A Thesis Submitted to the Faculty of Graduate Studies and Research, in Partial Fulfilment of the Requirements for the Degree of

Transcription

1 Origin, Timing, and Fluid Characteristics Associated with the Paleoproterozoic Jasper Lode-Gold Deposit, Saskatchewan, Canada. A Thesis Submitted to the Faculty of Graduate Studies and Research, in Partial Fulfilment of the Requirements for the Degree of Master of Science in Geology at the Department of Geological Sciences University of Saskatchewan Saskatoon, Canada By Frank Hrdy Spring, 1994 The University of Saskatchewan claims copyright in conjunction with the author. Use shall not be made of the material contained herein without proper acknowledgement. l

2 The author has agreed that the library, University of Saskatchewan, may make this thesis freely available for inspection. Moreover, the author has agreed that permission for extensive copying of this thesis for scholarly purposes may be granted by the professor or professors who supervised the thesis work recorded herein or, in their absence, by the Department Head or Dean of the college in which the thesis work was done. It is understood that due recognition will be given to the author for this thesis and to the University of Saskatchewan in any use of the material in this thesis. Copying or publication, or any other use of the thesis for financial gain, without approval by the University of Saskatchewan, and the author's written permission, is prohibited. Requests for permission to copy or to make any other use of material in this thesis, in whole or in part, should be addressed to: Department Head Department of Geological Sciences University of Saskatchewan S7N OWO Canada ll

3 ACKNOWLEDGMENTS The author would like to acknowledge the support and assistance provided by the faculty and staff in the Department of Geological sciences over the last number of years. In particular by Z. Szczepanik and B. Novakovski (thin sections), R. George (electron microprobe), D. Pezderic (stable isotopes), A. Vuletch (radiogenic isotopes), and J. Jain (trace elements). This thesis has benefited from critical evaluations by M. Stauffer, D. Stead, R. Kerrich, L.C. Coleman, H.E. Hendry, K. Ansdell, D. o Hanley, and in particular T.K. Kyser. The author would also like to thank v. Sopuck, R. Kusmirski, for logistical support and D. Billard for much helpful assistance in the field. I wish to thank Dr. Kevin Ansdell and Dr. Dave o Hanley for their valuable insights and sincere willingness to offer their help and support with this thesis. I also wish to thank Dale Schultz and Steve Gill for their true friendship and support and for the many memorable times which we shared. This work has also benefited from many useful discussions with B. Janser, T. Kotzer, P. Field, M. Fayek, and D. Schultz. I would like to thank Dr. T.K. Kyser for his guidance and teaching and for offering me the opportunity to do this work. Financial support for this project was provided by CAMECO and Natural Science and Engineering Research Council through a University-Industry Research Grant to T.K. Kyser, University of Saskatchewan. lll

4 TABLE OF CONTENTS Acknowledgments Table of contents v List of Tables v1 List of Figures v11 Abstract x 1. Introduction 1.1 Location, Access, and Physiography Exploration History of the Star Lake Area Objectives of Thesis Geology 2.1 Regional Geology Local Geology Vein Mineralogy and Alteration 3.1 Petrography and Mineral Paragenesis Hostrock Alteration Fluid Inclusion Study 4.1 Theoretical Overview Inclusion Types, Petrography and Microthermometric Results Discussion of Fluid Inclusion Data Stable Isotopes 5.1 Theoretical Overview Mineral Isotopic Compositions and Isotope Geothermometry Isotope Composition of Fluid Radiogenic Isotope Systematics 6.1 The Ar-Ar Method of Dating Ar-Ar Results The Rb-Sr Method of Dating Rb-Sr Results The Pb-Pb and Pb-Evaporation Methods of Dating Pb-Pb Results Results and Discussion References Appendices Al Sampling and Analytical Techniques A 1.1 Field Sampling A 1.2 Petrographic Preparation A 1.3 Sample Selection and Wafer lv

5 Preparation (Fluid Inclusions) A 1.4 Microthermometric Analysis A 1.5 Sample Selection (For Isotopic Study) A.1.6 Stable Isotope Analysis A.1.7 Radiogenic Isotope Analysis A.1.8 Elemental Analysis A2 A3 A4 XRF-Wholerock Analysis of Samples Collected Downhole of Drillhole # ICP-MS Analysis of Wholerock Samples Collected Downhole of Drillhole # Core and Rim Compositions of Individual Tourmaline Crystals AS Island Lake Pluton single Zircon Pb-Pb Data A6 Sample Descriptions v

6 LIST OF TABLES Table 1: Fluid Inclusion Measurements Table 2: Stable Isotope Measurements Table 3: Ar-Ar Data Table 4: Rb-Sr Data Table 5: Pb-Pb Data Vl

7 LIST OF FIGURES Figure 1: Province-Scale Geological Map... 2 Figure 2: Regional Geological Map... 3 Figure 3: Sample Location Map... 5 Figure 4: Ocean Ridge Granite (ORG) Normalized Trace Element Plot of Samples from the Island Lake Pluton Figure 5: Gold-Hosting Environments Figure 6: Vein Mineral Paragenesis Figure 7: Al-Fe-Mg Ternary Plot of Tourmaline Compositions 21 Figure 8: Tourmaline Elemental Compositions and Core-Rim Variations Figure 9: Variations in Select Trace Element Contents with Distance From Auriferous Veins Figure 10: Variations Between Values of Quartz, Biotite, and Wholerock with Distance From Auriferous Veins Figure 11: Isobaric T-X Plot for the System NaCl-H Figure 12: Depression of Freezing Point of H 2 0 as a Function of Wt% of Salt Figure 13(a): Density of Vapour-Saturated NaCl Fluids in the System NaCl-H (b) : Temperature Versus Density Plot for H (c): Degree of Fill Versus Total Density of Fluid (Fluid Inclusions) Figure 14: Relation Between the Density of C0 2 and Temperature of Homogenization of Liquid C Figure 15: Phase Diagram for H 2 0 with 0 & 25Wt% NaCl Figure 16: Histogram Plot of Fluid Inclusion Measurements 39 Figure 17: Histogram Plot of & 0 34 S of Minerals Occurring in Mineralized and Barren Veins Vll

8 Figure 18: Calculated & OD of Water in Equilibrium with Muscovite and Tourmaline Figure 19: Plot of Ar-Ar Data Derived from Vein Muscovite Figure 20: Plot of Rb-Sr Data Derived from Vein Muscovite and Tourmaline Figure 21: Variations in Pb Isotopic Compositions of the Crust Figure 22: Plot of Pb-Pb Data Derived from Vein Galena and Sphalerite Vlll

9 ABSTRACT The Jasper mesothermal gold deposit, in northern Saskatchewan, Canada, is situated within the Paleoproterozoic La Ronge domain of the Trans-Hudson orogen. The deposit occurs within a northeasterly striking, and steeply northwest-dipping, mylonitic shear zone which cross-cuts the Island Lake pluton having a zircon Pb-Pb age of /- 8Ma. Gold mineralization, which is hosted by subvertical quartz veins that occupy the most strained portions of the shear zone, occurs in late fractures and as particles within recrystallized quartz. The gold mineralized zones are 2-3 metres wide and plunge steeply to the northeast. Mineralized veins have a complex paragenesis wherein recrystallized quartz, muscovite, sphalerite, galena, and chalcopyrite are paragenetically associated with gold. Obvious alteration of the granitic hostrock adjacent to the veins is lacking except for slight 18 0-enrichments of wallrocks up to 20 metres from the veins. Quartz veins which occur peripheral to the most-strained regions of the shear zone are discontinuous bands with little to no subgrain development and do not contain gold. The values of this barren quartz average 11.1 per mil, whereas the values of quartz comprised of at least 50% subgrains, and associated with gold mineralization, average 12.9 per mil. Oxygen isotope fractionation between quartz and coexisting muscovite associated with gold indicate gold mineralization occurred at ca. 300 C. Calculated and 8D values for the ore-forming fluid are lx

10 compatible with fluids derived from, or which have interacted with, igneous or metamorphic rocks at low water/rock ratios. The initial 87 Sr/ 86 Sr ratio of the auriferous fluid is , which is similar to the surrounding igneous rocks, and implies that the strontium was likely derived by leaching of Paleoproterozoic rocks similar in age and strontium isotope composition to those presently exposed on surface. Two-phase secondary aqueous fluid inclusions outline and dominate healed fracture planes in both barren quartz veins and in the less deformed portions of mineralized quartz veins. The fluids in these inclusions have low salinities, generally not exceeding 7 wt% NaCl equivalent, and homogenization temperatures of C. Fluid inclusions within dynamically recrystallized quartz tend to concentrate at quartz subgrain boundaries along with gold, are vapour-rich, have complex gas and cation compositions, homogenization temperatures between 300 C and 375 C, and show characteristics indicative of fluid-phase immiscibility. The age of gold mineralization was close to 1720 Ma, as indicated by Ar-Ar systematics of gold-associated muscovite, and Rb-Sr ages of muscovite and tourmaline. The 1720 Ma age indicates gold mineralization occurred ca. 100 million years after peak regional metamorphism, initial development of the shear zone and quartz vein emplacement and the cessation, at ca Ma, of collision in this section of the Trans-Hudson orogen. These data are consistent with a model wherein earlier quartz veins were reactivated and partially recrystallized during a post- X

11 tectonic, gold-depositing fluid event. Gold distribution was regulated by the development of fracture-controlled permeability and by H 2 0-C0 2 phase separation of a low salinity, C0 2 -rich, metamorphic fluid at 300 C to 375 C, which was deriv~ from a source similar to the igneous rocks spatially associated with the deposit. Xl

12 1. INTRODUCTION 1.1 Location, Access, and Physiography The Jasper property is located in the Star Lake area, approximately 110 air kilometres northeast of La Ronge, Saskatchewan and 1 kilometre northwest of highway 102, at latitude 'N and longitude 56 00'W (Figure 1 and Figure 2). An ex tens ion to the former Star Lake mine road (S.M. D.C. I Starrex joint venture) provides all-weather road access to the property and to the outcrops which host the auriferous veins (Figure 3). The topography is typical of the Canadian Shield, with heavy overburden, abundant lakes and muskegs, thick forest cover comprised of jackpine, poplar and birch, and shallow slopes with moderate relief of metres. 1.2 Exploration History of the Star Lake Area Historical accounts of the regional and local exploration and production history are given by Murphy (1986) and Kusmirski (1991). Gold in the La Ronge domain was first reported in the 1940's by Cominco but this resulted in only minor mining-related activity, and no significant discoveries. In the 1960's, Mary and Eugene Herd employed a small crusher to mill auriferous ore which they mined from their small claim located at the south end of Rush Lake (Figure 2). The first attempt at commercial gold production occurred in the mid 1970's when Decade Development tried to operate a small mine-mill at Mallard Lake (Figure 2) but were unsuccessful. In 1983, the S.M.D.C./Starrex/U.E.M. joint venture exploration program led to the discovery of the 21-zone, which was later 1

13 2 :RAE-HEARN~ SUPERIOR LA PROVINCE..... O too. P5... km Fiqure 1. Geological map showing the lithotectonic domains of the Early Trans-Hudson Orogen, and adjacent Archean Rae, Hearne and Superior Provinces, and the location of the La Ronge Domain (after Hoffman, 1988).

14 'N 'W (3 GRANITE ~ MONZODIORITE E3 DIORITE II] FELSIC VOLCANIC ROCKS D INTERMEDIATE VOLCANIC ROCKS II ULTRAMAFIC VOLCANIC ROCKS ~ METASEDIMENTARY ROCKS E) CATACLASTICROCKS lkm MINED GOLD DEPOSIT..._ ~ SHEAR ZONE "'IHGHWAY Figure 2. Geological location map of the study area and locations of the Jasper lode-gold deposit and other, previously mined, gold occurrences (modified after Thomas, 1983).

15 4 Figure 3. Location of samples collected from the area around Jasper. The five boxes at the right represent enlarged views of the outcrops from which surface samples were taken. The points leading away from outcrop #5 are drill-hole sample locations projected to surface. The longitudinal section in upper left represents an idealized view of the mineable ore along survey line looooe.

16 5 Longitudinal Section 4700N 4800N 4900N 5000N 600m/ ~ D Overburden 13 Granite looooe Ill Ore Vein II Quartz Vein # m II Water I I I Drill-Hole Sample Projected to Surface 0 20m I I Q Outcrop

17 6 developed as the Star Lake gold mine. The 21-zone was a 2-to-14 metre-wide auriferous quartz vein associated with a 2 metre wide mafic dike, and was hosted within a shear zone which cross-cuts the monzonitic portion of the calc-alkaline Star Lake Pluton (Janser, 1992; Ibrahim, 1990) (Figure 2). The Star Lake mine was in operation in 1987 and 1988, and produced 83,000 oz of gold at an average ore grade of 0.48 oz of gold per ton of rock. At about the time that the 21-zone was going into production, the Mahogany/International Corona joint venture exploration program led to the discovery of the Rod Zone, in the same area as the old Decade mine, also hosted within the Star Lake Pluton but which is situated within its northeast dioritic rim. This discovery led to the development of the Jolu gold mine, which began production in the fall of 1988 and continued to the summer of 1991, and produced approximately 205,000 oz of gold at an average ore grade of 0.4 ounces of gold per ton of ore. In 1987, the S.M.D.C./Shore Gold Fund/Golden Rule Resources/International Mahogany joint venture initiated an exploration program designed to prospect and map the southern portion of the Island Lake Intrusion and some of the surrounding volcanic rocks. This led to the uncovering of gold-rich quartz veins hosted within the granitic portion of the Island Lake intrusion and the delineation of the Jasper gold occurrence (Figure 2). Underground development began during the winter of 1988 but legal disputes prevented the Jasper mine from opening until November, The mine stayed in operation until June, 1991, and

18 7 milling of the ore was completed in December, The total gold production from the Jasper mine was approximately 87,000 oz of gold at an average ore grade of 0.6 oz of gold per ton. Ore mined from the Jasper veins was milled at the Star Lake mine-site. However, to keep the Star Lake mill operational until the new ore reserves at Jasper could be developed, the Star Lake mlnlng group initiated development of the Rush Lake gold zone during the summer of The attempt to keep the mill open was unsuccessful but the endeavour did produce about 5000 ounces of gold. To this date regional gold production is in excess of 300,000 oz of gold and at least as much remains as reserves (i.e. Contact Lake Deposit). Development of the Contact Lake Deposit was initiated in the fall of 1993 but no gold has been produced to date. 1.3 Objectives of Thesis Mesothermal gold deposits in Proterozoic mobile belts of the Canadian Shield have broad similarities to some Archean lode gold deposits in terms of their structural control, mineral paragenesis, and ore-forming fluids (Kerrich, 1989), but tend to be less numerous and smaller. These observations may reflect a lack of understanding of these deposits in terms of their evolutionary history and relation to regional geologic events, and therefore, may not necessarily be indicative of the true economic potential of Proterozoic lode-gold deposits ln Canada. Alternatively, similarities in the characteristics of Proterozoic and of Archean

19 8 lode-gold deposits, but apparent differences in their reflect similar ore-forming processes, albeit in sizes, may different geodynamic settings. The Jasper gold deposit is situated within the Paleoproterozoic Central Volcanic Belt of the La Ronge Domain in northern Saskatchewan, Canada (Figure 1). It is the southernmost member of five gold occurrences, three of which were economic, that occur as structurally-hosted auriferous quartz vein systems within two adjoining and petrologically similar granitic plutons (Figure 2). The auriferous mineralization at Jasper occurs in shear zones which allowed infiltration and localization of ore depositing fluids, similar to gold deposits of Archean (Colvine, 1989; Kerrich, 1989), Paleoproterozoic (Fedorowich et al., 1991; Ibrahim and Kyser, 1991; Ansdell and Kyser, 1992), Paleozoic (Kontak et al., 1990), and Mesozoic age (Bohlke and Kistler, 1986; Goldfarb et al., 1988). A contrast in competency between the Island Lake intrusive that hosts the deposit and the surrounding volcanic rocks may have provided a secondary control wherein fluid was focused in the more brittle zones of the shears in the pluton. However, the occurrence of numerous barren quartz-veins in shear zones having the same northeast structural attitude and similar deformation features as mineralized veins, in the Jasper area (Kyser et al., 1986; Ibrahim and Kyser, 1991), indicates that, although fluid permeability was structurally controlled, not all shear zones hosted fluids with the appropriate spatial, temporal, or physicochemical characteristics

20 9 conducive to gold mineralization. This study describes the paragenesis of the veins which make up the Jasper lode-gold occurrence, and constrains the probable source and age of the mineralizing fluids using petrographic and fluid inclusion studies, and stable and radiogenic isotope systematics. In addition, the gold deposits within this area conspicuously lack the obvious alteration envelope that typifies many Archean counterparts (Kerrich, 1989). A systematic trace element and oxygen isotope study of the hostrocks was also conducted to provide information on cryptic alteration which may prove useful in exploration for other gold deposits in this region. The analytical techniques used are described in appendix 2.

21 10 2. GEOLOGY 2.1 Regional Geology The La Ronge Domain is located in northern Saskatchewan and Manitoba, Canada, and forms part of the Reindeer Lake Zone of the Trans-Hudson orogenic belt, the largest exposed Proterozoic orogenic terrane in the world (Stauffer, 1984). The lithotectonic evolution of this orogen has been reviewed by several authors who all propose that the Trans-Hudson Orogen is the result of an early Proterozoic lateral accretion of juvenile Paleoproterozoic volcanic arcs, and possibly other allocthonous terrains, between the Archean Superior and Churchill provinces (Stauffer, 1984; Lewry et al., 1987; Hoffman 1988; Lewry and Collerson 1990). Recent deep seismic surveys indicate that subduction may have been to the east along the eastern portion of the Trans-Hudson orogen and to the west in the western portion (Nelson et al., 1993). In this perspective, the La Ronge Domain represents the fragmentary remains of a juvenile volcanic arc within an accretionary prism, flanked by ensialic external belts. The La Ronge Domain itself consists of several lithotectonic belts, namely the Central Volcanic Belt (CVB), MacLean Lake Belt and Crew Lake Belt. The Jasper gold deposit occurs within the CVB (Figure 1), a northeast-trending volcano-plutonic complex with minor intercalated metasedimentary rocks (Lewry and Collerson, 1990; Thorn et al., 1990). Detailed petrologic descriptions of the rocks in the CVB are given by Coombe et al., (1986) and Harper et al., (1986). The CVB consists of Ga ultramafic to felsic

22 11 volcanic rocks intruded by Ga ultramafic to felsic uniform to multiphase plutons and minor intravolcanic metasedimentary rocks. Trace-element patterns of the volcanic rocks are similar to rocks derived from modern volcanic arcs and have relatively non-radiogenic initial 87 Sr/ 86 Sr ratios ( ) consistent with a subduction-related origin (Harper et al., 1986). The major plutons are calc-alkaline in composition and also have chemical compositions typical of derivation from a volcanic arc (Harper et al., 1986). Unlike the highly deformed rocks in the surrounding terranes, the rocks which make up the CVB display the effects of low, heterogeneous strain. However, localized zones of high strain, as evidenced by shear zones, are common and typically trend northeast, although local variations do occur (Coombe et al., 1986). The metamorphic grade is between lower and mid-amphibolite facies, as indicated by the minerals in mafic and pelitic metasedimentary rocks and, presumably, peaked at about 1820 Ma, shortly after plutonism in the area (Bickford et al., 1987). An increase in metamorphic grade outwards towards the margins of the belt and from northeast to southwest has also been observed (Harper et al., 1986). A regional 1.5km wide high-strain zone, termed the McLennan Lake Tectonic Zone (Thomas, 1984), separates the southeastern boundary of the CVB from the structurally underlying, but younger, dominantly metasedimentary, MacLean Lake Belt (Lewry, 1983; Coombe et al., 1986). To the northwest, an unnamed diffuse to highly strained zone separates the isoclinally folded metasedimentary

23 12 rocks of the Crew Lake Belt from the CVB (Coombe et al., 1986). 2.2 Local Geology Three outcrop exposures of the Jasper gold-mineralized quartz veins occur within a 300 metre strike length and along a 040 trend (Figure 3, outcrops 3,4,5). The veins are hosted in a northeasterly striking and steeply northwest-dipping mylonitic shear zone which cross-cuts the southwest portion of the Island Lake Intrusion (Figure 2). The shear structure extends into the bounding mafic metavolcanic rocks where it disperses into numerous, less prominent, smaller shears. The principal development of the shear zone was contemporaneous with that of the dominant regional foliation, which also strikes to the northeast and dips subvertically (Roberts, 1990). Although the shear zone and quartz veining have a strike length in excess of 600m, gold mineralization is restricted to the portion of the shear-zone hosted by the granitic phase of the Island Lake Intrusion. The gold is sited within 1-2 metre wide northeasterly-plunging ore shoots of variable grade in subvertical, banded quartz veins and is concentrated in those that occur within the highest strained portions of the shear zone. These mineralized veins display extensive shearing and commonly host mm-to-cm-sized wallrock ribbons which occur mainly along the edges of the veins. The extent and direction of shear displacement has been obscured by the high intensity of shearing and lack of lithological contrasts. However, Roberts (1990) reports a northeasterly trend and steep plunge of mineral lineations, indicating oblique-slip movement some

24 13 time during the deformational history of the veins. Quartz veins peripheral to the most intensely strained sections of the shear zone are unstrained white lenses and stringers with variable orientations, and are devoid of gold mineralization. The Island Lake Intrusion, which hosts the Jasper deposit, is a 4x9 km ovoidal granitic pluton intruded into predominantly intermediate to ultramafic metavolcanic rocks. A single-zircon Pb Pb age of 1855 ± 8 Ma (Hrdy et al., 1991) represents the time of crystallization of the pluton and is similar to the U-Pb zircon age of 1848 ± 14 Ma obtained for the adjoining Star Lake Pluton (Van Schrnus et al., 1987), which hosts the Star Lake and Jolu mesothermal gold deposits (Ibrahim and Kyser, 1991). Trace element contents of the Island Lake Intrusion are similar to those reported by Harper et al., (1986) for the proximal Star Lake Pluton, with LREE enrichments and normalized depletions of HFSE that typify volcanic-arc granites (Figure 4). Harper et al., (1986) have suggested crystal fractionation of a calc-alkaline parent magma with multiple injection episodes as the origin for the Star Lake Pluton. Given the close spatial association, similar crystallization age, comparable zoning and trace element compositions of the Island Lake Intrusion and the Star Lake Pluton, a similar origin for the Island Lake Intrusion is likely.

25 14 ISLAND LAKE PLUTON K20 Rb Ba Th Ta Nb Ce Hf Zr Sm Y Yb Figure 4. Ocean ridge granite (ORG) normalized compositions of four granitic whole-rock samples of the Island Lake Pluton. Samples were collected at least 40 metres from any quartz veins. The incompatible element pattern is indicative of a volcanic arc origin (Pearce et al., 1984).

26 15 3. VEIN MINERALOGY AND ALTERATION 3.1 Petrography and Mineral Paragenesis On an outcrop and handsample scale, the auriferous quartz has a dull-grey colour, and ribboned, chert-like character (Figure Sa). On a microscopic scale, pervasive quartz subgrain development is common, with local regions of undulose, ribbony quartz (Figure Sb). This feature 1s compatible with heterogeneous deformation at moderate temperatures, wherein variable strain gradients produced crystal distortion of quartz, undulose extinction, and eventually quartz recrystallization to subgrains in the most intensely strained regions (Kerrich and Allison, 1978). The auriferous quartz veins host a complex vein mineral paragenesis (Figure 6) with no obvious lateral or vertical mineralogical zoning. Modal proportions of vein minerals vary locally, but average about 70-80% quartz and 5-20% pyrite, with minor hematite, muscovite, tourmaline, biotite, chlorite, carbonate, chalcopyrite, sphalerite, bornite, galena, gold, and trace albite, Ag-Au tellurides, magnetite, pyrrhotite, molybdenite, scheelite, monazite, uraninite, and rutile. Two mineralogically distinct forms of gold mineralization occur in the Jasper Lode-gold deposit. The most common is free gold which has a high fineness and contains minor silver (3-8%) and selenium (2%), and trace bismuth (0.5%), mercury (3%) and tungsten (<0.5%). This gold occurs in late fractures which cross-cut both ribbony and subgrained quartz, and as isolated particles and particle trails in areas of quartz subgrains (Figure Sc). A less

27 16 Figure S(a) Outcrop hosting an auriferous quartz vein. The quartz is a dull-grey colour and has a ribbony, chert-like character. The granitic wallrock is mylonitic along the margins of the quartz. (b) Photomicrograph of "Highgrade #2" with crossed-nicols showing the two types of quartz observed in auriferous quartz veins. The quartz grain occupying the lower right half of the photo has not been strained to the same degree as the recrystallized, subgrained quartz, which occupies the upper left half of the photo. The grainy linear bands seen in the lower right half of the photo are secondary fluid inclusion planes that become dispersed within the recrystallized quartz. (c). Photomicrograph of "Highgrade #2" showing fracture-hosted gold and isolated gold particles hosted within recrystallized quartz. The fractures cross-cut both early and subgrained quartz. The gold particles in the centre of the photo have no apparent fracture association and occur only within subgrained quartz. (d) SEM back-scatter photomicrograph of a microfracture hosting muscovite, albite, gold, and gold tellurides which cross-cuts veinincorporated wallrock. The light grey material is potassium feldspar and the darker grey material is albite replacing the potassium feldspar. The slide was cut from sample #28.

28

29 18 QUARTZ PYRITE HEMATITE. MUSCOVITE TOURMALINE BIOTITE CHLORITE CARBONATE CHALCOPYRITE SPHALERITE BORNITE GALENA GOLD Ag-Au TELLURIDES ALBITE MAGNETITE PYRRHOTITE MOLYBDENITE SCHEELITE MONAZITE URANINITE RUTILE OLDEST RELATIVE Tll\{E ----YOUNGEST Figure 6. Mineral inventory and relative paragenesis in shear zones hosting the Jasper lode-gold deposit. Dashed lines represent less certain occurrence.

30 19 abundant form of gold mineralization occurs as silver-gold tellurides, having variable amounts of silver (14-80%), gold (0.2-24%), tellurium (9-57%), bismuth (0.5%), copper (0.5%), iron (0.5%), selenium (0.5%), tungsten (0.5%), and mercury (1%). The silver-gold tellurides typically occur in microfractures less than 10pmwide which cut vein-incorporated wallrock (Figure 5d), and are associated with trace minerals such as bornite, molybdenite, scheelite, monazite, uraninite, and rutile that are commonly visible only at the scale of an electron microprobe. Albitic alteration of potassium feldspar around these microfractures is another characteristic of this environment (Figure 5d). Common vein minerals which are paragenetically related to both forms of gold mineralization include muscovite, and to a lesser extent, albite, sphalerite, galena and chalcopyrite (Figure 6). Muscovite is relatively abundant 1n auriferous veins and therefore makes a good indicator mineral for gold exploration in this region. This mineral can also be used to determine the oxygen and hydrogen isotopic composition of the mineralizing fluid, and the age of gold mineralization with Rb-Sr and Ar-Ar isotope systematics, although the muscovite is usually intergrown with albite, making separation impossible. Some of the highest grade samples consist of chlorite-coated fractures with spectacular free gold overgrowing chlorite; however, chlorite is not a good indicator of gold mineralization due to its complex paragenesis. Pyrite is the dominant sulphide in the veins and typically

31 20 forms irregular interconnected blebs and stringers ranging between 0.5 and 5 em in size, with local subhedral to euhedral crystals. Gold and pyrite rarely occur together, and where they do, gold typically overgrows pyrite, indicating that much of the pyrite is not paragenetically related to gold. Tourmaline, which has an extensive paragenesis that overlaps that of gold (Figure 6), has a dravitic composition which plots out of the range determined for Archean mesothermal gold deposits on a Mg-Fe-Al ternary diagram (Figure 7), increases in its Mg, Fe, Ti, Cr, K, Ca, and Na elemental composition from core to rim (Figure 8), and is a minor, but common, constituent of the ore veins, especially within ribbons of the wallrock. Fractures in tourmaline commonly host other vein minerals such as pyrite and gold. Biotite is a major constituent of the hostrock and is finer grained the closer it is to the shear zone. It occurs within ribbons of vein-incorporated wallrock, commonly in association with muscovite, but is rare in the more pristine portions of the quartz veins. Most of the biotite formed prior to gold mineralization (Figure 6). Quartz ve1ns which occur peripheral to the most-strained portions of the shear zone rarely exceed a metre in length and are milky-white, discontinuous, commonly sigmoidal shaped, nonauriferous bands. Where these veins occur within the mylonite, they tend to be deflected towards parallelism with the mineralized veins, especially where strain was highest, but no direct crosscutting relations have been observed between the mineralized and

32 21 AI ELBAITE SCHORL BUERGERITE... I I.. I- e ALKALI-FREE DRAVITE ARCHEAN MESOTHERMAL GOLD DEPOSITS SAMPLE #28 Figure 7. Al-Fe-Mg plot of tourmaline compositions derived from sample #28 (Appendix 2). The shaded regions represent a compilation of tourmaline compositions from a variety of Archean mesothermal deposits (King, 1989).

33 =-wi Si02 Si0 2 CORE 1:1 Si0 2 RIM ~!IIIIIII!IIIIIIII Number of Sample Number of Sample Number of Sample FeO 1.0-r r , CrzOs Cr 2 o 3 I CORE D Cr203RIM D 1~~~~~~~~~~~ Number of Sample Number of Sample ,...,...,...,...,r-T""I""'T""'I"""'"""'"'"'""'"T""T...,...,r-T""r-T""' Number or Sample cao 0.06 I , 2.2 ~:: ooooooooom!jr ~ 2.0 II'< 2.1 o.oo ,...,...,...,..,0...,...,...,,5,...,...,...,...-f,20 Number of Sample Number or Sample ,.'"T"""''"T"""r-T""T"'T"T'"'I"'T"T'"T"""'-r-"r-T""'T""T"""f Number of Sample Figure 8. Tourmaline elemental compos! tions and compos! tional variations from core-to-rim. The tourmalines are dravitic and have relatively high Cr contents. All of the tourmalines analyzed are from sample #2 8 (Appendix 2).

34 23 barren veins. These barren veins consist of irregular, lensoidal, and ribbony quartz grains which display undulose extinction and have very minor subgrain development. These quartz veins contain small amounts of biotite, K-feldspar, and hematite. 3.2 Hostrock Alteration Drill-hole #62 (Figure 3) transected a high-grade ore section and was examined to assess the possible effects fluids in the shear zone had on the mineralogical and chemical compositions of the hostrocks. Biotite typically overgrows and replaces hornblende within 20 metres of the hanging-wall side of the ore zone, and within 5 metres of the footwall side. The grain size of the biotite also decreases closer to the ore zone. Muscovite occurs out to 2 metres from the ore zone, and trace amounts extend to 20 metres of the hanging-wall side. Major element contents do not vary with distance from the auriferous vein, although, lead, tungsten, antimony, tin, and zinc show minor enricr~ents within 10 metres of the ore zone (Figure 9). Enrichments in 18 0 of wallrock quartz, biotite and whole-rock also are evident up to 20 metres of the hanging-wall side of the vein (Figure 10). This implies that fluids associated with the vein affected a more extensive area than is indicated by field observations or by major and most trace element contents. The paucity of chemical alteration in the wallrock around the quartz veins, except for some variations in trace elements and oxygen isotopes, is evidence that the fluid was nearly in chemical equilibrium with the wallrock.

35 24 Figure 9. Variations in selected trace element contents (ppm) with distance from the centre of the auriferous quartz vein for samples collected from drill-hole #62 (see figure 3 and appendix 3 for locations and data, respectively). Samples of vein material are not included.

36 = ~ = = Hanging wall METERS Footwall Hanging wall METERS Footwall = 0.1 ~ Hanging wall METERS Footwall Hanging wall METERS Footwall u = z Hanging wall METERS Footwall Hanging wall METERS Footwall <ll u f L Hanging wall METERS Footwall Hanging wall METERS Footwall a 5 lo.s Hanging wall METERS Footwall Hanging wall METERS Footwall co ~ 0.16 ~ Hanging wall METERS Footwall Hanging wall METERS Footwall

37 = 3 CZl = 2 40 Hanging wall METERS Footwall Hanging wall METERS Footwall ~ E J N = Hanging wall METERS Footwall Hanging wall METERS Footwall 14 ~ ~ 2 40 Hanging wall METERS Footwall Hanging wall METERS Footwall ~ 0.3 > Hanging wall METERS Footwall Hanging wall METERS Footwall 10 j;;) 5 40 Hanging wall METERS Footwall

38 15 14 Hanging wall ve 1 in Footwall 0 13 r-. CIO ~ 12 I ~ llr-. u 0 I w ~ I 0 9 :::t: I ~ 8 I 7 - I 6 - I I Hanging wall Footwall- V~n 13 - N ~ 12 - I - <( a 11 - LL I CIO I 7 - I I! Hanging wall V~in Footwall 7 w 1- + i= 6- I - 0 in I LL 0 5 I 0 1 CIO ~ 4. I I 3 I I DISTANCE FROM VEIN ( METERS ) I Figure 10. Relation between o18o values of quartz, biotite and whole-rock samples from the hostrock granite at Jasper and distance from the auriferous quartz vein. The north arrow represents true north. All of the samples were collected from drill-hole #62 and were corrected for horizontal distance.

39 28 4. FLUID INCLUSION STUDY 4.1 Theoretical Overview Naturally occurring minerals host imperfections in their crystal structures which are commonly occupied by foreign phases, typically referred to as inclusions. Fluid inclusions make up a large portion of the inclusion population in many minerals and are unique in that they host a sample of the fluid which was prevalent at the time the inclusion was trapped. Fluid inclusions have been classified on the basis of composition, origin, and on the ratios of phases present, however, the most common and useful classification scheme is one that is based on the origin: primary, pseudosecondary, and secondary (Roedder, 1984). Primary fluid inclusions represent fluid which was trapped during crystal growth, pseudosecondary fluid inclusions represent fluid which was trapped in fractures developed during crystal growth, and secondary fluid inclusions represent fluid which was trapped at any time after crystallization of the hosting mineral. Microthermometry is a non-destructive, semi-quantitative analytical technique which can be applied to inclusions as small as 5~. The technique relies on observable phase changes which result from differential shrinkage between the hosting mineral and the fluid which occupies the inclusion because the original density of the fluid is maintained. Instrument requirements include a standard petrographic microscope, a heating-freezing sample stage, and a thermocouple. The apparatus is used to freeze and heat the sample

40 29 so that the temperature at which phase changes occur can be recorded. These data can then be used to help determine the composition, density, temperature, and pressure of the fluid at the time of trapping. Much can be determined about the composition of the fluid in fluid inclusions by studying the phase behaviour of the fluid in the inclusions at low temperature, although, experimental data on phase equilibria is limited to aqueous salt solutions hosting NaCl, KCl, CaCl 2, and MgC1 2 as the major solutes, and C0 2 -CH 4 gas systems (Roedder, 1984). Semi-quantitative analysis of fluid inclusions in ore-deposits is possible because most hydrothermal minerals host fluid inclusions which contain aqueous solutions that have 0-to SOwt% solutes consisting of Na, Ca, Mg, Cl, and S0 4, C0 2, and CH 4 (Roedder, 1984). Interpretation of components present in a fluid inclusion is first done at room temperature with the identification of inclusion type: one, two, or three-phase, and the state of phases present: vapour, liquid, solid. Because a large fraction of all fluid inclusions consist of H 2 0, C0 2, and NaCl, preliminary assumptions must assume these components are present in the phases observed. If the presence of C0 2 is suspected, the sample must be frozen to below -56 C, the eutectic point of C0 2, to determine its purity. Upon warming, if the initial melting of C0 2 (eutectic point) is observed to occur below -56 C, an additional component (e.g. CH 4, N 2, S0 4, H 2 S) is probably present (Roedder, 1984). Similarly, the eutectic point of the pure NaCl-H 2 0 system is at C (Figure

41 30 SOLUTION 8' ~ ~ + SOLUnON ICE + SOLUTION WEIGHT PERCENT NaCI Figure 11. Isobaric T-X plot for the system NaCl-H 2 0 in equilibrium with vapour at 1 bar total pressure. The diagram is used to demonstrate the effect of NaCl on the final melting temperature of ice (from Roedder/ 1984).

42 31 11), and is lowered in the presence of other solutes (e.g. CaCl 2, MgCl 2, LiCl, AlC1 3, FeC1 3 ); therefore, if initial melting of ice (Te) occurs below C, the presence of other solutes is indicated (Figure 12). The concentration of NaCl can be determined from the freezing point depression of ice formation as illustrated in Figure 12. However, fluid inclusions always show metastable supercooling, so the determination is always made on warming and is referred to as the temperature of melting of ice (Tmice). Potter et al., (1978) have experimentally determined the liquidus curve for this system and have derived the equations: 0.028] ws = o.oo e x 10-2 e x 10-4 e 3 [± e = Ws x 10-3 Ws x 10-4 Ws 3 [± O] 1 where e = the freezing point depression 1n C, and Ws = the weight percent NaCl in solution. However, the presence of other solutes will lower the liquidus below that of pure NaCl-H 2 0 and it is standard practice to report solute concentration as wt% NaCl equivalent, unless a daughter mineral is present and identifiable. Even though H 2 0 and C0 2 are almost completely immiscible at room temperature, estimation of salinity in H 2 0-C0 2 -NaCl fluid inclusions is difficult due to the formation of clathrates (gas hydrates, i.e. C0 2 x 5.75H 2 0). This can lead to an overestimation

43 32 0 wt % salt in solution (.) c: 0 KCJ:NaCI c. Cl c: N Q,) Q,) ~ c: 0 en en Q,) ~ c. CD 1:J Figure 12. Depression of the freezing point of water as a function of wt% salt in solution for KCl, NaCl, CaC1 2, MgC1 2 (from Shephard et al., 1985)

44 33 of salinity because part or all of the water present in the fluid inclusions may be consumed in the formation of the gas-hydrate, increasing the salt concentration in the remaining aqueous phase. A relation between the final melting temperature of the clathrate ('rrnc 1 ath.) and salt concentration has been derived (Bozzo et al., 1973), where the final melting temperature of the clathrate for low salinity fluid inclusions (~16wt% NaCl) corresponds to the salinity of the aqueous phase. Fluid inclusions provide the only direct way to measure the density of prehistoric fluids. Fluid inclusion densities can be estimated from the temperature of homogenization (Th-from heating measurements) and salinity (from freezing measurements) by applying a least-squares-fit polynomial equation describing the relationship between density, temperature and salinity (Bodnar, 1983; Figure 13a), or from an estimation of the liquid/vapour ratio at room temperature combined with salinity, as illustrated in figure 13b&c. If C0 2 is present, its density must be determined independently and combined with the density of the aqueous phases to determine the bulk density of the fluid inclusion. The density of C0 2 is estimated from the temperature of C0 2 homogenization and its phase relations, as depicted in Figure 14. The temperature of trapping can be estimated by heating the sample under observation to the point where all visible phases homogenize. This is referred to as the temperature of homogenization (Th), and represents the minimum temperature of trapping. The true temperature of trapping (Tt) equals Th only if

45 a oc DENSITIES (g/ccl OF VAPOR-SATURATED H 2 0-NaCI SOLUTIONS WT. Ofo NaCI 70 b. 600 c. 1.0 wt % NaCI ,u oo :I Q ~ QJ QJ 0, 200 QJ - homooenozation - 0 into the vapour stale densoty g cm- 3 (or degree ot 1111) total density of lluid in g em- 3 Figure 13(a) Density of vapour-saturated NaCl fluids in the system NaCl-H 2 0, calculated by Bodnar ( 1983) using a stepwise multiple regression from published data. (from Roedder, 1984). (b) Temperature-density plot for pure water showing the modes of homogenization for inclusions with high, medium and low bulk densities trapped at the same temperatures but different pressures (Tt, temperature of trapping; TH, temperature of homogenization; c.p., critical point). (c) Degree of fill versus total density of fluid demonstrating the effect of salt concentration (Shephard et al., 1985).

46 35 homogenization temperature oc homogenization into the (") 'e liquid state u Cll L+V - L > en c: a), crit. density =0.468 g em crit. temo. = C homogenization Into the vapour state 0.2 l+ v - v Figure 14. Relationship between density of the C0 2 phase and temperature of homogenization of liquid C0 2 Note that the critical point is at 31.1C and that it is important to distinguish whether the C0 2 homogenizes into the liquid or vapour states (from Shephard et al./ 1985)

47 there is evidence that phase immiscibility was occurring at the time of trapping (Roedder, 1984). However, the true temperature of 36 trapping can be calculated by applying a pressure correction, providing the density of the fluid in the inclusion is known and the pressure at the time of trapping is known. Figure 15 illustrates the relation between temperature, pressure, and fluid density (isochores). Fluid density and Th will define the appropriate isochore, and pressure will define the Tt along that isochore (see Shephard et al., 1983 for a more detailed description). Alternatively, if an independent geothermometer is available (i.e. mineral compositions, stable isotope geothermometry, etc), and the density of the fluid is known, a pressure-temperature isochore plot can be used to determine the pressure at the time of trapping Inclusion types, Petrography and Microthermometric Results A study of the fluid inclusions in quartz from the ore zone, and associated barren veins, of the Jasper deposit was conducted to obtain information on the history and physicochemical characteristics of the paleofluids, especially those related to gold deposition (Table 1; Figure 16). All of the quartz samples studied (auriferous and barren) contain abundant healed transgranular fractures defined by secondary fluid and solid inclusions. These planes of fluid inclusions are restricted to the less-intensely strained, ribbony quartz in auriferous samples and are not associated with gold (Figure 5b). The fractures normally occur in sets of two or three,

48 IIIII I I I I. I /, I, /. I, /,/./ ---WATtJI WT.'!oNaC ---2SWT'lNA:I aatdl. POINT fill Figure 15. A phase diagram for water and 10 and 25 wt% NaCl solutions, showing the liquid-vapour curves and several isochores (lines of constant density). Note that the critical point of water is increased, the density of the solution is increased, and the slope of the isochore is affected by NaCl content (from Roedder, 1984).

49 38 Table 1. Fluid inclusion measurements for barren and auriferous quartz veins from the Jasper gold occurrence. Sample locations shown in figure 3. Temperature is in C. Sample Quartz Type TmC02 Te Tmjce TmClath ThCO 2 Th Comments 26 barren S-3p 9.8 S-3p S-aq S-aq -1.9 S-aq -3.7 S-aq auriferous S-hv 330(d) Homogenize to vapour S-hv 365 Homogenize to vapour S-hv 280(d) S-hv 476(d) S-hv 476(d) 28 auriferous S-aq barren S-3p S-3p S-3p S-3p S-aq S-aq -1.0 S-aq S-aq S-aq -4.2 S-aq S-aq S-aq S-aq S-aq S-aq S-aq S-aq S-aq S-aq S-aq S-aq S-aq Highgrade #2 S-aq auriferous S-hv S-aq S-hv (d) S-hv -58 >550 S-aq -4.8 S-aq S-hv S-hv S-hv Homogenize to vapour S-hv S-hv S-hv -63 S-hv -64 S-hv -63 S-hv -66 S-hv -3.0 S-hv 578(d) S-3p -62 S-hv -62 S-hv abbreviations: S =secondary, aq =aqueous H20-C02, 3p =three-phase H20-C02, hv =high vapour H20-C02, d =decrepitation, TmC02 = temperature of initial C02 melting, Te = temperature of initial ice melting, Tmice = temperature of final ice melting, TmClath = temperature of clathrate melting, ThC02 = temperature of homogenization of C02, Th = temperature of bulk homogenization.

50 39 TmC02 Tmlce Temperature (OC) 10 Ia 9 ~ 8 "r;j = 7 "C 6 ~ 5 c... ~ 4 J 3 a ~ TmClath Temperature (OC) Temperature (OC) Th ~ 9.s 8.27 ~ 6 ::5 ~ 4 a 2 J3 ~~ Q Temperature (OC) Temperature (OC) Aqueous Fluid Inclusions D H20-C02 Fluid Inclusions il Fluid Inclusions in Dynamically Recrystallized Quartz. -1 Te 0-5 Figure 16. Microther.mometric measurements of secondary aqueous and and secondary three-phase H 2 o-co 2 fluid inclusions, and from fluid inclusions in dynamically recrystallized quartz. T.mC02 = melting temperature of co 2, TmClath. = clathrate melting temperature, Th = temperature of homogenization, Te = temperature of initial ice melting, T.mice = temperature of final ice melting. Data from Table 1.

51 40 but the lack of definitive cross-cutting relations makes their relative chronology ambiguous. They are dominated by two-phase aqueous fluid inclusions with uniform liquid to vapour ratios of 4:1 to 5:1, although three-phase H 2 0-C0 2 fluid inclusions occur locally. Salinities of the fluids which occupy these inclusion range from 1.6 to 10.6 wt% NaCl equivalent, but most are near 7 wt% NaCl equivalent. Temperatures for initial ice melting are variable and indicate a complex solute composition. Homogenization temperatures range from 140 C to 400 C, but most are between 150 C and 200 C (Figure 16). The range in homogenization temperatures most likely resulted from necking or leakage due to later deformation in some inclusions that was not evident from their morphology. The few measurements obtained for the three-phase, H20- C02 fluid inclusions indicate a salinity of 8 to 10 wt% NaCl, equivalent, similar to the aqueous inclusions, and the minor presence of another component in the gas phase such as methane. Fluid inclusions which occupy the subgrained regions of auriferous quartz occur randomly within the quartz subgrains but are most common at subgrain boundaries and are associated with gold (Figure Sc). These fluid inclusions are small (<2pm diameter) and vapour-rich, and clusters with variable liquid/vapour ratios are common. Temperatures of homogenization or decrepitation obtained from inclusions with visible liquid and vapour range between 225 C and 525 C, although most are between 300 C-375 C (Figure 16). These fluid inclusions have salinities of 4 to 7 wt% NaCl equivalent, similar to the range in salinities of the secondary aqueous fluid

52 41 inclusions, and their low and variable temperatures of initial ice melting (-21 to -29 C) imply a similar complex salt composition. They are C02-rich, but contain a larger proportion of other gases (e.g. H2S, N2, CH 4 ), as indicated by the wide interval of final melting of C02, from -66 C to -58 C (Figure 16). 4.3 Discussion of Fluid Inclusion Data Samples containing gold that is not fracture-hosted have a high percentage of subgrained quartz, and fluid inclusions, gold, and muscovite, are abundant along the subgrain boundaries of this dynamically recrystallized quartz. Cross-cutting relations between the healed fractures which are dominated by aqueous fluid inclusions and subgrained quartz, dominated by co2-vapour inclusions, indicate a relatively late origin for the inclusions which occur in subgrains and which are associated with gold (Figure Sb). The fluid inclusions which occur in this environment have variable liquid/vapour ratios and homogenize between 300 C and 375 C. This differs from the dominantly aqueous fluid inclusions which occupy transgranular healed fractures, have constant liquid/vapour ratios, and which homogenize between 150 C and 200 C. Variable liquid/vapour ratios can be indicative of H20-C02 phase immiscibility such that the temperatures of total homogenization measured for the vapour-rich fluid inclusions (most between C) should represent the temperature of the fluid at the time of trapping (Roedder, 1984). Alternatively, the brine content of earlier aqueous fluid inclusions may have been partially removed by.. dragging and breakaway 11 -type of interactions between

53 migrating grain boundaries and the fluid inclusions during quartz subgrain development, as described by Drury and Urai (1989) STABLE ISOTOPES Oxygen and hydrogen isotope compositions of select vein minerals can be used to distinguish the origin of the fluid (e.g. meteoric, magmatic, metamorphic, or oceanic) associated with vein formation and ore deposition. In addition, sulfur isotope compositions of sulfide minerals can provide information on the possible source of sulfur (Ohmoto and Rye, 1979), and oxygen and sulfur isotope fractionations between mineral pairs can be used as a geothermometer (e.g. Taylor, 1974; Kyser, 1987). 5.1 Theoretical Overview Isotope studies involving oxygen, hydrogen, and sulfur are common in geology because they provide insight about fluid and solute sources, equilibration temperatures of minerals, and the kinetics of chemical reactions. This is possible because these isotopes ( 1) have a low atomic mass, ( 2) are comprised of one abundant isotope and one or more minor isotopes, (3) are the main components of rocks, minerals, ore deposits, and fluids, (4) have ratios which vary in natural substances, and (5) have distributions that are not time-dependent, nor are a function of the chemical behaviour of a parent element, as is the case for radiogenic isotopes (Kyser, 1987). Isotopic fractionation is affected primarily by temperature, which makes it necessary to know the fractionation of isotopes

54 43 among various phases as a function of temperature. These fractionation factors can be determined from theoretical calculations, experimental analysis, or they can be empirically derived using natural samples. There is no consensus as to which method is best but the correspondence of two or more methods improves confidence. Isotope fractionation factors are equilibrium constants which describe how the isotopes are partitioned between two phases, and are defined as: (5.1) where a is the fractionation factor, A and B are the two phases, Ra is the ratio of the heavy (rare) to light (common) isotope in phase A, and Rb is this ratio in phase B. In order to standardize the notation in stable isotope geochemistry, and because it is more precise to measure the difference in absolute ratios between two substances rather than determining the absolute ratios in every phase, stable isotope abundances are reported as delta (0) values in units of per mil (~) relative to a standard such that: R -R 0 = A stnd X A Rstnd (5.2)

55 where Rstnd is the absolute ratio in the standard. The standards 44 currently used are: Vienna Standard Mean Ocean Water (VSMOW) for oxygen and hydrogen, and troilite from the Canyon Diablo iron meteorite (CDT) for sulfur. Values of alpha (a) are close to unity, therefore their relation to delta (0) values can be defined as: 1+oA/1ooo a A -B = B I (5.3) and expressed in units per mil (~) notation. Refer to Kyser, (1987) for a more in-depth overview. 5.2 Mineral Isotopic Compositions and Isotope Geothermometry Auriferous samples are situated within the mylonitic portion of the shear zone and display a dull grey cherty texture in hand sample because of the presence of quartz subgrains values of this quartz range from 12.8 to 14 per mil, whereas the values of quartz from barren structures, with minimal subgrain development, range from 10.3 to 11.5 per mil (Table 2; Figure 17). Quartz separated from the granitic pluton has much lower values from 8.5 to 9.3 per mil. The 1-3 per mil difference between the value of subgrain quartz paragenetically associated with gold and barren strained quartz indicates that the veins were deposited either by isotopically distinct fluids, or from fluids with the same isotopic composition but at temperatures that differed by 100 C to 150 C, or some combination of the two.

56 Table 2. Stable isotope measurements of quartz veins, vein-associated minerals, and wallrock samples. Equilibration temperatures were calculated from paragenetically related minerals (refer to appendix). For sample locations refer to figure 3. Equilibration stso 80 Temperature Quartz (Minerai/W.R.) (Mineral) (Mineral) (H20) (H20) (OC) Sample oj-so stso &Ws 80 Comment pluton quartz pluton quartz subgrained quartz r undulose quartz same vein, different locations r, undulose quartz subgrained quartz undulose quartz subgrained quartz subgrained quartz same vein, different locations undulose quartz undulose quartz undulose quartz subgrained quartz 13 (Bi)7.5 (Bi)-67 (Bi) 6.7 (Tour) 10.6 (I'our)-67 (Qz-Tour) 430 (four) 9.6 (Tour) -41 (Py) 5.8 (Py) subgrained quartz 13.8 (Muse) 10.2 (Qz-Muse) subgrained quartz 13.4 (Bi) 5.5 (Py) 2.4 Highgrade #1 subgrained quartz 13.3 (Gn) 2.1 (Sp) 5.2 (Gn-Sp) 200 (Cpy)4.7 (Py) 4.1 Highgrade #2 subgrained quartz 13.7 (Muse) 10.3 (Muse)-63 (Qz-Muse) 310 (Musc)7.8 (Muse)-17 (W.R.) 12.7 (Gn) 2.7 (Sp)4.4 (Gn-Sp) 370 (Py) wallrock from drillcote 9.5 (Bi)4.0 (W.R.) wallrock from drill core (W.R.) wallroek from drillcote 9.2 (Bi)4.2 (W.R.) wallrock from drill cote (W.R.) wallrock from drill core (W.R.) wallrock from drill core (W.R.) wallrock from drill core 11 (Bi)4.2 (W.R.) wallroek from drillcore 10 (Bi)4.3 (W.R.) wallroek from drillcore (W.R.) wallrock from drillcote (W.R.) wallrock from drillcore 11.1 (Bi)4.6 (W.R.) wallrock from drillcore 9.3 (Bi)4.7 (W.R.) wallrock from drillcote 12.4 (Bi) 5.6 (W.R.) wallroek from drill core (W.R.) wallrock fromdrillcore 10.5 (Bi) 3.3 (W.R.) wallroek from drillcore (W.R.) wallroek from drill core (W.R.) wallroek from drillcore (Bi)3.0 (W.R.) wallroek from drill core (W.R.) wallrock from drill core 9.4 (Bi) 2.9 (W.R.)8.2 Abbreviations: Qz = quartz, Py = pyrite, Cpy = chalcopyrite, Gn = galena, Sp Muse = muscovite, W.R. = wholerock, Tour = tourmaline. 45 sphalerite, Bi = biotite,

57 46 Auriferous quartz D Barren quartz Quartz-Muscovite ~ ~ 6 lzi Pluton quartz in hanging-wall at300 C ~ (-1m from vein) ~ 5 G) Pluton quartz < rjj 4 II Tourmaline at400 C Quartz-Tourmaline ~ m Muscovite 0 3 II Vein biotite ~ ~ 2 ~ ~ 1 ;J z t!l Galena rjj ~ 6 ~ Sphalerite ~ ~ Ill Chalcopyrite ~ 5 Pyrite B18ovALUE ~ 4 ~ 3 Sphalerite-galena at 200 C ~ Sphalerite-galena at 400 C ~ 2 ~ ~ 1 ;J z ~34s VALUE Figure 17. o18o and o34s values of minerals occurring in mineralized and barren quartz veins from the Jasper shear zone, and from associated hostrock quartz. Muscovite, galena, sphalerite, and chalcopyrite are paragenetically associated with gold. Also shown are the differences in the values of coexisting quartz-muscovite, quartz-tourmaline, and sphalerite-galena at 300 C, 400 C, and 200 C-490 C, respectively. Data from Table 2.

58 values of other vein minerals include for muscovite, 10.6 for tourmaline, and for vein biotite. Muscovite and subgrained quartz are in petrographic equilibrium and differ in their values by 3.4 to 3.6, corresponding to isotope equilibration temperatures of 300 to 310 C (Table 2). Minor amounts (10-15%) of albite intergrown with muscovite was detected with SEM (Figure 5d), however, the effect of the albite on the calculated temperature is negligible due to its small modal abundance. Tourmaline has a complex paragenesis (Figure 6), however, the values of quartz and tourmaline from sample #28 provide an apparent isotope equilibration temperature of 430 C. Sulfur-bearing minerals include pyrite, galena, sphalerite and chalcopyrite, the latter three being paragenetically associated with gold mineralization (Figure 6). The 0 34 S values of galena range from 2.1 to 2.7 and for sphalerite from 3.9 to 4.4 (Table 2; Figure 17). Sulfur isotope equilibration temperatures for coexisting sphalerite and galena are between 200 C and 370 C (Table 2). Five pyrite samples have 0 34 S values between 2.4 and 5.8 per mil (Figure 17), indicating that the sulfur isotopic composition of pyrite has been variably reset. The 0 34 S value of the pyrite does, however, fall within the range of 1 to 6 per mil exhibited by most mesothermal gold deposits of all ages (Kerrich, 1989). 5.3 Isotope Composition of Fluid 11 Muscovite derived from sample Highgrade #2.. (Figure 3) is associated with gold and has a OD value of -63. Assuming a

59 48 deposition temperature of 310 C, as determined from values of auriferous quartz and coexisting muscovite, the calculated oxygen and hydrogen isotope compositions of the fluid in equilibrium with this muscovite are 7.8 and -17 per mil, respectively (Figure 18; Table 2). Both tourmaline (#28) and vein biotite (#28) have a 8D value of -67. When combined with apparent equilibration temperatures of 430 C, determined from auriferous quartztourmaline (#2 8) fractionations, the calculated oxygen and hydrogen isotope composition of the fluid in equilibrium with tourmaline (#28) are 9.6 and -41 per mil, respectively (Figure 18; Table 2). Such values are similar to those expected for fluids that formed from, or interacted extensively with, metamorphic or igneous rocks like those in the environs of the deposit at moderate temperatures and under conditions of low water/rock ratios. 6. RADIOGENIC ISOTOPE SYSTEMATICS 6.1 The Ar-Ar Method of Dating The Ar-Ar method of dating is based on the radiogenic decay of 4 K to 40 Ar, but unlike the K-Ar method, can be applied to a single sample of relatively small size, only requires the measurement of isotope ratios, and can be used to determine the history of argon diffusion of the substance being studied. The method relies on the formation of 39 Ar by irradiating 39 K with neutrons in a nuclear reactor so that 39 Ar will represent the potassium composition of the sample. This is done because argon is an inert gas which diffuses relatively easily from a mineral, especially at higher

60 49,-... a '- ~ ~..._., 0 N = Q l,o Archean lode Au deposit waters u Magmatic Waters Metamorphic Waters C JASPER II Tourmaline Ill Muscovite Figure 18. o18o and OD Oxygen of water calculated to be in equilibrium with muscovite and tourmaline associated with gold from the Jasper lode-gold deposit. The isotopic compositions of meteoric waters (MWL), sea water (SMOW), Archean lode-gold deposits (Kerrich, 1987) and typical magmatic and metamorphic waters are shown for reference. Data from Table 2.

61 50 temperatures, and because the diffusion rates of 39 Ar and 40 Ar are 40 relatively the same, making it possible to derive a Ar/ 39 Ar ratio measurement which represents a meaningful geologic age. Reviews of the theories, applications, and examples of the Ar- Ar method of dating are given by McDougall and Harrison (1988), and Faure (1986). When a potassium-bearing sample is irradiated with neutrons, isotopes of argon are formed by several reactions involving potassium, calcium and chlorine. The number of 39 Ar atoms formed from 39 K is: (6.1) where 39 K is the number of atoms of this isotope in the irradiated sample, ~T is the time duration of the irradiation, ~( ) is the neutron flux density at energy, cr(e) is the capture cross section of 39 K for neutrons having energy E, and the integration is carried out over the entire energy spectrum of the neutrons (from Faure, 1986). The amount of 40 Ar produced by the decay of 4 K is: (6.2) where Ae is the decay constant of 4 K for electron capture (0.581 x y- 1 ) and A is the total decay constant of 4 K ( x y- 1 ) Combining equations 6.1 and 6.2 yields:

62 51 40Ar = "Ae 40K 1 39 Ar "A 39K 11T f<p(e)o(e)d (6.3) The neutron flux density and capture cross sections are difficult to evaluate but this problem can be circumvented by defining a parameter J: (6.4) which can be determined by irradiating a sample of known age (flux monitor) along with samples of unknown age. The 40 Ar/ 39 Ar ratios of the unknown samples then can then be used to calculate an age using: 1 t=-ln "A 4oA r_.j+1) 39Ar (6.5) The above ls an ideal case where all of the 40 Ar in the irradiated sample is radiogenic, and all of the 39 Ar is derived from 39 K. In natural samples, argon isotopes are also produced in the irradiation by several interfering reactions and atmospheric argon may contribute both 39 Ar and 40 Ar. Therefore it is necessary to perform a series of corrections and the reader is referred to McDougall and Harrison (1988) for a detailed description. Argon is not a major lattice constituent of any potassium-

63 52 bearing mineral, but rather occupies a variety of secondary structural sites, some of which are more robust than others. Thermal events can cause argon to diffuse from a mineral, making it difficult and often impossible to derive a reliable radiogenic age based on the K-Ar systematics in the mineral. However, some of the secondary sites which host argon may remain closed to argon diffusion, even at high temperatures. If a sample is step-heated, argon will diffuse from progressively more robust sites with increasing temperature, making it possible to analyze different fractions of argon from an individual mineral. This technique makes it possible to analyze the composition of argon which was less likely to have leaked and is therefore more representative of the true age of the mineral. If the sample has remained closed to potassium and argon diffusion, the calculated 40 Ar/ 39 Ar age should remain constant throughout all temperature steps. However, if radiogenic argon was lost from some crystallographic sites, but not 40 others, the Ar / 39 Ar ratios of gas released at different temperatures will vary. This data can then be used to gain insights on the cooling history of the sample. 6.2 Ar-Ar Results Ar-Ar isotope systematics of muscovite associated with gold which has a Rb-Sr age of 1720 Ma (Figure 19) indicate a maximum age of 1703 ± 3 Ma, although the spectrum is disturbed (Figure 19, Table 3). Lack of a plateau can result from the presence of an intergrown mineral or later disturbance. For this sample, there is minor albite intergrown with the muscovite (Figure Sd), so that the

64 53 Sample #28 Muscovite(+ Albite) = 10 ~ 1 =,.-... ~ '-"' 1680 Q.) ~ < % 38 Ar cumulative release Figure 19. Plot of Ar-Ar data derived from vein muscovite paragenetically associtate with gold. The muscovite was separated from 11 Highgrade #2 11 Data from table 3.

65 Table 3: Ar-Ar systematics for muscovite from sample #28 Temp. ~C) 40Ar/39Ar 38Ar/39Ar 37Ar/39Ar 36Ar/39Ar 39Ar% 40Ar% K/Ca APPARENT AGE (Ma) FUSE J = sample wt. = g Vl ~

66 argon released during step heating represents mixtures of the argon 55 released from the two minerals. Feldspars have a lower closure temperature to potassium diffusion than muscovite (McDougall and Harrison, 1988), implying that the maximum age from the spectra of muscovite of 1703 Ma represents a lower age for formation of muscovite. The age of muscovite formation from the Rb-Sr isotope systematics of 1720 Ma is not affected by the mineral intergrowth because albite is paragenetically related to muscovite, and the closure temperature to rubidium and strontium diffusion for both minerals is higher than the estimated temperature of ca. 300 C for vein formation. 6.3 The Rb-Sr Method of Dating The Rb-Sr method of dating is based on the formation of 87 Sr from the radiogenic decay of 87 Rb which has a half life of 1.42 x y- 1 (International Union of Geological Sciences accepted value). The method is typically used to determine the age of potassium-bearing minerals due to their high rubidium concentration. The relation between time and the amount of 87 Sr is represented by the equation: (6.6) where 87 Sr is the total amount of this isotope in a unit weight of mineral; 87 Sri is the amount of this isotope that was incorporated into the same unit weight of mineral at the time of its formation;

67 56 87 Rb is the amount of this isotope in the same unit weight of mineral at the present time; A is the decay constant for 87 Rb; and t is the time elapsed since the formation of the mineral. However, most potassium-bearing minerals have some initial 87 Sr and the amount must be known before it is possible to solve equation 6.6 for time ( t ). An alternative way of deriving an Rb-Sr age is through a mineral isochron. If the system being studied hosts two or more paragenetically related minerals having varying Rb and Sr contents, the line connecting a plot of their 87 Sr / 86 Sr versus 87 Rb/ 86 Sr ratios will define a slope (m) which is related to the age by: (6.7) where A is the decay constant for 87 Rb, and t = age. In addition, they-intercept of this line defines the initial 87 Sr/ 86 Sr ratio for the minerals used to generate the isochron. For a more detailed review of the Rb-Sr method of dating refer to Faure (1986). 6.4 Rb-Sr Results Rb-Sr isotope systematics in tourmaline and muscovite have an age of 1720 ± 8 Ma, and an initial 87 Sr/ 86 Sr ratio for the auriferous fluid of (Figure 20, Table 4). This age indicates that gold deposition occurred 130 million years after pluton emplacement and 100 million years after peak regional metamorphism (Gordob et al., 1990). 6.5 The Pb-Pb and Ph-Evaporation Methods of Dating Lead is widely distributed throughout the earth and displays

68 ~ Sr 86sr 0.8 Age= /- 8Ma Tourmaline Sr~ 6 sr Initial ratio Rb/B6sr 10 Figure 20. Plot of Rb-Sr data derived from vein muscovite and tourmaline paragenetically associated with gold. Data derived from table 4.

69 Table 4: Rb-Sr data from vein tourmaline and muscovite Sample Mineral Sr (ppm) Rb (ppm) 87Rb/86Sr Error % 87Sr/86Sr Error % #28 Tourmaline H.G#2 Muscovite abbreviations: H.G. = Highgrade (,11 co

70 59 a large range in its isotopic composition as a result of the radiogenic decay of uranium and thorium. The relevant reactions are: 23au ~ 206Pb + 8 4He + 6(3- + Q, su ~ 207pb + 7 4He + 4(3- + Q, Th ~ 2oaPb + 6 4He + 4(3- + Q where~- is a beta particle and Q is the decay energy. The evolution of lead in a particular reservoir is therefore dependent on the U/Pb and Th/Pb ratios. The U/Pb and Th/Pb ratios are changed by crystal fractionation a magma, hydrothermal fluids, metamorphism, and whethering and other low temperature processes (Faure, 1986). In addition, the isotopic composition of lead may be modified by mixing of lead having different isotopic compositions. Therefore, the isotopic composition of lead in rocks and ore deposits can reflect their particular geologic histories. The isotopic composition of lead in the earths crust has evolved through time due to the accumulation of radiogenic lead. It is possible to estimate the age of the lead in minerals with low U/Pb ratios from their lead isotopic compositions, providing that the isotopic evolution of the lead reservoir is known, there is no uranium present in the minerals, and the lead isotopic composition of the minerals has not been affected by secondary processes. The Stacey-Kramers two-stage model (Stacey and Kramers, 1975) for the evolution of crustal lead is commonly used to date leadbearing minerals because it takes into account observed discrepancies between single-stage lead dates derived from many ore

71 deposits and their ages determined by other dating methods. The model breaks up the evolution of lead into two stages; an early 60 stage between and Ga years ago, where a primordial isotope ratio for 238 U/ 204 Pb of is used, and a more recent stage, where the 238 U/ 204 Pb ratio of the reservoir was changed by geochemical differentiation to and remained constant to present (Faure, 1986). Lead which evolved in such a reservoir and was incorporated into lead-minerals at some time in the past, must have lead isotope ratios that lie on the growth curve between points Q and P in Figure 21. The time of separation from the reservoir can then be calculated from the equation of the isochron: 207pb pb 206pb pb 1 e J>.2T -e J>.2t ( e J>.lT -e A2t (6.11) where is the 207 Pb/ 204 Pb ratio at the start of stage 2 (i.e Ga), is the 206 Pb/ 204 Pb ratio at the start of stage 2, 1/ is the modern 235 U/ 238 U ratio, A. 1 is the half-life of 238 U, A. 2 is the half-life of 235 U, T = 3.70 x 10 9 y, and t = the age of the mineral (see Faure, 1986 for a detailed overview). 6.6 Pb-Pb Results The single zircon Pb-evaporation technique, as described by Kober (1986, 1987) and Ansdell and Kyser (1990), gives a Pb-Pb age of 1855 ± 8 Ma for the Island Lake Intrusive (Hrdy et al., 1991). A model Pb-Pb age of 1810 Ma was calculated for the galena and sphalerite assuming a Stacey-Kramers two-stage growth-curve

72 61 10~----~,o ,L ~, ,~ ~,s~----~ 206 Pb/ 204 Pb Figure 21. Variations in the Pb isotopic composition of the crust us1ng a two-stage Pb evolution model of Stacey and Kramers (1975). In this model Pb evolves from primordial isotope ratios between and Ga in a reservoir with 238 U/ 204 Pb = At point Q (t = 3.70Ga) on the evolution line, the 238 U/ 204 Pb ratio of the reservoir was changed by geochemical differentiation to Lead evolution then continued undisturbed to point P representing the average composition of modern crustal Pb. Straight lines connecting any point on the evolution line between 3.70 Ga and the present to Q are isochrons. The slopes of such isochrons are related to the time elapsed since a Pb sample was isolated from the reservoir (from Faure, 1986).

73 r-----r---, , ~ GALENA 15.8 II SPHALERITE Pb 204Pb Age=1810Ma Figure 22. Plot of Pb-Pb data derived from vein galena and sphalerite paragenetically associated with gold. Data from table 5.

74 Table 5: Pb-Pb data from vein galena and sphalerite Sample Mineral 206Pb/204Pb Error % 207Pb/204Pb Error % H.G.#1 Galena H.G.#2 Galena H.G.#1. Sphalerite m w

75 64 (Figure 22). The 207 Pb/ 206 Pb ratios of sphalerite and galena are indicative of the source of the lead or a mixture of lead derived from the source and lead from the surrounding rocks, especially under conditions of low water/rock ratios. Accordingly, 1810 Ma represents the maximum age of mineralization. 5. RESULTS AND DISCUSSION Gold mineralization at the Jasper mine 1s hosted in quartz veins, and occurs as steeply plunging ore-chutes, averaging 2-3 metre widths within the mylonitic portions of a northeast-trending shear structure that cross-cuts the granitic portion of a zoned pluton. Gold occurs 1n late brittle fractures in quartz, as micrometre particles between quartz subgrains, and as silver-gold tellurides occupying microfractures within vein-incorporated host rock. Gold which is not fracture-hosted always occurs as individual grains and grain-trails within subgrained quartz (Figure Sc). Quartz subgrains are a late feature of the shear zones and are indicative of ductile deformation. Therefore the petrography of gold indicates that it is associated with both ductile and brittle features. This can be explained by a process wherein gold was precipitated in fractures developed during brittle events, with concomitant deformation and even obliteration of these fractures during the ductile periods, when quartz was forming subgrains. This process would associate gold deposited in fractures with subgrain development and would eliminate a direct relation between gold and unrecrystallized quartz in most areas, as is observed. In addition,

76 the quartz subgrains have values near 13 per mil, which is 2-3 per mil enriched in 18 0 relative to barren quartz peripheral to 65 areas of the mylonite which lack subgrain development. This indicates that the fluid that equilibrated with the subgrained quartz differed in temperature or source relative to the fluid that was in equilibrium with the barren quartz. Petrographic and microthermometric characteristics of fluid inclusions in subgrain quartz indicate the mineralizing fluid was variably enriched in C0 2, probably as a result of C0 2 -H 2 0 immiscibility, had a complex gas and cation composition, and was trapped at temperatures between 300 C and 375 C. The characteristics of this fluid differ from the paragenetically earlier fluid, which is represented by aqueous fluid inclusions along healed fracture planes in barren quartz. This earlier fluid had a uniform C0 2 content, has lower homogenization temperatures, lower methane contents, and is not paragenetically related to gold. The development of quartz subgrains can cause migration of fluid inclusions toward grain boundaries, creating variable phase ratios as a result of fluid inclusion decrepitation during recrystallization (Drury and Urai, 1989). However, the corresponding fluid temperatures of C calculated from stable isotopic fractionations between subgrain quartz and muscovite, and those of C obtained from microthermometric measurements of fluid inclusions in quartz subgrains, would suggest these inclusions represent the fluid that was present when gold was precipitated. Fracture-hosted gold, variable phase ratios in gold-

77 66 associated fluid inclusions, and the petrographic disequilibrium between pyrite and gold indicate that sulfidation was not a major gold-depositing mechanism, but rather that H 2 0-C0 2 phase immiscibility was the most likely mechanism by which the gold was precipitated. Much remains unknown about how gold is transported in hydrothermal environments, but one of the most likely gold complexing ligands in moderate-temperature hydrothermal solutions of 250 to 400 C is the bisulfide molecule (Seward, 1983). If H 2 S, H 2, and CH 4 are partitioned with C0 2 during H 2 0-C0 2 phase separation, as they are during boiling, an increase in ph and oxidation potential of the residual liquid would result (Seward, 1989). A ph rise would, in turn, decrease the activity of the reduced sulfur, and cause destabilization of the hydrosulfidogold complex (Seward, 1989), resulting 1n gold deposition. The salinity of the golddepositing fluid at Jasper averages 7wt% NaCl equivalent and is higher than that of 2wt% equivalent that typifies Archean lode-gold deposits (Kerrich, 1987), so that the fluid at Jasper may have contained higher concentrations of base metals being transported in the form of chloride complexes. The simultaneous precipitation of galena and sphalerite with gold may have further affected the stability of the hydrosulfidogold complex by decreasing the reduced sulfur concentration (Barnes, 1979; Seward, 1989), and enhanced gold precipitation. This mechanism could explain the localized spectacular gold enrichments of up to several hundred ounces of gold per ton of ore and corresponding increases of galena,

78 67 sphalerite, and chalcopyrite encountered at the Jasper mine. It is not always possible to discriminate between magmatic and metamorphic fluids based solely on the hydrogen and oxygen data (e.g. Kerrich, 1989), and extraneous fluids, such as formation brines or meteoric waters, can evolve isotopically to various isotopic compositions by interaction with typical crustal rocks at low water/rock ratios (e.g. Field and Fifarek, 1975; Kyser, 1987). Accordingly, several lines of evidence must be used to limit or exclude the possible fluid sources involved in the genesis of ore deposits. The involvement of fluids exsolved from magmas in the formation of the Jasper lode-gold deposits (i.e. magmatic waters) can be discounted because all of the observed intrusive rocks in the region predate gold mineralization by at least 100 Ma and the properties of the auriferous fluid are dissimilar to those of magmatic fluids. Hydrothermal meteoric waters are unlikely because fluid inclusions indicate a moderately high C0 2 content for the auriferous fluid and the existence of a mechanism by which meteoric fluids are raised to lithostatic pressures (Kerrich, 1989) is questionable. The values of galena, sphalerite, chalcopyrite, and pyrite fall within a restricted range of 2 to 6 per mil, which is typical of sulfides in igneous and metamorphic rocks, but atypical of sulfur in most formational brines (Ohmoto and Rye, 1979). In addition, the relatively low salinity estimates from microthermometric analysis of fluid inclusions indicate that the auriferous fluid could not represent evolved formation brines, that characteristically are wt% NaCl equivalent (Roedder, 1984).

79 68 The initial strontium isotope composition of the surrounding volcanic rocks ( ; Harper et al., 1986) is similar to the initial 87 Sr/ 86 Sr ratios obtained from the muscovite-tourmaline ( ) mineral isochron (Figure 12b), given that 100 million years had passed prior to the influx of the auriferous fluid. This indicates either a source which had a similar strontium isotopic composition to the surrounding Proterozoic country rocks or that the strontium was derived by interactions between the fluid and the Proterozoic country rocks under conditions of low water/rock ratios. The observations and data from the Jasper lode-gold deposit are consistent with a model wherein barren quartz veins were emplaced prior to 1780 Ma, during the late stages of regional tectonic accretion. This is close to the termination of regional metamorphism and deformation in this portion of the Trans-Hudson orogen and coincident with emplacement of relatively undeformed pegrnatites in the La Range and Glennie Lake Domains (Sun et al., 1991). Gold mineralization occurred at 1720 Ma, about 100 Ma after the peak of regional metamorphism and regional tectonic accretion, and was associated with hydrothermal fluids which had low salinities, high C0 2 contents, and were not pervasive but only permeated some areas that had developed in the earlier fracture systems. The composition of this late hydrothermal fluid was influenced by the Proterozoic rocks in the area, which may have been the source of the gold. Gold was deposited during brittle episodes (fracturing) which enhanced permeability and caused H 2 0-C0 2

80 69 phase immiscibility in a system that was fluctuating between a brittle and ductile regime. This paragenetically late and localized hydrothermal event would explain why there are so many barren, shear-hosted, quartz veins and only local gold mineralization. The Star Lake lode-gold deposit (Ibrahim and Kyser, 1991) is a shear zone-hosted auriferous quartz vein system and occurs approximately 4km north of Jasper. However, gold at Star Lake was deposited at about 1740 Ma by a fluid which experienced H 2 0-C0 2 phase immiscibility at soooc (Ibrahim and Kyser, 1991). This is earlier and at a higher temperature than the gold-depositing event at Jasper and indicates that there was more than one period of gold deposition within this region.

81 70 References Ansdell, K.M., and Kyser, T.K., 1992, Mesothermal gold mineralization in a Proterozoic greenstone belt: Western Flin Flon Domain, Saskatchewan, Canada. Econ. Geol. v. 87, p Ansdell K.M., and Kyser, T.K., 1990, Age of granitoids from the Flin Flon Domain: An application of the single-zircon Phevaporation technique, Saskatchewan Geol. Surv., Misc. Rept. 90-4, p Barnes, H.L., 1979, Solubilities of ore minerals: in Barnes, H.L., ed., Geochemistry of hydrothermal ore deposits: New York, Wiley Intersci., p Bickford, M.E., Van Schmus, W.R., Collerson, K.D., and Macdonald, R., 1987, U-Pb zircon geochronology project: new results and interpretations: Saskatchewan Geol. Surv., Misc. Rept. 87-4, p Bigeleisen, J., Pearlman, M.L., and Prosser, H.C., 1952, Conversion of hydrogenic materials to hydrogen for isotope analysis: Anal. Chemistry, v. 24, p Bodnar, R.J., 1983, A method of calculating fluid-inclusion volumes based on vapour bubble diameters and P-V-T-X properties of inclusion fluids. Econ. Geol. v. 78, p Bohlke, J.K., and Kistler, R.W., 1986, Rb-Sr, K-Ar, and stable isotope evidence for the ages and sources of fluid components of gold-bearing quartz veins in the northern Sierra Nevada foothills metamorphic belt, California: Econ. Geol., v. 81, p Bottinga, Y., and Javoy, M., 1975, Oxygen isotope partitioning among the minerals in igneous and metamorphic rocks: Rev. Geophys. Space Phys. 13, p Bozzo, A.T., Chen, J.R. and Barduhn, A.J. 1973, The properties of hydrates of chlorine and carbon dioxide. in Fourth International Symposium on Fresh Water from the Sea, A. Delyannis and E. Delyannis, eds., 3, Clayton, R.N., and Mayeda, T.K., 1963, The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analysis: Geochim. et Cosmochim. Acta, v. 27, p Clayton, R.N., 0 Neil, J. R., and Mayeda, T. K., 1972, Oxygen isotope exchange between quartz and water: Journal of Geophy. Res., v. 77, p

82 Col vine, A.C., 1989, An empirical model for the formation of Archean gold deposits: Products of final cratonization of the Superior province, Canada: ECON. GEOL. MON. 6, p Coombe, W., Lewry, J.F., and Macdonald, R., 1986, Regional geological setting of gold in the La Ronge domain, northern Saskatchewan: Canadian Inst. Mining Metallurgy Spec. v. 38, p Czmanske, G.K. and Rye, R.O., 1974, Experimentally determined sulfur isotope fractionations between sphalerite and galena in the temperature range 600 C to 270 C: ECON. GEOL., v. 69, p Date, A.R. and Gray, A.L., 1989, Applications of inductively coupled plasma mass spectrometry: Chapman and Hall, New York, Drury, M.R., and Urai, J.L., 1989, Deformation-related recrystallization processes: Techtonophysics, v. 172, p Eslinger, E.V., Savin, S.M., and Yeh, H., 1979, Oxygen isotope geothermometry of diagenetically altered shales: SIPM Special Pub. No. 26, March, 1979, p Faure, G., 1986, Principles of Isotope Geology: John Wiley and Sons. Fedorowich, J., Stauffer, M., and Kerrich, R., 1991, Structural setting and fluid characteristics of the Proterozoic Tartan Lake gold deposit, Trans-Hudson Orogen, Northern Manitoba: ECON. GEOL. v. 86, p Field, C.W., and Fifarek, R.H., 1975, Light stable-isotope systematics in the epithermal environment, in Berger, B. R. and Bethke, P.M., Geology and Geochemistry of Epithermal Systems, Reviews in ECON. GEOL., v. 2, p Foland, K.A., Linden, J.S., Laskowski, T.E., and Grant, N.K., 1984, 40 Ar/ 39 Ar dating of glauconite: Measured 39 Ar recoil loss from wellcrystallized specimens: Chern. Geol. (Isot. Geoscience), v. 2, p Goldfarb, R.J., Leach, D.L., Pickthorn, W.J., and Paterson, C.J., 1988, Origin of lode-gold deposits of the Juneau gold belt, southeastern Alaska: Geology, v. 16, p Gordon, T.M., Hunt, P.A., Bailes, A.H., and Symem, E.C., 1990, U-Pb ages from the Flin Flon and Kisseynew belts, Manitoba: chronology of crust formation at an Early Proterozoic accretionary margin: The Trans-Hudson orogen: Extent, subdivision, and problems: Geol. Assoc. Canada, Spec. Paper 37, p Harper, C., Thomas, D., and Watters, B., 1986, Geology and 71

83 petrochemistry of the Star-Waddy Lake area, Saskatchewan: Canadian Inst. Mining Metallurgy spec. v. 38, p Hoffman, P.F., 1988, United plates of America, the birth of a craton: Early Proterozoic assembly and growth of Laurentia, Annual Review of Earth Planet. Sci., v. 16, p Hrdy, F., Kyser, T.K., and Kusrnirski, R.T., 1991, Mineral paragenesis, fluid characteristics and radiogenic isotopic data from the Proterozoic Jasper gold zone, La Ronge Domain: Saskatchewan Geol. Survey Misc. Rept. 91-4, p Ibrahim, M.S. and Kyser, T.K., 1991, Fluid inclusion and isotope systematics of the high-temperature Proterozoic Star lake gold deposit, northern Saskatchewan, Canada: ECON. GEOL., v. 86, p Ibrahim, M.S. 1990, History of the Fluids Associated with the Proterozoic Star Lake Lode-Gold Deposit, Northern Saskatchewan, Canada, M. Sc. thesis, Geol. Sciences Department, University of Saskatchewan. Janser, B.W. 1992, The Geology, Geochemistry, and Gold Metallogeny of the Star Lake Area, Northern Saskatchewan. Unpublished M.Sc. thesis, Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. Jenner, G.A., Longerich, H.P., Jackson, S.E., and Fryer, B.J., 1990, ICP-MS--A powerful tool for high precision trace-element analysis in earth sciences: Evidence from analysis of selected U.S.G.S. reference samples. Chern. Geol, 83, p Kerrich, R., 1989, Geochemical evidence on the source of fluids and solutes for shear zone hosted rnesotherrnal gold deposits: Geol. Assoc. Canada, short course, v. 6, p Kerrich, R., 1987, The stable geochemistry of Au-Ag vein deposits in metamorphic rocks, Kyser, T.K., ed., Mineralogical Assoc. of Canada, short course in Stable Isotope Geochern. of low temp. fluids, v. 13, p Kerrich, R. and Allison, I., 1978, Vein geometry and hydrostatics during Yellowknife mineralization. Can. J. Earth Sci. 15, p King, R.W., and Kerrich, R., 1989, Strontium isotope compositions of tourmaline from lode gold deposits of the Archean Abitibi Greenstone Belt (Ontario-Quebec, Canada): Implications for source reservoirs: Chemical geology (Isotope Geoscience Section), v. 79, p Kober, B. I 1986, Whole-grain evaporation for 207 Pb/ 206 Pb-age 72

84 investigations on single zircons using a double-filament thermal ion source: Contrib. Mineral. Petrol., v. 93, p , 1987, Single-grain evaporation combined with Pb+ emitter bedding for 207 Pb/ 206 Pb-age-investigations using thermal ion mass spectrometry, and implications to zirconology: Contrib. Mineral. Perol., v. 96, p Kontak, D.J., Smith, P.K., Kerrich, R., and Williams, P.F., 1990, Integrated model for Meguma Group lode gold deposits, Nova Scotia, Canada: Geology, v. 18, p Kotzer, T.G., Kyser, T.K., King, R.W., and Kerrich, R., 1993, An empirical oxygen and hydrogen isotope geothermometer for quartztourmaline and tourmaline-water: Geochim. Cosmochim. in press. Kyser, T.K., 1987, Equilibrium fractionation factors for stable isotopes, Min. Assoc. Canada, short course, v. 13, p Kusmirski, R.T., 1991, An overview of Intrusive Hosted Gold Deposits in the Southern La Ronge Domain, Saskatchewan. The Geological Society of CIM First Annual Field Conference, Saskatoon, Saskatchewan, September 5-13, 1991, Program and Abstracts, Paper no. 3, p Kyser, T.K., Janser, B.W., Wilson, M.R., and Gattie, I., 1986, Stable isotope geochemistry related to gold mineralization and exploration in the western shield: Canadian Institute Mining Metallurgy, spec. v. 38, p Kyser, T.K., and o Neil, J.R., 1984, Hydrogen isotope systematics of submarine basalts: Geochim. et Cosmochim. Acta, v. 48, p Lewry, J.F., and Collerson, K.D., 1990, The Trans-Hudson orogen: Extent, subdivision, and problems: Geol. Assoc. Canada, Spec. Paper 37, p Lewry, F. F., Macdonald, R., Livesey, C., Meyer, M., Van Schrnus, R., and Bickford, M.E., 1987, U-Pb geochronology of accreted terrains: Geol. Soc. Spec. Pub. 33, p Lewry, J. F., 1983, Character and structural relations of the.. McLennan Group.. meta-arkoses, McLennan-Jaysmi th area: Saskatchewan Geol. Survey, Misc. Rept., 83-84, p McDougall, I., and Harrison, T.M. 1988, Geochronology and thermochronology by the 40Ar/39Ar method, Oxford University Press, New York, Murphy, W.L., 1986, Geology and exploration history of the gold

85 74 mineralization in the Star Lake area, ( ed.), Gold in the Western Shield, Metallurgy spec. vol. 38, p Saskatchewan, Clark, L.A. Canadian Institute Mining Nelson, K.K., Baird, D.J., Walters, J.J., Hauck, M., Brown, L.D., Oliver, J.E., Ahern, H.L., Hajnal, Z., Jones, A.G., and Sloss, L.L., 1993, Trans-Hudson orogen and Williston basin in Montana and North Dakota: New COCORP deep-profiling results, v. 21, no. 5, p. 447~450. Ohrnoto, H., and Rye, R.O., 1979, Isotopes of sulfur and carbon, in Barnes, H.L. ed., Geochemistry of Hydrothermal Ore Deposits: New York, Wiley Intersci., p Potter, R.W., II, Clynne, M.A., and Brown, D.L., 1978, Freezing point depression of aqueous sodium chloride solutions, Econ. Geol., v.73, p Pearce, J.A., Harris, N.B.W., and Tindle, A.G., 1984, Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Jour. of Pet., v.25, part 4, p Potts, P.J., 1987, A handbook of silicate rock analysis, Blackie & Sons Ltd., Rafter, T. A., 1965, Recent sulfur isotope measurements on a variety of specimens examined in New Zealand: Bull. Volcanol., v. 28, p Roberts, R.G., 1990, Structural controls on gold deposits in the Star lake and Island lake plutons: Saskatchewan Geol. Survey Misc. Rept., 90-4, p Roedder, E., 1984, Fluid Inclusions: Rev. Mineralogy, v. 12. Seward, T.M., 1989, The hydrothermal chemistry of gold and its implications for ore formation: Boiling and conductive cooling as examples, ECON. GEOL. MON. 6, p , The transport and deposition of gold in hydrothermal systems: in Foster, R.P., ed., Gold 82: Rotterdam, A.A. Balkema Pub., p Shephard, T., Rankin, A.H., and Alderton, D.H.M., 1985, A Practical Guide to Fluid Inclusion Studies: Blackie and Sons Ltd., Glasgow. Stacey, J.S. and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planet. Sci. Letters, 26, Stauffer, M.R., central Canada, 1984, its Manikewan: An early Proterozoic igneous history an orogenic ocean in closure:

86 75 Precambrian Research, v. 25, p Sun, M., Stauffer, M.R., Lewry, J.R., Edwards, G., Kerrich, R., and Kyser, T.K., 1991, Chemical signatures of igneous and metasedimentary rocks from the Pelican Slide area: Saskatchewan Geol. Survey, Misc., Rept., 91-4, p Suzuoki, T., and Epstein, S., 1976, Hydrogen isotope fractionation between OR-bearing minerals and water: Geochim. et Cosmochim. Acta., v. 50, p Taylor, H.P. Jr., 1974, The application of oxygen and hydrogen isotope studies to problems of hydrothermal alteration and ore deposition. ECON. GEOL. v. 69, p Thomas, D.J. 1984, Geological mapping, Star lake area (part of NTS 73P-16 and74a-1): SaskatchewanGeol. Survey, Misc. Rept., 84-4, p Thorn, A., Arndt, N. T., Chauvel, C., and Stauffer, M.R., 1990, Flin Flon and west La Ronge belts, Saskatchewan: products of Proterozoic subduction-related volcanism: Geol. Assoc. of Canada, Spec. Paper 37, p Van Schmus, W.R., Bickford, M.E., Lewry, J.F., and Macdonald, R., 1987, U-Pb geochronology in the Trans-Hudson orogen, northern Saskatchewan Canada: Canadian Jour. of Earth Sci, v. 24, p

87 APPENDIX 1 SAMPLING AND ANALYTICAL METHODS A 1.1 Field Sampling Fieldwork was carried out over a total of four weeks within the 1989 and 1990 summer field seasons, and 53 locations were sampled (10 auriferous quartz vein locations, 6 barren quartz vein locations, 8 wallrock locations, 6 pluton locations, and 23 drillhole samples) (Figure 3). Complete and unfragmented widths of quartz veins from surface exposures were obtained with the aid of a diamond rocksaw. Underground exposures allowed sampling of ore which hosted large amounts of visible gold. However, limited access to underground locations and time constraints imposed by mining activities restricted this type of sampling. Drill-core samples of wallrocks were collected to test the extent of wallrock alteration away from the mineralized veins and hole 62 (Figure 3) was chosen because it provided a representative transect through the hangingwall, footwall, and auriferous vein. Drill-core samples were obtained every 2 metres (corrected for horizontal distance) within 20 metres of the auriferous veins, and at 10 metre intervals beyond that, to the limits of the hole. Care was taken to select samples which were not in proximity to any quartz veins, dikes, etc. A 1.2 Petrographic Preparation Petrographic thin sections were cut from every hostrock and countryrock sample, and polished thin sections were cut from each quartz vein sample before any analytical work was done. The thin sections and polished sections were prepared I in house I using standard cutting and polishing techniques as described by (Potts, 1987). Multi and individual grain mounts comprised of zircons, galena, sphalerite, muscovite, tourmaline, and gold were separated, embedded in epoxy resin and polished for detailed SEM and microprobe work. A 1.3 Sample Selection and Wafer Preparation A preliminary petrographic study of fluid inclusions was done on polished thin sections from quartz veins to identify samples hosting inclusions suitable for microthermometric analysis. Once suitable samples were identified doubly polished quartz wafers averaging a 70-to-150~ thickness were made. Samples cut thicker than 150~ were too cloudy, and samples cut thinner than 70~ lacked a third-dimension perspective. Gold was included in mineralized vein samples so that it could be related to a specific generation, or generations, of fluid inclusions. To make doubly-polished quartz fluid inclusion wafers the samples were first cut into thin section-sized chips and ground to a 3-Smm thickness. One side of the quartz chip was then glued to a glass slide which provided a firm, flat, stable surface. The free side was then ground and polished with standard grinding and polishing equipment. The sample was then immersed in acetone to free the quartz from the glass slide. The polished side was glued to a glass plate, ground to the appropriate thickness, polished and removed from the glass slide. 76

88 The prepared quartz wafers were then scanned under a petrographic microscope for fluid inclusions appropriate for measurement. Once such inclusions were located, the areas were marked and broken into 4-to-8rnrn sized chips, so that the samples could fit into the sample chamber of the heating-cooling stage. A 1.4 Microther.mometric Analysis Microthermometric data were obtained using a Fluid Inc. adapted U.S. Geological Survey-type gas-flow freezing-heating stage which was determined to have an error of ± 0.1 C at low temperatures, ± 0.4 C at high temperatures, and± 1.0 C maximum for other measurements. When possible, microthermometric measurements were obtained from fluid inclusions on: (1) the final melting temperature of the C0 2 (TrnC0 2 ), from which the C0 2 purity can be determined; (2) the initial melting temperature of ice (Te), from which an estimation of the type of salt present can be made; (3) the temperature of final ice melting (Trnice), from which fluid salinities are estimated; (4) the temperature at which the clathrate disappears ( Trnc 1 ath) ; also a measure of the salinity; ( 5) the temperature of bulk homogenization of the inclusion (Th), from which the minimum fluid trapping temperature is derived. All thermometric data were collected on inclusions that showed no petrographic evidence of necking. Thermometric data for vapour-rich inclusions could not be collected because the small size of the inclusions (average <2,u.m) prohibited measurements of phase changes. A 1.5 Sample Selection (For Isotopic Study) Each sample was evaluated petrographically before any mineral separates were made to insure that the minerals used for isotopic study were well constrained in terms of their vein paragenesis. Mineral separates were obtained by crushing and water-sieving handsized samples of vein, wallrock, and pluton through appropriate sieve-sizes, as indicated by petrography. If the mineral grain size was large enough, they were hand-picked. This technique was generally sufficient for quartz separates from both quartz veins and wallrock samples, and for biotite from wallrock samples. Sampling of subgrained quartz required viewing under a binocular microscope to obtain as pure a sample as possible. However, pure subgrained samples could not be obtained. Tourmaline separation required the use of heavy liquids, to concentrate the tourmaline, a Frantz electromagnetic separator, to separate the tourmaline from the other heavy minerals, namely pyrite, and hand picking under a binocular microscope, to purify the tourmaline mineral separate. Muscovite is very fine grained (10-SO,u.m) and required the use of a shaker table to separated it. The fraction containing muscovite was then run through a Frantz electromagnetic separator to remove residual quartz. Hand separation through a binocular microscope was employed to purify the mineral separate. Galena, sphalerite, and pyrite were drilled out from hand samples with a dental drill. This technique proved to be the 77

89 cleanest and most efficient way of separating the sulfide minerals but could not be applied to the silicates due to their small size. A 1.6 Stable Isotope Analysis Oxygen was obtained from silicates using the BrF 5 extraction method of Clayton and Mayeda (1963). Hydrogen was extracted using the uranium technique of Bigeleisen et al., (1952) as modified by Kyser and o Neil (1984), and sulfur was liberated by oxidizing sulphide minerals with CuO (Rafter, 1965). Isotopic data are reported as 8-values in units of per mil relative to a standard. Both oxygen and hydrogen isotope values are reported relative to Standard Mean Ocean Water (VSMOW), and sulfur isotopes to the Canyon Diablo troilite (CDT). Isotopic ratio measurements were made with a Finnigan-Mat 251 and a VG 602C isotope ratio mass spectrometers. Reproducibilities (2 sigma) of 8 values in per mil are± 0.2 for oxygen, ± 3 for hydrogen, and± 0.3 for sulfur. Mineralization temperatures were calculated from paragenetically related quartz-muscovite, quartz-tourmaline, and galenasphalerite mineral pairs using the fractionation factors of Eslinger et al., (1979), Katzer et al., (1993), and Czamanske and Rye, (1974), respectively. The oxygen and hydrogen isotopic composition of the auriferous fluid was calculated using the quartz-h20 fractionation factor of Clayton et al., (1972), for oxygen, and the muscovite-h20 fractionation factor of Suzuoki and Epstein, (1976), for hydrogen. A 1.7 Radiogenic Isotope Analysis Muscovite-tourmaline, and galena-sphalerite vein mineral separates were prepared for Rb-Sr, and Pb-Pb, respectively, isotope measurement through standard dissolution procedures in teflon vials and Rb, Sr, and Pb were separated by conventional cation-exchange techniques (Potts, 1987). Ratio analyses were performed on a Finnigan MAT 261 solid source mass spectrometer for muscovite, galena, and sphalerite, and the 87 Rb/ 86 Sr ratio for tourmaline was determined on a Perkin Elmer Sciex Elan 5000 ICP-MS, with the mass spectrometer optimized and calibrated on Rb and Sr, sample analysis performed in isotopic ratio mode at high resolution, and using blanks (0.2N HN0 3 acid) and standards (NBS987 for Sr, NBS984 for Rb) to correct for background levels of Rb and Sr and instrumental drift, respectively. Ar-Ar isotopic analyses were kindly performed by K. Foland at Ohio State University on muscovites from auriferous vein mineral separates using irradiation, extraction, mass spectroscopic and correction procedures described by Foland et al., (1984). A 1.8 Elemental Analysis Microprobe analyses were determined by wavelength-dispersive electron microscopy using a fully automated JEOL JXA-8600 X-ray microanalyzer. The accelerating voltage was set to 15Kv for silicates and 20Kv for sulfides and gold. The data were corrected and reduced using ZAF and Phi-Rho-Z correction programs provided by Noram Instruments, for silicates and sulfides, respectively. Major element oxide wt% are generally precise to ± 1% of the total, and 78