsettled with rapid changes. Short, generally cool summers are punctuated with numerous showers. Midsummer temperatures of 21 degrees Celsius and more, are common but hail or sleet storms of short duration can occur on any day. The region is in the rain shadow of the Coast Mountains and thus has only light precipitation of about 15 to 20 inches per year. However, rainfal l can accumulate very rapidly during 5 short, violent storms. In winter, snow is generally only a few feet deep on the valley floors and open sidehills but deeper snow accumulations, dr i f ts , and avalanche areas on northern and eastern slopes give rise to small permanent snowfields that sustain numerous small glaciers. Possibly the most adverse weather conditions for work in the area are caused by high winds that occasionally reach gale and hurricane force. Company records also show that dense fog sometimes enveloped the area for days at a time and reduced v is ib i l i ty to tens of feet. HISTORY OF EXPLORATION Prospecting in the Whitesail map-area has been continuous since arrival of settlers in the early 1900's and has resulted in the discovery of a number of lead-zinc-silver, si lver, gold-tungsten, copper, and more recently, copper-molybdenum and molybdenum deposits. In 1913, 'Kid' Price found placer gold and its source veins on Sibola Peak and precipitated a small rush to the area in 1914. From 1915 to the late 1920's a number of lead-zinc-silver and copper deposits were located, the most notable being the Emerald Glacier deposits on Sweeney Mountain, approximately 8.5 miles southeast of Berg property. Prospecting activity declined during the 1930's but was renewed during 1943-47 by discoveries of gold-tungsten mineralization on LIndquist Peak (Duffel, 1959). General activity in the area increased after 1947 when the Aluminum Company of Canada Ltd. (Alcan) started engineering studies for i ts Kitimat project and the Geological Survey of Canada initiated a programme of systematic regional mapping. 6 The Francois-Tahtsa Lake access road built by Alcan, and the raised level in a number of lakes provided access to many new regions and prompted a period of renewed exploration and property development in the early 1950's. During this time the Lead Empire Syndicate located claims on lead-zinc-silver veins along what is now the northern boundary of the Berg deposit and some mineral production was attained from the Emerald Glacier mine. The main brunt of exploration activity and an appreciation for the tremendous mineral potential of the area began in the early 1960's when exploration philosophy became oriented toward large tonnage deposits amenable to open-pit mining. Highly mobile, helicopter-assisted exploration teams with geochemical and geophysical fac i l i t ies , and assisted by a recently published geological map (Duffel, 1959, Geological Survey bf Canada, Map 1064A), found a large number of significant deposits and occurrences of copper-molybdenum and molybdenum. These include: Berg, Huckleberry, Whiting Creek, Ox Lake, Red Bird, Coles Creek, Lucky Ship, Troitsa, Bergette, Nanika, and others (see Carter, 1974). The property name 'Berg' is derived from local geographic features, Bergeland Creek and Bergeland Mountain. Evidence of Berg deposit had been known for a long time because a large, brightly coloured capping* most of which is above treeline, marks the mineralized zone. Exploration pits pre-dating the original staking in 1961 were found on a quartz-molybdenite vein in the centre of the Berg property. Claims were located in the late 1940's by the Lead Empire'Syndicate northeast of the colour anomaly on— -fissure veins with lead-zinc-copper-silver minerals that are peripheral to <; the zone of copper-molybdenum mineralization. 7 Berg prospect was f irst staked (28 mineral claims) in 1961 to cover the prominent capping developed on and around a small stock that is the locus of a strong geochemical anomaly. Stream sediment samples at the confluence of the north fork and Bergeland Creek, about 2 miles downstream from the deposit, are said to have returned values as high as 47,000 ppm copper and 600 ppm molybdenum (H. Goddard, 1974, personal communication). In spite of a strong geochemical expression, prospecting results were discouraging. Only minor surface expression of sulphides is apparent in the form of widespread molybdenite in quartz veins and some local concentrations of secondary copper minerals along borders of basalt dykes. In 1963 geologists with experience in southwestern United States recognized the presence of a leached capping and the profound effects of surface leaching. Increased exploration expenditure in 1964 enabled bulldozer trenching and diamond dr i l l ing that demonstrated the presence of supergene minerals, a feature not common in the Canadian Cordillera. Subsequent work revealed that rocks are leached, in places, to depths of 100 feet or more and are underlain by an extensive 'blanket' of supergene copper enrichment. Dri l l ing during 1965 and 1966 delineated two main mineralized zones. A northeast zone contains primary (hypogene) and some supergene mineralization, and a southeast zone has widespread supergene mineralization. At the end of the 1966 field season the property consisted of 108 mineral claims on which there had been a total of 12,371 feet of diamond dri l l ing in 23 holes. During 1967 a 12,000-foot d r i l l programme tested the south-east zone on a widely spaced grid and three holes explored areas peripheral to the main area of interest. From 1968 to 1970 the property was dormant but metallurgical testing was done on composite samples of d r i l l core. 8 In 1971 three holes were dri l led in the northeast zone. At the end of the 1971 exploration programme a total of 49 diamond-drill holes of mainly NQ and BQ core had been dril led with a total footage of 26,184 feet. In 1972 exploration and development of the property were taken over by Placer Development Limited (now Canex Placer Limited) under agreement with Kennco Explorations, (Western) Limited. Since that time (to 1975) 25 d r i l l holes of NQ core totalling 23,239 feet and 19 d r i l l holes of PQ core totalling 6,049 feet have been completed. The writer was f i rst introduced to Berg prospect in 1966 and spent three months at the property in 1967 logging d r i l l core, studying rock alteration, and mapping regional geology. Most of the materials and data for this study were collected during that time. Two separate vis i ts in 1969 solved a number of stratigraphic problems. An 11-day stay during the 1971 d r i l l programme and a one-day v is i t in 1974 permitted additional sampling, re-acquainted the writer with many of the field problems, and kept the writer abreast of recent developments. PHYSIOGRAPHY Berg deposit is in the Tahtsa Ranges, a 10 to 15-mile-wide belt of mountains within the Hazelton Mountains (Holland, 1964). The Hazelton Mountains l ie along the eastern flank of the Kitimat Ranges of the Coast Mountains and form part of the Skeena Arch, a northeasterly trending area that was tectonically positive and was a locus for intrusive activity throughout much of the Mesozoic. Duffel (1959) referred to the Tahtsa Ranges as 'transitional ranges* because they represent a transitional zone between the rugged, predominantly granitic Coast Mountains to the 9 west and the roll ing h i l l region of sedimentary and volcanic rocks that underlie the Nechako Plateau to the east. The Tahtsa Ranges are further subdivided into east-west to northeasterly trending ranges called, from north to south, the Tahtsa, Sibola, Whitesail, and Chikamln Ranges. These are separated by major valleys whose bottoms range in elevation from 2,600 to 3,100 feet and which are occupied by long lakes. From north to south these are Morice, Nanika, Tahtsa, Troitsa, Whitesail, and Eutsuk Lakes. A l l drain eastward into waterways of the Skeena or Fraser River drainage systems. The highest peak in the Tahtsa Ranges is an unnamed 8,103-foot peak east of Nanika Lake, about 2.5 miles north-northeast of the Berg camp. A number of other mountains and ridges 7,000 feet and more in elevation occur as serrate peaks formed by cirque glaciation. Many of the highest and most rugged peaks are underlain by granitic cores. Mountain flanks and valley walls generally have more subdued, glacially rounded profiles with small benches, dissected plateau-like areas, and hanging valleys at various elevations. GLACIATION The Tahtsa Ranges have undergone extensive glaciation. According to Tipper (1971), multiple glaciation is probable over much of central British Columbia. In the Berg area there is evidence for three types of glaciation: a continental or mountain ice sheet, valley glaciation, and alpine cirque glaciation. During the main (Wisconsin) glaciation and possibly a second ice advance that was localized in north-central British Columbia (Fraser 10 glaciation), ice from the Coast Mountains flowed northeasterly and easterly along the existing major valleys into the Nechako Plateau. As ice depths increased, glaciers overrode valley walls and a l l but the highest peaks were glaciated. In Berg area there is ample evidence from erratic boulders on small, dissected plateaus and beveled ridge crests to show that ice reached elevations of at least 5,500 feet. During deglaciation (circa 15,000 B.P. and later, as shown by Prest, 1970) valley glaciation, or surges during wasting and overall recession of the ice sheet, further modified valley walls. Evidence of valley glaciation is preserved as terraces and ridges along sidehills bounding the larger valleys. The ridges were f irst thought to be slump structures but their occurrence from ridge crests to valley floors, lateral continuity over hundreds of feet, subparallel alignment along topographic contours, and development on slopes devoid of soi l indicate that they are of glacial origin and may be poorly developed lateral moraines and lateral channels. Cirque glaciation has been the dominant influence in sculpturing present topography above 5,000 feet. Small active cirque glaciers and snowfields are found on eastern and northern slopes at elevations above 6,000 feet. At present, cirque glaciers are wasting and receding so that most cirques, alpine valleys, and gullies are mantled by recently deposited debris from terminal and recessional moraines, and by thin fluvioglacial deposits. 11 CHAPTER II GEOLOGY REGIONAL GEOLOGY OF TAHTSA RANGE INTRODUCTION Berg deposit is about 8 miles east of the Coast Plutonic Complex in a region of bedded Jurassic and Cretaceous volcanic and sedimentary rocks intruded by a number of Jurassic, Cretaceous, and Tertiary stocks (Carter, 1974). Mapping by Duffel (1959) provided a geological framework for the area but i t is undergoing considerable revision as a result of recent work. Duffel's 'Hazelton Group' includes rocks of pre-Middle Jurassic to Early Cretaceous age. Current work in the Whitesail Lake and other map-areas to the north, mainly by geologists of the Geological Survey of Canada (Tipper, 1972; Richards, 1974), has resulted in Hazelton Group rocks being subdivided into Lower and Middle Jurassic units and has shown that Cretaceous sedimentary and volcanic rocks constitute a mappable unit that is more widespread than previously recognized. Recent mapping In Tahtsa Lake vicinity by D. G. Maclntyre (1974, personal communication) has resulted in a more precise description of the boundary between Hazelton Group and Cretaceous volcanic rocks. Considerable refinement of intrusive history has been done with potassium-argon dating (Carter, 1974). A revised geological map of the area is shown on Figure 2. Geological mapping of about 20 square miles surrounding Berg deposit by the writer and C. S. Ney in 1967 and 1969 is shown on Map 1, cross sections, Map 1A, and Map 2. On the basis of this mapping, bedded FIGURE 2 GEOLOGY OF TAHTSA RANGE BASED ON DUFFEL, 1959, MAP 1064A (WHITESAIL LAKE) AND UNPUBLISHED REVISIONS BY N. C. CARTER, H. TIPPER. A. PANTELEYEV, AND O. MaclNTYRE SCALE-MILES SCALE-KILOMETRES INTRUSIVE ROCKS TERTIARY MIDDLE TO UPPER EOCENE MIDDLE EOCENE ~ I C O A S T P L U T O N I C C O M P L E X : QUARTZ MONZONITE PORPHYRY, SOME ____] GRANITIC ROCKS (MAY BE OLDER ^ ^ B l = E L S i T E INTRUSIONS; Cu AND M o -IN PART) BEARING STOCKS CRETACEOUS AND TERTIARY UPPER CRETACEOUS - PALEOCENE 'BULKLEY INTRUSIONS' (IN PART): MAINLY PORPHYRITIC QUARTZ MONZONITE. M o - C u , AND Mo—W—BEARING STOCKS JURASSIC LOWER AND MIDDLE JURASSIC •OMINECA INTRUSIONS' (IN PART): GRANODIORITE, QUARTZ DIORITE, SYENITE BEDDED ROCKS QUATERNARY PLEISTOCENE AND RECENT IX- I ALLUVIUM, GLACIAL OUTWASH, TILL, MORAINE CRETACEOUS 'SKEENA GROUP' LATE LOWER CRETACEOUS AND ? YOUNGER G R E Y W A C K E , S I L T S T O N E , CONGLOMERATE ; INCLUDES UNITS OF PCRPHYRITIC ANDESITE, DACITE, RHYOLITE FLOWS. BRECCIA, TUFF, AND RELATED SUUVOLCANIC INTRUSIONS JURASSIC HAZELTON GROUP MIDDLE JURASSIC (MAY INCLUDE SOME LOWER CRETACEOUS) GREEN, GREY, MAROON VOLCANIC BRECCIA, TUFF, FLOWS; SOME SEDIMENTARY ROCKS LOWER JURASSIC I GREEN, RED, PURPLE VOLCANIC BRECCIA, CONLOMGERATE. GREYWACKE; SOME INTER-I CALATED SEDIMENTARY ROCKS TRIASSIC AND EARLIER , \ f ^ GNEISS COMPLEX 13 rocks were subdivided into three lithologically similar units: a basal volcanic unit consisting of mainly pyroclastic and volcanic-source sedimentary rocks (Map 1, unit 1) overlain by a series of porphyritic volcanic flow rocks (unit 2); a locally derived sedimentary, largely greywacke, unit forming an eastward-thickening prism or clastic wedge (unit 3); and an upper volcanic unit of porphyritic, intermediate to siliceous flows, breccias, and tuffs (unit 4). On Whitesail Lake map (1064A) a l l these rocks are shown as Hazelton Group and are described as '(mainly) Middle Jurassic' volcanic rocks. However, the possibility that Lower Cretaceous rocks are included in this map unit is suggested (Duffel, 1959). C. S. Ney observed an angular discordance between volcanic rocks and overlying sedimentary rocks at the head of Kidprice Creek, south of Berg deposit. Thus, classification of these rocks as Hazelton Group became suspect and subsequent mapping In the Berg area revealed a gentle angular unconformity between volcanic rocks of the upper and lower map units (Map 1, units 4 and 2) at the pinchout of the intervening sedimentary unit (unit 3). Age relationships were established in 1972 when ammonites collected earlier from sedimentary rocks (unit 3) by the writer were identified by H. Tipper as Cleoniceras of Albian stage (late Lower Cretaceous). Recent regional mapping by the Geological Survey of Canada suggests that Cretaceous sedimentary and volcanic rocks may be equivalent, respectively, to the Brian Boru and Red Rose Formations of Sutherland Brown (1960), and are part of an extensive draping of Cretaceous rocks over Lower and Middle Jurassic Hazelton Group rocks that extends from Hazelton to south of Tahtsa Lake in Smithers and Hazelton map-areas. They are now classified as part of the newly resurrected 'Skeena Group* (Richards, 1974). 14 BEDDED ROCKS STRATIGRAPHIC RELATIONSHIPS Volcanic rocks of the Hazelton Group are seen throughout the entire western half of Berg map-area (Map 1). In the eastern half they underlie Cretaceous vesicular-amygdaloidal, in places trachytoid, feldspathic volcanic flows, sedimentary rocks, and brecciated porphyritic flows. Originally a l l volcanic rocks exposed in the west and underlying Albian sedimentary rocks in the centre of the map-area were considered to be part of the Hazelton Group. These rocks were divided into two sub-units: a thick lower pyroclastic unit (Map 1, unit 1) and an overlying thinner flow unit (unit 2). However, recent mapping by D. G. Maclntyre (1974, personal communication) has shown unequivocably that vesicular-amygdaloidal feldspathic volcanic rocks to the south near Tahtsa Lake overlie Hazelton Group pyroclastic rocks with pronounced angular uncon-formity and are therefore part of a younger volcanic-sedimentary succession rather than part of the Hazelton Group. The relationship between these two older map units (units 1 and 2) is obscured in Berg map-area by snowfields and quartz diorite intrusions. Although no dis-cordance is obvious between map units 1 and 2, the vesicular-amygdaloidal feldspathic (Cretaceous) volcanic rocks (unit 2) dip more gently eastward than underlying Hazelton Group pyroclastic rocks and rocks to the west (unit 1). This was rationalized during in i t ia l mapping as being due to flattening of a fold limb in Berg map-area. However, i t is now concluded that Cleoniceras-bearing (Albian) sedimentary strata (unit 3) overlie conformably or disconformably the feldspathic amygdaloidal lavas (unit 2) and are in turn overlain by intermediate to acidic volcanic rocks, mostly breccias (unit 3). 15 HAZELTON GROUP (MIDDLE JURASSIC: Map 1, Unit 1) Volcanic rocks of the Hazelton Group comprise a predominantly pyroclastic assemblage about 5,500 feet thick that underlies the miner-alized area, Bergeland Creek valley, and ridges to the west. The rocks are grey, green, maroon, and purple tuff, tuff breccia, and lesser units of volcanic flows, flow breccia, and tuffaceous or epiclastic sedimentary rocks. Base of the unit is not exposed but oldest strata are thick beds of flow breccia, massive flows, and tuff that pass into a sequence of thinly bedded shale, chert, and tuffaceous siltstone and sandstone. These well-bedded sedimentary rocks are seen mainly in the lower reaches of the north fork of Bergeland Creek. They are overlain by the principal ridge forming pyroclastic members in Berg area. These are massive to sorted and graded, coarse to fine-grained tuff with some units of massive, rarely amygdaloidal flows and thin units of flow and tuff breccia and reworked tuffaceous sedimentary members. Younger beds may be, in part, subaerial but are mainly shallow marine (intertidal or l i t toral ) . A number contain well-developed accretionary l a p i l l i , mud pellets, and one locality with oscillation ripple marks is known. Many of the originally porous, coarsely fragmental rocks have a limy or ferruginous si l t -s ized matrix. Near the top of the sequence a few cobble beds with reworked volcanic sandstone matrix and volcanic clasts were noted. None was seen to contain any clasts of intrusive rocks; exotic rocks are mainly chert and a few pieces of crystalline limestone. Based on some partial analyses by Church (1972), Hazelton Group volcanic rocks from Sibola Peak, Berg deposit, and other nearby areas are andesite or basaltic andesite. Regional alteration is of the sub-greenschist 16 facies (Richards, 1974) but In Berg map-area no prehnite nor pumpellyite and only one locality with zeolites were noted. Epidote, chlorite, calcite, tremolite, montmorillonite, albite, K-feldspar, and sericite are wide-spread in the map-area. Also small amounts of garnet, tourmaline, amphi-bole, scolecite, and other minerals are present in xenoliths within quartz diorite. The latter minerals are of apparent hydrothermal origin and formed in broad propylitic zones or small skarn zones associated with intrusive rocks. SKEENA GROUP (LOWER CRETACEOUS AND ? YOUNGER; Map 1 , Units 2 to 4) Skeena Group rocks underlie the eastern part of Berg map-area. They can be subdivided into three map units: a lower volcanic unit (unit 2), an intervening sedimentary unit (unit 3), and an upper volcanic unit (unit 4). Rocks of the lower volcanic unit (unit 2) generally occur along a north-south-trending belt, up to 1% miles wide, through the centre of Berg map-area (Map 1). Best outcrop exposures are on steep slopes east of the main granitic intrusions and west of Kidprice Creek. A maximum of about 2,000 feet of strata is present. The rocks were classified in the field and later from partial chemical analyses as andesite to trachy-andesite. Flows are commonly vesicular and amygdaloidal and are, therefore, mainly subaerial but may locally be subaqueous as in two localit ies they contain thin lenses of limestone. Small amygdules and vesicules contain abundant chlorite as radiating fibrous spherulites as well as calcite, quartz, and montmorillonite. Calcite with crystalline and chalcedonic quartz is common in larger vugs and cavities. 17 The tase of the rock unit is not well exposed in Berg map-area but south of Tahtsa Lake is marked by a purple conglomerate member (D. G. Maclntyre, 1974, personal communication). Based on this observation, two small outliers of boulder conglomerate unconformably capping the ridge northwest of Berg camp are mapped as Cretaceous rocks. Sedimentary rocks (unit 3) crop out in most of the eastern half of Berg map-area where they form a clastic wedge that overlies feldspathic trachytoid vesicular-amygdaloidal flow rocks of the Cretaceous lower volcanic unit (unit 2). About 1 mile east of Berg camp sedimentary strata are intruded and thermally metamorphosed by quartz diorite. At i ts maximum extent in the southeast corner of the Berg map sheet the clastic wedge is at least 1,600 feet thick. The pinchout can be traced along the northern boundary of the area mapped and just east of 8,103 peak (see cross sections, Map 1A). Sedimentary units are predominantly sandstone with abundant feldspar grains and small rock fragments in a fine-grained micaceous matrix. Abundance of detrital mica is a useful field criterion for recognizing Cretaceous sedimentary rocks in Smithers and Hazelton map-areas (H. Tipper, 1972, personal communication). Beds are massive, poorly sorted deposits whose monotony is broken rarely by conglomerate members and units of thinly bedded shale and graded siltstone that show load casts, rip-up clasts, and slump structures. Large spherical concretions about 1 foot in diameter are common in some beds. One cherty shale member contains a few specimens of ammonite Cleoniceras which establishes an Albian age for the strata. The top of the unit is marked by a 50-foot succession of thinly bedded to lamellar siltstone and shale beds. These are overlain by a distinctive 18 PLATE 1: 8,103 peak with unconformity between Hazelton Group v o l c a n i c rocks (MJ, Map 1, unit 1) and over l y i n g Skeena Group v o l c a n i c rocks (LK, Map 1, unit 4). Approximately 500 feet of s t r a t a are shown. PLATE 2: Skeena Group rocks about 2 miles east of 8,103 peak. Al b i a n sedimentary s t r a t a (Map 1, unit 3) are o v e r l a i n by eastward-thinning prisms and beds of vo l c a n i c rocks (Map 1, u n i t 4). The conformable (disconformable ?) contact i s marked by a columnar feldspar porphyry s i l l . Approximately 1,200 feet of s t r a t a are shown. 19 red bed conglomerate that Is a maximum of about 20 feet thick, and red to purple siltstone lenses. The red bed conglomerate forms a persistent marker unit in the northeast corner of the map-area and can' be regarded as either the top of the sedimentary unit or, perhaps better, as the basal conglomerate of the overlying volcanic unit. The conglomerate contains cobble to boulder-sized clasts of volcanic rocks in a ferruginous, gritty sand matrix. Late Lower Cretaceous and possibly younger volcanic rocks of the Skeena Group upper volcanic unit (Map 1, unit 4) are seen in two areas. The largest is In the northeast corner of the map sheet, V$ to r 2 miles east of 8,103 peak where volcanic rocks (unit 4) appear to l ie conformably on Albian sedimentary beds (unit 3) and are separated from them by a well-jointed feldspar porphyry s i l l that intrudes along the top of the red bed unit (Plate 2). The volcanic rocks form a flat-topped ridge with basal, dark-coloured, bedded volcanic flow rocks and an over-lying pile of massive, pale-coloured breccias. Basal beds are lenses or discontinuous, rapidly eastward-thinning prisms of coarse-grained tuffaceous sandstone subsequently overlain by brown siltstone and shale, a coarse volcanic breccia member, porphyritic tuff breccia, and, purple to mauve and grey, aphanitic and porphyritic flow members. The top of the volcanic unit is composed of cream-coloured breccia about 400 feet thick. Total thickness of volcanic rocks in unit 4 is about 700 feet. A second area in which volcanic rocks of the upper unit (unit 4) are seen is a steep ridge forming the crest and summit of 8,103 peak and on a ridge to the northeast. There, about 350 feet of porphyritic grey to grey-green volcanic breccia and flows sit unconformably on well-bedded, more steeply dipping, purplish Hazelton Group pyroclastic rocks (Plate 1). On the ridge leading north from 8,103 peak, purple pyroclastic rocks of the Hazelton Group are intruded by a dyke swarm of glassy, black to mauve, and cream-coloured rocks averaging about 5 to 10 feet in thickness that may be feeders for overlying Cretaceous volcanic rocks. The abundance of coarse-grained volcanic breccias and glassy dykes may indicate the proximity of a volcanic centre In the vicinity of 8,103 peak. Partial chemical analyses of lithologically similar volcanic rocks overlying Cretaceous sedimentary strata in Sibola Range about 6 miles east of Berg area indicate that the composition of these volcanic rocks is predominantly dacite and rhyolite, with lesser andesite (Church, 1972). This contrasts with the andesitic to basaltic composition of Hazelton Group volcanic rocks. INTRUSIVE BODIES Intrusive rocks have been grouped into three map units (Map 1): a quartz diorite/diorite stock and related intrusions; a small multiphase mineralized stock of quartz monzonite porphyry; and minor intrusions of various probable affinities and ages. QUARTZ DIORITE Quartz diorite forms the largest intrusive body mapped, a north-south -trending stock at least 2,000 feet wide in the centre of Berg map-area. The body has steep walls and forms the core of Tahtsa Range. The intrusion has been traced by the writer at least 4 miles to the south of Berg camp where i t widens to about 9,000 feet along the southern edge of 21 Berg map sheet. The stock was mapped by Duffel (1959) as 'gabbro' which 'closely resembles many of the diorites associated with the main mass of the coast intrusion.' More detailed mapping has shown the rock to be a fine-grained, locally porphyritic, biotite hornblende quartz diorite or diorite. A minor hornblende-rich contact phase is found where brecciated microporphyritic andesite has been metasomatized along the intrusive contact. About 1 mile south-southeast of camp, the core of the quartz diorite intrusion is composed of a porphyritic, pink, sericite-r ich granodiorite and quartz monzonite. The quartz monzonite phase is por-phyritic and has a gradational contact zone about 100 feet wide within quartz diorite. The porphyritic phase is seen as a 600-foot-wide zone of rusty, hydrothermally altered rock surrounded by less altered, jointed quartz diorite typical of the main intrusive mass. Small intrusions of biotite hornblende diorite and hornblende diorite/quartz diorite related to the main intrusion are found to the north of and peripherally around the stock. These smaller intrusions occur as small stocks and dykes that penetrate Hazelton Group and younger strata as jagged intrusive plugs without any appreciable disruptive effects on bedding. The largest of the peripheral bodies intrudes west of the Berg camp and is found along an east-northeast trend coaxial with the main mineralized quartz monzonite porphyry. Thermal metamorphic effects due to intrusion of the main diorite mass are evident as zones of purplish brown biotite hornfels formed across widths of up to 400 feet (commonly 100 feet or less) from the contact. Small areas and local patches of coarsely recrystallized, amphibole and biotite-bearing metasomatized rocks have a 'diorit ized' look. Along the 22 north and northeast contact local patches of garnet-epidote skarn have developed in calcite-bearing amygdaloidal flow volcanics of Cretaceous volcanic units. Quartz diorite intrusions cut and metamorphose Albian sedimentary rocks but are intruded, altered, and mineralized by quartz monzonite porphyry. Potassium-argon dating by Carter (1974) shows that the quartz diorite intrusion is equivalent in age to younger phases and satel l i t ic stocks of the Coast Plutonic Complex. Quartz diorite may be as young as about 47 million years and appears to be significantly younger than the 76.7±2.5 million year old intrusions on Sibola Peak 10 miles to the east. QUARTZ MONZONITE PORPHYRY The most economically significant Intrusive body in the map-area is a small composite stock of quartz monzonite porphyry about 2,100 feet in diameter that intrudes pyroclastic rocks near the northwest margin'of the quartz diorite intrusion (Map 2). A l l phases of quartz monzonite are hydrothermally altered and mineralized. The main mass of the quartz monzonite stock is roughly equi-dimensional at surface with fairly regular contacts. Exceptions are along the south and southwest contact and at depth where dykes and s i l l - l i k e bodies project into or along volcanic strata. The main intrusive mass is a composite of at least three phases of coarse-grained biotite quartz feldspar porphyry that are intruded by at least one distinctly cross-cutting phase of porphyry, namely hornblende quartz feldspar porphyry. This porphyry forms a northeasterly trending dyke that bisects the main quartz monzonite mass and intrudes hornfels and quartz diorite to the northeast. The main phases of quartz monzonite have not been observed to intrude quartz diorite and are separated from i t by a screen of hornfelsed volcanic rock about 300 feet wide. Quartz diorite close to quartz monzonite is strongly altered and mineralized. An intrusive breccia body that is similar to quartz monzonite in composition and alteration intensity underlies a large area about 1,500 feet southeast of the quartz monzonite stock. Potassium-argon dating by Carter (1974) of biotite from the quartz monzonite stock, altered quartz diorite, and whole rock specimens from the mineralized hornfels surrounding the stock indicates Eocene ages with a mean value of about 50 million years. MINOR INTRUSIONS A number of minor intrusions of various types have been mapped as shown on Map 1. The two largest are coarse-grained, strongly jointed feldspar porphyry s i l l s that are emplaced at the top of the Albian sedimentary succession in the eastern part of the map-area. The more northerly s i l l is up to 50 feet thick and has intruded along the contact between sedimentary and volcanic rocks (Map 1, units 3 and 4). Small outliers of the feldspar porphyry can be seen to the west of the rhyolite mass where they overlie red bed conglomerate (uppermost part of unit 3). A second, larger body of feldspar porphyry forms a dip-slope capping of approximately 0.'5 square mile in area, about 1.5 miles east of Berg camp. The thickness of this s i l l may be as much as 150 feet. Age of feldspar porphyries has not been determined but they may be intrusive equivalents of extrusive Cretaceous volcanic rocks. A 24 Tertiary age cannot be ruled out as thin feldspar porphyry dykes, possibly equivalent to the s i l l s , intrude the quartz diorite stock. Massive white to cream-coloured, weakly layered, microporphyritic rhyolite dykes, similar to brecciated rhyolite south of 'Sanfts' Creek, form small irregular intrusions on the ridge southwest of the camp and are associated with numerous glassy dykes northeast of 8,103 peak. They are „ probably intrusive equivalents of, and possibly feeders for, Cretaceous rhyolite flow and breccia members. The most abundant type of dyke in the region is biotite feldspar or quartz feldspar porphyry. These form small dykes commonly 5 to 50 feet, rarely exceeding 100 feet, in thickness. They are found in a l l the main map units except volcanics of the youngest map unit (Map 1, unit 4) and are believed to be related to the main Tertiary quartz monzonite intrusion. Miocene (and younger ?) basalt and possibly some andesite dykes intrude a l l major rock units throughout the map-area. They are commonly 1 to 10 feet wide although dykes up to 80 feet in width are known. Dykes are abundant at surface but are not concentrated in any one area. A greater than average number of thin basalt dykes has been intersected in d r i l l holes in the mineralized zone. STRUCTURE Bedded rocks in the map-area form an easterly dipping panel, commonly with 10 to 30-degree dips. Folding is weakly developed as large-scale undulations and flexures of strata about north to north-northeasterly fold axes. In a few areas slump folds, bed crenulations, FIGURE 3 : Air photo interpretation of fracture trends. Measurement of 87 most prominent photo linears in bedrock in Berg map-area. 26 and chaotic blocks with contorted strata are associated with small-scale de'collements. Such de'collement structures are seen on the west flank of 8,103 peak (Plate 2). Fracture patterns, as shown on Figure 3, indicate predominance of east-northeast and north to northeasterly trends. Where fault displacements or offsets can be measured, the most significant movements are, at most, a few hundred feet in magnitude and appear to have taken place along northwesterly breaks. Age of faulting is uncertain but Miocene basalt dykes that commonly invade the most intensely fractured zones rarely show any significant offsets. This implies that post-Miocene movements may have been minor relative to those during Cretaceous or Early Tertiary time. Structural controls on the emplacement of intrusive bodies are suggested by north-south elongation of the main quartz diorite stock and alignment of small diorite intrusions along the northern extension of the stock. Subsidiary, possibly younger, northeasterly trending structures or zones of weakness appear to have controlled emplacement of subsidiary quartz monzonite intrusions and younger dykes that bisect them. The youngest structural breaks are northwesterly zones that are invaded by basalt dykes and may offset younger ridge-forming porphyry dykes that cut the main stock. GEOLOGY OF BERG DEPOSIT INTRODUCTION Geology of the mineralized zone at Berg deposit was studied extensively and described by George 0. M. Stewart (1967). Stewart, 27 aided by some bulldozer trenches and a few diamond-drill holes, mapped highly weathered surface exposures. His interpretation of general geology, major map units, and locations of intrusive contacts is s t i l l essentially valid. Stewart described five main map units: hornfelsed and hydrothermally altered Hazelton Group volcanic and sedimentary rocks; a diorite/quartz diorite stock thought to be a satell ite of the Coast Plutonic Complex; a composite quartz monzonite porphyry stock about which copper-molybdenum mineralization is localized; a crosscutting 'quartz lat i te ' post-ore dyke phase; and an intrusive breccia pipe. Recent diamond dri l l ing in previously untested areas, principally in the core and near margins of the quartz monzonite stock, indicates that a number of porphyry phases can be dis-tinguished and internal intrusive relations are more complex than f i rst thought. Recent revisions of Stewart's mapping are shown on Map 2 and illustrated in Figures 4 and 5. Surface exposures are limonite-stained, deeply weathered, crumbly outcrops that are leached by oxidation and acid groundwaters. Slopes are generally devoid of vegetation and are mantled by slide debris and talus. The centre of the mineralized area is underlain by a quartz monzonite porphyry stock generally containing 2 per cent and less sulphide minerals. This stock is a roughly equidimensional plug about 2,100 feet in diameter and has a bulbous northwesterly trending lobe in the southwest. It is transected by a splayed northeasterly trending porphyry dyke that forms a spine-like ridge. Porphyritic intrusive rocks weather pale to yellow brown and form an elongated northeasterly trending mound in the centre of a broad, west-facing embayment in a prominent north-trending ridge. A broad horseshoe-shaped low-weathering area that opens Into Bergeland Creek tributary on the southwest surrounds the somewhat more PLATE 3 : Panoramic view of Berg prospect, view to n o r t h and e a s t . NJ 00 FIGURE 4 GEOLOGY - BERG DEPOSIT [—20 , 000 N • DRILL HOLE -VERTICAL DRILL HOLE - INCLINED Scale •ib'tf v ' ' i - ' V o O L -r><o ~ 7 c ' . ij.' v:- <• v1 ' « I ' .' V.<-, - > • C qtz monz-granodi or •j qtz bearing monzodi L(hbde QFP) qtz monzonite qtz d io r i te hornfels ,volcanics 30 Scale 0 800 1 • I feet Q M P ] breccia -qtz monz - granodi or qtz bearing monzodiorite (hbde Q F P ) qtz monzonite qtz diorite hornfels 31 r e s i s t a n t porphyry stock. This i s the zone of strongly f r a c t u r e d , mineralized, and a l t e r e d v o l c a n i c rocks. Rapid erosion of a l t e r e d rocks abetted by p e r c o l a t i o n of a c i d i c groundwater that removes gypsum from fr a c t u r e s has probably been more important than g l a c i a l scouring i n development of low-lying areas about the stock. The most h i g h l y eroded zones have r e l i e f of about 700 f e e t r e l a t i v e to the porphyry ridge c r e s t and are occupied by 'Red' Creek on the southeast and 'Pump' Creek on the northwest (Map 2). Rocks containing economically s i g n i f i c a n t sulphide minerals extend outward f o r at l e a s t 2,000 feet beyond the quartz monzonite contact and adjoining deeply eroded v o l c a n i c rocks. Rocks with sulphide minerals are marked by dark brown lim o n i t e - s t a i n e d outcrops. To the north of the quartz monzonite stock these are v o l c a n i c and sedimentary rocks and to the northeast and east, quartz d i o r i t e . Topography r e f l e c t s changes i n rock type and a l t e r a t i o n . Slopes are r e l a t i v e l y gentle near the stock, steepen to about 30 degrees on f l a n k i n g h i l l s i d e s , and at the outer edge of the limonite-stained zone steepen abruptly to about 45 degrees. Weakly a l t e r e d and sparsely mineralized v o l c a n i c rocks on the north and quartz d i o r i t e on the east form ridge c r e s t s that tower over the mineralized zone. Maximum r e l i e f i s approximately 1,800 feet on the ridge to the north and 2,400 feet on the ridge to the east of the quartz monzonite stock. BEDDED ROCKS Host rocks f o r i n t r u s i o n s and mineral deposits are Middle J u r a s s i c Hazelton Group v o l c a n i c rocks (Maps 1 and 2, unit 1 ) . These are mainly coarse to medium-grained t u f f s of andesitic composition as 32 w e l l as subordinate flow rocks, b r e c c i a s , e p i c l a s t i c v o l c a n i c s (reworked v o l c a n i c source sandstones or 'greywackes'), and minor amounts of marine shale and s i l t s t o n e . Outside the area of m i n e r a l i z a t i o n v o l c a n i c rocks are dark grey, grey-green, purple, and red i n colour with obvious fragmental textures and well-defined bedding. Closer to i n t r u s i o n s the v o l c a n i c rocks are r e c r y s t a l l i z e d to dark grey-brown and black rocks i n which o r i g i n a l fragments are seen as r e l i c t c l a s t s or are t o t a l l y o b l i t e r a t e d i n homogeneous-looking h o r n f e l s . The v o l c a n i c succession s t r i k e s approximately north-south and i s t i l t e d eastward at about 30 degrees. There i s no apparent r e p e t i t i o n by f a u l t i n g or other s t r u c t u r a l complications. Thus, an east-west s e c t i o n measured along Bergeland Creek and the ridge immediately north of Berg deposit represents a reasonably true geologic cross s e c t i o n with younger rocks or 'tops' to the east. A generalized succession subdivided i n t o s i x u n i t s representing about 5,000 feet of s t r a t a i s shown i n Figure 6. Oldest rocks are on the west and are shown as map unit A. Rocks of map unit A form a 1,000-foot-thick sequence of grey and grey-green, fine-grained to weakly p o r p h y r i t i c andesites, flow b r e c c i a s , and i n t e r c a l a t e d fine-grained sedimentary l a y e r s . The t u f f s , t u f f b r e c c i a s , and flows are seen along the north bank of upper Bergeland Creek and o v e r l i e about 1,000 feet of t h i n l y bedded shale, s i l t s t o n e , chert, and tuffaceous sediments exposed further downstream. Unit B c o n s i s t s of a 1,300-foot-thick p i l e of t u f f s , minor b r e c c i a s , and a few flow u n i t s i n c l u d i n g three paired u n i t s of purple l a p i l l i t u f f o v e r l a i n by grey and mauve ash t u f f . Purple members are made up of pale grey and cream l a p i l l i -s i z e d p o r p h y r i t i c fragments c o n s t i t u t i n g from 10 to 30 per cent of the Figure 6. Subdivision of Hazelton Group Volcanic Succesiion at Berg Deposit iii TUFFS. TUFFACEOUS SEDIMENTS. FLOWS FLOWS, FLOW BRECCIAS BRECCIA TUFFS TUFFS. BRECCIAS MINOR FLOWS FLOWS. FLOW BRECCIAS SEDIMENTS SECTION INTRUDED BY MINERALIZED QUARTZ MONZONITE PORPHYRIES TUFFS. BRECCIAS, FLOWS SHALE, SILTSTONE. CHERT. TUFFACEOUS SEDIMENTS 34 rock i n a dense v i t r i c groundmass. Overlying grey and mauve rocks are l i t h i c t u f f s i n which there Is abundant s o r t i n g of fragments. Most beds are graded and there i s much a l t e r n a t i o n between beds containing e i t h e r f i n e ash or coarse ash and l a p i l l i fragments. The three paired u n i t s are s u c c e s s i v e l y thinner; the older being over 200 feet i n thickness, the middle 150 f e e t , and the upper only 60 feet t h i c k . I n d i v i d u a l members wi t h i n these map un i t s are 1 inch to a few feet i n thickness. Above the paired purple-grey u n i t s are mainly dark purple, mauve, and grey, l o o s e l y packed, l i t h i c l a p i l l i and ash t u f f s that contain a few c r y s t a l l i n e limestone fragments. The top of unit B i s taken to be a 40-foot-thick succession of massive fine-grained flow v o l c a n i c s . Map unit C co n s i s t s of about 600 feet of red, purple, and grey l i t h i c t u f f s . The succession i s made up of t h i n l y bedded l a p i l l i t u f f s with fragments up to 5 centimetres i n s i z e , 0.5 to 1.5-centimetre fragments being most common i n an ash matrix. These t u f f s are very porous with l o o s e l y packed fragments i n a r e l a t i v e l y homogeneous nonsorted ash matrix. Some fragments are cindery and p e l l e t e d accretionary l a p i l l i probably deposited i n a s u b a e r i a l accumulation. Some beds co n s i s t of reworked tephra with a limy mud matrix and formed i n an apparently shallow subaqueous environment. Unit D c o n s i s t s of about 300 feet of pale and medium grey v o l c a n i c b r e c c i a with fragments up to 5 centimetres i n s i z e . This unit i s o v e r l a i n uncon-formably by a t h i n capping of Cretaceous boulder conglomerate on the ridg e northwest of the camp. Unit E i s a 300-foot succession of 'greenstone' flows and flow breccias which i s o v e r l a i n by unit F, a heterogeneous assemblage of t u f f s , fine-grained tuffaceous sediments i n c l u d i n g limy s i l t s t o n e s , v o l c a n i c sandstones, and flows t o t a l l i n g at le a s t 500 feet i n s t r a t i g r a p h i c thickness. 35 Rocks of u n i t s B, C, and upper part of A have been intruded, a l t e r e d , and mineralized. The rocks have been described as 'hornfels.* However there has been considerable metasomatism and, thus, the term 'hornfels' i s used i n an informal sense. At Berg deposit, Sutherland Brown (1967) d i s t i n g u i s h e d between b i o t i t i c h o r n f e l s i n a thermal aureole and hydrothermally metasomatized rocks, he termed skarn, containing r e c r y s t a l l i z e d quartz, b i o t i t e , and K-feldspar. He further subdivided hydrothermally a l t e r e d rocks i n t o a t h i r d group of mottled ' g r e i s e n - l i k e ' (quartz s e r i c i t e ) rocks. However, o r i g i n of b i o t i t e cannot always be ascribed on the b a s i s of appearance to e i t h e r purely contact metamorphism or metasomatism and the term 'ho r n f e l s ' w i l l be retained i n t h i s t h e s i s f o r purely d e s c r i p t i v e purposes. Thus, b i o t i t e hornfels r e f e r s to a l l the massive, dark, fine-grained metamorphosed rocks surrounding Berg i n t r u s i o n s . While some epidote and rare garnet occurs i n a l t e r e d calcareous beds along the quartz d i o r i t e contact or i n pendants i n quartz d i o r i t e , no skarn assemblages are present w i t h i n Berg deposit. INTRUSIVE ROCKS Two d i s t i n c t i v e i n t r u s i v e bodies are seen at Berg deposit. They d i f f e r i n composition, texture, shape, and e f f e c t on intruded rocks. The older rock i s a fine-grained b a s i c quartz d i o r i t e that has no inherent m i n e r a l i z a t i o n and has r e c r y s t a l l i z e d intruded rocks i n t o a dense, compact h o r n f e l s . Quartz d i o r i t e i s part of a large i n t r u s i v e body at l e a s t 2,000 feet wide that extends f o r at l e a s t 5 miles to the south of Berg deposit. The i n t r u s i v e contact i s steeply dipping, somewhat serrated i n plan, but continuous without known offshoots or p r o j e c t i o n s . 36 The younger i n t r u s i o n i s a composite stock of quartz monzonite porphyry not more than one-half mile i n diameter. Every i n t r u s i v e phase i s mineralized to some degree and adjoining v o l c a n i c rocks and quartz d i o r i t e are a l t e r e d and mineralized e x t e n s i v e l y . The core of the quartz monzonite stock i s p l u g - l i k e and i s flanked to the south and southwest by dykes, s i l l s , and i r r e g u l a r apophyses. Quartz monzonite does not intrude quartz d i o r i t e , but has a l t e r e d and mineralized i t . Both rock types are cut by one large and a number of smaller porphyry dykes r e l a t e d to quartz monzonite. Age and genetic r e l a t i o n s h i p s between Intrusive rock types are not c e r t a i n . P o r p h y r i t i c quartz monzonite i s found i n a zone a few hundred feet wide within quartz d i o r i t e 2 miles south of Berg deposit. The zone i s w i t h i n the centre of and widest" part of the quartz d i o r i t e i n t r u s i o n and appears to have gradational contacts with quartz d i o r i t e . Thus, p o r p h y r i t i c quartz monzonite may be a more highly d i f f e r e n t i a t e d phase of a parent quartz d i o r i t e magma. The mineralized quartz monzonite porphyry and quartz d i o r i t e at Berg deposit might be oogenetic. Description of i n t r u s i v e rocks i n Berg map-area at a r e g i o n a l scale has been done by D u f f e l (1959) and at the property by Kennco geologists (Stewart, 1967), Sutherland Brown (1967), and more r e c e n t l y Canex Placer g e o l o g i s t s . Nomenclature used i n t h i s study i s a m o d i f i -c a t i o n of the d e s c r i p t i v e c l a s s i f i c a t i o n used by Canex Placer g e o l o g i s t s (1974, personal communication). I t i s based l a r g e l y on diamond d r i l l i n g i n the core of the quartz monzonite stock since 1972. Quartz d i o r i t e was mapped by D u f f e l as gabbro. Along the contact the rock i n places contains l e s s than 10 per cent quartz and Is melanocratic 37 due to an abundance of hornblende. However, average p l a g i o c l a s e composition i s that of basic andesine (An,^); quartz content s l i g h t l y exceeds 10 per cent; and b i o t i t e accompanies hornblende as a mafic constituent. The rock i s b e t t e r c l a s s i f i e d as quartz d i o r i t e and has been so described by i n v e s t i g a t o r s subsequent to D u f f e l . The mineralized stock of quartz monzonite porphyry c o n s i s t s of at l e a s t two d i s t i n c t types of porphyry. The two are distinguished on the b a s i s of texture, mineralogy, f r a c t u r e i n t e n s i t y , degree of a l t e r a t i o n , and most r e a d i l y by d i f f e r e n c e s i n t h e i r weathering c h a r a c t e r i s t i c s i n outcrop. The younger porphyry dyke i s l e s s a l t e r e d and forms a r e s i s t a n t ridge c r o s s c u t t i n g the main mass of porphyry. From f i e l d observations Kennco geologists (Stewart, 1967) c a l l e d the main mass quartz-monzonite-porphyry-and-the-crosscutting-dyke - q u a r t z — — l a t i t e porphyry. Sutherland Brown (1967) on the basis of f i e l d mapping and microscopic examinations classed rocks as quartz monzonite porphyry and quartz-bearing monzonite porphyry. Both Stewart and Sutherland Brown recognized the presence of more than one phase of quartz monzonite i n the main stock and i n f e r r e d that i n t e r g r a d a t i o n a l r e l a t i o n s h i p s e x i s t between the phases. Recent d r i l l i n g by Canex Placer Limited has revealed that the mineralized stock (Map 2) i s composed of two phases of quartz monzonite, c a l l e d i n t h i s report, quartz monzonite porphyry (QMP; Map 2, unit 3), and s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (QPP, Map 2, unit 4), as w e l l as a t h i r d phase of quartz monzonite or quartz-bearing monzonite c a l l e d p l a g i o c l a s e b i o t i t e quartz porphyry (PBQP; Map 2, unit 5). The phases are most apparent on the basis of texture. Differences i n type, amount, and proportion of minerals are s l i g h t and are recognized only by c a r e f u l point counts and examination of rocks i n t h i n s e c t i o n . The porphyry dyke (QFP; Map 2, u n i t 6) that crosscuts the quartz monzonite stock i s d i s t i n c t on the b a s i s of mineralogy and texture. Descriptions of rock types as determined from point counts on phenocrysts i n large stained slabs and matrix i n t h i n s e c t i o n are given below, summarized i n Table 1, and i l l u s t r a t e d by a ternary p l o t i n Figure 7. QUARTZ DIORITE (Map 2, Unit 2) Quartz d i o r i t e i s a pale grey, f i n e to medium-grained rock i n which p l a g i o c l a s e , hornblende, and b i o t i t e are the most obvious components. Specimens range i n composition from d i o r i t e to granodiorite but quartz d i o r i t e i s most common. Laths of p l a g i o c l a s e about 1 m i l l i m e t r e i n s i z e are randomly oriented i n a matrix of hornblende, fine-grained b i o t i t e , and very f i n e anhedral grains of quartz and orthoclase. Some subhedral c r y s t a l s of hornblende are up to 5 m i l l i m e t r e s and more i n s i z e . A few specimens from near the i n t r u s i v e contact contain l e s s than 10 per cent quartz and have weak o r i e n t a t i o n of p l a g i o c l a s e l a t h s and hornblende c r y s t a l s . P l a g i o c l a s e i s normally zoned basic andesine to l a b r a d o r i t e (An,_ r o ) . C h l o r i t e formed a f t e r hornblende and l e s s commonly b i o t i t e . HZ-DO Other a l t e r a t i o n minerals include s e r i c i t e , epidote, and c a l c i t e . Magnetite, sphene, and apatite are accessory minerals. In the zone of m i n e r a l i z a t i o n near quartz monzonite, c h a l c o p y r i t e , p y r i t e , some molyb-denite, quartz veining, and t o t a l replacement of o r i g i n a l mafic minerals by fine-grained f e l t e d b i o t i t e are common. 39 QUARTZ MONZONITE STOCK AND DYKES (Map 2, Units 3 to 5) QUARTZ MONZONITE PORPHYRY PHASE (QMP, Unit 3) Quartz monzonite porphyry i s a grey to pink, coarse, two-feldspar quartz porphyry. I t contains about 45 per cent phenocrysts of mainly oligoclase-andesine (An^g)» quartz, b i o t i t e , and some orthoclase i n a fine-grained quartz feldspar matrix. P l a g i o c l a s e phenocrysts are chalky white to cream, grey, b u f f , and grey-green subhedral blocky l a t h s 2 to 8 m i l l i m e t r e s , averaging about 5 m i l l i m e t r e s , i n s i z e . Quartz and graphic q u a r t z - o l i g o c l a s e forms large, rounded, deeply embayed, s k e l e t a l grains averaging 4 to 6 m i l l i m e t r e s , i n a few cases up to 1 centimetre, i n s i z e . Orthoclase i s seen as scattered p o i k i l i t i c to myrmekitic phenocrysts about 5 m i l l i m e t r e s i n s i z e and as sparse, squat megacrysts up to 2 c e n t i -metres i n length. A few grains have rims of pla g i o c l a s e around orthoclase. B i o t i t e as tabular books 6 m i l l i m e t r e s i n length and 4 millimetres i n cross s e c t i o n i s the sole mafic c o n s t i t u e n t . A small amount of hornblende that was o r i g i n a l l y present i s now t o t a l l y replaced by b i o t i t e and s e r i c i t e . The matrix i s an all o t r i o m o r p h i c granular intergrowth of .04-millimetre grains of p l a g i o c l a s e , s l i g h t l y i n excess of equal amounts of s i m i l a r l y s i z e d quartz and orthoclase. In t h i n section quartz phenocrysts are very d i s t i n c t i v e with a myrmekitic or graphic appearance. Grains are strongly corroded with deep embayraents and contain i n c l u s i o n s of small o l i g o c l a s e ? grains. Grain boundaries appear to be resorbed r e s u l t i n g i n rea c t i o n rims of micro-c r y s t a l l i n e quartz. Large grains are sutured composite c r y s t a l s that appear to be cumulates of a number of smaller grains, or may simply be fra c t u r e d megacrysts. P l a g i o c l a s e phenocrysts are strongly s e r i c i t i z e d PLATES 4 and 5: Embayed s k e l e t a l myrmekitic quartz phenocrysts containing o l i g o c l a s e i n c l u s i o n s i n quartz monzonite porphyry. 41 and l o c a l l y a r g i l l i c . C r y s t a l s are strongly zoned i n an o s c i l l a t o r y -normal manner but twinning i s l a r g e l y obscured by a l t e r a t i o n and p l a g i o c l a s e determinations are d i f f i c u l t . On the basis of a few determinations p l a g i o c l a s e appears to be oligoclase-andesine (An^g). Hornblende which was o r i g i n a l l y present i n small amounts i s t o t a l l y replaced by fine-grained f e l t e d b i o t i t e . Fine-grained secondary b i o t i t e i s a l s o scattered throughout the matrix. In a d d i t i o n to s e r i c i t e , b i o t i t e , c h l o r i t e , c a l c i t e , and opaque minerals, some k a o l i n i t e and montmorillonite are a l t e r a t i o n products. Sphene, a p a t i t e , and z i r c o n are accessory minerals. Quartz veins and gypsum-filled f r a c t u r e s are common. A dyke phase of a s i m i l a r quartz monzonite porphyry commonly d i s p l a y s c h i l l e d contacts and can be seen to intrude quartz monzonite porphyry and p o s s i b l y p l a g i o c l a s e b i o t i t e quartz porphyry i n a number of d r i l l h oles. The dyke rock contains about 40 to 45 per cent coarse grained phenocrysts of p l a g i o c l a s e (An.jQ_.33) w * t n b i o t i t e , some quartz and orthoclase, i n a fine-grained matrix of mainly quartz and orthoclase. Quartz megacrysts up to 1 centimetre i n s i z e are the larges t grains seen. Matrix Is a d i s t i n c t i v e pinkish grey to orange-tinted grey or brown colour and i s considerably le s s a l t e r e d than i n other porphyry phases. B i o t i t e and plagioclase phenocrysts are also l i t t l e a l t e r e d and fresh l o o k i n g . Secondary b i o t i t e and other a l t e r a t i o n minerals are of minor abundance but fine-grained disseminated magnetite i s more abundant than i n other porphyry phases. In a d d i t i o n to c h i l l e d contacts and weak a l t e r a t i o n , strong magnetic response and paucity of ore minerals set t h i s rock type apart from other quartz monzonite porphyry phases. 42 SERICITIZED QUARTZ PLAGIOCLASE PORPHYRY PHASE (QPP; Map 2, Unit 4) This phase of quartz monzonite i s a medium-grained porphyry, the finest grained of a l l the types of porphyry recognized at Berg deposit. The rock i s strongly s e r i c i t i z e d , leucocratic buff to grey, rarely grading to medium brown i n colour. It contains about 35 per cent phenocrysts, mainly plagioclase (^30-32^ some quartz. Orthoclase phenocrysts are notably rare or absent as are large grains of bi o t i t e . Grain size of plagioclase and quartz phenocrysts varies from 1 millimetre to a maximum of 5 millimetres, 2 to 3 millimetres being the average. Fine-grained plagioclase phenocrysts are equant subhedral crystals that are evenly distributed to produce a rock with homogeneous appearance. Coarser phenocrysts vary i n size and are rounded, thereby giving a seriate texture to the porphyry. Quartz grains average 2 millimetres i n size and are strongly corroded. In thin section matrix can be seen to be composed of very fine granular intergrowth from .01 to .03 millimetre in size of plagioclase, orthoclase, and quartz. Plagioclase i s sl i g h t l y more abundant than ortho--tfit clase and appears to be^same composition as phenocrysts (^ n3o-32^ * Q u a r t z content i s variable, probably due to different degrees of s i l i c i f i c a t i o n . Where abundant, quartz in the matrix i s an accumulation of rounded, possibly overgrown grains. Quartz veins are common. Sericite i s abundant and pervasive; It replaces both plagioclase and orthoclase. Together with kaolinite, lesser chlorite, and montmorillonite, sericite comprises up to 10 per cent and more of the rock. It has formed mainly after feldspars but i s also found with pyrite, chlorite, and calcite replacing primary bi o t i t e (and hornblende ?). Almost a l l biot i t e now seen in the rock i s 43 present in the matrix as scattered, fine-grained secondary biotite. Where abundant, fine-grained biotite imparts a brownish cast to the matrix of the rock. Strong sericit ization, medium-sized phenocrysts, absence of orthoclase phenocrysts, and lack of large biotite grains readily set this phase apart from other phases of quartz monzonite. PLAGIOCLASE BIOTITE QUARTZ PORPHYRY (PBQP; Map 2, Unit 5) This rock type has less quartz and more plagioclase than the two quartz monzonite phases (units 3 and 4) and straddles the boundary of quartz monzonite and quartz-bearing monzonite fields (Figure 7). Hand specimens are relatively homogeneous in appearance with grey to pinkish grey or brown matrix in which evenly^ distributed fine and medium-grained phenocrysts form about 40 per cent of the rock. Plagio-clase phenocrysts are pale grey in colour and are of two sizes. Larger ones 4 to 7 millimetres, averaging 5 millimetres, in size comprise about 80 per cent of the feldspar phenocrysts; smaller ones are 1 to 2 m i l l i -metres in size. Quartz phenocrysts are corroded grains 3 millimetres and smaller in size. Orthoclase is seen as rare phenocrysts that are the same size or smaller than surrounding plagioclase grains. In a few crystals orthoclase forms rims or mantles on plagioclase. Biotite is unaltered looking, fresh euhedral platelets or short, stubby books about 2 millimetres in cross section. These contrast markedly with elongate coarse books of biotite in quartz monzonite porphyry (QMP) and highly sericitized biotite in quartz plagioclase porphyry. 44 In t h i n s e c t i o n , matrix i s seen to contain .02-millimetre-sized grains of mainly p l a g i o c l a s e , some orthoclase, and l e s s e r quartz. Plagio-clase i n matrix and phenocrysts i s moderately s e r i c i t i z e d but twinning, mainly as a l b i t e and combined Carlsbad-albite types, i s common and not much af f e c t e d by a l t e r a t i o n . C r y s t a l s are zoned i n an o s c i l l a t o r y - n o r m a l manner commonly with four to s i x c y c l e s . Measured p l a g i o c l a s e composition ranges from basic o l i g o c l a s e to andesine ^^n28-34^* Qv^zH mafic minerals i n t h i s rock type are about twice as abundant as i n quartz monzonite porphyry (QMP) and s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (QPP). The amount of secondary b i o t i t e i s reduced but i s compensated by the presence of increased amounts of fine-grained hornblende. B i o t i t e to hornblende r a t i o v a r i e s from 2:1 to 5:1. A l l fine-grained o r i g i n a l b i o t i t e and hornblende grains i n the matrix are c h l o r i t i z e d to some degree. Hornblende i s replaced extensively by b i o t i t e or c h l o r i t e , s e r i c i t e , c a l c i t e , and opaque minerals. QUARTZ MONZONITE-GRANODIORITE OR QUARTZ-BEARING MONZODIORITE DYKE (hornblende quartz feldspar porphyry, hbde QFP; Map 3, unit 6) This v a r i e t y of quartz feldspar porphyry i s a pale to medium grey coarse porphyry that s u p e r f i c i a l l y i s s i m i l a r to quartz monzonite phases of the mineralized stock that i t intrudes (units 3 to 5). Large phenocrysts of cream to p i n k i s h buff p l a g i o c l a s e , as we l l as quartz, b i o t i t e , and very sparse orthoclase, make up about 35 per cent of the rock. Near i n t r u s i v e contacts, the rock i s c h i l l e d and has small phenocrysts commonly 2 millimetres and smaller of p l a g i o c l a s e , quartz, mafic minerals, and some orthoclase i n a medium grey m i c r o c r y s t a l l i n e matrix. In the main mass of porphyry equant rounded phenocrysts of plagioclase are 5 to 7 mi l l i m e t r e s i n s i z e . Strongly corroded and resorbed quartz grains average 6 mil l i m e t r e s i n s i z e , but are 45 up to 1.2 centimetres i n some large cumulate grains. Orthoclase crystals are interspersed sporadically throughout the rock as a few, squat, euhedral mega-crysts up to 1.8 centimetres i n s i z e . Most orthoclase phenocrysts' are altered and extensively replaced by epidote. Mafic minerals are present as large elongate books of b i o t i t e up to 7 millimetres i n length and small laths of hornblende. Large grains of sphene are common as we l l as patches and c l o t s , 5 millimetres and more i n s i z e , of f i n e l y matted needles of epidote. The most obvious difference between t h i s rock type and other phases of porphyry i s seen i n the matrix. Quartz i s r e l a t i v e l y sparse, ranging from 6 to 12 per cent i n specimens examined. The matrix i s mostly plagioclase, p o i k i l i t i c almost i n t e r s e r t a l orthoclase, and fine-grained hornblende, b i o t i t e , opaque and a l t e r a t i o n minerals. Hornblende i s abundant, w e l l i n excess of b i o t i t e , and t o t a l mafic content of the rock i s about 20 per cent. Plagioclase phenocrysts are only s l i g h t l y altered. They are com-bined c r y s t a l s that display complex twins and simple normal zoning with r a r e l y more than three or four cycles. Anorthite content ranges from An-j^ to an observed maximum of An^« Secondary b i o t i t e i s present but i n minor amounts compared to quartz monzonite porphyries. Hornblende i s seen as small to medium-sized r e l i c t c r y s t a l s p a r t i a l l y or t o t a l l y replaced by c h l o r i t e , epidote, c a l c i t e , or fine-grained b i o t i t e . Overall, secondary b i o t i t e s e r i c i t e , quartz veins, and gypsum are weakly developed and epidote, c h l o r i t e , and c a l c i t e are main a l t e r a t i o n minerals. BASIC DYKES Dykes, other than those related to quartz monzonite porphyry, are a l l s i m i l a r , common looking, medium to dark grey, homogeneous, fine-grained 46 PLATES 6 and 7: Quartz monzonite porphyry (QMP; Map 2, unit 3). One specimen stained with sodium c o b a l t i n i t r a t e . Scale i s i n centimetres. 47 PLATE 8: Quartz monzonite porphyry (QMP; Map 2, u n i t 3). Stained polished specimen. T M i l l ! III M l ! MM M i l MM l l l l l l l l l M i l l II MM M i l MM Mi l M i l l m i "3 ! A .5 7 1 Q n. 1 PLATE 9: Quartz monzonite porphyry dyke (part of QMP; Map 2, unit 3). Specimen on r i g h t stained with sodium c o b a l t i n i t r a t e . Scale i s i n centimetres. 48 PLATE 10: S e r i c i t i z e d quartz p l a g i o c l a s e porphyry (QPP; Map 2, u n i t 4). Specimen on l e f t i s veined by quartz and Is dark grey due to abundant fine-grained b i o t i t e . Speci-men on r i g h t has pervasive quartz f l o o d i n g along f r a c t u r e s . Unstained portion ( l e f t specimen) i s t y p i c a l of most d r i l l core. Scale i s i n centimetres. PLATE 11: T y p i c a l s e r i c i t i z e d quartz plagioclase porphyry (QPP; Map 2, unit 4). Sodium c o b a l t i n i t r a t e s t a i n shows pervasive d i s t r i b u t i o n of s e r i c i t e i n matrix. PLATE 12: Plagioclase biotite quartz porphyry (PBQP; Map 2, unit 5). Specimen on right stained with sodium cobaltinitrate. PLATE 13: Hornblende quartz feldspar porphyry (hbde QFP; Map 2, unit 6). Dyke rock of quartz monzonite-granodiorite or quartz-bearing monzodiorite composition. 50 andesite or b a s a l t . They form t h i n steeply dipping sheets generally 10 feet or l e s s i n thickness. A number contains up to 5 per cent small phenocrysts of p l a g i o c l a s e but more commonly are massive with small amygdules of c a l c i t e . In t h i n s e c t i o n b a s ic dyke rocks are fine-grained f e l t e d to trachytoid Inter-growths of p l a g i o c l a s e and hornblende with abundant accessory, opaque minerals and a l t e r a t i o n products, mainly c h l o r i t e and c a l c i t e . CHEMICAL COMPOSITION Chemical compositions of representative samples of quartz monzonite porphyry (QMP; Map 2, unit 3) and p l a g i o c l a s e b i o t i t e quartz porphyry (PBQP; Map 2, u n i t 5), determined by wet chemical s i l i c a t e analyses, are given In Table 2. A n a l y t i c a l r e s u l t s and c a l c u l a t e d norms for p l a g i o c l a s e b i o t i t e quartz porphyry correspond very c l o s e l y to Daly's and Nockold's average quartz monzonite or adamelllte whereas quartz monzonite i s more akin to g r a n i t e . This i s probably due to increased amounts of K^O through orthoclase metasomatism and SiO^ due to quartz v e i n i n g . DISTRIBUTION AND GEOMETRY (Map 2) The roughly equidimensional core of the mineralized stock i s made up of two phases: quartz monzonite porphyry (unit 3) and p l a g i o c l a s e b i o t i t e quartz porphyry (unit 5). S e r i c i t i z e d quartz p l a g i o c l a s e porphyry (unit A) forms i r r e g u l a r bodies adjacent to the core i n the southwest. A l l three phases are transected by a northeasterly trending hornblende quartz f e l d s p a r porphyry dyke (unit 6) which i s the only porphyry phase that intrudes quartz d i o r i t e (unit 2). Older quartz monzonite porphyries are separated from quartz d i o r i t e by a screen of hornfelsed v o l c a n i c rocks. TABLE 1. MINERALOGICAL COMPOSITION OF INTRUSIVE ROCKS, BERG DEPOSIT Mean values of modal analyses, not r e c a l c u l a t e d to 100 per cent MAP 2 - Unit 3 Unit 4 Unit 5 Unit 6 Unit 2 S e r i c i t i c QMP QPP PBQP hbde QFP Qtz dio N=8 N=4 N=4 N=4 N=9 Phenocrysts Orthoclase 3.1 0.8 0.2 Quartz 6.4 5.7 5.3 5.1 Pla g i o c l a s e 27.3 25.9 28.1 26.0 --Matrix 54 65 59 63 To t a l Orthoclase 26.1 25.8 26.7 20.2 5.3 Quartz 27.1 26.7 15.1 10.4 12.6 Plag i o c l a s e 35.6 32.2 41 .4 43.0 61 .2 Mafics 7.5 5.2 13.3 19.9 16.8 Accessories 3.6 10.1 3.7 6.0 4.1 (including s e r i c i t e ) Mafics bio bio bio >hbde hbde >bio v a r i a b l e ( s e r i c i t i z e d ) hbde >bio Pl a g i o c l a s e An 30± 30-32± 31±3 38±4 50±3 TABLE 2. CHEMICAL COMPOSITIONS AND NORMS 1 2 3 4 5 Oxides Recalculated to 100-s i o 2 70.73 67.76 67.41 69.67 72.60 T i 0 2 0.53 0.55 0.51 0.56 0.37 A 1 2 ° 3 16.36 16.39 15.76 14.74 13.96 F e 2 0 3 1 .21 1 .78 1 .93 1 .23 0.87 FeO 0.80 0.92 1.96 2.29 1.68 MnO 0.02 0.07 0.06 0.06 0.06 MgO 1.09 1.62 1 .43 1 .00 0.52 CaO 1 .07 2.59 3.54 2.47 1 .34 Na 20 2.89 3.39 3.45 3.37 3.10 K 20 5.30 4.93 3.76 4.61 5.50 Oxides as Determined _ P 2 ° 5 0.30 0.18 0.19 0.20 0.18 H 20 1 .32 2.18 1 .15 0.54 0.53 s o 3 1 .92 4.53 - - ' - -c o 2 0.02 — - - - -BaO 0.12 CuO 0.38 V Molecular Norm-Quartz 30.5 24.7 21 .7 24.8 29.2 Orthoclase 31 .2 29.1 22.5 27.2 32.2 A l b i t e 25.9 30.4 31 .3 28.3 26.2 Anort h i t e 3.2 7.7 16.6 11.1 5.6 Pyroxene 3.0 4.8 5.1 4.7 3.0 Magnetite 1.4 2.0 2.0 1 .9 1 .4 Ilmenite 0.3 0.1 0.7 1.1 0.8 Unassigned 4.5 1 .2 0.1 0.9 1.6 1. Berg quartz monzonite porphyry (Map 2, un i t 3), NC-67-10 (DDH 19), S. Metcalfe, analyst, 1968. 2. Berg p l a g i o c l a s e b i o t i t e quartz porphyry (Map 2, unit 5), NC-67-11 (DDH 1), S. Metcalfe, 1968. 3. Average quartz monzonite, 20 analyses, Daly, 1933. 4. Average adamellite, 121 analyses, Nockolds, 1954. 5. Average c a l c - a l k a l i c g r a n ite, 72 analyses, Nockolds, 1954. Classification Modified from A. Streckeisen , 1967 O r FIGURE 7 MINERALOGICAL COMPOSITION OF INTRUSIVE ROCKS, BERG DEPOSIT O • T • A Qtz Dio QMP QMP dyke ser QPP PBQ P hbde QFP M o p 2, U n i t 2 • average composition 54 Quartz monzonite porphyry (unit 3) i s found as a s u b c i r c u l a r mass forming the southern and southeastern p o r t i o n of the mineralized plug. The porphyry i s thought to be a small, v e r t i c a l , p l u g - l i k e body that i s poss i b l y the most voluminous phase present. V e r t i c a l d r i l l holes (DDH 19, 27, and 34) c o l l a r e d a few feet from the contact pass i n and out of porphyry. The contact i s sharp but appears to undulate and protrude out-ward i n places, and l o c a l l y splays to form arborescent dyke and s i l l - l i k e p r o j e c t i o n s . Rocks near the contact are hig h l y a l t e r e d by Intense s e r i c i t i -z a t ion and quartz v e i n i n g , and hornfels at the contact i s brecciated i n places. P l a g i o c l a s e b i o t i t e quartz porphyry (unit 5) i s s l i g h t l y l e s s abundant than quartz monzonite porphyry and forms a s h e l l up to 600 feet t h i c k about the northern h a l f of the stock. On the basi s of l i m i t e d diamond d r i l l i n g i n t r u s i v e contacts with hornfels appear to be v e r t i c a l and simple with few (p o s s i b l y no) re l a t e d dykes and breccias.. Hornfels adjacent to p l a g i o c l a s e b i o t i t e quartz porphyry Is black, b i o t i t e - r i c h rock with some quartz v e i n i n g . Relationship to s e r i c i t i z e d quartz p l a g i o c l a s e porphyry i n the southwest Is uncertain and possibly complex. S e r i c i t i z e d quartz p l a g i o c l a s e porphyry (unit 4) intrudes as an i r r e g u l a r mass or group of coalescing bodies p e r i p h e r a l to the main stock on the southwest. The largest portion of t h i s rock type appears to form a northwesterly trending dyke, or pos s i b l y a l a c c o l i t h , i n the v i c i n i t y of d r i l l hole 13 (Map 2). The i n t r u s i o n may have a small p i p e - l i k e core i n the v i c i n i t y or northeast of d r i l l holes 7, 30, and 31 flanked by splaying elaborate dykes and s i l l s , two of which are in t e r s e c t e d by d r i l l holes 15 and 17. Two other areas i n which s e r i c i t i z e d quartz p l a g i o c l a s e porphyry may be present are at the north margin of the stock by d r i l l hole 1 and i n the main mass of quartz monzonite porphyry (unit 3) near d r i l l hole 69. In the v i c i n i t y of d r i l l hole 1, 'hybridized' rocks resembling quartz p l a g i o c l a s e porphyry were noted i n a brecciated body i n ho r n f e l s near the contact with p l a g i o c l a s e b i o t i t e quartz porphyry. Near diamond-drill hole 69 a poorly defined and l i t t l e understood metasomatized b r e c c i a zone may contain zones or fragments of quartz p l a g i o c l a s e porphyry. A hornblende quartz feldspar porphyry dyke (unit 6) crosscuts the three other porphyry phases and i s located, at l e a s t i n part, along the quartz monzonite porphyry-plagioclase b i o t i t e quartz porphyry contact. Exact shape of the i n t r u s i o n i s uncertain. In the centre of the mineral-ized stock, hornblende quartz feldspar porphyry forms a steep-walled dyke or n o r t h e a s t e r l y elongated plug up to 225 feet wide with a lobe to the south. D i s t a l p arts of the i n t r u s i o n are tabular, dyke-like sheets with c h i l l e d margins. The dyke splays i n t o three branches at i t s southwest extremity. In the northeast i t i s o f f s e t by f a u l t s and may change in t o a number of s u b p a r a l l e l dykes, two of which are seen at surface i n quartz d i o r i t e (unit 2 ). Int e r n a l contact r e l a t i o n s h i p s between phases are not known mainly because surface exposures are poor and diamond d r i l l i n g i s l i m i t e d . No d i s t i n c t contacts have been recognized i n d r i l l core between the three main quartz monzonite phases. This may be because d i f f e r e n c e s are subtle, rock types are i n t e r g r a d a t i o n a l , or a l t e r a t i o n and metasomatism mask o r i g i n a l t e x t u r a l and compositional d i f f e r e n c e s . On the other hand, contacts simply may not be intersected by d r i l l i n g to date. There i s some evidence from outcrop data that contacts of p l a g i o c l a s e b i o t i t e quartz 56 porphyry (unit 5) with quartz monzonite porphyry (unit 3) are sharp. In other places d r i l l - h o l e data suggest that contacts may be metasomatized b r e c c i a zones, e s p e c i a l l y where contacts trend northwesterly. The hornblende quartz feldspar porphyry dyke (unit 6) can be d i s t i n g u i s h e d from other phases i n d r i l l cores but no sharp contacts are known. The only rock type seen that has c h i l l e d margins i s a quartz monzonite porphyry dyke that i s included i n unit 3. AGE OF INTRUSIONS Re l a t i v e ages of i n t r u s i v e phases cannot be determined unequiv-ocably as only two rock types have been demonstrated to crosscut other phases. Hornblende quartz feldspar porphyry (unit 6) intrudes quartz d i o r i t e (unit 2) and a l l three main quartz monzonite phases (units 3 to 5). At l e a s t one phase of quartz monzonite dyke intrudes quartz monzonite porphyry of the main stock; both rock types are included i n unit 3, Map 2, because of t h e i r s i m i l a r composition and texture. Dykes of what appear to be p l a g i o c l a s e b i o t i t e quartz porphyry (unit 5) intrude s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (unit 4) but t h i s c l a s s i f i c a t i o n of the dykes i s not a c e r t a i n t y . These few observed r e l a t i o n s h i p s and the presence of s e r i c i t i z e d quartz p l a g i o c l a s e porphyry b r e c c i a fragments i n quartz monzonite porphyry, as well as considerable g e o l o g i c a l i n t u i t i o n , suggest the f o l l o w i n g sequence from oldest to youngest:* *Recent d r i l l i n g (A. D. Drummond, 1975, personal communication) has revealed that fragments of quartz monzonite porphyry (unit 3) are found i n s e r i c i t i z e d quartz plagioclase porphyry (unit 4). The b r e c c i a fragments of s e r i c i t i z e d quartz plagioclase porphyry (unit 4) r e f e r r e d to above are intruded i n t o quartz monzonite porphyry (unit 3) i n a 'volcanic neck.' Also p l a g i o c l a s e b i o t i t e quartz porphyry (unit 5) contains fragments said to be quartz monzonite porphyry (unit 3) and s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (unit 4). TABLE 3. POTASSIUM-ARGON AGES, BERG DEPOSIT (N. C. Carter, 1974) Sample No. Location Rock Type M a t e r i a l Sampled Age (m.y.) NC-67-12 DDH 20 b i o t i t e hornfels whole rock 52.0±3 NC-67-11 DDH 1 plagioclase b i o t i t e quartz porphyry b i o t i t e 52.0±2 NC-67-13 DDH 9 mineralized quartz d i o r i t e b i o t i t e 49.9+2.1 NC-67- 9 DDH 70 dyke quartz monzonite porphyry b i o t i t e 48.0±3 NC-67-10 DDH 19 quartz monzonite b i o t i t e porphyry b i o t i t e 47.0±3 NC-67- 8 13,000E quartz d i o r i t e c h l o r i t i z e d b i o t i t e 46.8±1.5 21,000N Mean 49.0+2.4 58 1. quartz d i o r i t e (Map 2 , unit 2) 2. quartz monzonite porphyry in c l u d i n g dykes with c h i l l e d margins that may be considerably younger (QMP, unit 3) 3 . s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (ser QPP, unit 4) 4. p l a g i o c l a s e b i o t i t e quartz porphyry (PBQP, unit 5) 5 . hornblende quartz feldspar porphyry (hbde QFP, unit 6) Absolute ages of rocks at Berg deposit have been determined by Carter (1974) using potassium-argon dating of b i o t i t e . Results ranging from 52.0 to 46.8 m i l l i o n years with a mean of 49.0+2.4 m i l l i o n years are l i s t e d i n Table 3 . No r e s o l u t i o n of i n t r u s i v e events or stages i s p o s s i b l e as a l l ages determined are within l i m i t s of a n a l y t i c a l e r r o r of the mean age. Age of quartz d i o r i t e i s not r e l i a b l e as b i o t i t e sampled was c h l o r i t i z e d and yie l d e d only 2.64 per cent potassium. Quartz d i o r i t e might be considerably older but b i o t i t e has been reset or c r y s t a l l i z e d during i n t r u s i o n of quartz monzonite bodies. Age of hornblende quartz feldspar porphyry (Map 2 , unit 6) i s needed to place an upper l i m i t on emplacement of quartz d i o r i t e and quartz monzonite i n t r u s i o n s (units 2 to 5 ) . BRECCIAS In t h i s t h e s i s the term 'breccia' i s used to describe fragmented rocks i n which fragments can be demonstrated to be displaced r e l a t i v e to t h e i r o r i g i n a l p o s i t i o n . Intensely fractured rocks surrounding the stock at Berg deposit have been described as 'crackle zones' or 'crackle b r e c c i a s ' but are not included i n t h i s discussion because rocks are shattered i n s i t u 59 and fragments d i s p l a y i n s i g n i f i c a n t displacement. Only one large body of b r e c c i a i n bedrock, an i n t r u s i v e b r e c c i a pipe, i s known to crop out. A number of other b r e c c i a bodies have been inte r s e c t e d i n d r i l l holes but t h e i r geometry i s not known and o r i g i n i s s p e c u l a t i v e . Newly formed, t h i n s u r f i c i a l deposits of ferruginous concretionary b r e c c i a s ( f e r r i c r e t e ) mantle small areas but these a c t i v e l y forming deposits are discussed elsewhere. INTRUSIVE PEBBLE BRECCIA PIPE The centre of the i n t r u s i v e b r e c c i a pipe i s about 2,500 feet to the southeast of Berg camp. The b r e c c i a mass i s e l l i p t i c a l i n plan, approxi-mately 1,900 f e e t along i t s longer east-southeast axis and about 500 feet wide. It intrudes quartz d i o r i t e and p y r i t i c v o l c a n i c rocks at the outer edge of the zone of m i n e r a l i z a t i o n . Outcrops are deeply weathered, pale cream to yellow, and contrast sharply with surrounding darker brown outcrops. B r e c c i a , i n t e r s e c t e d -for 521 feet i n diamond-drill hole 21, i s r e l a t i v e l y uniform i n appearance with a cream to l i g h t grey colour. I t i s composed of approximately equal amounts of strongly m i l l e d fragments, f i n e l y comminuted groundmass, and pervasive a l t e r a t i o n minerals. Fragments are subangular to subrounded grains commonly 1 to 4 m i l l i m e t r e s i n s i z e of quartz, f e l d s p a r , and a few rock fragments. Some rock fragments are l a r g e r than 1 centimetre, 3.2 centimetres being the l a r g e s t seen. Rock fragments are quartz monzonite porphyry, one or more p o r p h y r i t i c species not recognized elsewhere, or andesite, and s i l t s t o n e . Matrix i s a cream to buff, f i n e l y comminuted mass of quartz and a l k a l i feldspars with i n t e r -spersed a l t e r a t i o n minerals. Both matrix and fragments are e x t e n s i v e l y 60 a l t e r e d by carbonate, c l a y s (mainly montmorillonite), s e r i c i t e , and c h l o r i t e . P y r i t e , much of which i s present as small euhedral grains i n the matrix, c o n s t i t u t e s about 3 per cent of the rock. In fragments as well matrix c h a l c o p y r i t e i s minor and molybdenite i s r a r e . Sulphide and accessory minerals i n c l u d i n g a p a t i t e , z i r c o n , topaz, r u t i l e , and p o s s i b l y sphene, c o n s t i t u t e 4 to 6 per cent of the rock, mainly i n the matrix. The b r e c c i a pipe i s thought to be explosive i n o r i g i n and formed by venting of v o l a t i l e s r e l a t e d to magma i n t r u s i o n ; the v o l a t i l e s being of e i t h e r magmatic or phreatic explosion o r i g i n . Abundance of porphyry fragments and presence of a few myrmekitic quartz grains i n d i c a t e that the b r e c c i a i s r e l a t e d g e n e t i c a l l y to the mineralized stock. C. S. Ney (1969, personal communication) and Sutherland Brown (1967) have suggested that the b r e c c i a pipe i s a l a t e structure r e l a t e d to emplacement of young i n t r u s i v e phase(s) p o s s i b l y 'quartz l a t i t e porphyry' (now c a l l e d hornblende quartz feldspar porphyry). However, the b r e c c i a may be o l d e r . B r e c c i a t i o n post-dates at l e a s t one period of m i n e r a l i z a t i o n as quartz v e i n l e t s with molybdenite were seen i n a m i l l e d b r e c c i a fragment. OTHER BRECCIAS (OBSERVED ONLY IN DIAMOND-DRILL CORE) BRECCIA 1 A shatter b r e c c i a i s seen only -in the bottom 20 feet of diamond-d r i l l hole 35. Therefore, the extent of t h i s b r e c c i a i s not established. This b r e c c i a i s composed of abraded angular fragments up to 5 centimetres i n s i z e of a l t e r e d v o l c a n i c rocks i n a pulverized matrix that forms not more than 10 per cent of the rock. A l t e r a t i o n minerals are s i m i l a r to those i n the i n t r u s i v e b r e c c i a pipe although quartz f l o o d i n g i s more 61 abundant. A l t e r a t i o n i s not as intense as many of the lar g e r fragments have weakly a l t e r e d cores surrounded by more a l t e r e d rims. P y r i t e as f i n e to medium-sized grains c o n s t i t u t e s about 8 per cent of the rock examined. Chalcopyrite and molybdenite are rare but i r r e g u l a r grains of s p h a l e r i t e , t e t r a h e d r i t e , and traces of galena were noted i n the matrix. B r e c c i a t i o n post-dates deposition of molybdenite i n f r a c t u r e s and quartz v e i n l e t s . The b r e c c i a may be a l a t e formed diatreme i n a weakly vented zone of l i m i t e d gas streaming. BRECCIA 2 Breccias i n which fragmented country rocks are engulfed i n a magmatic matrix are developed along the main contact of quartz monzonite porphyry phase, adjacent to r e l a t e d dykes, and pos s i b l y with parts of the s e r i c i t i c quartz p l a g i o c l a s e porphyry i n t r u s i o n ( s ) . O r i g i n i s not from co l l a p s e or removal of magma support but rather by hyd r a u l i c ramming during magma pul s a t i o n s that cause b r e c c i a t i o n and invasion of brecciated country rocks by magma. This apparently takes place most commonly at Berg deposit where dykes splay outward from the main i n t r u s i v e body. Breccia zones form envelopes a few feet to tens of feet thick surrounding porphyry dykes. Generally volume of i n t r u s i v e rock i n br e c c i a decreases progressively outward from massive i n t r u s i v e dyke cores as proportion, s i z e , and ang u l a r i t y of country rock fragments increase. Examples of t h i s type of b r e c c i a were noted i n diamond-drill holes 14, 25, and 35. Si m i l a r b r e c c i a , but l a c k i n g a massive i n t r u s i v e core, was seen i n a 180-foot d r i l l i n t e r c e p t i n diamond-drill hole 71. In t h i s b r e c c i a weakly ass i m i l a t e d f i s t - s i z e d fragments of mineralized b i o t i t e h o r n f e l s are contained i n an approximately equal amount of sparsely mineralized quartz 62 monzonite porphyry matrix. Molybdenite m i n e r a l i z a t i o n took place during at l e a s t two periods, one before and the other a f t e r b r e c c i a t i o n . E a r l y generation quartz molybdenite v e i n l e t s are seen i n transported b r e c c i a fragments whereas younger quartz molybdenite v e i n l e t s crosscut both h o r n f e l s fragments and quartz monzonite matrix. BRECCIA 3 Breccias w i t h i n the stock are poorly documented; t h e i r o r i g i n and composition are uncertain. Apparently breccias are most common i n quartz monzonite porphyry (unit 3) and s e r i c i t i c quartz p l a g i o c l a s e porphyry (unit 4) whereas p l a g i o c l a s e b i o t i t e quartz porphyry (unit 5) and dyke rocks are not known to be brecciated except near f a u l t s . One b r e c c i a has been i n t e r s e c t e d i n diamond-drill hole 69 where a strongly al t e r e d 'hybridized' zone at l e a s t 90 feet thick contains porphyry f r a g -ments i n the hangingwall of a l t e r e d s e r i c i t i c quartz p l a g i o c l a s e porphyry. Canex Placer geologists (1974, P. G. Beaudoin, personal communication) have suggested that a 'neck' of s e r i c i t i c quartz p l a g i o c l a s e porphyry may be present w i t h i r l j ^ u a r t z monzonite porphyry phase i n t h i s v i c i n i t y . BRECCIA 4 Tectonic breccias are present; most are r e l a t e d to northwesterly and northeasterly trending f a u l t s . These b r e c c i a s , as seen i n a number of diamond-drill cores, are crushed or s i l i c i f i e d zones, some with abundant gouge. F a u l t - r e l a t e d breccias are only inches to a few tens of feet i n width and form steeply dipping tabular bodies. A number of such b r e c c i a zones are bounded or intruded by massive basic dykes. STRUCTURE Outcrops at Berg deposit are so high l y a l t e r e d , leached, and dis i n t e g r a t e d that few s t r u c t u r a l features can be measured. De t a i l e d observations and measurements can be made only from d r i l l core and much of t h i s i s h i g h l y f r a c t u r e d and crushed. For these reasons s t r u c t u r a l data are minimal and a d d i t i o n a l information from large diameter d r i l l core or underground openings i s desirable and i s being c o l l e c t e d by Canex Placer Limited. I n t r u s i v e rocks forming small stocks, plugs, dykes, and s i l l s have been described i n a previous s e c t i o n . Intrusions were f o r c e f u l l y emplaced i n t o g e n e t i c a l l y unrelated host rocks. There was l i t t l e apparent d i s r u p t i o n of the moderately eastward dipping homoclinal succession of vo l c a n i c and l o c a l l y derived sedimentary rocks. Beds were truncated without any d i s c e r n i b l e development of f o l i a t i o n or f o l d i n g . Room f o r i n t r u s i v e rocks uiais made by shouldering aside country rocks, b r e c c i a t i o n , some magmatic stoping, and a s s i m i l a t i o n along with intense f r a c t u r i n g , metasomatism, and extensive r e c r y s t a l l i z a t i o n near the stock. On the basis of st r u c t u r e and s t y l e of emplacement of porphyries, Sutherland Brown (1969) c l a s s i f i e d Berg deposit as a 'simple porphyry deposit;' more r e c e n t l y (1974, 1975) he has described i t as t y p i c a l of a c l a s s of porphyry deposits c a l l e d ' p h a l l i c porphyry deposits.' Evidence of s t r u c t u r a l controls f o r emplacement of i n t r u s i v e bodies was searched f o r during regional mapping; none was found. Fa u l t s trending mainly no r t h e a s t e r l y or northwesterly cause only small o f f s e t s and appear to be of minor importance. 64 F r a c t u r i n g of rocks i s widespread In the area of the Berg deposit but i s most concentrated adjacent to the main i n t r u s i v e contact. This corresponds to the zone of best copper-molybdenum m i n e r a l i z a t i o n i n which numerous generations of fractures have reduced the rock to a 'crackle b r e c c i a ' of 1 to 3-centimetre fragments (Ney, 1972). E a r l y generation fractures include r e t i c u l a t e quartz stockworks, fr a c t u r e s f i l l e d with sulphide grains or v e i n l e t s , and fractures with a l t e r a t i o n envelopes. Younger fr a c t u r e s f i l l e d with gypsum crosscut e a r l y f r a c t u r e s , sulphide grains, gangue, and a l t e r a t i o n mineral grains as a subhorizontal f r a c t u r e cleavage. The cleavage i s a c l o s e l y spaced set of p a r a l l e l h a i r l i n e fractures up to 1 m i l l i m e t r e thick that has been c a l l e d sheeting, poker chip cleavage, and sheet f r a c t u r e s ( A l l e n , 1971). Twenty to 30 f r a c t u r e s per foot are most common at Berg deposit, although rocks with as many as 100 or more f r a c t u r e s per foot are known. In d e t a i l f r a c t u r e s splay and interconnect r e s u l t i n g i n a r e t i c u l a t e pattern, although subhorizontal fractures are dominant. Cleavage fractures have no v i s i b l e a l t e r a t i o n e f f e c t on the rocks they crosscut other than being f i l l e d with the low temperature mineral gypsum. Thus, fra c t u r e cleavage appears to be much younger than other f r a c t u r e s . The sequence of events r e s u l t i n g i n f r a c t u r i n g would be as f o l l o w s : (1) i n t r u s i o n s of porphyries accompanied by invasion of hydrothermal f l u i d s ; (2) e a r l y f r a c t u r i n g and quartz veining to form a crackled zone; (3) widespread hydrothermal a l t e r a t i o n , a d d i t i o n a l quartz ve i n i n g , b r e c c i a t i o n , and some f r a c t u r i n g of i n t r u s i v e rocks; and (4) development of subhorizontal fracture cleavage and gypsum f r a c t u r e f i l l i n g (possibly at a much l a t e r date). 65 The presence of subhorizontal f r a c t u r e cleavage with gypsum fracture f i l l i n g i s known i n a number of deposits i n the Canadian C o r d i l l e r a (Barr, 1966; A l l e n , 1971; Godwin, 1975) as well as elsewhere i n North and South America (Howell and Molloy, 1960; Lowell and G u i l b e r t , 1970). A number of theories have been proposed to explain o r i g i n of sheet f r a c t u r e cleavage i n porphyry deposits but no s i n g l e explanation seems s a t i s f a c t o r y nor can be applied to Berg deposit. The problem i s t h r e e f o l d : f i r s t l y to explain the subhorizontal f r a c t u r e cleavage, secondly to explain presence of gypsum i n these f r a c t u r e s , and t h i r d l y to explain the high frequency of f r a c t u r e . A l l e n (1971) has developed a model for the Galore Creek copper deposits i n which sheet f r a c t u r e s are formed along with concomitant depo-s i t i o n of gypsum as a consequence of near surface hydration of anhydrite. In s i t u hydration of gypsum i s accompanied by a 63-per-cent increase i n volume r e s u l t i n g i n f r a c t u r e s p a r a l l e l to the topographic surface, perpen-d i c u l a r to s t r e s s r e l i e f . Fractures are further opened by mechanical force of c r y s t a l l i z a t i o n as gypsum i s redeposited from saturated meteoric s o l u t i o n s . The model i s a t t r a c t i v e f o r the deposits studied by A l l e n as rocks at depth contain anhydrite up to 20 per cent by volume as a pervasive rock constituent. At shallow depths where sheet f r a c t u r i n g i s most Intense, anhydrite i s t o t a l l y hydrated to gypsum. The model i s not convincing f o r Berg deposit where anhydrite i s found i n only small amounts mainly as a vein constituent together with quartz or c a l c i t e . These anhydrite-bearing veins are cut by gypsum-f i l l e d f r a ctures but anhydrite r a r e l y shows any e f f e c t s of hydration. Other i n v e s t i g a t o r s discuss alternate o r i g i n s of f r a c t u r e cleavage that place l i t t l e or no emphasis on hydration of anhydrite as a causative 66 process. Suggested mechanisms of cleavage development include explosive b r e c c i a t i o n , chemical b r e c c i a t i o n , and hydraulic f r a c t u r i n g . Godwin (1973) has suggested that explosive b r e c c i a t i o n might be accompanied by development of subhorizontal fracture cleavage caused by r e f l e c t i o n of shock waves from the a i r - r o c k i n t e r f a c e . However, at Berg deposit no young b r e c c i a body has been recognized to which the l a t e stage cleavage can be g e n e t i c a l l y r e l a t e d . Also the mechanism does not explain why a l t e r e d rocks close to the i n t r u s i v e stock are strongly cleaved and veined by gypsum whereas i n t r u s i v e rocks are only weakly fractured and veined. Chemical b r e c c i a t i o n as discussed by Sawkins and S i l l i t o e (1971) has been used to r e l a t e v e r t i c a l sheeting and associated f l a t - l y i n g cleavage to b r e c c i a pipes. S i m i l a r to explosive b r e c c i a t i o n , the mechanism i s possibly adequate to explain c e r t a i n fractures proximal to b r e c c i a bodies but i s inadequate to explain the very widespread and l a t e development of f r a c t u r e cleavage at Berg deposit. The t h i r d and p o s s i b l y most promising theory advanced to explain fracture cleavage i s that of h y d r a u l i c f r a c t u r e . I t suggests that sub-h o r i z o n t a l f r a c t u r e cleavage may be formed by near surface f r a c t u r i n g perpendicular to the d i r e c t i o n of s t r e s s r e l i e f i n the presence of a f l u i d ( P h i l l i p s , 1972; Shearman et a l . , 1972). D i f f e r e n t i a l s t r e s s could be developed i n intruded rocks by emplacement of i n t r u s i v e rocks or magma i n what P h i l l i p s (1972) describes as a process i n v o l v i n g nonpenetrative f l u i d s . At the same time pore pressure i n intruded rocks would be increased by penetrative f l u i d s such as hydrothermal solutions or magmatically heated groundwater. Hydraulic f r a c t u r i n g would take place i n stressed rocks 67 surrounding the i n t r u s i v e stock as hydrothermal f l u i d s were generated and f l u i d volume increased. This has r e c e n t l y been r e f e r r e d to as a 'hydro-magmafract process' by W. Burnham (Annual Report, 1974-1975, Geophysical Laboratory, 1975, p. 627) i n which c r y s t a l l i z a t i o n of water-saturated magma r e s u l t s i n release of water and a concurrent large volume Increase. 68 CHAPTER III HYDRO-THERMAL ALTERATION INTRODUCTION Alteration patterns at Berg deposit, as defined by changes in non-sulphide mineralogy in diamond-drill cores, are grossly similar to those in porphyry copper models described by Lowell and Guilbert (1970) and Rose (1970). Refinements by Guilbert and Lowell (1974) and Carson and Jambor (1974) embellished older models and made them more appropriate for Berg and other Cordilleran deposits where volcanic rocks are hosts for major portions of the mineralized systems. These are the wallrock or combined wallrock-intrusion porphyry copper type deposits of Titley (1972). This study Is concerned primarily with hypogene alteration types and zoning patterns. At Berg deposit the distinction between rocks with solely hypogene or hypogene and supergene alteration is indicated clearly in d r i l l core by fractures f i l led with gypsum that mark the limit to which ground waters have circulated. Supergene alteration has taken place only near surface where gypsum is leached. In the zone with gypsum-healed fractures, ground water flow following hydrothermal activity has been minimized and a l l alteration can be assumed to be hydrothermal and hypogene. Supergene alteration caused by weathering, oxidation, and leaching by acidic solutions is extensive and has resulted in a thick leached capping containing mainly quartz, limonite, sericite, chlorite, and clay minerals. Thin section and X-ray diffraction analyses of clay-sized minerals in the capping reveal marked increases in amounts of 69 k a o l i n i t e , s e r i c i t e , and c h l o r i t e compared to rocks subjected only to hypogene a l t e r a t i o n . At Berg deposit zones with quartz-orthoclase and q u a r t z - s e r i c i t e a l t e r a t i o n are developed c e n t r a l l y i n the weakly mineralized quartz monzonite stock and are surrounded by a l t e r a t i o n aureoles containing, f i r s t , b i o t i t i c cupriferous rocks, then, p y r i t i c c h l o r i t e - c a l c i t e - e p i d o t e - b e a r i n g rocks. Q u a r t z - s e r l c i t e - p y r i t e zones occur e x t e n s i v e l y along the i n t r u s i v e contact of the quartz monzonite stock and clay-bearing zones are developed l o c a l l y i n p o s i t i o n s intermediate between the i n t r u s i v e core and p y r i t i c periphery. Quantities and a s s o c i a t i o n s of a l t e r a t i o n minerals i n 10-foot sections of d r i l l core were recorded i n d e s c r i p t i v e and graphic d r i l l l o g s . A l l diamond-drill core a v a i l a b l e to 1971 was catalogued by the w r i t e r with p a r t i c u l a r regard f o r : quartz, orthoclase, b i o t i t e , s e r i c i t e (muscovite), magnetite, c a l c i t e , epidote, anhydrite, and gypsum. Clay minerals were i d e n t i f i e d l a t e r in' the laboratory by X-ray d i f f r a c t i o n (Appendix C). Location of gypsum was noted and number of cleavage f r a c t u r e s per foot of core was recorded. Limonite minerals, where present, were described i n terms of colour, abundance, and character. An estimate based on limonite colour was made of the proportions of goethite and j a r o s i t e . S i g n i f i c a n t d i f f e r e n c e s i n appearance of diamond-drill core and hand specimens were used to define various a l t e r a t i o n types and a l t e r a t i o n i n t e n s i t i e s . A standardized cataloguing procedure enabled a l t e r a t i o n i n t e n s i t i e s to be ranked and thereby q u a n t i f i e d (Appendix B). Ranked values of a l t e r a t i o n i n t e n s i t i e s were p l o t t e d and contoured on a geologic plan and were used to define hypogene zoning patterns (Figure 8). 70 DEFINITION OF ALTERATION FACIES AND ZONES ^ Diagnostic a l t e r a t i o n minerals and mineral associations can be used to define a number of a l t e r a t i o n types, or f a c i e s (Creasy, 1959, 1966; Burnham, 1962; Meyer and Hemley, 1967). A l l commonly used types are recognized at Berg deposit (Figure 8) i n c l u d i n g p o t a s s i c , p h y l l i c , p r o p y l i t i c , and a r g i l l i c f a c i e s as well as a b i o t i t i c a l t e r a t i o n f a c i e s ( b i o t i t e h o r n f e l s ) . B i o t i t i c a l t e r a t i o n i s more c l o s e l y associated with chalcopyrite concentrations than are other a l t e r a t i o n types. Because of t h i s important r e l a t i o n s h i p , i t i s considered here separately rather than part of the potassic zone as done by some authors. A l t e r a t i o n e f f e c t s are most obvious i n v o l c a n i c rocks surrounding the quartz monzonite stock, close to the i n t r u s i v e contact. A l t e r a t i o n of quartz monzonite v a r i e s i n i n t e n s i t y i n d i f f e r e n t zones and rock types within the stock. Most intensely a l t e r e d rock types are quartz monzonite porphyry (Map 2, u n i t 3) and s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (Map 2, unit 4). Most subtle a l t e r a t i o n i s i n p l a g i o c l a s e b i o t i t e quartz porphyry (Map 3, u n i t 5) and hornblende quartz feldspar porphyry (Map 2, unit 6). Intrusive contacts i n the southern part of the stock and the northwesterly trending f r a c t u r e or b r e c c i a zones are the most h i g h l y a l t e r e d zones within the stock. POTASSIC ALTERATION Potassic (quartz-orthoclase) a l t e r a t i o n can be found within the mineralized stock where i t appears to be r e s t r i c t e d to quartz monzonite porphyry (Map 2, unit 3). However, recent d r i l l i n g (A. D. Drummond, 1975, personal communication) i n d i c a t e s that s e r i c i t i z a t i o n i s more widespread than o r i g i n a l l y thought and potassic a l t e r a t i o n might not be as extensive as shown i n Figure 8. 71 Orthoclase, quartz, s e r i c i t e , and b i o t i t e are main a l t e r a t i o n minerals together with anhydrite and l e s s e r amounts of sulphide minerals, c h l o r i t e , magnetite, k a o l i n i t e , and montmorillonite. Potassic a l t e r a t i o n i s seen as a pervasive pink c o l o u r a t i o n i n the rock matrix caused by orthoclase f l o o d i n g (Plate 14). In t h i n s e c t i o n i t i s seen as a very fine - g r a i n e d mosaic of o r t h o c l a s e - q u a r t z - p l a g i o c l a s e - s e r i c i t e . In specimens examined ( a l l from d r i l l hole 1 and 6) about 5 per cent orthoclase appears to have been added during orthoclase metasomatism, generally r e p l a c i n g p l a g i o -c l a s e or r a r e l y as orthoclase rims on p l a g i o c l a s e phenocrysts. In most str o n g l y a l t e r e d rocks quartz veins exceed 10 per cent and p l a g i o c l a s e phenocrysts proximal to quartz veins are s e r i c i t i z e d and, i n rare cases, a r g i l l i z e d ; a l t e r e d p l a g i o c l a s e has a c h a r a c t e r i s t i c pale green to buff colour. Where quartz veins are l e s s than 10 per cent of the rock volume, p l a g i o c l a s e c r y s t a l s are unaltered or s l i g h t l y clouded i n appearance. Mafic phenocrysts ( o r i g i n a l l y b i o t i t e and hornblende) i n strongly a l t e r e d rocks are replaced t o t a l l y by fine-grained, f e l t e d b i o t i t e and l e s s common s e r i c i t e , magnetite, sulphide minerals, a n d - c h l o r i t e . In weakly a l t e r e d zones of porphyry, only hornblende i s replaced by secondary b i o t i t e and b i o t i t e pheno-c r y s t s are e i t h e r p a r t i a l l y replaced or remain as euhedral c r y s t a l s . PHYLLIC ALTERATION P h y l l i c ( q u a r t z - s e r i c i t e - p y r i t e ) a l t e r a t i o n of rocks i s e a s i l y recognized by a bleached and chalky weathered appearance (Plate 15). Bleaching i s caused by thorough q u a r t z - s e r i c i t e a l t e r a t i o n of p l a g i o c l a s e , s e r i c i t e , and quartz a l t e r a t i o n of orthoclase, and breakdown of mafic minerals to dominantly s e r i c i t e and l e s s e r amounts of b i o t i t e , quartz, c h l o r i t e , and p y r i t e . Magnetite i s absent but p y r i t e and small amounts of 72 hematite are present. In t h i n s e c t i o n rocks with p h y l l i c a l t e r a t i o n appear as a fine-granular, mosaic intergrowth of q u a r t z - s e r i c i t e among r e l i c t , s e r i c i t i z e d , and weakly k a o l i n i z e d f e l d s p a r phenocrysts. Scattered, shredded grains of secondary b i o t i t e and minor c h l o r i t e are mafic c o n s t i t u -ents. In s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (Map 2, unit 4) f i n e -grained b i o t i t e i s l o c a l l y abundant (up to 6 per cent) and imparts a tan to medium brown colour to the rock matrix (Plate 10). Topaz, f i r s t reported to be present at Berg deposit by Dahl and Norton (1967) , i s a minor a l t e r -a t i o n mineral i n p h y l l i c assemblages. The zone of p h y l l i c a l t e r a t i o n i s developed most extensively along the southern and southwestern i n t r u s i v e contacts and i s discontinuous around the northeast contact nearest quartz d i o r i t e and i n p l a g i o c l a s e b i o t i t e quartz porphyry which i s l i t t l e a l t e r e d (Figure 8). P h y l l i c a l t e r a t i o n crosses the quartz monzonite contact i n the south and southeast and extends outward for a few metres i n t o h i g h l y fractured v o l canic rocks. A small zone with p h y l l i c a l t e r a t i o n was a l s o i n t e r s e c t e d at depth i n d r i l l hole 1 along the northern boundary of the stock. Relationships i n t h i s area are complicated, however, because more than one i n t r u s i v e phase probably i s emplaced. P h y l l i c a l t e r a t i o n i s developed p e r i p h e r a l l y to potassic a l t e r a t i o n but the zone of p h y l l i c a l t e r a t i o n encroaches potassic zones. A h i g h l y i r r e g u l a r contact following interconnected zones of intense f r a c t u r i n g and b r e c c i a t i o n l o c a l l y i s o l a t e s ' i s l a n d s ' of rocks with potassic a l t e r a t i o n . PROPYLITIC ALTERATION P r o p y l i t i c a l t e r a t i o n coincides with strongly p y r i t i z e d v o l c a n i c rocks and quartz d i o r i t e p e r i p h e r a l to e i t h e r p h y l l i c a l t e r a t i o n zones i n 73 quartz monzonite porphyry or biotite hornfels formed along the Intrusive contact (Figure 8 ) . Presence of sulphide minerals, mainly pyrite, was the sole criterion used to distinguish rocks with hydrothermal propylitic alteration from those having greenschist regional metamorphism. Propylitic alteration is recognized by an overall green colour-ation in rocks caused by abundant and pervasive chlorite and epidote. Locally propylitized rocks have a mottled appearance due to bleached borders of fractures and veins (Plates 17 and 19). Where fractures are abundant, crosscutting, and interconnected, propylitic rocks are pervas-ively bleached to a pale grey-green to olive drab colour. Possibly the best indicator of propylitic alteration and most reliable criterion for distinguishing propylitized rocks from chloritic biotite hornfels is presence of calcite. Invariably, abundant calcite coincides with rocks in which chlorite exceeds biotite in abundance and epidote as well as magnetite are common. In addition to the chlorite, calcite, and magnetite above, albitized plagioclase, sericite, epidote, and pyrite are abundant along with lesser quantities of montmorillonite, kaolinite, dolomite, tremolite, gypsum, ruti le, leucoxene, and hematite. Detailed examination of propylitized rocks reveals three common mineral associations: (1) chlorite-epidote-calcite (widespread), (2) chlorite-epidote-tremolite (in basic volcanic rocks), and (3) chlorite-kaolinite-dolomite (localized in three small zones of argi l l ic alteration). Bleached margins of quartz-pyrite veins consist of very fine-grained mixtures of calcite-gypsura-montmorillonite as well as chlorite-albite and possibly sericite. Bleached vein margins in the propylitic zone are dis-tinguished from phyllic alteration by sparseness of sericite. 74 P r o p y l i t i c a l t e r a t i o n i s a l s o found i n hornblende quartz feldspar porphyry (Map 2, u n i t 6), the youngest phase of the quartz monzonite stock. However, u n l i k e v o l c a n i c rocks and quartz d i o r i t e i n the p r o p y l i t i c zone p e r i p h e r a l to the composite stock, quartz f e l d s p a r porphyry i s only weakly p y r l t i z e d . ARGILLIC ALTERATION A r g i l l i c (clay) a l t e r a t i o n Is recognized at Berg by presence of abundant montmorillonite and k a o l i n i t e . A r g i l l i c rocks are known to occur i n three zones (Figure 8). The zones appear to be small, l i m i t e d to a few tens of metres i n width, but t h e i r extent i s poorly documented due to l i m i t e d subsurface information. One zone i s associated with the a l t e r e d southwestern contact of s e r i c i t i z e d quartz p l a g i o c l a s e porphyry (Map 2, unit 4). The a r g i l l i c zones l i e between p h y l l i c and p r o p y l i t i c a l t e r a t i o n zones In the p o s i t i o n predicted by porphyry copper models. The two other zones are i n p r o p y l i t i z e d v o l c a n i c rocks north and southeast of the composite stock and along the quartz d i o r i t e contact.. In a l l three zones containing clay minerals, strong calcium leaching, one of the main requirements of the a r g i l l i c a l t e r a t i o n f a c i e s according to Creasey (1966), i s not evident. Therefore, clay-bearing rocks at Berg deposit might be regarded simply as clay-bearing, aluminous subfacies of p r o p y l i t i c a l t e r a t i o n . BIOTITIC ALTERATION B i o t i t i c a l t e r a t i o n , also r e f e r r e d to as b i o t i t e h o r n f e l s , i s most i n t e n s e l y developed i n volcanic rocks adjacent to p h y l l i c or potassic a l t e r a t i o n zones formed i n quartz monzonite (Figure 8). B i o t i t i c a l t e r a t i o n c o i n c i d e s with zones of most intense copper m i n e r a l i z a t i o n . This intimate 75 association of copper sulphides with a zone of biot i t ic alteration is characteristic of many porphyry deposits and, therefore, makes recognition and definition of biot i t ic alteration zones a useful product of alteration studies in ore search. Rocks with biotit ic alteration at Berg deposit are andesitic metavolcanic rocks which are easily recognized by their dark brown to black colour and velvety hornfelsic texture. Biotit ic alteration is also seen in quartz diorite which has a spotted 'salt and pepper' appearance where i t is biotitized near quartz monzonite. As much as 50 per cent biotite is present in some altered rocks but most commonly biotite content is 20 to 35 per cent. Other alteration minerals associated with biotite are: quartz, orthoclase, plagioclase, sericite, anhydrite, epidote, chlorite, magnetite, and minor calcite, clay minerals, and ruti le. Chlorite from the biot i t ic zone at Berg is a magnesian clinochore, leuchtenberglte (Dahl and Norton, 1967). The zone of biotit ic alteration can be regarded as a transitional zone between potassic (quartz-orthoclase) or phyllic alteration and the peripheral propylitic alteration zone. Biotite hornfels can be classified as part of either the potassic or propylitic alteration facies, depending on which alteration minerals accompany biotite. Classification of biotit ic rocks into zones of either potassic or ;propylltic alteration is not always obvious, as pointed out by Titley (1972), and depends on whether potash metasomatism can be demonstrated to have taken place. At Berg deposit in the southern half of the quartz monzonite stock and along part of the northern contact, biotite hornfels flanks rocks with phyllic alteration. The biot it ic rocks contain epidote, chlorite, magnetite, and traces of clay 76 minerals and c a l c i t e , but no a d d i t i o n of potash i s evident. B i o t i t i c rocks i n t h i s zone, therefore, are compatible with the p r o p y l i t i c a l t e r a t i o n f a c i e s and the a l t e r a t i o n zoning sequence from quartz monzonite core outward i s : p o t a s s i c ( q u a r t z - o r t h o c l a s e - s e r i c i t e ) , then p h y l l i c , and f i n a l l y p r o p y l i t i c i n the b i o t i t e h o r n f e l s , a normal zoning sequence. Along the northeast contact of the quartz monzonite stock i n the screen of hornfelsed v o l c a n i c rocks between quartz monzonite and quartz d i o r i t e i n t r u s i o n s (and p o s s i b l y also along the northwestern quartz monzonite c o n t a c t ) , p h y l l i c a l t e r a t i o n i s poorly developed or i s absent. In these zones b i o t i t i c rocks adjoin i n t r u s i v e rocks with potassic a l t e r a t i o n and are veined by quartz-orthoclase-anhydrite, quartz-orthoclase, and ortho-c l a s e veins (Plates 16 and 18). In such zones b i o t i t i c v o l c a n i c rocks are laced by a quartz v e i n stockwork that i s w e l l mineralized with molybdenite. Mineralogy of t h i s v e i n i n g i s compatible with the potassic a l t e r a t i o n f a c i e s . The a l t e r a t i o n zoning sequence i s : potassic (vein and pervasive quartz-orthoclase) i n quartz monzonite, potassic (orthoclase veined b i o t i t i c a l t e r a t i o n ) i n hornfelsed volcanic rocks near the i n t r u s i v e stock and grading outward to p r o p y l i t i c i n quartz d i o r i t e and v o l c a n i c rocks further from the quartz monzonite contact. The presence of potassic f a c i e s (orthoclase-veined) b i o t i t i c rocks might be r e s t r i c t e d to that zone i n which v o l c a n i c rocks have been, f i r s t , thermally metamorphosed by quartz d i o r i t e and, then overlapped by a quartz stockwork and b i o t i t i c hydrothermal a l t e r a t i o n r e l a t e d to quartz monzonite. Elsewhere along the quartz d i o r i t e contact where hydrothermal f l u i d s were more remote from quartz monzonite, b i o t i t e hornfels that was formed along the quartz d i o r i t e contact has degenerated, mainly by c h l o r i t i z a t i o n of b i o t i t e , to rocks of p r o p y l i t i c aspect. 1 Figure 8 Quartz-K felds-biotite- sericite GENERALIZED ALTERATION :4V::v:J Bi'ofjfe Qtz • sericite-pyrite Argillic Propylitic ZONES, BERG DEPOSIT Hypogene Alteration Determined From Drill Core • diamond drill site h-20.000 N \ •/.•••.••.vV..-. i l i l i • i f f ^"7 / / N 7000 SCALE - FEET 0 300 SCALE-METRES | | breccia j | qtz bearing monzodi. | | qtz monzonite ? | | qtz diorite | | hornfels .volcanics PLATE 14. Potassic a l t e r a t i o n i n quartz monzonite porphyry (DDH 6). Pervasive pink appear-ance i s from orthoclase flooding i n matrix. H a i r l i n e fractures contain gypsum. Quartz grains are grey, plagioclase grains are pale grey to white. PLATE 15. P h y l l i c ( q u a r t z - s e r i c i t e - p y r i t e ) a l t e r a t i o n of quartz monzonite porphyry (DDH 25). The small v e i n l e t s contain quartz. Subhedral p l a g i o c l a s e c r y s t a l s are chalky; quartz grains are grey; scattered black minerals are b i o t i t e . Quartz veins at bottom of sample contain molybdenite. Scale i s i n m i l l i m e t r e s . PLATE 1 Potassic alteration of b i o t i t i c volcanic rocks (DDH 43) (quartz-orthoclase veined biotite hornfels). The ribboned quartz-molybdenite vein has an orthoclase envelope. Micro vein-lets are quartz bearing and some have sl i g h t l y s e r i c i t i z e d margins (brown). Note lack of bleaching on larger vein margins. Scale i s i n millimetres. I 111111111IIIII MM l l l l i l l l 11II Mil I M 111III MM MM MM MM PLATE 17. Propylitic alteration of b i o t i t i c volcanic rock (DDH 26). Mottled appearance i s from bleached margins on p y r i t i c quartz veins and fractures. Pervasive (brown-green) alteration consists of chlorite-calcite-gypsura-clay minerals in chlor-i t i c b i o t i t i z e d rock (black). Scale i s in millimetres. PLATE 18, Potassic a l t e r a t i o n of b i o t i t i c v o l c a n i c rock (DDH 43). An orthoclase vein i s cut by a quartz-anhydrite vein containing fine-grained b i o t i t e . Note lack of a l t e r a t i o n envelopes on v e i n s . Scale i s i n centimetres. I l l l l l l l i l i M I I I I I IMIIIIM PLATE 19. P r o p y l i t i c a l t e r a t i o n i n l a p i l l i t u f f (DDH 68) with bleached fracture margins. Bleaching i s from a l t e r a t i o n to calcite-gypsum-clay minerals and/or s e r i c i t e bordering p y r i t i c , quartz-bearing f r a c t u r e s . Scale i s i n m i l l i m e t r e s . 81 VEINS Veins are found throughout the hydrothermally a l t e r e d and mineralized zone. They form a stockwork of small v e i n l e t s (mainly sulphide-bearing quartz veins) that surrounds the composite Berg stock. The v e i n -stockwork i s most c l o s e l y associated with quartz monzonite porphyry and p l a g i o c l a s e b i o t i t e quartz porphyry although I t i s imposed on hornfelsed rocks and a l l Intrusive phases except quartz feldspar porphyry and basalt dykes. The zone with highest density of veins i s found within i n t r u s i v e and hornfelsed rocks near the main i n t r u s i v e contacts. Abundance of veins decreases more r a p i d l y inward than outward from the contact. The a l t e r a t i o n f a c i e s described i n preceding pages represent large pervasive a l t e r a t i o n zones. Veins, on the other hand, are only p a r t l y synchronous with pervasive a l t e r a t i o n processes. They are i n many cases superimposed on pervasively a l t e r e d rocks and r e f l e c t changes i n hydrothermal f l u i d s that passed through and were confined to fractures and other channelways. Hydrothermal f l u i d s from which some vein minerals were deposited caused l i t t l e a l t e r a t i o n of enclosing rocks and veins cut host rocks without appreciable a l t e r a t i o n e f f e c t s . In other host rocks reactions with f l u i d s i n fractures r e s u l t e d i n a l t e r a t i o n envelopes i n which minerals adjacent to veins were metasomatized or r e c r y s t a l l i z e d and made over to mainly quartz, K-feldspar, s e r i c i t e , and b i o t i t e . S t i l l other veins have bleached v e i n margins i n which r e l i c t primary textures are maintained, and rock-forming minerals are broken down to mainly quartz, c h l o r i t e , clay minerals, carbonate, s e r i c i t e , and gypsum (Plate 19). Thus, where s i g n i f i c a n t metasomatism (most obviously orthoclase-quartz) has taken place, a l t e r e d vein borders are c a l l e d envelopes. Where retrograde breakdown of rock-forming 82 constituents has taken place but original textures remain, altered vein borders are referred to as alteration margins. In zones of extensive fracturing away from the stock, bleached margins on veins result in a mottled appearance or coalesce to form large bleached zones. In general, alteration envelopes are most abundant on veins within the stock and along Its contacts where the quartz stockwork is best developed. Veins with alteration envelopes decrease in abundance away from the composite stock and are exceeded by veins with bleached margins. Bleached alteration margins are most noticeable in pyritic hornfelsic and propylitic rocks. A l l three vein types (with alteration envelopes, without envelopes, and with bleached margins) can be found in the same rock. They have formed in sequence as a staged vein series. The sequence is complicated to decipher . and cannot be resolved completely without additional detailed study. The following sequence from oldest to youngest Is suggested. Stage 1 A. Quartz-pyrite-chalcopyrite-molybdenite veins with alteration envelopes of quartz-sericite (common), chlorite (less common), or K-feldspar (rare). B. Quartz-pyrite-chalcopyrite-molybdenite veins without envelopes. The above associations are modified by presence of other minerals including chlorite, anhydrite (purple and clear), epidote, carbonate, clay minerals, and magnetite. Stage 2 Quartz-molybdenite (or molybdenite alone) veins without envelopes. 83 Stage 3 Quartz-pyrite veins with or without envelopes, many with bleached margins. Veins may also contain chalcopyrite, rare epidote, and magnetite. Stage 4 Quartz-carbonate (common) and quartz-anydrite-carbonate (rare) veins, many with bleached margins. These inay contain pyrite, chalcopyrite, sphalerite, tetra-hedrite, galena, and epidote. Anydrite is partially to completely hydrated (hemihydrite to gypsum). Stage 5 Gypsum-filled fractures. Crosscutting relationships permit at least five periods of Stage 1 veining to be postualted (A. D. Drummond, 1975, personal communication). However, as a rule, Stage 1 veins display complex relationships and suggest that Stage 1 veins have f i l led a previously crackled zone rather than generated a sequential, crosscutting stockwork system. Stage 1 veins generally consist of massive quartz intergrowths although many have cockscomb structures and vugs with drusy lining. In some veins vugs are f i l led with anhydrite; in others, cavities are open and quartz crystals are overgrown by fine-grained chlorite. Stage 2 veins are massive and composed of compact, fine-grained quartz or are ribboned with granulated quartz grains inter-spersed by bands of fine-grained molybdenite. Stage 3 veins are ubiquitous and are possibly the most abundant veins in the stockwork. Except where they are clearly crosscutting, Stage 3 veins are indistinguishable from Stage 1 or any other quartz-pyrite veins. Stage 4 veins up to 3 millimetres in width have been noted in diamond-drill core but are rare overall. In pyritic rocks surrounding the composite stock a number of quartz-carbonate-pyrite-sphalerite-galena-tetrahedrite veins up to a few feet in width are known to occur. Stage 5 gypsum-filled fractures are part of the subhorizontal fracture cleavage 34 PLATE 20. Subhorizontal gypsum-bearing fracture cleavage crosscutting pyrite and chalcopyrite grains (DDH 28). The sulphide-bearing fracture cuts an older quartz-epidote-pyrite-chalcopyrite vein (top r i g h t ) . Length of bar scale i s 2.5 centimetres. 85 that crosscuts a l l primary a l t e r a t i o n and ore minerals and po s s i b l y formed long a f t e r veins of Stages 1 to 4. ORIGIN OF HYPOGENE ALTERATION AND ZONING PRINCIPLES Various a l t e r a t i o n and ore mineral assemblages occur i n zones centred on and enveloping the composite Berg stock. Zones are defined by mineral assemblages i n which p r e - e x i s t i n g minerals have r e - e q u i l i b r i a t e d and new minerals (most s i g n i f i c a n t l y ore minerals) are added. Zoning i s , i n essence, a response to temperature, pressure, and chemical gradients caused by (1) the emplacement and presence of magma, (2) the cooling and c r y s t a l l i z a t i o n of the stock, (3) generation and flow of hydrothermal f l u i d s i n and around the stock, (4) int r o d u c t i o n , transport, and deposition of metals and other substances by hydrothermal f l u i d s , and (5) reactions i n f l u i d s or between f l u i d s and rocks i n and outside the stock. The p r e r e q u i s i t e f o r a l t e r a t i o n and m i n e r a l i z a t i o n was emplacement of a magma although the f u l l r o l e and products of magmatism i n the a l t e r a t i o n - m i n e r a l i z a t i o n process i s contentious. P o s s i b l y the s i n g l e most s i g n i f i c a n t c o n t r i b u t i o n of magma i s the supply of heat. Temperatures from 700 to 900 degrees centigrade are ca l c u l a t e d from Ab-Or-Q-^O sol i d u s curves f o r g r a n o d i o r i t e or quartz monzonite stocks with which most porphyry copper deposits are associated (Theodore and Blake, 1975). 750 to 300 degrees centigrade was estimated for quartz monzonite i n t r u s i o n s (Whitney, 1975) comparable to the one at Berg deposit. Country rocks were cooler with temperatures from ambient to 150 degrees centigrade depending on depths of emplacement and geothermal gradients. 86 Magmas may contain up to 14 or 15 per cent R^O (Burnham, 1967; Holland, 1972) but in shallow environments as in porphyry copper deposits from 2 to 6 per cent H20 in magma can be expected (Holland, 1972). Whitney (1975) assumes 3 to 4 per cent to be present although as much as 8 per cent H^ O might be necessary to faci l i tate extensive brecciation such as at Casino deposit (Godwin, 1975). Magmas lose volatile components during ascent and contain from h to 1 per cent H20 when crystallized (Holland, 1972). Thus, during crystallization magmas liberate fluids equivalent to 1 to 5 per cent of the magma's weight. Fluids liberated late in the magmatic stage (juvenile fluids ?) have been long considered to be the source and transporting agent of metals (Bowen, 1933; Fenner, 1973; Emmons, 1933; Lindgren, 1937). Similar ortho-magmatlc models of porphyry copper deposits are s t i l l used (Nielsen, 1968; Holland, 1972) and passage of magmatic fluids outward from crystallizing stocks with attendant mineralization and alteration in margins of stocks and their surrounding rocks is thought to be the main ore-forming process in many porphyry deposits (Fournier, 1967; Rose, 1970; Lowell and Guilbert, 1970; Whitney, 1975). Evolution of vapour during crystallization would result in a zone of high water activity surrounding the stock and in an overlying cupola. If vapour is evolved rapidly in magma, fluid pressures may exceed lithostatic pressures and brecciation may take place or cracks may be propagated (Nielsen, 1968; Whitney, 1975). Connate and meteoric waters in country rocks would not be expected to flow against the temperature gradient and into the zone of high water pressure (Whitney, 1975). However, stable isotope data (Sheppard, Nielsen, and Taylor, 1969, 1971; Taylor, 1973) suggest that meteoric hydro-87 thermal solutions are present in outer alteration zones (most notably zones of phyllic alteration) and do invade at least marginal parts of cooling stocks. Therefore, mixing of juvenile fluids and groundwater .evidently takes place in porphyry copper deposits. Models with convective flow of such mixed source hydrothermal fluids were described by White, Muffler, and Truesdell, 1970; Cathles and Norton, 1974; Whitney, 1975; and Norton, 1975. Metals introduced by hydrothermal fluids are deposited in intrusive rocks or near intrusive contacts. Source of metals is uncertain; i t may be the stock i tse l f , a larger reservoir of magma at depth, or intruded rocks. The efficiency of concentration of metallic elements during crystallization of a wet magma is well documented (Ringwood, 1955; Burnham, 1967; Holland, 1972). Estimates of heavy metal concentrations in hydrothermal fluids range 4 from dilute to concentrated solutions (1-10 ppm, Barnes and Czamanske, 1967, p. 335). In porphyry copper deposits heavy metal concentrations of less than 100 ppm are suggested by Roedder (1971) and 1,000 to 2,000 ppm copper by Rose (1970). At Berg deposit the crystalline core (all except quartz feldspar porphyry) contains about 1,500 ppm copper and country rocks contain about 75 ppm copper (the average copper content of six samples of volcanic rocks from outside the hydrothermally altered zone). Thus considerable metal-bearing hydrothermal fluid has passed through the margin of the stock in order to produce the large zone containing in excess of 0.2 per cent copper. Fluid pressures are dependent on depth of magma emplacement, cooling rate, and composition. Fluid pressures in excess of hydrostatic pressure or even exceeding lithostatic pressure (250 to 285 bars/km) must exist at least briefly in many porphyry deposits as suggested by boiling of hydrothermal fluids (Roedder, 1967 and 1971) and explosive brecciation. Tops 88 of stocks with porphyry copper deposits are commonly 1.5 to 3 kilometres in depth (Lowell and Guilbert, 1970; Si l l i toe, 1973). Processes of mineralization can extend into plutonic roots at depths of 8 kilometres (Si l l i toe, 1973) but maximum depths near 4.5 kilometres is suggested by Whitney (1975) for porphyry copper deposits associated with porphyritic quartz monzonite intrusions as this is the depth at which vapour is f i rst liberated in quantity. Roedder (1971) suggested a depth of 4.2 kilometres for mineralization at the Bingham plutonic porphyry copper deposit. Most other porphyry deposits are believed to form at depths under 3.2 kilometres (Cox, Gonzales, and Nash, 1975) and may be as shallow as 450 metres (Nielsen, 1968). Relief of 900 metres at Berg deposit suggests that this is the minimum depth at which the intrusion was emplaced. Temperatures of ore-forming fluids are best estimated from fluid inclusion homogenization temperatures which are generally higher than 250 degrees centigrade and can be as high as 725 degrees centigrade (Roedder, 1971). Many porphyry deposits, especially those with potassic alteration have highly saline fluid inclusions and temperatures are greater than 500 degrees centigrade (Roedder, 1971; Dawson, 1972; Moore and Nash, 1974). Others, commonly with widespread phyllic and argi l l ic alteration, have less saline fluids and are cooler with temperatures from 300 to 400 degrees centigrade (Nash and Theodore, 1971; Nash and Cunningham, 1974; Cox, et a l . , 1975). Corroborating temperature estimates of 450 to 600 degrees centigrade (Beane, 1974) and 790 to 382 degrees centigrade (Batchelder and Blake, 1975) are available from thermodynamic data applied to biotite compositions. Temperatures of 310 to 550 degrees centigrade (Field, Jones, and Bruce, 1971) and 300 to 600 degrees centigrade (Field, 1973) are estimated from sulphur Isotope measurements of equilibrium chalcopyrite-anhydrite pairs. 89 Changes in physic-chemical conditions in pregnant hydrothermal solutions result in deposition of ore and alteration minerals (Holland, 1967; Barnes and Czamanske, 1967; Barton and Skinner, 1967; Helgeson, 1970; Holland, 1972). Possibly most important is cooling of fluids by outward and upward flow along a geothermal gradient outward from a crystallizing stock, adiabatic expansion during in i t ia l and second or multiple boiling (Roedder, 1971), heat exchange and reactions with wallrocks, or mixing and dilution with meteoric fluids (Barnes and Czamanske, 1967; Toulmin and Clark, 1967; Rose, 1970). Not a l l components in solutions need be pre-• cipitated nor diluted as a result of cooling. For example, salinity may increase as a result of boiling and i f vapour-dominated hydrothermal systems are recharged with condensate, sulphate and s i l i ca may be concentrated (White, et a l . , 1970; Roedder, 1971). In addition to cooling and dilution of hydrothermal f luids, redox reactions during hydrothermal alteration change and buffer solute and gas concentrations resulting in decreased solubilities of metal-bearing complexes (Raymahashay and Holland, 1969; Helgeson, 1970). Limiting conditions for aqueous phases, f02» fS2» pH, and temperature can be deduced from mineral stability diagrams such as those of Barnes and Czamanske, 1967, page 351, and Meyer and Hemley, 1967, p. 220. There is evidently delicate interplay between f0£ and fS^ in early potassic alteration stages (K-feldspar, sericite, biotite, anhydrite, sulphide, magnetite) as well as stockworks with quartz-sulphide and quartz-sulphide-sulphate veins. Precipitation of magnetite and anhydrite wi l l decrease f0£ and increase fS^ whereas oxidation of -2 sulphur-bearing complexes decreases a ^ S , aHS, aS and leads to sulphide deposition (Barnes and Czamanske, 1967). 9 0 Oxidation of hydrothermal f l u i d s a l s o simultaneously releases H + ions leading to decrease i n pH (Barnes and Czamanske, 1 9 6 7 ) . Presence of a c i d i c hydrothermal f l u i d s during a l t e r a t i o n has been discussed by Hemley and Jones, 1 9 6 4 ; Meyer and Hemley, 1 9 6 7 ; and Holland, 1 9 7 2 . pH gradients and consequent changes i n i n t e n s i t y of hydrogen metasomatism are considered to cause a l t e r a t i o n zoning (Hemley and Jones, 1 9 6 4 ; Helgeson, 1 9 7 0 ) , metal zoning (Holland, 1 9 7 2 ) , and changes i n f l u i d s during cooling (Meyer and Hemley, 1 9 6 7 ) . Zoning may also r e s u l t from increased m o b i l i t y of H + r e l a t i v e to OH during i n f i l t r a t i o n processes as described by K o r z h i n s h i i ( 1 9 5 7 ) . Hydrolysis e q u i l i b r i a studies (Helmey, 1 9 5 9 ; Hemley, et a l . , 1 9 6 1 ; Hemley, et a l . , 1 9 7 0 ) can be used to e x p l a i n the commonly observed a l t e r a t i o n sequence of p o t a s s i c - p h y l l i c - a r g i l l i c f a c i e s as a r e s u l t of decreasing temperature and potassium or sodium to hydrogen ion r a t i o s (Meyer and Hemley, 1 9 6 7 ) . Changes i n hydrothermal f l u i d s with time are documented at Endako deposit (Drummond and Kimura, 1 9 6 9 ; Dawson, 1 9 7 2 ) and at Yandera (Grant and Nielsen, 1 9 7 5 ) where v e i n a l t e r a t i o n envelopes i n a staged stockwork show the same trend from p o t a s s i c to p h y l l i c and a r g i l l i c a l t e r a t i o n thereby suggesting s i m i l a r changes i n temperature and a l k a l i to hydrogen ion r a t i o s as i n pervasive a l t e r a t i o n zones. HYDROTHERMAL PROCESSES IN THE FORMATION OF BERG DEPOSIT With the preceding d e s c r i p t i o n of a l t e r a t i o n f a c i e s at Berg deposit and d i s c u s s i o n of p r i n c i p l e s i n mind, a l t e r a t i o n zoning at Berg deposit can be i n t e r p r e t e d i n terms of decreasing temperature outward from the stock, d i f f e r e n c e s i n bulk rock composition, and changes i n hydrothermal f l u i d s . The composite stock i s surrounded by b i o t i t e - b e a r i n g metavolcanic rocks (hornfels) that extend up to 6 0 0 feet from the contact. The l a r g e r 91 quartz diorite stock has similar biotite hornfels along its intrusive contact but hornfels there is commonly 100 feet or less in width. Conductive thermal effects of igneous intrusions have been described by Lovering, 1955; Jaeger, 1959, 1964; and Whitney, 1975. Based on their models and earlier calculations on a small stock (Panteleyev, 1969) , temperature at the contact of a stock the size of Berg intrusion containing quartz monzonite magma at 800 degrees centigrade would be 400 to slightly in excess of 500 degrees centigrade. Temperatures would decrease outward from the contact but the limit to which purely conductive heat transfer would cause biotite hornfels to form is uncertain. Heat flow models are imprecise and allow great latitude in determinations of conductive heat flow. For example, at Copper Canyon, Nevada, a granodiorite stock was suggested to impose temperatures by con-duction of only 150 degrees centigrade (Steiger and Hart, 1967) whereas Winkler (1965, pages 61-63) suggested temperatures equal to 60 per cent of magma temperature could be conducted for up to 200 feet from a stock the size of that at Berg deposit. In any case, even i f thermal conduction is as effective as stated by Winkler, the extensive zone of biotite.hornfels sur-rounding Berg deposit could not have formed solely by thermal metamorphism due to conduction alone. It must have been expanded by more efficient heat transfer involving outward flowing hydrothermal fluids in the manner discussed by Rose (1970). The entire zone containing biotite is referred to either as a biotite hornfels or a biot it ic alteration zone because products of contact metamorphism (purely conductive heating) cannot be distinguished in the field from those of hydrothermal alteration. In this case presence of a heated fluid that abetted heat transfer is regarded to be the onset of hydrothermal alteration regardless of whether mass transfer occurred. Imposition of heat on the different rocks at Berg deposit (quartz monzonite, andesite, quartz diorite) results in a number of zoned alteration 92 assemblages that reflect differences in bulk rock composition as illustrated (Figure 9) by ACF and A'KF diagrams (Winkler, 1965). The expected alteration assemblages under the same temperature conditions wi l l be quartz-biotite-chlorite-epidote (biotite hornfels) in altered andesite and quartz diorite closest to the quartz monzonite stock, and quartz-sericite-biotite-chlorite-epidote-kaolinite (K-feldspar stable, plagioclase degenerative alteration) in quartz monzonite. There is no justification for placing biotite hornfels within the potassic (potassium-silicate) facies as no evidence for widespread potash enrichment can be found and none is necessary to produce the observed biot i t ic zone (biotite hornfels). Chloritic rocks outside the zone in which biotite recrystallized belong to the propylitic facies. Presence of pyrite can be used to delineate the area subjected to hydrothermal activity and to distinguish the propylitic zone from rocks with (sub) greenschist facies regional metamorphism. The foregoing discussion is used to explain observed zoning that can be related to the simplest possible (idealized) geologic situation -Increase in temperature within a closed chemical system. In addition to re-equilibriation of minerals due simply to elevated temperature, chemical reactions take place involving fluids. Pervasive changes in rocks can be interpreted to result from hydrolysis reactions which are most evident in feldspars. In the core of the stock K-feldspar is unaltered; in the margin of the stock, throughout the quartz plagioclase porphyry, and in highly fractured zones within the stock K-feldspar is sericitized; and at the extremity of the sheet-like quartz plagioclase intrusion in the southwest K-feldspar is sericitized and arg i l l i c . Plagioclase in the core of the stock Is unaltered or contains minor montmorillonite and in the periphery of the stock is kaolinized. These changes can be interpreted on the basis of C tremolite p F Figure 9. Mineral Assemblages In Thermally Metamorphosed Andesite, Quartz Diorite, and Quartz Monzonite. Average Rock Compositions From Nockolds , 1954 . 94 feldspar stabil it ies in a regime with outward decreasing temperature and increasing ratio hydrogen ion activity with respect to potassium ion activity as illustrated in the now familiar hydrolysis equilibria studies of Hemley (1959), and Hemley, et a l . (1961, 1970). Fluids in staged fractures resulted in deposition of a series of veins and fracture-associated alteration zones that suggest the fluids changed during the alteration sequence. The sequence of veins and fractures reveals that they, in i t ia l ly had l i t t l e effect on host rocks and fluids were evidently in equilibrium with minerals present. Later veins and fractures superimposed local conditions of disequilibrium on areas of pervasive alteration and older fracture-controlled alteration, each younger stage causing retrogressive breakdown of rock-forming and older alteration minerals. Early veins (Stage 1 and 2) are vuggy, ribboned, or mass^ive and commonly contain molybdenite. Vuggy and massive coarsely granular quartz veins that contain anhydrite commonly have orthoclase associated with them whereas ribboned and finely granular quartz veins rarely have orthoclase envelopes. Most Stage 1 and 2 veins are bereft of alteration envelopes or bleached margins and crosscut host rocks without apparent alteration effects. Therefore early veins and fractures formed under conditions in which biotite and feldspars were stable - probably at elevated temperatures during horn-felsing. Where alteration envelopes are present about Stage 1 veins, the envelopes are sericit ic or have s i l i c i f ied metasomatic selvages containing orthoclase. Most younger veins (Stage 3 and 4) alter enclosing rocks and therefore have alteration envelopes or bleached margins. Such alteration can be interpreted in terms of localized hydrolysis reactions and feldspar-95 mafic mineral instability in a manner similar to pervasive alteration zoning. At Berg deposit minerals adjacent to f lu id - f i l led fractures or veins were unstable and recrystallized to form s i l i c i f ied ser ic i t ic alteration envelopes (Plate 10), or degenerated to form bleached arg l l l i c (quartz-clay-chlorite-carbonate-gypsum) vein margins or formed combined ser ic i t ic envelopes with argl l l ic margins. The sequence orthoclase-sericite-clay minerals has not been recognized in any altered vein margin. This suggests that quartz-orthoclase metasomatism of Stage 1 veins and Stage 1 and 2 veins that lack alteration envelopes did not progress into nor were overlapped in the same vein by retrogressive sericite/clay alteration such as that in Stage 3 and 4 veins. Evidently early (Stage 1 and 2) and late (Stage 3 and 4) vein-forming processes were distinct and mutually exclusive. Additional support for presence of unique solutions during various vein stages and changes during the vein sequence is provided by vein mineralogy as was described in preceding paragraphs. The nature of fluids involved in alteration processes can be deduced from examination and heating of fluid inclusions. In this study 20 samples of various vein types were examined in detail and 20 of the better f luid inclusions from four samples of molybdenite-bearing Stage 1 veins were heated on a Unitron-500 microscope heating stage. Fluid inclusions are abundant in a l l quartz veins and can also be seen in anhydrite and pale-coloured zones in sphalerite. Fluid inclusions commonly are less than 2 microns and rarely up to 20^ A in size. In quartz they are particularly abundant and occur as two or three-phase negative crystal cavities, spheres, ovoids, or irregularly shaped bodies of primary and secondary origin as defined by Roedder (1967). In anhydrite fluid 96 i n c l u s i o n s are t h i n r o d - l i k e bodies that probably formed as secondary i n c l u s i o n s along cleavage i n t e r s e c t i o n s and contain only l i q u i d or r a r e l y are two phase with minute vapour bubbles. In outer growth zones of sph a l e r i t e " c r y s t a l s f l u i d i n c l u s i o n s were seen as negative c r y s t a l c a v i t i e s . Two-phase i n c l u s i o n s are present i n s p h a l e r i t e but i n some samples the vapour bubble contains a small amount of l i q u i d CC^. De t a i l e d examination of quartz reveals that two and three-phase f l u i d i n c l u s i o n s are present i n quartz from Stage 1 v e i n s . The s o l i d phase i n three-phase i n c l u s i o n s i s h a l i t e which forms small cubic c r y s t a l s generally smaller than 2 per cent by volume. In a d d i t i o n a few samples contain minute tabular c r y s t a l s (gypsum ?) and equant opaque grains (sulphides or hematite ? ) . Stage 2 veins commonly contain two-phase i n c l u s i o n s but three-phase i n c l u s i o n s might be present. Stage 3 and 4 veins appear to con-t a i n only two-phase i n c l u s i o n s although two species of l i q u i d are present (brine and CO^) i n s p h a l e r i t e from Stage 4 v e i n s . From these data (Appendix D) i t can be concluded that i n i t i a l l y vein-forming f l u i d s were saturated or close to s a t u r a t i o n by NaCl and that s a l i n i t y had decreased when younger veins were deposited. Volume of vapour i n Stage 1 and 2 veins v a r i e s from 1 to 70 per cent. Vapour volumes vary widely even i n the same v e i n or vein specimen although most f l u i d i n c l u s i o n s contain 10 to 30 per cent vapour. Such v a r i a b i l i t y and high vapour content are considered to be evidence for b o i l -i n g i f homogenization temperatures are.equal (Roedder, 1967 and 1971) and therefore sustained or repeated b o i l i n g e v i d e n t l y took place during at l e a s t e a r l y v e i n development at Berg deposit. Evidence f o r b o i l i n g also implies that hydrothermal f l u i d s were maintained «t h y d r o s t a t i c pressure f o r sustained p e r i o d s . 97 The 20 f l u i d i n c l u s i o n s examined from four specimens of Stage 1 veins i n c l u d e : fourteen i n c l u s i o n s i n quartz from three quartz-anhydrite-molybdenite-pyrite-chalcopyrite-bearing veins i n well-mineralized b i o t i t e h o r n f e l s , and s i x f l u i d i n c l u s i o n s from terminated quartz c r y s t a l s i n a vuggy, coarsely c r y s t a l l i n e quartz-molybdenite v e i n from quartz monzonite porphyry with strong p h y l l i c ( q u a r t z - s e r i c i t e - p y r i t e ) a l t e r a t i o n . Size of f l u i d i n c l u s i o n s ranged from 5 to 15yn , most being 10 to 12y^ i n s i z e and containing about 10 per cent vapour. Only one of the 20 f l u i d i n c l u s i o n s contained a r e a d i l y v i s i b l e h a l i t e c r y s t a l . A d d i t i o n a l i n c l u s i o n s are believed to:contain minute s a l t c r y s t a l s but they were so small that t h e i r presence could not be confirmed with the a v a i l a b l e apparatus and could only be intimated from aberrations and anomalous spots of l i g h t transmittance on walls of f l u i d i n c l u s i o n s . Upon heating 18 of the 20 f l u i d i n c l u s i o n s were not homogenized at temperatures up to 406 degrees centigrade and at t h i s temperature a reduction i n vapour volume of only about 10 per cent was achieved. Therefore, Stage 1 veins appear to have been deposited at temperatures w e l l i n excess of 406 degrees centigrade and probably c l o s e r to 500 degrees centigrade or higher. One 12/A two-phase negative c r y s t a l c a v i t y f l u i d i n c l u s i o n with 10 per cent vapour from an anhydrite-bearing Stage 1 v e i n homogenized at 392+15 degrees centigrade. This i n d i c a t e s that secondary i n c l u s i o n s are present i n Stage 1 veins or that a considerable decrease i n temperature might have taken place during development of Stage 1 v e i n s . Another two-phase f l u i d i n c l u s i o n that i s associated with a number of high temperature i n c l u s i o n s i n a Stage 1 quartz-anhydrite-molybdenite-pyrite-c h a l c o p y r i t e v e i n appears to be primary but homogenized at 284+2 degrees centigrade and i s probably secondary or a r e s u l t of necking down. 98 Stage 5 gypsum-filled f r a c t u r e s do not have any apparent a l t e r a t i o n e f f e c t s on host rocks or minerals along f r a c t u r e selvages. Gypsum appears to have been deposited as open-space f i l l i n g and there i s no suggestion even from deep d r i l l holes that anhydrite was f i r s t p r e c i p i t a t e d and then hydrated to gypsum. Fracture f i l l i n g by gypsum therefore took place at temperatures below 57 degrees centigrade because at higher temperature anhydrite i s p r e c i p i t a t e d by i t s e l f or along with gypsum from aqueous s o l u t i o n (Holland, 1967). The widespread presence of gypsum i n late-stage cleavage f r a c t u r e s i n the mineralized zone and a l l but the youngest i n t r u s i v e phase of the composite stock might be because s o l u b i l i t y of gypsum (and carbonate) i n aqueous s o l u t i o n decreases with i n c r e a s i n g temperature and decreasing pressure (Holland, 1967). Thus gypsum was probably deposited by heating of c i r c u l a t i n g and upwelling sulphate-bearing f l u i d s during l a t e c o o l i ng of the stock. The a s s o c i a t i o n of these late-forming gypsum-filled f r a c t u r e s with the zone of m i n e r a l i z a t i o n and i n t r u s i o n i s p o s s i b l y the best evidence at Berg deposit that convective flow i n v o l v i n g meteoric sulphate-bearing hydrothermal f l u i d s has taken place as described i n the model of White, Mu f f l e r , and T r u e s d e l l (1970). 99 CHAPTER IV MINERALIZATION INTRODUCTION Widespread copper-molybdenum m i n e r a l i z a t i o n i s associated with rocks intruded by quartz monzonite. D r i l l indicated g e o l o g i c a l reserves of 394 m i l l i o n tons grading 0.32 per cent copper and 0.054 per cent molybdenite using a 0.25 per cent copper equivalent c u t - o f f grade have been estimated by Canex Placer Limited (1974, P. G. Beaudoin, personal communication). A considerably smaller mining reserve i s ind i c a t e d because of high s t r i p p i n g r a t i o s over much of the deposit. P y r i t e and chalcopyrite are the most abundant sulphide minerals and occur p r i m a r i l y i n f r a c t u r e s , i n quartz veins, and as disseminations. Molybdenite i s contained mainly i n quartz veins. Secondary copper sulphides are found i n an enrichment blanket over most of the deposit. 'Chalcocite' (probably mainly digenite) and c o v e l l i t e are the most important secondary copper minerals. They occur as t h i n coatings on p y r i t e and chalc o p y r i t e and are deposited i n a large, well-defined zone of supergene enrichment. Near surface sulphide minerals are extensively leached and secondary copper minerals are present i n small amounts as copper oxides or carbonates and native copper. Primary ore minerals are most abundant i n an asymmetrical annular zone of b i o t i t i c h o r n f e l s surrounding the quartz monzonite stock. Best grades of copper and molybdenum are found i n b i o t i t i c quartz d i o r i t e i n the northeast sector of the deposit, weakest m i n e r a l i z a t i o n i s along the western margin of the i n t r u s i o n . Copper-molybdenum m i n e r a l i z a t i o n decreases i n i n t e n s i t y away from the main quartz monzonite contact. Outward from 100 the contact, p y r i t e increases to form a p y r i t i c halo about the zone of copper-molybdenum m i n e r a l i z a t i o n , then decreases abruptly. Within the quartz monzonite stock copper and molybdenum grades decrease away from the contact and r a r e l y exceed 0.15 per cent copper and 0.05 per cent molybdenite. Sphalerite with p y r i t e and some tennantite and galena are found i n veins within and p e r i p h e r a l to the p y r i t i c halo as w e l l as i n small late-forming quartz and quartz carbonate v e i n l e t s i n the main copper-molybdenum zone. D i s t r i b u t i o n of primary minerals i s not r e a d i l y seen i n outcrop due to weathering and sulphide leaching by a c i d i c s o l u t i o n s . At surface, rocks are bleached, crumbly masses commonly stained and cemented by limonite i n an extensive capping. Sulphide minerals are s t r o n g l y corroded or leached to a maximum depth of about 125 f e e t . Secondary copper minerals are deposited below the oxidized and leached rocks i n a zone of supergene copper m i n e r a l i z a t i o n with a maximum thickness of about 300 f e e t . The combined e f f e c t s of o x i d a t i o n , leaching, and supergene enrichment impart a pronounced v e r t i c a l zoning to the deposit that overlaps, and to a large degree, mask primary zoning patterns. V e r t i c a l zoning i s i l l u s t r a t e d i n Figure 15 which shows copper depletion and molybdenum concentration i n the s t r o n g l y o x i d i z e d zone near surface, copper enrichment beginning approximately at the present water table, and primary m i n e r a l i z a t i o n at depth below the 'gypsum l i n e , ' the elevation below which f r a c t u r e s are t i g h t l y cemented by gypsum and there has been minimal groundwater c i r c u l a t i o n . PRIMARY MINERALIZATION AND LATERAL ZONING Primary (hypogene) ore minerals are present mainly as p y r i t e , c h a l c o p y r i t e , and molybdenite. In addition to the three main ore minerals, 101 magnetite, s p h a l e r i t e , tennantite, and galena are present as are trace amounts of arsenopyrite, p y r r h o t i t e , s c h e e l i t e , i l m e n i t e , hematite, and r u t i l e . Bornite has been reported (Owens, 1968) i n minute amounts as 2 to 10 micron-sized i n c l u s i o n s i n p y r i t e but does not contribute s i g n i f i -cantly to ore value. Gold and s i l v e r assays, as determined from a few composite samples of d r i l l core, are low and only minor c r e d i t f o r s i l v e r i s a n t i c i p a t e d . Zoning patterns, as defined by v a r i a b l e amounts of the main ore minerals, are i l l u s t r a t e d i n Figures 10, 11, 12, 13, and 14. These patterns are based on a l l information a v a i l a b l e to 1971 and some " s e l e c t e d data from more recent d r i l l i n g . No v e r t i c a l zoning can be demonstrated i n primary m i n e r a l i z a t i o n within 1,000 fee t of surface but deeper d r i l l i n g suggests that molybdenite grades increase at depths greater than 1,500 feet whereas copper grades decrease below 2,000 feet from surface (P. G. Beaudoin, 1975, personal communication). P y r i t e Is present as f r a c t u r e - c o n t r o l l e d and disseminated grains averaging about 1 m i l l i m e t r e i n s i z e as well as more coarsely c r y s t a l l i n e euhedral grains and aggregates i n a number of successive generations of p y r i t e and q u a r t z - p y r i t e v e i n s . Chalcopyrite i s i n t i m a t e l y associated with p y r i t e but i s f i n e r grained and commonly present as d i s c r e t e 0.1 to 0.3 milli m e t r e g r a i n s . A s i g n i f i c a n t proportion i s found as 10 to 50-mlcron i n c l u s i o n s i n p r y i t e . Some blebs of chalcopyrite 10 microns and smaller i n s i z e are scattered throughout and t o t a l l y encapsulated i n p y r i t e and l e s s commonly magnetite. Such chalcopyrite may be d i f f i c u l t to l i b e r a t e by con-ve n t i o n a l m i l l i n g of ore. Molybdenite i s most commonly found as f i n e -grained flakes w i t h i n s e v e r a l generations of quartz-bearing v e i n l e t s . I t also occurs as very f i n e grains or 'paint' i n ribboned quartz v e i n s , as c r y s t a l s along quartz v e i n selvages, and les s commonly i n fra c t u r e s with 102 p y r i t e and/or c h a l c o p y r i t e . Some coarse c r y s t a l s of molybdenite are engulfed and mechanically transported i n gypsum. D i s t r i b u t i o n of p y r i t e represented as mean volume per cent c a l c u l a t e d over long d r i l l i n t e r c e p t s i s shown i n Figure 10. P y r i t e i n quartz monzonite averages 2 per cent or le s s by volume and increases pr o g r e s s i v e l y outward everywhere except i n the northeast sector of the deposit where the zoning symmetry i s i n t e r r u p t e d by a zone with l i t t l e p y r i t e i n b i o t i t i c quartz d i o r i t e . P y r i t e increases to a maximum of about 6 per cent or more i n the p y r i t e halo about 500 feet or more from the main quartz monzonite contact. The p y r i t e halo envelopes the zone of best copper-molybdenum m i n e r a l i z a t i o n with best grades corresponding to a p y r i t e content of about 2 to 3 per cent. Chalcopyrite i s most concentrated i n b i o t i t i c h o r n f e l s adjacent to the quartz monzonite stock and i n b i o t i t i z e d quartz d i o r i t e i n the north-east zone. Chalcopyrite content decreases p r o g r e s s i v e l y away from the-main i n t r u s i v e contact i n an inverse manner to p y r i t e . Relationship of chalco-p y r i t e to p y r i t e i s i l l u s t r a t e d as a p y r i t e - c h a l c o p y r i t e r a t i o i n Figure 11. Chalcopyrite exceeds p y r i t e i n abundance only i n quartz d i o r i t e of the w e l l -mineralized northeast sector and i n a low p y r i t e zone encountered i n a.single d r i l l hole at the southern contact of the quartz monzonite i n t r u s i o n . Out-ward from the i n t r u s i v e contact p y r i t e - c h a l c o p y r i t e r a t i o of 4:1 s i g n i f i e s the s t a r t of the p y r i t e halo and a rapid increase i n amount of p y r i t e . Within the p y r i t e halo p y r i t e - c h a l c o p y r i t e r a t i o exceeds 10:1 and l o c a l l y i s greater than 50:1. P y r i t e - c h a l c o p y r i t e r a t i o remains f a i r l y constant i n any given zone even where t o t a l volume of sulphides v a r i e s . 103 105 FIGURE 12 PRIMARY MINERALS 4 breccia qtz bearing monzodi. qtz monzonite qtz diorite hornfels .volcanics 106 T 107 Chalcopyrite and molybdenite concentrations expressed as per cent copper and molybdenite are shown in Figures 12 and 13. The annular pattern of mineralization and intimate relationship of copper-molybdenite mineral-ization with intensely fractured and hydrothermally altered rocks along the quartz monzonite contact are evident. The pattern and zoning trends are remarkably consistent throughout the mineralized area. Areas underlain by 20 feet and more of 0.4 per cent copper with the larger zones of -0.2 per cent copper are shown. The -0.4 per cent copper grade is an arbitrary value used to indicate zones of better grade mineralization. Twenty feet is taken to be the minimum thickness of rock from which a bench of ore could be * developed. In plan view small areas underlain by rocks with better copper grades cluster around the quartz monzonite stock or are localized in biot i t ic quartz diorite In the northeast sector. Grades of copper and molybdenite when averaged over long d r i l l ~ intercepts and plotted in : .relation to distance from the main quartz monzonite contact (Figure 14) document behaviour of chalcopyrite and molybdenite more explicitly. Both copper and molybdenum decrease in intensity in a regular manner away from the quartz monzonite contact but two separate regimes are evident: hornfels and quartz diorite. Quartz diorite is superior to hornfels as a host for copper and molybdenum sulphides, even though in many localit ies i t - i s some distance from the quartz monzonite stock. The same grade is-developed in quartz diorite twice as far from the quartz monzonite contact as hornfels. Conversely, at the same distance from the quartz monzonite contact grades of copper and molybdenite in quartz diorite are about double those in hornfels. Best grades of copper discovered to date are in quartz diorite, but some of the higher values shown in Figure 14 (marked by ?) may 1 0 8 not be representative as they are based on poor core recoveries (from 1 0 to 25 per cent). Trends of copper-molybdenum m i n e r a l i z a t i o n shown i n Figure 1 4 are s i m i l a r but some d i f f e r e n c e s are i n d i c a t e d . Best m i n e r a l i z a t i o n has taken place i n h o r n f e l s near the quartz monzonite stock. Copper i s most concentrated at a s l i g h t distance from the main contact whereas molybdenum min e r a l i z a t i o n straddled the i n t r u s i v e contact and molybdenite i s maximized along i t . Copper values e x h i b i t two d i s t i n c t l e v e l s of concentration with quartz monzonite having only about one-half the copper content o f - h o r n f e l s v A s i m i l a r observation was noted i n b r e c c i a bodies outside the main i n t r u s i v e mass where ore grades derived mainly from well-mineralized h o r n f e l s f r a g -ments were d i l u t e d i n proportion to the amount of quartz monzonite matrix present. These patterns (Figure 1 4 ) i n d i c a t e that molybdenite mineral-i z a t i o n was superimposed on the main i n t r u s i v e contact zone and grades diminish i n a regular manner away from the contact. The main c o n t r o l f o r molybdenite i s f r a c t u r e i n t e n s i t y and quartz v e i n i n g . Copper grades, on the other hand, diminish abruptly within i n t r u s i v e rocks and i n a d d i t i o n to f r a c t u r e i n t e n s i t y appear to be influenced more than molybdenite by rock composition. SECONDARY MINERALIZATION AND VERTICAL ZONING INTRODUCTION V e r t i c a l zoning defined by progressive changes i n mineralogy and ore tenor with depth i s _ a _ r e s u l t of oxidation, sulphide leaching, and super-QTZ M O N Z 1 r . 5 -.4-. 3 — .2— • • 1 r .14 — .12 — < >-z o <M Ok O z < 5 IO -% MoS2 HORNFELS . Q T Z D/OR/TE » 1 » T r ~i r . 5 -C u qtz monz hornfels > qtz diorite T i 1 1 r IOOO' ~i r 2000' M o S 2 i r F i g u r e 14 t PRIMARY Cu and MoS 2 GRADE IN RELATION TO DISTANCE FROM MAIN INTRUSIVE CONTACT AO — • I • 0 8 -. 0 6 -0 4 — •02 — INCREASING DISTANCE FROM MAIN QMP CONTACT i r——o i 1 1 1 1 ; i 2 0 0 2 0 0 ' oOO' IOOO 1 "* ' r I4O0' 2 O 0 O FEET o 110 gene processes. At surface, In subcrop, and at r e l a t i v e l y shallow depths abundance of sulphide minerals and ore value are reduced due to o x i d a t i o n and leaching by a c i d i c s o l u t i o n s . In t h i s environment copper i s mobile whereas molybdenum i s immobile (Ga r r e l s , 1954; Sato, 1960; T i t l e y , 1963; Hansuld, 1966). Thus, when sulphide minerals break down copper i s depleted but molybdenum remains and may be concentrated. Figure 15 i l l u s t r a t e s v e r t i c a l zonation as defined by ore tenor. Copper i s c o n s i s t e n t l y depleted from rocks near surface except near b a s i c dykes where copper oxides and hydrated copper carbonates are deposited ( f o r example, diamond-drill hole 23). Molybdenum i s more v a r i a b l e In i t s behaviour. Molybdenite grades of outcrops commonly compare with those of primary m i n e r a l i z a t i o n ( f o r example, diamond-drill hole 74). In c e r t a i n areas of s t r o n g l y oxidized rocks, molybdenum i s i n the form of molybdates and complexes with f e r r i c hydroxide as w e l l as molybdenite i n quartz veins where i t was protected from leach s o l u t i o n s . Mineralogy of strongly oxidized rocks w i l l be discussed i n more d e t a i l i n a succeeding s e c t i o n . Supergene copper m i n e r a l i z a t i o n r e s u l t i n g i n enrichment of primary grade ore takes place below the zone of oxidation i n the zone containing groundwater. Copper contained i n downward pe r c o l a t i n g a c i d i c leach solutions replaces c h a l c o p y r i t e and p y r i t e as so l u t i o n s become n e u t r a l i z e d at depth forming secondary copper sulphides and oxides. Enrichment of primary copper grade averages about 25 per cent (that i s , 1:25 to 1 e n r i c h -ment factor) and i s maximized near the top of the groundwater table immedi-a t e l y below zones of o x i d i z i n g primary m i n e r a l i z a t i o n as i n diamond-drill hole 23. Increase i n i n t e n s i t y of enrichment with depth shown by diamond-d r i l l hole 19 i s only apparent and r e f l e c t s increasing primary grade as the VERTICAL ZONING OF Cu andMoS2 GRADES IN DIAMOND DRILL CORES 112 i n t r u s i v e contact i s approached. Away from the contact (at greater depth) primary grade diminishes as does the amount of supergene copper enrichment. EXTENT OF LEACHING AND SUPERGENE MINERALIZATION Maximum thickness of the strongly oxidized zone with sulphide leaching i s about 125 f e e t ; the supergene zone i s up to 300 feet t h i c k . Base of the s t r o n g l y oxidized zone i s c l e a r l y shown by marked increases i n copper grade and amount of sulphide minerals, presence of secondary copper sulphides, and minor amounts of native copper, as w e l l as a decrease i n the amount o f limonite and a n o t i c e a b l e change i n limonite colour from yellow-brown or orange to dark brown. Base of supergene copper m i n e r a l i z a t i o n i s c l e a r l y marked i n d r i l l holes by the 'gypsum l i n e ' - the l i m i t of ground-water c i r c u l a t i o n below which f r a c t u r e s are t i g h t l y cemented by gypsum. Depth of strong o x i d a t i o n with sulphide leaching and thickness of the supergene copper zone i s i l l u s t r a t e d as isopach maps i n Figures 17 and 18. The e l e v a t i o n below which gypsum i s present (the gypsum surface) that defines the s t a r t of primary m i n e r a l i z a t i o n at depth i s shown In Figure 16. The isopachs and gypsum surface are trend surface maps computed using double Fou r i e r s e r i e s analyses of i r r e g u l a r l y spaced data a f t e r a method described by James (1966). Data input from 54 l o c a t i o n s were u t i l i z e d using a wavelength of 2,200 or 2,300 feet and 25 terms i n s e r i e s representing _~ a second harmonic surface. The waveform generated approximates the present topographic p r o f i l e at Berg deposit (shown i n Figure 16) to which the depth - of oxidation and supergene m i n e r a l i z a t i o n are r e l a t e d . A wavelength of about 2,200 feet i s compatible with the dimensions of the i n t r u s i v e system, zone of hydrothermal a l t e r a t i o n and m i n e r a l i z a t i o n , and topographic r e l i e f . The 113 'goodness of f i t ' of trend surfaces generated are about 63, 70, and 88 per cent, thus achieving an acceptable and g e o l o g i c a l l y u s e f u l degree of smoothing of the observed data. Contours r e l a t i v e to sea l e v e l marking the s t a r t of gypsum i n fr a c t u r e s define a 'gypsum plane.' This surface i s shown i n Figure 16, and unequiyocably defines the base of groundwater c i r c u l a t i o n below which . oxidation and supergene e f f e c t s are minimal and confined to a few narrow zones of intense f r a c t u r i n g or f a u l t i n g . Depth of gypsum s o l u t i o n i s a function of groundwater flow patterns and degree of a c i d i t y . Flow patterns i n bedrock are influenced at Berg deposit mainly by topography, major and subsid i a r y s u r f i c i a l drainage patterns within the c i r q u e - l i k e basin, and i n t e n s i t y of f r a c t u r i n g . The zone of gypsum leaching defined by diamond d r i l l i n g forms a nort h e a s t e r l y elongated depression that r i s e s i n e l e v a t i o n to the northeast roughly p a r a l l e l to present topography. The zone of deepest gypsum leaching i s c o a x i a l with mineralized i n t r u s i o n s p a r a l l e l to 'Red' and 'Pump' Creeks but perpendicular to the north fork of Bergeland Creek, the major drainage system. A trend surface isopach map-of oxidized rocks from which copper -i s leached i s shown i n Figure 17 and one of supergene copper m i n e r a l i z a t i o n i s shown i n Figure 18. S i m i l a r trends are apparent with maximum thicknesses i n the southeast and east sectors of the mineralized zone along-the quartz monzonite contact and i n ho r n f e l s adjoining quartz d i o r i t e . Strongest oxidation and most advanced leaching are seen i n rocks i n the v i c i n i t y of 'Red' Creek and i t s branches where the deeply i n c i s e d creek e f f i c i e n t l y conveys away surface runoff and shallow groundwaters from fl a n k i n g slopes allowing intense oxidation. Deep oxidation takes place where a c i d i c s o l u t i o n s from o x i d i z i n g p y r i t e - r i c h rocks penetrate the most h i g h l y fractured zones i n FIGURE 16 TREND SURFACE ELEVATION MARKING START OF GVPSUM IN FRACTURES Elevations in feet ASL 87.6 % sum of squorei contribuI ion I I breccia | qtt bearing monzodio. qtz monzonite | qtz diorite I volcanics , hornfels 21000 N O 19000 N -17000 N cy-st) FIGURE 18 TREND SURFACE ISOPACH MAP, SUPERGENE Cu MINERALIZATION Thrcknau in f»*t 63-4 Y, turn of iquorai contribution I I breccia | qtz bearing monzodio. qtz monzonite | qtz diorite | volcanic* , hornfela 117 hornfels between quartz monzonite and quartz d i o r i t e i n t r u s i o n s . D i u r n a l , p e r i o d i c , and seasonal f l u c t u a t i o n s i n groundwater flow and chemistry f a c i l i t a t e deep, complete o x i d a t i o n and sulphide leaching. The southeasterly extension of the deeply o x i d i z e d zone may be l o c a l i z e d by increased permeability i n northwest-southeast-trending zones of b r e c c i a t i o n and f a u l t i n g . Supergene copper minerals are found i n a zone that i s more wide-spread than the zone of intense sulphide leaching. Maximum thickness of the supergene zone i s developed along the eastern part of the mineralized zone between the major i n t r u s i o n s . A westward-projecting lobe i n d i c a t e d by thick supergene zones i n two d r i l l holes i n the i n t r u s i v e stock i s coincident with quartz monzonite porphyry (Map 2, unit 3). Thickness of the zone with supergene copper m i n e r a l i z a t i o n i n quartz d i o r i t e shown i n Figure 18 i s exaggerated as values p l o t t e d are v e r t i c a l d r i l l hole i n t e r -cepts on slopes that commonly approach 45 degrees. The pattern shown i n Figure 18 i s almost e n t i r e l y a r e s u l t of downslope migration of a c i d i c copper-bearing leach s o l u t i o n s generated by oxidation of weakly cupriferous p y r i t e - r i c h rocks i n the p y r i t e halo and i n t e r a c t i o n with a r e l a t i v e l y stable water table i n the zone of intense f r a c t u r i n g . The thickest zone of secondary copper sulphides i n quartz monzonite i s coincident with zones having most advanced s e r i c i t e - q u a r t z - p y r i t e a l t e r a t i o n (mainly quartz monzonite porphyry and s e r i c i t i z e d quartz p l a g i o c l a s e porphyry, Map 2, u n i t s 3 and 4). MINERALOGY AND PROCESSES OF FORMATION ZONE OF OXIDATION AND SULPHIDE LEACHING Breakdown of sulphide minerals near surface has resu l t e d i n a leached capping c o n s i s t i n g of mainly quartz, s e r i c i t e , clay minerals, 118 l i m o n i t e , and opaline s i l i c a . Limonite i s composed p r i m a r i l y of amorphous f e r r i c hydroxide [hydrogoethite, FeCOH)^], goethite (FeOOH), and minor hematite ( F e ^ ) with l o c a l l y developed j a r o s i t e [K(Fe, A 1 ) 3 ( S 0 ^ ) 2 ( 0 H ) & ] . Other minerals observed i n small amounts i n the zone of oxidation are: c u p r i t e , t e n o r i t e , native copper, malachite, a z u r i t e , brochantite, chalchanthite, f e r r i m o l y b d i t e , p o s s i b l y akaganeite (molybdenum-bearing beta l i m o n i t e ) , and black amorphous iron-manganese oxides formed from lead-zinc-bearing carbonate v e i n s . Owens (1968) has reported d e l a f o s s i t e . Freshly deposited limonite i s amorphous 'ac t i v e ' hydrogoethite which changes with time to a more s t a b l e amorphous v a r i e t y - ' i n a c t i v e ' hydrogoethite or c r y s t a l l i n e goethite (McAndrew, Wang, and Brown, 1975). Most limonite observed i n outcrop i s a pervasive or s u r f i c i a l pulverulent v a r i e t y . Granular, coagulated and caked, b o t r y o i d a l or f l a t c r usts are seen i n p i t s and f r a c t u r e s at depth. Some r e l i e f - t y p e limonite and s i n t e r e d crusts are present but c e l l u l a r boxwork and sponges are rare or absent. According to the,terminology of Locke (1926) and Blanchard (1968), most limonite studied would be c l a s s i f i e d as f r i n g i n g (contiguous) or e x o t i c (transported) types i n which a s p e c i f i c source of i r o n cannot be i d e n t i f i e d . Indigenous limonites would be expected i n quartz d i o r i t e with high c h a l c o p y r i t e - p y r i t e r a t i o s but none was observed. Instead, reddish brown, resinous 'pitch l i m o n i t e s ' with high copper (and molybdenum) content are present. F l u f f y , fibrous star-shaped and f l a k e - l i k e limonite i s found i n and proximal to basic/(reducing) dykes along with amorphous, black, copper-bearing oxides ( t e n o r i t e ?, melaconite ?). J a r o s i t e i s present i n various amounts throughout much of the de p o s i t . I t i s most prominent at surface and shallow depths along the 119 eastern margin of the quartz monzonite stock and along the mineralized quart d i o r i t e contact. L o c a l l y j a r o s i t e Is the dominant limonite constituent. Zones with j a r o s i t e i n excess of goethite are coincident with the most in t e n s e l y oxidized and leached rocks. J a r o s i t e normally accompanied by ferrimolybdite imparts a yellow colour to the capping. At depth and i n l e s s intensely leached rocks away from the j a r o s i t i c zone colour of limonite changes p r o g r e s s i v e l y from yellow-brown to orange, brown, and dark brown c h a r a c t e r i s t i c of goethite. The most abundant accumulation of limonite i s f e r r i c r e t e , a r e l a t i v e l y homogeneous deposit of f e r r i c hydroxide. F e r r i c r e t e i s trans-ported amorphous hydrogoethite and goethite p r e c i p i t a t e d on surface or i n overburden as s o f t , porous, f r i a b l e l i m o n i t e . F e r r i c r e t e deposits commonly contain plant and rock fragments and other d e t r i t u s . Some f e r r i c r e t e forms a matrix i n s o i l and t a l u s deposits r e s u l t i n g In cemented s o i l and b r e c c i a -l i k e deposits. At Berg f e r r i c r e t e i s being deposited a c t i v e l y i n creek g u l l i e s and along the base of slopes where groundwater discharges. Such deposits mantle much of the lower slopes along the north fork of Bergeland Creek and l o c a l l y are f i v e f e e t , and greater, i n thickness over hundreds of square f e e t . P a r t i a l chemical analyses of limonites are l i s t e d i n Table 4. Analyses show concentration of-copper but values of molybdenum; manganese, and other metals are low. In bulk, Berg f e r r i c r e t e c l o s e l y resembles bog i r o n ores and g o e t h i t i c 'soft ore' exploited at Steep Rock ( J o l l i f f e , 1955) and elsewhere. I t i s higher i n i r o n content and has les s impurities than l i m o n i t i c i r o n ores deposited as erosion and t e r r e s t r i a l weathering products such as those being evaluated i n Iraq (Skocek, et a l . , 1971). However, 120 TABLE 4 PARTIAL ANALYSES OF IRON ORES AND BERG FERRICRETE ( i n per cent) 1 2 3 4 Berg Berg Steep Wadi F e r r i c r e t e F e r r i c r e t e Rock Husainiya ; (massive) Crusts Fe Ore Iraq (newly deposited) * Fe t o t a l 55.24 39.8 57.0 38.3 S 1 .24 4.6 0.04 P 0.043 0.08 0.020 0.065 Mn 0.08 0.001 0.20 0.014 A 1 2 0 3 0.25 0.3 0.81 10.8 Cr 0.003 0.001 -- .009 T10 2 0.010 0.01 — 1.59 CaO 0.05 0.12 0.32 6.3 MgO 0.05 0.01 0.27 • 0.41 sio 2 1.0 3.1 15.3 Moisture 7.0 5.5 Loss on i g n i t i o n 20.9 7.6 --Note: -- = not reported 1 - Assay, Steep Rock Iron Mines, courtesy of A. W. J o l l i f f e , 1968. 2 - P. Ralph, analyst, B r i t i s h Columbia Department of Mines and Petroleum Resources, 1974. 3 - An t i c i p a t e d average grade, H. M. Roberts and M. W. B a r t l e y , Ec. Geol., V o l . 38, 1943, pp. 1-24. 4 - Average of f i v e samples, V. Skocek, et a l . , Ec. Geol., V o l . 66, 1971, pp. 986-994. GEOCHEMICAL. DETERMINATIONS, BERG FERRICRETES ( i n ppm) 1 2 3 Cu 2875 461 270 Mo 115 333 300 Zn 39 100 — Pb 32 100 Ag 3.4 5 --N i 12 100 Co 18 50 --Mn . 38 10 --1 - H. Goddard, analyst, Kennco Explorations, (Western) Limited, 1968. 2 — P. Ralph and R. Hibberson, analysts, B r i t i s h Columbia Department of Mines and Petroleum Resources, 1974. _3--_A..-Mariano, analyst, Ledgemont Laboratory, 1968. 121 despite s i m i l a r i t i e s i n composition, appearance, and p o s s i b l y o r i g i n with some commercial i r o n deposits, Berg f e r r i c r e t e i s too l i m i t e d i n quantity and too high i n sulphur content to be of present economic i n t e r e s t . Molybdenum i s an important constituent of limonite at Berg deposit. I t s presence i n the capping i n nonsulphide minerals i s an important i n d i c a t o r of primary sulphide m i n e r a l i z a t i o n at depth. L o c a l l y molybdenum i s concentrated i n the zone of oxidation and grades exceed those of hypogene zones i n underlying rocks as shown i n Figure 15. These observations are i n marked contrast to data presented by Pokalov and Orlov (1974) who state that molybdenum i s c o n s i s t e n t l y depleted from the zone of oxidation i n molybdenum and copper-molybdenum deposits. Molybdenum enrichment accompanying sulphide leaching and copper d e p l e t i o n near surface was noted e a r l y during exploration at Berg deposit. C. S i Ney, D. L. Norton, and G.O.M. Stewart found enrichment to be generally r e l a t e d to v i t r e o u s , b r i t t l e , violet-brown, l a c q u e r - l i k e limonite crusts r e f e r r e d to as 'Berg-X.' Studies by Norton and Mariano (1967) found 5 to -'15 per cent molybdenum i n s e l e c t c r u s t s of 'Berg-X' and widespread zones with limonite containing 1 to 2 per cent molybdenum. These r e s u l t s are consistent with observations made by Carpenter (1968) who reports up to 7.5 ••- -- - p e r c e n t molybdenum i n limonite at Questa; also J . C. Wilson (unpublished : r e p o r t , Kennecott Copper Corporation, 1965) who states that up to 7 per cent molybdenum i s present i n limonites i n a number of porphyry deposits, and Pokalov and Orlov (1974) who report an average of 1.26 per cent molybdenum i n limonite from a number of Soviet deposits. I f s u f f i c i e n t amounts of such limonites accumulate i n oxidized rocks, molybdenum enrichment would 122 take place. I t apparently has taken place at Questa where, according to Carpenter (1968), both chemical and mechanical concentration r e s u l t i n s o i l s with 1 per cent r e s i d u a l molybdenum and gossans (presumably from sulphide-bearing veins) having greater than 27 per cent molybdenum content. Identity of molybdenum-bearing substances at Berg deposit i s only p a r t i a l l y resolved. Ferrlmolybdlte i s common and together with molybdenum-bearing f e r r i c hydroxide might co n s t i t u t e a considerable proportion of t o t a l molybdenum i n the capping. Some molybdenum may al s o be present i n j a r o s i t e which according to Pokalov and Orlov (1974) may contain up to 1.75 per cent molybdenum, probably as minute i n c l u s i o n s of MoO^. In add i t i o n , a s e r i e s of molybdenum-bearing f e r r i c hydroxides r e l a t e d to ferrlmolybdlte have been described by Carpenter (1968) and suggested to be present at Berg by Barakso and Bradshaw (1971). These are various pH dependent, amorphous to very fine-grained, orange-brown f e r r i c molybdate hydrate phases having d i f f e r e n t Fe:Mo r a t i o s . The b r i t t l e , wine-coloured 'Berg-X' i s probably an altogether d i f f e r e n t and ra r e r limonite compound. Preliminary i n v e s t i g a t i o n s by Norton and Mariano (1967) i n c l u d i n g e l e c t r o n microscopic, d i f f r a c t i o n , and micro-probe analyses suggest that 'Berg-X' may be, i n part, 0.2 micron-sized c r y s t a l l i t e s of Mo0 2 ( t e n t a t i v e l y c a l l e d S i b o l a i t e ) as w e l l as a s p i n e l mineral, probably Fe2MoO^,. No other n a t u r a l occurrences of Mo0 2 are known but Jager, et a l . (1959), Norton and Mariano (1967), as w e l l as Pokalov and Orlov (1974) synthesized Mo0 2 at low temperatures i n l a b o r a t o r i e s . E l e c t r o n microprobe a n a l y s i s of 'Berg-X' limonite crusts by t h i s w r i t e r revealed p e r i o d i c , intermittent molybdenum enrichment took place during deposition of banded limonite c r u s t s . Zoning of 123 molybdenum i s evident w i t h i n some i n d i v i d u a l limonite layers i n d i c a t i n g progressively changing rates of molybdenum incorporation during d e p o s i t i o n of limonite. S i m i l a r observations of p e r i o d i c molybdenum enrichment i n limonite at Questa have been made by Carpenter (1968). Behaviour of sulphide minerals under o x i d i z i n g conditions and r e s u l t i n g products are summarized and i l l u s t r a t e d i n Figure 19. In porphyry deposits conditions i n the zone of oxidation commonly vary from pH 3 to 6 and oxidation p o t e n t i a l (Eh) of 0.4 to 0.8 v o l t (Sato, 1960). More a c i d i c conditions with pH 1.6, and l e s s , are pos s i b l e ; o x i d i z i n g veins at Questa have measured pH of 1 to 1.5 (Carpenter, 1968). At Berg deposit Barakso and Bradshaw (1971) report pH of 3.1 to 5.9 and Eh from 0.4 to 0.9 v o l t i n waters from streams, springs, and d r i l l - h o l e discharge. Waters as a c i d as pH 2.8 were measured during prolonged summer dry s p e l l s . Eh of 0.9 v o l t implies the presence of b a c t e r i a (probably t h i o b a c i l l i and f e r r o b a c i l l i ) according to Baas Becking, et a l . (1960). Under h i g h l y o x i d i z i n g conditions such as at Berg and other porphyry deposits a l l sulphide minerals d i s s o l v e (that i s , are leached) except rare sulphide grains where they are protected from leach s o l u t i o n s by nonreactive quartz gangue. Under milder o x i d i z i n g and l e s s a c i d i c conditions such as weathering of zones with l i t t l e p y r i t e content, molybdenite remains stable and only copper and/or i r o n sulphide minerals are leached. Oxidation of sulphides, abetted to some degree by o x i d i z i n g b a c t e r i a , generates ferrous or f e r r i c sulphate and sulphuric a c i d s o l u t i o n s . Copper as cuprous i o n i s mobile under a c i d i c conditions and i s removed i n aqueous s o l u t i o n s . Iron p r e c i p i t a t e s through hydrolysis as f e r r i c hydroxide and forms limonite, a mixture of mainly hydrogoethite and goethite. Hematite i s a minor limonite constituent at Berg deposit. Under PLATES 21, 22, and 23: E l e c t r o n microprobe beam scans of Berg limonite ('Berg X') showing Mo concentration i n rim. 125 h i g h l y a c i d i c o x i d i z i n g conditions (pH l e s s than 3) and dependent on a c t i v i t i e s of potassium, sulphur, and i r o n , j a r o s i t e i s stable (Brown, 1971). At Berg deposit j a r o s i t e i s widespread and l o c a l l y i s the dominant limonite constituent. Its presence coi n c i d e s with zones of int e n s e l y leached rocks, probably where potassium i s a v a i l a b l e by degradation of pota s s i c a l t e r a t i o n minerals. The widespread d i s t r i b u t i o n and persistence of j a r o s i t e i n the capping under moderately a c i d i c conditions i s explained by Brown (1971) as being due to slu g g i s h r e a c t i o n r a t e s . Molybdenum released from s o l u t i o n of molybdenite i s immobile under a c i d i c conditions and i s taken up by f e r r i m o l y b d i t e , l i m o n i t e , and i n s o l u b l e i r o n and molybdenum oxides as discussed e a r l i e r , ZONE OF SUPERGENE ENRICHMENT Supergene enrichment by secondary copper minerals takes place at or below the water table where downward migrating a c i d i c oxygenated leach s o l u t i o n s containing cuprous i on are reduced and n e u t r a l i z e d . Secondary copper minerals s e l e c t i v e l y replace p r e - e x i s t i n g sulphide minerals or under c e r t a i n conditions i n the t r a n s i t i o n zone between the o x i d i z i n g and primary sulphide zone p r e c i p i t a t e as native copper, copper oxides, or carbonates. Native copper and oxide minerals may a l s o form i f groundwater table f l u c t u a t i o n s expose secondary copper sulphide minerals and oxidation takes place when the water table i s depressed. Reactions and products of the supergene process can be i l l u s t r a t e d i n a s i m p l i f i e d manner i n an Eh-pH diagram showing mineral s t a b i l i t y f i e l d s of common minerals, as shown i n Figure 20 . Three processes can be envisioned as ind i c a t e d by paths A — > B, B — > A, and A —>• C. More a c i d i c conditions Figure 19 MINERAL STABILITY FIELDS AT 25°C , 1 AIM. A Cu-Fe-S-O-H MODIFIED FROM GARRELS(1960 ) 8. Mo-Fe-S-O-H AFTER BARAKSO AND BRADSHAW(T971) C. Fe-S-O-H IN PRESENCE OF K+, AFTER BROWN (1971) FIELD OF WEATHERING AFTER SATO (1960) I I ' . i I L 1— ; 1 1 1—: 1 1 2 4 6 8 10 12 pH Figure 20 STABILITY FIELDS IN Cu - H20 -C02 - 02-S SYSTEM (INCLUDING CHALCOPYRITE) AT 25°C AND 7 ATM MODIFIED FROM GARRELS (1960) ARROWS INDICATE PATHS OF SOLUTIONS IN THE ZONE OF OXIDATION AND SUPERGENE ENRICHMENT 128 than those suggested by Sato (1960) and shown In Figure 20 probably occur i n porphyry deposits. Thus points A and B may be s h i f t e d to the l e f t i n the diagram. A to B i s the r e s u l t of downward p e r c o l a t i n g leach s o l u t i o n s entering a r e l a t i v e l y stable zone of groundwater s a t u r a t i o n . P r e - e x i s t i n g sulphide minerals, f i r s t chalcopyrite (or b o r n i t e ) , l a t e r p y r i t e , are rimmed and replaced by 'chalcocite.'. Near the water table n e u t r a l i z e d s o l u t i o n s i n the presence of oxygen may form t e n o r i t e or c u p r i t e and native copper i f reduction takes place. Path B to A i s the r e s u l t of i n s i t u reactions where sulphide minerals react with pore waters whose a c i d i t y and oxidation p o t e n t i a l are i n c r e a s i n g . This i s the case where the water table i s being depressed and the zone of oxidation i s encroaching on e x i s t i n g sulphide minerals, or groundwater flow patterns change r e s u l t i n g i n a d d i t i o n s of leach s o l u t i o n s . As a c i d i t y increases i r o n and sulphur are leached from copper-iron sulphides i n the presence of copper ions. Secondary copper sulphides are deposited s t a r t i n g with c o v e l l i t e , followed under i d e a l conditions by minerals with s u c c e s s i v e l y higher copper content, i d e a l l y : a n i l i t e , d i g e n i t e , d j u r l e i t e , c h a l c o c i t e , and p o s s i b l y copper oxides and n a t i v e copper. Path A to C i s followed where leach solutions encounter r e a c t i v e host rocks that n e u t r a l i z e and b u f f e r s o l u t i o n s . Solutions i n presence of c a l c i t e w i l l not exceed pH 8.3 and, i f h y d r o l y s i s of s i l i c a t e minerals takes place, pH w i l l range from 6 to 10 (Sato, 1960). Most commonly n e u t r a l i z i n g r e a c t i o n s take place i n limestone, along borders of basic dykes or other rocks with s i g n i f i c a n t n e u t r a l i z i n g p o t e n t i a l and at depth where hydro l y s i s e q u i l i b r i a reactions take place i n the zone of water saturated primary m i n e r a l i z a t i o n . Cuprite, brochantite, t e n o r i t e , and native copper may form with ' f l u f f y ' limonite as w e l l as malachite and a z u r i t e where C0„ concentration i s high. 129 At Berg deposit processes described by a l l three s o l u t i o n paths shown i n Figure 20yare taking place simultaneously i n d i f f e r e n t parts of the deposit. Path B to A takes place i n the p y r i t i c halo where p r o p y l i t i c p y r i t e - r i c h rocks are o x i d i z i n g . I n i t i a l conditions are described by area 'B* as oxidation begins i n mineralized rocks exposed by erosion. As oxidation proceeds so l u t i o n s and products f o l l o w the path toward 'A.' Path B to A also describes on-going processes w i t h i n the supergene zone as erosion proceeds r e s u l t i n g i n a downward migrating groundwater table and encroachment of oxidation (weathering) conditions upon the zone of primary m i n e r a l i z a t i o n . Path A to B i s followed by concentrated a c i d i c leach s o l u t i o n s generated by oxidation (point 'A') which migrate downslope u n t i l they i n t e r a c t with the r e l a t i v e l y stable groundwater table i n the low-lying, h i g h l y fractured area around the quartz monzonite stock. I n t e r a c t i o n of leach s o l u t i o n s with groundwaters r e s u l t s i n migration of solutions from A to B (less a c i d i c , more reducing c o n d i t i o n s ) . Path A to C i s followed l o c a l l y where leach solutions encounter c a l c i t e - b e a r i n g dykes and are r a p i d l y n e u t r a l i z e d . This takes place both above and below the water table and accounts f o r copper enrichment by oxide and carbonate minerals i n the zone of sulphide leaching and prevalence of cuprite (together with some brochantite) i n andesite dykes below the water t a b l e . Secondary copper sulphide minerals l o o s e l y described at Berg deposit as 'chalcocite' are i d e n t i f i e d by X-ray d i f f r a c t i o n by Owens (1968) and t h i s w r i t e r as c o v e l l i t e and d i g e n i t e . Owens (1968) also reports traces of c h a l c o c i t e and d e l a f o s s i t e . Digenite and c o v e l l i t e are both found as p a r t i a l replacement rims on chalc o p y r i t e and p y r i t e . Complete replacement of small chalcopyrite grains up to 100 microns i n s i z e was seen by Owens (1968) but generally replacement rims are l e s s than 10 microns thick and 130 cove/lite cv CuS blaubleibender covellite bbcv ....Cui.jS - C U 1 . 4 S anilite .an Cu ].75 S digenite di Cui./65S-Cuh79S djurleite dj Cu].o0S chalcocite cc C1/2S cha/copyrife cp CuFeS2 bornite bn Cu5FeS4 MINERAL COMPOSITIONS SHOWING POSSIBLE PHASE RELATIONSHIPS MODIFIED FROM RUNNELS , 7969 Figure 21 131 commonly are not more than t a r n i s h . In specimens examined by the w r i t e r c o v e l l i t e i s more abundant than digenite whereas Owens (1968) reports d i g e n i t e i n excess of c o v e l l i t e . Mineral a s s o c i a t i o n s found (Figure 21) are c h a l c o p y r i t e - p y r i t e - c o v e l l i t e and c h a l c o p y r i t e - c o v e l l l t e - d i g e n i t e -p y r i t e (a non-equilibrium assemblage). The observed supergene assemblages are compatible with phase r e l a t i o n s suggested by studies i n system Cu-Fe-S and Cu-S (Roseboom, 1966; Runnels, 1969; Morimoto and Koto, 1971; and Barton, 1973) and are consistent with the b e l i e f that supergene enrichment i s i n i t s i n i t i a l stages at Berg deposit. Result of supergene copper mineral deposition with an in d i c a t e d enrichment f a c t o r of 1.25 or 25 per cent i s shown i n Figure 15. In plan (Figure 22) zones underlain by 20 feet or more of 0.4 per cent copper i n the supergene zone overlap e x t e n s i v e l y zones of primary or 'protore' with 0.2 per cent copper and thereby considerably expand ore reserves. O r i g i n of the supergene copper enrichment zone i s by contemporary on-going processes. Supergene m i n e r a l i z a t i o n i s believed to be a s i n g l e stage p o s t - g l a c i a l phenomenon that began a f t e r Fraser (Wisconsin) g l a c i a t i o n or, at e a r l i e s t , during d e g l a c i a t i o n . I t i s d i f f i c u l t to envision other simple or more probable a l t e r n a t i v e s to how the enrichment blanket, which i s so in t i m a t e l y r e l a t e d to present topography, could have survived repeated g l a c i a t i o n i f i t was pre-Pleistocene or an i n t e r g l a c i a l feature. Hematite, a common mineral i n multiple stage supergene zones, i s generally absent at Berg deposit. A short duration of enrichment i s suggested by mineralogy and i n c i p i e n t replacement textures of secondary sulphide minerals. Further-more, the presence of Cretaceous rocks on ridges i n Berg map-area (Map 1) makes i t doubtful that Berg deposit was exhumed by erosion p r i o r to f—20,000 N 132 FIGURE 22. PRIMARY AND MINERALS — BY ^ .4 % Cu SUPERGENE COPPER ZONES UNDERLAIN PRIMARY 1 J SUPERGENE Scale breccia I | Q t z bearing monzodi] I 1 qtz monzonite | | qtz diorite | | hornfels .volcanics 133 Pleistocene g l a c i a t i o n . Thus, as deduced from a map showing speculative ice-marginal p o s i t i o n s (V. K. Prest, 1970, pp. 706, 707, i n : Geology and Economic Minerals of Canada), supergene processes were probably i n i t i a t e d not e a r l i e r than 10,000 to 12,000 B.P. Ten thousand years following g l a c i a t i o n i s ample time f o r observed supergene e f f e c t s to be developed and the 125-foot-thick leached zone to form i n the hig h l y fractured, s t r o n g l y d i s s e c t e d terrane at Berg deposit. Lovering (1948) c a l c u l a t e d that at San Manuel t o t a l oxidation of 3.5 to 5 per cent p y r i t e could take place to depths of 500 to 600 feet i n 40,000 to 47,000 years. Also, leach dumps i n the southwestern United States (whose p o r o s i t y i s not much greater than that of weathered crackled zones i n porphyry deposits) have complete oxi d a t i o n of 5 per cent p y r i t e to a depth of 100 feet i n a few tens of years (D. Norton, 1966, unpublished report, Kennecott Copper Corporation). T i t l e y (1975) has described porphyry deposits i n which extensive leached and supergene enrichment zones are forming where m i n e r a l i z a t i o n i s as young as 1.11 m i l l i o n years. 134 CHAPTER V MINOR ELEMENTS IN PYRITE INTRODUCTION Minor element content of pyrite was investigated in order to: (i) Define concentration levels of minor elements in pyrite from a porphyry copper-molybdenum deposit, ( i i ) Test i f zoning of minor elements in pyrite is evident. (Iii) Relate zoning patterns and concentration ranges of minor elements in pyrite to mineralogical zoning (particularly the zone of primary copper sulphides). (iv) Test i f host rock compositions and different paragenetic types of pyrite influence the character or quantity of minor elements in pyrite. Pyrite was selected because i t is the most abundant sulphide mineral in porphyry copper deposits, is ubiquitous throughout mineralized areas, and is treated relatively easily to obtain a clean concentrate. Representative samples from almost every d r i l l hole and a few surface exposures were taken to give maximum possible geologic coverage of the area. Pyrite was classified according to location, host rock, texture, mineral associations, and paragenesis. Clean concentrates or hand-picked pyrite grains were analysed by emission spectrograph^. The method, procedure, and calibrated curves used to Interpret analytical results were available to the author at Queen's University as part of a routine 135 analytical f a c i l i t y . The attraction of this analytical method over others i s that only small amounts of pyrite are needed for analysis. This i s a major consideration when minerals are sparse and fine grained, as i n porphyry copper deposits, and only small samples, such as s p l i t diamond-d r i l l core, are available. Analytical results (Appendix G) were treated s t a t i s t i c a l l y using existing computer programmes and the University of B r i t i s h Columbia Computing Centre's I.B.M. 360, Model 67 computer. Conventional s t a t i s t i c a l methods were applied using univariate, bivariate, and multivariate pro-cedures. S t a t i s t i c a l results were interpreted on the basis of surface mapping and diamond-drill information. One hundred pyrite samples were selected as a representative sample set, from approximately 24,000 feet of diamond-drill core from 45 holes. A l l d r i l l holes without highly oxidized rocks were sampled and, where possible, two or more samples were taken at different depths. A l l major types of host rock, ore mineral associations, alteration, and paragenetic types of pyrite were sampled. The sample set of one hundred pyrites consists of seventy-eight specimens of disseminated or fracture-controlled finely dispersed sulphides (hereafter collectively referred to as 'disseminated* pyrite), and twenty-two vein specimens. Of the seventy-eight disseminated pyrites, forty-seven were taken from hornfels, nine from quartz di o r i t e , eighteen from quartz monzonite, and four from peripheral volcanic rocks. Vein pyrite was mainly from quartz veins with various sulphide and gangue associations. In addition to pyrite, five chalcopyrite and one sphalerite samples were analysed to determine the effects of contamination by these minerals i n pyrite. 136 The samples do not constitute a random sample set because the diamond dr i l l ing programme tested specific areas with economic mineral potential rather than random areas. Bias i s , thus, introduced into the statist ical basis of the data by a preponderance of samples from the zone of copper-molybdenum mineralization. There is proportionally less representation of pyrite from the barren core, pyritic halo, and weakly mineralized peripheral rocks. However, any weakness introduced into the statist ical basis of this study by non-random sampling is possibly over-shadowed by having a maximum of information from the mineralized zone. Pyrite-bearing core and hand specimens were classif ied, described' in detai l , and selected portions of the samples were marked and chipped off or cut out with a diamond saw. Clean pyrite concentrates were prepared in a sequence of steps involving crushing, screening, panning, heavy l iquid, and electromagnetic techniques. A l l concentrates were examined under a binocular microscope and a few polished grain mounts were prepared. If a concentrate was unacceptable due to contamination, pyrite was selected for analysis by hand picking pyrite grains. Samples were prepared for analysis by one or both of two methods. The standard method utilized pulverized and homogenized pyrite concentrate and a direct electrode-loading method util ized crushed, hand-picked pyrite grains. Each sample electrode was volatilized with a DC constant current arc in a 2-metre Jarrell-Ash emission spectrograph, using a two-stage procedure developed by Mr. Leo Mes (Analyst, Department of Geological Sciences, Queen 's University). Spectra were recorded on film and line intensities of diagnostic wavelengths of specific elements, as well as a palladium reference l ine, were read with a NSL Spec Reader micro-137 densitometer (Appendix F) . Transmittance measurements were converted to intensity ratios using 0.01 per cent palladium as an internal reference standard. Concentrations of elements in parts per million were obtained by referring the calculated intensity ratios to working curves calibrated with prepared pyrite standards. Preparation of standards and working curves used in this method are discussed in detail by Gosh-Dastidar (1970), and the analytical method is summarized by Dawson (1972) and Dawson and Sinclair (1974). One hundred and thirty-five analyses were performed uti l iz ing a total of one hundred pyrite samples. In the case of multiple analyses, mean values were used as analytical results. Duplicates were run on a routine basis to check rel iabi l i ty of the spectrographs method, homogeneity of samples, and to provide replicate pairs of analyses for computation of analytical error. Sample variabil ity (Appendices E and G) is readily evident; some can be explained by analytical (including sampling) error but precision (Table 5) and accuracy-(Table 6) of - the spectroscopic-method used are sufficient for zoning to be demonstrated. Calculation of analytical (including sampling) error from paired analyses was done with a computer programme written by A.C.L. Fox based on the procedure described by Garrett (1969). Comparison between 27 samples prepared from pyrite concentrates and 13 from hand-picked pyrite grains indicates values of B i , Co, Ni , and Cu from hand-picked grains are about only one-half as precise as those from pyrite concentrates; but are about the same for Ag and Zn. Analytical values of Pb and Mo from hand-picked pyrite appear to be more precise than those from concentrates, probably 138 because the possibility of contamination was minimized. In any case, there appears to be no extreme difference in precision between analyses of pyrites from concentrates or hand-picked grains and analytical data are treated as one data set. A summary of the calculated analytical precision is given in Table 5. Precision is computed using log values of the analytical results and is given as a per cent at 95 per cent confidence level. Accuracy, or the.relation of pyrite analyses to their true values, is d i f f icul t to appraise. An independent check of spectrographs results by atomic absorption (AA) analyses of the same pyrite concentrates is shown in Table 6. TABLE 5. ANALYTICAL PRECISION (FOR LOGGED DATA) Pyrite Concentrates Hand-picked Pyrite No. of Paired Precision* No. of Paired Precision* Analyses (%) Analyses (%) Bi 19 29.9 10 74.0 Co 27 5.8 13 14.2 Ni 27 5.4 . 13 9.3 Cu 10 9.5 10 13.7 Pb 27 23.3 13 8.2 Zn 27 • - • 17.1 10 14.3 Ag 7 57.6 13 59.0 Mo 23 98.8 10 29.5 ALL DATA No. of Paired Analyses Analytical Precision (%)* As 10 8.9 Bi 29 31.4 Co 40 8.7 Ni 40 6.5 Cu 20 11.6 Pb 40 18.5 Zn 37 17.1 Ag 40 58.4 Ti 20 14.2 Mo 33 81.0 Mn 25 33.7 *Two standard deviations. 1 3 9 TABLE 6. COMPARISON OF SPECTROGRAPHIC AND ATOMIC ABSORPTION ANALYSIS* OF PYRITE CONCENTRATES (ALL ANALYSES IN PPM) Sample No. Mo Cu Zn Pb Ag Ni Co Mn Bi 15-187 Spec 1 6 500 16 20.5 2.5 168 115 5 2 Spec i i 1 490 21 12 2.5 142 93 5 4 AA 11 470 50 22 4.0 160 117 12 5 29-226 Spec 6 330 53 18.5 8.0 62 620 5 1.5 AA 1 415 60 18 4.7 60 520 9 5 37-480 Spec i 0 198 80 20.5 1.5 850 560 5 3 Spec i i 1 102 52 16 1.0 1000 600 5.5 7.5 AA 1 122 44 21 2.1 1000 415 45 5 *Atomic absorption analyses performed by Mr. H. Goddard, Kennco Explorations, (Western) Limited, 1968. Comparison of results shows roughly the same hierarchy as analytical precision — correspondence between the two analytical methods i s best for Co, Ni, Cu, and Pb; i s f a i r for Zn, Bi, and Ag; and i s poor for Mo and Mn. In Berg pyrite a number of minor elements are consistently present and are useful i n zoning studies. Their usefulness i s based on several requirements including: (I) . . elements must be incorporated i n some manner in.the pyrite structure and cannot be contaminants from included grains of other minerals. ( i i ) the analytical method must be sensitive with a s u f f i c i e n t l y low detection l i m i t to allow trace concentrations to be determined, ( i i i ) enough samples must contain detectable amounts of minor elements to provide a representative, s t a t i s t i c a l l y meaningful data set. (iv) analytical precision must be sufficiently high that v a r i a b i l i t y • can be attributed to actual differences in element concentrations rather than analytical error. 140 The following elements i n Berg pyrite tota l l y or p a r t i a l l y satisfy the conditions l i s t e d above: As, Bi, Cu, Co, Ni, Pb, Zn, Ag, Mo, T i , and Mn. This assemblage can be ranked I to V i n order of suspected value and r e l i a b i l i t y of the data. I. Co and Ni: a l l conditions mentioned above are s a t i s f i e d . II. Pb, Zn, Ag, B i , and Mn: may be affected by contamination and have less analytical precision than Co and Ni. III. As: high detection limit (300 ppm). Provides a small sample group as only 30 out of 100 analyses have detectable As. IV. Cu and Mo: are affected severely by contamination. Mo has analytical problems with Fe interference and poor precision. Both elements may be useful, however, because hand-picked samples from veins and possibly a few disseminated samples may be accurate. V. ~ T i : a unique constituent. Judging from i t s erratic distribution i t i s undoubtedly present as included grains. However, T i may be useful, regardless of i t s source, as an indicator of genetic type of pyrite, zone of copper mineralization, and host rock. Zirconium was detected i n a few samples and might be another useful element i n other pyrite studies. Sn was detected i n only 10 samples; Cr and V i n about 5. Cd and Sb were found only where there was sphalerite or tetrahedrite contamination. UNIVARIATE ANALYSIS A set of numerical data, such as pyrite analyses, can be simply yet lucidly represented and described by relative frequency histograms. 141 Histograms, i f properly drawn, enable a visual appraisal of data and allow rapid comparison of variables. The apparent concensus of long standing arguments about which distribution functions best describe minor element data is summarized by Shaw (1961) who states: "The concentration of a camouflaged trace element in a crystallizing rock under conditions of chemical equilibrium wil l correspond closely to a lognormal law' (a camouflaged trace element is a minor element that is incorporated in the crystal lattice of a mineral). Histograms il lustrating distributions of minor elements in Berg pyrite are shown in Figures 23, 24, and 25. A normal curve, using the observed mean and standard deviation is fitted to the transformed data in Figure 23. The mathematical expression for such ideal, Gaussian (normal) distributions and tables of numerical constants necessary for their calculation are taken from Dixon and Massey (1969). A l l data are summarized in Table 8 which gives the number of analyses, means (measure of central tendency), and standard deviations (measure of dispersion of the data). Both arithmetic and logarithmic values are given for comparison. It is evident in a few histograms (e.g., Figure 25) that some minor element distributions might contain more than one population. Arsenic appears to be bimodal and Co could contain three populations. The two apparent populations of As might be simply due to sampling error for the sample set contains only 33 analyses. Three populations of Co appear to be present and appear to be due to pyrite from different host rocks. Populations of Co from vein pyrite and two types of dis-seminated pyrite (one from quartz monzonite, the other from hornfels and O czo • Zn cso O C8t> o z cn H m C M z M l o K J J TI rcz PYR m fH a a 3 3 m Z o K> CO 2 P E R C E N T A G E v ? g * s * ill8/ P E R C E N T A G E g y y y N 3 * • • • o" g£§ a P E R C E N T A G E 3 S 8 8 0 oot 0 0 1 oot oor-oos 009 00^ 008 OOo-0001-8 § g 8. P E R C E N T A G E z ^ • 6" o c ZD m 0 OS 001 OSI 001 ocz ooc oct oor osr-P E R C E N T A G E -4 ?_ • • • • •o r aoro nro £060 ttCl P E R C E N T A G E 8 8 1=» — <* M Z • • P S 8«f P E R C E N T A G E 4-8 - 3 S - , a-— Crt M X % m B a 144 X -25 -20 -15 -10 As N 33 X 2.826 (670ppm) S 0.2645 I 0.066 CN m CN CM "IT 8! rt co n • rt 1-25 r 20 H5 10 <D1. Co N 100 X 2.307(203ppm) S 0.703 I 0.176 H Hornfels • Veins H Qtz.Monzonite • Qtz Diorite O Oi — —1 CN CN CN rt r-20 hio ~5 Q <b up cs CK r> co CN *»o C K n o O O cS • ~ <-' ~ CN C N rt - P > 1 Ti N 62 X 2.053(U3ppm) S 0 7 3 0 I 0.183 • Diss. M Veins FIGURE 25 FREQUENCY DISTRIBUTIONS OFAs.Co.andTi LOG1 0(PP™) TABLE 7. SUMMARY - MEANS AND STANDARD DEVIATIONS OF ALL ANALYSES No. of Arithmetic (ppm) Logarithmic Log 1 0 (ppm) Element Samples Mean Std. Dev. Mean Std. Dev. As 34 1237 2528 2.860 (725) 0.343 Bi 96 12.4 21.9 0.551 (3.6) 0.738 Co 100 406 354 2.307 (203) 0.703 Ni 100 156 200 1.886 ( 77) 0.587 Cu 55 263 194 2.257 (181) 0.461 Pb 93 84 104 1.613 ( 41) 0.602 Zn 92 59 82 1.518 ( 33) 0.462 Ag 93 13.0 17.3 0.481 (3.0) 0.847 Mo 75 13.0 20.0 0.3741 (2.4) 1.0335 Ti 62 256 225 2.053 (113) 0.730 Mn 89 5.5 10.5 0.0001 (1.0) 0.960 146 quartz diorite) appear to be different populations. T i distribution i s not readily explained; the two apparent populations are composed of pyrite from veins and a l l host rock types. One attribute of Berg minor element data shown by frequency distributions i s that vein pyrite generally has lower concentrations of elements than disseminated pyrite. Thus, an hypothesis can be tested using t and F tests that one cause of polymodal distributions i s mixing of vein pyrite and disseminated pyrite, both distinct populations. Figure 26 shows Ni distribution in which vein and disseminated pyrite i s differentiated and tested by t and F tests. Table 8 summarizes t and F tests of vein versus disseminated pyrite for a l l elements determined. - The results summarized in Table 8 are defi n i t i v e . F and t probabilities of Co, Ni, Cu* Zn, T i , and possibly Pb, Ag, Mo, and Mn are su f f i c i e n t l y low that i t can be assumed populations of vein pyrite are distinct from those of disseminated pyrite. The only exceptions are As and Bi which are the only two o f ' a l l elements determined that are believed to be incorporated i n pyrite.by_anion .substitution_.rather_than. cation substitution, inclusion i n la t t i c e defects, or location in i n t e r s t i t i a l ~ sites (see Appendix E). Polymodal distributions resulting from mixing of pyrite from different rock types are evident for certain elements; for example, Co i n Figure 25. A more subtle indication of polymodal populations can be seen i n Figure 26 where the distribution function of Ni i n disseminated pyrite i s much greater In amplitude than the normal curve f i t t e d to the data. It can be assumed, therefore, that a number of (partially ?) coincident populations are present. Figure 27 shows the distribution of F i g u r e 2 6 B i m o d a l D i s t r i b u t i o n c o n t a i n i n g V e i n a n d D i s s e m i n a t e d P y r i t e P o p u l a t i o n s . •15 7. -10 0.31 x D i s s e m i n a t e d x V e i n s N i l o g 1 0 ( p p m ) V e i n D i s s e m i n a t e d N 2 2 X 1 . 1 4 S 0 . 6 6 0.89 1.48 2.06 2.63 74 2 . 0 6 0 . 3 6 V e i n : D i s s e m i n a t e d t v a l u e 6 . 2 6 t p r o b a b i l i t y 0 . 0 0 0 F p r o b a b i l i t y 0 . 0 0 0 TABLE 8. CALCULATED t AND F PROBABILITY OF VEIN PYRITE VERSUS DISSEMINATED PYRITE (BASED ON LOG VALUES OF ALL AVAILABLE DATA) Lement N Vein X S.D. N Disseminated X S.D. F Prob. -t prol As 6 2.898 0.242' 24 2.808 0.272 .87 .46 Bi 22 0.532 0.746 66 0.697 0.595 .16 .36 Co 22 1.296 0.730 74 2.572 0.333 .00 .00 Ni 22 1.143 0.659 74 2.060 0.358 .00 .00 Cu 19 1.889 0.522 33 2.459 0.252 .00 .00 Pb 20 1.423 0.872 69 1.643 0.498 .00 .29 Zn 20 1.260 0.582 68 1.560 0.389 .02 .04 Ag 20 0.664 0.508 69 0.922 0.426 .29 .05 Mo 20 0.381 0.494 51 0.808 0.639 .22 .00 T i 20 1.389 0.729 39 2.375 0.496 .04 .00 Mn 20 0.275 0.447 48 0.515 0.493 .65 .04 00 149 Ni i n disseminated pyrite (the disseminated pyrite portion of Figure 26) with separate plots of pyrite from different sources. An hypothesis can be tested that the polymodal distribution of Ni i n disseminated pyrite i s due to a number of populations representing pyrite from different host rocks, t and F tests comparing distributions of pyrite from hornfels, quartz monzonite, and d i o r i t e are summarized in Table 9 and i l l u s t r a t e d i n Figure 26. Vein pyrites are also compared to pyrite from other host rocks. -TABLE 9. F AND t TESTS - Ni IN PYRITE (No. of Samples: Hornfels, 47; Diorite, 9; Quartz Monzonite, 18; Veins, 22) Source F Probability t Probability Hornfels: Quartz Monzonite 0.03 0.37 Hornfels: Diorite 0.01 0.10 Quartz Monzonite: Diorite 0.27 0.01 Hornfels: Veins 0.01 0.00 Quartz Monzonite: Veins 0.00 0.00 Diorite: Veins 0.00 0.00 The F and t tests indicate with a high confidence level (99 per cent or greater) that Ni i n vein pyrite i s a discrete population compared to Ni i n disseminated pyrite from any of the three host rock types. The p o s s i b i l i t y of disseminated pyrite containing two or more populations of Ni i s not nearly so certain. A 90-per-cent t and 99-per-cent F probability allows the conclusion that hornfels and dio r i t e may contain distinct populations of Ni i n pyrite, but pyrite from hornfels and quartz monzonite cannot be distinguished and may be part of the same population. A summary of t and F tests of a l l elements from pyrite i n different rock types Is given i n Table 10. All Disseminated Pyrite N 74 X 2.06 S 036 I 0.15 A Hornfels N 47 X 2.06 S 0.41 C Quartz Monzonite N 18 X 1.98 S 0.25 D Diorite Veins N 9 N22 X 2.20 X 1.14 S 0.17 S 0.66 FIGURE 27 DISTRIBUTION OF Ni IN PYRITE. DATA GROUPED ACCORDING TO HOST ROCK. A,C,D ARE FITTED NORMAL CURVES. 151 TABLE 10. SUMMARY OF t AND F TESTS FOR ALL ELEMENTS (SIGNIFICANCE OF HOST ROCK TYPE) No. of. No. of Element Samples* t Prob. F Prob. Element Samples* t Prob. F Prob. HORNFELS : QUARTZ MONZONITE As 17 : 2 .02* .41 Bi 46 ; 18 .08 .58 Co 47 : 18 .00** .69 Ni 47 ! . 18 .37 .03* Cu 22 : 9 .33 .78 Pb 45 : 16 .00** .31 Zn 45 : 16 .02* .01** Ag 45 ! . 16 .78 .35 Mo 34 : : 15 .21 .88 T i 33 ! 5 .07 .28 Mn 45 : 16 .45 .77 QUARTZ MONZONITE : DIORITE As 2 : 5 .14 .45 Bi 18 . : 8 .20 .91 Co 18 : 9 .00** .09 Ni 18 : • 9 .01** .27 Cu 9 • : 2 .62 .69 Pb 16 : 8 .67 .35 Zn 16 : : 7 .70 .81 Ag 16 : : 8 .06 .92 Mo 15 : 6 .53 .96 T i 5 i 1 Mn 16 : 8 .20 .39 HORNFELS : DIORITE As 17 : 5 .74 .85 Bi 46 : 8 .86 .80 Co 47 : 9 .20 .05 Ni 47 : 9 .10 .01** Cu 22 : 2 .86 .60 Pb 45 : 8 .02* .80 Zn 45 : 7 .08 .04* Ag 45 : 8 .03* .58 Mo 34 : 6 .14 .88 T i 33 : 1 Mn 45 : 8 .03* .46 VEINS : HORNFELS As 6 : 17 .35 .75 Bi 22 : 46 .62 .13 Co 22 : 47 .00** .00** Ni 22 t 47 .00** .00** Cu 19 : 22 .00** .00** Pb 20 >. 45 .78 .00** Zn 20 : 45 .18 .00** Ag 20 : 45 .12 .13 Mo 20 t 34 .05* .22 Ti 20 : 33 .00** .07 Mn 20 : 45 .17 .67 VEINS : QUARTZ MONZONITE As 6 i 2 .26 .46 Bi 22 : 18 .07 .48 Co 22 : 18 .00** .00** Ni 22 : 18 .00** .00** Cu 19 , t 9 .00** .06 Pb 20 : 16 .03* .00** Zn 20 : 16 .01** .40 Ag 20 : 16 .15 .72 Mo 20 : 15 .01** .37 T i 20 , : 5 .00** .09 Mn 20 : 16 .09 .55 VEINS : DIORITE As 6 : 5 .49 .93 Bi 22 : 8 .84 .53 Co 22 • : 9 .15 .00** Ni 19 ! • 9 .00** .00** Cu 20 ! 2 .69 .76 Pb 20 : 8 .87 .12 Zn 20 : 7 .22 .71 Ag 20 ! 8 .17 .70 Mo 20 ! 6 .01** .56 T i 20 ! 1 Mn 20 ! 8 .00** .65 •Number of samples varies because only samples with detectable ( i . e . measurable) minor element concentrations can be compared. 152 Conclusions drawn from t and F tests (Tables 8, 9, and 10) are: (1) Vein pyrite i s part of a separate population from the set of a l l disseminated pyrite on the basis of Co, Ni, Cu, Zn, T i , and possibly Pb, Ag, Mo, and Mn; but not As and Bi. However, except on the basis of Co and Ni, vein pyrite cannot be distinguished with any certainty from disseminated pyrite i f disseminated pyrite i s further subdivided into smaller groups according to host rock type. Large sample sets from each type of host rock could possibly overcome this problem. (2) Only a few elements i n disseminated pyrite can be shown to constitute separate populations on the basis of host rock composition. For example, for Zn there Is a 98-per-cent or greater t and F probability that pyrite from hornfels i s distinct from that i n quartz monzonite. Similar high probabilities for Ni and Zn indicate that separate populations of pyrite-are present i n hornfels and quartz d i o r i t e . Also, Co i n pyrite from quartz diorite i s distinct from that i n quartz monzonite. In a number of other cases, .separate populations are inferred by low F probabilities but t probabilities are high, and vice versa. Thus, no generalization can be made on the basis of t and F tests about populations of minor elements in dissemianted pyrite from different host rocks. Polymodal distributions may, but" need not be, caused by mixing samples from different host rocks. Each element must be looked at on an individual basis. Graphic description, interpretation, and resolution of polymodal data is possible, using cumulative probability plots. The technique has been long known to biologists and sedimentologists (Harding, 1949; Cassie, 153 1950, 1954, 1963; Harris, 1958; and others) but has only recently been applied on a routine basis to geochemical data (Tennant and White, 1959; Lepeltler, 1969; Bolviken, 1971; Woodsworth, 1972; Sinclair, 1974; and Parslow, 1974). Form of cumulative probability curves can be used to determine If distributions are normal, lognormal, or polymodal. A second use i s resolution of polymodal data into components (constituent populations) and definition of parameters of constituent populations. Use of probability plots i s discussed i n d e t a i l and clearly illustrated by Sinclair (1974). In this study cumulative probability plots are used as a supplement to other univariate procedures of data analysis. If a l l Berg minor element data are plotted on a cumulative probability plot (except arsenic for which there i s insufficient data), the following results are apparent: (1) B i , Co, Ni, Cu, Pb, Zn distributions appear to be polymodal, each consisting of at least two lognormal populations. (2) Ag and Mo have single, lognormally distributed populations. (3) T i has a single, normally distributed population, or the distribution i s a complex, polymodal mixture of lognormal populations. Interpretation of polymodal cumulative probability curves suggest that bimodal populations of Co, Ni, Cu, and Pb consist of one large group of samples with generally higher values than the smaller population. This i s readily interpreted to be a result of mixing disseminated and vein pyrite. Zinc distribution i s polymodal but i s d i f f i c u l t to interpret. Two populations of about equal proportions appear to be present, but the two are partly coincident and mask each other. Bismuth and manganese can be interpreted to consist of two populations - one with detectable amounts of metal, the other with amounts below the analytical detection l i m i t . 154 Normal distribution of titanium i s anomalous. On the basis of i t s err a t i c behaviour i t is suspected that T i i s present in included mineral grains. Normal distribution of analytical results might, therefore, be one criterion of contamination i n minor element studies. Resolution of polymodal data into component populations using .cumulative probability plots i s not necessary i n this study since type of pyrite, i t s source, geological significance, mean and variance of each sample group, and the proportions of a l l component populations are known from sampling. However, the method can be il l u s t r a t e d and con-clusions from other univariate procedures can be double checked. F and t tests as well as histograms show, with the exception of B i , that vein and disseminated pyrites are distinct and, with very few exceptions, disseminated pyrite appears to constitute single populations of minor elements regardless of host rock. Disseminated pyrite (Figure 28) appears to approximate single, lognormally distributed, measured- populations of Cu, Pb, Ag, and possibly Mo, B i , and Mn. A second population of B i , Mn, and Mo can be postulated i f samples with less than detectable amounts of these elements are considered. Exceptions are Co, Ni, and Zn which appear polymodal in the cumulative probability plot, but this was indicated earlier on the basis of t and F tests which suggested the following: Co i n pyrite from diorite and quartz monzonite; Ni and Zn i n pyrite from hornfels and diorite; and Zn i n pyrite from hornfels and quartz monzonite are distinct populations. Thus, probability plots are a powerful analytical method, in this case capable of resulting i n similar conclusions as t and F tests i n conjunction with frequency distribution data. CUMULATIVE PROBABILITY FIGURE 28 M I N O R E L E M E N T S I N D I S S E M I N A T E D P Y R I T E 156 A third, small population containing high Ni and low Co values i s suggested i n histograms but i s clearly shown i n probability plots. The population i s made up of only five samples but they are a l l from the p y r i t i c halo zone. Further sampling might reveal that pyrite-rich rocks peripheral to the zone of copper-molybdenum mineralization are represented by Ni-rich pyrite that constitutes a separate population. BIVARIATE ANALYSIS Bivariate analysis including correlation and simple regression was undertaken to examine relationships between paired variables. Correlation describes the interaction or association of variables without casual effect. Correlation co-efficients were computed for a l l pairs of variables (Table 11). The data were treated, f i r s t collectively, and then subdivided into groups according to source of pyrite to see i f any trends or significant differences between various types of pyrite are apparent. Simple (linear) regression examines the interdependent relation-ships of paired variables and can be used to measure the amount or degree of variation i n a variable due to variation i n the other variable. The proportion of total variation or measure of variation explained by the interdependence of the variables compared to the total variation i s called 2 2 R . Table 12 l i s t s R and F ratios (variance ratios) for pairs of variables with significant correlation as l i s t e d in Table 11. From the preceding tables i t i s apparent that the greatest amount of association at s t a t i s t i c a l l y significant levels i s between Co and Ni and also Pb and Zn. A least squares regression line described by the equation Y » a + bX can be calculated for the paired variables as shown in Figure 29. FIGURE 29 LINEAR LEAST SQUARES REGRESSION LINE Y=a+bX For Co-Ni(A) & Pb= Zn(B) 3.300-2 9 5 0 -2 6 0 0 -2.250 1.900-1550 1.200 0.850r-05001 Co:Ni a = 0 4 2 0 b=i.ooi e =0.364 Ff->(X735 Co log ppm DETECTION LIMIT' Ni log ppm o C O o o o o o o . 8 a o . 8 o o 8 oo o o o B 2400r-Zn=Pb a =0.679 b =0.524 e =0.342 R 2=0.457 TABLE 11. CORRELATION OF PAIRED VARIABLES A l l Data N - 100 Var. As Bi Co As 1.000 Bi -0.1500 1.0000 Co 0.0827 -0.0489 1.0000 Ni 0.2143 0.0026 0.8574 Cu -0.1670 -0.0896 0.6342 Pb 0.2261 0.4951 0.1438 Zn 0.1543 0.3254 0.3568 Ag 0.0717 0.5107 0.3455 Mo -0.2260 0.1196 0.3066 T i -0.5396 0.1457 0.4502 Mn 0.2790 0.0538 0.2936 Hornfels and Quartz Diorite N - 56 Var. As Bi Co As 1.0000 Bi -0.2342 1.0000 Co 0.1080 -0.1338 1.0000 Ni 0.1953 0.0435 0.5314 Cu 0.2595 -0.3998 0.4382 Pb -0.1129 0.4801 0.1740 Zn 0.0013 0.2294 0.2538 Ag 0.0118 0.4215 0.3849 Mo -0.2950 0.1794 0.3192 T i -0.1479 0.4864 -0.2577 Mn 0.2526 0.0260 0.1968 Ni Cu Pb Zn Ag Mo T i 1.0000 0.5356 1.0000 0.1745 -0.1522 1.0000 0.3619 0.1749 0.6762 1.0000 0.2066 0.1422 0.5229 0.4437 1.0000 0.2490 0.1892 0.2564 0.1867 0.5285 1.0000 0.3681 0.5816 0.0740 0.2330 0.0946 0.2055 1.0000 0.3301 -10.0186 0.3862 0.3962 0.2400 0.0614 0.1477 Mn 1.0000 Ni Cu Pb Zn Ag Mo T i Mn 1.0000 -0.0988 1.0000 0.1469 0.0520 1.0000 0.1999 0.0206 0.6335 1.0000 0.0827 0.4806 0.5696 0.4510 1.0000 0.2056 0.1358 0.3998 0.2568 0.5971 1.0000 -0.0980 -0.2966 0.2349 0.4308 0.1960 -0.0562 1.0000 0.2053 0.0104 0.3484 0.3091 0.3077 0.1901 -0.0546 1.0000 TABLE 11. CORRELATION OF PAIRED VARIABLES (continued) Quartz Monzonite N - 18 Var. As Bi Co Ni Cu Pb Zn As Bi 1.0000 Co -0.4595 1.0000 Ni -0.1865 0.7992 1.0000 Cu -0.3645 0.2566 -0.2042 1.0000 Pb 0.1528 0.3603 0.4926 -0.1257 1.0000 Zn -0.3599 0.3310 0.4328 -0.2084 0.5215 1.0000 Ag 0.2298 0.4931 0.5741 0.0887 0.6861 0.2650 Mo -0.1584 0.5021 0.3179 0.3146 0.1031 -0.0380 T i -0.8157 0.3616 -0.2986 0.6492 -0.7887 -0.3107 Mn -0.0158 0.4083 0.4048- .-0.0553 0.4306 0.3398 Ag 1.0000 0.6777 •0.6585 0.3731 Mo T i Mn 1 .0000 0.2334 0.1434 1.0000 0.3759 1.0000 Veins N - 22 Var. As Bi Co Ni Cu Pb Zn Ag Mo As 1.0000 Bi -0.2943 1.0000 Co 0.3568 -0.0941 1.0000 Ni 0.5479 -0.1753 0.8745 1.0000 Cu 0.2950 -0.0496 0.4397 0.5351 1.0000 Pb -0.7512 0.6052 -0.0275 -0.0702 -0.3390 1.0000 Zn 0.1834 0.6813 0.2621 0.1282 0.1338 0.7222 1.0000 Ag 0.5528 0.7868 0.3512 0.1665 0.1437 0.5481 0.7470 1.0000 Mo 0.3719 0.0660 0.2993 0.2742 0.0647 0.2008 0.3383 0.3015 1.0000 T i -0.7326 -0.0978 -0.0200 -0.0314 0.4562 -0.3402 -0.1174 -0.1655 0.1782 Mn -0.4897 0.0643 0.0761 -0.0103 -0.3954 0.3567 0.2185 0.2029 -0.0111 T i Mn 1.0000 0.0452 1.0000 In 160 TABLE 12. R AND F RATIOS FOR ALL DATA OF ALL PAIRS OF VARIABLES HAVING SIGNIFICANT CORRELATION Variables F Ratio R 2 Co : Ni 272 0.735** Pb : Zn 75.8 0.457* Co : Cu 35.7 0.402 Ni : Cu 21.3 0.287 Cu : T i 19.A 0.338 Pb : Ag 34.3 0.273 Ag : Mo 27.9 0.279 BI : Ag 31.8 0.261 Pb : Bi 29.3 0.246 Ag : Zn 22.1 0.197 Level of Significance: * • 95 per cent; ** • 99 per cent A regression plot of Co as a function of Ni i s useful as a further means of discriminating between types'of pyrite, as shown in Figure 30. Pyrite from different sources f a l l s into separate fields on the diagram. Vein pyrite and disseminated pyrite are the most distinct types. Within the group of disseminated pyrite, samples from peripheral volcanic rocks, - quartz d i o r i t e , quartz monzonite, and many samples from hornfels occur i n separate f i e l d s , although pyrite .from hornfels shows wide dispersion. Overlap of some vein and disseminated. pyrite_is_.to be. expected., since, the group of 'disseminated' pyrite i n the sample set includes both disseminated -and fracture-controlled pyrite and the distinction between fracture-controlled and vein pyrite i s entirely arbitrary. As a generalization, most of the -disseminated pyrite i n the field-of-mixed vein and disseminated pyrite i n Figure 30 i s from the p y r i t i c halo, and the majority of pyrite in the disseminated f i e l d i s from the zone of copper-molybdenum mineralization. Differences i n amounts of Co and Ni i n pyrite appear to be proportional to amounts of these elements i n the host rocks. In general, Co and Ni contents decrease with increasing acidity of igneous rocks (Price, 1972). Similarly original temperatures decrease from relatively FIGURE 30 C O B A L T - N I C K E L S C A T T E R D I A G R A M S H O W I N G P Y R I T E A C C O R D I N G T O S O U R C E 1 0 0 1 0 1 0 0 N i p p m SOURCE OF PYRITE 1 0 0 0 + Hornfels x Diorite • Qtz. Monzonite • Qtz.Monz.Dyke • Veins • Volcanic Rocks 1 0 0 1 0 0 0 T A Mean Values 162 high temperatures i n basic volcanics, lower ones in intermediate and acidic intrusions, and considerably cooler ones i n hydrothermal veins. Thus, differences i n amount of Co and Ni seen in Figure 30 appear to correspond to changes i n host rock composition and might also be influenced by temperatures at which pyrite crystallized. Cobalt-nickel ratios (Figure 31) i n pyrite from veins and quartz monzonite are similar and these are distinct from pyrite i n hornfels, diorite, and possibly regional volcanics, which are similar. The mean cobalt-nickel ratio for 96 samples with detectable amounts of both elements i s 3.8. Price (1972) noted that this ratio i s s t a t i s t i c a l l y indistinguishable from the mean cobalt-nickel ratio of pyrite from the large Endako and Casino porphyry deposits but i s dissimilar to pyrites from smaller porphyry deposits at Tchentlo Lake and Molymine, British Columbia, which have cobalt-nickel ratios of 31 and 27 respectively. 40 20 Co/Ni N=96 X=3.80 S =3.00 I =0.75 VEINS N ~ ! . 8 „ X = 2.40 S = 2.10 0 3.0 6.0 9.0 X 20 10 1 QTZ. MONZONITE N = • X -in, -3D 6.0 9.0 % 10 r-, HORNFELS, DIORITE, VOLCANICS N o = 6 0 0 1.5 3.0 4.5 6.0 7.5 9.0 10.512.0 FIGURE 31 C o - N i RATIOS OF PYRITE 163 Some Ni enrichment i s evident in vein pyrite (Co/Ni - 2.40) compared to disseminated pyrite (Co/Ni - 4.28). Since most veins are late stage crosscutting features, late magmatic-hydrothermal fluids from which pyrite crystallized were enriched in nickel as i s the case in many other hydrothermal and advanced magmatic environments (Price, 1972). This implies that nickel-rich.pyrite from the periphery of the p y r i t i c halo may have formed during late mineralization as well (see Figure 33 and discussion of zoning, page 174). Generally, use of cobalt-nickel ratios and quantities to characterize pyrite types or sources within individual deposits i s limited due to large variations i n minor element concentrations. Where differences are consistent and s u f f i c i e n t l y large, such as between vein and disseminated pyrite at Berg deposit, concentration ranges and means of Co and Ni are characteristic and pyrite from unknown sources can be c l a s s i f i e d into fundamental-groups. Price (1972) has concluded that amounts of Co and Ni, and to a lesser extent cobalt-nickel ratios, are useful in distinguishing different types of pyrite from genetically distinct mineral deposits, namely: syngenetic (sedimentary), hydrothermal (including porphyry, vein, and skarn), and massive sulphide. Characteristic amounts of Co and Ni determined by Price are shown in Table 13. TABLE 13. CHARACTERISTIC Co AND Ni CONCENTRATIONS IN PPM (After Price, 1972) Syngenetic Hydrothermal Massive Sulphide Co 41 Ni 65 Co/Ni .63 141 121 1.17 486 56 8.7 164 Mean concentrations of Co (203 ppm) and nickel (77 ppm) of Berg pyrite are comparable to hydrothermal pyrite. Mean values of Co (374 ppm) and Ni (415 ppm) i n disseminated pyrite can be distinguished with any certainty only from syngenetic pyrite. Furthermore, when only vein pyrite i s considered (Co - 20, Ni - 14 ppm), mean concentrations are most comparable to syngenetic pyrite but are also similar to hydro-thermal (low temperature) lead-zinc deposits (Price, 1972) and disseminated pyrite i n Tasmanian granites (Loftus-Hills and Solomon, 1967). Therefore, any genetic classification of mineral deposits u t i l i z i n g bivariate analysis and based on Co and Ni content of pyrite (and possibly any other pair of elements) i s , at best, tenuous. MULTIVARIATE ANALYSIS Multivariate s t a t i s t i c a l analysis defines relationships between a number of variables or between samples for which three or more variables are measured. Factor analysis i s a technique by which measured variables are combined in N-dimensional space into linear combinations of new variables (factors) by a mathematically sophisticated extension of correlation -analysis. Relationships between variables are defined by R-mode analysis and those between samples or sample sites by Q-mode analysis. In this study Q-mode factor analysis i s applied to the seven most frequently detected elements i n the sample set - B i , Co, Ni, Pb, Zn, Ag, and Mn, as well as Cu in vein pyrite. The technique has been described by Imbrie and Van Andel, 1964 and Klovan, 1968, and applied to geochemical data by Nichol, Garrett, and Webb, 1969, Wilson and Sinclair-, 1969, and Dawson and Sinclair, 1974. Treatment of pyrite geochemical data by Q-mode factor analysis accomplishes three main purposes: 165 (1) The number of variables i s reduced since the measured quantities are combined into multivariable 'factors.' (2) Associations and interrelations among variables are often realized that are not apparent on the basis of intuitive or subjective data examination. (3) The data generated are quantified and can be plotted on a map and contoured-to reveal zoning patterns and areas of interest. Data for factor analysis are divided into two fundamental groups - disseminated and vein pyrite - and the two groups are treated separately (Appendix H). Sixty-one sample sites of disseminated pyrite are plotted representing seventy-four analyses (Appendix I ) . Six factors account for 96.3 per cent of the variance but the four factors that explain 81 per cent of the variance are considered to be the most significant. These four factors define distinct zoning patterns and additional factors simply duplicate - observed patterns and are redundant or are simply 'noise*'-' that cannot be related to any geological cause or process. The successive varimax factor components computed are lis t e d in Table 14 and the scores of the four factors plotted, in Table 15. A l l four factors, i n a general way, outline annular zones centred on the quartz monzonite stock and have value maxima roughly coincident with-the-zone of copper-molybdenum mineralization. Zoning patterns" are similar to those of individual elements but may be more significant i n defining zoning trends as factors integrate behaviour of a number of elements. However, the geological significance of factors i s not always obvious and explanations or interpretations are subjective and may be speculative. No outstanding relationships between specific factors and ore or waste, such as that found at Endako (Dawson and Sinclair, 1974) are evident. TABLE 14. SUCCESSIVE Q-MODE VARIMAX FACTOR COMPONENTS - DISSEMINATED PYRITE % of Factor Components Var. F1 -Ag, Co, (Mn, Zn, Pbj +BI Ni) 25.3 F2 -Bi, Mn, Ni, Pb +(Co, Zn, Ag) 21.0 F3 -Mn 16.7 +Bi, Zn, (Ag, Pb) -Ag, (Mn, B i , Pb, Zn) +Ni. Co FA 13.8 F5 -Bi, Co, Ag +Zn, Pb, Ni, (Mn) •13.2 F6 -Zn, (Mn, Bi, Co) :2b, (Ag) cum. 6.3 96.3 F1 -Ag, Co, (Mn, Pb, Zn, +Bi Ni) 25.0 F2 -Mn, B i , Ni, (Pb) +(Co, Ag) 21.1 F3 -Mn +Bi, Zn, Pb, (Ag, Ni) 17.3 FA -Bi, Ag, Co 13.9 +Zn, Pb, (Mn) -Ag, (Mn, Pb, Bi) +Co, Ni, (Zn) F5 13.8 cum. 91.1 % of Factor Components Var. F1 -Co, Ag, Zn, Pb, (Mn, Ni) 25.2 +Bi F2 -Bi, Ni, Mn, (Pb, Zn) 25.0 + (Co) F3 -Co. Ni. (Mn) 15.7 +Zn, Pb, (Ag, Bi) FA -Bi, Ag, (Co) 1A.9 •tifa. (Zn, Ni) cum. 80.8 FT -Ni, B i , Pb, Ag, Co, Mn, Zn 32.A F2 -Co. Ni. (Mn) 18.3 +Bi, Pb, Zn F3 ;Bi, (Co, Ni) 17.3 +Zn, Mn, (Pb) cum. 68.0 F1 -Pb. Mn. Zn, Ni, Ag, (Co, Bi) 3A.0 F2 -Co, (Mn, Ni) 21.1 +Bi, (Pb, Ag, Zn) cum. 55.1 TABLE 15. Q-MODE VARIMAX FACTOR SCORES - DISSEMINATED PYRITE Variable Factor 1 Factor 2 Factor 3 Factor 4 Bi Co Ni Pb Zn Ag Mn 0.910 -1.3576* -0.388 -0.909 -1.171 -1.341* -0.441 -1.875* 0.265 -1.178 -0.882 -0.276 -0.008 -1.077 0.152 -1.551* -1.395* 0.949 1.230 0.414 -0.203 -1.284 -0.623 0.278 -0.089 0.476 -1.257 1.754* Variance per cent 25.2 25.0 15.7 14.9 Cumulative variance per cent 25.2 50.2 65.9 80.8 •Denotes important component factor. TABLE 16. SUCCESSIVE Q-MODE VARIMAX FACTOR COMPONENTS - VEIN PYRITE % of Factor Components Var. F1 -(Cu) +Pb, Zn, Ag, (Bi, Mn, Co, Ni) 29.3 F2 -Bi, Mn, (Ag) +Ni, Co, (Cu, Pb, Zn) 23.7 F3 -Mn, (Pb, Zn) 16.2 +Bi, Cu. A R . F4 -Mn, Co, (Ni, Ag, Cu) 14.3 +Zn, Pb F5 -Cu. Zn, Mn 9.9 +(Co, Ni, B i , Ag, Pb) F6 -Zn, Co 4.3 +Pb, (Cu, Ni, Mn, Ag) cum. 97.7 F1 -(Cu) +Pb, Zn, Ag, Bi, (Mn, Co, Ni) 29.4 F2 -Bi, Mn, (Ag) +Ni. Co, (Cu, Zn, Pb) 23.5 F3 -Mn. Pb, (Ni) +Bi, Cu, Ag, (Co) 17.0 F4 -Mn, Co, Ag, Ni, +Pb, Zn 15.2 F5 -Cu, Mn, Zn 9.9 +(Co, Bi , Ni, Ag) cum. 95.0 Factor Components % of Var. Fl -(Cu) +Pb. Zn, Ag. B i . (Mn, Co) 29.6 F2 -(Bi, Pb, Mn) +Co, Ni, (Cu, Ag, Zn) 30.5 F3 -Mn, (Co, Pb) +Cu, Bi, (Ag, Zn) 18.8 F4 ^Cu, Mn, (Zn, Ag) +(Co, Pb, Ni) 10.2 cum. 89.1 F1 -(Cu) +Pb, Zn, Ag, B i , (Mn, Co) 30.1 F2 -(Bi, Mn, Pb) +Ni, Co, (Cu, Ag, Zn) 30.7 F3 -Mn, (Co, Ni, Pb) +Cu, B i , (Ag, Zn) 18.6 cum. 79.4 F 1 +Bi, Pb. Zn. Ap. (Mn) 30.9 F2 -(B i , Mn, Pb) •»Ki« Co. (Cu, Ag, Zn) 30.6 cum. 61.5 CO 169 • Factor 1 i s characterized by high (negative) scores of Co and Ag with moderate contributions from Zn and Pb, and minor contributions from Mn and Ni. The only element that does not contribute to the (negative) factor value i s Bi and, thus, the factor can be interpreted as a measure of the amount of cation substitution i n pyrite. Factor 2 i s largely a measure of Bi with moderate contributions from Ni, Mn, and Pb scores. It compliments Factor 1 i n as much as the most important factor components are those elements least significant i n Factor 1; Factor 2 also indicates the amount of minor element substitution i n pyrite, but because Bi i s the main component in the factor value, the factor may be a measure of the. amount of anion substitution. If indeed Bi has a closer geochemical a f f i n i t y i n pyrite with anions rather than cations, Factor 2 might indicate zones that supplied sulphur during mineralization. Factor 3 i s composed of two antithetic pairs of elements whose pronounced correlation was observed i n a preceding section, cobalt-nickel as a negative factor component and lead-zinc as a positive one. The factor i s possibly the most interesting from a zoning point of view as high (positive) factor values with high lead-zinc and low cobalt-nickel are found mainly in quartz monzonite and i n hornfels or quartz diorite near the quartz monzonite contact. The high content of lead and zinc i n pyrite from intrusive rocks was noted e a r l i e r i n discussion of univariate minor element data. Thus, lead and zinc i n Factor 3 may be postulated to represent a hydrothermal contribution by quartz monzonite, whereas cobalt-nickel might be a contribution of elements to pyrite from country rocks (volcanics and quartz d i o r i t e ) . Factor 4 contains high (positive) manganese scores and modest (negative) Bi and Ag scores. High factor values are found in a series of isolated zones that encompass the quartz monzonite stock but are located 170 at some distance from the contact. Highest (negative) factor values occur i n biotite-bearing hornfels and quartz d i o r i t e . Factor 4 i s possibly the best indicator of a l l four factors of the limits of the zone containing i n excess of 0.2 per cent copper. Factor analysis of vein pyrite (Table 16) includes values of copper (Appendix J ) . Two groups of elements account for most variance i n vein pyrite - Pb-Zn-Ag (and Bi) and Co-Ni. Two other factors, one composed largely of Mn, the other of Cu, account for much of the remaining variation. Together, these four factors account for 89 per cent of total variance. Factors of vein pyrite are not the same as those of disseminated pyrite (Table 14), probably because the two types of pyrite are of different origins. Certainly combinations of elements from vein pyrite In factors provide geologically familiar and geochemically acceptable associations (e.g. Ni and Co; B i , Pb, Zn, Ag), but otherwise very l i t t l e i s revealed about zoning of vein pyrite because of the erratic distribution of the small group of samples. MINOR ELEMENT ZONING IN THE DEPOSIT INTRODUCTION Zoning, a systematic variation i n space, of minor elements i n pyrite i s evident i n plots of univariate and factor analysis data. Con-centrations of impurity elements and high factor scores generally occur near the contact of the quartz monzonite stock although the most intense concentration of a l l elements i s in pyrite from quartz diorite i n the well-mineralized northeast zone. Coincidence of high factor values and individual element concentrations with the zone of copper-molybdemum mineralization i s remarkably consistent. Concentrations decrease away 171 from the intrusive contact, both within the stock and intruded rocks. Five specimens of weakly altered peripheral volcanic rocks with only traces of pyrite do not f i t the zoning pattern. These few samples suggest that zoning of minor elements i n pyrite i s confined to the main zone of mineralized and hydrothermally altered rocks, possibly a maximum of two thousand feet from the quartz monzonite contact. Zoning patterns of most individual elements are centred on the quartz monzonite stock and are similar. Consistent patterns of different elements and factors i n disseminated pyrite may indicate that a single, all-encompassing hydrothermal system prevailed during the main stages of mineralization. The variable most commonly considered to regulate incor-poration of minor elements i s temperature, and zoning i s interpreted to be a response to temperature gradients. Undoubtedly there has been interplay of numerous other variables during sulphide deposition. These include: a v a i l a b i l i t y of elements — both metals and complexing ions; concentrations of elements and their partitioning between f l u i d and solid phases (Rose, 1970); rates of precipitation, mobility (of elements) governed by f l u i d migration patterns, permeability, and diffusion rates; confining pressure, p a r t i a l pressures of components i n hydrothermal fluids - particularly those containing sulphur; changes in mineralizing solutions caused by interaction with ground water and wall rock reactions; and many others. Berg pyrite data were examined to see i f there i s any relation between quantity of pyrite and amount of minor elements i n pyrite. It was concluded that the zoning observed reflects differences i n absolute amounts of impurity elements and i s not caused by dilution of a constant quantity of elements by different amounts of pyrite. Numerous studies have intimated 172 that different paragenetic stages may have different contents of impurity elements. This fact has already been i l l u s t r a t e d i n this study by comparison of vein and disseminated pyrite. Therefore, zoning patterns considered here are based on analyses of carefully selected disseminated pyrite of the same paragenetic type and from rocks of apparently similar o r i g i n . Except for a few samples from the supergene zone, most samples analysed are from primary mineralization below the zone of oxidation. Regional metamorphism i s low grade and mineralization has undergone a uniform post-depositional history. Credibility of zoning patterns i s based on the premise that minor element concentrations are not erratic at different depths but vary as a function of distance from the stock, and therefore, one or two samples per d r i l l hole are representative of a large area. Vertical zoning of primary sulphide minerals and hypogene rock alteration was not recognized over depths of a few hundred feet but may be present over greater depths. Presumably minor element distributions behave i n a similar manner. The abundance of minor elements was found to be f a i r l y consistent * with depth - i f specimens of similar rock and alteration types were compared. Table 17 i l l u s t r a t e s v a r i a b i l i t y of minor element concentrations at different depths. The specimens from d r i l l hole 71 are a l l from hornfels but were selected to represent maximum variation i n type and amount of rock alteration. In comparison, specimens from d r i l l holes 16 (diorite) and 23 (biotite hornfels) are representative specimens from d r i l l holes with uniform rock type and alteration throughout the length of the hole. As a group, pyrite from d r i l l hole 71 shows considerable variation but specimens from similar alteration zones are comparable. As most pyrite in this study was taken from biotite hornfels of a s u p e r f i c i a l l y similar type, the amount of TABLE 17. VERTICAL VARIATION OF MINOR ELEMENTS IN PYRITE Sample T i Mn ( d r i l l hole and footage) As Bi Co Ni Pb Zn Ag Mo Biotite Hornfels 55 71-420 N N 720 230 1 8 4.0 N N 71-667 N 1.0 950 140 7 9 7.0 28 8 20 71-738 N 1.0 560 168 1 18 2.5 N 450 N Brecciated Hornfels 71-533 N 1.0 430 330 64 20 5.5 26 10 N 71-569 530 17.0 400 98 36 19 9.0 10 64 6 Sericite Hornfels 71-869 1050 26.0 305 107 63 30 18.0 31 380 N 71-915 400 12.0 435 74 105 34 19.0 14 G 5 Diorite 16-495 N N 380 172 25 26 8.0 8 G 5.5 16-600 N N 353 154 24 31 3.5 2 G 7.5 Biotite Hornfels 23-328 N N 615 55 13 10 6.5 N 40 N 23-434 575 N 640 67 24 28 7.0 6 270 12 N denotes less than detection limit; G denotes greater than detection l i m i t . 174 v e r t i c a l variation indicated by hole 71 i s possibly the maximum that would be expected. It i s concluded that zoning patterns can be reproduced at different depths i f zones are defined by large, yet s t a t i s t i c a l l y meaningful, contour intervals such as values greater than the mean of a l l analyses (>X) and greater than the mean plus one standard deviation (>X + s.d.). Samples from different depths might change the detailed configurations of zones i f different alteration zones were intersected but usually general patterns are not affected. For example, i f each analysis from hole 71 was plotted successively, only about one-third would cause any change i n the position of zone contours and most of the changes would be due to erratic behaviour of Mo, T i , and Mn. UNIVARIATE MINOR ELEMENT ZONING Zoning of individual minor element concentrations i n pyrite i s shown in Figures 32, 33, and 34. Zoning patterns are similar, with concentration maxima seen as annular zones about the quartz monzonite stock near the intrusive contact. Zones are not symmetrical about the stock as concentration contours bulge into diorite to the east and northeast of the quartz monzonite intrusion, and continuity of contours i s disrupted i n the south-west by irregular masses of quartz monzonite. This i s similar to the distribution of copper. Co, Ni, Pb, Zn, Ag, Mo, and Mn are concentrated in pyrite near the quartz monzonite intrusive contact with concentration maxima most common in the northeast zone of mineralization in hornfels and quartz di o r i t e . Cobalt-nickel ratios have maximum values in hornfels about 500 feet from the contact. Four samples i n the south suggest that nickel content increases outward from the zone of cobalt-nickel highs and pyrite SOURCE OF PYRITE o HORNFELS • QUARTZ MONZONITE A QUARTZ DIORITE ZONING OF MINOR ELEMENTS IN PYRITE FIGURE 32 176 FIGURE 33. ZONING OF MINOR ELEMENTS IN PYRITE IZZ 178 south of this zone contains nickel in excess of cobalt over distances of a few hundred feet. Bismuth distribution i s much l i k e that of other elements with high values found in a zone projecting out into the p y r i t i c halo to the south. Bismuth (and possibly lead, zinc, and silver) may be concentrated there i n pyrite related to north-south-trending structures. Detectable arsenic (>300 ppm) i s found in a l l samples outside the main copper-bearing zone but small zones consisting of a few samples with detectable arsenic are coincident with the highest grades of copper within the area of copper mineralization. Additional sampling may reveal that arsenic i s most abundant in pyrite from the p y r i t i c halo and weakly mineralized peripheral volcanic rocks and therefore useful as a pathfinder element. Titanium concentrations are erratic and highest values (those above the detection limit) are associated with intrusive rocks or their contacts. Values of T i below the mean of the sample group are found within zones of copper mineralization. Concentration- maxima of-single elements or-small -groups of elements do not coincide exactly with best copper or molybdenum grades, but zones of best mineralization are clearly defined when a l l concen-tration highs are superimposed (Figure 35). Ovchinnikov (1967) states: 'An increase i n the quantity of the 'host' mineral i s accompanied by a simultaneous increase in the relative concentration of the impurity elements i n i t . ' Although this may be true i n massive, p y r i t i c deposits, i n this study and perhaps porphyry deposits i n general, highest concen-trations of minor elements in pyrite are intermediate between the p y r i t i c halo and the sparsely mineralized intrusive core. At Berg deposit con-centration maxima of minor elements in pyrite are not coincident with maximum amounts of the host pyrite. Instead, highest minor element 179 180 concentrations are more closely related to the amounts of copper and molybdenum minerals present within a zone containing 2 to 4 per cent pyrite. A consistent zoning sequence i s not evident. This may be, in part, because inhomogeneous s t r a t i f i e d rocks are mineralized and rock compositions may have influenced composition of pyrite. Possibly minor element distributions in pyrite from homogeneous host rocks might display zoning sequences. There i s some suggestion of this i n diorite of the northeast copper zone where maxima of manganese, s i l v e r , and cobalt are clearly peripheral to highest Ni, B i , Pb, and Zn values. A most noteworthy aspect of zoning of minor elements i n pyrite i s that minor elements do not imitate sulphide mineral zoning patterns i n porphyry deposits. When Pb, Zn, Ag, and Mn minerals are found they most commonly occur i n late-stage veinlets peripheral to the main zone of intrusion, alteration, and Cu-Mo mineralization. However as minor elements i n pyrite Pb, Zn, Ag, and Mn appear to be concentrated i n pyrite from the ~ ore zone, intrusive rocks, or rocks near the intrusive contact; whereas maxima of As, Co, and Ni form peripheral highs i n the p y r i t i c halo. Depletion of minor elements or low element concentrations do not appear to have any defined patterns with the exception of manganese. Manganese lows are found only in areas with low concentrations of other minor elements i n pyrite or areas with only few elements. Zones with low manganese content (less than the detection limit) border zones of high concentrations of other minor elements. Manganese lows may be potentially useful, as i n a l l cases observed, manganese lows border zones with best copper grades. 181 ZONING OF FACTORS (MULTIVARIATE ANALYSIS) Contoured plots of factor values are shown i n Figure 36. Factors have values ranging from 1 to -1 and are interpreted as follows: large negative values are caused by large amounts of negative variables and small amounts of positive variables. Similarly, large positive values imply large amounts of positive variables and small amounts of negative variables i n the factors. Factor 1 (negative) values define a broad, asymmetrical girdle about the quartz monzonite stock that coincides closely with the most highly altered and mineralized rocks. Highest (negative) factor values are associated with rocks containing about 3 to 4 per cent pyrite and occur i n an area bounded by positive factor values that correspond to weakly mineralized rocks of the barren intrusive core and p y r i t i c halo. Factor 2 has a similar zoning relationship as Factor 1. Highest (negative) factor values occur i n areas of copper"mineralization and are" flanked by ~ positive factor values. Factor maxima l i e i n areas with less pyrite (about 2 per cent) than those of Factor 1, and define smaller zones more closely related to intrusive contacts particularly quartz d i o r i t e . If Factor 2 i s , indeed, an indicator of anion substitution i n pyrite, i t may be more closely a l l i e d to a v a i l a b i l i t y of sulphur in the mineralizing process. Thus, i t would appear that the quartz diorite contact may have been a source area for sulphur during pyrite formation. Factors 1 and 2, because of their similar zoning patterns and close relationship to the zone of copper-molybdenum mineralization, may be made up of factor components contributed by the hydrothermal system and mineralizing processes. 182 CONTOURED PLAN OF Q - M O D E FACTOR VALUES FIGURE 36 183 'Zones of Factor 3 and 4 values do not correspond to any constant amount of pyrite and are more transgressive to pyrite contours. Factor 3 clearly exhibits mutually exclusive, antithetic-zoning relationships between lead-zinc and cobalt-nickel, but zoning relationships to copper-molybdenum mineralization are not consistent. In the eastern part of the mineralized zone, positive factor values (high lead-zinc, low cobalt-nickel) define very closely the quartz monzonite contact and the adjoining zone of molybdenum-copper mineralization, whereas high negative values define the p y r i t i c halo i n hornfels and d i o r i t e . In southwest and west part8 of the mineralized zone, high positive values again define the quartz monzonite contact but highest negative values correspond with copper-molybdenum mineralization in hornfels. Zones of Factor 4 values are the least continuous of the four factors and are seen as isolated areas with negative factor values (Bi, Ag component) spread around the quartz monzonite stock. Most areas are i n copper-bearing hornfels with only a very few sample sites within intrusive rocks. The zone of mineralization defined i s the copper zone, i n most cases adjoining the s h e l l of copper-molybdenum mineralization. The outer edge of areas with negative factor values defines approximately the furthest limit of 0.2 per cent, and greater, copper mineralization and i s coincident with the start of the p y r i t i c halo. Factors 3 and 4, i n view of their somewhat transgressive relation to zones of similar pyrite content, yet consistent association with specific rock types, may represent factors whose components are (partly) derived from country rocks during mineralization; i n this case, lead-zinc from quartz monzonite, cobalt-nickel from hornfels and quartz d i o r i t e , and bismuth-silver from hornfels. 185 •Zoning patterns of factors are generally similar to those of individual minor elements with factor maxima concentrated i n an annulus about the quartz monzonite stock roughly coincident with the zone of copper and molybdenum sulphides (Figure 37). Composite highest factor values (-0.5) shown i n Figure 37 clearly coincide with the zone of best copper-molybdenum mineralization. Factor zoning patterns, while similar to those of individual minor elements or composites of minor element concentrations, appear to be more useful in more precisely outlining the copper-molybdenum ore zone. 186 t. , CHAPTER VI SUMMARY AND CONCLUSIONS The Berg deposit i s a large tonnage low-grade copper-molybdenum deposit whose potential was appreciated only after the profound effects of near-surface oxidation and weathering were recognized. Prospecting indications of copper-molybdenum mineralization were provided by the presence of some.molybdenite-bearing veins i n a quartz stockwork and by secondary copper minerals i n margins of basic dykes. The p o s s i b i l i t y of interesting copper-molybdenum mineralization was suggested by highly anomalous s i l t and water geochemical results and leached capping appraisals but considerable diamond d r i l l i n g was required to demonstrate the presence of economically significant hypogene copper-molybdenum and supergene copper minerals. The p o s s i b i l i t y of significant supergene mineralization had been largely overlooked because of the presence of glaciers and a history of extensive and-multiple glaciation throughout the area. The deposit i s located i n a predominantly volcanic terrane that has been intruded by many small stocks and plutons. The area i s part of a transitional zone between the granitoid-metamorphic Coast Plutonic Complex on the west and weakly deformed volcanic and sedimentary rocks of the Nechako Plateau (part of the Intermontane Belt) on the east. Bedded rocks i n Berg map-area are present i n two major time-rock units - Middle Jurassic Hazelton Group and Cretaceous Skeena Group. Skeena rocks were not recognized in the area prior to this study. Hazelton rocks are subaqueous and in part subaerial andesitic pyroclastic rocks with subordinate volcanic flows and loc a l l y derived 187 sediments\ Subaerial members are recognized by their maroon colour or 'red bed' appearance and by the presence of accretionary l a p i l l i and pelleted tephra. About 5,500 feet of the bedded sequence i s exposed i n Berg map-area and has been subdivided into six l i t h o l o g i c a l l y distinct units. Skeena rocks overlie Hazelton rocks i n the eastern half of Berg map-area. Skeena rocks were divided into three map units - a lower volcanic unit of feldspathic andesitic to trachyandesitic flows and breccias; a sedimentary unit composed mainly of bedded micaceous sandstone containing beds with Clepniceras, an Albian (late Lower Cretaceous) ammonite; and an upper volcanic unit of andesitic to r h y o l i t i c flows, breccia, and tuff. The oldest Skeena unit i s poorly exposed in Berg map-area where i t s contact with Hazelton rocks i s intruded, faulted, or obscured by snowfields. Closer to Tahtsa Lake the contact i s known to be an angular unconformity and the base of the Skeena succession i s marked by conglomerate (D. G. Maclntyre, 1974, personal communication). The sedimentary unit forms a cl a s t i c wedge that pinches out westward and thickens eastward where i t has a thickness of at least 1,600 feet along the eastern boundary of the map-area. The upper-most volcanic unit appears to conformably overlie sedimentary rocks except where the c l a s t i c wedge has pinched out i n the area of 8,103-foot peak. There Cretaceous rocks of the younger volcanic map unit can be seen to rest unconformably on l i t h o l o g i c a l l y similar Hazelton volcanic rocks. Intrusive rocks i n Berg map-area consist of two main bodies. The older and larger intrusion i s a steep-walled elongate stock of quartz dior i t e that has been traced southward for 6 miles to Tahtsa Lake. The younger intrusion i s a cylindrical quartz monzonite stock about 2,100 feet i n diameter that has intruded, altered, and mineralized enclosing Hazelton rocks and part of the quartz diorite stock. 188 • The quartz monzonite intrusion i s a composite stock i n which four intrusive phases have been recognized on the basis of crosscutting relation-ships and presence of fragments of one rock type i n another. Five K-Ar age determinations by Carter (1974) date the stock as Eocene (49.0+2.4 m.y.). No closer resolution of the intrusive sequence nor duration between crystal-l i z a t i o n of the intrusive phases i s possible as the dates are indistinguish-able s t a t i s t i c a l l y . The four intrusive phases are cla s s i f i e d (from oldest to youngest) on a largely descriptive basis as: quartz monzonite porphyry (QMP); quartz plagioclase porphyry (QPP); plagioclase biotite quartz porphyry (PBQP); and quartz feldspar porphyry (QFP). Classification based on compositions as determined by modal determinations and two f u l l s i l i c a t e analyses reveal that quartz monzonite porphyry and quartz plagioclase porphyry are equivalent in composition to quartz monzonite, plagioclase biot i t e quartz porphyry i s equivalent in composition to quartz monzonite or quartz-bearing monzonite, quartz feldspar porphyry i s equivalent in composition to quartz monzonite/ granodiorite or quartz-bearing monzodiorite according to a cl a s s i f i c a t i o n based on Streckeisen (1967). Intrusive rocks are grey and rarely pink when fresh or cream to orange or brick pink when weathered. They are a l l characterized by abundant strongly zoned plagioclase phenocrysts, rare p o i k i l i t i c K-feldspar megacrysts (absent i n QPP), large skeletal quartz grains, and coarse-grained elongate books of b i o t i t e . The phenocrysts together with a very fine granular to microcrystalline matrix make up a slight seriate crowded porphyry that can be likened to 'quench type' porphyries i n other high-level intrusions and some volcanic rocks. Differences between the various phases are most obvious on the basis of texture. Mineralogical differences 189 are slight but can be documented by determining abundances of quartz, plagioclase, and K-feldspar, degree of feldspar alteration, b i o t i t e -hornblende ratios, and presence of magnetite and sphene. A breccia pipe intrudes Hazelton rocks and quartz d i o r i t e south-east of the composite stock. It is a polymictic milled breccia that i s explosive i n origin and Is related genetically to the composite stock. Breccia i s mineralized with pyrite but postdates development of molybdenum-bearing quartz stockwork. A gypsum-filled subhorizontal fracture cleavage cuts a l l rocks except quartz plagioclase porphyry and basalt dykes. The cleavage i s a late feature relative to quartz veining and copper-molybdemum mineralization that has been documented in a number of other porphyry deposits. Its origin at Berg deposit i s uncertain but might be related to hydraulic fracture as described by P h i l l i p s (1972) and Shearman et a l . (1972). Beneath weathered rocks and a zone of supergene alteration a number of different hypogene alteration assemblages are present i n and around the composite stock. Pervasive alteration-types recognized are: (1) potassic (quartz-K-feldspar-biotite-sericite-chlorite) within the core of the stock; (2) p h y l l i c (quartz-sericite-pyrite) around much of the margin of the stock; and (3) propylitic (chlorite-epidote-carbonate) in p y r i t i c rocks surrounding the entire stock. A r g i l l i c alteration i s absent or i s very restricted i n i t s distribution. In addition, b i o t i t i c alteration i s developed adjacent to the composite stock as an annular zone of biotite hornfels. Most of the b i o t i t i c zone belongs to the propylitic facies but a small part i n the northeast belongs to the potassic facies. Superimposed on pervasively altered rocks are at least four stages of sulphide-bearing veins and a late stage gypsum-bearing fracture cleavage. 190 Many early veins of the quartz stockwork (Stages 1 and 2) have l i t t l e effect on wall rocks although some veins have metasomatic quartz-orthoclase selvages or s e r i c i t i c alteration envelopes. Younger veins (Stages 3 and 4) generally have alteration envelopes or bleached margins i n which retro-gressive metamorphic reactions have taken place, most commonly bi o t i t e and feldspars are degenerated to fine-grained mixtures of quartz-sericite-chlorite-carbonate-clay minerals. Alteration zones are centred on and encompass the composite stock. The various alteration assemblages can be interpreted to result from temperature gradients i n the stock and outward from i t s contact; differences i n bulk composition between quartz monzonite and the quartz diorite and andesitic country rocks; changes in hydrothermal fluids with time as the intrusive system cooled; and changes in hydrothermal fluids due to flow of juvenile fluids outward from the stock, possible inter-action with meteroic or connate fl u i d s , and flow of mixed source fluids upward along the margins of the stock as modelled by Norton ( 1 9 7 5 ) T h e — core of the intrusion contains an average 1,500 ppm copper and country rocks contain about 75 ppm copper, thus, large quantities of hydrothermal solutions must have passed through the margin of the stock and adjacent country rocks i n order to produce the large zone containing greater than 0.2 per cent copper. The extensive zone of b i o t i t i c alteration surrounding the stock (biotite hornfels) cannot have formed solely by thermal metamorphism through conduction of heat from the stock. The zone had to be expanded by convective heat transfer by outward flowing flui d s . However, there i s no evidence except where some orthoclase veins are present i n the north-east to suggest that the zone of b i o t i t i c alteration had any potassium 191 enrichment. Therefore, most of the b i o t i t i c zone cannot be included i n the zone of potassic alteration and biotite hornfels i s a contact alteration type. It could have formed i n andesitic rocks solely i n response to increased temperature and i s equivalent to the albite-epidote facies of contact metamorphism. Data from a study of a few two and three-phase f l u i d inclusions from Stage 1 veins from quartz monzonite with phyllic alteration and b i o t i t e hornfels indicate that hydrothermal fluids, at least i n early vein stages, were highly saline and at temperatures well i n excess of 406 degrees centi-grade. There i s no evidence that Stage 1 and 2 quartz veins i n the p h y l l i c zone were deposited from cooler or less saline flu i d s . Younger veins con-tain two-phase inclusions and probably were formed from cooler and less saline solutions. Some evidence for boiling i s suggested by f l u i d inclusions i n Stage 1 and 2 veins. The boiling was sustained or repeated and hydrothermal fluids were probably maintained under conditions of hydrostatic pressure. Recurrent boiling might have occurred during emplacement of each vapour-saturated phase of the stock and i t i s possibly during periods of boiling that successive periods or stages of fracturing and vein f i l l i n g "took place.". Interaction of juvenile and meteoric solutions has not 'been proven. Possibly the best evidence for.a convective hydrothermal regime involving groundwater i s the presence and confinement of gypsum to late subhorizontal fracture cleavage i n the zone of mineralization. Gypsum precipitates from aqueous solution as temperature increases and, thus, inflowing sulphate-bearing groundwater that was heated during late cooling of the composite stock might be the dominant factor in gypsum deposition. 192 FIGURE 38 BERG DEPOSIT Idealized Geological Sections SECTION 9800 E (LOOKING WEST) 6000' 5000' 1525m 1Z000N 19,000 N 21000N 4000' SECTION A-A' SEE FIGURE 4 (LOOKING NORTHWEST) .t t' +++ + + + + +++>**; /'+ + + + + + + + + + + + * • + * * * * „ < f + + + + + + + + + + + + + * * * * * * * , . F + + + + + + + + + + + + + + * « * * * * * * * * * ! + + + + ±+*+$ + + + ++++++ ,•*•'-> v>l " - - 1 / 1 - /J/ 6000' 5000' 1525m 0 300 SCALE-METRES 0 1= 1000 I ;.*;*;*. -.j Chalcocite blanket 1 1 i 0.2% Co (primary) Intrusive Breccia SCALE-FEET Q F Porphyry t ± t ± t PBQ Porphyry o o o Porphyritic Q M r 1 :','oi.' Qfz Diorite QP Porphyry HazeltonGroup volcanic rocks Gyptum Surface Marks Commencement of G y p s u m - F i l l e d Fractures at Depth 193 .Mineralization at Berg deposit i s assocaited with a l l rocks of the composite stock except the youngest phase (quartz feldspar porphyry) and resulted i n deposition of pyrite, chalcopyrite, and molybdenite i n an area approximately 7,000 feet i n diameter. Zones with these minerals are centred on the weakly mineralized stock and surround i t as concentric, partly overlapping shells or cylinders i n which one mineral dominates. This results i n l a t e r a l zoning of primary ore minerals. Molybdenite i s most abundant along the contact of the stock where a quartz stockwork i s best developed. Chalcopyrite i s most abundant at the outer edge of the molybdenite zone about 100 to 200 feet from the quartz monzonite contact as fracture f i l l i n g i n b i o t i t e hornfels and i n quartz diorite along the northeast part of the mineralized zone. Best copper grades are found i n quartz diorite where intergranular permeability has produced disseminated as well as fracture-controlled mineralization. Pyrite i n the intrusive core i s 2 per cent or less and increases outward to an average of about 6 per cent i n the p y r i t i c halo that surrounds the chalcopyrite zone. Oxidation and leaching during weathering and attendant supergene processes have resulted in development of pronounced v e r t i c a l zoning i n the deposit (Figure 38). An extensive leached capping has formed to a depth of 125 feet and a zone of supergene copper enrichment (with an enrichment factor of 1.25) i s developed to a maximum thickness of around 300 feet. The depth limit to which supergene processes have been effective i s marked by presence of gypsum i n fractures. This datum which clearly marks the limit of primary sulphides in diamond-drill holes i s called the •gypsum l i n e . ' In the leached capping under acidic oxidizing conditions (measured pH 2.8 - 5.9 and Eh 0.4 - 0.9 volts) pyrite, chalcopyrite, and 194 some molybdenite are leached. Copper has been removed; molybdenum i s immobile and present i n ferrimolybdite and a number of poorly defined limonite compounds that, where abundant, cause molybdenum enrichment; and iron i s precipitated l o c a l l y or redeposited elsewhere as limonite (goethite and jarosite). Berg deposit i s one of the rare deposits i n the Canadian Cordillera that contains economically significant supergene sulphides. The deposit might be unique in that supergene enrichment i s probably a post-Pleistocene phenomenon. Economically important supergene enrichment has taken place where highly fractured (crackled) rocks are leached of gypsum allowing an influx of leach solutions. Solutions are reduced and neutralized in the zone of groundwater saturation where replacement of primary sulphides by covellite and chalcocite (mainly digenite) takes place. In margins of basic dykes and in a thin zone at the top of the water table where supergene sulphides are being oxidized during fluctuations of the air-groundwater interface, native copper, copper oxides, carbonates, and possibly traces of hematite are deposited. Origin of the supergene zone i s by contemporaneous ongoing processes that were i n i t i a t e d , at earliest", during deglaciation following Fraser glaciation (circa 10,000 years B.P.). It i s most unlikely on the basis of mineralogy and incipient replacement textures observed that an older, mature enrichment blanket has survived alpine glaciation. Minor elements in pyrite display lateral zoning around the composite stock i n a manner similar to alteration and sulphide zoning. Elements found to be most useful are Co and Ni, moderately useful are Pb, Zn, Ag, B i , and Mn, and possibly useful are As, Cu, Mo, and T i . 195 Data were examined and compared easily by plotting histograms. These inferred that minor elements are lognormally distributed and are polymodal. Another effective method of data presentation i s using cumulative probability paper. Probability plots are effective i n resolving and des-cribing polymodal populations. One cause of polymodal data as indicated by histograms, t and F tests, and cumulative probability curves i s mixing of vein and disseminated pyrite. There i s an indication that the identity and quantity of some minor elements i s influenced by host rock but this has not been demonstrated to be a general principle. Associations between paired variables were demonstrated using correlation and simple regression analyses. Most significant correlation and interrelationships are between Co-Ni and Pb-Zn. Cobalt-nickel ratios and regression plots show wide ranges i n pyrite from Berg deposit. Use of such plots might enable different types of pyrite from the same deposit to be grouped but genetic c l a s s i f i c a t i o n of mineral deposits based on cobalt-nickel and probably other element ratios or quantities i s tenuous. Associations between samples based on multiple elements were -demonstrated using Q-mode factor analysis. Four factors accounted for 81 per cent of total sample v a r i a b i l i t y and were considered to be geologically meaningful. Two factors might be related to amount of minor element sub-sti t u t i o n i n p y r i t e — o n e measuring total cation substitution and the second measuring anion substitution i n the pyrite l a t t i c e . The remaining two factors are interpreted to represent areas with significant concentration of certain minor elements from host rocks or hydrothermal fl u i d s . Contoured concentrations of individual and composite minor elements and factor values reveal zoning i n which pyrite with highest minor element 196 concentrations coincides with the zone of best copper mineralization and only modest amounts of pyrite. This refutes Ovchinnikov's (1967) statement that highest concentrations of minor elements i n a host mineral w i l l occur where that mineral i s most abundant. Instead, i t appears that minor elements are most abundant in zones of best mineralization, that i s , zones where other metal sulphides are abundant i n addition to pyrite. This observation Is i n accord with studies by Kurz, Brownlow, and Park (1975). Thus, a high degree of contamination of pyrite by impurity elements might be useful as a guide to ore and can be a favourable indication of ore potential. Comparisons between Berg deposit and the 'typical' porphyry copper deposit of Lowell and Guilbert (1970) are generally v a l i d . Of the 40 c r i t e r i a used to define the idealized 'typical' porphyry copper deposit, Berg prospect i s equivalent i n 30 categories, and pa r t i a l l y satisfies another five c r i t e r i a . It i s not equivalent to five categories and these are: 1. Host rocks at Berg deposit are Middle Jurassic volcanics, not Precambrian to Cretaceous sediments and metasedimentary rocks. 2. Diameter of the mineralized intrusion at Berg deposit i s smaller -(2,100 feet as opposed to 4,000 by 6,000 feet). 3. Alteration patterns are not equivalent, especially with respect to b i o t i t i c alteration (biotite hornfels). Alteration is more equivalent to models revised by Guilbert and Lowell (1974) i n which importance of volcanic rocks are stressed. 4. 'Typical' porphyry copper deposits have 70 per cent of ore i n intrusive rocks and 30 per cent i n country rocks. At Berg deposit these quantities are reversed. 197 5. (Grade of copper at Berg deposit i s about one-half that of 'typical* porphyry deposits (0.4 versus 0.8 per cent copper i n the supergene zone; 0.2 versus 0.45 per cent copper i n the hypogene zone). Molybdenite at Berg deposit i s 3.5 times more abundant than that i n 'typical' porphyry deposits (.055 versus .015 per cent molybdenite). In the terminology of Ti t l e y (1972), porphyry deposits i n south-western United States (those described by Lowell and Guilbert, 1970) are 'intrusion porphyry copper deposits;' the Berg deposit typifies a number of deposits i n the Canadian Cordillera that can be called 'wall rock porphyry deposits.' Sutherland Brown (1969) described Berg deposit as a 'simple' type porphyry deposit because annular zones of alteration and mineralization are regular and persistent and symmetrically arranged around a plug-like intrusive core. More recently (1974) he has classified i t morphologically as a 'phallic-type' porphyry deposit, one in which a simple steep-walled plug penetrates host rocks. A model suggested by this study i s an orthomagmatic one i n which an inherently copper-molybdenura-rich stock of quartz monzonite composition has intruded, altered, and mineralized enclosing volcanic rocks and part of a quartz diorite stock. During f i n a l crystallization of the stock a :  : water-rich :fluid phase evolved and migrated into early crystallized parts of the intrusive body and intensely fractured wall rocks. Onset of hydro-thermal activity Is regarded to be when convective heat exchange involving a fl u i d took place between the crystallizing stock and country rocks. The i n i t i a l hydrothermal f l u i d was largely heated connate or meteoric waters whose flow was controlled by intergranular and fracture permeability and 198 resulted i n a pervasive zone of biot i t e hornfels around the stock. Extensive flow of hydrothermal fluids along the margin of the stock was sustained by successive emplacement and crystallization of at least four major Intrusive phases. .The bulk of alteration and sulphide minerals are fracture controlled and were deposited during emplacement of the l a t t e r intrusive phases. Mineral zoning around the composite stock i s i n response to mainly decreasing temperature and chemical changes in hydrothermal flui d s (pH and oxidation state) outward from the stock. Hydrothermal a c t i v i t y culminated i n explosive brecciation that postdated a l l significant quartz veining and copper-molybdenum mineralization. Brecciation was followed by influx of meteoric water that deposited gypsum in late cleavage fractures possibly as a result of slight heating of sulphate-bearing solutions during late stage cooling of the stock. 199 BIBLIOGRAPHY Allen, D. G. (1971): The Origin of Sheet Fractures i n the Galore Creek Copper Deposits, British Columbia, Can. Jour. 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APPENDIX A CHEMICAL ANALYSES OF QUARTZ MONZONITE PORPHYRIES DDH 19 (126 - 300 feet) DDH 1 (626 - 640 feet; 645 - 672 feet) QMP PBQP sio 2 67.54 62.50 A1 20 3 15.62 15.12 Fe 20 3 1.16 1.64 FeO 0.76 0.85 P2°5 0.30 0.18 CaO 1.02 2.39 MgO 1.04 1.49 T i 0 2 0.51 0.51 so 3 1.92 4.53 MnO 0.02 0.06 Na20 2.76 3.13 K 2 ° 5.06 4.55 H20+ 1.32 2.18 H 20- 0.31 0.95 co2 0.02 0.01 BaO 0.12 CuO 0.38 M 0 O 3 PbO 99.86 100.09 Samples submitted by N. C. Carter, 1967. Analyses by S. Metcalfe, Analytical Laboratory, British Columbia Department of Mines and Petroleum Resources, 1968. 212 APPENDIX B ALTERATION: CATALOGUING OF CORE AND ESTIMATION OF ALTERATION INTENSITY A l l d r i l l core available to 1971 (26,184 feet i n 49 diamond-d r i l l holes) was examined in de t a i l . Alteration minerals and their abundances from 10-foot intervals were noted; these include: quartz (veins and pervasive s i l i c i f i c a t i o n ) , b i o t i t e , chlorite, s e r i c i t e (including muscovite), magnetite, calcite, gypsum, orthoclase, epidote, and clay minerals. Less common alteration minerals include anhydrite, tremolite, hematite, dolomite, sphene, and r u t i l e . In supergene zones limonite was described according to colour, abundance, and texture. Differences i n appearance of cores and hand specimens were used i n i t i a l l y to define significant grades or ranks of alteration intensity. Various alteration types are clearly associated with certain sulphide mineral concentrations. Later, examination of thin sections and laboratory studies (C. L. Dahl and D. Norton, 1967, private report, Kennecott Copper Corporation) described rock types more completely. From these f i e l d and laboratory descriptions, standardized core logging procedures and alteration intensity ranking were devised and followed throughout this study. Alteration intensities were i n i t i a l l y described on a relative scale and later quantified corresponding to: trace = 1, weak = 3, moderate ™ 5, and strong = 7. For biotite, s e r i c i t e , chlorite (including epidote), and quartz, weak, moderate, strong correspond to: less than 10 per cent, 10 to 25 per cent, more than 25 per cent of the rock volume. Quantity of b i o t i t e , s e r i c i t e , and chlorite could be estimated using colour 213 index. Quartz was measured as volume of quartz veins and amount of pervasive s l l i c i f i c a t i o n estimated from scratching core with a knife. Amount of calcite was estimated by observing and listening to response of unsplit d r i l l core to 5 per cent HCI sprayed on a 10-foot section of core. ... Magnetite content was estimated from response of a suspended magnet to s p l i t core. Abundances of other minerals were recorded as number of grains or veins per 10-foot section of core. Clay minerals (less than 2-micron-sized fraction i n crushed diamond-drill core) were separated from 46 representative specimens using a water suspension and centrifuging technique (Appendix C). A satisfactory separation of various-sized fractions was attained, thus enabling i d e n t i f i -cation by X-ray di f f r a c t i o n and comparison of different-sized fractions. Untreated, glycolated, and heated specimens were X-rayed to identify and estimate abundances of s e r i c i t e ( l o A ), kaolinite (7A) and chlorite (14A) i n the manner described by Carroll (1970). Ranked values of alteration Intensities of a l l abundant hydro-thermal minerals were averaged over the entire d r i l l hole i n v e r t i c a l holes or averaged over long intercepts i n angle holes. Contoured rank values define concentrations of individual and related alteration minerals and define zoning patterns (Figure 8). 214 APPENDIX C CLAY SEPARATION TECHNIQUE The <2 micron-sized fraction from crushed d r i l l core was separated for qualitative X-ray diffraction determination of clay mineral content. The technique developed by C. Pharo, D. G. C a r g i l l , and the writer i s a simple routine procedure that results i n quick and effective separation and recovery of fine-grained materials. The technique i s based on Stokes Law and uses both gravity settling and centrifuging i n water suspension. Material used i n this study was approximately 5 grams of assay pulp (-100 mesh, 60 per cent -200 mesh crushed d r i l l core). REDUCTION OF SAMPLE SIZE Sample size can be reduced by gravity settling i n a water suspension. Assuming a mean sample specific gravity of 2.65 and with a 5-centimetre suspension depth, settling times for various-sized fractions are as follows: Particle Diameter in Suspension Time Required Time Required Microns @ 20° C @ 25° C < 50 22 seconds <20 2 minutes 20 seconds < 5 37 minutes 30 seconds In this study a 22-second settling time to recover the <50-micron-sized fraction was used. 20 seconds 2 minutes 5 seconds 33 minutes 20 seconds 215 RECOVERY OF < 2 MICRON-SIZED FRACTION FROM SUSPENSION The water suspension containing <50-micron-sized fraction was centrifuged to retrieve the <2-micron-sized fraction. Centrifuging time (t min) i s a function of centrifuge speed (RPM) and can be calculated from the following relation which i s a modification of Stokes Law: 63.0 x 1 0 ^ l o g 1 0 J I » \ twin j ~" ^ f ? '}j P (Nm) ( D U ) Z ( A S ) < £ ^ f .-icenrrlfuae vessel r o t a t i o n where: R • radius of rotation to top of sediment S «• radius of rotation to top of suspension Nm - RPM t\ « viscosity i n poises (.00958) DL< • particle diameter (in microns) AS = difference i n specific gravity between particles and solvent Times used in this study: <2 micron fraction @ 1000 RPM - 3.5 minutes @ 1250 RPM - 2 minutes 55 seconds <5 micron fraction @ 660 RPM - 1 minute 18 seconds APPENDIX D. SPECIMEN MINERALOGY VEIN STACE HOST 71-632 A, B, C Qtz-MoS -py cp-anhya 1 Q u a r t z 25-442 Qtz-MoS, A n h y d r i t e 1 o r 2 Q u a r t z HS22.6.A 12-191 30-363 HS-M1 MS-M2 1-583 3-72A C a l c i t e Gyps-py-t e t r a h e d - g a l -s p h a l G y p s - c a r b o n a t e -s p h a l - g a l - p y Qtz-MoS 2 • Q t z - c a r b o n a t e -p y - s p h a l - g a l Q t z - c a l c i t e -s e l e n i t e - p y s p h a l - g a l Quartz-MoS. Amygdule C a l c i t e 4 Gypsum ( S e l e n i t e ) 4 S p h a l e r i t e 1 o r 2 Q u a r t z 4 Q u a r t z 4 S e l e n i t e 1 o r 2 Q u a r t z 3-72B Q t z - ( c a r b o n a t e ? ) - 3 py Q u a r t z FLUID INCLUSION DATA ABUNDANCE Many Rare Many Rare Rare SHAPE I r r e g u l a r , o v o i d Round I r r e g u l a r R o d - l i k e , o v o i d R o d - l i k e PHASES 2 ( L , V) and 3 ( L , V, S) V - 1 t o 70%, S - N a C l , opaque 2 ( L , V) 2 ( L , V) and 3 ( L , V, S) V - 1 t o 70%, 20% common S - N a C l 1 ( L ) , L ( C 0 2 and b r i n e ) 1 ( L ) H0M0GENIZATION TEMPERATURE ( i n ° C) 1 2 - > 4 0 6 1-392+15 1-248+2 6- 406 N.D. N.D. Few i n p a l e N e g a t i v e X l growth zones c a v i t i e s Many Few Rare I r r e g u l a r N e g a t i v e x l c a v i t i e s R o d - l i k e 2 ( L , V) V - 10 t o 20% N.D. L ( C 0 2 and b r i n e ) 2 ( L , V ) , some 3 ( L , V, S) N.D. 1 ( L ) and r a r e 2 ( L , V) N.D. 1 ( L ) , v e r y r a r e 2 ( L , V) N.D. V - 0 t o 2% Many Many N e g a t i v e x l c a v i t i e s N e g a t i v e x l c a v i t i e s 2 ( L , V) and 3 ( L , V, S) N.D. V - 20 t o 50%, S - N a C l , opaque 2 and 3 p h a s e s - d e t a i l s N.D. i n d e t e r m i n a b l e SPECIMEN 71-655 71-718 71-677A 71-677B H S - S a n f t s v e i n 12-191 HS-22.6.B MINERALOGY Q t z - a n h y d r i t e -p y - c p - c a r b o n a t e Q t z - a n h y d r i t e -MoS -cp-py-c a r E o n a t e - c h l o r i t e Q t z - c p - p y -M o S _ - c h l o r i t e Q t z - a n h y d r i t e -py-MoS 2 Q t z - c a r b o n a t e - p y -g a l - s p h a l G y p s - t e t r a h e d - p y -cp Q t z - c h a l c e d o n y VEIN STAGE HOST 1?- Q u a r t z A n h y d r i t e 1 Q u a r t z A n h y d r i t e 1 • Q u a r t z 1 Q u a r t z 4 Q u a r t z 4 Geode Q u a r t z ABUNDANCE SHAPE Rare • E l l i p s o i d Rare R o d - l i k e Few E l l i p s o i d , r o u n d Few Cubes Many I r r e g u l a r , e l l i p -s o i d s , n e g a t i v e x l c a v i t i e s Many N e g a t i v e x l c a v i t i e s , o v o i d , e l l i p s o i d Many I n d e t e r m i n a b l e (minute < 1y* ) None r e c o g n i z e d Rare ( i n E l o n g a t e x l l i n e c o r e ) Rare ( i n rim) O v o i d PHASES 2 ( 1 , V ) , V • 5 t o 10% 1 (W HOMOGENIZAXICN TEMPERATURE ( i n ° C) N.D. 2 ( L , V) and ? 3 ( L , V, S) N.D. V - 5 t o 40% 2 ( L , V ) , V - 20 t o 30% 1 ( L ) , m a i n l y 2 ( L , V ) , and 3 ( L , V, S) S - minu t e N a C l x l s N.D. 2 ( L , V ) , some 3 ( L , V, S) N.D. minut e N a C l x l s N.D. 1 (L) and 2 ( L , V?) V? - 0 t o 1% (V may be l i q u i d C 0 2 ) 1 (L) N.D. N.D. >3 218 APPENDIX E MINOR ELEMENTS IN PYRITE: SAMPLE VARIABILITY The quantity and composition of minor elements (trace elements) i n pyrite are controlled by both the environment of formation and the supply of elements. Four mechanisms are commonly used to explain the manner by which elements are incorporated i n pyrite. +2 -2 (i) Substitution or proxy of certain elements for Fe and S i n true s o l i d solution, ( i i ) Accommodation of elements i n t e r s t i t i a l l y between l a t t i c e sites or at sites of l a t t i c e defects and along growth surfaces, ( i i i ) Adsorption, (iv) Inclusion as minute discrete grains of other mineral phases. The wide variety of minor elements and their ranges of concen-tration are summarized by Fleischer (1955). There are numerous other studies reported i n the literature but a particularly lucid summary of minor elements i n pyrites from a variety of environments i s by Mitchell (1968). He states: 'From a consideration of metal-sulphur bond lengths i n sulphides, stereochemistry of bonds, and experimentally investigated sulphide phase e q u i l i b r i a , i t i s concluded (Mitchell, 1968) that T i , V, Cr, Mn, Co, Ni, Cu, Zr, Mo, Nb, and Sn can replace iron and that As, Se, Te, Sb, and Bi can replace sulphur at la t t i c e sites i n pyrite. The degree of replacement varies from trace amounts (Mo) to complete replace-ment (Co). The incorporation of Zn, Ga, Au, Hg, Pb, Th, and U occurs at defect sites i n the l a t t i c e . ' [Also] ... 'Of. the overall trace element 219 assemblage only broad generalizations can be made. A l l the pyrites are seen to contain T i , V, Cr, Mn, Co, Ni, Cu, Zn, As, and Se. The hydrothermal pyrites typically contain Ag and Sn ....' The analytical procedure used i n this study provides an indication as to the manner in which elements are incorporated i n pyrite (assuming they are not from included grains). The spectrographs method uses a two-stage excitation of samples. A short duration f i r s t stage involves a low-intensity burn in air that releases so-called v o l a t i l e elements Sb, As, Cd, Ag, Sn, and Zn. The second stage i s a longer, higher intensity bum i n an argon-oxygen atmosphere that i s used to determine more refractory (non-volatile) elements Cr, Co, Cu, Mn, Mo, Ni, T i , V, and Zr. It i s evident from Mitchell's (1968) conclusions and other studies that, with the possible exception of Sn, v o l a t i l e elements are those that are incorporated i n pyrite by anion substitution, adsorption, and accommodation i n i n t e r s t i t i a l and l a t t i c e defect s i t e s . The non-volatile elements are cations that substitute for iron i n l a t t i c e s i t e s . Two levels of excitation energy can be used i n the analytical procedure because bond strengths of the v o l a t i l e elements are weaker than those of cations proxying for iron i n the pyrite l a t t i c e . For a more thorough discussion of pyrite geochemistry, one' i s referred to an excellent compendium by Price (1972). 220 APPENDIX F ELEMENTS DETECTED IN BERG PYRITE Line spectra of a large number of elements were checked i n a group of sixteen pyrite concentrates constituting an orientation sample set. The samples were examined i n i t i a l l y only on a qualitative basis. The following elements were detected i n one or more samples. Undoubtedly, some are contaminants from admixed gangue and sulphide grains: A l Co Ag Sb Pb Sr As Mg Sn Ba Mn T i Cd Mo V Ca Ni Zn Cr Si Zr The following were not detected. These may be present but i f so, concentrations are below spectrographic detection limits: Be B Ce Cb Ga Ge Detection limits of the spectrographic method used are approximately in the 0.1 to 1000 ppm range, but each element behaves individually and has a characteristic upper and lower limit of detection. Characteristic wavelengths and 'index points' of elements for which standards were available are shown i n Table 18. The 'index point' i s simply a concen-tration convenient for describing calibration curves. Commonly maximum and minimum detection limits of elements shown are approximately 10 times and .10 of the 'index points.* Au La Pt Re Sc Se Te Th W U Yb Y 221 TABLE 18. SPECTROGRAPHIC ANALYSIS OF PYRITE ELEMENTS FOR WHICH CONCENTRATIONS WERE DETERMINED Standard Reference Line: Pd 3421. 2 I Index Index Element Wavelength Point Element Wavelength Point X ppm A ppm Sb 2598.0 370 Pb 2833.0 65 As 2860.5 3200 Mg 2779.8 720 2780.2 1800 Mn 2798.0 54 Ba 4554.0 4.2 Mo 3170.3 96 4130.6 330 Ni 3414.7 27 Be 3130.4 11 Ag 3382.8 4 Bi 3067.7 12.5 Sr 4Q77.7 2.4 B 2497.7 92 3464.5 225 Cd 3261.2 49 Sn 3175.0 32 Ca 3158.9 2100 T i 3361.2 32 Cr 4254.3 18 2942.0 1500 Co 3453.4 27 V 3185.3 100 Cu 3273.9 - 12.5 Zn 3345.0 32 Ga 2943.6 24 3345.5 210 Ge 3039.1 46 Zr 3273.1 57 Contamination of pyrite concentrates by gangue and sulphide inclusions i i s inevitable. Si to 1 per cent, Al to 0.5 per cent, and some Sr, Ba, Mg, Ca, and Zr were detected and are believed to be due to quartz, feldspar, chlorite, c a l c i t e , or gypsum, and zircon inclusions. Gangue minerals are not considered to be serious contaminants i f they are present in minute quantities since most elements introduced are not contained in the pyrite l a t t i c e . Contamination of pyrite by other sulphide minerals i s the main source of concern. The main sulphide contaminant i s chalcopyrite. Polished sections show that chalcopyrite i s intimately intergrown with pyrite i n the copper-molybdenum zone as minute 'encapsulated' grains within pyrite grain boundaries and as f i l l i n g s i n micro-fractures. Pyrite i n peripheral volcanic rocks, the p y r i t i c halo zone, and crystals from a l l types of veins generally have negligible chalcopyrite intergrowths. Five chalco-pyrite samples from different areas within the deposit were analysed to determine effects of chalcopyrite contaminations. Results are shown i n Table 19. TABLE 19. MINOR ELEMENT CONTENT OF CHALCOPYRITE (IN PPM) Sample No. Pb Zn Ag Mn Mo T i Sn 1 12 180 35.0 .5 164 14.0 2 38 365 43.0 8.0 DL 5.0 3 23 680 1.0 52.0 1.0 38 - - -4 10 16 20.0 21.0 12.0 5 23 620 14.5 26.0 1.0 4 8.0 Note: Sb, As, B i , Co, Ni, and Cd were not detected. --- means less than detection l i m i t . From these data, assuming a maximum chalcopyrite content of 1 per cent in a pyrite concentrate, i t appears that the only significant contribution to the analytical results by chalcopyrite w i l l be copper and possibly minor amount of zinc (e.g., 6.8 ppm i n sample 3). Ag, Mn, Pb, and T i present as contamination i n pyrite from chalcopyrite w i l l be below the detection l i m i t . Sphalerite i s the second most abundant sulphide contaminant. It i s found mainly i n the vein and breccia specimens and a few samples from outside the copper-molybdenum zone. Analysis of a single sample of zoned, pale to medium brown sphalerite gave the following results: Pb 1000 ppm T i 80 ppm As 6300 ppm Sb 990 ppm Cu 6800 ppm Cd 22,000 ppm Ag 250 ppm Fe 10,000 ppm Mn 2350 ppm Note: B i , Co, Ni, Mo, and Sn were not detected. 223 Sphalerite with this composition would contribute a number of elements in significant amounts to analytical results for pyrite. However, based on this and other analyses of mixed pyrite-sphalerite grains, Cd appears to be always present and i s , thus, useful as an indicator of sphalerite contamination. Every pyrite analysis containing Cd (seven from the total 100 samples) also contains high values of Zn and commonly Mn, Pb, and Ag. In a l l these seven cases i t i s assumed that sphalerite i s present and only analytical values of Bi, Co, Ni, Mo, and Sn ( i f present) were u t i l i z e d . Other potential contaminants are molybdenite, galena, tetra-hedrite, and c o v e l l i t e , but these can be avoided by careful sample selection and hand picking of pyrite grains. APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn HORNFELS 1-260 1.0 728 740 900 106 106 108 500 460 C 92 52 97 216 134 120 14.0 10.0 8.5 8 2 12 210 245 C 5.0 13.0 3-267 416 370 62 45 300 C 52 107 26 21 4.0 5.5 46 20 230 485 4-220 620 3.0 1100 820 C 46 35 3.0 C C 5-248 1150 770 C 12 18 4.0 C 310 7.5 8-271 510 16.0 .760 162 C 140 95 18.0 C C 7.0 8-490 820 18.0 1320 405 C 102 68 49.0 C 355 11.5 10-253 48.0 740 114 C 52 55 7.0 C 600 12-430 10.5 7.0 785 590 78 67 C C 15 10 23 17 12.5 4.5 54 83 480 390 4.0 5.0 12-597 700 410 44 C 15 33 5.0 6 310 4.0 13-385 9.0 355 50 C 20 28 2.5 1 C . 13-693 142 16 370 12 8 3.0 190 14-432 11.0 600 172 C 92 82 17.0 C C Sn Cd 10.0 1.0 NOTE: A blank space denotes not detected; C denotes greater than maximum detection l i m i t . APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn HORNFELS (continued) 3.5 63 148 5.0 14-727 5.0 700 128 C 13 31 8.0 820 175 C 8 29 35.0 11 215 12.0 14-1163 400 2.0 420 35 650 22 46 7.0 C 15-187 2.0 115 168 500 21 16 2.5 6 560 4.0 93 142 490 12 21 2.5 1 500 17-105 • 3.0 70 128 100 13 15 1.5 C 7.0 18-232 1.0 260 60 240 12 16 2.5 1 385 4.0 1.5 325 60 c 21 46 3.0 6 C 5.0 19-465 9.0 460 244 160 75 36 3.5 17 395 5.0 18.0 570 265 C 110 36 4.5 35 C 9.5 20-295 4.5 600 260 68 84 7.0 315 18.5 22-197 448 44 215 11 13 7.5 6 475 23-328 980 6.8 C 9 10 5.5 5 64 600 60 C 17 230 8.0 1 50 385 34 640 12 12 8.0 29 485 58 640 21 8 3.5 20 23-434 600 1.0 650 70 630 25 33 8.0 19 300 10.0 450 2.0 630 63 C 23 22 6.0 1 240 5.0 25-165 21.5 70 47 196 19 12 2.0 4 26-437 11.0 188 32 181 28 17 8.0 1 395 5.0 10.0 180 31 C 64 51 12.0 4 C 9.0 APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn HORNFELS (continued) 26-437 1200 500 3.0 2.5 55 64 17 21 38 10 30 26 7 7 5.0 4.0 7 6 27-584 400 55.0 120 74 C c C C C C C 28-410 300 1.5 390 86 360 48 34 11.0 22 385 29-226 620 62 330 19 53 8.0 6 100 30-325 2.0 1200 550 C 92 28 7.5 c 265 8.0 32-277 640 132 C 42 13 4.0 C 29 4.0 33A-558 2050 1280 114 90 880 760 52 44 20 18 7.0 6.5 47 43 34-316 4.5 295 106 C 41 32 7.5 12 C 11.5 35-367 500 52.0 670 54 C 58 42 16.0 C 640 35-376 4.5 375 70 C 20 15 9.0 C 610 36-582 400 450 19.0 9.0 550 392 108 94 C C 58 37 27 25 20.0 11.0 86 31 C C 4.0 37-480 3.0 7.5 560 640 850 1000 198 102 21 16 80 52 1.5 1.0 C C 43-281 450 C 285 66 C 57 41 84.0 C C 9.0 63-141 630 1400 4.0 7.0 790 570 310 245 540 400 82 98 36 37 9.0 2.5 450 210 92.0 81.0 APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn Sn Cd HORNFELS (continued) 65-129 3050 3.0 340 78 430 320 C 17.0 C 140 2290 3.0 295 88 390 260 C 9.5 C 146 C 3.5 350 100 590 235 C 8.0 800 110 C 2.5 275 83 430 220 C 5.0 610 152 68-74 300 24.0 140 28 103 72 44 8.0 625 7.0 71-420 720 230 C 1 8 4.0 55 71-533 1.0 430 330 C 64 20 5.5 26 10 71-569 530 17.0 400 98 360 36 19 9.0 10 64 6.0 71-667 1.0 950 140 280 7 9 7.0 28 8 20.0 71-738 1.0 560 168 C 1 18 2.5 450 71-869 1050 26.0 305 107 C 63 30 18.0 31 380 71-915 400 12.0 435 74 600 105 34 19.0 14 C 5.0 72-400 18.0 1140 1150 C 79 24 96.0 17 610 16.5 570 800 C 29 11 29.0 11 405 5.0 )IORITE 4-446 850 C 445 200 C C C C C C 9-155 1190 3.5 600 140 c 67 182 50.0 C C 8.0 8.5 41 54 28 30 to >4 APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn Sn DIORITE continued 9-430 300 34.0 1040 .285 C C 100 86.0 C C 5.0 18.0 9-724 950 7.5 820 148 C 124 33 29.0 24 C 18.0 10-510 500 400 3.0 4.0 560 510 214 225 C C 192 173 620 367 21.0 18.5 94 86 C C 16.0 9.5 10-803 660 71 C 76 32 19.0 27 C 7.0 4.0 16-495 380 172 510 25 26 8.0 8 C 5.5 16-600 300 405 144 164 215 C 16 32 24 37 2.0 4.5 1 8 C C 5.0 15.0 10.6.6 17.0 450 130 C 380 C 17.0 7 680 C 12.0 QUARTZ MONZONITE t 1-547 7.5 300 106 c 116 10 20.0 15 C 5-552 5.0 610 225 c 116 118 20.0 C C 11.0 6-350 450 91 540 34 20 4.0 36 960 4.0 6-449 11.0 11.0 11.0 . 76 88 90 50 52 48 325 270 C 64 16 59 16 13 12 3.0 3.0 2.5 6 7 6 500 530 C ro ro CO APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn QUARTZ MONZONITE continued 6-724 13.0 225 104 C 78 49 11.5 C C 4.0 7-235 290 112 C 148 208 25.0 33 C 21.0 10-683 89.0 77 25 250 C C C 3 C C 11-404 9.5 104 92 C 30 20 5.5 20 C 13-134 21.0 90 74 360 21 27 2.5 C 17-290 2.0 90 47 132 35 44 1.5 3 C 4.0 20-512 3.5 310 122 420 122 69 3.0 4 320 8.0 21-502 1325 1110 40.0 34.0 216 216 194 184 55 94 30 73 48 37 0.5 4.5 1 30 500 C 5.0 8.5 24-541 40.0 56.0 160 120 132 84 C C 270 196 38 85 39.0 13.0 C C C C 20.0 38.0 25-396 21 .0 164 120 180 430 148 17.0 6 172 27-358 27.0 86 46 C C C c 13 C C 31-337 1.5 2.0 256 230 132 122 175 325 80 270 330 510 3.0 6.0 670 C 5.0 9.5 34-368 2.0 325 140 C 58 260 13.0 87 C Sn Cd 34 4 ro so APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo Ti Mn QUARTZ MONZONITE continued 69-463 1030 54.0 900 38.0 390 332 220 205 C C 212 141 50 42 65.0 29.0 51 88 C C 15.0 12.5 VEIN 1-596 180 50 116 41 18 3.5 C 5 12-191 500 35.0 10 8 67 380 72 18.0 C 14-261 72.0 21 17 600 45 16 17.5 7.5 144 23-545 9 8 590 1 9 4.0 52 24-355 9 13 102 1 6 0.5 260 25-165 1 1 15 1 1 0.5 9 26-437 850 3.0 60 19 24 28 7 4.5 4 30-363 900 29.0 700 50.0 29 14 54 56 C 430 360 440 C 215 27.0 34.0 C C 33A-558 1.0 13 11 30 14 7 1.5 8 6.5 35-627 900 24.0 64 9 180 136 148 36.0 5 4.0 37-390 83 loo 122 53 15 8.0 20 7 to o APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn Sn Cd VEIN continued 43-355 7.0 1 1 600 19 8 2.5 C 235 63-251 148.0 20 6 20 410 300 80.0 11 7 9.5 68-68 400 1.5 5 5 6 290 13 1.5 3 C 20.0 69-480 272 34 140 1 14 3.0 6 90 70-515 74 77 54 80 500 305 16 15 34 31 4.0 3.0 38 24 174 122 71-580 2.0 106 260 600 30 26 3.0 6 1.0 71-804 225 72 134 10 7 8.0 174 8.0 M.24.6 1 1 60 70 9 1.5 8 Fissure 1960 2100 15 9 24 18 30 50 290 415 520 C 12.0 3.0 C 6 6 13.5 5.0 11 11 M3 22.0 26.0 5 18 5 5 53 C 210 450 122 205 3.5 7.0 12 1 17 59 84 3.22.7 33 24 144 57 34 4.0 3 140 8.0 VOLCANIC ROCKS 3.25.7 C . C 3.0 3.0 2400 1300 940 550 42 74 390 350 154 104 11.0 13.0 6 1 C 5 30.0 40.0 APPENDIX G. ANALYTICAL RESULTS - MINOR ELEMENTS IN PYRITE (IN PPM) - continued Sample As Bi Co Ni Cu Pb Zn Ag Mo T i Mn Sn Cd VOLCANIC ROCKS continued 1.8.6 350 2.0 920 570 650 42 128 1.0 148 24.0 3.21.6 600 2.0 880 680 C 84 173 1.0 220 52.0 3.24.6 39.0 29.0 550 395 400 360 300" 350 130 97 78 98 27.0 25.0 6 5 230 215 38.0 34.0 CHALCOPYRITE 1-596 Major 12 180 35.0 164 5.0 14.0 28 10-510 i Major 38 365 43.0 C 8.0 5.0 5 14-1003 Major 23 680 1.0 1 38 53.0 56 26-437 Major 10 16 20.0 12 21.0 34 71-677 Major 23 620 14.5 1 4 26.0 8.0 SPHALERITE 30-363 6300 6800 Major Major 250 80 2350 also: Sb 990 ppm Fe 1% Cd 2.2% N> APPENDIX II DATA PARAMETERS AND COMPUTED O i l SQUARE VALUES-233 ~~ATP~ANT EL EY EV — FACTOR A N A L Y S I S — 8 VAR I A P . L E S — M A R C H 0 6 1 9 7 2 -OATA P A R A M E T E R S V A R I A B L E MEAN STAN OEV B I 1 5 . 8 7 5 0 VEIN PYRITE T t r N I N - 20 CU 3 5 . 4 5 0 0 2 0 0 . 2 9 9 9 3 4 . 9 5 9 3 PB ZN AG sfc.649<; 4 5 . 3 4 9 9 1 0 . 3 0 0 C 5 8 . 1 3 1 7 2 1 5 . 7 0 5 7 1 3 3 . 1 2 3 4 7 3 . 2 6 * 1 1 7 . 98C1 CHI A 3 . 5 0 9 8 . -Z9TTATJT5 1 5 . 6 1 8 6 2 5 . 5140 2 5 . 7 5 9 3 " -2 1 . 5 7 6 3 3 5 . 1 7 1 9 4 7 . 9 4 3 0 ; Rfl 2.8700 TRANSFORMED CATA PARAMETERS VARIABLE MEAN B I 0 . 5 0 5 6 5.0592 STAN DEV 0 . 7 1 6 0 0 . 7 4 6 0 0 . 6594 0 . 5 6 5 3 0 . 8 4 9 6 CHI 2 8 . 7 6 0 9 6 . 7 0 9 7 NI CU ~PTT 1 . 3 0 4 6 1 . 1 0 4 4 1w9999 ZN AG 1 . 4 2 2 6 1 . 2 6 0 3 0 . 6 6 4 4 0 . 2 7 5 0 " 0 . 5 6 7 4 0 . 4 9 5 2 0 . 4 3 5 4 ' 5 . 9 9 4 8 1 5 . 1 1 1 9 1 8 . 3 7 7 5 1 2 . 6 4 0 3 7 . 8 9 9 0 4 9 . 9 2 9 0 A . P A N T E L g Y E V — PACTOR A N A L Y S I S - - / V A R I A B L E S — M A R C H Ub ivf<: CATA PARAMET ERS VARIABLE MEAN STAN CEV DISSEMINATED PYRITE B I -CTJ -NI PB 9 . 8 4 1 0 4 S Si / S 5 1 2 . 4 3 7 8 312 . 4 6 7 3 1 8 9 . 2 7 8 2 7 6 . 6 7 1 8 N - 61 "TTT AG bb . 4 9 T 5 ~ 1 4 . 5 8 5 2 7 . 3655 TRANSFORMtC CATA PARAMETERS VAK 1 ArBrTf~~ MEAN B I CO -rrr 0 . 6 7 8 4 2 . 5 9 0 9 PB ZN -A-tr-MN - 2 T 0 9 T 5 -1 . 7 C 4 8 1 . 6 1 8 8 - C . m 9 9 2 1 3 . 1 2 4 5 8 3 . 7 e 6 4 B 7 . 6 5 7 6 1 8 . 2 1 3 4 1 2 . 5 9 6 6 SI AN LEV 0 . 5 5 1 4 0 . 3 3 2 6 - 0 7 3 7 9 T -0 . 3 9 0 3 0 . 3 8 4 1 - 0 7 ^ 5 26 0 . 5 7 9 2 0 . 4 9 9 9 CHI 5 5 . 1 2 3 7 1 4 . 2 4 3 2 4 9 . 7 2 2 7 3 0 . 8 1 6 6 4 B . 4 2 2 1 4 0 . 6 2 3 1 41 . 3 4 1 6 C H I 2 8 . 4 4 1 1 1 2 . 8 7 9 6 5 . 3 0 3 4 6 . 5 8 6 1 5 . 3 0 2 6 J . 4 562 5 5 . 8327 APPENDIX I VARIMAX FACTOR MATRIX, DISSEMINATED PYRITE "TTPAfftliTffYf V ^ T T C T r r f T ^ X A T V V r ? ~ - 7 A T I n r S - " - VJTPTH 0 6 197T" VARIMAX FACTOR MATRIX NG • 1 2 3 4 ^3 6 7 8 9 10 T T 12 13 14 15 16 - I T -ID HI 26 H326 H422 F524 ~Hfl2T~ H849 H102 H124 H125 H133 H 1 ib H144 HI 4 7 H141 h l51 HI 71 TTTET X 1CC8 1C06 1117 066 T C 9 T 1112 1067 919 917 80 8 18 19 20 21 22 - n r 24 25 26 27 28 ~Z9 -30 31 32 33 34 T T 36 37 38 39 40 - 4 T -42 43 44 45 46 H194 H202 H221 F2 3A H251 H264 H284 H292 H3C3 H322 H335 H343 H3 5A H365 F.374 H432 H631 H6 8U H71A H724 D915 0543 C972 H1.U5 1C89 1108 1135 836 771 "11 04 960 922 1C07 1049 980 Y 2C26 2060 15CE 1911 T9TT3 1 9C3 2006 2032 2042 1942 195/ 1637 18 37 1 £37 1763 1810 2 I t 8 1791 1823 2C75 1777 1766 580 906 881 880 933 1C2 8 1 7 38 1812 1797 1653 1768 1765 CCM.M. C. 9122 0 . 6 3 7 7 0 . 5 3 1 0 C .946 2 C .96 47 C . 6 6 5 0 0 . 6 6 4 5 C. E569 0 . 7 9 4 1 U.M4H 1 C. 7779 0 . 4 1 6 8 0 . 8 9 4 9 C . 7 7 6 4 0 . 9 1 9 6 , 7237 ,9587 56C8 .7418 ,9964 , 6583 1 - 0 . 8 4 6 C 0 . 1 2 5 2 - 0 . 1 0 7 1 - 0 . 0 6 3 3 =rrr65vr-- 0 . 6 844 0 . 1443 0 . 3 9 5 0 0.2384 0 . 7 4 8 9 2 C.1461 0 . 1 5 1 9 - 0 . 7 1 5 8 - C . 9 C 8 2 - tm "3T8 -- 0 . 2 6 7 5 - C . 0481 - C . 4 7 3 7 - C . 0 7 4 3 - C . C C 7 8 3 0 . 3 5 0 9 - 0 . 0 6 8 5 - 0 . 0 8 2 9 C . 3 1 4 5 - U . 2 3 3 3 - 0 . 7 6 2 3 - 0 . 7 3 7 0 - 0 . 3 - 9 9 9 0 . 3 2 0 1 - 0 . 2 6 4 1 U .64 26 - 0 . 4 3 4 1 - 0 . 0 5 2 8 0 .2142 0.8C9B 0 . 8 1 3 3 U . 1 U 5 1 -C .1583 - C . 6 0 2 7 0 . 2 C 7 4 - C . 03CC - 0 . 0 3 1 6 C 0 c c c -r 0 . 8 6 4 5 . 0 . 8 8 5 6 . C . 8665 0 . 7 7 5 4 C. 8235 1U33 1058 1C80 1C79 i c e i 631 1'J 1' 931 110 5 1093 11C7 1132 I f 7 3 IHJ3 1810 1793 1735 197C 1919 1535 1797 16C7 1965 1977 19£6 2f26 C. 5305-0.8967 C.9134 <-.:49c 0.4370 C.E564 f . S A s r -0. 0831 - 0 . 5 3 9 5 0 .3573 0 . 0 6 7 2 0 . 9 5 9 8 0 . 4 8 9 7 " - 0 . 0 4 6 6 - 0 . 0 6 7 1 - 0 .514 1 0 . 1 1 6 6 - 0 . 2 C99 —'J . 267H 0 . 3 1 5 8 0.1712 C .175C - 0 . 5 0 1 7 - C . 3 0 2 1 / 0 . 8 1 0 5 C. 8058 0 . 8 3 3 4 0 . 9 7 7 5 0 . 6 4 1 2 ' , ' . 4 1 4 1 , ' 0 . 4 3 / 1 0 . 2 3 2 5 - 0 . 2e37 - 0 . 8 5 9 1 - 0 . 6 5 8 7 - 0 : 6 2 6 1 -U.l'4 84 ' - C . 3 5 5 7 - 0 . 2 2 0 3 - 0 . 2 3 2 2 - C . 3 9 7 5 0 . 2 1 1 7 — C . b 6 0 0 0 . 1 1 2 2 - 0 . 0 8 0 1 - C . 7133 - 0 . 6 2 6 8 - 0 . 5 0 7 8 - C. UC59 C . 0 5 2 1 - 0 . 0 7 2 1 - C . 5557 C . 3 1 8 4 - 0 . 3 2 7 5 C. /216 - 0 . 7 6 6 7 - C . 5 2 C 9 G .26S5 C .1245 - C . 1432 0T0T98 - 0 . 7 2 0 7 - C . 1 9 3 6 - 0 . 2 1 7 5 0 .0953 0 . 4 9 C 9 (' . 2 5 6 3 -C .0256 0 . 5 7 1 9 - 0 . 1 5 5 3 0 . 3 2 3 4 - 0 . 1 3 3 9 - 0 . 1 3 1 2 - C . 3 3 8 8 - 0 . 1 2 7 7 C .21C8 0 . 2 8 8 2 - 0 . 1 6 5 7 — U . 6 5 2 1 - C . 8 8 9 0 - 0 .9286 0 • A 5 £ 5 0 . 0 2 C 9 C.5818 - C . U452 - 0 . 2 6 5 0 - C . 5 4 9 2 - 0 . 0 3 8 1 - 0 . 4 2 7 3 - 0 . 0 5 7 2 0803 D16A 0154 0555 0635 48 49 50 51 52 53 54 55 56 57 58 C649 Q677 C723 0114 0131 01 72 "7J2TJ5~ C215 Q245 025 3 0313 0343 1C79 1193 icce e86 1049 1C53 1C76 805 1C6 5 794 77 0 975 981 980 857 1033 ~5T" 60 61 ~E6V4 HS18 HS32 ~xrwr 61 S 996 2C4E 1949 2CC7 1914 1R94 18S4 1894 1872 1 821 193C 1809 Terr 1699 1 796 1764 1840 1835 - T 8 7 5 -1959 219C C . 6 3 7 7 0 . 8 9 4 6 0 . 4 8 8 7 C. 5926 0 . 9 0 2 2 C . 9 3 3 4 -C . 9 6 7 7 0 . 9 6 9 8 0 . 8 8 5 3 C . 9 4 2 0 0 . 9 8 5 8 — C r F G T B -, 0 . 8 9 5 8 0 . 8 4 9 9 0 . 8 1 5 6 0 . 7 3 7 0 C. 491 9 C . 1 : 5 9 4 ' " 0 . 7 6 9 5 C .9291 VAP IANCF CUM.VAR. -D .774C - 0 . 6 2 92 0 . 0 7 2 7 0 . 2 0 3 7 - 0 . 84 05 0 . 2 2 9 3 L.3584 - 0 . 0 1 2 9 - C . 4528 0 . 0 4 9 7 C .1129 - C . 3 7 1 3 ( ' .2432 0 . 1 4 7 6 0 . 6 5 1 6 - 0 . 6 6 5 0 0 . 1 4 3 5 0. 42e7 (j.a /84 0. 2058 - 0 . 7 0 7 3 0 . 854 9 0. 9189 0 . 6 4 1 1 C . 3 4 6 2 C. 7046 0 . 4 9 5 5 C . 2 6 8 9 0. 2720 C . 4 4 8 3 -o.o/H'r 0 . 6 4 4 2 - 0 . 0 9 4 B - 0 . 1788 - 0 . 4 4 3 8 - 0 . 4 4 6 8 -U. 3TT5-- 0 . 2 1 8 9 - 0 . 4 1 3 1 2 5 . 1 9 7 2 5 . 1 9 7 — C . 3 4 9 C C . 0 5 4 4 -0 .5151 C . 7 0 7 2 C .5688 C.4771 CTTBTT-- 0 . 4 2 5 8 C .0006 1 5 . 6 7 7 4 0 . 8 7 4 - 0 . 1 4 / 2 - 0 . 2 7 2 4 0 . 4 6 3 3 - 0 . 2 4 8 1 - 0 . 1 5 C 3 0 . 5 2 2 3 0 .6B49 • 0 . 0 4 3 5 0 . 0 2 3 8 - 0 . 3 5 1 4 o .4653 - 0 . 0 8 0 2 - 0 . 2733" 0 .6931 0 .0666 14 .933 5 5 . 8 0 7 4 0 . 2 2 8 1 0 . 7 7 0 9 - 0 . 0 1 3 7 0 .1360 •^ Tjr65r5— - 0 . 5 9 6 6 - 0 . 3 1 4 1 0 .3514 0 . 8 3 1 9 0 .4C44 — U . I i i i - 0 . 2 1 2 2 0. 1154 0 . 8 7 1 1 0 .3327 0 . 1 2 7 0 — 0 . 7 6 6 3 - 0 . 7 6 7 9 - 0 . 5405 0 . 8 6 9 0 0. 6887 0 .1112 .0 .U/B1 0.e573 0 .9265 - 0 . 2 2 1 2 0. 53*7 0 .7030 -a.lB^y 0 . 0 6 2 0 - 0 . 1 2 R 8 - C . C789 0 . 2 8 8 9 - 0 . 5 6 5 1 - U . 2 4 1 2 - 0 . 3 1 3 5 ^ 0 . 3 9 0 4 - 0 . 1459 - 0 . 5 8 7 4 - 0 . 4 7 4 7 -0.36341 0 . 4 6 8 9 0 .5C56 0 . 0 4 9 7 - 0 . 5 0 2 9 0. 7266 U. 142 / - 0 . 5 9 5 5 - O . C 9 7 0 0 . 1 4 3 6 0.0324 0.3180 - 0 . 2 9 3 0 - 0 . 6 8 9 8 - 0 . 7 5 9 5 - 0 . 4 0 0 0 0 .0052 0 .2411 -=OTTC73-- 0 . 2 4 4 5 - 0 . 8 6 8 4 24 .947 8 0 . 7 54 ^ f A ^ T T f W f T v ^ S C T T j r T r ^ ^ VARIMAX FACTOR SC OR F MATRIX FACTOR VAKIAULE 81 cn M pn - 7 » r AG MN C. 9C9 5 - 1 . 356', - 0 . 388') - c . w u - - i T n n v -1 .141 1 -0.44U6 C . l r , 2 3 - 1. 5509 - 1 . 3 9 5 ? 0 .9V90 — 1 V 2 3 C 0 " 0 . 4 1 39 - 0 . 2 0 2 5 -1.2841 -1.8750 -0.6237 0.2649 0 .2777 - 1 . 1781 -0.0801 -0.BK21 •-C.-4755 ~0:?761 ' -1.2566 -0.0075 1.7537 -1 .0769 235 APPENDIX J VARIMAX FACTOR MATRIX, VEIN PYRITE A . P A N T E L E Y E V — F A C T O R A N A L Y S I S — 8 V A R I A B L E S — K A R C H 0 6 1 9 7 2 -V A R I M A X F A C T O R K A T R I X NO I O X Y C C M M . 1 2 3 4 1 V 1 5 9 1 C 0 9 2 0 0 4 C . e 8 3 1 - 0 . 1 5 6 9 0 . 8 5 7 6 0 . 0 1 9 1 0 . 3 5 0 2 2 V J 2 1 9 2 2 2 0 1 7 0 . 9 9 2 2 0 . 3 3 2 1 - C . 2 5 0 0 0 . 4 6 8 1 0 . 1 3 4 7 3 V 1 4 2 1 C 7 8 1 8 3 7 C . 7 6 1 8 0 . 3 6 9 . 1 0 . 0 7 0 8 0 . 7 5 4 4 - 0 . 2 2 6 8 4 V 2 3 5 1 0 4 9 1 7 7 7 C . S 2 8 3 - 0 . 8 1 6 8 C . C C 6 8 0 . 3 5 9 2 - 0 . 3 6 3 5 V 2 4 3 9 8 1 1 7 9 6 0 . 9 3 4 f - 0 . 9 5 4 7 - 0 . 1 0 4 9 - 0 . 0 2 7 8 0 . 1 0 7 0 6 V 2 5 1 S R C 17 f t 0 . 9 6 6 6 - 0 . 6 7 7 1 - 0 . 6 2 1 1 - 0 . 1 7 1 8 0 . 3 0 4 7 7 V 2 6 4 9 8 0 1 7 3 8 C . - 5 3 7 8 - - . 0 . 1 1 1 6 0 . 1 9 C 9 - 0 . 1 4 1 8 0 . 9 3 2 1 8 V 3 3 A 1 0 ? 8 1 7 6 5 C . 9 8 3 1 - 0 . 3 7 0 5 - 0 . 2 3 4 8 - 0 . 8 8 7 5 0 . C 5 4 2 9 V 3 5 6 1 0 5 8 1 P 1 C C . <=274 0 . 3 7 0 C 0 . 1 3 3 0 0 . 2 C 8 3 - n . 3 3 0 7 1 0 V 3 7 3 1 0 7 9 1 7 3 5 0 . 8 4 2 6 - 0 . 1 9 3 1 0 . 8 6 4 4 0 . 1 0 2 7 0 . 2 9 1 5 11 V 4 3 3 K 8 l 1 c . 7 C ' 0 . 9 2 lb " - 0 . 3 5 6 4 - 0 . / 0 4 9 0 . 4 4 6 8 . 'i'i'i'i 12 V 6 3 2 6 3 1 1 9 1 9 C.9148 0 . 9 36 2 - C . 1 X 3 9 - 0 . 0 2 5 1 - 0 . 1 0 3 8 13. V 6 8 6 1 0 1 7 1 5 3 5 0 . 9 6 6 4 0 . 2 2 5 9 - C . 4 3 6 9 - 0 . 8 4 5 4 0 . C 9 9 0 1A V 6 9 4 . <=81 1 8 2 5 0 . 7 9 1 4 - 0 . 5 9 C 7 0 . 6 5 0 7 0 . 0 5 4 3 0 . 1 2 6 9 1 5 V 7 0 5 9 3 1 1 8 5 4 C . 8 7 6 9 - C . 2 9 8 2 0 . 8 2 C 6 0 . 2 94 8 - 0 . 1 6 6 5 1 6 V 7 1 5 9 3 0 1 7 9 8 0 . 8 3 6 6 - 0 . 1 5 0 3 0 . 8 4 9 0 0 . 2 7 8 8 - 0 . 1 2 4 5 17 V 7 1 3 93? I 7 9 t C. 6 2 6 0 o . r o 11 - 0 . 5 2 8 5 -0 . ~dOO<£ 18 V H S 1 1 0 3 5 2 2 < 2 C . 7 9 5 7 - 0 . 3 4 1 1 - 0 . 8 1 1 2 - 0 . 0 1 5 8 0 . 1 4 4 9 19 V H S 2 111 5 2 1 7 8 C . 8 0 2 3 0 . 6 5 9 1 - 0 . 4 8 7 1 C . 3 4 7 5 0 . 0 9 9 4 2 0 V H S 3 5 1 2 1 8 7 7 C . "5316 0 . 2 2 2 1 0 . 3 4 7 3 - 0 . 6 8 4 9 - 0 . 5 4 0 9 VAR I A N C E 2 9 . 5 9 3 3 0 . 5 2 1 1 8 . 8 0 9 1 0 . 2 1 0 C C M . V A R . 2 9 . 5 9 3 6 0 . 1 1 4 7 8 . 9 2 3 8 9 . 1 3 3 A . P A N T E L E Y E V — F A C T O R ANAL.VS I S -VAR IMAX F A C T O R SCORE M A T R I X - 8 V A R I A B L E S — M A R C H 0 6 1 9 7 2 — F A C T O R VAR I A f l L E 2 81 CO N I . C U pe ZN AG MN 1 . 1 8 7 2 0 . 3 2 0 2 0 . 0 6 1 . 1 - C . 5 8 2 1 - C . 6 3 9 9 1 . 8 5 1 7 1 . 8 6 2 8 0 . 6 5 2 6 1 . 6 0 7 4 - 0 . 1 4 3 6 1 . 2 4 0 3 0 . 2 1 8 2 1 . 2 4 9 3 0 . 3 7 3 9 0 . 6 6 8 7 - 0 . 1 0 7 5 1 . 0 5 3 4 0 . 0 4 8 4 - C . 2 4 2 4 C . 6 0 0 7 - 0 . 1 6 9 1 0 . 2 1 4 5 1 . 3 2 8 2 - 2 . 0 7 8 6 - 0 . 1 5 C 6 0 . 4 5 7 3 0 . 3 7 5 4 - 0 . 7 3 1 4 0 . 6 2 6 3 - 0 . 1 8 8 1 - 2 . 1 1 3 6 - 1 . 5 7 9 1 

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