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Geochemistry of fluid inclusions and hydrothermal alteration in vein- and fracture-controlled mineralization,… Bloom, Mark Stephen 1983

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GEOCHEMISTRY OF FLUID INCLUSIONS AND HYDROTHERMAL ALTERATION VEIN- AND FRACTURE-CONTROLLED MINERALIZATION, STOCKWORK '• MOLYBDENUM DEPOSITS by MARK STEPHEN BLOOM B S c , New Mexico I n s t i t u t e of Mining and Technology, 1972 MSc, New Mexico I n s t i t u t e of Mining and Technology, 1975 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department - of Geological Sciences We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February 1983 © Mark Stephen Bloom, 1983 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t 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 f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of 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 o f my department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department o f Geological Sciences  The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date 16 April, 1983 Abstract Molybdenum mineralization and coextensive a l t e r a t i o n at Questa, Hudson Bay Mountain, and Endako occur in single/composite v e i n l e t s which exhibit d i s t i n c t i v e a l t e r a t i o n assemblages and paragenesis. F l u i d inclusion populations from each ve'inlet type are compositionally d i s t i n c t . Early f l u o r i n e r i c h , b i o t i t e - s t a b l e a l t e r a t i o n i s associated with hypersaline brines. These inclusions homogenize most frequently by h a l i t e d i s s o l u t i o n at temperatures from 350°-600°+C. Molybdenum miner a l i z a t i o n also coincides with 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 and inclusions having moderate to high s a l i n i t y and lower (£350°C) temperatures of entrapment. Ubiquitous lo w - s a l i n i t y inclusions in addition to inclusion types which characterize each v e i n l e t type suggest superposition of meteoric-dominated convective c i r c u l a t i o n . These data are evidence for magmatic fluids, separate in both space and time from ingress of meteoric hydrothermal solutions. Hypersaline brines were precursors to those solutions which p r e c i p i t a t e d d i s t i n c t i v e a l t e r a t i o n asso-c i a t i o n s , and formed by boiling/condensation of f l u i d s released by episodic fracturing and ensuing adiabatic decompression. Highly variable and complex compositional zoning charac-t e r i z e s (K,Na)-feldspar, b i o t i t e , and muscovite s o l i d solutions Although zoning within i n d i v i d u a l grains i s common, composition a l trends in the averaged compositions can be correlated with both position in the emplacement sequence and textural charac-t e r i s t i c s of these a l t e r a t i o n phases. A l k a l i feldspars coexist ing in v e i n l e t s constitute se n s i t i v e geothermometers which pro-vide r e l i a b l e depositional temperatures (£350°C). X(annite) i s highest in magmatic b i o t i t e , intermediate in b i o t i t e which exhi-b i t s replacement textures, and s i g n i f i c a n t l y lower 0 in veinlet assemblages. X(fluorphlogopite) systematically increases from magmatic to v e i n l e t b i o t i t e associations; f(H 20/HF) r a t i o s com-puted from these compositions predict log f(HF) of approximately -4.0. Departures from muscovite stoichiometry p e r s i s t among d i f f e r e n t v e i n l e t assemblages and textural associations, but were not sampled with enough r e g u l a r i t y to define trends in spa-t i a l d i s p o s i t i o n . A l t e r a t i o n geochemistry indicates that mineralization oc-curred from solutions e q u i l i b r a t e d with v e i n l e t assemblages. Fluid-mineral e q u i l i b r i a computations imply chemical character-i s t i c s of the ore-forming solutions similar to those measured in high-temperature geothermal f l u i d s . Molybdenite s o l u b i l i t y shows extreme dependence on temperature, pH, f ( 0 2 ) , and f(HF). Molybdenum concentrations up to lOOppm are predicted in oxidized solutions at 350°C. In near-neutral solutions s i g n i f i c a n t amounts of molybdenum are transported as Mo03F" and HMoO,", with lesser amounts as H 2MoO f t° and Mo02*. Chloride and s u l f i d e com-plex concentrations are not s i g n i f i c a n t . Mo03F" becomes the primary transporter of molybdenum in acid solutions and high f(HF). Table of Contents A b s t r a c t i i L i s t of Tables v i i L i s t of F i g u r e s : v i i i Acknowledgements x Chapter I CHEMISTRY OF INCLUSION FLUIDS: STOCKWORK MOLYBDENUM DEPOSITS FROM QUESTA, NEW MEXICO, AND HUDSON BAY MOUNTAIN AND ENDAKO, BRITISH COLUMBIA 1 INTRODUCTION 1 GEOLOGY OF QUESTA, HUDSON BAY MOUNTAIN, AND ENDAKO 2 COGENETIC INTRUSIVE ROCKS 3 ALTERATION AND MINERALIZATION 4 1. F r a c t u r e C o n t r o l 4 2. C r o s s c u t t i n g R e l a t i o n s 5 a. Pre-molybdenite Quartz 6 b. Q u a r t z - K - f e l d s p a r - B i o t i t e 6 c. Q u a r t z - M o S 2 / Q u a r t z - S e r i c i t e - P y r i t e - M o S 2 7 FLUID INCLUSION PETROLOGY 8 INTRODUCTION 8 CLASSIFICATION AND DESCRIPTION OF FLUID INCLUSIONS 10 DISTRIBUTION OF THE FLUID INCLUSIONS 12 HOMOGENIZATION DATA 14 INTRODUCTION 14 QUESTA, NEW MEXICO 15 HUDSON BAY MOUNTAIN, BRITISH COLUMBIA 17 ENDAKO, BRITISH COLUMBIA 18 INTERPRETATION OF THE FLUID INCLUSION DATA 19 SALINITIES OF INCLUSION FLUIDS 19 ESTIMATES OF PRESSURE AND DEPTH 22 TEMPERATURE AND SALINITY DISPERSION 30 PRESSURE CORRECTION 32 SOURCE AND EVOLUTION OF THE INCLUSION FLUIDS 33 EVOLUTION OF INCLUSION POPULATIONS 36 CONCLUSIONS 42 Chapter II GEOCHEMISTRY OF HYDROTHERMAL ALTERATION 44 INTRODUCTION 44 ALTERATION PETROGRAPHY 45 RELATIVE AGE RELATIONS 45 TEXTURAL VARIATIONS 46 V METHOD OF INVESTIGATION AND ANALYTICAL TECHNIQUES 49 DATA PRESENTATION FOR MULTICOMPONENT SOLID SOLUTIONS ..52 INTRODUCTION 52 COMPONENTS AND COMPOSITIONAL SPACE .....53 1. D i o c t a h e d r a l Layer S i l i c a t e s 55 2. T r i o c t a h e d r a l Layer S i l i c a t e s 58 ACTIVITY-COMPOSITION RELATIONS 61 ALKALI FELDSPARS 61 SCHEELITE-POWELLITE 65 WHITE MICA 67 TRIOCTAHEDRAL LAYER SILICATES 68 DISCUSSION 69 BINARY SOLID SOLUTIONS 69 MUSCOVITE/SERICITE SOLID SOLUTIONS 72 BIOTITE SOLID SOLUTION 76 CONCLUSIONS 86 Chapter III THEORETICAL PREDICTION OF FLUID-MINERAL EQUILIBRIA 89 INTRODUCTION 89 THEORETICAL CONSIDERATION OF THE THERMODYNAMIC MODEL ..90 THERMOCHEMICAL DATA AND CONVENTIONS 90 COMPUTATION OF FLUID CHEMISTRY 93 LIMITATIONS OF THE MODEL 95 ASSERTIONS AND PHYSICAL DESCRIPTION OF THE MODEL 95 TEMPERATURE-PRESSURE 96 SALINITY, IONIC STRENGTH, AND A(H 20) 97 THERMODYNAMIC COMPONENTS AS CONSTRAINTS FOR SOLUTE SPECIES 98 DISCUSSION OF FLUID-MINERAL EQUILIBRIA 105 ACTIVITY RATIOS OF SOLUTE SPECIES 105 1. V o l a t i l e Species 105 2. [ a ( K + ) / a ( H + ) ] and [ a ( F e 2 + ) / a ( H + ) 2 ] 107 3. [ a ( M g 2 + ) / a ( H + ) 2 ] and [ a ( C a 2 + ) / a ( H + ) 2 ] 109 4. [ a ( A l 3 + ) / a ( H + ) 3 ] and a(H,SiO,) 114 AQUEOUS MOLYBDENUM SPECIATION 117 ABSOLUTE SOLUTE CONCENTRATIONS 127 1. Hydrogen Ion C o n c e n t r a t i o n 129 2. E r r o r Propogation , 129 3. Molybdenum Co n c e n t r a t i o n and P r e c i p i t a t i o n Mechanisms .130 CONCLUSIONS 135 LITERATURE CITED 137 v i APPENDIX A - MEAN ELECTRON MICROPROBE ANALYSES OF HYDROTHERMAL ALKALI FELDSPARS 147 APPENDIX B - MEAN ELECTRON MICROPROBE ANALYSES OF HYDROTHERMAL TRIOCTAHEDRAL MICAS 152 APPENDIX C - MEAN ELECTRON MICROPROBE ANALYSES OF HYDROTHERMAL DIOCTAHEDRAL MICAS 159 APPENDIX D - MEAN ELECTRON MICROPROBE ANALYSES OF HYDROTHERMAL AMPHIBOLES FROM HUDSON BAY MOUNTAIN 162 APPENDIX E - MEAN ELECTRON MICROPROBE ANALYSES FOR SCHEELITE-POWELLITE FROM HUDSON BAY MOUNTAIN 163 v i i L i s t of Tables I. Average WDS e l e c t r o n microprobe analyses of s o l i d so-l u t i o n phase standards 51 I I . S o l i d s o l u t i o n d e s c r i p t o r s 56 I I I . Mean WDS e l e c t r o n microprobe analyses of hydrothermal white mica s o l i d s o l u t i o n s 57 IV. Mean WDS e l e c t r o n microprobe analyses of hydrothermal b i o t i t e s o l i d s o l u t i o n s 59 V. A c t i v i t y - c o m p o s i t i o n r e l a t i o n s of n a t u r a l s o l i d s o l u -t i o n s 62 VI. Mean WDS e l e c t r o n microprobe analyses of hydrothermal a l k a l i f e l d s p a r s o l i d s o l u t i o n s 63 V I I . Mean WDS e l e c t r o n microprobe analyses of s c h e e l i t e s o l i d s o l u t i o n s from Hudson Bay Mountain 66 V I I I . Thermochemical data f o r molybdenum and f l u o r i n e -b e a r i n g m i n e rals 92 IX. D i s s o c i a t i o n a l e q u i l i b r i a f o r thermodynamic components and e x p r e s s i o n s f o r s o l u t e a c t i v i t i e s 100 X. Thermochemical data f o r gases and aqueous molybdenum s p e c i e s 119 XI. Computed f l u i d - m i n e r a l e q u i l i b r i a at 350°C 128 XI I . E r r o r propogation i n the d i s t r i b u t i o n of aqueous spe-c i e s u sing the Monte C a r l o method ; 131 v i i i L i s t of Figures 1. F l u i d Inclusion Types Observed in Fracture-Controlled, Molybdenum-Mineralized Veinlets and Stockworks 11 2. F l u i d Inclusion Homogenization ( f i l l i n g ) Temperatures 16 3. Temperature-Salinity Determinations for Types A, C, and D Inclusion Fluids 20 4. Compositions of Hypersaline Fluids and the "Halite Trend" for Type D Inclusion Fluids 23 5. Vapor Pressure Estimates for Specific Type C and D Inclusions or Inclusion Pairs 24 6. F l u i d Inclusion Populations from Questa (B), Hudson Bay Mountain (A), and Endako(C) 26 7. S o l u b i l i t y Curve Approximating the Questa and Hudson Bay Mountain Halite Trends in the NaCl-KCl-H 20 System .37 8. Temperature-Pressure Diagram Showing the Effect of Isenthalpic Cooling 41 9. D i s t r i b u t i o n of End Members in Binary Sol i d Solutions 70 10. D i s t r i b u t i o n of End Members in Hydrothermal White Mica S o l i d Solution 73 11. D i s t r i b u t i o n of End Members' in Hydrothermal B i o t i t e S o l i d Solution 77 12. Compositional Spaces for Hydrothermal Mica S o l i d Solutions 82 13. Phase relations in the system MoS 2-FeS~FeS 2-H 20 in the presence of steam-saturated aqueous solution at 350°C 106 14. Phase relations in the system K 20-A120 3-Si02-H 20-HF in the presence of quartz and steam-saturated aqueous solu-tion at 350°C 108 15. Phase Relations in the System K 20-Al 20 3-Si0 2-FeO-MgO-H20-H2S-HC1-HF in the Presence of Quartz and Steam-Saturated Aqueous Solution at 350°C 110 16. Phase Relations in the System K 20-A1 20 3-Si0 2-Fe0-Mg0-ix H20-H2S-HC1-HF in the Presence of Quartz and Steam-Saturated Aqueous Solution at 350°C .. 111 17. Phase Relations in the System K 20-A1 20 3-Si0 2-FeO-MgO-H20-H2S-HC1-HF in the Presence of Quartz and Steam-Saturated Aqueous Solution at 350°C 113 18. Phase Relations in the System K 20-A1 20 3-Si0 2-FeO-MgO-H20-H2S-HC1-HF in the Presence of Quartz and Steam-Saturated Aquoues Solution at 350°C 115 19. Phase Relations in the System K 20-A1 20 3-Si0 2-FeO-MgO-H20-H2S-HC1-HF in the Presence of Steam-Saturated Aqueous Solution at 350°C 116 20. A c t i v i t y - A c t i v i t y Diagrams Depicting the Predominant Oxidized Molybdenum Species in Steam-Saturated Aqueous Solution at 350°C 122 X Acknowledgements The research reported in t h i s paper reports the author's Ph.D: di s s e r t a t i o n at The University of B r i t i s h Columbia, Vancouver. I am indebted to T.H. Brown for h i s guidance and many useful discussions throughout t h i s study. I also wish to thank H.J. Greenwood, C.I. Godwin, A.E. Soregaroli, and E.H. Perkins, and others among the friends and colleagues at U.B.C. who provided helpful suggestions, assistance and encouragement throughout the course of t h i s re-search. Various aspects of the project were supported by the National Research Council of Canada and the Australian Research Grants Committee. The computer centres of The University of B r i t i s h Columbia, Vancouver, and Monash University, Melbourne, provided computing funds for t h i s project. F i n a l l y , I would l i k e to express my appreciation to geologists M.P. Martineau and G.H. Heinemeyer of Kennecott Copper Corporation, and to T. Gregory and D. Mann at the Los Alamos S c i e n t i f i c Laboratory for their valuable as-sistance in various parts of the study and for off e r i n g many help f u l suggestions for improvement. \ 1 I. CHEMISTRY OF INCLUSION FLUIDS: STOCKWORK MOLYBDENUM DEPOSITS  FROM QUESTA, NEW MEXICO, AND HUDSON BAY MOUNTAIN AND ENDAKO, BRITISH COLUMBIA INTRODUCTION The importance of superposition and interaction of succes-sive hydrothermal events in modifying individual ore-related processes and obscuring the source(s) of ore-forming f l u i d s in porphyry-type deposits i s now commonly recognized. The associa-tion of molybdenum mineralization with composite rh y o l i t e por-phyries and porphyritic granites and the genetic r e l a t i o n to multiple intrusive events are firmly established (Wallace et a l . , 1968, 1978; Sharp, 1978, 1979). The close s p a t i a l and tem-poral a f f i n i t y of these intrusions with molybdenum mineraliz-ation i s prima facie evidence for a s i g n i f i c a n t magmatic c o n t r i -bution to the ore-forming f l u i d s . F l u i d inclusion studies of well-preserved a l t e r a t i o n assem-blages in porphyry-type deposits (Preece and Beane, 1979; Wilson et a l . , 1980) suggest, that hydrothermal solutions may be of both di r e c t magmatic and subsequent meteoric o r i g i n . Detailed stu-dies of molybdenum-mineralized stockworks reveal a cross-cutting sequence of veinlets and associated a l t e r a t i o n which recurs with such frequency as to imply similar f l u i d s and processes common to the evolution of these porphyry-type deposits. They provide an excellent opportunity to obtain information on the hydrother-mal solutions and to speculate on the processes which produced 2 stockwork molybdenum orebodies. The present work describes reconnaissance f l u i d inclusion studies of evolving fracture-controlled mineralization, a l t e r a -t i o n , and related f l u i d s in the Questa, New Mexico (36° 42'N, 105° 29'W), Hudson Bay Mountain (54° 49'N, 125° 07'W) and Endako, B r i t i s h Columbia (54° 02'N, 125° 07'W) orebodies. Samples used in the study were coll e c t e d from areas of the Questa and Endako deposits that were a c t i v e l y mined during 1976 (the 8480 and 3069 benches, respectively) and from d r i l l holes c o l l a r e d on the 3500 exploration l e v e l at Hudson Bay Mountain. GEOLOGY OF QUESTA, HUDSON BAY MOUNTAIN, AND ENDAKO General c h a r a c t e r i s t i c s of the Questa, Hudson Bay Mountain, and Endako deposits and t h e i r related intrusive rocks suggest that they are similar to stockwork molybdenum systems elsewhere in North America (Clark, 1972; Soregaroli and Sutherland Brown, 1976). Each d i f f e r s in one or more respects from the configura-t i o n , emplacement, or paragenesis associated with well-preserved and documented molybdenum orebodies (Wallace et a l . , 1968, 1978). These differences as outlined below are ref l e c t e d by the observed f l u i d inclusion populations and interpretations of the inclusion f l u i d chemistry. 3 Coqenetic Intrusive Rocks The Questa and Hudson Bay Mountain deposits are associated with f e l s i c , epizonal to hypabyssal intrusive complexes. At Questa, mid-Tertiary intrusions penetrate a column of andesite flow-breccias, c r y s t a l - l i t h i c t u f f s , and s i l i c i c ignimbrites. By contrast, a late-Oligocene plug at Hudson Bay Mountain sharp-ly and discordantly intrudes a pre-molybdenite granodiorite sheet, i t s e l f intrusive into Jurassic pyroclastic and sedimen-tary rocks. The Endako mineralization i s l o c a l i z e d e n t i r e l y within a zoned Jurassic batholith without apparent s p a t i a l r e l a -tion to an intrusion of stock- or plug-like extent. Intrusions associated with Questa and Hudson Bay Mountain are characterized by a variety of textural rock types including a p l i t e , porphyries and crowded porphyries with variable phenocryst/ groundmass r a t i o s , and equigranular to seriate bio-t i t e granites and quartz monzonites. The porphyries and crowded porphyries commonly contain quartz, K-feldspar, and minor bio-t i t e phenocrysts in aphanitic to a p l i t i c groundmasses and in bulk compositions approximating the quartz-orthoclase-albite ternary minimum. Small systematic differences in bulk composi-tion exist among the textural variations which imply a dynamic and strongly d i f f e r e n t i a t i n g source intrusion (Ishihara, 1967; Hudson et a l . , 1979). C l a s t i c and fragmental textures are commonly observed where s t r u c t u r a l l y high parts of intrusive complexes are preserved (e.g., Questa). Porphyries are dominant at intermediate depths and are truncated by deep-seated g r a n i t i c rocks (e.g., Questa 4 and Hudson Bay Mountain). I n t e r m i n e r a l dikes and b r e c c i a s (Kirkham, 1971) are common f e a t u r e s which c l e a r l y e s t a b l i s h a c l o s e s p a c i a l and g e n e t i c r e l a t i o n between the i n t r u s i v e e v e n t ( s ) , m i n e r a l i z a t i o n , and a l t e r a t i o n . The Endako stockwork m i n e r a l i z a t i o n occurs wholly w i t h i n an e q u i g r a n u l a r to weakly s e r i a t e quartz monzonitic phase (Endako Quartz Monzonite) of the l a t e - J u r a s s i c Topley I n t r u s i o n s (Kimura et a l . , 1976). Hypabyssal a p l i t e , g r a n i t e porphyry and q u a r t z -f e l d s p a r porphyry d i k e s , a l l of pre-molybdenite r e l a t i v e age and c h e m i c a l l y as w e l l as m i n e r a l o g i c a l l y s i m i l a r to o r e - r e l a t e d i n t r u s i o n s at Questa, Hudson Bay Mountain and other molybdenum-m i n e r a l i z e d systems, i n t r u d e the Endako Quartz Monzonite. Dike i n t r u s i o n i s an immediate p r e c u r s o r to the ore-forming e v e n t ( s ) . M i n e r a l i z a t i o n and a l t e r a t i o n . , while p o s s i b l y r e l a t e d to l a t e stages of the same magmatic episode that produced the Toply I n t r u s i o n s , are not c o n c l u s i v e l y c o g e n e t i c with the Endako Quartz Monzonite. 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 1 . F r a c t u r e C o n t r o l Questa, Hudson Bay Mountain, and Endako each show evidence f o r m u l t i p l e f r a c t u r i n g events with consanguineous m i n e r a l i z -a t i o n and a l t e r a t i o n . Ingress of ore-forming s o l u t i o n s and geometry of i n d i v i d u a l orebodies was l a r g e l y c o n t r o l l e d by de-velopment of f r a c t u r e s , v e i n l e t s , and m u l t i p l e v e i n systems. At Questa, well-developed v e i n systems p a r a l l e l the c o n t a c t between a n d e s i t e and a p l i t e porphyry i n an e a s t e r l y - t r e n d i n g , south-dip-5 ping zone within the inferred source intrusion (Carpenter, 1968). Barren to weakly-mineralized stockworks have developed immediately adjacent to and separating the major veins. The Hudson Bay Mountain deposit contains stockworks immediately above, and gently-inclined vein systems within and largely par-a l l e l to the granodiorite sheet (Bright and Jonson, 1976). The r h y o l i t e porphyry plug intrusive into the granodiorite i s capped by a stockwork of pre-molybdenite v e i n l e t s . The Endako orebody, by comparison, i s a complex array of mineralized fractures dominated by continuous, prominent vein systems without r e l a t i o n to l i t h o l o g i c boundaries. Major veins are surrounded by complex veinlet arrays which form stockworks complementing major vein trends (Kimura et a l . , 1976). 2. Crosscutting Relations Fracture i n t e n s i t i e s in the orebodies were generally not s u f f i c i e n t to produce widespread coalescing of v e i n l e t s and a l -teration envelopes or to form pervasive zones of a l t e r a t i o n . In each deposit, molybdenum mineralization and coextensive a l t e r a -tion occur as single and composite veinlets which exhibit an ordered sequence of emplacement. Among the samples studied, f i v e main mineralization-alteration associations have been ob-served: • (1) pre-molybdenite quartz; • (2) quartz-biotite-K-feldspar-molybdenite; • (3) quartz-molybdenite; • (4) quartz-sericite-pyrite-molybdenite; and 6 • (5) quartz-base metal s u l f i d e v e i n l e t s . The e f f e c t s of individual hydrothermal events may be se-parated and i d e n t i f i e d with these s p e c i f i c v e i nlet assemblages. A. Pre-molybdenite Quartz Pre-molybdenite, barren quartz from vei n l e t s and di f f u s e s i l i c i f i e d envelopes has been observed from each deposit. In areas of high fracture density the veinlets increase in concen-t r a t i o n , coalesce and form pervasive zones of s i l i c i f i c a t i o n . Such a zone of s i l i c a replacement at Hudson Bay Mountain sug-gests that f l u i d s were introduced through a stockwork l o c a l i z e d at the apex of the rhyolite porphyry plug. The e a r l i e s t recog-nized hydrothermal event at Questa i s a similar stockwork of barren quartz v e i n l e t s , there l o c a l i z e d in a p l i t e porphyry im-mediately beneath the contact between the source intrusion and andesite. Pre-molybdenite quartz vei n l e t s are present in the footwall of the Endako orebody, but unlike Questa and Hudson Bay Mountain they are associated with d i s t i n c t i v e K-feldspar- and b i o t i t e - s t a b l e a l t e r a t i o n envelopes. B. Quartz-K-feldspar-Biotite Quartz-K-feldspar-biotite "potassic" assemblages in the veinlet sequence mark the onset of molybdenum mineralization. K-feldspar occurs in thin selvages along fractures and irr e g u l a r patches in v e i n l e t s , and in pervasive replacement of host rock separating v e i n l e t s . Concentrations of secondary minerals in h a i r l i n e fractures, and wide-spread replacement of both ground-7 mass and phenocryst feldspars by b i o t i t e , K-feldspar and magne-t i t e , are recognized in each of the deposits. Development of the potassic assemblage, although favored by the bulk rock compositions (Bloom and Brown, 1977), is not always associated with the e a r l i e s t ore-forming event. For example, b i o t i t e - s t a b l e a l t e r a t i o n preceded molybdenum mineral-ization at Questa and Hudson Bay Mountain. Composite vein l e t s with quartz-molybdenite i n t e r i o r s at Questa frequently exhibit barren, biotite-bearing selvages and envelopes. Veinlets which pre-date molybdenum mineralization at Hudson Bay Mountain also exhibit b i o t i t e selvages. By contrast, b i o t i t e - s t a b l e a l t e r a -tion i s coextensive with mineralization at Endako. C. Quartz-MoS 2 /Quartz-Sericite-Pyrite-MoS 2 One or more stages of quartz-molybdenite and quartz-s e r i c i t e - p y r i t e ± molybdenite mineralization are superimposed on the barren quartz and potassic v e i n l e t s , and are coeval with the bulk of the stockwork mineralization. The abundance and d i s t r i -bution of the " p h y l l i c " a l t e r a t i o n assemblage i s controlled by fracture-related veins and stockworks. Prominent veins at Questa have developed wide p h y l l i c envelopes surrounding the potassic assemblages, and coalescing a l t e r a t i o n envelopes have produced l o c a l l y pervasive q u a r t z - s e r i c i t e - p y r i t e zones. Molybdenite-bearing v e i n l e t s at Hudson Bay Mountain are of two types distinguished by textural and mineralogical features. The e a r l i e r veinlets contain fine-grained disseminated molybdenite in layers alternating with barren quartz ("ribbon veins"). 8 Gangue minerals other than quartz are uncommon, and the veinlets rarely have appreciable a l t e r a t i o n haloes. The later v e i n l e t s usually cut across and reopen e a r l i e r v e i n l e t s , but l o c a l l y also exhibit contrary cross-cutting or gradational relations along a single v e i n l e t . They contain coarse molybdenite flakes and ro-settes associated with minor amounts of s e r i c i t e , K-feldspar and scheelite i r r e g u l a r l y d i s t r i b u t e d in coarse-grained, vuggy quartz. Quartz-sericite-pyrite a l t e r a t i o n envelopes surround these v e i n l e t s . Hydrothermal events related to Endako mineralization are also defined by a sequence of r e l a t i v e veinlet ages; molybdenum mineralization i s associated with v e i n l e t s having both early potassic and crosscutting p h y l l i c a l t e r a t i o n envelopes. FLUID INCLUSION PETROLOGY Introduction The major vein systems at Questa, Hudson Bay Mountain and Endako exhibit ribbon texture and l o c a l c r u s t i f i c a t i o n . They appear to have formed by d i l a t i o n and f i l l i n g of pre-existing v e i n l e t s . Episodic reopening of the prominent veins permitted ingress of f l u i d s throughout the evolution of the respective ore-forming systems, and resulted in complex overlapping of f l u i d inclusion populations. F l u i d inclusions in stockwork quartz v e i n l e t s which are consistently related to molybdenite have been studied wherever possible. These ve i n l e t s formed by non-destructive d i l a t i o n and f i l l i n g , and presented more homoge-neous inclusion populations. 9 It is very d i f f i c u l t to demonstrate a primary o r i g i n for s p e c i f i c inclusions (cf. Roedder, 1971). Primary inclusions were i d e n t i f i e d by their s o l i t a r y location, presence along crys-t a l growth zones, and absence of evidence for secondary o r i g i n . Because i s o l a t i o n as a c r i t e r i o n for the i d e n t i f i c a t i o n of p r i -mary inclusions i s not s u f f i c i e n t (Wilkins and Bird, 1980), ad-d i t i o n a l c r i t e r i a were used to recognize inclusions formed at or near the time of mineralization and a l t e r a t i o n . Quartz grains showing l i t t l e evidence of recurrent fracturing were favored; those grains e n t i r e l y contained within minerals having weak i n -terlayer bond strengths (molybdenite, b i o t i t e , s e r i c i t e ) were frequently s t r a i n - f r e e and without well-defined, multiple-stage inclusion populations. They often contained only large, s o l i -tary inclusions. This observation i s evidence that, such grains have been protected from repeated fracturing and the ensuing f l u i d s . Another l i n e of evidence favoring primary o r i g i n for "primary" inclusions i s equivalent temperature estimates ob-tained by an independent technique. When two subsolidus a l k a l i feldspar s o l i d solutions coexist in a v e i n l e t assemblage, a unique temperature can be obtained using the d i s t r i b u t i o n of K A l S i 3 0 B component between the coexisting feldspars (Chapter 2). Temperatures so calculated are in good agreement with the f l u i d inclusion data, thus i n f e r r i n g primary o r i g i n for the i n c l u -sions. The method i s not conspicuously pressure-dependent and is used subsequently in th i s communication to obtain f i r s t ap-proximations to entrapment pressures. 10 C l a s s i f i c a t i o n and Description of F l u i d Inclusions Inclusions from the. three deposits, i l l u s t r a t e d in Figure 1, were separated into fi v e types: • Type A: inclusions with 60 volume percent or less vapor and without h a l i t e or s y l v i t e daughter minerals (L + V); • Type B: inclusions with greater than 60 volume percent vapor and occasional h a l i t e daughter mineral (V); • Type C: inclusions with less than 60 volume percent vapor and with a h a l i t e daughter mineral (L + V + H); • Type D: inclusions with less than 60 volume percent vapor and with both h a l i t e and s y l v i t e daughter minerals (L + V + H + S); and • Type E: inclusions with 60 volume percent vapor and with a C 0 2 - r i c h l i q u i d phase (L + V + C0 2). The presence of h a l i t e and s y l v i t e in types C and D i n c l u -sions has been inferred from o p t i c a l examination. Other phases present in the inclusions are: (1) hematite, which occurs in some types A and B and many types C and D inclusions; (2) nearly opaque, hexagonal molybdenite, which i s confined to types C and D inclusions and distinguished from frequently coexisting hema-t i t e by i t s d i s t i n c t i v e color (Kamilli, 1978); and (3) small, opaque, non-magnetic phases which are present in some types C and D inclusions (tetragonal disphenoids observed in a few i n -clusions suggest that t h i s opaque phase may be chalcopyrite). Some types C and D inclusions also contain unidentified anhedral grains with high birefringence and high r e f r a c t i v e index, and unidentified rhombic prisms with symmetrical extinction and ex-treme birefringence. In view of the irregular d i s t r i b u t i o n and the uncertain compositions of some s o l i d phases, no further sub-11 liquid-rich type A liquid (L) +vapor (V) ihematite (Hm) vapor-rich type B liquid (L) +vapor (V) ± hematite (Hm) saline type B liquid (L)+vapor (V) ± hematite (Hm)± halite (H) saline type C liquid (L)+ vapor (V) +halite (H) ±hematite (Hm) Hm hypersaline type D liquid (L) + vapor (V) + halite (H) + sylvite (S)±hematite (Hm) ±molybdenite (M)±unknown (U) C0 2-rich type E liquid (L)+vapor (V)+C02 Figure 1. F l u i d inclusion types observed in fr a c t u r e - c o n t r o l l e d , molybdenum-mineralized vein l e t s and stockworks at Questa, New Mexico and Hudson Bay Mountain and Endako, B r i t i s h Columbia. The inclusions vary from 10 to 50 microns in their largest dimen-sion. Abbreviations for the inclusion phases are as indicated. 12 d i v i s i o n of inclusion types C and D has been made. Dis t r i b u t i o n of the F l u i d Inclusions The paragenetic relations among veinl e t s are so consistent-ly observed that an ordered ingress of f l u i d s i s strongly sug-gested. This sequence may be used to relate stages of mineral-ization and a l t e r a t i o n to d i s t i n c t inclusion populations in the individual orebodies, and generally records the evolution from a l l i e d magmatic- to meteoric-hydrothermal events. Within any single v e i n l e t , i t i s v i r t u a l l y impossible to establish convincing age relations among the d i f f e r e n t i n c l u -sions. One or more types of inclusion commonly are superimposed to form a complex array of a l l inclusion types. Successive overprinting has caused pronounced changes in the type and abun-dance of primary inclusions preserved. It i s possible, by a' process of elimination similar to that applied by Chivas and Wilkins (1977) but using cross-cutting relations of ve i n l e t s together with the abundance and d i s t r i b u t i o n of contained f l u i d inclusions, to deduce the ordered sequence of f l u i d s which gave ri s e to the observed mineralization and a l t e r a t i o n . Inclusion types D and C are largely r e s t r i c t e d to v e i n l e t s having r e l a t i v e ages and a l t e r a t i o n assemblages considered pre-molybdenite (barren quartz, quartz-K-feldspar-biotite) or co-genetic with the ore-forming event(s) (quartz-K-feldspar ± moly-bdenite, quartz-molybdenite, q u a r t z - s e r i c i t e - p y r i t e ± molybdenite). The e a r l i e s t events recorded at Questa and Hudson Bay Mountain are hypersaline brines (type D i n c l u s i o n s ) . The 13 presence of type D inclusions in pre-molybdenite veinlets i s evidence that hypersaline precursors to the ore-forming solu-tions were present and are related to cogenetic intrusive rocks. The conspicuous absence of similar f l u i d s at Endako may infer the absence of intrusions coeval with the molybdenum mineraliz-ation. The r e l a t i v e abundance of type D inclusions at Questa and Hudson Bay Mountain decreases markedly with the appearance and intensity of p h y l l i c a l t e r a t i o n . The f l u i d inclusion record from quartz-molybdenite and quartz-pyrite ± molybdenite veinlets having p h y l l i c a l t e r a t i o n envelopes indicates the dominance of more d i l u t e , but s t i l l saline solutions. In each deposit, molybdenum mineralization i s associated most commonly with l i q u i d - r i c h type A followed in abundance by saline type C i n c l u -sions. As in other porphyry-type deposits (Chivas and Wilkins, 1977; Preece and Beane, 1979; Wilson et a l . , 1980), type D i n -clusions are found with potassic a l t e r a t i o n assemblages and type C inclusions occur with p h y l l i c a l t e r a t i o n . The position of vapor-rich type B inclusions in the para-genesis, and their r e l a t i o n to types D, C and A inclusions are variable and not firmly established. They occur in veinlets having both potassic and p h y l l i c a l t e r a t i o n envelopes. At Questa, type B and types C or D inclusions coexist in small iso-lated groups. S a l i n i t i e s inferred by the presence of h a l i t e daughter minerals in some type B inclusions cannot be readily explained without assuming entrapment of mixed l i q u i d and vapor. Hypersaline brines and low-density f l u i d s must have coexisted at least intermittently prior to and/or during molybdenite deposi-1 4 tio n . The presence of low-density f l u i d s coexisting with the solutions which gave r i s e to type A inclusions i s also indicated during the la t e r stages of a c t i v i t y at Hudson Bay Mountain, when no hypersaline brines are observed in the f l u i d inclusion popu-la t i o n s . Vapor-rich inclusions are not present in the f l u i d inclusion record at Endako. Clearly depths, confining pressures and fracture h i s t o r i e s of the individual orebodies bear on the abundance and d i s t r i b u t i o n of type B inclusions. HOMOGENIZATION DATA Introduction A Chaixmeca heating/freezing stage was used for temperature measurement. Nine standards were used for c a l i b r a t i o n from -100°C to +70°C, and ten were used in the +70°C to +600°C range. Repeated freezing and melting of single inclusions and standard compounds indicated that recorded melting points in the low range were accurate within 0.5°C with a precision of 0.2°C (2a). For temperature measurements above approximately 70°C, deviation of observed temperature from actual melting point was s t a t i s t i -c a l l y s i g n i f i c a n t . Corrections to the readout temperature were calculated using the high temperature melting point measurements regressed and smoothly joined with the lower temperature data. Repeated observations on potassium dichromate indicate an ac-curacy of 4.2°C, reproducible within 2.0°C at the 95% confidence l e v e l . Sample chips were generally heated only once to avoid spurious measurements caused by stretching and/or rupture of 15 inclusion walls. In many l i q u i d - r i c h (types A, C and D) i n c l u -sions, one or more daughter minerals persisted beyond the tem-perature of vapor disappearance. Homogenization by dissolution of h a l i t e after disappearance of the vapor phase was common in types C and D inclusions. Probable reasons for the persistence of h a l i t e above the temperature of vapor dissappeance are nec-king down, trapping of s o l i d NaCl, and large pressure correc-tions (Ahmad and Rose, 1980) or entrapment under r e l a t i v e l y un-usual P-T conditions exceeding those of the s o l u b i l i t y surface in the NaCl system (Wilson et a l . , 1980). Refractory daughter minerals (chalcopyrite, hematite, and/or molybdenite) remain present in some types A, C and D inclusions after both h a l i t e d i s s o l u t i o n and vapor disappearance. Their persistence i s as-cribed to dis s o l u t i o n kinetics or post-entrapment oxidation of the inclusion f l u i d s (Roedder, 1971). The highest temperature of reversible phase disappearance i s accepted as the homogeniza-tion temperature. Questa, New Mexico The temperature of reversible phase changes and the homo-genization behavior of 98 primary inclusions were recorded from 10 Questa samples (Figure 2). L i q u i d - r i c h inclusions that homo-genized by vapor disappearance (types A, C and D) exhibit a skewed d i s t r i b u t i o n of homogenization temperatures with a mode at about 390°C. Vapor-rich (type B) inclusions homogenized in the vapor phase by expansion of the vapor, and show a similar temperature d i s t r i b u t i o n and mode which coincide with those of 16 0 5 10 15 20 25 30 35 0 5 0 5 !0 15 20 25 30 35 0 5 FREQUENCY (NUMBER OF INCLUSIONS! Figure 2. F l u i d inclusion homogenization ( f i l l i n g ) temperatures (uncorrected for pressure) from Questa, Hudson Bay Mountain, and Endako. Separate histrograms are shown for inclusion types A, B,C, and D (Figure 1) as well as for inclusions which homogenize by h a l i t e d i s s o l u t i o n (types C and D only) and by vapor disap-pearance ( a l l types).. Refer to text for discussion of t h i s homogenization behavior. 1 7 the l i q u i d - r i c h inclusions. A bimodal d i s t r i b u t i o n of homogeni-zation temperatures i s suggested by a lower temperature mode at 300°C. Without s p e c i f i c r e l a t i o n to growth features and method of c o r r e l a t i o n among samples, errors in sampling d i s t i n c t i n c l u -sions populations are implied. Temperatures at which i d e n t i f i a b l e daughter minerals d i s -solved during the heating experiments were recorded for types C and D inclusions that homogenized both by vapor disappearance and by h a l i t e d i s s o l u t i o n . The h a l i t e d i s s o l u t i o n temperatures e n t i r e l y overlap one another, with a mode at s l i g h t l y higher temperature (400°C) than that of inclusions which homogenize by vapor disappearance. A bimodal d i s t r i b u t i o n of halite-homogeni-zing type C inclusions i s also present, with a lower-temperature mode at 330°C in agreement with vapor-homogenizing types A and C inclusions. Hudson Bay Mountain, B r i t i s h Columbia A t o t a l of 156 primary inclusions in 13 samples were heated and their homogenization c h a r a c t e r i s t i c s observed (Figure 2). Li q u i d - r i c h inclusions without h a l i t e or s y l v i t e and which homo-genize by vapor disappearance (type A) were more abundant in the population of inclusions at Hudson Bay Mountain than at Questa. They occurred in a bimodal population with the higher tempera-ture mode d i v i s i b l e into two subclasses at 350°C and 390°C, and the lower temperature mode at 150°C. L i q u i d - r i c h inclusions, some having a C 0 2 - r i c h l i q u i d phase (type E) decorate healed fractures and homogenize at temperatures overlapping these 18 modes; owing to their unmistakable secondary o r i g i n , they are not included in Figure 2. The mode of vapor-homogenizing (type B) inclusions (360°C) concurs with that of type A and i s skewed toward higher temperature. Types C and D inclusions which homo-genized by vapor disappearance did so from 140°C to 400°C and from 320°C to +600°C, respectively, but occurred so infrequently that d e f i n i t e modes were not established. Types C and D inclusions which homogenized by h a l i t e disso-l u t i o n form a bimodal temperature d i s t r i b u t i o n with modes at 170°C and 390°C. The higher-temperature mode corresponds to early mineralization, whereas the lower-temperature mode is cor-r e l a t i v e with later molybdenite- and base metal sulfide-bearing v e i n l e t s . Note that the lower-temperature population shown by types A and C i s shown by type D inclusions. Dissolution tem-peratures for i d e n t i f i a b l e daughter minerals were 150°C to 400°C for h a l i t e in type C and 330°C to +600°C for h a l i t e in type D inclusions, and 70°C to 120°C for s y l v i t e in type D inclusions. Endako, B r i t i s h Columbia In contrast to observations of the Questa and Hudson Bay Mountain populations, 133 inclusions in 9 samples from Endako form a population dominated by l i q u i d - r i c h type A inclusions which homogenized by vapor-disappearance (Figure 2). The single mode at 370°C i s weakly skewed toward lower temperatures. Vapor-rich (type B) and l i q u i d - r i c h type D inclusions seen at Questa and Hudson Bay Mountain are missing from the Endako popu-l a t i o n ; only type C inclusions are present. Type C inclusions 19 which homogenize by h a l i t e d i s s o l u t i o n occur at higher tempera-tures than do those which homogenize by vapor disappearance; liquid-homogenizing type C inclusions f i l l at temperatures which overlap those of type A inclusions. INTERPRETATION OF THE FLUID INCLUSION DATA S a l i n i t i e s of Inclusion Fluids S a l i n i t i e s of the inclusion f l u i d s are separable into d i s -t i n c t groups dominated by a single inclusion type, but the groups formed by inclusions from d i f f e r e n t deposits appreciably overlap (Figure 3). Type A inclusions contain no h a l i t e or s y l -v i t e daughter minerals at 25°C. The bulk composition in the system NaCl-KCl-H 20 must not exceed 21 and 11 weight percent NaCl and KC1, respectively. Direct s a l i n i t y estimates were made on a number of type A inclusion f l u i d s from each deposit by mea-surement of ice fusion temperatures and comparison with the data of Potter et a l . (1978) for aqueous NaCl solutions. Type A inclusion f l u i d s vary in s a l i n i t y from about 2 to 15 percent NaCl equivalent (Figure 3). Complete heating data were not ob-tained for a l l type A inclusions on which freezing experiments were made owing to their s i z e , extreme internal r e f l e c t i o n , and d i f f i c u l t y in relocating s p e c i f i c inclusions. C o l l i n s (1979) has shown that measurement of the depression of ice fusion temperatures by dissolved s a l t s gives r i s e to i n -accurate s a l i n i t y estimates when cla t h r a t i o n of carbon dioxide< hydrate occurs. Cursory crushing tests performed on type A i n -clusions resulted in s l i g h t to moderate expansion of vapor at 20 70 60 50 A 40 -\ 30 20 QUESTA 1 1 1 1 1 100 200 300 400 500 600 TEMPERATURE CC) 70-! 60 H 50 i 40 30 % 20 ENDAKO 100 200 300 400 500 600 TEMPERATURE CC) 80 70 60 50 H m 40 30 20 H HUDSON BAY MOUNTAIN i 1 1 1 1 100 200 300 400 500 600 TEMPERATURE (°C) a Type A inclusions Type C inclusions o Vapor disappearance 9 Halite dissolution Type D inclusions & Vapor disappearance A Halite dissolution Figure 3. Temperature-salinity determinations for types A,C, and D inclusion f l u i d s from Questa, Hudson Bay Mountain, and Endako. S a l i n i t i e s given in equivalent weight percent NaCl (types A and C) and NaCl + KC1 (type D) and determined from measured d i s s o l u -tion temperatures of h a l i t e and s y l v i t e daughter phases. Clustering into low and high s a l i n i t y populations and the array approximating the li q u i d - v a p o r - h a l i t e boundary discussed in text. 21 Questa and Hudson Bay Mountain (but not Endako), indicating low p a r t i a l pressures of gases other than H 20 in the inclusions. The presence of type E inclusions which have C 0 2 - r i c h l i q u i d phase imply that many type A inclusions may also contain suf-f i c i e n t C0 2 to produce c l a t h r a t i o n . It i s suspected that ice and C0 2 gas hydrate may have frozen out simultaneously from some type A inclusions. Because the temperature of C0 2 hydrate de-composition was not observed, the s a l i n i t y estimates for type A inclusions could be in error by as much as 50 percent ( C o l l i n s , 1979). Nevertheless, separation of type A from types C and D inclusion f l u i d s (Figure 3) remains as evidence that the type A are compositionally d i s t i n c t from types C and D inclusion f l u i d s . For more concentrated solutions saturated with respect to h a l i t e but not s y l v i t e (type C inclusi o n s ) , s a l i n i t y was appro-ximated by observing the dis s o l u t i o n temperature of h a l i t e and converting to NaCl equivalents using regressed s o l u b i l i t y data (Potter and Clynne, 1978; Linke, 1965; Keevil, 1942). The e s t i -mates for Questa, Hudson Bay Mountain and Endako are 31 to 58, 31 to 52 and 32 to 61 percent NaCl equivalent, respectively. Type C inclusions that homogenize by h a l i t e d i s s o l u t ion form an array that approximates the s o l u b i l i t y curve in Figure 3. Vapor-homogenizing type C inclusions f a l l upon or near the high-temperature side of the boundary. The s a l i n i t i e s of hypersaline (type D) inclusion f l u i d s were obtained d i r e c t l y from the h a l i t e and s y l v i t e d i s s o l u t i on temperatures and the NaCl-KCl-H 20 diagram of Roedder (1971) 22 (Figure 4). Individual inclusions from Questa and Hudson Bay Mountain exhibit the following s a l i n i t i e s for these inclusion f l u i d s : Questa, minimum 33.5 and 10, and maximum 51 and 19 per-cent NaCl and KC1, respectively; Hudson Bay Mountain, minimum 19.5 and 13.5, and maximum 60.5 and 19 percent NaCl and KC1, respectively. The mean s a l i n i t y (wt% NaCl + wt% KC1) i s 52 per-cent at both Questa and Hudson Bay Mountain. Type D inclusions that homogenized by vapor disappearance do not form groups sepa-rate from those that homogenized by h a l i t e d i s s o l u t i o n on Figure 3. Saline and hypersaline (types C and D) inclusion f l u i d s occupy r e l a t i v e l y small, compositionally d i s t i n c t regions of the NaCl-KCl-H 20 system. Type D inclusion f l u i d s also form linear arrays similar to those noted by Cloke and Kesler (1979) and designated h a l i t e trends (cf. Erwood et a l . , 1979; Wilson et a l . , 1980). The inclusion compositions from Questa and Hudson Bay Mountain produce individual trends that d i f f e r s l i g h t l y in orientation, but project to similar points on the NaCl-KCl j o i n . Inclusions that homogenized both by h a l i t e d i s s o l u t ion and by vapor disappearance f a l l along the h a l i t e trends in Figure 4. Estimates of Pressure and Depth No unequivocal determination of pressure can be obtained from the Questa, Hudson Bay Mountain or Endako f l u i d inclusion data, but estimates of vapor pressure from individual inclusion f l u i d s l i m i t the range of entrapment pressures (Figure 5). Close approximations to actual pressures are obtained from i n d i -vidual saline (type C) and hypersaline (type D) inclusions 23 Figure 4. Compositions of hypersaline type D inclusion f l u i d s from Questa (squares) and Hudson Bay Mountain (triangles) in the NaCl-KCl-H 20 system (Roedder, 1967). Stippled area shows the range of compositions for saline type C inclusion f l u i d s . En-larged area shows the " h a l i t e trend" (Cloke and Kesler, 1979) defined by individual inclusions which homogenize by h a l i t e d i s -solution ( s o l i d symbols) and vapor disappearance (open symbols). 24 HUDSON BAY MOUNTAIN 300 350 400 (minimum vapor pressures) 350 400 T E M P E R A T U R E ( ° c e n t i g r a d e ) TYPE C INCLUSIONS TYPE D INCLUSIONS O V a p o r d i s a p p e a r a n c e # H a l i t e d i s a p p e a r a n c e 9 S i m u l t a n e o u s v a p o r - h a l i t e TYPES B and C or D PAIRS • C o e x i s t i n g l i q u i d a n d v a p o r _j S i m u l t a n e o u s v a p o r - h a l i t e h o m o g e n i z a t i o n h o m o g e n i z a t i o n A K - N a f e l d s p a r g e o t h e r m o m e t r y Figure 5. Vapor pressure e s t i Questa, Hudson Bay Mountain, C inclusions on the s o l u b i l i t (Roedder and Bodnar, 1980), i boi l i n g (or condensation), mi prevent b o i l i n g , and K/Na f e l for feldspar geothermometry a undefined). Tie li n e s connect pressure estimates obtained f Shaded areas are estimates of mates for inclusion f l u i d s from and Endako. Shown are s p e c i f i c type y surface or in the l i q u i d f i e l d nclusion pairs showing evidence for nimum vapor pressures required to dspar geothermometry (temperatures nd minimum vapor pressures points to show the range of vapor or saline (type C) inclusions. l i t h o s t a t i c and hydrostatic load. 25 trapped on the s o l u b i l i t y surface, and from inclusion pairs which infer b o i l i n g . Those type C inclusions in which h a l i t e d i s s o l u t i o n and vapor disappearance temperatures d i f f e r by 10°C or less are assumed to have been trapped along the s o l u b i l i t y surface. The pressure maximum along t h i s boundary decreases with addition of KC1 approximating the h a l i t e trend exhibited by type D inclusions from Questa and Hudson Bay Mountain, but vapor pressure estimates from types C and D inclusions are comparable. The presence of vapor-rich inclusions among populations dominated by l i q u i d - r i c h types suggests that at least some f l u i d s were trapped on a liquid-vapor boundary. Pairs of low density (type B) and saline or hypersaline (types C or D) i n c l u -sions at Questa homogenize by simultaneous disappearance of vapor and l i q u i d in l i q u i d - and vapor-rich inclusions, respec-t i v e l y . One or more vapor-rich inclusions may also contain a h a l i t e daughter mineral (Figures 1 and 6). High s a l i n i t i e s i n -ferred from these inclusions are not possible under b o i l i n g con-di t i o n s in the range of observed temperatures, and suggest random proportions of vapor and high s a l i n i t y l i q u i d trapped in the inclusion. Samples from Hudson Bay Mountain also show e v i -dence of coexisting l i q u i d and vapor by virtue of coexisting l i q u i d - (type A) and vapor-rich inclusions. Alternate methods to estimate vapor pressures of individual inclusions provide only minimum estimates of entrapment pres-sure. Inclusion f l u i d s which do not show evidence of b o i l i n g may also have been trapped at higher temperatures and pressures along appropriate isochores above the point of homogenization. 26 Figure 6. F l u i d inclusion populations from Questa (B), Hudson Bay Mountain (A), and Endako (C). Abbreviations for daughter phases as in Figure 1. Note type A populations with both l i q u i d -and vapor-rich inclusions (boiling implied) at Hudson Bay Mountain and with coexisting hypersaline, l i q u i d - r i c h (type D) and saline, vapor-rich (type B) inclusions which suggest b o i l i n g and/or condensation at Questa, but the uniformity of l i q u i d -vapor ratios in inclusions from Endako. 27 The density of the homogeneous inclusion f l u i d together with the P-V-T-X measurements of Urusova (1975) was used to obtain the vapor pressure of saline (type C) inclusions that homogenize by h a l i t e d i s s o l u t i o n (Roedder and Bodnar, 1980) and thus could not have been b o i l i n g . This method was used in preference to vapor pressures at temperatures of vapor disappearance on the s o l u b i l -i t y surface, which are the absolute minimum pressures required to prevent b o i l i n g . Minimum pressures of entrapment necessary to prevent coexisting l i q u i d and vapor were also estimated for type C inclusions that homogenized by vapor disappearance using s a l i n i t y data and the appropriate two-phase liquid-vapor curve (Sourarijan and Kennedy, 1962). F i r s t approximations of pressure were also obtained using the P-T-X dependence of subsolidus, hydrothermal minerals which exhibit s o l i d solution. The d i s t r i b u t i o n of orthoclase com-ponent between coexisting a l k a l i feldspars which occur in vein-l e t s of d i f f e r e n t r e l a t i v e ages from Questa and Hudson Bay Mountain i s discussed in Chapter 2. Equations for the excess free energy of K- and Na-rich feldspar s o l i d solutions were solved for unique temperatures of deposition. Temperatures so obtained are nearly pressure independent (-12°C/kbar correction required) and were thus used to estimate pressures of entrap-ment. The feldspar temperatures are equivalent to as much as 166°C greater than the homogenization temperatures of cogenetic f l u i d inclusions, suggesting that some but not a l l of the f l u i d inclusion data require a pressure correction. S p e c i f i c depths approximating any of the vapor pressure 28 estimates shown on Figure 5 are d i f f i c u l t to assign. Absolute minimums would be l i t h o s t a t i c conditions which give r i s e to these vapor pressures, but depths in accord with reasonable es-timates of geologic cover require pressures that varied between the extremes of l i t h o s t a t i c and hydrostatic load. For example, reconstruction of late-Oligocene volcanic cover above the Questa deposit (Carpenter, 1968; Ishihara, 1967) suggests emplacement at depths of 1000 to 1600 meters. Maximum l i t h o s t a t i c loads of 275 to 400 bars, depending on the locus of mineralization, or hydrostatic pressures of 80 to 100 bars correspond to these depths. Inclusion populations which show evidence of b o i l i n g have vapor pressures which infer hydrostatic load, whereas mini-mum pressures required to prevent b o i l i n g of saline and hypersa-l i n e f l u i d s and type C inclusions which homogenize by h a l i t e d i s s o l u t i o n both infer vapor pressures in excess of reconstruc-ted l i t h o s t a t i c load. Although i t i s impossible to estimate the depth of ore for-mation by reconstructing the stratigraphy at Hudson Bay Mountain, Kirkham (1969) has estimated a minimum depth of 2000 meters from the present topography. Type C inclusions which homogenize on the s o l u b i l i t y surface and minimum pressures ne-cessary to prevent b o i l i n g approximate hydrostatic or greater pressures at t h i s depth. Vapor pressures estimated from type C inclusions which homogenize by h a l i t e disappearance are in accord with two kilometers depth i f l i t h o s t a t i c conditions are assumed. At Endako, evidence i s not available for an independent 29 estimate of geologic cover, but inferred vapor pressures may be u t i l i z e d to reconstruct possible depths of mineralization. The most accurate estimate of vapor pressure i s probably obtained from the single type C inclusion that homogenized at 385°C on the s o l u b i l i t y surface. The estimate of 160 bars corresponds to depths of about 600 and 2000 meters under l i t h o s t a t i c and hydro-s t a t i c conditions, respectively. The minimum depths required to prevent b o i l i n g of saline type C inclusion f l u i d s varies from 250 to 570 meters assuming l i t h o s t a t i c load, or 800 to 2000 meters i f hydrostatic load i s assumed. The hydrostatic depth of approximately two kilometers i s consistent with high-level em-placement inferred from c h i l l e d , porphyritic margins and miaro-l y t i c c a v i t i e s in the a p l i t e , granite porphyry and quartz-feld-spar porphyry dikes which were immediate predecessors of miner-a l i z a t i o n , whereas unreasonably shallow estimates of depths are generated i f l i t h o s t a t i c load i s assumed. Several features are conspicuous on inspection of Figure 5. The range and overlap of vapor pressure estimates suggests that inclusion f l u i d s were trapped under widely varying pressure con-d i t i o n s . The highest estimates of vapor pressure ( 800 bars) were obtained from inclusions in vei n l e t s which exhibit early-stage cross-cutting relations and a l t e r a t i o n . Lower estimates ( 100 to about 300 bars) were obtained from inclusions in veinlets having both early and late emplacement h i s t o r i e s and a l t e r a t i o n . Coexisting l i q u i d and vapor appears to have been intermittent and to have occurred throughout a range of temperatures and pressures. Overpressures exceeding reasonable estimates of l i -30 thostatic load may from time to time have prevailed in the ore-forming system(s). The range and overlap of f l u i d inclusion homogenization temperatures, inferred vapor pressures and a l k a l i feldspar geothermometry are not consistent with a simple, mono-tonic decline in the temperature of solutions which flowed through the fractures. Processes more closely related to the composition and hence the source of the ore-forming solution(s) are envisioned to produce the observed sequence of veinlets and dominant a l t e r a t i o n assemblages. Temperature and S a l i n i t y Dispersion The inclusion populations of Questa, Hudson Bay Mountain and Endako present a remarkable uniformity of modes although over a range of temperatures and s a l i n i t i e s . A variety of pro-cesses can give r i s e to the range of temperatures (cf. Ahmad and Rose, 1980). Homogenization temperatures ^ 500°C can be explained by trapping random mixtures of coexisting l i q u i d and vapor (cf. Wilson et a l . , 1980); however, d i l u t i o n of a single high s a l i n i t y l i q u i d with vapor in proportions which homogenize by vapor disappearance cannot produce the wide range of s a l i n i -t i e s observed. Inclusions which homogenize by h a l i t e d i s s o l u t i o n may give r i s e to estimates of entrapment temperatures more accurate than those provided by vapor-homogenizing inclusions. Cloke and Kesler (ibid.) have shown, however, that t h i s behavior requires p r e c i p i t a t i o n of h a l i t e from hydrothermal solutions before the f l u i d was trapped as inclusions. Although no evidence for th i s 31 phenomenon was observed (halite xenocrysts in the ore assemblage or host mineral), minute h a l i t e grains serving as l o c i for f l u i d inclusion formation cannot be rejected. Inclusions which so nucleated would give r i s e to anomalous s a l i n i t i e s and homogeni-zation temperatures which closely approximate the s o l u b i l i t y curve in the NaCl-H 20 system; many type C inclusions (Figure 3) do in fact cluster near or on the s o l u b i l i t y curve between 30 and 60 percent NaCl equivalent. The temperatures of h a l i t e d i s -solution presented here, however, are in excellent agreement with both NaCl-saturated (types C and D) and undersaturated (type A) inclusions which homogenize by vapor disappearance. The h a l i t e dissolution temperatures do not appear anomalous and nucleation of f l u i d inclusions on h a l i t e xenocrysts i s not a major mechanism for dispersion of homogenization temperatures and s a l i n i t y . The most sa t i s f a c t o r y explanation for the range of homogen-izat i o n temperatures and s a l i n i t i e s i s that the inclusions are from an inhomogeneous population. Three compositionally d i s -t i n c t inclusion f l u i d s and thus three recognizable hydrothermal solutions are present in the Questa and Hudson Bay Mountain de-posits, as shown by the separation of f i e l d s representing types A, C and D inclusions on Figures 3 and 4. Fluids with two gen-er a l ranges of s a l i n i t y were present during the evolution of the ore-forming systems, one with 1 to 20 and another with 30 to 60 percent NaCl equivalent. More importantly, the high s a l i n i t y solutions form two compositionally d i s t i n c t groups distinguished by their K/Na atomic r a t i o s , types C and D having < 0.2 and ^ 32 0.2 K/Na, respectively. Although inclusions containing each solution type are found throughout the v e r t i c a l extent of the orebodies, the abundance and d i s t r i b u t i o n of inclusion types are related to vein l e t s having di f f e r e n t r e l a t i v e ages and d i s t i n c -t i v e mineral assemblages and/or wallrock a l t e r a t i o n . The ob-served cross-cutting relations of these veinlets suggest that the general order of appearance for the solutions i s represented by type D (absent at Endako), type C and f i n a l l y type A i n c l u -sion f l u i d s . Extensive and recurrent fracturing must have per-mitted ingress of solution i n d i v i d u a l l y from time to time at any given location in the ore-forming systems. Some of the varia-t i o n , however, might s t i l l r e f l e c t mixed-phase entrapment, modi-f i c a t i o n s (necking down or opening of inclusions), and mixing of f l u i d s , and the p o s s i b i l i t y of unrecognized secondary inclusions cannot be discounted. Pressure Correction The homogenization temperatures are uncorrected for the effe c t s of pressure. The presence of vapor-rich inclusions and the equivalence of some feldspar temperatures suggest that at least some inclusions were trapped on the s o l u b i l i t y surface and therefore that their homogenization temperatures do not require a pressure correction. Other inclusions give r i s e to vapor pressure estimates which infer entrapment pressures between hy-drostatic and l i t h o s t a t i c load conditions, and s t i l l others in f e r pressures in excess of reasonable l i t h o s t a t i c load. These observations indicate that pressure varied during mineraliz-33 ation, so that d i f f e r e n t pressure corrections are required for d i f f e r e n t inclusions. It i s not possible, therefore, to obtain a universal pressure correction which can be applied to a l l data from a given deposit (except perhaps at Endako, where a hydros-t a t i c load of approximately 160 bars has been i n f e r r e d ) . Pressure variation at hydrostatic depths of about 2 kilometers gives pressure corrections on the order of 10°C or less for so-lutions of 5 to 25 percent NaCl equivalent (Potter, 1977). The e f f e c t of individual pressure corrections on temperatures of mineralization at Questa and Hudson Bay Mountain are d i f f i c u l t to assess, but there i s no evidence to support excessive i n -creases in modes or dispersion of the homogenization tempera-tures when pressure corrections are applied. SOURCE AND EVOLUTION OF THE INCLUSION FLUIDS Because the Questa and Hudson Bay Mountain deposits are s p a t i a l l y and temporally related to r h y o l i t e porphyries, and mineralization at Endako i s preceded by compositionally similar dikes intrusive into the Endako Quartz Monzonite, i t i s l o g i c a l to appeal to the g r a n i t i c intrusions as a source of hydrothermal solutions. The K/Na atomic ra t i o s of the inclusion f l u i d s toge-ther with observed homogenization data and temperatures inferred by K/Na feldspar compositions can be used to test t h i s generali-zation. K/Na r a t i o s of type D inclusion f l u i d s y i e l d average temperatures for water-rock equilibrium in the K A l S i 3 0 8 -NaAlSi 30 8-NaCl-KCl-H 20 system of 645°C and 712°C for Questa and Hudson Bay Mountain, respectively (Lagache and Weisbrod, 1977). 34 Most equilibrium temperatures do not agree with the lower f l u i d inclusion temperatures, but the K/Na feldspar data predict tem-peratures remarkably close to the ternary minimum. Ca contents (assuming type D inclusion f l u i d s at Questa and Hudson Bay Mountain are in equilibrium with g r a n i t i c rock at the appropriate K/Na feldspar and f l u i d inclusion homogenization temperatures) have been estimated using the K-Na-Ca geothermome-ter of Fournier and Truesdell (1973). The K/Na feldspar temper-atures give r i s e to Ca m o l a l i t i e s of 0.2 to 3.1 and 0.7 to 3.2 for Questa and Hudson Bay Mountain, respectively. If the ob-served f l u i d inclusion homogenization temperatures are used, Ca m o l a l i t i e s range from 0.7 to 30.6 and 3.2 to 18.9 for the same deposits. The presence of f l u o r i t e in many quartz-molybdenite veins and the fluorine concentration of the ore-forming solu-tions calculated from H20-HF fugacity r a t i o s derived from f l u o r i n e - r i c h b i o t i t e (Chapters 2 and 3) e f f e c t i v e l y l i m i t Ca concentrations. K/Na feldspar temperatures predict Ca concen-trations well within these l i m i t s ; however, only the highest f l u i d inclusion homogenization temperatures could give r i s e to Ca concentrations indicative of water-rock equilibrium. Following the reasoning of Wilson et a l . (1980), these observa-tions indicate that type D inclusion f l u i d s maintained e q u i l i -brium with g r a n i t i c rocks only at temperatures of 500°C or more, and suggest that type D inclusion exsolved d i r e c t l y from a source intrusion of g r a n i t i c composition. Experimental data of Lagache and Weisbrod (1977) show'that type C inclusion f l u i d s e q u i l i b r a t e with g r a n i t i c rocks at 500°C 35 or less. Because th i s temperature i s well below the ternary minimum, type C inclusion f l u i d s could not have exsolved d i r e c t -ly from a g r a n i t i c source intrusion. Alternative methods of producing type C inclusion f l u i d s are: 1) r e - e q u i l i b r a t i o n of type D inclusion f l u i d s with the source intrusion; 2) b o i l i n g of less saline solutions; and, 3) d i l u t i o n of hypersaline brines. Processes such as isothermal or isenthalpic decompression, liquid-vapor phase separation ( b o i l i n g ) , or d i l u t i o n of hypersa-l i n e brines cause K/Na exchange between f l u i d and rock and cor-responding adjustments of the K/Na r a t i o in the f l u i d to reach new equilibrium conditions. The molal K/Na ra t i o s and a l t e r a -tion assemblages attending these water-rock interactions are consistent with re- e q u i l i b r a t i o n of types D or A inclusion f l u i d s and the rhyolite porphyries at Questa and Hudson Bay Mountain to form type C inclusion f l u i d s , and supported by tran-s i t i o n s from type D to type C inclusions in the veinlets with changes from potassic to p h y l l i c a l t e r a t i o n assemblages. Derivation of type C inclusion f l u i d s by e q u i l i b r a t i o n of mete-oric solutions with the source intrusion(s) and attainment of their high s a l i n i t i e s by b o i l i n g i s also possible. An o r i g i n by b o i l i n g of a low s a l i n i t y l i q u i d , however, generates large v o l -umes of vapor which are not evident in the f l u i d inclusion record as an abundance of vapor-rich inclusions. Type C i n c l u -sion f l u i d s could also have originated from ingress of less saline solutions which remove NaCl precipitated along the h a l i t e trend by e a r l i e r hypersaline f l u i d s (cf. Erwood et a l . , 1979). The agreement of type C l inclusion homogenization temperatures j 36 with those of types A, B and D, however, argues against random incorporation of h a l i t e xenocrysts in the inclusions. The absence of s a l i n i t i e s intermediate between about 15 and 30 percent NaCl equivalent i s not unique to molybdenum-mineral-ized stockworks; in fact, i t i s commonly recognized in porphry-type deposits. The s a l i n i t y hiatus in Figure 3 and d i s c o n t i n u i -ty of the h a l i t e trend toward the H 20 apex in Figure 4 suggest that although the f l u i d s were completely miscible, there was l i t t l e or no mixing of types C or D inclusion f l u i d s with mete-oric solutions. The true source(s) of hypersaline (type D) and saline (type C) inclusion f l u i d s i s doubtless much more complex than the alternatives presented here, but magmatic derivation of these solutions under fluctuating hydrostatic to l i t h o s t a t i c load (with occasional overpressure) appears to best explain the observations. Evolution of Inclusion Populations No single path exists on a pressure-temperature projection of the NaCl-H 20 system (Figure 7) that w i l l produce a mixed pop-ulation which includes both l i q u i d - and vapor-rich inclusions, exhibits a wide range of homogenization temperatures and con-tains types C and D inclusions homogenizing by h a l i t e d i s s o l u -tion as well as vapor disappearance (Cloke and Kesler, 1979). Saline and hypersaline (types C a n d D) inclusion f l u i d s which homogenize by h a l i t e d i s s o l u t ion are trapped under temperature- . pressure conditions exceeding the s a l i n i t y surface (Wilson et a l . , 1980). Solutions under normal hydrostatic pressure flowing 37 i j 200 400 TEMPERATURE (©centigrade) Figure 7. S o l u b i l i t y curve approximating the Questa and Hudson Bay Mountain h a l i t e trends in the NaCl-KCl-H 20. system (modified a f t e r Cloke and Kesler, 1979). Heavy and medium s o l i d l i n e s are boundaries for vapor + h a l i t e , l i q u i d + vapor, l i q u i d , and l i q u i d + h a l i t e stable regions at 30 (stippled) and 50 percent NaCl equivalent (Sourarijan and Kennedy, 1962). Fine l i n e s are paths by which types C and D inclusions could have formed. See text for discussion of points U to ZZ. 38 out of an intrusion along U-V-W on Figure 7 decrease rapidly in temperature at nearly constant pressure. A solution with a t o t a l s a l i n i t y of 50% at U w i l l saturate with h a l i t e at V and p r e c i p i t a t e h a l i t e along V-W as the solution becomes less sa-l i n e . Such c i r c u l a t i o n loops involve increasingly smaller ex-cursions in temperature as an intrusion cools (Cathles, 1977). Similar paths could thus exist at lower pressure e n t i r e l y within the l i q u i d f i e l d of less saline solutions to produce homogeneous inclusion populations which homogenize by vapor-disappearance (cf. Endako). The f l u i d containing 50 percent NaCl equivalent at U could, with migration of the hydrothermal solution, drop in pressure and temperature to X on Figure 7. Further cooling w i l l occur along the isochore X-Y i f part of t h i s solution i s trapped as an inclusion" at X. Cooling proceeds along a constant-volume path across the l i q u i d + vapor region to W, where h a l i t e begins to separate, and then along the s o l u b i l i t y curve to ambient condi-tions. Small proportions of type C inclusions from Endako and types C and D inclusions from Questa and Hudson Bay Mountain homogenize by simultaneous disappearance of vapor and h a l i t e . This behavior requires entrapment of l i q u i d without vapor along the s o l u b i l i t y curve W-Z. Further cooling at pressures exceed-ing the s o l u b i l i t y curve along Z-ZZ produces inclusions which homogenize by h a l i t e d i s s o l u t i o n . A decline in pressure can thus produce a series of inclusions on the h a l i t e trend which homogenize over a range of temperatures by vapor disappearance or h a l i t e d i s s o l u t i o n . 39 Dynamic systems exhibiting sharp fluctuations in pressure and temperature account for mixed-phase entrapment in regions where vapor cannot stably coexist with l i q u i d under conditions which produce inclusions homogenizing by h a l i t e d i s s o l u t i o n . The pre-entrapment vapor necessary to produce coexisting hyper-saline and vapor-rich (types D and B) inclusions at Questa and Hudson Bay Mountain could result from cooling along U-UU in Figure 7, in which b o i l i n g accompanies a rapid drop in pressure. Solutions trapped as f l u i d inclusions above the s o l u b i l i t y curve and temperatures within the l i q u i d (XX) or l i q u i d + vapor (YY) f i e l d s can develop, simultaneously, vapor- and l i q u i d - r i c h i n -clusions homogenizing by vapor disappearance. Further pressure reduction into the vapor + h a l i t e f i e l d (UU) prior to entrapment w i l l cause b o i l i n g and p r e c i p i t a t i o n of h a l i t e . Liquids on the h a l i t e trend are produced simultaneously with vapor, and cool to points such as W or Z on the s o l u b i l i t y curve. If the l i q u i d s at W or Z were separated from coexisting vapor, cooling to WW or ZZ would produce more l i q u i d s on the h a l i t e trend which, when trapped as inclusions, homogenize by h a l i t e d i s s o l u t i o n . One mechanism capable of generating the observed inclusion populations i s accumulation and episodic release of f l u i d s ex-solved d i r e c t l y from the source intrusion(s) (Ganster, 1977). The f l u i d s so released would undergo i r r e v e r s i b l e , isenthalpic decompression (Barton and Toulmin, 1961). I n i t i a l fracture den-s i t y need not be great and the r e s u l t i n g pressure drop could produce vapor pressures intermediate between l i t h o s t a t i c and hydrostatic load. The associated expansion of the f l u i d s and 40 closure of the fractures by mineral deposition, however, would promote thorough and repeated fracture events consistent with the cross-cutting relations and multiple-stage introduction of solutions observed. Fracture propagation would eventually breach to hydrostatic pressures and convective c i r c u l a t i o n in a normal hydrostatic environment would ensue, as evidenced by l i g h t stable isotope data (Hall et a l . , 1974) indicative of ex-tensive mixing of magmatic and meteoric solutions. The conse-quences of i r r e v e r s i b l e isenthalpic decompression with respect to cooling of the hydrothermal solutions can be v i s u a l i z e d with the aid of Figure 8. A pressure decrease corresponding to the upper and lower l i m i t s of vapor pressures estimated from the f l u i d inclusion data w i l l cause cooling of the f l u i d from s o l i -dus temperatures to about 400°C, in excellent agreement with the observed temperature modes for the ore-forming solutions. It should be noted that cooling by isenthalpic decompression as shown on Figure 8 i s for pure H 20 only; l i t t l e i s known about the effect of dissolved solutes on the enthalpy of solution. Kasper et a l . (1979) have d i r e c t l y measured the enthalpy of NaCl solutions at temperatures to 800°C and pressures to 1000 bars over a concentration range of 0 to 6 molal. Their data in the single-phase region of the NaCl-H 20 system shows that up to about 300°C and 500 bars the s p e c i f i c enthalpy of solutions 3 molal NaCl cannot be distinguished from that of pure H 20, and the s i m i l a r i t y extends to higher NaCl concentration at 1000 bars. Thus, Figure 8 i s a reasonable f i r s t approximation for the cooling e f f e c t s of isenthalpic decompression at low NaCl 41 10000 1000 100 P R E S S U R E (bars) Figure 8. Temperature-pressure diagram showing the ef f e c t of i r r e v e r s i b l e , isenthalpic cooling by decompression, without con-ductive or convective heat exchange (modified af t e r Barton and Toulmin, 1961). S o l i d arrow traces possible path of f l u i d under-going decompression from pressures approximating l i t h o s t a t i c conditions to hydrostatic load as implied by the f l u i d inclusion vapor pressure estimates in Figure 5. 42 concentrations. S i g n i f i c a n t deviations from Figure 8 can be expected for hypersaline brines, as evidenced by extremely nega-tive p a r t i a l molal volumes for NaCl derived by Urusova (1975), and the ef f e c t of decreasing NaCl concentration as a consequence of NaCl p r e c i p i t a t i o n along the h a l i t e trend i s unknown. Further work i s necessary to v e r i f y i r r e v e r s i b l e isenthalpic decompression as a feasible mechanism for cooling precursors to the ore-forming solutions in stockwork molybdenum deposits. CONCLUSIONS The data and interpretations presented above permit the following tentative conclusions about the general evolution of ore-forming and related events in stockwork molybdenum deposits and the s p e c i f i c environments of deposition in the Questa, Hudson Bay Mountain and Endako orebodies. Early barren quartz and quartz-K-feldspar-biotite ± molybdenite vei n l e t s at Questa and Hudson Bay Mountain formed from solutions with s a l i n i t i e s of up to 70 percent NaCl + KC1 and K/Na atomic rat i o s of 0.2 or more. These hypersaline f l u i d s were in general precursors to the actual ore-forming solutions. They evolved d i r e c t l y from the source intrusions under l i t h o s t a t i c load or reasonable over-pressures and at temperatures approximating the K A l S i 3 0 8 -NaAlSi 30 8-Si0 2-H 20 ternary minimum down to about 500°C. These solutions are not evident in the f l u i d inclusion record at Endako, but the presence of pre-ore rh y o l i t e porphyry dikes i n -dicates that a similar intrusive event and similar inclusion populations could exist at depth. 43 Recurrent fracturing gave r i s e to multiple-stage mineraliz-ation and a l t e r a t i o n . The bulk of the molybdenum mineralization at Questa, Hudson Bay Mountain and Endako i s associated with 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 from f l u i d s with s a l i n i t i e s similar to the e a r l i e r hypersaline brines, but K/Na atomic ratios less than 0.2. Temperatures of homogenization from about 300° to 600°C with d e f i n i t e modes occurring at 390°C were ob-served. E q u i l i b r a t i o n with the source intrusion and/or scaven-ging of NaCl precipitated in the veinlet assemblage by e a r l i e r hypersaline f l u i d s evolving along the h a l i t e trend could explain the similar s a l i n i t i e s but d i f f e r e n t K/Na r a t i o s . A s i g n i f i c a n t increase in s a l i n i t y by b o i l i n g , however, i s not consistent with the f l u i d inclusion evidence for only l o c a l i z e d , intermittent b o i l i n g . The f l u i d inclusion record provides evidence for pressure fluctuations between the extremes of l i t h o s t a t i c and hydrostatic load and lends support to intermittent, perhaps c y c l i c overpres-sure. Fracture events with ensuing i r r e v e r s i b l e adiabatic de-compression of escaping f l u i d s i s suggested as a possible me-chanism of cooling the hydrothermal solutions from near-magmatic temperatures. Further fracturing of the hydrothermal systems permitted ingress of meteoric water which formed the ubiquitous low s a l i n i t y inclusions. The ore-forming events at Endako may have occurred only during these late stages of evolution. 4 4 I I . GEOCHEMISTRY OF HYDROTHERMAL ALTERATION  INTRODUCTION Geochemists have in recent years had considerable success in reconstructing hydrothermal processes by experimentally or t h e o r e t i c a l l y predicting phase relations among minerals and aqueous solutions from a l t e r a t i o n assemblages deposited in par-t i c u l a r ore-forming environments. For example, studies of mica geochemistry in stockwork molybdenum deposits (Gunow et a l . , 1980) have successfully shown the important role of fluorine in magmatic-hydrothermal f l u i d s , and further understanding of ore-forming processes in porphyry-type systems has been gained by ca l c u l a t i n g phase relations among s i l i c a t e s , copper-iron s u l -fides, and aqueous solutions at magmatic temperatures (McKenzie and Helgeson, 1980). Knowledge of the composition of mineral phases i s a necessary prerequisite for computing chemical char-a c t e r i s t i c s of the hydrothermal f l u i d s coexisting with observed a l t e r a t i o n assemblages and zonation. Vein- and fracture-controlled mineralization in stockwork molybdenum deposits contains a l t e r a t i o n assemblages in which c r y s t a l l i n e s o l i d solutions are common constituents. This paper reports electron microprobe-analyses of a l k a l i feldspar, scheel-i t e , muscovite, and b i o t i t e s o l i d solutions in samples from the Hudson Bay Mountain and Endako ( B r i t i s h Columbia, Canada) and Questa (New Mexico, U.S.A.) stockwork molybdenum deposits. Activity-composition relations for representative analyses are 45 estimated in t h i s communication, and the composition of aqueous solutions coexisting with the a l t e r a t i o n assemblages as well as implications for the ore-forming process(es) are considered in Chapter 3. ALTERATION PETROGRAPHY A comprehensive review of the geology of Climax-type molyb-denum deposits (White et a l . , 1981) has demonstrated close spa-t i a l and temporal relations of stockwork mineralization to spe-c i f i c intrusive phases, fracturing and hydrothermal events. Detailed studies of Questa, Hudson Bay Mountain, and Endako, have been presented by Carpenter (1968) and Dunlop et a l . (1978); Bright and Johnson (1976); and Kimura et a l . (1976), respectively. Important features of the veinlet and fracture-controlled assemblages of these deposits are documented here in an abbreviated format to aid interpretation of the hydrothermal a l t e r a t i o n and to application to computation of aqueous solution compositons. Relative Age Relations The configuration and l o c a l i z a t i o n of mineralization, a l -teration zoning, and vein paragenesis are strongly influenced by multiple events of intrusion and fracture. A generalized para-genesis of cross-cutting single and composite vei n l e t s has been described for Questa, Hudson Bay Mountain, and Endako (Chapter 1 and Bloom, 1981) which indicates an ordered sequence of emplace-ment. The earliest-formed veinlets consist of barren 4 6 (molybdenite-free) quartz ± selvages of a l k a l i feldspar and bio-t i t e . Beyond ve i n l e t walls the o r i g i n a l igneous textures are preserved and mesoscopic a l t e r a t i o n envelopes are absent. The e a r l i e s t molybdenum mineralization i s associated with quartz-a l k a l i f e l d s p a r - b i o t i t e ± f l u o r i t e veinlets that exhibit a l t e r a -tion envelopes of similar mineralogy* One or more stages of quartz-molybdenite and q u a r t z - s e r i c i t e - p y r i t e molybdenite miner-a l i z a t i o n are superimposed on v e i n l e t s having the b i o t i t e - s t a b l e a l t e r a t i o n assemblage. Early b i o t i t e - s t a b l e and later s e r i c i t e -stable assemblages may l o c a l l y present contrary cross-cutting or gradational r e l a t i o n s along a single v e i n l e t ; however, as a group the s e r i c i t e - b e a r i n g v e i n l e t s invariably cut across and/or reopen e a r l i e r biotite-bearing veinlets which themselves may exhibit 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 envelopes. A l k a l i feldspar i s common to both b i o t i t e - and s e r i c i t e - s t a b l e veinlet assemblages, p a r t i c u l a r l y at Hudson Bay Mountain. A l l three veinlet assemblages may contain topaz s o l i d solution in addition to the minerals that characterize them. S t i l l later base-metal s u l f i d e (chalcopyrite-sphalerite-galena) v e i n l e t s with quartz-p y r i t e ± carbonate ± f l u o r i t e gangue have selvages and/or enve-lopes of s e r i c i t e ± a l k a l i feldspar and cut across molybdenite-bearing v e i n l e t s . Textural Variations Textural c r i t e r i a as well as r e l a t i v e position in the para-genetic sequence may also be used to d i s t i n g u i s h d i f f e r e n t o r i g -ins for the a l t e r a t i o n minerals b i o t i t e , white mica, and a l k a l i feldspar. Textures of a l t e r a t i o n minerals range from very f i n e -47 g r a i n e d aggregates to coarse, a p p a r e n t l y unreacted g r a i n s . The c r i t e r i a f o r i d e n t i f y i n g d i f f e r e n t o r i g i n s f o r the a l t e r a t i o n i n c l u d e : 1) t e x t u r a l evidence that the mineral was formed by s u b s o l i d u s r e a c t i o n of a magmatic phase with an aqueous f l u i d or by d i r e c t c o n t a c t with the f l u i d phase and 2) the s p a t i a l d i s p o -s i t i o n of a l t e r a t i o n phases w i t h i n s i n g l e v e i n l e t s and composite v e i n s . Magmatic b i o t i t e s from Questa and Hudsons Bay Mountain occur c h a r a c t e r i s t i c a l l y as coarse g r a i n e d , subhedral to euhe-d r a l g r a i n s that are g e n e r a l l y u n a l t e r e d to other phases, f r e e of c leavage, show uniform e x t i n c t i o n , and have s t r a i g h t boun-d a r i e s a g a i n s t adjacent m i n e r a l s . S i m i l a r , a p p a r e n t l y magmatic b i o t i t e from Endako appears on chemical grounds presented i n t h i s study to be completely r e c r y s t a l l i z e d to g r a i n s e n r i c h e d i n f l u o r i n e and magnesium r e l a t i v e to t h e i r o r i g i n a l igneous coun-t e r p a r t s . Magmatic b i o t i t e s may be p a r t i a l l y to e n t i r e l y r e -p l a c e d by s h e a t h - l i k e forms, r a d i a l fan-shaped a r r a y s , and p o o r l y - d e f i n e d but o p t i c a l l y continuous patches. Such r e p l a c e -ments occur p r o g r e s s i v e l y inward from o r i g i n a l g r a i n boundaries, and the maximum i n d i v i d u a l g r a i n s i z e r a r e l y exceeds 0.5mm. The replacement of magmatic g r a i n s i s s e l e c t i v e , because adjacent g r a i n s o f t e n remain u n a l t e r e d . F i n e g r a i n e d b i o t i t e composi-t i o n a l l y i d e n t i c a l to the replacement b i o t i t e occurs s c a t t e r e d along g r a i n boundaries of framework quartz and f e l d s p a r , or as patchy aggregates of g r a i n s r e p l a c i n g f e l d s p a r . Coarse g r a i n e d hydrothermal b i o t i t e most commonly occurs as sheaves of randomly o r i e n t e d , l e n t i c u l a r to t a b u l a r masses i n selvages along v e i n l e t 48 w a l l s . Composite veins o f t e n e x h i b i t a b i o t i t e selvage and one or more t r a i n s of b i o t i t e ± a l k a l i f e l d s p a r ± molybdenite which are s u b p a r a l l e l to the v e i n w a l l s and separated by quartz-molyb-d e n i t e or barren q u a r t z . T h i s f e a t u r e i s evidence f o r r e c u r r e n t f r a c t u r i n g and reopening of the v e i n s with i n g r e s s of aqueous f l u i d s . S e r i c i t e i s rare i n assemblages dominated by b i o t i t e - s t a b l e a l t e r a t i o n , and where present i s r e s t r i c t e d to minute f l a k e s wholly w i t h i n s l i g h t y a l t e r e d f e l d s p a r , or to r a r e s c a t t e r e d aggregates. Moderate development of white mica occurs p e r i -p h e r a l l y to more intense f r a c t u r e - c o n t r o l l e d a l t e r a t i o n . The s e r i c i t e c o n s i s t s of aggregates of minute, u n o r i e n t e d , almost equant f l a k e s l e s s than 0 .1mm i n maximum dimension. S e r i c i t e w i t h i n a l t e r a t i o n envelopes occurs as f e l t e d masses which r e -p l a c e a l l c o n s t i t u e n t s except q u a r t z , and which o c c a s i o n a l l y show a vague p r e f e r r e d o r i e n t a t i o n . F r a c t u r e i n t e n s i t i e s were g e n e r a l l y not s u f f i c i e n t to produce widespread c o a l e s c i n g of v e i n l e t s and a l t e r a t i o n envelopes to form p e r v a s i v e zones of a l t e r a t i o n . S e r i c i t e w i t h i n the v e i n l e t occurs as selvages l i n i n g the v e i n l e t w a l l s , as well-developed s o l i d - p h a s e i n c l u -s i o n t r a i l s encased i n q u a r t z , and as e n c r u s t a t i o n s upon or i n -t i m a t e l y intergrown with quartz-molybdenite + s c h e e l i t e (at Hudson Bay Mountain only) + base metal s u l f i d e assemblages i n open space f i l l i n g s . A l k a l i f e l d s p a r s occur as t r a i n s of euhedral c r y s t a l s which may c o a l e s c e to form monomineralic f i b r e s a l i g n e d e i t h e r normal to or p a r a l l e l with w a l l s of composite v e i n s , as i r r e g u l a r l y 49 dis t r i b u t e d s o l i t a r y grains in single v e i n l e t s , and as metasoma-t i c floodin'g adjacent to v e i n l e t s . METHOD OF INVESTIGATION AND ANALYTICAL TECHNIQUES Hand specimens were co l l e c t e d from each d i s t i n c t i v e stage in the sequence of veinlet emplacement as well as from the diag-nostic textural groups outlined herein. Sampling at regular intervals and over large portions of the known ore deposits to determine possible s p a t i a l and temporal trends accompanying mineralogic changes in a l t e r a t i o n assemblages, however, was not undertaken. Samples were taken from the 8480 and 3069 bench levels at Questa and Endako, respectively, and from d r i l l core at Questa and Hudson Bay Mountain. Petrographic examinations were undertaken on polished thin sections, and electron micro-probe analyses were made on selected magmatic and hydrothermal minerals in the v e i n l e t s . Some minerals from a l t e r a t i o n enve-lopes were analyzed, but emphasis was placed on those assemblag-es within veinlets in which position in the paragenesis r e l a t i v e to molybdenum mineralization could be established. Mineral analyses were obtained using normal wavelength-dis-persive (WDS) and energy-dispersive (EDS) methods on an au-tomated Cameca MBX electron microprobe at the Los Alamos S c i e n t i f i c Laboratory, New Mexico. WDS analyses were made with a constant accelerating potential of 15 kV and a specimen cur-rent of 0.05 micro-amperes, measured on brass. Beam diameters were adjusted from 5 to 20 microns to maximize count rates with minimum a l k a l i v o l a t i l i z a t i o n , and counts were accumulated to a 50 constant, integrated beam current. A l l c a l i b r a t i o n s were car-ried out u t i l i z i n g s t r u c t u r a l l y similar synthetic and natural b i o t i t e s , muscovite, and feldspars with Bence-Albee correction procedures. A t o t a l of 550 individual microprobe analyses of b i o t i t e , white mica, a l k a l i feldspar, and scheelite were made. Analyses reported in thi s communication represent a minimum of 10 spot analyses on each of several grains. Adjacent grains of each mineral in an assemblage were analyzed with repeated counts on several grains, and traverses across individual grains were made in an e f f o r t to determine compositional homogeneities within individual samples. Accuracy and precision were evaluated using replicate analyses of standard.mineral grains (Table I ) . Mean compositions and sample variances were calculated from the" mul-t i p l e spot analyses. Mean analyses were combined to form the overall mean and standard error when separate grains from the same veinlet assemblage did not d i f f e r s i g n i f i c a n t l y in composi-tio n . When indi v i d u a l , o p t i c a l l y continuous grains exhibited compositional v a r i a t i o n , only those analyses corresponding to the rims of those grains were employed here and used in the com-putations presented in Chapter 3. Highly variable and complex compositional zoning i s charac-t e r i s t i c of b i o t i t e and to lesser extent white mica and a l k a l i feldspar s o l i d solutions from these assemblages. Although zoning within individual c r y s t a l s i s common, compositional trends in the averaged compositions can be correlated with posi-tion in the paragenetic sequence or coexisting mineral assem-T a b l e I. Average WDS E l e c t r o n Microprobe A n a l y s e s of s t a n d a r d S o l i d S o l u t i o n Phases. S o l i d S o l u t i o n F e l d s p a r B i o t i t e B i o t i t e White M1ca St a n d a r d OR-1' FPHL' B65F ] MU-1' tt Anal 1n Mean 16 51 27 16 S101 TiO* Al iO, F e O MnO MgO CaO BaO NazO K i O F 64.18+0.72 18.82±0.16 0.01810.016 0.884+0.080 1.003±0.068 14.65+0.19 42.74+0.36 12.15+0.20 28.60+0.25 0.0110.01 11.0810.24 8.9510.27 34.3910.29 10.9610.16 35.4410.28 0.6310.12 1.1810.14 0.0110.01 0.24+0.08 8.35+0.23 45.40 0.63 31 .42 5.21 0.04 0.89 0.45 10.23 S u b t o t a l 0 = F HiO T o t a l 99.62+0.47 103.53 91 .20 94 . 27 'Amel1a A l b l t e 'WestMch and Navrotsky, 1981 ' P i k e s Peak B a t h o l l t h 'Evans, 1965. 52 blage. Compositional fluctuations within a single phase could be due either to true c r y s t a l l i n e s o l i d solution or to i n t e r -layering of a s t r u c t u r a l l y similar second phase (Page and Wenk, 1979). Because the l a t t e r scale of heterogeneity cannot be re-solved with the electron microprobe, l o c a l differences in compo-s i t i o n were ascribed e n t i r e l y to s o l i d solution. DATA PRESENTATION FOR MULTICOMPONENT SOLID SOLUTIONS Introduction Compilations of a l t e r a t i o n phase compositions from stock-work molybdenum (Gunow et a l . , 1980), porphyry copper (Jacobs and Parry, 1979; Guilbert and Schafer, 1979), and active geo-thermal systems (McDowell and Elders, 1980) report data for c r y s t a l l i n e s o l i d solution phases as s i t e occupancies or end member mole fractions derived from st r u c t u r a l formulae. This paper departs from this convention because procedures for calcu-l a t i n g the structural formulae of layer s i l i c a t e s assume that 1) the chemical analyses are both perfectly accurate and complete, and 2) either complete octahedral and/or tetrahedral s i t e occu-pancy or a constant sum of positive cation charges per unit c e l l i s achieved. The alternate methods each give r i s e to d i f f e r i n g mole fractions of end members, p a r t i c u l a r l y halogen s i t e occu-pancies, in the s o l i d solution which appear negl i g i b l e but which can become s i g n i f i c a n t when employing activity-composition r e l a -tions to predict the composition of coexisting aqueous solu-t i o n s . Regression methods for the c a l c u l a t i o n of end member mole fractions have been adopted which are not dependent on the 53 s t r u c t u r a l formulae and which consider a n a l y t i c a l uncertainties in the compositional data. Electron microprobe analyses of se-condary mineral in pre-molybdenite and molybdenum-mineralized ve i n l e t s and a l t e r a t i o n envelopes are presented here as absolute oxide weight percentage and as mole fractions of component end members derived from the regression models; a more detailed pre-sentation of analyses, including provisional s t r u c t u r a l formulae and individual analyses i s given in the appendices. Components and Compositional Space A key to interpretation of the compositional space for any s o l i d solution i s the number of substitutions possible in a naturally-occurring mineral, each complete substitution defining an end member. Whenever possible, s o l i d solution phases have been described in terms of binary s o l i d solution models. Both the a l k a l i feldspar (orthoclase-albite) and scheelite (scheelite-powellite) s o l i d solutions are so described. There i s , however, no generally accepted s o l i d solution model for any mineral with greater than two s o l i d solution end members, and in the case of layer s i l i c a t e s , there i s i n s u f f i c i e n t data to make such models. As a f i r s t approximation, multi-component s o l i d solutions for white mica and b i o t i t e assume ideal s i t e substitu-tion (Kerrick and Darken, 1975). The s i t e occupancy of an ana-lysed s o l i d solution phase can be expressed independently of any assumptions made to calculate structural formulae, and can be related d i r e c t l y to mole fractions of end members using descrip-tors for the compositional space. 54 Soli d solution descriptors relate the mole fractions of end members in binary substitution schemes to s i t e occupancies in multi-component s o l i d solutions as well as to expressions for stru c t u r a l formulae. To i l l u s t r a t e t h i s concept, consider a s o l i d solution phase in which isomorphic substitution occurs on two independent crystallographic s i t e s , as in octahedral (Fe, Mg) and hydroxyl (OH, F) substitution in b i o t i t e . In thi s simple example one descriptor, say p, defines the mole fr a c t i o n of octahedral magnesium end member (phlogopite), and another (q) defines the fluorine end member mole fraction (fluorphlogopite). Note that, since the mole fractions of end members in binary substitution schemes are l i n e a r l y dependent, one descriptor i s s u f f i c i e n t to describe each binary in terms of i t s end members. The mole fr a c t i o n of each end member within t h i s compositional space i s proportional to the area of the rectangular cross sec-tion opposite the sp e c i f i e d end member. For example, X(fluorphlogopite) in t h i s model equals ( 1 - p ) ( l - q ) . Thus, the composition of any phase within t h i s subset of compositional space i s uniquely defined by specifying a value for any two i n -dependent descriptors. If the compositional space i s expanded to include substitution on one additional s i t e (e.g., K-Na sub-s t i t u t i o n on the interlayer s i t e ) , then one additional descrip-tor i s necessary to describe any analysis within the composi-t i o n a l space. A term must appear in each s o l i d solution d e s c r i -ptor for each l i k e substitution in the compositional space. The s o l i d solution descriptors used in t h i s study have been determined by least-squares regression of the electron micro-55 probe data for end member mole fractions in the compositional space. The framework oxides of Si and Al were corrected for minor-element substitution, so that imaginary end members such as Ti b i o t i t e were not considered. Stepwise linear regression of oxide weight percentages were subject to the constraint that the c o e f f i c i e n t (mole fraction) of each end member in the model remain p o s i t i v e , i . e . the chemical analysis l i e s within the com-po s i t i o n a l space defined by the chosen set of end members. A pa r t i c u l a r combination of end members i s considered s i g n i f i c a n t only i f the residual between the observed compositions in terms of oxides and the modeled compositions in terms of end members is minimized r e l a t i v e to a l l other possible sets of end members which could describe the compositional space. The end members used in the regression analyses to describe the natural s o l i d solutions together with equations r e l a t i n g measured mineral com-positions to s o l i d solution descriptors are given in Table I I . 1. Dioctahedral Layer S i l i c a t e s Average compositions for white micas from Questa and Hudson Bay Mountain expressed both as oxide t o t a l s and as end member mole fractions are l i s t e d in Table I I I . Mole fractions of end members corresponding to stoichiometric K A 1 2 ( A l S i 3 0 , 0 ) ( O H ) 2 , N a A l 2 ( A l S i 3 0 1 0 ) ( O H ) 2 , and (K,Na)(Al,Fe,Mg) 2(Si«0, 0)(OH) 2) (mus-covite, paragonite, K-Na Fe-Mg-Al celadonite, respectively) were used as a f i r s t approximation to the compositional space repre-senting white mica. This assumes that Fe and Mg are energetic-a l l y equivalent when substituting for octahedral A l , because T a b l e I I . D e s c r i p t o r s and S t r u c t u r a l Formulae f o r N a t u r a l S o l i d S o l u t i o n s . Sol i d S o l u t i o n D e s c r i p t o r s w h i t e mica P = X ( p r g n t ) / [ X ( m s c v t ) + X ( p r g n t ) + X ( c l d n t ) + X ( F - c l d n t ) ] q = X ( c l d n t ) + X ( F - c l d n t ) r = X ( F - c l d n t ) b i o t i t e P - rX(Mg)>/[X(Mg)+3X(annite)+3X(F-minnesotaite)] q = X ( e a s t o n i t e ) r = X ( F - p h l o g o p i t e ) + X ( F - m i n n e s o t a i te) s X(F-minnesota1te) s c h e e l i te P = X ( p o w e l 1 1 t e ) / [ X ( p o w e l 1 1 t e ) + X ( s c h e e l i t e ) + X ( s t o l z i t e ) q X ( s t o l z i te) 'IMg = 3 X ( p h l o g o p i t e ) + 2 . 5 X ( e a s t o n i t e ) + 3 X ( F - p h l o g o p i t e ) in S o l i d S o l u t i o n S t r u c t u r a l Formulae w h i t e mica b i o t i t e s c h e e l 1 te K( 1-p)Al [ M g ( s ) F e ( q - s ) A l ( 1-q)]Al ( 1 -q)S i ( 3+q)0 o (OH) ( 2 - 2 r ) F ( 2r) K ( 1 - s ) M g ( 3 - q / 2 ) p F e ( 3 - q / 2 ) ( 1 - p ) A l ( q / 2 ) A l ( 1 + q / 2 - s ) S i ( 3 - q / 2 + s ) 0 . o ( 2 - 2 r ) F ( 2 r ) Ca(1-q)W0.(1-p) Table III. Mean WDS Electron Microprobe Analyses Of Hydrothermal White Mica Solid Solutions. Locat1on Sample It anal Questa QDH27-30 6 Questa QDH27-30 4 Questa HBM1 QDH78-67 H77-368.5 HBM H92-2 5 HBM H96-209.5 HBM H72-2156 SIOi TIOi Al >0i FeO MnO MgO CaO BaO NatO K»0 F 47 .98 0. 193 30.79 1 .635 .055 .40 .033 1 18 .417 O. 2. O. O. 0. 10.72 NA 44.75 0.282 34.54 2.675 0.038 1 .00 0.005 0.048 0.682 10.20 NA 48 .92 0.400 30.99 2 . 382 0.089 2.38 0.014 NA 0.418 10.76 0.777 47.20 0.078 30.03 2 .601 0.028 1.51 0.021 NA 0.076 10.97 0.268 45 .87 0.476 29.34 4.564 .030 .36 .022 .058 120 O. 3. 0. O. 0. 10.43 NA 49.21 0. 164 28 .68 3 .032 0.0 2.50 0.037 NA 0.061 10.88 1 . 148 49.58 0.118 33. 14 1 .856 0. 0. 0. 10 . B6 .058 NA 0.064 10.76 0. 192 Subtotal 94.35 94.22 97 . 13 92.78 94.27 95.71 96 .64 o = F HzO Total 0.327 3.936 100.74 0.113 3.983 96.65 0.483 3.698 98.93 0.081 4.233 100.79 Molecular Percent End Members Muscovlte Paragonlte K(Fe.Mg) CeladonIte F Celadonlte 0.657 0.065 0.271 0.005 0.773 0. 102 0. 110 0.013 0.585 0.093 0.280 0.083 0.682 0.029 0.274 0.029 0.622 0.049 0.298 0.028 0.488 0.032 0.355 0. 120 0.719 0.057 0.222 0.008 Total 0.998 0.998 1 .041 1 .015 0.997 0.994 1 .005 'Hudson Bay Mountain 58 ordering occurs in the two octahedral s i t e s only with mole frac-tions of celadonite greater than 0.5 (Velde, 1978). Substitution schemes which e n t a i l tetrahedrally-coordinated Al and Si coupled to substitution of bivalent Fe or Mg for octahe-dral Al are not included here or in the activity-composition expressions. S i g n i f i c a n t amounts of fluorine in the analyses suggest that addition of f l u o r i n e - r i c h end members to the compo-s i t i o n a l space would more accurately describe the naturally-oc-curring phases. Addition of A l 2 S i , 0 , 0 ( O H ) 2 (pyrophyllite) to account for coupled interlayer-tetrahedral substitution did not result in any meaningful improvement of the regression models. Regression models of the white mica analyses in t h i s composi-t i o n a l space are best described employing the three independent end members muscovite, fluormuscovite, and K-(Fe,Mg) c e l a d o n i t e v 2. Trioctahedral Layer S i l i c a t e s Average b i o t i t e analyses and mole fraction data tabulated according to r e l a t i v e age and a l t e r a t i o n environment have been l i s t e d in Table IV. The range of substitution and hence the extent of s o l i d solution in trioctahedral layer s i l i c a t e s (bio-t i t e ) from ore-forming systems i s largely unknown. Regression models using only isomorphic substitution in octahedral or hy-droxyl s i t e occupancies provided very poor f i t s to the oxide t o t a l s . Coupled substitutions between cations in octahedral and tetrahedral coordination combined with the isomorphic substitu-tions gave much-improved f i t s to the data. T e t r a s i l i c i c annite and phlogopite (Sabatier and Velde, 1970; S i e f e r t and Schreyer, Table IV. Mean WDS Electron Mlcroprobe Analyses Of Hydrothermal B i o t i t e S o l i d Solutions. Locat ion Questa Questa Questa HBM HBM Endako Endako Sample 0DH27-3O Q43 1"04'° Q57''66° 0 H72-2148.5 H72-2191 E74''06'0 EQM H anal 5 3 6 5 1 1 12 12 Textures V M-R V V M V M SiOi 42 .60 39, . 26 43.89 39.23 38 .61 39 .61 37 .44 TiOi 1 , .623 2. .516 0.904 2 .637 3, .596 1 , .888 2.953 Al >0> 11 . 46 13, . 10 10.29 13.85 13, .84 13 . 86 15.59 FeO 6. .989 13. .79 5.664 13.28 16 .53 1 1 , .00 16.100 MnO 0. .416 0, .797 0.261 0.872 0, .444 0, .767 0.717 MgO 22. .28 15, ,46 22.70 16.20 13, .78 18. .56 15. 19 CaO 0. .032 0. .042 0.013 0.014 0, .065 0. .049 0.064 BaO NA NA NA NA NA NA NA Na:0 0 .337 0, . 226 0.290 0. 149 0, .094 0. . 152 0. 160 K,0 9. .939 9. .857 10.24 9.910 9 , .399 10. ,36 9.575 F 7 . 377 3, ,641 7 . 165 2.438 0, , 755 3 . ,346 0.716 Subtotal 103. .05 98. 69 101.42 98.58 97. , 1 1 99. ,59 98 . 50 0 = F 3. . 106 1 . ,533 3.017 1 .027 0. ,318 1 . ,409 0. 301 0. .691 2. . 180 0.803 2.752 3. .468 2 . 384 3.530 Total 1O0. .64 99. 34 99.20 100.31 100. ,26 100. 57 101.73 Molecular Percent End Members Anni te 0. ,038 0. 209 0.014 0. 197 0. 236 0. 183 0.257 Phlogoptte 0. ,010 0. 041 0. 141 0. 160 0. 263 0. 139 0. 180 F-Phlogopi te 0. ,706 0. 308 0.680 0. 170 0. ,059 0. 316 0.000 Eastonite 0. ,111 0. 306 0.026 0.346 0. 395 0. 282 0.465 F-minnesotai te 0. . 199 0. 109 0. 131 0. 101 0. 131 0. 059 0.077 Total 0. ,984 0. 973 0.992 0.974 1 . 016 0. 979 0.979 'Hudson Bay Mountain 60 1965, 1971) which create octahedral deficiences as a means to balance charge i n e q u a l i t i e s were also considered, but addition of these end members to the regression model did not further improve the f i t . In most cases, such models could not describe the chemical analyses within the chosen compositional space. Substitution schemes with negative valence d e f i c i e n c i e s (e.g. t e t r a s i l i c i c phlogopite; Forbes, 1972 and PD-oxyannite Beane, 1974) were not considered as the chemical analyses report only t o t a l iron concentration. Consistently low a l k a l i oxide t o t a l s in the analyses of t h i s study which cannot readily be explained by the a n a l y t i c a l uncertainties r e f l e c t vacancies in the interlayer s i t e . Fe and Mg end members derived from t r i -octahedral layer s i l i c a t e s by complete removal of a l l interlayer cations and f i l l i n g tetrahedral occupancy with s i l i c a (minneso-t a i t e and t a l c , respectively) were added to the compositional space to include provision for the interlayer d e f i c i e n c i e s with the resulting regression models showing further improvement. The compositional space which best represents b i o t i t e s from t h i s study includes six hydroxyl end members and six fl u o r i n e -bearing counterparts. The set of end member components which uniquely defines analyses within t h i s space correspond in s t o i -choimetry to K F e 3 ( A l S i 3 0 1 0 ) ( O H ) 2 , KMg 3(AlSi 30, 0)(OH) 2), K ( M g 2 . 5 A l o . 5 ) ( A l 1 . 5 S i 2 . 5 0 1 0 ) ( O H ) 2 , K M g 3 ( A l S i 3 0 1 0 ) ( F ) 2 , and F e 3 ( S i 4 0 1 0 ) ( F ) 2 (annite, phlogopite, eastonite, fluorphlogopite, and fluorminnesotaite, r e s p e c t i v e l y ) . 61 ACTIVITY-COMPOSITION RELATIONS Any attempt to model the composition of a hydrothermal f l u i d in equilibrium with a given assemblage of c r y s t a l l i n e s o l i d solution phases must taken into account the a c t i v i t y of end member components. Equations r e l a t i n g measured mineral com-positions to a c t i v i t i e s of end member components used to repre-sent the natural s o l i d solution are given in Table V. The activity-composition relations corresponding to observed s o l i d solution phases are summarized in the discussions below. A l k a l i Feldspars Compositions of a l k a l i feldspars from Questa, Hudson Bay Mountain and Endako which coexist with pre-molybdenite and molybdenum-mineralized veinlet assemblages are presented in Table VI. Because these subsolidus a l k a l i feldspars generally have mole fractions less than .006 combined (Ca+Ba) end members, they are treated as a binary orthocalse(Or)-albite(Ab) s o l i d solution. Individual feldspar grains are complexly zoned, with adjacent zones d i f f e r i n g by as much as 0.10 X(orthoclase). Generally, however, X(orthoclase) l i e s between the extremes of 0.86 and 0.96, and X(albite) in coexisting Na-rich feldspars within the much narrower range from 0.92 to 0.99. Two a l k a l i feldspars, one K-rich and one Na-rich s o l i d solution phase, co-exist in some veinlet assemblages from Hudson Bay Mountain. In such s p e c i f i c cases, a unique temperature of formation at a given pressure can be obtained. In the general case, however, only one a l k a l i feldspar i s present and temperature can only be T a b l e V. A c t i v i t y - C o m p o s i t i o n R e l a t i o n s f o r Thermodynamic Components In N a t u r a l S o l i d S o l u t i o n s . Sol i d Thermodynamic Act 1v1ty-Compos i t i on S o l u t i o n Component R e l a t 1 on White M1ca K A l t ( A 1 S 1 i ) 0 i o ( O H ) t a = ( 1 - p ) ( 1 - q ) [ | 2 ( 1 - r 2 ) ' ] N a A l . ( A 1 S 1 i ) 0 i o ( O H ) i a = p ( 1 - q ) [ | 2 ( 1 - r 2 ) ' ] B i o t i t e K F e i ( A 1 S 1 1 ) 0 i o ( O H ) i a = ( 1 - s ) ( 1 - p ) ' ( 1 - q ) ° ' s ( l - r ) ! K M g j ( A l S l 3 ) 0 i o ( O H ) i a = (1-s)(p)'(1-q)°" s(1-r)' K M g 3 ( A l S i i ) 0 i o ( F ) t a = ( l - s ) ( p ) ' ( 1 - q ) ° s ( r ) ' A l k a l 1 F e l d s p a r K A l S l i O . 1 n a : = [X'(Ab)(W ?i+2X(0r)(W ,*-W . . ))]aRT + l n X N a A l S i 1 O 1 1 n a : = [ X ! ( 0 r ) ( W i;+2X(Ab)(W !.-W , z )) ]aRT + l n X S c h e e l 1 t e CaWO. a = ( l - p ) O - q ) CaMoOa a = ( p ) ( 1 - q ) Table VI. Mean WDS electron microprobe analyses' of hydrothermal a l k a l i feldspar s o l i d solutions LocatIon Sample ff anal Questa QDH27-30 6 Questa QDH315 32 ! 3 Questa Q57"'66 0 0 2 HBM1 H58-980 10 HBM H58-980 6 HBM H77-368.5 8 HBM H96-209.5 4 S10. Al *0, CaO Na*0 K*0 BaO 64.42+0.33 18.7910.25 0.03+0.02 0.4310.11 16.08+0.24 0.21+0.09 66.12+0.52 18.33±0.06 0.015+0.02 1.86±0.18 13.8110.39 O.1010.05 64.14+0.19 18.0210.04 0.0110.01 0.54+0.03 15.7710.01 0.0710.01 65.45+0.16 18.81+0.15 0.02+0.02 1.1810.20 14.8810.35 0.19+0.09 64.5910.61 18.6610.22 .0410.03 .47+0.17 15.9210.40 0.2510.05 0. 0. 68.32+0.23 19.4010.23 0.07+0.02 11.7010.13 0.11+0.02 0.05+0.06 64.8210.15 18.2710.01 0.0510.02 2.1810.30 13.61+0.40 0. 1210.1 i Total 99 .96 100.24 99.55 100.53 99.93 99.65 99 .06 Molecu!ar Percent End Members Or thoclase A l b l t e Anorth i te Celslan 0.958 0.040 0.002 0.004 0.827 0. 168 0.000 0.001 0.949 0.050 0.000 0.001 0.889 0. 107 0.001 0.004 0.951 0.043 0.002 0.005 0.002 0.994 0.003 0.001 0.799 0. 195 0.003 0.002 Total 1 .004 0.995 1 .000 1 .001 1 .001 1 .000 0.999 'analyst: M.S. Bloom •Hudson Bay Mountain 64 i n d i r e c t l y estimated from f l u i d inclusion studies (Chapter 1 and Bloom, 1981). A c t i v i t i e s of end members in any s o l i d solution can be written as a = 7X (1 ) In t h i s equation, a i s the a c t i v i t y of the species and X i s the mole fraction obtained from the regression model. For a l k a l i feldspars, t h i s statement i s expressed as aRTln7(0r) = X 2(Ab)(W 2 1 + 2X(0r)(W 1 2 - w 2 1 ) ) , (2) and aRTln 7(Ab) = X 2(Or)(W 1 2 + 2X(Ab)(W 2,-W 1 2 ) ) . (3) In equations (2) and (3) a i s the number of possible mixing s i t e s , T i s temperature in Kelvins, and R i s the gas constant. W 2 1 and W 1 2 are Margule's excess free energy parameters (Thompson, 1967) for the f i r s t and second end members of the binary s o l i d solution, respectively. Experimental determination of the solvus for disordered a l k a l i feldspars has been c r i t i c a l -ly reviewed by Parsons (1978), and revised values for the Margule's parameters are given in Brown and Parsons (1981). The expression for excess free energy of solution given by Thompson and Hovis (1979) has been used to generate these a c t i v i t i e s , but other expressions of the Margule's formulation could also be used. Values of a(orthoclase) so obtained are nearly i d e n t i c a l to those calculated by using the Thompson and Hovis (1979) excess function for temperatures > 500°C, but increasingly nega-tive deviations occur at lower temperatures (approximately one percent at 300°C). 65 Scheelite-Powellite A m u l t i - s i t e s o l i d solution of the type (Ca,Pb)(W,Mo)0, has the four possible end members corresponding to the stoichiometry of scheelite (CaWO„), powellite (CaMoO„), s t o l z i t e (PbWOfl), and wulfenite (PbM60«). Binary oxide s o l i d solutions with mixing on more that one s i t e can be expected to show ideal behavior i f the molar volumes of the two end members are nearly i d e n t i c a l and i f both are in the same crystallographic system (Kerrick and Darken, 1975). Each of the above end members s a t i s f i e s the cry-stallographic c r i t e r i a for ideal behavior in that a l l exhibit 14 /a space group symmetry. Molar volumes along the scheelite-po-w e l l i t e and s t o l z i t e - w u l f e n i t e binary joins generated by substi-tution in the tetrahedrally coordinated anion s i t e s d i f f e r by 0.08 and 0.44 percent, respectively, and can thus be assumed to show ideal behavior. Molar volumes along the binary joins generated by cation substitution ( s c h e e l i t e - s t o l z i t e and powel-l i t e wulfenite), however, each d i f f e r by approximately 13 per-cent, and Hsu (1981) has experimentally demonstrated an asymme-t r i c solvus along the s c h e e l i t e - s t o l z i t e binary j o i n . In view of the n e g l i g i b l e stolzite-wulfenite component indicated by ele-ctron microprobe analyses of (Ca,Pb)(W,Mo)0„ s o l i d solution phases from Hudson Bay Mountain (Table VIII), compositions in t h i s s o l i d solution are assumed to l i e along to the scheelite-powellite binary j o i n . Table VII. Mean WDS electron microprobe analyses' of Hudson Bay Mountain sch e e l i t e s o l i d solutions. Sample H anal Paragenes1s H92-2 4 C H92-2 2 R 3 H120-156.5 2 C H120-156.5 4 I • H120-156.5 3 R 3 H127-141 2 I H127-141 3 R 3 M 0 O 3 19 . 745 5 . 175 20 .005 10 .592 0.117 7 .73 0 . 140 PbO 0 .02 0.0 0 .0 0 .025 0.010 0 .017 0 .0 CaO 19 .710 18.37 19 .965 16 .422 17.870 18 .693 17 .705 WO, 61 . 192 75.610 60. . 330 70. .830 81.953 73 .493 81 .470 Total 100 .667 99.155 100. . 300 97 . 869 99.950 99 .276 99. .315 Molecular Percent End Members Scheeli te 0 .649 0.896 0. 649 0. 760 0.988 0. ,864 0. 987 Powel11te 0 .325 , 0.089 0. 334 0. 153 0.000 0. , 125 0. ,0 Stolz i te 0 .013 0.007 0. 009 0. 044 0.010 0. 006 0. 01 1 Total 0 .987 0.992 0. 992 0. 957 0.998 0. 998 0. 991 1 core ' intermediate 1 rim * analyst: M.S. Bloom 67 White Mica Activity-composition relations for muscovite and paragonite end members in hydrothermal white micas are complicated by non-i d e a l i t y of the K-Na interaction at least along the muscovite-paragonite join and by the ubiquitous presence of celadonite and fluorine-bearing end members. Any a c t i v i t y model for white micas must consider at least these e f f e c t s . Excess functions in white mica compositional space have been experimentally determined only for Na-K interaction along the muscovite-paragonite binary j o i n . Methods to calculate ac-t i v i t i e s of end members require interaction (Margules) parame-ters to describe the excess behavior of natural white mica s o l i d solutions. A mixing model could be constructed assuming that Margules parameters for K-Na interaction are i d e n t i c a l for the muscovite-paragonite and K-Na celadonite binary joins, and that s o l i d solution toward celadonite and fluorine-bearing end member is i d e a l . Such an approach does not seem warranted in the ab-sence of nearly a l l the interaction parameters, and a c t i v i t y -composition relations are employed assuming ideal s i t e substitu-t i o n . The expressions for muscovite and paragonite (the only c r y s t a l l i n e end members for which thermodynamic data are a v a i l -able) are given in Table V. 68 Trioctahedral Layer S i l i c a t e s The body of data which describes s o l i d solution behavior of b i o t i t e i s incomplete and inconclusive. Isomorphic substitution of octahedrally coordinated Fe and Mg occurs on energetically equivalent s i t e s , as shown by c r y s t a l structure analysis (Hazen and Burnham, 1973) and nuclear magmatic resonance (NMR) studies (Sanz and Stone, 1977). The expected ideal s o l i d solution beha-vior along t h i s binary i s further supported by the nearly linear volume composition r e l a t i o n shown over a large range of Fe-Mg substitution at fixed octahedral aluminum contect. Molar volume data along the phlogopite-fluorphlogopite binary j o i n , when cor-rected for minor element substitution in the interlayer s i t e , also describe a linear function of X(fluorphlogopite) and ideal behavior can be assumed (Bloom, 1976). Interaction of the two ideal isomorphous substitutions, however, produces possible or-dering of F and OH in the phlogopite and annite structures and non-ideal behavior is predicted. NMR study of Fe, F, and OH d i s t r i b u t i o n in the octahedral sheet of phlogopite (Sanz and Stone, 1979) shows that OH and F are highly d i f f e r e n t i a t e d with respect to c a t i o n i c association, and that homogeneous F-rich domains ( i . e . , l o c a l ordering) occurs. Octahedral Al substitu-tion at various fixed Mg/(Mg+Fe) rati o s also give r i s e to a non-line a r volume-composition r e l a t i o n and thus non-ideal s o l i d so-l u t i o n behavior (Newton and Wood, 1980). In the absence of thermochemical evidence and interaction parameters for non-ideal behavior, natural F-bearing b i o t i t e s o l i d solutions are treated in t h i s study as ideal s i t e mixing 69 models assuming no complications from A l - S i disorder. A c t i v i t y expressions for end members are given in Table V. . DISCUSSION Binary S o l i d Solutions The compositional v a r i a t i o n of a l k a l i feldspars, scheelite, and the layer s i l i c a t e s have been summarized in Figures 9, 10, and 11 in the form of histograms for mole fractions of component end members. Unlike the multi-component layer s i l i c a t e s o l i d solutions which show regular compositional v a r i a t i o n with r e l a -t i v e position in the paragenetic sequence, histograms for the binary a l k a l i feldspar and scheelite s o l i d solutions each exhi-b i t a d i s t i n c t l y bimodal d i s t r i b u t i o n regardless of the r e l a t i v e age. The signature of late-stage hydrothermal a c t i v i t y and re-mobilization of ore-forming components i s shown by the presence of both s c h e e l i t e - r i c h and r e l a t i v e l y scheelite-poor populations in the s o l i d solution from Hudson Bay Mountain (Figure 9a). The electron microprobe studies reveal that where early molybdenum-r i c h scheelite grains are in contact with a subsequent a l t e r a -tion assemblage, thin irregular patches decorating healed f r a c -tures and along c r y s t a l faces become progressively depleted in the powellite component u n t i l the latest-observed scheelite s o l i d solution (which occurs as euhedral c r y s t a l s projecting into open vugs and as encrustations on intergrowths of quartz-s e r i c i t e - p y r i t e ± molybdenite) correspond with the powellite-poor population of Figure 9a. This i s consistent with the gen-er a l transport model for remobilization of molybdenum from W-Mo 70 100 — i 0. 0 0. 1 0.2 0.3 0. 4 0.5 0. 6 0.7 0. 8 0.9 1.0 ^ Scheelite F i g u r e 9. D i s t r i b u t i o n of end members i n b i n a r y s o l i d s o l u t i o n s , a) S c h e e l i t e - p o w e l l i t e from Hudson Bay Mountain; skewed d i s t r i b u t i o n toward lower s c h e e l i t e mole f r a c t i o n s r e -f l e c t s s o l v a t i o n and r e d e p o s i t i o n of s c h e e l i t e by post-magmatic s o l u t i o n s ; b) A l k a l i f e l d s p a r s o l i d s o l u t i o n s from Questa ( s o l i d bars) and Hudson Bay Mountain (hatchured b a r s ) ; note K- and Na-r i c h compositions which provide an independant means to estimate temperatures of d e p o s i t i o n . 71 deposits by late meteoric f l u i d s proposed by Wesolowski and Ohmoto (1981). In the case of the orthoclase end member (Figure 9b), the presence of two coexisting a l k a l i feldspars in equilibrium with the ore-forming.solutions can be observed or inferred. Inter-growths of two compositionally d i s t i n c t a l k a l i feldspars in the same vein assemblage have been observed only from Hudson Bay Mountain, but vein associations do occur from Questa in which two feldspars are present. The f a i l u r e to form discrete i n t e r -growths which unambiguously define equilibrium i s envisioned to be the result of discrete, randomly-distributed nucleation s i t e s one the substrate vein walls. The averaged compositions of K-r i c h a l k a l i feldspar from Questa and Hudson Bay Mountain overlap one another and are similar to compositions reported from other vein and fracture-controlled styles of mineralization (Brimhall, 1977). The range of compositions observed at a single location and in individual grains, however, exhibits marked variation which i s not resolved on Figure 9b. The mole fractio n of the orthoclase end member shows small and l o c a l l y o s c i l l a t i n g , but ove r a l l regular increases with approach toward molybdenite or chalcopyrite grains. This behavior i s consistent with decrease in temperature as inferred in Chapter 1 and Bloom, 1981 and at-tendant r e d i s t r i b u t i o n of a l k a l i chlorides in the aqueous f l u i d s (Lagache and Weisbrod, 1977; Pascal and Roux, 1981), and with the variation in a c t i v i t y r a t i o s of aqueous species as a func-tion of temperature computed by Bird and Norton, (1981). 72 MUSCOVITE/SERICITE SOLID SOLUTIONS Histograms for the end members in a l t e r a t i o n white micas show consistent values for a l k a l i s in interlayer positions, a consistent range of departures from tetrahedral S i - A l s t o i -chiometry (coupled with Fe and Mg substitution in octahedral coordination), and substantial substitution of fluorine for OH in the hydroxyl s i t e . Figure 10 presents a remarkably uniform range of X(muscovite); both Questa and Hudson Bay Mountain have a near normal d i s t r i b u t i o n with a standard deviation (1a) of 0.14 about the mean of 0.65. The corresponding range of the Na-bearing end member i s confined to 0.0 ^ X(paragonite) 5 0.1 and 0.0 ^ X(paragonite) < 0.2 at Hudson Bay Mountain and Questa, respectively (Figure 10). Departures from pure muscovite s t o i -chiometry toward more trioctahedral celodonite-rich micas i s suggested by the X(celadonite) component shown in Figure 10. The range of substitution i s consistent and 0.0 ^ X(Fe,Mg cel a -donite) ^ 0.3 with Fe/Mg generally ^ 1.0. Although the poten-t i a l for wide va r i a t i o n in fluorine content i s produced by the evolving a l t e r a t i o n process, the histogram of X(fluormuscovite) (Figure 11d) shows that the extent of fluorine substitution i s limited at Questa and Hudson Bay Mountain to 0.14±0.04 (1a) in accord with the experimental results of Munoz and Luddington (1977). The wider range of paragonite mole fractions at Questa sug-gests an isothermal hydrothermal solution of higher Na/K r a t i o coexisting with the white mica a l t e r a t i o n phase during one or more stages of the paragenesis, but i s also in agreement with 73 100 - i 8 0 H 0. 0 0, 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1.0 F-muscovite Figure 10. D i s t r i b u t i o n of end members muscovite (a) and f l u o r -muscovite (b) in hydrothermal white mica s o l i d solutions from Questa ( s o l i d bars) and Hudson Bay Mountain (hatchured bars). Note confluence of modes between deposits as well as from tex-t u r a l types within i n d i v i d u a l deposits. 74 the observation by Capuano and Cole (1982) that s o l i d solution in white mica i s temperature-dependent and must be included in ca l c u l a t i o n of component a c t i v i t i e s for fluid-mineral e q u i l i -b r i a . The dependence of compositional v a r i a t i o n , both with the tetrahedral and octahedral s i t e s , upon l a t e r a l and v e r t i c a l po-s i t i o n as observed by Guilbert and Schafer (1979) was not de-tected in th i s study; white micas were not sampled with enough regularity to define trends in their d i s t r i b u t i o n or make unam-biguous interpretations regarding their octahedral s i t e occupan-cies or dependencies on possible physical gradients. Compositions of white mica projected to the p:q, p:r, and (p+q):r descriptor faces of the compositional space are shown in Figure 12. White mica compositions from the Henderson stockwork molybdenum deposit (Gunow et a l . , 1980), from the Santa Rita porphyry copper deposit (Jacobs and Parry, 1979), and from the Salton Sea geothermal system (McDowell and Elders, 1980) are also shown for comparison. (The reader must exercise d i s c r e t i o n with interpretations from the l a t t e r , as the models do not i n -clude analyses for f l u o r i n e ; they are included here to demon-strate the possible problems a r i s i n g from a n a l y t i c a l data which do not include f l u o r i n e ) . White micas from Henderson and Santa Rita occupy separate, d i s t i n c t f i e l d s on the muscovite-paragonite-(K,Na)(Fe,Mg) c e l a -donte ( i . e . , p:q face) with Henderson micas having the higher celadonite component. Dioctahedral layer s i l i c a t e s from Questa and Hudson Bay Mountain, however have compositions that are not r e s t r i c t e d to either f i e l d . Both exhibit a narrow range of com-75 position along the K-Na binary join and a wider range of cela-donite component. A regular progression of layer s i l i c a t e com-position i s shown by the Salton Sea s e r i c i t e s (McDowell and Elders, 1980), with regular compositional and textural changes as the a l t e r a t i o n assemblage varies with temperature. There i s a s i g n i f i c a n t and regular approach toward pure muscovite s t o i -chiometry u n t i l at the higher temperatures reported by McDowell and Elders (1980) and compatible with those inferred for white micas from t h i s study, the compositions cannot be distinguished. There i s an obvious separation of the micas from t h i s study as well as from Santa Rita and those reported at Henderson when the analyses are projected to fluor-hydroxyl (p:r) compositional space. This indicates that the analysed white micas from Questa, Hudson Bay Mountain, and Santa Rita formed in a fluorine-poor environment r e l a t i v e to Henderson. Henderson s e r i c i t e s tend to be more f l u o r i n e - r i c h in character, as ex-pressed by the compositions enriched in the fluormuscovite end member. Note, however, that the most fluorine-depleted white micas from Henderson overlap the most f l u o r i n e - r i c h compositions from this study, i n f e r r i n g similar chemical potentials of f l u o r -ine during the d i f f e r e n t ore-forming processes. Rotation of the compositional space and projection to the combined f l u o r -hydroxyl-(K,Na) mica-(K,Na)(Fe,Mg) celadonite face ((p+q):r des-c r i p t o r ) also emphasizes the anamolously high fluorine in Henderson s e r i c i t e when compared to samples c o l l e c t e d from Questa, Hudson Bay Mountain, and Santa Rita. It i s apparent that projections which do not consider fluorine-bearing com-76 ponent end members do not adequately distinguish white micas from stockwork molybdenum and copper porphyry environments of deposition. It follows from the anomalously high fluorine values found in Henderson s e r i c i t e , contrasted with the lower values found in similar molybdenum-mineralized deposits, that high fluorine although often diagnostic of molybdenum-bearing hydrothermal systems i s not necessarily required for the mobili-zation, transport and deposition of molybdenum. B i o t i t e S o l i d Solution Histograms presenting the d i s t r i b u t i o n s of end members for trioctahedral layer s i l i c a t e s at Questa, Hudson Bay Mountain and Endako are given in Figure 11. Wide, consistent ranges of phlo-gopite and eastonite component end member mole fractions are evident (Figures 11b and 11c) regardless of r e l a t i v e age, where-as the mole fractions of component annite, fluorphlogopite, and fluorminnesotaite (Figures 11a , 11d , and l i e ) exhibit d i s t r i b u -tions in which the textural (paragenetic) variants can be de-duced. Figures 11b and 11c show uniform ranges of 0.0 ^ X(phlogopite) ^ 0.3 and 0.0 £ X(eastonite) ^ 0.2, respectively. No d i s t i n c t i o n among the various textural types i s possible in any deposit, p a r t i c u l a r l y for X(phlogopite). The apparent asym-metry of the populations (especially Questa) toward lower X(phlogopite) and higher X(eastonite) i s probably an a r t i f a c t of a sampling bias favoring vein b i o t i t e s . B i o t i t e s from Endako maintain an eastonite component consistently lower than either Questa or Hudson Bay Mountain. 77 Figure 1 1 . D i s t r u b i t i o n of end members annite (a), phlogopite (b), eastonite (c), fluorphlogopite (d) , and fluorminnesotaite (e) in hydrothermal b i o t i t e s o l i d solutions from Questa ( s o l i d bars), Hudson Bay Mountain (hatchured bars), and Endako (open bars). Textural and/or genetic variations are discussed in text. 78 250 - i 200 O 150H 2 UJ ZD o CC 100 50 0. 0 0. 1 0. 2 0 . 3 0 . 4 0. 5 Phlogopite >• O z LU D O UJ cc u_ 250 - i 200 150 H 100 H err, L- Hytffr,.-^ 0 - p ^ S ^ M 0 . 0 0 . 1 0. 3 0. 4 0 . 5 Eastonite FREQUENCY ca CD 80 The d i s t r i b u t i o n of the annite end member i s presented in Figure 11a. The range of annite contents shown i s rather wide (0.0 < X(annite) £ 0.4) but can be grouped according to r e l a t i v e position in the paragenesis. Vein b i o t i t e s o l i d solutions from Questa exhibit compositions r e s t r i c t e d to 0.0 ^ X(annite) < 0.1; the annite content increases in replacement b i o t i t e s o l i d solu-tion, u n t i l in magmatic phases X(annite) ranges between 0.3 and 0.4. Note the faint suggestion of a bimodal population that can again be ascribed to sampling bias. B i o t i t e s o l i d solutions from Hudson Bay Mountain span the compositional range for vein and replacement b i o t i t e s shown by Questa. The s i m i l a r i t y be-tween b i o t i t e textures and compositions at Hudson Bay Mountian and Questa as well as resemblance of the f l u i d inclusion data can be used to imply isothermal conditions and/or constant chem-i c a l c h a r a c t e r i s t i c s of the aqueous f l u i d . Note that b i o t i t e s o l i d solutions from Endako are within the range 0.2 < X(annite) < 0.4, in agreement with grains which show magmatic a f f i n i t i e s from both Hudson Bay Mountain and Questa. Si g n i f i c a n t departures from the hydroxyl subset of composi-t i o n a l space toward f l u o r i n e - r i c h end members i s suggested by the X(fluorphlogopite) and X(fluorminnesotaite) histograms (Figures 11d and 11e, respectively). Questa shows the widest range of fluorphlogopite mole fractions, with 0.2 ^ X(fluorphlogopite) ^ 0.8 for replacement and vein textures, but 0.0 to 0.1 for magmatic v a r i e t i e s . Hudson Bay Mountain and Endako both exhibit a narrower range at .'lower values, with 0.0 ^ X(fluorphlogopite) ^ 0.4. This i s compelling evidence that the 81 chemical potential of fluorine was considerably higher at Questa than at Hudson Bay Mountain or Endako. A similar although less pronounced separation i s evident (Figure 11e) for the component end member fluorminnesotaite. The population of s o l i d solutions from Questa suggests a bimodal d i s t r i b u t i o n , with vein associations showing less (0.0 ^ X(fluorminnesotaite) ^ 0.2) and replacement plus magmatic asso-ci a t i o n s greater (0.0 < X(fluorminnesotaite) ^ 0.5) mole~frac-tions of t h i s end member. The d i s t r i b u t i o n from Hudson Bay Mountain shows the same range and i s consistent with t h i s obser-vation (vein b i o t i t e s show fewer interlayer vacancies than those having intermediate replacement textures or magmatic a f f i n i t i e s ) . Analyses from Endako give r i s e to a more r e s t r i c t -ed range (0.2 < X(fluorminnesotaite) < 0.5) which reinforces the compositional variation shown in magmatic and replacement bio-t i t e s from Questa and Hudson Bay Mountian. B i o t i t e compositions projected to the p:q, p:r and (p+q:r) descriptor faces for that portion of the compositional space which includes the end members annite, phlogopite, siderophyl-l i t e , eastonite, and their fluorine counterparts are shown in Figure 12b. B i o t i t e compositions from Henderson (Gunow et a l . , 1980), Santa Rita (Jacobs and Parry, 1979), and the Salton Sea geothermal system (McDowell and Elders, 1980) are again shown for comparison. Regular compositiona changes occur as a func-tion of textural variant or of relevant position in the para-genetic sequence. The o v e r a l l pattern i s p a r t i c u l a r l y well-developed on the 82 Na(Fe, Mg) celadonite K(Fe, Mg) celadonite F-muscovite Paragonite Muscovite B F-paragonite F-celadonite V>t'*o% M u s c o v i t e F-<K, Na) muscovite Paragonite Celadonite T (K, Na) muscovite Figure 12. Compositional spaces for hydrothermal mica s o l i d so-lu t i o n s . End members of s o l i d solution hypervolumes from regression analyses of electron microprobe data; composition points projected from hypervolume to faces of cube, a) White micas from Questa (open c i r c l e s ) and Hudson Bay Mountain ( t r i a n g l e s ) . Analyses from Henderson ( s o l i d t r i a n g l e s ) , Santa Rita (pluses), and Salton Sea ( s o l i d diamonds) also shown for comparison, b) B i o t i t e s from Questa, Hudson Bay Mountain, and Endako (symbols as for white micas). Also shown for comparison are Henderson, Santa Rita, and Salton Sea b i o t i t e s . 8 3 Eastonite Siderophyllite Phlogopite Annite F-annite B F-phlogopite F-eastonite F-phlogopite Annite Phlogopite Eastonite Phlogopite 84 hydroxyl (p:q) face of the compositional space i s one of a grad-ual approach of the naturally-occurring b i o t i t e from aluminous (eastonite-siderophyllite) compositions toward the most Mg-en-riched end member phlogopite. The linear trend proceeds from compositions near the siderophyllite-eastonite join (Henderson b i o t i t e from p h y l l i c alteration) to those on the annite-phlogo-pite join (hydrothermal vein b i o t i t e s from Questa). Analyzed b i o t i t e s from Questa, Hudson Bay Mountain, and Endako as well as Henderson, Santa Rita, and the Salton Sea f a l l along this trend without any apparent means for d i s t i n c t i o n . Note p a r t i c u l a r l y that magmatic b i o t i t e cannot be distinguished from hydrothermal b i o t i t e . This trend might suggest control of b i o t i t e composi-tions by the chemistry of an aqueous solution or by temperature, pressure, etc. - c h a r a c t e r i s t i c s common to numerous ore-forming processes (despite the d i f f e r i n g and unique geological environ-ment of the individual deposits), but could also be a conse-quence of the free energy surface for b i o t i t e . Compositional trends between the various textural variants, and esp e c i a l l y between the same variant associated with d i f -ferent deposits, are shown by projecting to the p:r face. The b i o t i t e from Questa, Hudson Bay Mountain, and Endako i s similar in phlogopite content to hydrothermal b i o t i t e associated with porphyry copper deposits and active geothermal systems, while the fluorine contents are higher from the molybdenum-mineralized systems. B i o t i t e compositions from Hudson Bay Mountain and Endako occupy a position intermediate between the extremes of fluorine content shown by "Climax-type" stockwork molybdenum and 85 porphyry copper deposits or active geothermal systems. Note that magmatic b i o t i t e s from Henderson are d i s t i n c t l y separate from a l l other textural and/or paragenetic variants, containing among the lowest fluorine end member and the highest annite end member of the b i o t i t e s associated with molybdenum mineraliz-ation. It would appear from th i s separation and from a similar separation on the projection to the (p+q):r face, that the t o t a l content of fluorine-bearing end members does provide a chemical d i s t i n c t i o n between b i o t i t e s of d e f i n i t e magmatic or i g i n and those of certain hydrothermal o r i g i n . Another interesting fea-ture i s the much wider scatter of compositions. The var i a t i o n of these end members i s similar to that noted by McDowell and Elders (1980) for b i o t i t e compositions in the Salton Sea geo-thermal system. On increasing temperature, there i s a s i g n i f i -cant and regular trend away from the phlogopite-fluorphlogopite join on thi s diagram. B i o t i t e s from th i s study as well as from Henderson follow t h i s same trend, with hydrothermal vein bio-t i t e s for Questa occurring nearest the j o i n . The Endako b i o t i t e compositions, and to some extent those from Hudson Bay Mountain, infer a r e l a t i v e l y higher magmatic component for these phases. Clearly, additional research i s required to esta b l i s h the r e l a -t i v e magmatic and hydrothermal contribution to the b i o t i t e com-position, and the dependence on temperature. i 86 CONCLUSIONS Highly variable and complex compositional zoning i s charac-t e r i s t i c of s o l i d solutions phases ( a l k a l i feldspar, scheelite, white mica, and b i o t i t e ) from vein assemblages in molybdenum-mineralized ore-forming systems at Questa, New Mexico and Hudson Bay Mountain and Endako, B r i t i s h Columbia. Although zoning within individual grains i s common, compositional trends in the averaged compositions of these s o l i d solution phases can be cor-related with r e l a t i v e position of a vein assemblage in the para-genetic sequence and/or textural c h a r a c t e r i s t i c s of the phases. The key to interpretation of compositional space for any of these s o l i d solutions i s the number of substitutions possible in the naturally-occurring mineral. Whenever possible, a c t i v i t y -composition relations for s o l i d solution phases have been de-scribed in terms of binary s o l i d solution models; however, ideal s i t e substitution has been employed as a f i r s t approximation when multi-component s o l i d solutions must be described using more than two end members. The s i t e occupancies of the analysed s o l i d solution phases have been expressed independently of any assumptions made to calculate structural formulae, and using regression techniques have been related d i r e c t l y to mole frac-tions of end members used as descriptors for the compositional space. Histograms of the end members for the binary a l k a l i f e l d -spar and scheelite s o l i d solutions each exhibit d i s t i n c t l y bimo-dal frequency d i s t r i b u t i o n s . The two coexisting a l k a l i f e l d -spars, one K-rich and the other Na-rich, are assumed to have 87 grown from the same aqueous f l u i d . Combined with Margule's parameters used to describe excess free energy functions of thi s s o l i d solution, the a n a l y t i c a l data constitutes a sensitive and r e l i a b l e geothermometer which can provide a unique temperature of deposition (or a minimum estimate i f only one a l k a l i feldspar is present). The two populations shown by scheelite s o l i d solu-tion are considered the product of ingress of meteoric hydro-thermal solutions which gave r i s e to the r e d i s t r i b u t i o n of ore-forming components. Departures from pure white mica and b i o t i t e end member stoichiometries are persistent among di f f e r e n t vein assemblages and textural associations. Analysed white micas contain non-t r i v i a l values of fluor i n e , and s i g n i f i c a n t substitution on oc-tahedral s i t e s which suggest that addition of celadonite and f l u o r i n e - r i c h end members to the compositional space more ac-curately describes the naturally-occurring phases than a ternary model. White micas were not sampled with enough regularity, however, to define trends in s p a t i a l d i s p o s i t i o n , or to make unambiguous interpretations regarding their octahedral s i t e oc-cupancies. Systematic compositional v a r i a t i o n i s common to three of the five end members chosen to describe b i o t i t e s o l i d solutions. Mole fractions of the annite component end member are highest in magmatic b i o t i t e s o l i d solutions, intermediate in those which exhibit replacement textures, and s i g n i f i c a n t l y lower in b i o t i t e s o l i d solutions from vein assemblages. The d i s t r i b u t i o n of component fluorine-bearing end member (f l u o r -phlogopite and fluorminnesotaite) mole fractions also show sys-88 tematic change with paragenesis. There i s a regular decrease in the mole fraction of fluorminnesotaite, and thus progressively fewer interlayer vacancies, from magmatic to vein b i o t i t e s o l i d solution associations. The fluorphlogopite end member mole fra c t i o n i s greater by a factor of approximately 5 in vein bio-t i t e s o l i d solution than i s i t s magmatic counterpart. An important implication from the data of mole fractions describing white mica and b i o t i t e s o l i d solutions involves the influence of temperature on the d i s t r i b u t i o n of components. A number of authors (Capuano and Cole, 1982; Bird and Norton, 1981; McDowell and Elders, 1980) have noted that both b i o t i t e and white mica s o l i d solutions are temperature dependent. A l -though f l u i d inclusion data (Chapter 1 and Bloom, 1981) indicate similar depositional temperatures for the assemblages examined in t h i s study, no attempt has been made to separate the effects of evolving isothermal f l u i d composition from temperature-depen-dence. Additional research i s required to establish the r e l a -t i v e contributions of coexisting aqueous f l u i d s and the depen-dence of temperature on layer s i l i c a t e s o l i d solutions. 89 I I I . THEORETICAL PREDICTION OF FLUID-MINERAL EQUILIBRIA  INTRODUCTION The o r i g i n and evolution of certain hydrothermal solutions can be understood in terms of the e q u i l i b r a t i o n of an aqueous phase with i t s mineralogical environment. Probably the best known work of t h i s general nature i s on active geothermal sys-tems (Bird and Norton, 1981; Capuano and Cole, 1982), which pro-vide a unique glimpse at the chemical and physical processes that occur during hydrothermal a l t e r a t i o n . Other works which have discussed the influence that temperature, pressure, and f l u i d composition have on the formation of coexisting mineral phases include Merino ( 1975), Knight (.1977) , and McKenzie and Helgeson (1979). Our perception of hydrothermal environments, however, and p a r t i c u l a r l y those which have resulted in p r e c i p i t a t i o n of ore components, i s impaired by our i n a b i l i t y to sample hydrothermal solutions in an active ore-forming system. Detailed petrograph-ic and geochemical investigations of hydrothermal a l t e r a t i o n phases have led to the use of a l t e r a t i o n mineralogy and composi-t i o n a l v a r i a t i o n therein to discriminate among a l t e r a t i o n assem-blages of d i f f e r e n t o r i g i n , and to assess possible origins of the ore-forming s o l u t i o n ( s ) . The known chemistry of these min-e r a l assemblages places l i m i t s upon the temperature, pressure, and f l u i d composition under which the assemblage can form and allows reasonable estimation of the composition of such ore-for-90 ming solutions. A l t e r a t i o n mineralogy c h a r a c t e r i s t i c of molybdenum mineral-ized granite-molybdenum systems i s used in thi s paper to evalu-ate quant i t a t i v e l y fluid-mineral e q u i l i b r i a . The calculations employ mineral compositions and associations reported in Chapter 2. The purpose of thi s chapter i s twofold. F i r s t , i t i s to characterize, with the aid of logarithmic a c t i v i t y and fugacity diagrams, phase relations among minerals and aqueous solutions in the system K 20-MgO-FeO-Fe 203-Al 203-Si02-Mo02-H2S-HF-HCl-H 20. Secondly, the dependence of the coexisting f l u i d chemistry upon compositional variation among phases of the a l t e r a t i o n assem-blage most cl o s e l y associated with molybdenum mineralization i s assessed. THEORETICAL CONSIDERATION OF THE THERMODYNAMIC MODEL  Thermochemical Data and Conventions Evaluation of chemical e q u i l i b r i a between minerals and aqueous solutions in hydrothermal systems has been accomplished using equilibrium constants for dis s o c i a t i o n reactions of depen-dent aqueous species and the hydrolysis reactions of s o l i d min-er a l phases. The source of thermochemical data for aqueous spe-cies considered in these calculations i s Helgeson (1969), supp-lemented by data from CODATA (1976,1977), and Smith (pers. comm.). Thermochemical equilibrium constants for miner-al s and gases are calculated using data reported by Helgeson et a l . (1978), unless otherwise s p e c i f i e d . Explanation of the sources and data treatment for those s o l i d phases and gases not 91 considered by Helgeson et a l . (1978) i s given in Table XI. Although these data may not be e n t i r e l y consistent with the Helgeson et a l . (1978) data base, they at least provide a rea-sonable approximation of the actual equilibrium conditions. In the calculations which follow, the standard state for H 20 and the i n t e r c r y s t a l l i n e standard state for sol i d s is unit a c t i v i t y of the pure component at any temperature and pressure. The i n t r a c r y s t a l l i n e standard state for s o l i d solution minerals requires that a l l a c t i v i t y c o e f f i c i e n t s of atoms on the l a t t i c e s i t e s approach unity as the mole fractions of the atoms on the site s approach those of the stoichiometric end member species chosen as thermodynamic components at any pressure and tempera-ture. The standard state for aqueous species other than H 20 i s one of unit a c t i v i t y in a hypothetical one molal solution re-ferenced to i n f i n i t e d i l u t i o n at any pressure and temperature. For gases the standard state i s one of unit a c t i v i t y of the hy-pothetical ideal gas at one bar and any temperature. The spe-c i f i c expressions for ca l c u l a t i n g a c t i v i t i e s of the components, l i s t e d in Chapter 2, are derived from the general equation r e l a -ting s i t e occupancy in the given mineral to the a c t i v i t y of the thermodynamic component as reported in Chapter 2. These expres-sions are consistent with those presented in Helgeson et a l . (1978) and Helgeson and Aagaard (1981), except that p r e f e r e n t i a l s i t e occupancies and order-disorder in tetrahedral coordination have not been considered. The d i s t r i b u t i o n of element concentrations among aqueous species i s calculated using program PATH (Helgeson et a l . , 1970) Table VIII. Thermochemical data for molybdenum and f l u o r i n e minerals. Cp c o e f f i c i e n t s Phase AH °* . i S ° m a bx10 3 cx10" 5 CM F1uortopaz 1 -3084 .45 105 .40 225 .20 -1 .46 -78. .31 F1uorph1ogop i t e ' -6268 .05 317 .57 414 .26 80 .04 -0 .84 Molybdenum 0 .0 28. .61 20 .41 8 . 20 0. .0 Molybdenum dioxide -587.85 50. .0 50 .95 30. .08 O. O Molybdenum t r i o x i d e -745 . 17 77 . 76 65 . 1 1 43, .92 0. .0 Molybdeni te -275 .31 62 . 59 73 .30 5. .89 -10. ,87 Powel11te -1546 .07 122. .59 88 .62 72. .56 18.04 'Barton et a l . , (1982) 'Westrich and Navrotsky, (1981) 93 rewritten by T.H. Brown and E.H. Perkins (Perkins, 1981). The a c t i v i t y diagrams presented heren were calculated using program NEWDIAG (Brown, pers. com.) and error propogations using program ERRPROP (Bloom, 1982). A l l software was written for an IBM 370H and subsequently modified by the author to compile and execute on a VAX 11/780. Diagrams depicting equilibrium phase relations were prepared by computer program DIAGPLT (Bloom, 1982). Computation of F l u i d Chemistry Numerous methods for computing homogeneous chemical e q u i l i -bria in aqueous solution (the d i s t r i b u t i o n of aqueous species) have been presented in the geochemical l i t e r a t u r e and are com-prehensively reviewed by Nordstrom et a l . (1979) and Wolery (1979). Few of the existing numerical algorithms have been adapted for computing heterogeneous e q u i l i b r i a in geochemical systems. Wolery (1979) and Reed (1982) have described methods for c a l c u l a t i n g the c h a r a c t e r i s t i c s of heterogeneous chemical e q u i l i b r i a for sp e c i f i e d bulk compositions, temperature, and pressure. The approach employed here for solving the heteroge-neous equilibrium problem i s e s s e n t i a l l y the monotone sequences technique (Wolery and Walters, 1975), modified for a heteroge-neous chemical system consisting of an aqueous phase with d i s -solved ions and complexes and one or more s o l i d and gas phases. Unlike other methods described in the l i t e r a t u r e , the algorithm does not require that an i n i t i a l fluid/rock r a t i o be spec i f i e d , although i t should be stated that other techniques may be better . suited for al t e r n a t i v e applications of chemical e q u i l i b r i a com-94 putat ions. In any system at equilibrium, there i s one mass balance equation for each component and one independent mass action equation for each non-component phase or species in the system. The mass balance and mass action equations constitute a set of non-linear equations in the concentration of the species present and must be solved simultaneously using i t e r a t i v e techniques. Ionic and uncharged complexes are generally used to describe components in the aqueous phase. The only thermodynamic con-st r a i n t upon the nature and number of components, however, i s that the components must form an independent basis vector for the compositional space of a l l possible phases and species. Within these broad l i m i t s there i s no unique choice of com-ponents and any independent basis w i l l s u f f i c e to describe the system. In th i s study, mineral phases in equilibrium with the coexisting aqueous solution have been chosen as part of the com-ponent basis. The monotone sequences technique for computing equilibrium d i s t r i b u t i o n s of aqueous speicies has thus been mo-d i f i e d to provide for changing of the component basis to include s o l i d phases in equilibrium with the aqueous solution. Other modifications include provision for aqueous species or gases whose a c t i v i t i e s or fugacities are known and/or fixed, and for constraints on the a c t i v i t y of water (Perkins, 1981). 95 Limitations of the Model Recent advances in t h e o r e t i c a l geochemistry allow quantita-t i v e description of the chemical c h a r a c t e r i s t i c s of s u p e r c r i t i -cal hydrothermal solutions from detailed observations of a l t e r a -tion mineralogy. These advances permit cal c u l a t i o n of the ther-modynamic properties of aqueous solutions, gases, and minerals from the equations presented by Helgeson and Kirkham (I974a,b; 1976) and Helgeson et a l . (1981). A consideration of supercri-t i c a l fluid-mineral e q u i l i b r i a (cf. McKenzie and Helgeson, 1979; McKenzie, 1981), however, i s beyond the scope of t h i s study. Bird and Norton (1981) have shown that although reaction-dependent, the dramatic e f f e c t s of the thermochemical properties of aqueous species near the c r i t i c a l point are n e g l i -gible for liquid-vapor equilibrium below approximately 300° to 350°C. The computation of fluid-mineral e q u i l i b r i a in the pre-sent communication are thus an acceptable f i r s t approximation to the chemical c h a r a c t e r i s t i c s of the aqueous solutions, but the numerical r e s u l t s w i l l be further improved by consideration of these e f f e c t s . ASSERTIONS AND PHYSICAL DESCRIPTION OF THE MODEL The assumption made here in computing chemical characteris-t i c s of the ore-forming f l u i d s i s equilibrium among stoichiome-t r i c minerals, s o l i d solution phases, and solutes in the aqueous solution. Although overa l l equilibrium is rarely attained in natural processes, the recurrence of s p e c i f i c a l t e r a t i o n assem-blages associated both in space and time with molybdenum miner-96 a l i z a t i o n (Chapter 2) attests to the widespread occurrence of l o c a l equilibrium conditions. • C r i t i c a l to the results of such calculations i s selection of a s p e c i f i c temperature, s a l i n i t y , and hydrogen ion concentra-tion (pH) at which the calculations are performed. The c a l c u l a -tions may also be sensitive to the standard state thermodynamic data, the chemical analyses of a l t e r a t i o n minerals here presumed to coexist in an equilibrium state with the aqueous solution, and approximations of the activity-composition relations of s o l i d solution phases. Whenever possible, these variables have been fixed at values which are expected to be representative of the equilibrium conditions which prec i p i t a t e d the documented a l t e r a t i o n assemblages. The e f f e c t s of those variables which could not be fixed d i r e c t l y were examined and the results of these tests are described later in t h i s communication. Temperature-Pressure • The temperature at which the calculations are performed can be chosen from several independent l i n e s of evidence. It may correspond with dir e c t measurements of temperature in active hydrothermal environments having a l t e r a t i o n assemblages similar to those described for molybdenum-mineralized systems (Chapter 2), or i t may represent fluid-mineral e q u i l i b r i a defined by i n -dependent geothermometry. The extensive data base on the Salton Sea geothermal system (Helgeson,1968) provides measured tempera-tures which range from 300° to 350°C for aqueous solutions in equilibrium with stoichiometric quartz and s o l i d solutions of i • 97 b i o t i t e , white mica, and a l k a l i feldspar. Homogenization tem-peratures of primary f l u i d inclusions observed in a l t e r a t i o n assemblages which t y p i f y the onset of molybdenum mineralization (Chapter 1 and Bloom, 1981) exhibit a range of temperatures from approximately 320° to 400°+C. The d i s t r i b u t i o n of orthoclase component between coexisting a l k a l i feldspars in the a l t e r a t i o n assemblages (Chapter 2) also indicates depositional temperatures in the range 320° to 400°+C. A single temperature (350°C) con-sistent with these observed temperatures has been chosen to model the fluid-mineral e q u i l i b r i a . S a l i n i t y , Ionic Strength, and a(H 2 0) The s a l i n i t y at which the computations are performed, while not a f f e c t i n g the a c t i v i t y r a t i o s for aqueous species, w i l l have a s i g n i f i c a n t e f f e c t on the t o t a l m o l a l i t i e s of solutes and the predominant dissolved species. S a l i n i t y i s here assumed to be controlled by equilibrium between h a l i t e and the f l u i d (Cloke, 1979). The aqueous phase coexisting with h a l i t e and the s i l i -cate a l t e r a t i o n assemblage contains large concentrations of NaCl and KC1 with stoichiometric ionic strength less than ten. Hy-persaline brines are commonly reported in porphyry-type depos-i t s . . Both dir e c t evolution from a c r y s t a l l i z i n g magma and par-t i t i o n i n g of dissolved constituents into an aqueous solution attending condensation of a s u p e r c r i t i c a l magmatic f l u i d (Henley and McNabb, 1978; Eastoe, 1981) are possible contributors to the hypersaline solutions. The high concentrations of e l e c t r o l y t e s associated with molybdenum mineralization and documented in 98 Chapter 1, Bloom(1981), and White et a l . (1981) are here re-garded as products of processes that operated on f l u i d s that were progenitors of those considered in this study. The hyper-saline f l u i d s present a multitude of geochemical problems, and here i t i s intended to examine only the fluid-mineral e q u i l i b r i a associated with the primary deposition of molybdenum at 350°C. High concentrations of el e c t r o l y t e s notwithstanding, the a c t i v i -ty of H 20 r e l a t i v e to the l i q u i d standard state i s commonly close to unity (Helgeson, 1981). The phase relations among min-erals and aqueous solutions presented below were generated for a(H 20) = 1.0 in the a c t i v i t y and fugacity diagrams, and for a(H 20) = X(H 20) in the f l u i d for d i s t r i b u t i o n of aqueous spe-c i e s . THERMODYNAMIC COMPONENTS AS CONSTRAINTS FOR SOLUTE SPECIES E q u i l i b r i a among any a l t e r a t i o n mineral, or any spe c i f i e d s o l i d phase in the presence of an aqueous f l u i d , and ionic or complexed aqueous species can be written (Bird and Norton, 1981) 0 = Ir}(i,r),//(i) + Z i ? ( l f r ) 0 ( l ) (4) where the subscripts i and 1 respectively denote the mineral and the species (<}>) in the coexisting f l u i d . In t h i s equation TJ i s the stoichiometric reaction c o e f f i c i e n t for the rth reac-tion which i s positi v e for products and negative for reactants. The logarithm of the law of mass action for equation (4) allows the thermodynamic a c t i v i t i e s of aqueous species to be written 9 9 Z i 7 ( l , r ) l o g [ a 0 ( l ) / a ( H + ) ] = log K(P,T,r) - Zr?(i,r)log arj/d) (5) K(P,T,r) in equation (5) i s the equilibrium constant for the statement of reaction (4) at a s p e c i f i e d pressure and tempera-ture; a i s the a c t i v i t y of the subscripted reaction component, and z i s the charge of the i t h aqueous species. Simultaneous evaluation of s p e c i f i c statements of equation (5) for e q u i l i b r i a between a mineral phase and an aqueous solution, computed impli-c i t l y with the modified monotone sequences algorithm, are used in this study to calculate the chemical c h a r a c t e r i s t i c s of an ore-forming f l u i d compatible with the observed mineral assem-blages from molybdenum mineralized systems. Minerals included as constraints to the fluid-mineral e q u i l i b r i a are those de-scribed as a l t e r a t i o n phases i n F - r i c h , b i o t i t e - s t a b l e assem-blages reported in Chapter 2. The choice of mineral phases used in the model to constrain solutes in the aqueous phase and im-p l i c a t i o n s for the computed fluid-mineral e q u i l i b r i a are consid-ered in the following discussion. Typical reactions used to evaluate thermodynamic a c t i v i t i e s and fugacities of solute spe-cies in the aqueous solution are summarized in Table IX. The d e f i n i t i o n of components states that, for any geochemi-ca l system involving oxidation-reduction equilibrium, the mini-mum number of thermodynamic components necessary to completely describe the system i s the number of elements plus one. Inspec-tion of Table IX reveals a t o t a l of 13 elements. Any combination of 14 stoichiometric s o l i d s , s o l i d solution end mem-bers, gases, and aqueous species w i l l then quantify the chemical T a b l e IX. D i s s o c i a t l o n a l E q u i l i b r i a f o r Thermodynamic Components and E x p r e s s i o n s f o r S o l u t e A c t i v i t i e s E1ement D i s s o l u t i o n / H y d r o l y s i s r e a c t i o n S p e c i e s S o l u t e A c t i v i t y H H i O = 2H* + 1/20! + 2e- [H*] ( [ K * ] [ A l 3 * ] 3 [ H . S i 0 4 ] 3 / [ K A l ] S l 3 0 , o ( O H ) 1 ] K ) - ' ° 0 f ( o . ) e x t e r n a l l y f i x e d F CaF. = Ca'* + 2F" [F-] (K[CaF»]/[Ca'*])-» Na NaAlSI.O. + 4H* + 4 H J O = Na* + A l ' * + 3H4S10. NaCl = Na* + CI -[Na* ] K [ N a A l S 1 . 0 e ] [ H 2 0 ] ' [ H * ] ' / [ A 1 3 * ] [ H 4 S 1 0 4 K [ N a C l ] / [ C l " ] ]' Mg KMg.AlSI.OiOF!+8H*+2HIO = K*+3Mg'*+A1 3*+3H«S10«+2F" [Mg"*] (K[KMg.A1S1 101o F 1 ] [ H . 0 ] ' [ H * ] ' / [ K * ] [ A 1 ' 4 ] [ H . S 1 0 . ] 3 [ F Al A l i S i O . F . + 4H* = 2A1'* + H.SiO. + 2F" K A 1 J S I I O I o ( O H ) t + 10H * = K * + 3A1 5* + 3H4S10.0. [ A l ' * ] ( K [ A 1 i S 1 0 . F i ] [ H + ] V [ H 4 S 1 0 . ] [ F - ] ' ) " ' ( K [ K A 1 . S 1 . O i o ( O H ) . ] [ H * ] ' ° / [ K * ] [ H 4 S 1 0 . ]')"3 S1 S10» + 2H.0 = H4SIO4 [ H 4 S I O 4 ] K/[S10i][H»0] S f(S») e x t e r n a l l y f i x e d CI NaCl = Na* + CI" [C1-] K [ N a C l ] / [ N a * ] K KA1S1.0. + 4H* + 4H.0 = K* + A l 3 * + 3H.S104 KA 1 1 S 1 1 0 1 0 ( O H ) 1 + 10H* = K* + 3A1>* + 3H4SIO4 [K*] K [ K A l S i . 0 > ] [ H . 0 ] ' [ H * ] V [ A l ' * ] [ H . S i 0 . ] 3 K[KA1.SI.Oi o(OH)»][H*] " > / [ A l 3 * ] 3 [ H « S i O « ] 3 Ca CaS04 + 2H* = Ca'* + 1 / 2 S i + 3/20. + H.O [ C a 1 * j K [ C a S O . ] [ H * ] ' / [ S . ] " [ H . O ] Fe F e i O i + 6H* = 2 F e 3 * + 3H.0 K F e . A l S I . O i o(OH). + 10H* = K* + 3Fe< * + A l 3 * + 3H4SIO4 [Fe'*] [Fe'*] K [ F e I 0 . ] [ H * ] « / [ H . O ] ' ( K f K F e . A I S i . 0 . o ( O H ) . ] [ H * ] '°/[K*][Al'* ] [ H . S i 0 4 ] ' ) - ' Mo MoS. + H.O + 320. = M0O4--+S1 + 2H* [M0O4""] K [ H . 0 ] [ 0 ! ] " [ S . ] [ H * ] ' 101 c h a r a c t e r i s t i c s of the aqueous solution, provided that the entire component basis i s l i n e a r l y independent. It has been shown (Chapter 2) that a l t e r a t i o n assemblages and f l u i d inclusions most closely associated with the onset of molybdenum mineralization at Questa, Hudson Bay Mountain, and Endako contain the s o l i d solution phases a l k a l i feldspar, bio-t i t e , and white mica as well as stoichiometric anhydrite, f l u o r i t e , h a l i t e , hematite, molybdenite, and quartz. In addi-ti o n , the f ( 0 2 ) , f ( S 2 ) , f(HF), and pH are independently calcu-lated or measured. This set of components (including the end members of s o l i d solutions) overdetermines the geochemical sys-tem, and in so doing v i o l a t e s the phase rule. This i s not to say that the mineral assemblage under consideration here i s not in equilibrium, although in some instances t h i s may c e r t a i n l y be the case. Indeed, the superposition and interaction of hydro-thermal events and assemblages i s commonly recognized. Rather, i t indicates that each thermodynamic component can be used to constrain only one non-component species, giving some f l e x i b i l i -ty to the selection of stoichiometric s o l i d phases or s o l i d so-l u t i o n end members to be s p e c i f i e d as components in the model assemblage. The ultimate and most r e l i a b l e check of equilibrium conditions and the selection of constraining components l i e s in comparing the observed a l t e r a t i o n assemblages with s o l u b i l i t i e s of minerals found in the altered rock and the computed concen-t r a t i o n of dissolved species. In the paragraphs which follow, i t i s convenient to i d e n t i f y s p e c i f i c components as constraints for i n d i v i d u a l solutes. It i s important to note, however, that 1 02 the computational algorithm does not make such d i s t i n c t i o n s , but simultaneously evaluates the set of a l l mass action expressions. A select group of phases can place l i m i t s on only one inde-pendent species. Molybdenite i s the only molybdenum phase found in s u f f i c i e n t abundance to be considered the primary ore miner-a l . It is used throughout t h i s study to constrain the molybde-num concentration in the aqueous phase. Fluorphlogopite, ha-l i t e , and quartz are likewise used exclusively to constrain the respective concentrations of Mg2 + , Na +, and H f tSiO„. Constraints for aqueous A l 3 + and K+ can be from among the orthoclase component of a l k a l i feldspar, the muscovite component of white mica, and fluortopaz. These phases do not contain d i -valent cations and thus cannot serve as constraints for C a 2 + , Mg 2 +, or F e 2 + . Different permutations of these phases each give r i s e to d i f f e r i n g a c t i v i t i e s of K +; A l 3 + remains e s s e n t i a l l y constant regardless of the phase eliminated from the model as-semblage. Computations assuming the muscovite component as the K+ constraint result in u n r e a l i s t i c Na +/K + ratios in the f l u i d which are not in agreement with the ratios inferred from saline f l u i d inclusions. Because white mica i s the predominant phase in lower temperature a l t e r a t i o n assemblages (Chapter 1 and Bloom, 1981), i t i s here regarded as the possible product of overprinting and omitted as part of the model assemblage. It w i l l be reintroduced subsequently to test hydrogen ion a c t i v i -t i e s . Fluortopaz also contains fluorine, and along with f l u o r i t e and fluorphlogopite can serve as the constraint for dissolved f l u o r i n e . Fluorphlogopite places l i m i t s on Mg 2 +, 103 which precludes th i s end member as a constraint for other cons-t i t u e n t s . Together with fluortopaz and fluorphlogopite as parts of the model assemblage, f l u o r i t e places reasonable l i m i t s on F~ concentrations. The log H20/HF values so predicted by the model are consistent with those reported by Gunow et a l . (1980) and calculated in thi s study. F l u o r i t e i s common to another group of phases capable of placing l i m i t s upon the concentration of aqueous C a 2 + . Stepwise addition of anhydrite, anorthite, and c l i n o z o i s i t e to the model assemblage containing f l u o r i t e conclusively demonstrates that anhydrite sets the upper l i m i t for dissolved C a 2 + . C l i n o z o i s i t e and anorthite both result in an aqueous phase supersaturated with respect to f l u o r i t e , even when vanishingly small a c t i v i t i e s of the end members are employed. Moreover, c l i n o z o i s i t e has not been observed in the a l t e r a t i o n assemblages and anorthite i s c l e a r l y a reactant phase and i s not in equilibrium with the aqueous solution. The constraint on F e 2 + may be from among the stoichiometric phases hematite and magnetite, and the end member annite (for which an a c t i v i t y has been calculated). Hematite i s the most plausible constraint. The occurrence of both hematite and, to a lesser extent, magnetite in the al t e r a t i o n assemblage suggests that f ( 0 2 ) cannot-be far removed from the hematite-magnetite boundary. This i s in agreement with direct measurement of f l u i d inclusion gas fugacities (Smith and Norman, 1981) which place f ( 0 2 ) within the hematite s t a b i l i t y f i e l d , and with hematite observed as a daughter product in f l u i d inclusions (Chapter 1 1 04 and Bloom, 1981). F i n a l l y , three to four independent variables ( f ( 0 2 ) and f( S 2 ) , pH, and CI) have been fixed for each computation. The gas fugacities are consistent with the f l u i d inclusion gas anal-yses reported by Smith and Norman (1981) and the pH with the assumption of a hydrothermal solution approximately one pH unit below n e u t r a l i t y . Gas fugacities could also be constrained by s o l i d - s o l i d gas buffers which employ end member species of s o l i d solutions not yet used as thermodynamic components. The annite component of b i o t i t e s o l i d solution could constrain f ( 0 2 ) by the reaction 2KFe 3AlSi 3Oio(OH) 2 + 3/2 0 2 = 2KAlSi 30 8 + 3Fe 20 3 + 2H20 (6) By replacing f ( 0 2 ) w i t h ' a c t i v i t i e s of the annite component ran-ging from 0.001 to 0.1 (Chapter 2), f ( 0 2 ) in the narrow range from -24 to -27 i s obtained, in excellent agreement with the measured value. Chloride ion i s fixed as an independent com-ponent because one ionic species must be present in the com-ponent basis for balancing e l e c t r i c a l n e utrality in the aqueous f l u i d . 1 05 DISCUSSION OF FLUID-MINERAL EQUILIBRIA  A c t i v i t y Ratios of Solute Species Evaluation of chemical e q u i l i b r i a between minerals and so-lutions in molybdenum-mineralized hydrothermal systems requires determination of the s o l u b i l i t i e s of ore and gangue minerals known to occur in the altered rocks as well as aqueous molybde-num speciation. In the f i r s t instance, fluid-mineral e q u i l i -brium i s represented as a c t i v i t y and fugacity r a t i o s in the ore-forming f l u i d s without consideration of molybdenum in the aqueous phase; the molybdenum speciation and concentration w i l l be addressed subsequently. The s t a b i l i t y f i e l d boundaries in Figures 13 through 19 depicting phase relations among a l t e r a t i o n minerals, gases, and the aqueous solution were generated for 350°C using thermochemical data c i t e d previously. 1. V o l a t i l e Species Phase relations among minerals in the system Mo-Fe-O-H-F-S are depicted in Figure 13 as a function of log f ( 0 2 ) and f ( S 2 ) in the f l u i d phase. The bold curves and labels delimit s t a b i l i -ty f i e l d s for minerals in the subsystem Mo-O-H-S in the presence of an aqueous solution. The l i g h t curves and labels represent phase relations for minerals in the subsystem Fe-O-H-S in the presence of an aqueous phase and either iron oxide, magnetite, hematite, pyrrhotite, or p y r i t e . The f ( 0 2 ) and f ( S 2 ) at which hematite and molybdenite are compatible i s quite limited i f these phases are in equilibrium. These l i m i t s are between -22 and -28 for log f ( 0 2 ) and -3 to -9 for log f ( S 2 ) . A much 106 2 0 OH CO <X CD L U CD >-X o 2 ~ 4 f l -CD O - 6 0 J L MOLYBDITE MELflNTERITE HEMATITE MAGNETITE PYRRHOTITE - 8 0 MOLYBDENUM - 4 0 - 3 0 - p . - 2 0 -10 PYRITE MOLYBDENITE ! 10 LOG fl(SULFUR GRS) Figure 13. Phase re l a t i o n s in the system MoS 2-FeS-FeS 2-H 20 in the presence of an aqueous solution at 350°C and steam satura-t i o n . Bold and fine phase boundaries for the molybdenum and iron subsystems, respectively. Sources of thermochemical data for phase diagrams in Figures 13 through 19 discussed in text. 1 07 larger range of f ( 0 2 ) and f ( S 2 ) i s attainable in molybdenite-pyrite v e i n l e t s for which f ( 0 2 ) i s not constrained by the pre-sence of hematite or magnetite. Although reasonable to allow f ( S 2 ) and f ( 0 2 ) to be wholly dependent on coexisting phases, f l u i d inclusion gas analyses calculated by Smith and Norman (1981) place values for these fugacities within the hematite s t a b i l i t y boundaries. In the computations which follow, the respective log f ( 0 2 ) and log f ( S 2 ) are -26 and -9 unless other-wise s p e c i f i e d . 2. [a(K+)/a(H+)] and [a(Fe 2+)/a(H+) 2] The consequences of variable f(HF) in the f l u i d phase on mineral compositions, c o m p a t i b i l i t i e s and [a(K +)/a(H +)] are shown in Figure 14. It can be seen that at quartz saturation the s t a b i l i t y f i e l d for stoichiometric muscovite i s located at larger log [a(K +)/a(H +)] values than i s the andalusite s t a b i l i t y f i e l d . At even greater log [a(K +)/a(H +)] orthoclase i s stable. Stoichiometric K-feldspar and muscovite are here depicted by the bold phase boundaries. The superimposed boundaries shown in lig h t e r l i n e s are for a(K-feldspar) and a(muscovite) equals 0.96 and 0.66, respectively (Chapter 2). It can be seen that these s o l i d solutions may coexist with stoichiometric fluortopaz only a log f(HF) near -2.75, remarkably close to the f(HF) calculated from F - b i o t i t e compositions, and at [a(K +)/a(H +)] of approxi-mately 4.7. The eff e c t of compositional variation in fluortopaz s o l i d solution on the respective [a(K +)/a(H +)] and f(HF) in aqueous solution i s to s h i f t the fluortopaz phase boundary to more negative values of log f(HF). The range of a(fluortopaz) 108 8 7 -6 -5 5 + CD 3 O 2H 0 - f K-FELDSPAR MUSCOVITE ANDALUSITE T -7 -6 T -5 -4 FLU0RT0PRZ - 3 - 2 T -1 LOG A(HF GAS) Figure 14. Phase r e l a t i o n s in the system K 20-Al203-Si0 2-H 20-HF as a function of log [a(K +)/a(H +)] and log f(HF). Computed for presence of an aqueous solution at 350°C saturated with respect to steam and quartz. Stoichiometric compositions (bold boun-daries) and those adjusted for the a c t i v i t i e s of orthoclase and muscovite in a l k a l i feldspar and white mica s o l i d solutions (fine boundaries) considered as well as flourtopaz a c t i v i t y (equals 1.0 for bold and 0.1 for fine boundaries). 109 shown here is 0.1 to 1.0; topaz analyses from molybdenum-miner-a l i z e d systems, however, indicate compositions very near s t o i -chiometric fluortopaz. The corresponding a c t i v i t i e s calculated from the activity-composition relations for topaz reported in Barton et a l . (1982) are consistent with log f(HF) between -2.7 and -2.8. Phase relations in the subsequent a c t i v i t y and fuga-c i t y diagrams depict e q u i l i b r i a for K-feldspar and muscovite s o l i d solutions and stoichiometric fluortopaz. E q u i l i b r i a among stoichiometric k a o l i n i t e and the musco-v i t e , K-feldspar, and b i o t i t e s o l i d solutions in the presence of an aqueous f l u i d are depicted in Figure 15 as a function of log [ a ( F e 2 + ) / a ( H + ) 2 ] and log [ a ( K + ) / a ( H + ) ] . It can be seen in t h i s -figure that K-feldspar and muscovite s o l i d solutions may coexist with b i o t i t e s o l i d solution having log a(annite) between -1.0 and -3.0 over a wide range of [ a ( F e 2 + ) / a ( H + ) 2 ] . The range of [ a ( F e 2 + ) / a ( H + ) 2 ] consistent with b i o t i t e s o l i d solution in which a(annite) i s similar to that reported in Chapter 2 i s r e s t r i c t e d to log [ a ( F e 2 + ) / a ( H + ) 2 ] between 0.0 and 0.5 and i s independent of [a(K +)/a(H +)] i f i t i s to coexist with the K-feldspar s o l i d solution. 3. [ a ( M g 2 * ) / a ( H + ) 2 3 and [a(Ca 2+)/a(H+) 2] The r e l a t i v e s t a b i l i t i e s of stoichiometric k a o l i n i t e and fluortopaz and the K-feldspar and fluorphlogopite s o l i d solu-tions are shown in Figure 16 as a function of log [a(Mg 2 +)/a(H +) 2] and log [ a ( K + ) / a ( H + ) ] . The a(fluorphlogopite) in t h i s diagram equals 0.8 (Chapter 2). As f(HF) in the f l u i d phase increases, lower magnesium rat i o s are required to s t a b i -110 LOG fl(K+)/fl(H+) Figure 15. Phase rel a t i o n s in the system K 20-Al 20 3-Si0 2-FeO-H 20 as a function of log [a(K*)/a(H*)] and log [a(Fe 2 *)/a(H*) 2 ]. Computed for steam-saturated water at 350°C in the presence of quartz. Muscovite and a l k a l i feldspar phase boundaries c a l c u l a -ted for a c t i v i t i e s of respective end members in corresponding s o l i d solution. Annite a c t i v i t y varied from 0.1 (bold boun-daries) to 0.001 (fine boundaries). 111 LOG fi(K+)/fl(H+) Figure 16. Phase relations in the system K 2G~Al 20 3-Si0 2-MgO-H 20-HF as a function of log [a(K*)/a(H +)] and log [a(Mg 2 +)/a(H*) 2]. Computed for steam-saturated water in the presence of quartz. Muscovite and K-feldsar phase boundaries calculated as in Figure 15. Log f(HF) varies from -4.0 (bold boundaries) to -2.0* (fine boundaries); note that fluortopaz i s increasingly stable with respect to muscovite + K-feldspar such that the assemblage fluorphlogopite + fluortopaz + muscovite + K-feldspar defines a unique log f(HF). 1 12 l i z e fluorphlogopite at a given potassium r a t i o . Note that at log f(HF) greater than approximately -3.0 kaolin i t e disappears and i s replaced by fluortopaz as the stable phase. The s t a b i l i -ty boundary of fluortopaz s h i f t s to larger [a(K +)/a(H +)] values with increasing f(HF), and muscovite i s s i m i l a r l y replaced as the stable phase at log f(HF) > -2.3. It can be deduced from Figure 16 that equilibrium among the fluorphlogopite, and It-feldspar s o l i d solutions, stoichiometric fluortopaz and quartz and an aqueous phase with log f(HF) from -2.5 to -3.0 requires log [a(Mg 2 +)/a(H +) 2] in the limited range from 8.0 to 8.5. Compositional constraints imposed for calcium in the aqueous phase are shown as a function of log [ a ( C a 2 + ) / a ( H + ) 2 ] and log [a(K +)/a(H +)] in Figure 17. Calcium-bearing s i l i c a t e s which have not been observed in the a l t e r a t i o n assemblage ( c l i n o z o i s i t e and grossular) are depicted on t h i s diagram at vanishingly small a c t i v i t i e s (log a c t i v i t y equals -3.0). The absence of c l i n o z o i s i t e s o l i d solution establishes the upper l i m i t for log [ a ( C a 2 + ) / a ( H + ) 2 ] at a value dependent upon log f(HF) in the f l u i d . At log f(HF) less than approximately -3.0, stoichiometric fluortopaz does not occur as a stable s o l i d phase. An increase in f(HF) progressively replaces f i r s t kao-l i n i t e followed by muscovite with fluortopaz, u n t i l at log f(HF) = -2.75 only fluortopaz and K-feldspar can stably coexist. Con-tours of f l u o r i t e saturation as a function of log f(HF) estab-l i s h log [ a ( C a 2 + ) / a ( H + ) 2 ] consistent with the absense of c l i n o -z o i s i t e and the assemblage fluorite-K-feldspar-(muscovite)-quartz at -6.0. 113 10 14 H 12 H C N T C X J 8 CC o CE « J CD O 2H GROSSULAR FLUORlTE SATURATION @ LOG F(HF)=? CLIN0Z0ISITE KAOL r o FLUORTOPAZ MUSCOVITE T 2 T 3 I 4 T S K1FELDSPAR T 6 T 7 8 LOG fl(K+)/fi(H+) Figure 17. Phase relations in the system K 20-Al 203-Si02-CaO-H 2C-HF as a function of log [a(K +)/a<H*)] and log [ a ( C a 2 + ) / a ( H + ) 2 ] . Computed for the presence of an aqueous solution at 350°C satu-rated with respect to steam, quartz, and f l u o r i t e at log f(HF) equals -4.0 (fine boundaries) and -2.0 (bold boundaries). Ab-sence of c l i n o z o i s i t e in the a l t e r a t i o n assemblage places upper l i m i t on r e l a t i v e Ca 2 _ ,+ concentration. Increasing log f (HF) progressively s t a b i l i z e s fluortopaz at the expense of muscovite and K-feldspar as in Figure 16. 1 14 4. [a(Al 3+)/a(H+) 3] and a(H„ SiO a ) Phase relations among stoichiometric quartz, k a o l i n i t e , and fluortopaz and the K-feldspar and white mica s o l i d solutions are shown as a function of log [a(K +)/a(H +)] and log [ a ( A l 3 + ) / a ( H + ) 3 ] in Figure 18. Increase in log f(HF) from -4.0 to -2.0 results in a s h i f t of the fluortopaz phase boundary to smaller values of log [ a ( A l 3 + ) / a ( H + ) 3 ] . Simultaneously, the muscovite-fluortopaz boundary moves to higher values of log [a(K +)/a(H +)] for a given log [ a ( A l 3 + ) / a ( H + ) 3 ] . Increasing HF thus favors fluortopaz r e l a t i v e to other s i l i c a t e minerals con-sidered in t h i s study. Kaolinite i s no longer a stable phase when log f(HF) exceeds approximately -3.5, but e q u i l i b r i a among quartz, K-feldspar, and fluortopaz cannot be achieved u n t i l log f(HF) equals approximately -2.75 owing to the presence of the muscovite s o l i d solution. At greater HF fugacities the K-feldspar-fluortopaz assemblage progressively s t a b i l i z e s at the expense of the muscovite s o l i d solution s t a b i l i t y f i e l d . It can be deduced from Figure 18 that stoichiometric quartz and f l u o r -topaz are stable in the presence of the K-feldspar and muscovite s o l i d solutions and an aqueous phase at log [ a ( A l 3 + ) / a ( H + ) 3 ] equal to approximately -1.9. F i n a l l y , the dependence of the equilibrium composition for an aqueous phase coexisting with stoichiometric quartz and fluortopaz and the K-feldspar and muscovite s o l i d solutions on log f(HF) can be assessed with the aid of Figure 19, shown as a function of log [ a ( A l 3 + ) / a ( H + ) 3 ] and log a ^ S i O , ) . The acces-s i b l e aqueous f i e l d i s limited by the saturation boundaries of 1 15. -4 I L LOG R(AL+++)/fl(H+)3 T 3 Figure 18. Phase relations in the system K 20-A1 20 3-Si0 2-H 20-HF as a function of log [a(K*)/a(H +)] and log [ a ( A l 3 * ) / a ( H + ) 3 3 . Computed for the presence of steam-saturated water at 350°C with log f(HF) from -2.0 (bold boundaries) to -4.0 (fine boundaries). Increasing log f(HF) progressively s t a b i l i z e s fluortopaz at lower values of log [ a ( A l 3 + ) / a ( H + ) 3 ] . 1 16 8 6H CO H K~FELDSPflR - 6 H - 8 - 5 - 4 -3 T -t T - 2 t 0 LOG RCH4SI04) Figure 19. Phase relations in the system KjO-AljOa-SiG^-HjO-HF as a function of log [ a ( A l 3 + ) / a ( H + ) 3 3 and log a(H„SiO a) . Compu-ted for steam-saturated water at 350°C with log f(HF) from -2.0 (bold' boundaries) to -4.0 (fine boundaries). Presence of the assemblage quartz + K-feldspar + muscovite + fluortopaz with a c t i v i t i e s of s o l i d solution phases as in Figure 15 uniquely defines log f(HF). 1 17 stoichiometric gibbsite, andalusite, fluortopaz, and quartz. At quartz saturation, the value of log a(H„SiO f l) equals -2.05. The accessible values of log [ a ( A l 3 + ) / a ( H + ) 3 ] are established by • f(HF) in the f l u i d phase. Fluortopaz saturation approaches that of andalusite at a log f(HF) value of approximately -3.0. It i s clear from t h i s diagram that andalusite i s precluded from the a l t e r a t i o n assemblage by the presence of fluortopaz at log f(HF) consistent with the inferred values. Aqueous Molybdenum Speciation Complexed ions of molybdenum in oxidation states from (III) to (VI) are known to exist in low-temperature aqueous solutions. Hexavalent molybdenum i s present in oxidized solutions over a wide pH range as an oxy-cation or an oxy-acid anion. The exis-tance and properties of the Mo0 2 2 + ion in extremely acid solu-tions (Nazarenko and Shelikhina, 1971) and of the MoO„~ ion in a l k a l i n e solutions (Zhidikova et a l . , 1973) are well known. In solutions of intermediate concentration and pH, molybdic acid (H 2Mo0 4°) dissociates to bimolybdate (HMoO„~) ion. Hydrolysis and polymerization are known to occur in d i l u t e solutions (Kinslinskaya et a l . , 1977). The speciation and properties of monomeric and dimeric hydroxo-complexes have been reported by Shpak et a l . (1977). Table V l i s t s the thermochemical data for aqueous molybde-num species at 25°C. Dissociation constants for the complexes have been measured only at room temperature, and entropies of very few of these molybdenum complexes are known (Deillen et a l . , 1976). Third law entropies were thus estimated from entro-118 py c o r r e l a t i o n plots (Cobble, 1964a, 1964b). Properties for twelve molybdenum species have been considered. These include hydroxo-, chloro-, fluo.r-, and sulfo-complexes of hexavalent molybdenum, as well as the molybdyl ion and a chloride complex of pentavalent molybdenum. Much less i s known about the speciation and s t a b i l i t y of molybdenum species in lower oxidation states and in reduced aqueous solutions. Kudrin et a l . (1980) have suggested that in acid and near-neutral solutions at 450°C buffered by Ni-NiO, reduced molybdenum (V, IV, and III) predominates and have pre-sented free energy data for the neutral complex Mo0 2(OH)°. Mit'kina et a l . (1978) have investigated complex formation of molybdenum (III) with hydroxide ions at 20°C in reduced solu-tions of unknown f ( 0 2 ) . Westrich (1974) studied the s o l u b i l i t y of molybdenite in pH-buffered KCl-HCl f l u i d s coexisting with the pyrite-pyrrhotite-magnetite f ( 0 2 ) - f ( S 2 ) buffer. S o l u b i l i t i e s of up to several hundred ppm were found to be dependent on tem-perature and chloride concentration. These data suggest molyb-denum complexing with chloride at f ( 0 2 ) less than those at which the molybdenum (VI) aqueous species are stable. Only oxidized molybdenum species have been considered in t h i s study. Reduced aqueous complexes and the a l k a l i metal and s i l i c a complexes implied by Zhidikova et a l . (1973) and Westra and Keith (1982) might conceivably enhance the s o l u b i l i t y of molybdenite. It should also be noted that natural analogs for the reduced conditions studied experimentally (Westrich, 1974) exist (e.g. Trout Lake, B r i t i s h Columbia), suggesting that re-T a b l e X. Thermochemical Data For Gases And Aqueous Molybdenum S p e c i e s . Cp c o e f f i c i e n t s S p e c i e s A H 0 . . e S° 2 9 1 a MoO.- - -997047 38 .07 -481 .16 HMoO A " -980740 .172 .80 12,73 H 1 M 0 O 4 0 -970328 246 .02 145. 19 MoO.(0H) + -718378 82 . 38 307.36 MoOi 2 * -461933 -77 .49 430.48 MoO1F- -1056005 159 . 16 43.88 MoOzS* " - -553975 1 16 .69 -219.68 MoO:C1 * -619917 3 .93 212.76 M 0 O 1 C I 1 0 -780138 74 .06 -53.60 M o O i C l 3 - -932427 144 . 18 320.07 MoO* + -530996 -5 .90 366.80 MoOCl 3 0 -701903 252 . 17 2 .708 HF" -321691 93 .51 -297.022 NaCl 0 -417868 62 .76 183.259 C l g 0.0 222 .97 34.642 HClg -92312 186 .80 25.724 HFg -272546 173 .67 26.148 bx10 5 cx10- 5 2.677 5.676 3 .886 -1.7499 -2.2282 120 duced molybdenum species may contribute s i g n i f i c a n t l y to the ore-forming process in some i f not many molybdenum-mineralized deposits. The numerical values of molybdenite s o l u b i l i t y pre-sented here may thus change as estimates of the thermochemical properties for reduced aqueous molybdenum species become a v a i l -able . Using the thermochemical properties of oxidized molybdenum species reported at 25°C, the high-temperature properties of the complexes have been estimated. The temperature dependence of equilibrium constants involving the dissocia t i o n of aqueous com-plexes to Mo04"" and bare anions i s expressed in terms of Helgeson's (1967) equation of state describing aqueous d i s s o c i a -tion reactions. The average heat capacity of the molybdate ion was computed using the correspondence p r i n c i p l e (Criss and Cobble, 1964a, 1964b). Average heat capacity values for aqueous complexes were computed from ACp(reaction) values (Smith, pers. com.) using corresponding properties of the other reac-tants and products from Table XII and Helgeson et a l . (1978). The thermochemical data for dissolved molybdenum species and molybdenum minerals, when combined with the thermodynamic properties for other aqueous species and s o l i d phases in the system can be used to compute aqueous molybdenum speciation. To properly evaluate the r e l a t i v e importance of the various com-plexes, however, i t i s necessary to compare their equilibrium d i s t r i b u t i o n s in hydrothermal solutions that contain concentra-tions of the complexing ligands t y p i c a l for the a l t e r a t i o n as-semblage. Figure 20 shows the eff e c t of important intensive 121 variables on the aqueous molybdenum speciation at 350°C. The r e l a t i v e importance of molybdenum complexes for t y p i c a l concentrations of fluorid e , chloride, and su l f i d e ligands i s presented in Figure 20a as a function of log f ( 0 2 ) and pH. Fluorine and sulfur have been varied and values separating equal abundances of the complexes are shown as bold and medium li n e s for log f(HF) equals -2.0 and -4.0 at log f ( S 2 ) of -9.0, and for log f ( S 2 ) of -6.0 at log f(HF) equals -2.0 by l i g h t l i n e s , re-spectively. This diagram indicates that in near-neutral solu-tions and log f ( 0 2 ) 's between -25.0 and -30.0, two complexes (HMo04" and M 0 O 3 F " ) with lesser amounts of H 2MoO a° and Mo0 2 + contribute to the transport of molybdenum. Chloride complexes, although considered in the cal c u l a t i o n s , do not occupy separate regions of predominance; s i m i l a r l y , s u l f i d e complexes do not predominate at any geologically reasonable pH or f ( 0 2 ) . Chloride and su l f i d e complexes are therefore unimportant to the transport of molybdenum under oxidizing conditions. The central s t a b i l i t y f i e l d in Figure 20a i s indicated as a region of predominance for both HMoO,,- and M0O3F". At any log f(HF) less than approximately -2.2 HMo04" i s in greater abun-dance than M0O3F". Increasing log f(HF) above -2.2 in the f l u i d leads to an enlarged region for the fluoride complex at the ex-pense of H2MOOK° at acid pH values and of Mo0 4 2~ in alk a l i n e solution. Simultaneously, the Mo0 2 +/Mo0 3F" and Mo02S22"/M0O3F" boundaries s h i f t to more negative values of log f ( 0 2 ) at a given pH. With increasing log f ( S 2 ) the region for Mo0 2S 2 2' every-where s h i f t s to greater log f ( 0 2 ) values at a given pH. 122 O-f-i 5 r -V- I L « LOG fl(H+) Figure 20. A c t i v i t y - a c t i v i t y diagrams depicting the predominant oxidized aqueous molybdenum species in steam-saturated water at 350°C. A l l boudaries drawn at equal abundances of the complexes, Thermochemical data from Table X. Relations shown as functions of a) log f ( 0 2 ) and pH at log f ( S 2 ) equals -9.0 and log f(HF) from -4.0 (bold boundaries) to -2.0 (fine boundaries); note large central s t a b i l i t y f i e l d in which Mo03F" predominates over HMoOa" at log f(HF) greater than -2.2, and the e f f e c t of i n -creasing log f ( S 2 ) to -6.0 (dashed boundary); b) log f(HF) and pH where log f ( S 2 ) equals -9.0 and log f ( 0 2 ) varies from -26.0 (bold boundaries) to -24.0 (fine boundaries); c) log f ( 0 2 ) and log f(HF) at pH equals 5.0 and log f ( S 2 ) varies from -9.0 (bold boundaries) to -6.0 (fine boundaries); d) log f ( 0 2 ) and log f ( S 2 ) at pH equals 5.0; note phase boundaries for the system MoS2-H2S-H20-HF as in Figure 13 indicates speciation pre-dominated by Mo03F" and/or HMo04" depending on log f(HF). 123 124 2 0 J ! ' ' J L IH to cr CD 2 -20 UJ CD >-X o cc CD O HMo04-WW Mo03F~ -60 H M.O02S2--80 -6 -8 -7 -s -4 T - 2 " T -1 LOG fl(HF GflS) 125 - 4 0 - 3 0 - 2 0 -10 0 10 LOG MSULFUR GflS) 126 The apparent reversal in the predominance of HMoO„~ and M 0 O 3 F " can be better understood by inspection of Figure 20b, which shows aqueous molybdenum speciation as functions of log f(HF) and pH in the f l u i d at constant log f ( 0 2 ) (-26.0) and log f ( S 2 ) (-9.0). For the conditions s p e c i f i e d in the construction of t h i s diagram, the M 0 O 3 F " and HMoO„~ are in equal abundance at approximately log f(HF) of -2.2. Above this value, Mo03F~ pre-dominates and becomes increasingly important whereas at log f(HF) less than -2.2 i t i s replaced by HMo00". It can also be seen that a narrow region of H 2Mo0 4° predominance separates the Mo0 2 + and HMoOtt" f i e l d s . This region enlarges at the expense of Mo0 2 + with increasing log f ( 0 2 ) , but vanishes e n t i r e l y when log f ( 0 2 ) drops below -26.0. This further emphasises the importance of molybdenum (VI) species in oxidized solutions. At constant f(HF) and increasing f ( 0 2 ) , the Mo03F~ region enlarges by a s h i f t toward lower pH values. This infers that with a decrease in pH at constant f ( 0 2 ) and f(HF), the fluorine complex becomes increasingly important as a transporter of molybdenum. The e f f e c t of log f ( S 2 ) on aqueous molybdenum speciation can be examined with the aid of Figure 20c, which shows the pre-dominant complexes as functions of log f ( 0 2 ) and log f(HF) at a pH of 5. The large region for Mo0 2S 2 2" progressively encroaches upon f i r s t the Mo0 2 + and Mo03F" followed by the HMo04~ and Mo03F" regions toward higher values of log f ( 0 2 ) with an i n -crease in log f ( S 2 ) . The magnitude of this s h i f t i s such that the s u l f i d e complex cannot contribute s i g n i f i c a n t l y to the tran-sport of molybdenum are near-neutral pH u n t i l the log f ( S 2 ) ex-127 ceeds approximately -3.0 i f log f ( 0 2 ) between -25.0 and -30.0 are s t i l l in e f f e c t . In extremely a l k a l i n e solutions, much lower f ( S 2 ) are required to enter the predominant region for Mo0 2S 2 2'. Gas analyses of inclusion f l u i d s from Questa (Smith and Norman, 1981) indicate log f ( S 2 ) as high as -3.0 during the f i n a l stages of mineralization. Sulfide complexes may thus have become important in late H 2S-rich f l u i d s ; however, Mo0 2S 2 2~ i s unimportant to molybdenum transport in early stages of alteration/mineralization where the observed mineral assemblages infer log f ( S 2 ) several orders of magnitude lower. Having established which aqueous molybdenum species are plausible contributors to molybdenum transport, i t i s now pos-s i b l e to examine the relevant speciation under the f ( 0 2 ) - f ( S 2 ) conditions imposed by fluid-mineral equilibrium in the subsystem Mo-Fe-O-H-S-F (Figure 20d) and consistent with the observed s i -l i c a t e a l t e r a t i o n assemblage. In near-neutral but s t i l l a cid solutions the regions for Mo03F~ and HMoO/," coincide with the molybdenite-hematite-(pyrite) association. Values of pH one or more units below n e u t r a l i t y increase the H2MoOj,° and Mo0 2 + con-centration, whereas values on the al k a l i n e side of neu t r a l i t y progressively favor Mo0 2S 2 2". Absolute Solute Concentrations The equilibrium r e l a t i o n s h i p between the a l t e r a t i o n assemblage, ore mineralogy, and the coexisting hydrothermal solution i s quantitatively calculated at 350°C and the results of these c a l -culations are discussed below. Table VIII shows the computed fluid-mineral equilibrium for T a b l e XI. F l u i d / M i n e r a l E q u i l i b r i a : Computed 1 C o n c e n t r a t i o n of Aqueous S p e c i e s C o e x i s t i n g w i t h A l t e r a t i o n Phases' at 350°C. S p e c i e s l o g m o l a l i t y l o g grams/kgm H*0 c o n c e n t r a t i o n ( p p m ) Al ' • -14, .40 -12 .97 0 .00 A l ( O H ) 4 " -6, .05 -4 .08 0. .04 K + 0, .39 1 .98 46391, Na + 0. .91 2 .27 90447. CI - 1 , .01 2 .56 177824. NaCl 0 0. .82 2 .59 189436, Ca' * -3. , 76 -2, . 15 3 . 41 Mg' • -4. .65 -3, . 27 0. .26 MgSO.° -3 , 25 -1 . 17 32 . 85 Fe' + -7 , . 39 -5 .65 0. .00 Fe' • -19. .08 -17 . 34 0. .00 F- -3 . 04 -1 , .76 8 . 35 H.SiO. -2. 49 -0, .51 151 . 10 S' - -11. 81 -10, .31 0. .00 SO 4 ' - -1 . ,36 0, .63 2065. H.S° -4 . ,70 -3, , 17 0. . 33 H M 0 O 4 " -4 . 27 -2 , .06 4. . 22 H.MoO.0 -6. . 16 -3. .95 0. .06 MoO1F" -4. 1 1 -1 . 90 6. . 10 M0O1 • -5. ,09 -2. .98 0. ,51 'pH=5, l o g f ( S i ) = - 9 . 0 , and l o g f ( 0 i ) = - 2 6 . 0 ' M o l y b d e n l t e - b i o t l t e s o l i d s o l u t i o n - q u a r t z -f 1 u o r t o p a z - f 1 u o r 1 t e - h a l 1 t e - h e m a t 1 t e - a n h y d r 1 t e 1 29 the mineral association outlined below. Only the d i s t r i b u t i o n of bare ions and the predominant aqueous species i s given in the table, along with the predominant molybdenum species. 1. Hydrogen Ion Concentration F l u i d inclusion analyses and thermochemical calculations indicate that hydrothermal solutions are near-neutral to a c i d i c , chloride solutions (McKenzie, 1981). The pH used in the compu-tations presented here (5) i s for a hydrothermal solution ap-proximately one pH unit below n e u t r a l i t y . The pH value fixed for these computed fluid-mineral e q u i l i b r i a can be e x p l i c i t l y cross-checked using a l t e r a t i o n mineral compatibility. Replacing the fixed hydrogen ion a c t i v i t y with a s p e c i f i c a c t i v i t y of end member muscovite component permits c a l c u l a t i o n of pH values con-sistent with a(muscovite). The pH so computed varies between 4 and 6 for a range of muscovite a c t i v i t i e s from 0.6 to 0.7, in remarkable agreement with those calculated from the white mica analyses. 2. Error Propoqation The chemical-thermodynamic model of fluid-mineral e q u i l i -bria presented in t h i s communication involves the use of mineral analyses and activity-composition relations which are themselves associated with numerical uncertainties and are subject to errors which are poorly known at best. The form of these uncer-t a i n t i e s or error d i s t r i b u t i o n s of the input a c t i v i t i e s are also largely unknown. It i s therefore of considerable interest to estimate how sensitive the chemical c h a r a c t e r i s t i c s computed 1 30 from the model are to possible errors in the mineral a c t i v i t i e s used to constrain thermodynamic components. The Monte Carlo method of error propagation (Anderson, 1976) has been imple-mented to study the e f f e c t s of these errors and uncertainties, and consisted of repeated computations of heterogeneous e q u i l i -brium constrained by the presence of a given mineral or mineral assemblage, each time varying the input a c t i v i t y of one or more constraining s o l i d solution phases randomly within the observed l i m i t s using a 'rectangular' or 'uniform' error p r o b a b i l i t y d i s -t r i b u t i o n . The calculated aqueous speciation then shows the ef f e c t of the imprecision of the constraining a c t i v i t i e s . Im-precision and systematic error in the electron microprobe analy-ses are i m p l i c i t l y accounted for, and e x p l i c i t treatment of errors introduced in the activity-composition relations or by the f a i l u r e to unambiguously i d e n t i f y the equilibrium a l t e r a t i o n assemblage i s possible. Results of error propagation c a l c u l a -tions are summarized for various solute species and a c t i v i t y r a t i o s respectively in Table IX. These results indicate that, although absolute uncertainties in both compositions and thermo-chemical data can be s i g n i f i c a n t , the e f f e c t s are not apparent in the f i n a l computations. 3. Molybdenum Concentration and P r e c i p i t a t i o n Mechanisms Fluid-mineral equilibrium calculations at 350°C show that molybdenite i s soluble to the extent of only a few ppm for any geologically reasonable range of pH, f ( 0 2 ) , and f ( S 2 ) where fluorine i s present only in t r i v i a l concentrations. S i g n i f i -Table XII. Monte Carlo Simulation of Error Propogatlon m Computed D i s t r i b u t i o n of Aqueous Species. log molality log grams/kgm HzO concentration(ppm) •phase varied mean 1<j species' mean \<s mean 1o mean \o fluorphlogopite 0. 214 0. .09 Mg' • -4 . 67 -5. 45 -3. ,29 -4 . ,06 0. 25 0.04 MgSO.0 -3. 26 -4 . ,04 -1 . , 18 -1 . ,95 32.30 5.44 K * 0. 32 -5. ,64 1 . ,92 -4 . ,05 40480. 0. 18 fluortopaz 0. 900 0. . 10 Al 1 * -14. .35 -15. 52 -12. .92 -14 . ,09 0.00 0.00 A1(0H)'- -5. .99 -7 . ,05 -4. ,01 -5. , 10 0.05 0.004 K + 0. .33 -0. ,77 1 . 92 0. 82 40755. 3086. K-feldspar 0. .55 0. .05 K* 0. .90 0, ,01 2. ,49 1 , 61 133160. 14433. Na + 0. 82 -0. ,61 2. . 18 0. .75 65317. 3957 . CI - 1 . . 15 -0, , 12 2. ,70 1 . 43 215488 . 6597 . NaCl 0 0. . 73 -0. 66 2. .49 1 , 10 134852. 8593. Ca' * -3 . ,71 -5 , 63 -2. . 10 -4 , 02 3.41 0.04 Mg' + -4 . , 79 -6 , .26 -3. .41 -4 . 88 0. 17 0.01 MgSO 4 ° -3 . 52 -4 , 61 - 1 , .44 -2 . 53 15 .63 1 .64 H4S104 -2 . 53 -10, .93 -0, .54 0. .00 124 .0 2.85 K-feldspar 0. .06 0. .04 K * -1 . 30 -1 , .43 0, . 29 0. . 17 1001 . 747 .0 Na + 0. ,95 -1 , 85 2. .31 -0, .49 104666. 234.0 CI - 0, .95 -1 , .66 2, .50 -0, , 1 1 159876. 292.0 NaCl 0 0, .87 -1 . 91 2, .64 -0 . 14 220365. 510.0 Ca'* -3 . 79 -6 .68 -2, . 19 -5, .08 3.29 0.00 Mg' + -4 . 06 -4, .50 -2 .68 -3, . 12 1 .08 0.39 MgSO40 -2. .59 -5, . 37 -0 .47 -3 .39 159.0 57.91 H4Si04 -2 .45 -5 .37 -0 .47 -3 . 39 172.0 0.32 a l l phases' 0 .30 0 .25 K + 0 .33 0 .20 1 .92 1 .79 39872. 27887. Na* 0 .92 -0 .29 2 .28 1 .07 92580. 8482. c i - 1 .00 0.001 2 .56 1 .55 175403. 11474. NaCl 0 0 .83 -0 .35 2 .60 1 .41 194085. 18421 . Ca' * -3 .76 -5 .06 -2 . 16 -3 .46 3.39 0.06 Mg' + -4 .59 -4 .99 -3 .21 -3 .60 0.31 0.13 MgSO4 0 -3 . 17 -3 .40 -1 .09 -1 . 39 40.46 21.. 10 r U S i 0 4 -2 .48 -3 .78 -0 .50 -1 .80 154 .0 12.38 'bare ions and predominate complexes which vary by more than 0.1 log unit 'K-feldspar a c t i v i t y equals 0.30 + 0.25, other s o l i d solution phases as above 1 32 cantly higher molybdenum leve l s in solution are predicted in the presence of fluoride complexing, although the importance of fluor i d e complexing decreases markedly in a model where the aqueous solution i s undersaturated with respect to f l u o r i t e . The s o l u b i l i t y computations presented here d i f f e r in d e t a i l from those reported by Smith et a l . (1980). Although these d i f -ferences may considerably aff e c t the quantitative results of aqueous molybdenum speciation, the trends and p r e c i p i t a t i o n me-chanisms presented in thi s study are probably much as shown. The example of computed molybdenite s o l u b i l i t y (Table XIV) shows that approximately 12 ppm molybdenum can be transported in a s l i g h t l y acid solution at 350°C. The H20/HF rati o s resulting from the calculations are in the range for Questa presented here and for the Henderson deposit reported by Gunow et a l . , (1980), and are consistent with dissolved f l u o r i n e constrained by f l u i d -f l u o r i t e equilibrium. At the le v e l of molybdenum concentration predicted by fluid-molybdenite e q u i l i b r i a , approximately 105 kilograms of solvent H 20 is required to deposit one kilogram molybdenum as molybdenite, and 4X10 1 3 kilograms water are neces-sary to account for the 4.14X105 metric tons molybdenite present in a t y p i c a l stockwork deposit. This resulting 'geologic s o l u b i l i t y ' of molybdenite i s plausible in l i g h t of the f l u i d flux calculated by numerical models of meteoric-hydrothermal convective c i r c u l a t i o n (Cathles, 1977) i f 100 percent e f f i c i e n c y in extracting molybdenum from the aqueous solution i s assumed. Such low concentrations are not in agreement, however, with the magmatic-hydrothermal model in which molybdenum-bearing f l u i d s 1 33 are exsolved d i r e c t l y from a s i l i c a t e melt (Ganster, 1978) and deposited d i r e c t l y from the r i s i n g column or plume of magmatic f l u i d . The 'geologic s o l u b i l i t y ' thus infers that precursors to the solutions which gave r i s e to the F-biotite-K-feldspar-q u a r t z - f l u o r i t e ± molybdenite a l t e r a t i o n assemblage were s i g n i -f i c a n t l y enriched in molybdenum r e l a t i v e to the computed f l u i d -mineral e q u i l i b r i a at 350°C. P r e c i p i t a t i o n of molybdenite from such progenitor solutions could have been controlled primarily by physical temperature gradients as inferred from f l u i d i n c l u -sion data (Chapter 1 and Bloom, 1981) and suggested by Carten et a l . (1981). Indeed, the extreme temperature dependence of mo-lybdenite s o l u b i l i t y reported by Smith et a l . (1980) predicts that r i s i n g ore-forming solution(s) would deposit molybdenite in a harrow, confined zone as temperature decreased. Fluid-mineral e q u i l i b r i a , however, do infer that controls on molybdenite deposition by reactions which involve f l u o r i n e -bearing phases and/or K-feldspar can also be extremely e f f e c t i v e under isothermal conditions. One such reaction (Carten et a l . , 1981) i s 3KAlSi 30 B+MoF a°+2H 2S° = KAl 3Si 30 1 0(F) 2+6Si0 2+MoS 2+H 20+2KF° (8). This reaction assumes the presence of Mo(IV) in solution. Simi-l a r reactions using oxidized fluormolybdenum complexing may be written as 3KAlSi 30 8 +4Mo0 3F-+8H 2S°+4H + = KAl 3Si 30,o(F) 2+2KF°+6Si0 2+4MoS 2+10H 2O+20 2 (9) and 134 KAlSi 30 8+Mo0 3F-+3MgF 2 0+2H 2S°+H + = KMg 3AlSi 30,o(F) 2+MoS 2+ 5HF° +1/202 ( 1 0) . The widespread occurrence of the assemblage K-feldspar-fluorphlogopite-quartz-white mica-molybdenite which coincides with the bulk of the molybdenum mineralization i s thus explained in terms of reaction of the ore-forming f l u i d with the K-feld-spar component of the wall rock. P a r t i t i o n i n g of fluoride ion from the aqueous phase into a s o l i d phase such as f l u o r i t e , fluorphlogopite, or fluortopaz can also reduce Mo(VI) mobility in hydrothermal solutions and lead to p r e c i p i t a t i o n of molyb-denite by a reaction such as MoS2+l/2CaF2+10H++5/2O2 = Mo03F-+2S~- +1/2Ca2++5H20 (11). Note that any such reaction which involves reduction of Mo(Vl) to Mo(IV) evolves oxygen and thus progressively oxidizes the coexisting f l u i d . Roedder and Bodnar (1980) have suggested that the occurrence of hematite as a daughter product in f l u i d inclusions may be the product of post-entrapment oxidation i n -duced by hydrogen d i f f u s i o n through the quartz l a t t i c e . P r e c i -p i t a t i o n of molybdenite or cooling of trapped inclusion f l u i d containing dissolved molybdenum could, however, e f f e c t post-en-trapment oxidation without hydrogen d i f f u s i o n . Temperature de-crease redistributes aqueous molybdenum species from fluormoly-date to bimolydate complexes, and in so doing decreases the s o l -u b i l i t y of molybdenite. Reduction of Mo (VI) to Mo(lV) aqueous species i s thus an 'auto-oxidation' process which could give r i s e to concurrent p r e c i p i t a t i o n of hematite from solution given 135 the proper mass balance of dissolved iron. CONCLUSIONS Studies of a l t e r a t i o n geochemistry in molybdenum-mineral-ized hydrothermal systems (Chapter 2) indicate that mineraliz-ation occurred from solutions that were in equilibrium with vein mineral assemblages. The compositions of a l t e r a t i o n minerals from these assemblages and activity-composition relations for the s o l i d solution phases reported in Chapter 2 have been used as constraints in a chemical-thermodynamic model to deduce the composition of the coexisting aqueous solutions. The composi-tion of the ore-forming f l u i d at 350°C i s similar in composition to f l u i d s found in high-temperature geothermal systems. The a c t i v i t y of mineral components and the approximation that d i s -solved s i l i c a a c t i v i t y equal a(H«SiOi,) at quartz saturation and a(H 20) = X(H 20) are used to calculate [a(K +)/a(H +)], [a(Fe 2 + ) / a ( H + ) 2 ] , [a(Mg 2*)/a(H +) 2], [a(Ca 2 * ) / a ( H + ) 2 ] , and [ a ( A l 3 + ) / a ( H + ) 3 ] in the f l u i d phase for s p e c i f i c statements of the mass action equations. The model also permits computation of minimum molybdenite s o l u b i l i t i e s in the coexisting aqueous solution using thermo-chemical properties of oxidized molybdenum aqueous species. Molybdenite i s soluble to the extent of tens to several hundred ppm in oxidized ore-forming solutions at 350°C. S i g n i f i c a n t amounts of molybdenum are transported as fluormolybdate and b i -molybdate species; chloride and s u l f i d e complexes are not s i g n i -ficant under the conditions inferred from f l u i d inclusion data 136 (Chapter 1 and Bloom, 1981) and the phase relations discussed here. Mo03F~ and HMoO«" are present in subequal proportions at the near-neutral values of pH inferred from observed mineral c o m p a t i b i l i t i e s and calculated H20/HF ra t i o s , but Mo03F" becomes increasingly important in more ac i d solutions and at higher f(HF). The occurrence of fluorine-bearing minerals in a molybdenum-mineralized intrusion i s not a p r i o r i evidence for molybdenum transport as fluoride complexes. Computations of fluid-mineral e q u i l i b r i a presented in this study, however, i n d i -cate that under constraints imposed by f l u o r i t e saturation at 350°C, the fluormolybdate complexing i s often the primary trans-porter of molybdenum. 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APPENDIX A - MEAN ELECTRON MICROPROBE ANALYSES OF HYDROTHERMAL ALKALI FELDSPARS Sample Ana 1yses 0DH31«32' 3 QDH31 832' 2 0DH31»32» 1 0DH31»32» 1 0DH27-3O 6 QDH27-30 2 0DH27-3O 1 H92-2 3 Na.O Al .0, SiO* KiO CaO BaO 1 .860 18.330 66. 120 13.810 0.015 0. 100 1 . 170 18. 180 65.360 15.040 0.020 NA1 0.730 18.580 66.040 14.700 0.010 NA 4.610 18.610 67.720 18 . 140 0.040 NA 0.428 18.790 64.420 16.080 0.030 0.210 0.875 18 .950 63.920 15.450 0.020 0. 145 1 .570 18.920 65.370 14.480 0.0 0. 140 1 .720 18.790 65.210 14 . 170 0.083 0. 180 T o t a l 100.235 99.770 100.060 109.120 99.958 99.360 100.480 100.153 S t r u c t u r a l Formulae on the B a s i s of 32 (0) S i • 4 Al + 1 11.942 3.992 11.962 3.992 11.965 3.992 1 1 .899 3 .977 1 1 .938 4 .076 11.913 4 . 102 1 1 .959 4.052 1 1 .955 4 .057 E T e t r a h e d r a l C a t i o n s 15.934 15.954 15.957 15.876 16.014 16.015 16.011 16.012 Ca*' N a + 1 K + 1 Ba* ' 0.003 0.670 3.305 0.006 0.004 0.422 3.563 0.0 0.002 0. 294 3.693 0.0 0.008 1 .663 2.298 O.O 0.032 0. 144 3.788 0.041 0.046 0. 278 3.627 0.053 0.566 3.387 0.050 O.O 029 .623 .326 .025 E A l k a l 1 C a t i o n s 3 .984 3.989 3.989 3.969 4.005 4 .004 4.003 4 .003 Component Mole F r a c t i o n s O r t h o c l a s e A l b l t e A n o r t h i t e C e l s l a n 0.826 0. 168 0.001 0.001 891 105 001 O 0.923 0.073 0.001 0.0 574 416 002 O 0.947 0.036 0.008 0.010 0.907 0.070 0.01 1 0.013 0.847 0. 142 0.0 0.012 832 156 007 006 T o t a l O. 996 0.997 0.997 0.994 1 .001 1 .001 1 .001 1 .001 'No A n a l y s i s ' A n a l y s t : M.S. Bloom Sample H92-2 H92-2 H92-2 H92-2 H70-536 H70-536 H70-536 H70-536 A n a l y s e s 6 1 1 1 6 2 1 1 Na.O Al . O i SIO. K.O CaO BaO T o t a l 1 . 380 18.830 65.420 14.690 0.037 0.228 100.585 2. 1 10 18.670 65.1 10 13.620 0.040 0.21O 99.760 1 .090 18.960 64.830 14.730 0.020 0. 250 99.880 0.640 18.590 64.750 15.550 0.0 0.320 99.850 1 .500 18.760 65. 1 10 14.360 0.045 0.312 100.087 2.040 18.940 65.210 13 .680 0.070 0.290 100.230 0.210 18.670 64.750 16. 150 0.040 0.200 100.020 1 . 160 18.860 64.220 14 . 890 0.020 0. 300 99.450 S t r u c t u r a l Formulae on the B a s i s of 32 (0) S i + • Al * 1 C a + ' Na + 1 CO K + 1 1 1 .960 4 .057 E T e t r a h e d r a l C a t i o n s 16.017 Ba* 0.022 0.507 3.445 0.031 1 1 .967 4 .042 16.009 0.016 0.760 3.202 0.024 1 1 .933 4 . 104 16.037 0.040 0.421 3.493 0.055 1 1 .966 4 .050 16.016 0.259 3 .698 0.046 0.0 11 .955 4 .063 16.018 0.023 0.557 3.388 0.036 1 1 .940 4.076 16.016 0.032 0.731 3.201 0.040 1 1 .957 4.068 16.025 0.027 0. 106 3.839 0.034 1 1 .924 4 .093 16.017 0.035 0.405 3.511 0.053 l A l k a l 1 C a t i o n s 4 .005 4 .002 4 .009 4.003 4 .004 4 .004 4 .006 4 .004 Component Mole F r a c t i o n s O r t h o c l a s e A l b l t e A n o r t h l t e C e l s 1 an 0.861 O. 127 0.005 0.008 0.800 0. 190 0.004 0.006 873 105 010 014 925 065 0 01 1 0.847 0. 139 0.006 0.009 800 183 008 010 0.960 0.027 0.007 0.009 0.878 C. 101 0.009 0.013 T o t a l 1 .001 1 .000 1 .002 1 .001 1 .001 1 .001 1 .003 1 .001 ' A n a l y s t : M.S. Bloom Samp 1e Ana 1yses H83-601 4 H83-601 2 H83-601 1 H83-601 1 H79-402 2 H79-402 3 H79-402 2 H77-368.5 8 Na,0 Al , 0 J S I O I KiO CaO BaO T o t a l 1 .420 18.900 65.200 14.550 0.040 O. 220 100.330 1 . 130 18.720 65.130 14.720 0.030 O. 240 99.970 1 .910 19.890 65.480 13.710 0.050 0. 200 101.240 2.530 19.060 65.800 13 . 180 0.050 0.260 100.880 1 .560 18.210 64.690 14.620 0.045 O. 150 99.275 0.800 18.100 64.940 15.600 0.043 O. 387 9*9.870 1 . 120 18.210 64.550 15.120 0.035 O. 260 99.295 1 1 .700 19.400 68.320 0. 105 0.071 0.049 99.645 S t r u c t u r a l Formulae on the B a s i s of 32 (0) S1 • 4 Al * 1 1 1 .948 4 .074 1 1 .962 4.067 1 1 .866 4. 187 1 1 .947 4 .064 1 1 .965 4.012 1 1 .920 4.018 1 1 .957 4 .018 1 1 .986 4 .009 E T e t r a h e d r a l C a t i o n s 16.022 16.029 16.053 16.011 15.977 15.938 15.975 15.995 CTi Ca* ' Na + ' K* 1B a + ' 0.030 O. 520 3.417 0.038 0.024 0.448 3.499 0.036 0.085 0.673 3 . 167 0.089 0.026 0.890 3.051 0.035 0.009 0.556 3.420 0.010 0.008 0. 285 3 .666 0.026 0.007 0.401 3.568 0.018 0.010 3.972 .016 .0 O. C. E A l k a l i C a t i o n s 4 .005 4 .007 4.014 4 .002 3.995 3.985 3.994 3.998 Component Mole F r a c t i o n s O r t h o c l a s e A l b l t e A n o r t h 1 t e C e l s l a n 854 130 008 010 0.875 O. 112 0.006 0.009 792 168 021 022 0.763 0.223 0.007 0.009 855 139 002 002 917 071 002 006 0.892 0. 100 0.002 0.004 004 993 003 0 T o t a l 1 .002 1 .002 1 .003 1 .002 0.998 0.996 0.998 1 .000 • A n a l y s t : M.S. Bloom Sample H96-209.5 H96-209.5 H96-209.5 H72-2148.5 H72-2148.5 H72-2148.5 H58-980 H58-980 A n a l y s e s 2 4 3 2 3 2 6 10 Na.O Al .Oi S10. K.O CaO BaO T o t a l 2.040 18.40 64 . 46 13.74 0.070 0. 235 98.945 2. 180 18.270 64.820 13.610 0.052 O. 125 99.057 1 . 500 18.220 64.480 14;510 0.046 0.343 99.099 1 .740 18.120 65.240 14.320 0.045 0.080 99.545 1 .670 18. 130 64.800 14.560 0.043 0.243 99.446 1 .750 18.360 64.880 14. 180 0.035 0. 165 99.370 0.465 18.660 64.590 15.920 0.043 0.250 99.928 1 . 180 18.81 65.45 14.88 0.023 O. 186 100.53 S t r u c t u r a l Formulae on the B a s i s of 32 (0) O S 1 + 4 11.971 A l + ' 4.024 E T e t r a h e d r a l C a t i o n s 15.995 C a " 0.011 Na*' 0.727 K + 1 3.246 Ba*' 0.014 E A l k a l l C a t i o n s 3.998 11 .966 4.013 15.979 0.010 0. 780 3 . 196 0.008 3 .994 1 1 .947 4 .026 15.973 0.009 0.538 3.422 0.024 3 .993 1 1 .948 3.999 15.947 0.006 0.620 3.354 0.004 3.986 1 1 .947 4.013 15.960 0.008 0. 591 3 . 376 0.015 3.990 1 1 .991 4 .009 16.000 002 637 354 007 4 .000 11 .952 4.063 16.015 0.025 0. 177 3.768 0.034 4.004 1 1 .965 4 .059 1S.024 0.022 0.449 3 .504 0.031 4 .006 O r t h o c l a s e A l b l t e A n o r t h i t e C e l s l a n T o t a l 0.812 0. 182 0.003 0.004 1 .001 799 195 003 002 Component Mole F r a c t i o n s 0.999 0.856 0. 135 0.002 0.006 0.999 0.839 0. 155 0.002 0.001 0.997 0 844 148 0.002 0.004 0.998 0.839 0. 159 0.001 0.002 1 .001 0.942 0.044 0.006 0.009 1 .001 0.876 0.112 0.005 0.008 1 .001 ' A n a l y s t : M.S. Bloom Sample A n a l y s e s Q 5 3 " 6 8 ° ' 4 0 5 3 ' • 6 8 ° ' 1 057''66°° 2 057''66 0 0 2 059''67' 5 Q58"65* • 5 Na.O A l . O i S10» KiO CaO BaO T o t a l 1 .010 18.210 64 .980 15.300 0.016 0.02 1 99.537 0. 395 18. 120 63.990 16.150 0.030 O. 109 98.794 0.541 18.020 64.140 15.770 0.008 0.069 98.548 0.781 18 . 140 65.040 15.520 0.024 NA 1 99.505 0.944 18.100 65.020 15.050 0.018 0.023 99.155 0.558 18.230 64.910 15.370 0.022 0.113 99.203 S t r u c t u r a l Formulae on the B a s i s of 32 (0) SI + ' Al + ' I T e t r a h e d r a l C a t i o n s Ca + ' Na + ' K* ' in B a 4 EA1kal1 Cat i o n s 11 .976 3.997 15.973 0.003 O. 364 3.625 0.001 3.993 1 1 .992 4 .003 15.995 0.001 0. 139 3.856 0.003 3.999 1 1 .976 4 .OOO 15.976 0.001 0. 199 3.789 0.004 3.993 1 1 .964 3.994 15.958 0.004 0.285 3.700 0.0 3.989 1 1 .958 3.991 15.949 0.003 0. 349 3.634 0.001 3.987 11 .957 4.002 15.959 0.004 0.217 3.760 0.008 3.989 O r t h o c l a s e A l b i t e A n o r t h i t e C e l s i a n 0.906 0.091 0.001 0.0 Component Mole F r a c t i o n s 0.964 0.035 0.0 0.001 0.947 0.050 0.0 0.001 0.925 0.071 0.001 0.0 909 087 0O1 0 0.940 0.054 0.001 0.002 T o t a l 0.998 1 .OOO 0.998 0.997 0.997 0.997 'No A n a l y s i s ' A n a l y s t : M.S. Bloom 152 APPENDIX B - MEAN ELECTRON M1CROPROBE ANALYSES OF HYDROTHERMAL TRIOCTAHEDRAL MICAS Sample Ana 1yses QDH27-30 5 039 s"57" 0 6 Q39 5 °57» » 4 043 1°04» 0 3 Q53« «68'•' 10 053'•68"' 10 053 ' " 6 8 ° • 4 05 3 • " 6 8 ° • 5 S IO i TIO. A l ,0. FeO' MnO MgO CaO BaO Na.O K.O F S u b t o t a l 0 = F H.O T o t a l 42.60 1 .623 1 1 .46 6.989 0.416 22 . 28 0.032 NA' 0. 337 9.939 7 . 377 103.05 3. 106 0.691 100.64 41 .66 1 .576 14.95 7.818 0.496 18.13 0.026 0.024 0. 288 10.21 NA 95. 18 0.0 3.933 99 . 1 1 42.67 1 .651 1 1 .45 7 .644 -0. 395 22.02 0.020 NA O. 309 9.865 7 . 049 103.07 2.968 0.829 100.93 39.26 2.516 13. 10 13.790 0.797 15.46 0.042 NA 0. 226 9.857 3.64 1 98.69 1 .533 2 . 180 99.34 41 .98 1 .769 11.51 8.567 0.342 21 . 28 0.029 NA 0. 309 10.03 5.732 101.55 2.413 1 . 383 100.52 4 1 .54 2 .021 1 1 .46 9.212 0. 270 20.32 0.028 NA 0.303 9.876 6. 162 101.19 2.595 1 . 174 99.77 43.32 1 . 326 1 1 .33 6.511 0.257 22. 1 1 . 0.031 NA 0. 261 10.02 7 .336 102.50 3 .089 O. 724 100.14 41 .90 2.119 1 1 .37 9.422 0.294 20.81 0.015 NA 0.371 9.873 5.900 102.07 2 .484 1 .301 100.89 S t r u c t u r a l Formulae on the B a s i s of 22 (O.OH.F) S i *' 6 .089 6 . 165 5 .996 6 . 175 6 .090 6 .161 5, .868 5 .984 6 .045 6 . 1 19 6 .047 6 . 135 6 . 193 6 . 298 6 .033 6 . 107 A 1 * 4 1 .911 1 . .835 2 .004 1 .825 1 .910 1 . .839 2 . 132 2, .016 1 .963 1 .881. 1 .953 1 .865 1 .807 1 .702 1 , .939 1 . 893 E T e t r a h e d r a l 8 .000 8 .000 8 .000 8 .OOO 8 .000 8 . 000 8 OOO 8 , .000 8 .008 8 .000 8 .000 8 .000 8 .000 8 .000 7 , .972 8 .000 A l * ' 0. .030 O. . 120 0 .545 0 .787 0. .026 0. . 1 10 0, . 187 0, , 338 0 .0 0 .096 0 .023 0 .130 0, .112 0, .240 O, ,0 0 .061 T 1 + * o. . 174 0. . 177 0 .171 O . 176 0. . 177 O. . 179 0, . 283 O. , 288 0 . 192 O . 194 0 . 2 2 1 0 . 224 O, . 143 0, . 145 0, . 229 O . 232 Fe*' 0. .835 0. 846 0 .941 0, .969 0. .912 0. ,923 1 . ,724 1 . 758 1 , .032 1 .044 1 . 121 1 138 0, .778 0. .792 1 , , 135 1 . 149 Mn 4 ' o. .050 0. .051 0 .060 O .062 0. .048 0. .048 0. 101 0. 103 0, ,04 2 0 .042 0 .033 O. ,034 0. .031 0, ,032 o. ,036 0, .036 Mg * • 4 . , 748 4 . 807 3 . 890 4 . 006 4 . 685 4 . ,740 3 . ,445 3 . 513 4, . 568 4 , .624 4 , .410 4 , .474 4 . ,712 4 . , 792 4 . 467 4 , .522 i o c t a h e d r a l 5. 838 6. 000 5 . ,608 6. .000 5. .849 6. 000 5. 739 6. 000 5. ,833 6. 000 5, ,809 6. ,000 5 . 776 6 . ,000 5. ,867 6. .000 Ca*' 0.005 0.005 0.004 0.004 Ba*' O.O O.O 0.0O1 0.001 Na*' 0.063 0.064 0.054 0.056 K*' 1.812 1.835 1.875 1.931 E I n t e r l a y e r 1.880 1.904 1.934 1.992 F" ' 3.303 3.376 0.0 O.O OH" 1 0.697 0.624 4.OOO 4.000. 0, .003 0, .003 0, .007 0, .007 0, .004 0. .005 0, .0 0, .0 0 .0 O. O O O 0, O , 0 .058 0. .058 0, .044 0, .045 0. .058 0. .059 1 .796 1 . 8 17 1 , .879 1 .917 1 . 842 1 .865 1. .857 1 . 878 1 . .930 1 . ,968 1 , 905 1 , .928 3. , 164 3 . 219 1 . ,698 1 . .755 2. 593 2 . 642 0. 836 0. 781 2 . 302 2 . ,245 i . 407 1 . , 358 0, .004 0. .004 0 .005 0, ,005 0 .002 0 .002 O, ,0 0. ,0 O .0 O, ,0 0. .O O O 0, 058 0. ,058-_ 0, .04 9 0. .050 0, .070 0, .071 1 . ,834 1. ,861 1 . .827 1 . ,858 1 .813 1 . ,836 1 . 896 1. ,924 1 . 88 1 1 . 913 1 . 885 1 . 909 2 . 793 2 878 3 . ,269 3 . 373 2 . 677 2 . , 720 1 . 207 1 . 122 0. ,731 O. 627 1 . 323 1 . 280 Component Mole F r a c t i o n s A n n i t e 0.038 P h l o g o p i t e 0.010 F - P h l o g o p i t e 0.706 E a s t o n l t e 0.111 F - M i n n e s o t a 1 t e 0.199 T o t a l 0.984 0.045 0.039 .663 1 13 123 0. O. O. 0.983 0.209 0.04 1 0. 308 O. 306 O. 109 0.973 0.089 0. 146 0.544 O. 104 0.099 O. 982 0.097 0.061 0.590 O. 124 O. 109 0.981 0,016 0.029 0.682 O. 120 O. 140 0.987 0.098 O. 1 19 0.555 102 106 0. 0. 0.980 ' T o t a l I r o n as FeO 'No A n a l y s i s ' A n a l y s t : M.S. Bloom 153 Sample Q 5 4 " 8 1 ° ' Q 5 4 " 8 1 ° ' Q 5 4 " 8 1 ° , OSS'^eV1 0S5''67'' Q U 5 5 " 6 7 ' ° Q56'°68°* 056'° A n a l y s e s 3 4 3 6 4 5 5 5 SIO. •TiO. Al .0, FeO' MnO MgO CaO BaO Na.O K.O F 42 .91 1 . 154 10.87 8.535 0.325 21 .56 0.037 NA' 0.215 10.07 6 .001 43.07 1 . 198 10.87 8 . 496 0. 34 1 2 1 .78 0.021 NA 0. 224 10. 13 6.036 43.61 1 .007 10.60 7 .809 0.348 21 .96 0.057 NA O. 250 9.659 6.865 43.65 1 .291 10. 55 8.202 0.352 21 .74 0.016 NA 0.320 9.627 7 .055 43.91 1 . 215 10.44 7.510 0.319 22 .06 0.021 NA O. 328 9.678 7.214 43.34 1 . 374 10.30 7.048 0.289 22 . 12 0.021 NA 0.326 9.966 7.832 43.43 1 . 353 10.67 7 .903 0. 336 22 . 16 0.020 NA 0.278 9 .671 7 .099 43 .65 1 .461 10. 29 7 . 760 0. 302 21 .85 0.015 NA 0. 308 10.04 6 .437 S u b t o t a l 0 = F H.O T o t a l 101.68 2.527 1 .271 100.42. 102.17 2 . 54 1 1 . 262 1O0.89 102.16 2.891 0.914 100.19 102.80 2.971 0.828 100.66 102.69 3 .037 0. 770 100.43 102.62 3 . 298 0.491 99.81 102.92 2 .989 0.811 100.74 102. 1 1 2.710 1 .097 100.50 S t r u c t u r a l Formulae on the B a s i s of 22 (O.OH.F) S i * ' 6 173 6 248 6 167 6 239 6 253 6 332 6 243 6 325 6 275 6 366 6 246 6 345 6 202 6 271 6 251 6 353 A 1 ' * 1 827 1 752 1 833 1 761 1 747 1 668 1 757 1 675 1 725 1 634 1 758 1 655 1 805 1 729 1 745 1 647 E T e t r a h e d r a 1 8 000 8 000 8 000 8 OOO 8 000 8 OOO 8 000 8 000 8 000 8 000 8 004 8 000 8 007 8 000 7 996 8 000 A l * • 0 025 0 114 0 010 0 095 0 054 0 146 0 030 0 126 0 042 O 150 0 0 0 122 0 0 O 087 0 0 0 1 18 T i * ' 0 125 0 126 0 129 0 131 0 109 0 1 10 0 139 0 141 0 131 0 132 0 149 0 151 0 145 0 147 0 157 0 160 Fe* ' 1 027 1 039 1 017 1 029 0 936 0 948 0 981 0 994 0 898 0 91 1 0 849 0 863 0 944 0 954 0 929 0 944 Mn* ' 0 040 0 040 0 041 0 04 2 0 042 0 043 0 043 0 043 0 039 0 039 0 035 0 036 0 04 1 O 04 1 0 037 0 037 Mg* ' 4 624 4 680 4 649 4 703 4 694 4 753 4 635 4 696 4 700 4 768 4 752 4 828 4 718 4 770 4 665 4 741 EOctahedra1 5 840 6 OOO 5 847 6 OOO 5 836 6 000 5 828 6 000 5 808 6 000 5 786 6 000 5 847 6 000 5 788 6 OOO Ca* ' 0 006 0 006 O O03 0 003 O 009 0 009 0 002 0 002 0 003 0 003 0 003 0 003 0 003 0 003 0 002 O 002 Ba* ' 0 O 0 0 O O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Na* 1 0 040 0 04 1 0 042 0 042 0 047 0 047 0 060 0 061 0 061 0 062 0 061 0 062 0 052 0 052 0 058 0 059 K * ' 1 848 1 871 1 850 1 872 1 767 1 789 1 756 1 779 1 764 1 790 1 832 1 86 1 1 762 1 781 1 834 1 864 E I n t e r 1ayer 1 894 1 917 1 895 1 918 1 822 1 845 1 819 1 842 1 829 1 855 1 897 1 927 1 817 1 837 1 894 1 925 F" 1 2 708 2 764 2 724 2 765 3 073 3 152 3 163 3 233 3 223 3 308 3 500 3 626 3 181 3 242 2 890 2 963 OH- 1 1 292 1 236 1 276 1 235 0 927 0 848 0 837 0 767 0 777 0 692 0 500 0 374 0 819 0 758 1 1 10 1 037 Component Mole F r a c t i o n s A n n i t e 0.079 P h l o g o p i t e O.179 F - P h l o g o p i t e 0.565 E a s t o n i t e 0.054 F - M i n n e s o t a i t e 0.111 0.080 0. 184 0. 570 0.046 0. 107 0.021 O. 125 0.618 0.071 0. 155 O.026 O. 100 0.633 0.070 O. 157 0.011 O. 105 0.647 0.064 0.161 35 035 754 031 130 0.029 0.098 0.650 0.065 0. 144 0.049 O. 190 0.590 0.026 O. 131 T o t a l 0.988 0. 987 0.990 0.986 0.988 0.985 0.986 0. 986 ' T o t a l I r o n as FeO •No A n a l y s i s ' A n a l y s t : M.S. Bloom 1 5 4 Sample Ana 1yses Q57 3 166 0 0 057 3'66 0 0 4 057 3 '67» 1 5 057' °65"> 10 58°'69 5 s 8 058°'69 5 » 2 058°'69» » 5 058"'65® 5 S10. ' TiO. Al , 0 i FeO 1 MnO MgO CaO BaO Na.O K.O F Subtotal 0 = F H.O Total 43 .89 0.904 10.29 5.664 0.261 22 :70 0.013 NA' O. 290 10.24 7. 165 101.42 3.017 0.803 99.20 44.23 1 . 159 10.78 6.694 0. 244 22 .33 0.036 NA 0. 283 10. 18 6. 744 102.68 2.840 0.990 100.83 43. 13 1 .860 10.45 8.733 0. 287 21 .36 0.023 NA 0. 204 9.815 5.740 101.60 2.417 1 .392 100.58 41 .70 1 .978 1 1 .84 8.448 0.277 21 .02 0.039 NA 0.221 10.25 4 . 550 100.32 1.916 1 .904 100.31 41 .85 1 .907 1 1 .68 9.248 0.363 20.76 0.030 NA 0. 229 9.795 5 . 273 101.13 2.220 1 .58 1 100.50 42.58 1 .758 11.16 8.354 0.320 21.18 0.020 NA 0.248 9 .829 5 . 880 101.33 2 .476 1 . 328 100.18 43.47 1 .235 1 1 .00 7. 173 0.323 22.39 0.053 NA 0.262 9.810 7 . 101 102.82 2.990 0.822 100.65 43.22 1 . 387 10.99 8.205 0.281 21 .64 0.032 NA O. 240 9.550 7 . 146 102.69 3.009 0.788 100.47 Structural Formulae on the Basis of 22 (O.OH.F) SI * * Al * ' ETetrahedral Al 1 • T I * * Fe* ' Mn* ' Mg* ' roctahedral Ca* » Ba* ' Na* 1 K* 1 I I n t e r 1ayer F- ' OH" 1 6 .317 6 .434 6 .275 6 . 390 6 . 188 6 .274 6 .009 6 .095 6 .032 6 . lOI 6 . 130 6 .217 6 . 195 6 . 273 6 . 190 6 . 265 1 . 683 1 . 566 1 .725 1 .610 1 .776 1 . 726 1 .991 1 .905 1 .968 1 .899 1 .870 1 .783 1 .805 1 . 727 1 .810 1 . 735 8 .OOO 8 .000 8 .000 8 .000 7 .964 8 .000 8 .000 8 .000 a .000 8 .000 8 .000 8 -OOO 8 .000 8 .000 8 .000 8 .000 O .071 0 .212 O .086 0 . 226 0 .0 0 .066 0 .030 0 . 135 0 .026 0 . 107 0 .033 0 . 137 O .051 0 . 144 O .055 0 . 143 0 .098 0 . 100 O . 124 0 . 126 0 .201 0 .204 0 .214 0 .217 0 . 207 0 . 209 0 . 190 0 . 193 0 . 132 0 . 134 0 . 149 0 .151 0 .682 0 .694 0 .794 0 .809 1 .048 1 .062 1 .018 1 .033 1 . 1 15 1 . 127 1 .006 1 .020 0 .855 0 .866 0 .983 0 .995 O .032 0 .032 0 .029 0 .030 0 .035 0 .035 0 .034 0 .034 0 .044 0 .045 0, .039 0 .040 O .039 0. .039 0 .034 0 .035 4 . 870 4 .961 4 .723 4 .810 4 .569 4 .632 4 .516 4 , .580 4 .461 4 .511 4 .546 4 , .610 4, .757 4 , .817 4 .621 4 , . 677 5 . 752 6, 000 5 .756 6 .000 5 .852 6. .000 5 .812 6 .000 5, .853 6 . 000 5, , 8 14 6 . 000 5, .834 6 . 000 5, .842 6 . 000 O. .002 0. .002 O .005 0. .006 0. .004 O. ,004 0, .006 0. ,006 0. .005 0. , 005 0. .003 0. ,003 O. .008 0. .008 0. .005 0. ,005 0. 0 0. .0 0, O 0. 0 0. .0 0. O 0. .0 0. 0 0. .0 0. .0 0. 0 0. 0 O. 0 0. 0 O. .0 0. O 0. 055 0. 056 O. .052 0. 053 0. 038 0. ,039 0. .042 0. 042 0. 04 3 0. ,044 0. 047 0. 047 0. 049 0. 049 0. ,045 0. 045 1. 880 1 . 915 1 . 842 1 . 876 1 . 796 1 . 821 1 . .884 1 . 911 1 . 801 1 . 321 1 . 805 1 . 831 1 . 783 1 . 806 1 . 745 1 . 766 1. 93.6 1 . 973 1 . 900 1 . 935 1 . 838 1 . 864 1 . 932 1 . 960 1 . 849 1 . 870 1 . 855 1 . 881 1 . 840 1 . 863 1 . 795 1 . 816 3. 184 3. 322 3. 008 3. 082 2 . 589 2 . 641 2. 062 2 . 103 2. 390 2 . 431 ?.. 649 2 . 715 3. 173 3. 241 3. 203 3. 276 0. 816 0. 678 0. 992 0. 918 1 . 411 1 . 359 1 . 938 1 . 897 1 . 610 1 . 369 1 . 351 1 . 285 0. 827 0. 759 0. 797 0. 724 Component Mole Fractions Annite 0.014 Phlogoplte O.141 F-Phlogoplte 0.680 Eastonlte 0.026 F-Hinnesotalte 0.131 Total Q.992 'Total Iron as FeO 'No Analysis 3 A n a l y s t : M.S. Bloom 0.019 O. 151 0.608 0.068 O. 142 0.988 062 234 510 044 132 0.982 0. 103 O. 248 0.423 0. 122 0.086 0.982 0.085 0. 169 0.476 0. 136 0.115 0.981 0.058 0. 159 0.530 0. 105 0. 130 0.982 0.019 0.086 0.651 0.089 O. 142 0.987 0.025 0.052 0.645 O. 107 O. 156 0.985 1 5 5 Sample O S S ' ^ " 0 5 9 , , 6 8 , ° Q 5 9 " 6 8 « 0 Q59«'68'° OGO^'SS" Q 6 2 ' l ° 6 4 " Q62" 064 ,> Q68''68 : A n a l y s e s 10 6 4 4 10 3 7 6 SiO . T i O . Al .0. FeO 1 MnO MgO CaO BaO Na.O K.O F 42 .80 1.414 10.81 7.538 0. 287 22 , 32 0.044 NA' 0. 220 10.00 6.778 41 .69 1 .738 1 1 .76 9.696 0.474 20.40 0.032 NA 0.279 10.04 6.592 42.50 1 .652 10.72 8. 101 O. 343 21 . 29 0.020 NA 0.282 10.26 6 .020 42 . 58 1 .538 10.96 7 .584 0.350 21 .38 0.029 NA 0. 259 10. 32 6 .868 42.74 1 .426 10.90 7 .479 0.251 22.51 0.051 NA 0. 246 9.935 7 . 135 39.89 2. 374 13.47 10.170 0. 229 19.60 0.038 NA 0.240 9.892 4 .435 40.76 2.310 12.74 8.458 0.292 2 1 .20 0.020 NA O. 221 9.876 4.338 39.73 2.161 13.84 7.464 0. 152 20.73 0.029 NA 0. 238 10. 17 5.078 S u b t o t a l 0 = F H.O T o t a l 102.21 2 .854 0.943 100.30 1 10.70 2.776 0.963 100.89 101.19 2.535 1 . 253 99.91 101.87 2 . 892 O.S90 99.87 102.67 3 .004 0.790 100.46 100.34 1 .867 1 . 925 100.40 100.21 1 .827 2 .002 100.39 99.59 2 . 138 1 . 6GO 99 . 1 1 S t r u c t u r a l Formulae on the B a s i s of 22 (O.OH.F) 51 4 4 6 145 6 214 5 700 6 094 6 152 6 251 6 157 6 264 6 127 6 189 5 789 5 850 5 864 5 917 5 784 5 859 Al 4 • 1 838 1 786 1 905 1 906 1 838 1 749 1 843 1 736 1 851 1 81 1 2 2 1 1 2 150 2 136 2 083 2 2 16 2 14 1 E T e t r a h e d r a l 7 983 8 000 7 605 8 000 7 990 8 000 8 000 8 000 7 977 8 000 8 000 8 000 8 000 8 000 8 000 8 000 A l 4 « 0 0 0 064 0 0 0 120 0 0 0 1 10 0 034 0 164 0 0 0 049 0 105 O 178 0 036 0 097 0 170 0 264 T i 4 • 0 153 0 154 0 179 O 191 0 180 0 183 0 167 0 170 0 154 0 155 0 259 0 262 0 250 0 252 0 237 0 240 Fe 4 1 0 905 0 915 1 109 1 185 0 98 1 0 997 0 917 0 933 0 897 0 906 1 234 1 247 1 018 1 027 0 909 0 920 Mn4 ' 0 035 0 035 0 055 0 059 0 042 0 04 3 0 04 3 0 044 0 030 0 031 0 028 0 028 0 036 0 036 0 019 0 019 Mg' ' 4 777 4 831 4 158 4 445 4 594 4 668 4 609 4 689 4 810 4 859 4 24 1 4 285 4 547 4 583 4 499 4 557 EOctahedra1 5 870 6 000 5 501 6 000 5 797 6 000 5 770 6 000 5 891 6 000 5 867 6 OOO 5 886 6 000 5 833 6 OOO C a 4 1 0 007 0 007 1 177 1 258 0 003 0 003 0 004 0 005 0 008 0 008 0 006 0 006 0 003 0 003 0 005 0 005 B a 4 ' 0 0 0 0 0 0 O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 O 0 0 0 0 0 Na + ' 0 04 1 0 042 0 050 0 053 O 053 0 054 0 049 O 050 0 046 0 047 0 046 0 046 0 04 2 0 042 0 045 0 046 K 4 1 1 832 1 852 1 751 1 872 1 894 1 925 1 904 1 937 1 817 1 335 1 831 1 850 1 813 1 829 1 889 1 913 E I n t e r 1ayer 1 880 1 901 2 978 3 183 1 951 1 982 1 957 1 991 1 871 1 890 1 883 1 902 1 857 1 874 1 938 1 963 F- 1 3 043 3 1 12 3 070 3 047 2 718 2 80O 3 090 3 195 3 200 3 268 2 026 2 057 1 965 1 992 2 293 2 368 OH" 1 0 957 0 888 0 930 0 953 1 282 1 200 0 910 0 805 0 800 0 732 1 974 1 943 2 035 2 008 1 707 1 632 Component Mole F r a c t i o n s A n n i t e 0.058 P h l o g o p i t e 0.120 F - P h l o g o p i t e 0.654 E a s t o n i t e 0.046 F - M i n n e s o t a i t e 0.108 0. 109 0.019 0.586 O. 128 0.094 0.091 0. 172 0.584 0.040 0.097 0.079 0.066 0.677 0.063 0. 101 0.054 0.079 0.692 0.052 O. 109 O. 133 0.080 0.414 0.267 0.083 089 207 393 200 089 0.096 0.021 0.503 0.289 0.071 T o t a l 0.986 0.936 0.984 0.986 0.986 0.977 0.979 0.980 ' T o t a l I r o n as.FeO 'No A n a l y s i s ' A n a l y s t : M.S. Bloom r 156 Sample Ana 1yses 074°"00°° 8 QDH78-67 5 0DH78-67 4 0DH78-67 6 H58-980 5 H72-2148.5 5 H72-2191 1 1 H77-781.5 2 S10, TIO.. A l . O . FeO 1 MnO MgO CaO BaO NaiO K.O F S u b t o t a l 0 = F H r O T o t a l 40.00 2.254 13.39 13.4 70 0.406 14 .68 0.042 NA * 0. 196 9.563 4 .025 98 .03 1 .695 2 .020 98 . 35 41.18 1 .565 13.68 12.860 0.584 17 . 16 0.022 NA 0. 194 9.859 5.457 102.56 2.298 1 . 457 101.72 4 1 .93 1 . 336 14.79 10.600 O. 334 17.70 O.095 NA 0. 199 9.916 5.272 102.17 2 . 220 1 . 593 101.55 40.59 1 .658 14 . 24 12.990 0.536 16.79 0.018 NA 0. 200 9.916 4.631 101.57 1 .950 1.818 101.44 39.72 1 .37 1 13.62 14.320 0.803 15.54 0.062 NA 0.080 9. 763 2. 223 97.50 0.936 2 .8 Hi 99 . 351 39.23 2 .637 13.85 13 . 280 0.872 16.20 0.014 NA 0. 149 9 .910 2.438 98 .58 1 .027 2 . 752 100.31 38.6 1 3 . 596 13.84 16.530 0.444 13 . 78 0.065 NA 0.094 9.399 0.755 97. 11 0.318 3.468 100.26 39.89 2.862 13. 12 13.690 0.244 16.57 O.023 . NA 0. 112 9. 756 1 . 167 97.43 0.491 3.335 100.28 S I * * 5.993 6.156 5.954 6.049 A l * ' 2.007 1.844 2.046 1.951 E T e t r a h e d r a l 8.000 8.000 8.000 8.OOO A l " 0.370 0.585 0.296 0.417 T l * ' 0.254 0.261 0.170 0.173 Fe*' 1.688 1.734 1.555 1.580 Mn' ! 0.052 0.053 0.072 0.073 Mg*>" 3.279 3.368 3.699 3.758 E O c t a h e d r a l 5.642 6.000 5.791 6.000 Ca*' 0.007 0.007 0.003 0.003 Ba*' 0.0 0.0 0.0 0.0 Na*' 0.038 0.039 0.037 0.037 K* 1 1.828 1.877 1.818 1.847 E I n t e r l a y e r 1.873 1.924 1.858 1.888 F-' 1.861 1.959 2.511 2.535 OH"' 2.139 2.041 1.489 1.465 S t r u c t u r a l Formulae on the B a s i s of 22 (O.OH 5 .986 6 . 121 5 .888 5 .984 5 .914 6 .003 2 .014 1 .879 2 .112 2 .016 2 .086 1 , 997 8 .000 8 .OOO 8 .000 8 .000 8 .000 8 .000 O .487 O .666 0 . 334 0 . 458 0 .316 0 430 0 . 143 0 . 147 0 . 181 O . 184 0 . 154 0 . 156 1 . 266 1 . 294 1 .576 1 .601 1 .783 1 .810 0 .040 0 .04 1 0 .066 0, .067 0 . 101 0 . 103 3 . 767 3 .852 3. .631 3 . 690 3 .450 3 . 502 5 . 703 6 .000 5. .787 6 . 000 5. .804 6. 000 0. .015 0. .015 0. 003 O. 003 0. ,010 0. 010 0. 0 0. ,0 0. 0 0. 0 0. 0 0. 0 0. 037 0. 038 0. 038 0. 039 0. 016 0. 016 1 . 806 1 . 847 1 . 835 1 . 865 1 . 854 1 . 882 1 . 857 1 . 899 1 . 875 1 . 906 1 . 880 1 . 908 2 . 393 2. 434 2 . 136 2 . 159 1 . 037 1 . 063 1 . 607 1 . 566 1 . 864 1 . 841 2 . 963 2 . 937 ,F) 5 .779 5 .872 5 .741 5 .852 5 .852 5 .950 2 .221 2 . 128 2 . 259 2 . 148 2 . 148 2 .050 8 .000 8 .000 8 .OOO 8 .000 8 .000 8 .000 0 . 196 0 .315 0 . 178 O . 324 0 . 132 0 . 256 0 . 292 0 .297 0 .402 0 .410 0 .316 0 . 32 1 1 .636 1 .662 2 .055 2 .095 1 .680 1 . 708 0. . 109 0 .111 0 .056 0, .057 0. .030 0 .03 1 3 , .558 3. .615 3 .054 3 .114 3 . 624 3 .684 5. .791 6, .000 5, .746 6 . 000 5. ,782 6 , .OOO 0. 002 0. ,002 0. .010 0. 01 1 0. 004 0. .004 0. 0 0. 0 0. ,0 0. 0 0. 0 0. .0 0. 029 0. 029 0. 018 0. 013 0. 021 0. 022 1 . 862 1 . 892 1 . 783 1 . 817 1 . 826 1 . 856 1 . 893 1 . 924 1 . 811 1 . 846 1 . 851 1 . 882 1 . 135 1 . 154 0. 356 0. 362 0. 543 0. 551 2 . 865 2. 846 3. 644 3. 638 3. 457 3. 449 Component Mole F r a c t i o n s Ann1te O.152 P h l o g o p i t e -0.035 F - P h l o g o p t t e 0.294 E a s t o n l t e 0.396 F-M1nnesota1te 0.172 T o t a l 0.979 • T o t a l I r o n as FeO ' N o ' A n a l y s i s ' A n a l y s t : M.S. Bloom O. 145 -0.112 0.475 0.335 0. 140 0.983 069 122 410 452 179 0.988 O. 158 -0.076 O. 391 0.379 0.131 0.983 0. 0. 0. . 2O0 182 129 0. 349 0.125 0.985 0. 197 0. 160 O. 170 0. 346 0. 101 0.974 0.236 0.263 0.059 0.395 O. 131 1 .016 O. 190 O. 376 0.01 1 0.285 O. 1 1 1 0.973 157 Sample Ana 1yses S10. •no. ' A l . O J FeO' MnO MgO CaO B a O Na. 0 K.O F Subtotal 0 = F H.O Total H79-295 3 39.65 1 .872 13.68 14 . 230 O. 788 15.68 0.025 NA' 0.116 9.778 2 . 378 98 . 20 1 .001 2.763 99.96 H83-601 5 39.66 2 . 260 13. 33 9.558 O. 386 19.91 0.020 0.114 0. 172 9.876 NA 95.29 0.0 3.879 99. 17 H92-2 3 37.72 1 .853 14.72 16.580 0.933 15.46 O. 123 0. 140 0.067 8.400 NA 96 .00 0.0 3 . 797 99.79 H92-728.5 40.40 0. 794 12.86 13.440 1.015 17.96 0.016 NA 0.112 9 . 334 2 .466 98.40 1 .038 2 .750 100.11 H106-475 39 . 34 1 .642 13.22 13.210 0.677 15.06 0.037" MA 0. 1 16 9.527 2.727 98.56 1 . 148 2.575 99.98 HI 13-580 38.94 1 .757 14 . 74 13.430 0.457 15.87 0.023 NA 0. 143 9.801 3. 146 98.31 1 . 325 2 .422 99 . 40 HI 13-1139 41.01 1 . 245 13.87 9.112 0.355 19.40 0.017 NA 0. 164 10.03 3.748 98.95 1 .578 2.246 99.62 H132-314 39.92 1.54 1 14.18 12.370 O. 297 17 .04 0.042 NA 0. 1 16 9.874 2.242 97.62 0.944 2.855 99.53 Structural Formulae on the Basis of 22 (0,OH,F) SI * 4 5 .871 5 . 961 5 . 787 5 .840 5 .624 5 .608 5 .939 5 .952 5 .876 5 .939 5 . 779 5 .868 5 .944 6 .035 5 .869 5 .959 Al * 4 2 . 129 2 .039 2 .213 2 . 160 2 . 376 2 .392 2 .061 2 .048 2 . 124 2 .061 2 .221 2 . 132 2 .056 1 .965 2 .131 2 .041 ETetrahedra1 8 .000 8 .000 8 .000 8 .000 8 .000 8 .OOO 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 8 .OOO 8 .OOO 8 .000 Al 4 « 0 . 270 0 . 385 0 .091 0 . 154 0 .224 0 . 187 0 . 179 0 . 185 0 .215 0 . 291 0 . 371 0 . 485 0 . 326 0 .441 0 .338 0 . 453 T 1 * • 0 . 208 0 .212 0 . 248 0 .250 0 . 208 0 . 207 0 .088 O .088 0 . 184 0 . 186 0 . 196 0 . 199 0 . 136 0 . 138 0 . 170 0 . 173 Fe' ' 1 . .762 1 . . 789 1 . 166 1 . 177 2 .068 2 .061 1 .652 1 .656 2 .025 2 .047 1 .667 1 .632 1 . 105 1 . 121 1 .521 1 .544 Mn1 ' 0 .099 0. . 100 0 .048 0 .048 0 . 1 18 0 .117 0 . 126 O . 127 0 .086 0 .087 0 .057 0 .058 0, .044 0. .044 0 .037 0 .038 Mg*' 3 . 461 3, .514 4 . 331 4 . 37 1 3, .437 3 .427 3. .936 3 .945 3 . 353 3, .389 3 .511 3, .565 4 . 192 4 , . 256 3. .735 3 . 792 EOotahedra1 5 . 800 6. .000 5. .885 6 .000 6. .054 6 .OOO 5 . 981 6 .000 5 .863 6, .000 5 .803 6, .000 5 . 802 6 .000 5 .801 6 .OOO Ca* " 0. .004 0. .004 O. .003 O .003 0. ,020 0, ,020 0. O03 O. .003 0. ,006 0. .006 0. ,004 0. 004 0. 003 0. .003 0. .007 0, .007 Ba*' 0. .0 0. ,0 0. .007 0. .007 0. .008 0, .008 O. ,0 0. .0 0. .0 0. .0 0. .0 0. ,0 0. ,0 0. .0 0. ,0 0, .0 Na* 1 0. .022 0. 023 0. 033 0. .033 0. ,013 0 .013 0. 022 0. .022 0. 023 0. 023 0. ,028 0. 028 0. 031 0. 032 0. ,022 0. .023 K* 1 1 . 847 1 . 875 1 . 838 1 . 855 1 . 598 1 . ,593 1 . 750 1 . 754 1 . 815 1 . 835 1 . 856 1 . 884 1 . 855 1 . 883 1 . 852 1 . ,880 EInterlayer 1 . 873 1 . 902 1 . 881 1 . 898 1 . 639 1 . ,634 1 . 774 1 . 778 1 . 844 1 . 864 1 . 887 1 . 916 1 . 888 1 . 917 1 . 881 1 . .909 F" 1 1 . 109 1 . 131 0. 0 0. 0 0. 0 0. 0 1 . 144 1 . 149 1 . 282 1 . 302 1 . 460 1 . 499 1 . 700 1 . 744 1 . 034 1 . 058 OH" 1 2. 891 2. 869 4 . OOO 4 . 000 4 . 000 4. OOO 2 . 856 2. 851 2. 718 2. 698 2. 540 2 . 501 2. 300 2. 256 2. 966 2 . 942 Component Mole Fractions Annite 0.200 Phlogopite 0.164 F-Phtogoplte 0.148 Eastonlte 0.348 F-M1nnesota1te 0.120 Total 0.980 155 293 154 2.59 127 0.988 C. 239 C. 122 0. 198 C . 308 0. 1 15 0.982 'Total Iron as FeO 'No Analysis 'Analyst: M.S. Bloom 0. 189 0.001 0.247 0.433 0.113 0.983 0.086 0. 147 0.300 0.332 0. 124 0.989 0. 159 0.200 O. 135 O. 374 O. 1 18 0.986 l I 158 Samp 1e Ana 1yses E64'°08•' 6 E6G''08'• 6 E69° «08'» E 6 9 ° ' 0 8 ' 0 10 E74''06' ° E74''OG' 0 4 E77°'07°' 10 EOM 1 12 SIO. 'TiO. Al .0, FeO 1 MnO MgO CaO BaO Na.O K,0 F S u b t o t a l 0 = F H.O T o t a l 37 .42 2.071 14 . 24 15.750 O. 709 14 .93 0.021 NA 1 O. 137 10. 35 3.263 98.89 1 .374 2 . 304 99.82 38.32 2.312 14 . 29 15.140 0.632 15.71 0.027 NA O. 138 10. 31 2.988 99.87 1 .258 2.481 101.09 37.94 2 .080 14.36 15.310 0.639 15 . 29 0.022 NA O. 135 10. 44 2.867 99.08 1 .207 2.508 100.38 38.09 2 .059 14.11 14.800 0.525 15.71 0.029 NA O. 137 10. 50 3.242 99 . 20 1 . 365 2 . 344 100.18 39.61 1 .888 13.86 11.000 0. 767 18.56 0.049 NA O. 152 10. 3G 3.346 99.59 1 .409 2 . 384 100.57 38 . 60 2 .040 14.12 13.770 0.391 16.74 0.023 NA O. 150 10.38 2 . 988 99.20 1 . 258 2.492 100.44 38.24 2.056 14 . 78 14.120 0. 585 15.25 0.038 NA 0.116 10.33 2.881 98.40 1.213 2.514 99. 70 37.44 2.953 15.59 16.100 0.717 15. 19 0.064 NA 0. 160 9.575 0.716 98.50 0. 301 3.530 101.73 Si 5 .644 5 .707 5 .670 5 . 737 Al *' 2 . 356 2 .293 2 . 330 2 . 263 E T e t r a h e d r a l 8 .000 8 .000 8 .000 8 .000 Al * • 0 . 187 0 . 267 0 . 174 0 . 258 T 1 * • 0 . 235 O .238 0 .257 0 . 260 Fe* ' 1 .987 2 .009 1 . 873 1 .895 Mn* ' 0 .091 0 .092 0 .079 0 .080 Mg*' 3. . 357 3 . 395 3, . 465 3 . 506 E O c t a h e d r a l 5. .856 6 OOO 5 , 849 6 OOO Ca* ' 0. ,003 O. ,003 0. 004 0. 004 Ba* ' 0. 0 0. 0 0. 0 0. 0 Na* 1 0. 027 0. 027 0. 027 0. 027 K * 1 1 . 991 2. 014 1 . 946 1 . 969 E l n t e r l a y e r 2 . 022 2. 044 1 . 977 2 . 000 F- 1 1 . 545 1 . 574 1 . 407 1 . 415 OH ' 2. 455 2. 426 2 . 593 2. 585 S t r u c t u r a l Formulae on the B a s i s of 22 (0, 5 .666 5 .738 5 .690 5 . 764 5 . 777 5 .844 2 . 334 2 . 262 2 .310 2 . 236 2 . 223 2 . 156 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 0 . 207 0 . 298 0 . 186 0 . 281 0 .171 0 . 255 0 .234 0 .237 0 . 231 0 . 234 0 . 207 0 . 2 10 1 .912 1 .936 1 . 849 1 .873 1 . 342 1 . 357 0. .08 1 0 .082 0 .066 O .067 0 .095 0 .096 3, .404 3 .447 3. . 498 3 . 544 4 . 036 4 .033 5 , .838 6 .000 5. ,83 1 6. .OOO 5 . 851 6 .000 0. 004 0. .004 0. 005 0. 005 0. 008 0. 008 0. 0 0. 0 0. 0 0. 0 0. 0 0. 0 0. 026 0. 027 0. 027 0. 027 0. 029 0. 029 1 . 989 2 . 014 2 . 001 2 . 027 1. 928 1 . 950 2 . 019 2. 044 2. 032 2 t 059 1. 964 4 987 1 . 353 1 . 371 1 . 526 1 . 552 1. 543 1 . 561 2. 647 2. 629 2. 474 2. 448 2. 457 2 . 439 ,F) 5 . 708 5 .775 5 . 706 5 .804 5 .496 5 .532 2 . 292 2 .225 2 .294 2 . 196 2 .504 2 .468 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 0 .181 0 . 265 0 .318 0 . 447 0 .206 0 .247 0 . 227 0 . 230 0 .231 0 . 235 0 . 326 0 .328 1 . 703 1 . 723 1 .762 1 . 792 1 .976 1 .989 0 .049 0 .050 0 .074 0 .075 0 .089 0 .090 3 .690 3 . 734 3, . 392 3 .450 3 . 324 3 .346 5. . 850 6 .000 5 , .777 6 .OOO 5 .922 6 , .000 0. 004 0. ,004 0. 006 0. .006 0. ,010 0. .010 0. 0 0. 0 0. 0 0. ,0 0. 0 0. 0 0. 029 0. 029 0. 023 0. 023 0. 031 0. 031 1 . 958 1 . 981 1 . 966 2 . 000 1 . 793 1 . 805 1 . 991 2 . 014 1 . 995 2 . 029 1 . 834 1 . 846 1 . 397 1 . 4 14 1 . 349 1 . 383 0. 338 0. 335 2. 603 2 . 586 2. 651 2. 617 3. 662 3 . 665 Component Mole F r a c t i o n s A n n i t e 0.327 P h l o g o p i t e -0.048 F - P h l o g o p l t e 0.357 E a s t o n i t e 0.321 F - M i n n e s o t a 1 t e 0.021 T o t a l 0.978 ' T o t a l I r o n as FeO 'No A n a l y s i s 'Endako Q u a r t z Monzonite ' A n a l y s t : M.S. Bloom 0.288 O. 288 .029 . 322 .041 O. O. O. 0.977 0. 309 0.015 0.299 0.326 0.029 0.978 0.303 0.005 0. 348 0.299 0.024 0.978 0. 183 O. 139 0.316 O. 282 0.059 O. 979 0. 262 0.080 0.302 0. 299 0.038 0.98 1 0.258 -0.006 0. 267 0.398 0.062 0.979 0.257 O. 180 -0.009 0.465 0.077 0.988 159 APPENDIX C - MEAN ELECTRON MICROPROBE ANALYSES OF HYDROTHERMAL DIOCTAHEDRAL MICAS Samp 1 e Ana I y s e s • SIO. T10. Al >OJ FeO' MnO Mgo CaO BaO Na.O K.C F S u b t o t a l Q = F H.O T o t a l 0DH27-3O 6 0DH27-3O 4 0DH78-67 H70-959 H70-2011 H72-2156 47.98 44 .75 48 .92 48 .06 47.98 49.33 0. 193 0.282 0.400 0. 258 0.322 0. 196 30. 79 34 . 54 30.99 29 . 37 29.8 1 30.99 1.635 2 .675 2 . 382 4.563 3 . 908 3. 131 0.055 0.038 0.089 0.052 0.067 0.013 2.40 1 .OO 2 . 38 1 .68 2.45 1 .46 0.033 0.005 0.014 0.056 0.027 0.059 0.118 0.048 NA NA NA NA 0.417 0.682 0.418 0.090 0.116 0.071 10. 72 10. 20 10. 76 10.58 10.85 . 1 1 .04 NA' NA 0.777 0.241 0.427 0.215 94 . 35 94 . 22 97 . 13 94.95 95.96 96.51 0.0 O.O 0. 327 0.101 0. 180 0.091 4. 191 4.161 3 .936 4 .057 4.015 4.171 98 . 54 98 . 38 100.74 98 .90 99 . 79 100.59 H72-2156 49.58 0.118 33. 14 1 .856 0.010 0.86 0.058 NA 0.064 10. 76 O. 192 96 .64 0.081 4 . 233 100.79 H77-368.5 46. 40 0.410 27.96 3.738 0.010 3.37 0.015 NA O. 122 10.92 0.406 93.35 0.171 3.898 97.07 S1 * 4 6 . 481 6 .439 6 087 6 .004 Al * 4 1 .519 1 .561 1 .913 1 .996 E T e t r a h e d r a 1 8 .000 8 .000 8 .000 8 .000 A l * • 3 . 407 3 .310 3 .653 3 .467 T i *• 0 .020 0 .019 0 .029 0 .028 Fe* ' 0 . 185 0 . 184 0 . 304 0 .300 Mn* ' 0 .006 0 .006 0 .004 0 .004 Mg*' 0, , 484 O .481 0, . 203 0 . 200 E O c t a h e d r a l 4 , . 102 4 .OOO 4 , . 194 4 , .OOO C a + ' 0. ,005 O .005 0, O 0. .0 Ba* ' 0. .006 0. .006 0. 003 0. 003 Na* 1 0. ,074 0, .073 0. ,121 0. 120 K* 1 1. .847 1. 835 1 . 770 1 . 746 E I n t e r 1 a y e r 1. 932 1. 919 1 . 895 1 . 869 F- 1 OH" ' 4 . 000 4 . OOO 4. OOO 4 . 000. S t r u c t u r a l Formulae on the B a s i s of 22 (O.OH, 6 . 483 6 .425 6 . 540 6 .463 6 .470 6 . 374 1 .517 1 .575 1 .460 1 .537 1 .530 1 .626 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 3 . 348 3 . 223 3 .275 3 .119 3 .231 3 .041 0 .040 0 .040 0 .026 0 .026 0 .033 0 .032 0 .264 0, .262 0 .519 0 .513 0 .441 0 .434 0 .010 0 .010 0 .006 0 .006 0 .008 0 .008 O, .471 o, . 466 O . 340 0, .336 O .492 O, . 485 4 , . 133 4 . OOO 4 , . 167 4 , .OOO 4, . 205 4 , .000 0. .002 0. 002 0 ,008 0. .008 0, .004 0. ,004 0. O 0. 0 O. O 0. .0 0. ,0 0. 0 0. ,072 0. 072 0. .016 0. ,016 0. ,020 0. 020 1 . 819 1. 803 1 . 837 1 . 815 1 . 866 1 . 839 1 . 893 1. 877 1 . 861 1 . 839 1 . 891 1 . 863 0. 314 0. 323 0. 099 0. 103 0. 174 O. 179 3. 686 3. 677 3. 901 3. 897 3. 826 3 . 821 F) 6 . 550 6 .519 6 .503 6 .497 6 .458 6 . 34 1 1 .450 1 .481 1 .497 1 .503 1 .542 1 .659 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 3 .423 3 . 345 3 .651 3 .616 3 .068 2 . 844 0 .020 0 .019 0 .012 0 .012 0 .043 0 .042 0 . 348 0 . 346 0 .204 0 . 203 0 .435 0 . 427 0 .001 0 .001 0 .001 0 .001 0, .001 0 .001 0 . 289 0 . 288 O. . 168 0 . 168 0. .698 0 .686 4 .081 4 .000 4 . ,036 4 .000 4 . 246 4 , .000 O, .008 0, .008 0. 008 0, .008 0. .002 0. .002 0, .0 0. .0 0. 0 0. .0 0. 0 0. 0 0. 012 0. .012 0. 01 1 0. ,01 1 0. 022 0. 022 1. 870 1 . 861 1 . 800 1. 799 1 . 939 1 . 904 1. 891 1 . 882 1 . 819 1. 818 1 . 963 1 . 928 0. 087 0. 090 0. 077 0. 080 0. 166 0. 175 3. 913 3. 910 3. 923 3. 920 3. 834 3. 825 Component Mole F r a c t i o n s M u s c o v l t e P a r a g o n i t e K-Fe C l d n t 4 K-Mg C l d n t F K-Mg C l d n t T o t a l 0.657 0.065 0.063 0. 208 0.005 0.998 ' T o t a l I r o n as FeO 'No A n a l y s i s ' A n a l y s t : M.S. Bloom 4 C e l a d o n l t e 773 102 087 023 013 0.998 0.585 0.093 0. 130 0. 150 0.083 1 .041 0.610 0.052 0.219 0.098 0.031 1 .010 0.608 0.052 168 138 .056 0. 0. 0. 1 .022 0.661 0.04 1 0. 168 0.118 0.020 1 .008 0.719 0.057 0. 124 0.098 0.008 1 .005 0.583 0.036 0. 136 O. 203 0.065 1 .024 160 Sample H77-368.5 H79-402 H79-402 H79-512 HaTHaO^ H83-437 H83-601 H83-601 A n a l y s e s 1 2 4 6 G 2 3 " " y SIO. T i O . A l .0. FeO 1 MnO MgO CaO BaO Na.O K.O F S u b t o t a l 0 = F H.O T o t a l 47 . 20 0.078 30.03 2 .601 0.028 1.51 0.021 NA' 0.076 10.97 O. 268 92 . 78 0.113 3 . 983 96 .65 46. 40 0.029 35.47 0.727 0.029 0.08 0.022 NA 0. 171 11.01 0. 146 94 .08 0.061 4 . 144 98 . 16 4 7.66 0. 199 28.54 3.481 0.034 2 . 20 0.023 NA 0.116 10.90 0. 242 93.40 0. 102 3.999 97.29 48.51 O. 190 29.32 3.476 0.034 1 . 74 0.057 NA 0.072 10.84 0. 2 10 94 . 45 0.088 4 .072 98 . 43 49. 17 0.061 29.63 3 . 146 0.024 1 .82 0.051 NA 0.050 10. 74 0.493 95. 19 0. 203 3.983 98.97 46 . 79 0.089 34.36 2.642 0.038 0.71 O. 1 18 NA 0.241 10. 27 0.058 95 . 32 0.024 4.211 99.51 47.90 0.287 30. 80 3.303 0.017 1 .57 0.015 0.073 0.063 10.72 NA 94 . 75 0.0 4 . 187 98 .94 48. 14 0.220 32. 20 2 .795 0.010 1 .54 0.040 0.055 0.075 10.66 NA 95. 74 0.0 4 .248 99. 99 S i 4 4 6 .526 6 .503 6 . 245 6 . 258 Al * 4 1 . 474 1 .497 1 .755 1 . 742 E T e t r a h e d r a l 8 .OOO 8 000 8 .000 8 .000 Al * « 3 .444 3 380 3 .900 3 896 T | 4 « O 008 0 008 0 003 0 003 Fe* ' 0 301 0 300 0 082 0 082 Mn* ' 0 003 0 003 0 003 0 003 Mg* ' 0 310 0 309 0 015 O 015 r O c t a h e d r a l 4 066 4 000 4 003 4 000 Ca* ' 0 003 0 003 0 003 0 003 Ba* ' 0 0 0 0 0 0 0 0 Na* 1 0 014 o 014 0 030 0 030 K • 1 1 935 1 928 1 890 1 894 E I n t e r l a y e r 1 952 1 945 1 924 1 928 F- 1 0 109 0. 117 0 059 0. 062 OH - 1 3. 891 3 . 883 3. 941 3. 938 S t r u c t u r a l Formulae on the B a s i s of 22 (0,0H, 6 . 580 6 .524 6 .600 6 . 560 6 .632 G .592 1 . 420 1 .476 1 .400 1 .440 1 . 368 1 .408 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 3 .247 3 128 3 .325 3 .233 3 .365 3 274 0 021 0 020 0 019 0 019 0 006 0 006 0 402 0 398 0 396 0 393 0 355 0 353 0 004 0 004 0 004 0 004 0 003 0 003 0 453 0 449 0 353 0 351 0 366 0 364 4 127 4 000 4 098 4 000 4 095 4 000 0 003 0 003 0 O08 0 008 0 007 0 007 0 0 0 0 O 0 0 0 0 0 0 0 0 021 0 021 0 013 0 013 0 009 0 009 1 920 1 903 1 881 1 870 1 848 1 837 1 944 1 927 1 903 1 891 1 864 1 853 0. 099 0 105 0. 085 0 090 0. 200 0 209 3. 901 3. 895 3 . 915 3. 910 3 . 800 3 . 791 F) 6 . 254 6 . 193 6 . 476 6 .420 6 .415 6 . 355 1 .746 1 .807 1 .524 i . 580 1 .585 1 . 645 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 3 .694 3 554 3 .408 3 285 3 .497 3 .365 0 009 0 009 0 029 0 029 0 022 0 022 0 295 0 292 0 373 0 370 0 31 1 0 309 0 004 0 004 0 002 0 002 0 001 0 001 0 142 0 14 1 0 316 0 314 0 306 O 303 4 144 4 000 4 129 4 OOO 4 138 4 OOO 0 017 0 017 0 002 0 002 0 006 O 006 0 0 0 0 0 004 0 004 0 003 0 003 0 042 0 042 0 01 1 0 01 1 0 013 O 013 1 751 1 734 1 849 1 833 1 812 1 795 1 810 1 792 1 866 1 850 1 834 1 817 0. 023 0. 024 O. 0 0. 0 0 O O O 3. 977 3 . 976 4 . OOO 4 . 000 4 . OOO 4 . 000 Component Mole F r a c t i o n s Muscov1te P a r a g o n i te K-Fe C l d n t 4 K-Mg C l d n t F K-Mg C l d n t T o t a l 0.682 0.029 O. 149 O. 125 0.029 1 .015 ' T o t a l I r o n as FeO 'No A n a l y s i s ' A n a l y s t : M.S. Bloom 4 C e l a d o n i t e 0.849 0.041 0.065 0.017 0.032 1 .004 0.612 0.034 0. 170 0. 163 0.033 1 .013 0.626 0.040 O. 182 O. 138 0.023 1 .009 0.60;'. 0.054 0. 182 O. 139 0.048 1 .026 0.768 0.077 0:115 0.032 0.006 -0.999 681 040 151 1 19 003 0.994 O.710 0.050 0.119 0. 115 0.002 0. 995 1 6 1 Sample A n a l y s e s S10, 'TIO; Al ,0. FeO 1 MnO MgO CaO BaO Na 10 K.O F S u b t o t a l 0 = F H,0 T o t a l H85-563 6 47.62 0.255 29.23 3.803 0.035 2 .47 0.072 NA * 0.083 10. 79 O. 321 94.67 0. 135 4.012 98.55 . H92-2 5 45.87 0.476 29.34 4 . 564 0.030 3. 36 0.022 0.058 O. 120 10.43 NA 94 . 27 0.0 4. 1 16 98.39 H92-234 5 49. 10 O. 184 30. 15 3.610 0.051 1 .69 0.027 NA 0.096 1 1 .00 O. 187 96.09 O.079 4 . 15 1 100.17 H96-209.5 1 49.21 O. 164 28.68 3.032 0.0 2 . 50 0.037 NA 0.06 1 10.88 1 . 148 95 . 7 1 0. 483 3.698 96.93 H112-304 48 . 12 0.314 29.39 3.802 0.032 2.12 0.3J51 NA 0.099 10.!38 0. 330 95 .159 0. 1G0 4.019 99.45 H118-178 49. 14 O. 198 28 .92 2 .970 0.031 2.38 0.033 NA 0.080 1 1 .07 O. 586 95.41 0. 247 3 .943 99. 1 1 H1 18-589 48.25 0.077 30.80 3.062 0.018 1 . 34 0.055 NA 0.097 10.62 O. 303 94.62 O. 128 4 .054 98.55 H124-629.5 48.40 0.312 28.88 3 . 732 0.038 3 . 33 0.060 NA 0. 109 1 1 .Ol 0.553 96.42 0.233 3.972 100.16 S t r u c t u r a l Formulae on the B a s i s of 22 (O.OH.F) S I * ' 6 . 499 6 .410 6 . 309 6 . 139 6 .568 6 . 52 1 6 .65* 6 . 606 6 .515 6 .462 A 1 * " 1 . 501 1 . 590 1 .691 1 .061 1 .432 1 . 479 1 . 344 1 .394 1 .485 1 . 538 E T e t r a h e d r a l 8 .000 8 .000 8 .000 8 .000 8 .000 8 .000 ti .OOO 8 . OOO 8 . 000 8 .000 Al • • 3 . 224 3 .047 3 .089 2 . 767 3 .345 3 . 24 t 3 . 251 3 . 143 3 . 229 :.) .113 I 1 ' • 0 .026 0 .026 n .049 0 .048 0 .019 0 .018 0 .017 O .017 0 .032 0 .032 Fe* 1 0 .434 0 .4 28 0 .525 0 .511 0 .404 0 . 401 0 . 343 0 . 340 0 .431 0 .427 Mn* ' 0 . 004 0 .004 0 . 003 0 . 003 0 .001 0 . 006 0 .0 0 .0 0 .004 0 .004 Mg*' 0 .502 0. .495 0 .689 0 .670 0. .337 0 .334 0. . 504 0. .500 0 .428 0 .424 E G c t a h e d r a l 4 . 190 4 , .000 4 . 355 4 .000 • 1 10 4 . 000 4 . 115 4 .000 4 , . 123 4 .000 Ca* ' 0. .011 O. OIO 0. .003 0. .003 0. .004 O. 004 0. 005 0 005 0. .051 0. .051 Ba* ' 0. 0 0. 0 0. .003 0 .003 0. 0 O. 0 0. O 0. 0 0. 0 0. ,0 Na* 1 0. 015 0. 015 0. 022 0. .021 0. 017 0. 017 0. 011 0. 01 1 0. 018 0. 017 K* ' 1. 8 79 1 . 853 1. 830 1 . 781 1. .877 1 . 864 j . 877 1 . 863 1 . 896 1 . 881 I I n t e r 1ayar 1. 904 1 . 878 1. 858 1 808 1. 893 1 . 384 1. 893 1 . 879 1 . 965 1 . 949 F- ' 0. 131 0. 137 0. 0 0. 0 0. 076 0. 079 0. 4C5 0. 487 0. 155 0. 161 OH" ' 3 . 869 3. 863 4 . OOO 4 . 000 3. 924 3 . 92.1 3. 535 3. 1)13 3. 845 3 . 839 6.636 6.593 1.364 1.407 8.000 8.000 3. 262 3.167 0.020 0.020 0.335 0.333 0.004 0.004 0.480 0.476 4.100 4.000 0.0 6.531 6.492 1.469 1.508 8.000 8.000 3.469 3.376 0.008 0.008 0.347 0.345 0.002 0.002 0.271 0.269 4.096 4.000 6.509 6.397 1.491 1.603 8.OOO 8.000 3.109 2.896 0.032 0.031 0.420 0.413 0.004 0.004 0.668 0.656 4 . 232 4.000 005 0 .008 0 .008 O .009 0 .008 0 0 .0 0 .0 0. .0 0 .0 014 0. .017 0. ,017 0, .019 0, .019 895 1 . 834 1 . ,823 1 . ,889 1 .656 914 1 . ,859 1 . 848 1 . ,916 1 . 884 249 0. 123 0. 129 0. 226 0. 231 751 3. 877 3. 871 3. 774 3 . 769 Component Mole F r a c t i o n s Muscov1te P a r a g o n l t e K- Fe C l d n t * K-Mg C l d n t F K-Mg C l d n t T o t a l 0.611 0.044 O. 164 0. 153 0.045 1.017 FeO ' T o t a l I r o n as 'No A n a l y s i s ' A n a l y s t : M.S. Bloom ' C e l a d o n i t e 0.622 0.049 O. 122 0. 176 0.028 O. 997 0.637 0.04 1 O. 182 0. 127 0.021 1 .008 O. 0. O. .488 .032 137 0.218 O. 120 0.994 0.612 0.04 1 0. 183 0. 134 0.047 1.018 0.581 0.045 0. 167 0. 176 0.063 1 .032 0.659 0.055 O. 169 0. 102 0.029 1 .014 0. 562 0.050 0. 147 0. 197 0.074 1 .031 162 APPENDIX D - MEAN ELECTRON MICROPROBE ANALYSES OF HYDROTHERMAL AMPHIBOLES FROM HUDSON BAY MOUNTAIN Samp 1e H58-980-1 H58-980-2 H58-980-3 H58-980-4 Ana 1yses 10 5 8 2 SiO* 50.4 4 49.71 50.41 50. 97 TiO, 0. 253 0.270 0. 199 0.265 Al ,Oi 3.90 3 .64 3.89 3.95 FeO 1 12.97 12.89 12.81 12.97 MnO 1 .361 1 . 322 1 .349 1.443 MgO 15.09 15 .00 15.22 15.12 CaO 11.71 1 1 . 57 1 1 . 30 1 1 . 73 Na,0 1 .027 0.817 1 .006 0.875 KiO 0.478 0. 484 0.420 0.463 F 0.877 0.886 0.698 0.610 S u b t o t a l 98. 10 96 . 59 97 . 30 98. 39 0 = F O. 369 O. 373 0.294 0.257 H.O 3.310 3.255 3 . 374 3.450 T o t a l 101.04 99.47 100.38 101.59 S t r u c t u r a l Formulae on the B a s i s of 48 i (O.OH.F) S1 + 4 15.50 14.80 15.52 14.79 (15.55 14.86 15.55 14.85 A 1 • 4 0.497 1.203 0.482 1.214 0.446 1.144 0.453 1.155 ET e t r a h e d r a 1 16.00 16.00 16.00 16.00 16.00 16.00 16.00 16.00 Al * • 0.922 0.144 0.864 0.062 0.975 0.207 0.974 0.201 T 1 * • 0.058 0.056 0.063 0.060 0.046 0.044 0.061 0.058 Fe* ' 3.33 3.18 3.37 3.21 3.31 3. 16 3.31 3.16 Mg*' 6.914 6.599 6.981 6.651 7.001 6.687 6.875 6.565 Mn* ' 0.211 0.019 0.219 0.020 0.088 0.0 0.206 0.017 M2 C a t i o n s 11.44 10.00 11.49 10.00 11.42 10.10 11.42 10.00 Ca*' 3.856 3.681 3.870 3.687 3.736 3.568 3.834 3.661 Mn* « O.144 O.319 0.130 0.313 0.264 0.337 0. 166 0.339 M4 C a t i o n s 4.000 4.OOO 4.OOO 4.OOO 4.OOO 3.905 4.000 4.000 Na* 1 0.412 0.394 0.333 0.317 0.406 0.387 0.349 0.333 K+ 1 O.187 0.179 0.193 0.184 0.165 0.158 0.180 0.172 A C a t i o n s 0.600 0.572 0.526 0.501 0.571 0.545 0.529 0.505 F- 1 0.812 0.814' 0.820 0.833 0.644 0.651 0.564 0.562 OH- 1 3.188 3. 186 3.180 3.167 3.356 3.349 3.436 3.438 Component Mole F r a c t i o n s T r e m o l I t e 0.295 0.324 0.300 0.305 (Na,K) E d e m t e 0.370 0.343 0.373 0. 362 F e r r o e d e n 1 t e 0. 338 0.336 0.335 0.341 T o t a l 1 .003 1 .003 1 .003 1 .008 ' T o t a l I r o n as FeO ' A n a l y s t : M.S.' Bloom APPENDIX E - MEAN ELECTRON MICROPROBE ANALYSES FOR SCHEELITE-POWELLITE FROM HUDSON BAY MOUNTAIN Sample Ana 1yses H92-4 H92-2 1 2 H127-141' 3 H127-141' 2 H126-127.5 1 5 H126-127.5' 5 H126-127.5 1 3 H120-156.5' 4 MoOi PbO CaO WOi T o t a l 19.745 0.020 19.710 61 . 192 100.667 5. 175 0.0 18.370 75.610 99.155 7 .073 0.017 18.693 73.493 99.276 O. 140 0.0 17.705 81 .470 99.315 7 .076 0.010 18.678 74 .412 100.176 2.514 0.058 18.216 78.992 99.780 0.483 0.020 17.366 81 .677 99.546 10.592 0.025 16.422 70.830 97.869 S t r u c t u r a l Formulae on the B a s i s of 16 (0) C a + 1 Pb + ' oo y +1 "° M o " 0.974 0.013 0.662 O. 325 0.985 0.007 0. 903 0.089 0.989 0.006 0.870 0. 125 0.979 0.000 0.997 0.011 .983 .008 0.870 0.121 0. O. 0.985 0.008 0.953 0.040 0. 965 0.000 0.991 0.018 0.912 0.044 0.804 O. 153 Component Mole F r a c t i o n s S c h e e l 1 t e Powel11te S t o l z l t e T o t a l 649 325 013 0.987 0.896 0.089 0.007 0.992 0.864 O. 125 0.006 0.995 0.987 0.000 0.011 0.998 0.862 0.121 0.008 0.991 945 040 008 0.993 0.973 0.000 0.018 0.991 0.760 0. 153 0.044 0.957 •cor e * I n t e r m e d i a t e 'ri m ' a n a l y s t : M.S. «»B 1 oom Sample Ana 1yses H120-156.5' 3 H120 -156 . 3 5' HI 20 -156.5' 2 H118-178' 2 H70-2011 2 H79-572 2 H126-127.5' 1 MoO 3 PbO CaO WO 3 T o t a l 1 . 273 0.057 17.843 80.790 99.963 0. 0. 17 81 99 117 010 .870 .953 .950 20.005 0.0 19.965 60.330 100.300 0.315 0.015 17.820 81.305 99.455 5.760 0.010 18. 165 75.590 99.525 6. 0. 18 74 99 080 025 .375 .835 i .315 25.360 0. 100 20.720 53.680 99 .860 S t r u c t u r a l Formulae on the B a s i s of 16 (0) Ca*' Pb* ' w+. Mo* • 0.976 0.013 0.976 0.012 0. 0. 0. 0. 981 000 998 010 0. 0. 0. 0. 983 009 658 334 0.981 0.000 0.994 0.010 0.975 0.013 0.893 0.094 0. 0. 0. 0. 982 009 887 104 0.992 0.005 0.576 0.421 Component Mole F r a c t i o n s S c h e e l 1 t e Powel11te S t o l z l t e 0.963 0.012 0.013 0. O. O. 988 000 010 0. 0. 0. 649 334 009 0.984 0.000 0.010 0.880 0.094 0.013 0. 0. 0. 878 104 009 0.571 0.421 O.0O5 T o t a l 0.988 0. 998 0. 992 0.994 0.987 0. 991 0.997 1 c o r e • I n t e r m e d i a t e ' r i m ' a n a l y s t : M.S. ©Bloom 

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