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Galena lead isotope study of mineral deposits in the Eagle Bay Formation, southeastern British Columbia Goutier, Françoise Mélanie 1986

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GALENA LEAD ISOTOPE STUDY OF MINERAL DEPOSITS IN THE EAGLE BAY FORMATION, SOUTHEASTERN BRITISH COLUMBIA by FRANCOISE MELANIE GOUTIER B.Sc UNIVERSITE DE MONTREAL, 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA OCTOBER, 1986 @ Francoise Melanie Goutier, 1986 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. 1 further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6(3/81) ABSTRACT The Eagle Bay Formation in the Adams Plateau-Clearwater area, 35km northeast of Kamloops, hosts several economic and sub-economic mineralized occurrences. The age and genesis of these mineral deposits can be estimated by using a specific growth curve which depicts the lead evolution for the Eagle Bay Formation. This curve, named the remodeled curve, represents a local deviation from the average 'shale' curve of Godwin and Sinclair (1982) for the autochthonous part of the Canadian Cordillera. This remodeled curve is specifically applicable to the Adams Plateau-Clearwater area. The lead isotope data from the deposits of the Eagle Bay Formation plot in three distinct clusters along the curve indicating that the lead isotopic signature of the Eagle Bay Formation is upper crustal, and that three periods of mineralization can be recognized or 'fingerprinted'. Accordingly, mineralization oogenetic with Devonian volcanism, and veins related to Cretaceous magmatism can be distinguished by location of galena-lead isotope values within clusters 1 or 3 respectively. Cluster 2 reflects a Late Triassic pulse of mineralization and includes epigenetic veins and stratiform deposits. These deposits are either replacement or oogenetic with their host. The Triassic model age for mineralization that is apparently stratiform and oogenetic raises questions about the currently assigned Cambrian age of associated host rock. To accommodate the lead isotope data a new Upper Triassic unit (T-EBG) within the Eagle Bay Formation is defined. The distinctive lead isotopic signature between deposits hosted by the Eagle Bay Formation is valuable as a guide for future mineral exploration programs in the Adams Plateau-Clearwater area. Recognition of lead isotopic fields that fingerprint types of mineral deposits, provides a useful and practical framework for the classification and evaluation of new mineralized prospects in the area. iii Table of Contents ABSTRACT ii LIST OF TABLES viLIST OF FIGURES viiACKNOWLEDGMENTS ix 1. GENERAL INTRODUCTION 1 2. GENERAL GEOLOGY OF THE ADAMS PLATEAU-CLEARWATER AREA 4 2.1 INTRODUCTION2.2 STRATIGRAPHY 9 2.3 INTRUSIONS 13 2.3.1 DEVONIAN INTRUSIONS . 13 2.3.2 CRETACEOUS INTRUSIONS 14 2.3.3 LAMPROPHYRE DYKES 17 2.4 STRUCTURE 12.4.1 PRE-JURASSIC STRUCTURES 18 2.4.2 JURASSIC STRUCTURES 12.4.3 CRETACEOUS STRUCTURES 9 2.4.4 TERTIARY STRUCTURES 20 3. LEAD ISOTOPE SYSTEMATICS 22 3.1 HISTORY OF LEAD ISOTOPE INTERPRETATION 22 3.2 BASIC PRINCIPLES AND EQUATIONS 26 3.3 ANALYTICAL PROCEDURES 31 iv 3.3.1 SAMPLE DESCRIPTION 31 3.3.2 ANALYTICAL PRECISION3.3.3 CALCULATION OF AVERAGE VALUES FOR THE DEPOSITS 34 3.4 THE REMODELED CURVE FOR THE EAGLE BAY FORMATION 39 3.4.1 DEPARTURE TIME, INITIAL COMPOSITION AND U VALUE 47 3.4.2 W VALUE 51 3.4.3 SUMMARY 2 3.5 MODEL AGE DETERMINATION 53 4. LEAD ISOTOPES, MINERAL DEPOSITS AND STRATIGRAPHY .- 55 4.1 INTRODUCTION 54.2 CLUSTER 1: DEVONIAN COGENETIC DEPOSITS 58 4.3 LEAD DATA BETWEEN CLUSTER 1 & 2 63 4.4 CLUSTER 2: TRIASSIC STRATIFORM AND VEIN DEPOSITS 64 4.4.1 DEPOSITS GEOLOGY 64.4.2 MULTIPLE INTERPRETATION OF LEAD DATA 70 4.4.3 SUMMARY 84.5 LEAD DATA BETWEEN CLUSTER 2 & 3 80 4.6 CLUSTER 3: CRETACEOUS VEINS 83 v 4.7 LEAD DATA BEYOND CLUSTER 3 87 4.8 SUMMARY 88 5. CONCLUSIONS 90 REFERENCES CITED 93 APPENDIX A 10APPENDIX B 147 APPENDIX C 9 vi LIST OF TABLES TABLE 3.0 Equations used in lead isotopic model calculation 28 TABLE 3.1 Statistics related to the calculation of mass fractionation factors using Broken Hill Standard (BHS:UBC1) 33 TABLE 3.2 Representative calculation of average galena lead isotopic values for a given deposit 35 TABLE 3.3 Average galena lead isotope values for ore deposits in the Eagle Bay Formation 37 TABLE 3.4 Lead isotope values for the remodeled shale curve 48 TABLE 4.0 Classification and name of deposits within discrete clusters of data defined in Figures 3.3 to 3.5 56 TABLE A.l Mineral deposits in the Adams Plateau area described in appendix A 104 vi i LIST OF FIGURES FIGURE 1.0 Generalized tectonic map of the Canadian Cordillera 2 FIGURE 2.0 Regional geologic map of the Adams Plateau-Clearwater area 5 FIGURE 2.1 Geology of the Eagle Bay Formation showing major rock units and faults 10 FIGURE 3.0 Model evolution of lead with time. A: Diagram 207pb/204pD vs. 206pb/204pb B: Diagram 208pb/204pb vs. 206pb/204pb 23 FIGURE 3.1 Schematic evolution of the lead in galena from the Eagle Bay Formation 9 FIGURE 3.2 207pb/204pb vs. 206pb/204pb diagram showing the isotopic distribution of all analyses from the Birk Creek area 36 FIGURE 3.3 207pb/204pb vs. 206pb/204pb diagram for deposits hosted by the Eagle Bay Formation using data from Table 3.3 41 FIGURE 3.4 208pb/204pb vs. 206pb/204pb diagram for deposits hosted by the Eagle Bay Formation using data from Table 3.3 3 FIGURE 3.5 206pb/208pb vs. 206pb/207pb diagram for deposits hosted by the Eagle Bay Formation using data from Table 3.3 45 FIGURE 4.0 Geology of the Eagle Bay Formation with location of the sampled mineral deposits 59 FIGURE 4.1 Folded mineralized layers, Lucky Coon deposit 67 FIGURE A.1 Map of the Homestake property 121 FIGURE A.2 Lower hemisphere equal area projection of structural elements, Homestake deposit area 123 FIGURE A.3 Vertical section (97+00) through the RG 8 sulphide barite lens, Rea Gold deposit 126 FIGURE A.4 Equal area projections onto lower hemisphere of structural elements Rea Gold deposit 128 FIGURE A.5 Detailed sections A-A1 and B-B' from the north side of Birk Creek area 131 vni ACKNOWLEDGEMENTS I acknowledge the British Columbia Ministry of Energy, Mines and Petroleum Resources for financial support of field work. Many from the Ministry were helpful. I am particularly grateful to Trygve Hoy, with whom it was a pleasure to work, for his encouragement and supportive attitude, and to Paul Schiarizza for ideas and critical discussions which influenced my thinking throughout this research. Sincere thanks are extended to my advisor Dr. C.I. Godwin for his direction, encouragement and supervision of my thesis, and to Dr. R.L. Armstrong for providing access to his Geochronological Laboratory at The University of British Columbia. I wish to thank all students, faculty and staff members in the department of Geological Sciences who contributed by their knowledge and friendship to the completion of this thesis. I also thank Alex Davidson and Ian Pirie of Corporation Falconbridge Copper and Glen Shevchenko of Noranda Exploration Co. Ltd. for their availability and for discussing some aspects of this project with me. The information and galena samples they provided are greatly appreciated. ix 1 1. GENERAL INTRODUCTION The Eagle Bay Formation is in the Adams Plateau-Clearwater area, centred 35km northeast of Kamloops in southeastern British Columbia (Fig. 1.0). The formation is a multiply-deformed sequence of low-grade meta-sediments and volcanic rocks stacked as imbricated slices on the southwestern flank of the Shuswap Metamorphic Complex. It hosts several economic and sub-economic lead-zinc-silver-gold occurrences of various types and affinities that were intermitently in production during the first half of the century. Recent discovery of the polymetallic Rea Gold deposit, a gold-arsenopyrite-rich volcanogenic Kuroko type deposit near Johnson Lake, regenerated interest in the area by providing evidence of potentially significant economic mineralization. This thesis was initiated to assess whether galena lead isotope studies would aid interpretations of the nature and age of the different deposits occurring within the Eagle Bay Formation. It also was intended to provide a practical and useful framework for guiding exploration programs in the Adams Plateau-Clearwater area. Observations (and in some cases detailed mapping) were made on 37 mineralized occurrences which were sampled for this study (Appendix A). Field work was conducted over the summers of 1984 and 1985. Remains from past 2 Figure 1.0. Generalized tectonic map of the Canadian Cordillera showing the major structural divisions and location of the study area (after Wheeler and Gabriesle, 1972). 3 mining activities and logging roads in the area facilitated access to the visited properties. The first part of this study presents an overview of the geology of the Eagle Bay Formation and of adjacent areas. The second part outlines the basic principles which govern uses of the common lead method for model age determinations. A remodeled version of the 'shale' growth curve of Godwin and Sinclair (1982) is used to interpret the lead isotopic data from deposits hosted by the Eagle Bay Formation. The third part of this thesis interprets galena lead model ages of deposits defined by the remodeled curve. Implications of the clustering of the data into three distinct groups (Devonian, Triassic and mid-Cretaceous) are presented. The discrepancy between Triassic lead model age obtained for several stratiform deposits and their geological setting is discussed, and leads to the interpretation that if the mineralization is not of Triassic replacement type, but rather oogenetic with its host then the stratigraphy of the Eagle Bay Formation should include a Triassic unit. The results are fundamental to geological understanding and to mineral exploration in the Adams Plateau-Clearwater area. 4 2. GENERAL GEOLOGY OF THE ADAMS PLATEAU-CLEARWATER AREA 2.1 INTRODUCTION Mineral deposits and occurrences in the Adams Plateau-Clearwater area are hosted by the Eagle Bay Formation, which is composed of a multiply deformed sequence of low-grade meta sediments and volcanic rocks. The Eagle Bay Formation lies within Kootenay Terrane (Monger, 1985) along the western flank of the Monashee Terrane in the Omineca Belt (Fig. 2.0). The Eagle Bay Formation ranges in age from Cambrian to Permian (Schiarizza and Preto, 1984). However, as defined in this thesis it contains rocks that may be as young as Upper Triassic. Much of the area adjacent to and east of the Eagle Bay Formation is called the Northwestern Shuswap Complex (Okulitch, 1984). This complex, along with the Monashee Complex (Read and Brown, 1981) and the Okanagan Plutonic and Metamorphic Complex, is part of the larger Shuswap Metamorphic Complex that currently is included in Monashee Terrane (Monger, 1985). The boundary between the Eagle Bay Formation and the Northwestern Shuswap Complex now is recognized to be a low angle detachment fault rather than a metamorphic or intrusive contact (Brock, 1934; Fyson, 1970). This fault, named the Eagle River fault in recent 5 Figure 2.0 Regional geologic map of the Adams Plateau-Clearwater area showing the location of the Eagle Bay Formation relative to other major formations and groups, majors intrusions, and regionaly important faults (modified: from Okulitch and Cameron, 1976; Journeay, 1986; Jung, 1986). 6 LEGEND Jurassic & Cretaceous I***;*) Granitic rocks Upper Triassic | NCL | Undiff. Nicola Group rocks Upper Triassic and older Eagle Bay Formation 1 FNL | Fennell Formation Undetermined age j Sicamous Formation Undiff. Paleozoic rocks Undiff. Paleoz. intrusives Und SYMBOLS High angle faults Eagle River Detachment Quesnel Lake thrust 0.7060 initial 87Sr/86Sr ratio, isotopic contour line 7 mapping (Journeay, 1986; Fig. 2.0), is interpreted as the break-away zone for the southern Okanagan detachment (Journeay, 1986) and therefore is part of the major extensional fault system related to the Eocene thermal event identified in south-central British Columbia (Ross, 1974; Journeay, 1986: Coney, 1980; Tempelman-Kluit, 1984; Bardoux, 1984; Parkinson, 1985; Parrish, 1985). The Eagle Bay Formation is bordered on the west by the Fennell Formation of the Slide Mountain Group (Campbell and Tipper, 1971). The Fennell Formation is composed of an oceanic assemblage of pillowed basalts, diorite and ribbon cherts (Uglow, 1922). These two formations are separated by an easterly directed thrust fault (Okulitch, 1979; Schiarizza and Preto, 1984). To the south the formation is inferred to be in fault contact with the Upper Triassic(?) Sicamous Formation (Okulitch, 1 984 ; Daughtry in Preto et a_l.,1985; see section 4.4.3). The formation is truncated to the north by the Raft batholith (Fig. 2.0). Monashee Terrane (Monger, 1986) is exposed in a series of domal metamorphic complexes. Each is characterized by a core of older metamorphic plutonic basement, which either crops out or is covered by polydeformed and regionally metamorphosed mixed sequences of sedimentary and volcanic rocks (Brown and Read, 8 1983; Coney, 1980). Rocks within the complexes range in age from possibly Archean to earliest Jurassic (Duncan, 1982; Okulitch, 1984). The Shuswap Metamorphic Complex is regarded as the core zone of the Columbian Orogeny which caused major defor mation in the Omineca Belt—and in the Eagle Bay Formation— during Jurassic time (Reesor and Moore, 1970; Okulitch, 1984). Unambiguous evidence for pre-Jurassic deformation in the belt is lacking, although some of the structures may have been generated in previous orogenies such as Kenoran, the Hudsonian, or the East Kootenay (Okulitch, 1979). Evidence of a major Eocene thermal and extensional event is widespread throughout the Intermontane and Omineca Belts. Parrish (1985) argues that the unroofing of metamorphic core complexes is primarily a result of Tertiary extensional tectonics, rather than of Mesozoic compression as suggested by Brown and Read (1983). Thus, the Eagle Bay and the Fennell Formations, as well as the Raft and the Baldy batholiths, would have been located above the Monashee Complex at the time of their formation and would have slid off the metamorphic complex approximately 50Ma ago. The Eagle River detachment fault zone (Journeay, 1986; Fig. 2.0), and numerous normal faults of Tertiary age and related Tertiary volcanic rocks (Schiarizza, 1985; Hickson, 1986) are also attributed to the Eocene thermal and deformational event. However problems arise when the 9 initial 87sr/86sr ratios of the Raft and the Baldy batholiths are taken into account. Values considerably higher than those present, ranging from 0.7083 to 0.7101, are to be expected from intrusions that pass through the Monashee Complex during their ascent. Therefore, Jung (1986) argues that the present position of the Raft and Baldy batholiths correspond to their original emplacement position, and that it is improbable that they ever were located over the Monashee Complex. This argument is also in agreement with the interpretation of Okulitch (1979) that the roots of the batholiths are in the Northwestern Shuswap Complex. 2.2 STRATIGRAPHY The Eagle Bay Formation was first mapped by Dawson (1898) as the Adams Lake and Nisconlith Series. Subsequently Daly (1915) divided the Adams Lake Series into three informal formations called the Adams Lake greenstone, the Tshinakin limestone, and the Bastion schists. Rice and Jones (1948) and Jones (1959) renamed many of the rocks previously included in the above series, and defined the Mount Ida Group within which the Eagle Bay Formation was the youngest conformable member. The Eagle Bay formation then included much of Dawson's Adams Lake Series and Daly's (1915) greenstone formation; it contained three members: a thick basal succession of chloritic schist, a mixed sedimentary sequence including the prominent Tshinakin 1 0 Devonian to Permian Fennell Formation 1 1 [bH Upper structural division: pillowed and massive meta-basalt, minor chert I IF I Lower structural division: pillowed and massive meta-basalt and ribbon chert, limestone, diorite, gabbro, quartzteldspar, porphyry, rhyolite Mississippian I E8P I Phyllite and slate with interbedded sandstone and grits Devonian and/or Mississippian I EBF | Feldspathic phyllite (intermediate to felsic tuft) Devonian | EB.A | Sericite-quartz-phyllite and schist (intermediate to felsic volcanics and volcanoclastics) Devonian and/or older | EBS j Mixed meta-sedimentary sequence (phyllites) | EBG [ Calcareous chlorite-schist. fragmental schist (matic to intermediate volcanics) ]j Tshinakin limestone ^--^ mixed phyllite (EBCp) f—*-j quartzite ( EBCq ) f | polymictic conglomerate (EBCcg) | | T-EBC ( ? Triassic ) Lower Cambrian and/or older I EBQ | Chlorite-muscovite quartzite. chlorite-muscovite-quartz schist and minor meta-sediments (SDQl I EBH | Quartzite, grit and chlorite-sericite-quartz schist Intrusives Jurassic & Cretaceous E;;:' ;l Raft batholith. Baldy batholith, Scotch Creek plug Late Devonian | Dgn I Granite and granodiorite orthogneiss '123 Fossil locality: Mississippian. Pennsylvanian, Permian f Cambrian rk, z. Rb Isotopic date: K/Ar, uranium-lead, Rb/Sr Faults Thrust fault (this study) ^M*' Thrust fault (Schlarlzza et al. 1984) Figure 2.1 Geology of the Eagle Bay Formation showing major rock units and faults (modified from Schiarizza and Preto, 1984). 1 2 Limestone, and an upper sequence of chloritic schist. Sub sequent work by Campbell and Tipper (1971), Okulitch (1979), Schiarizza and Preto (1984), Preto and Schiarizza (1985), and Schiarizza (1986, 1986b) refined the understanding of the stratigraphy of both the Eagle Bay Formation and the adjacent Fennell Formation. Recent work by Preto and Schiarizza (1985) indicates that the Eagle Bay Formation is exposed in four imbricated slices separated by southwesterly directed thrust faults (Fig. 2.1; Schiarizza and Preto, 1984; Schiarizza, 1986b). Stratigraphic ages and/or contact relationships established by Schiarizza and Preto (1984) have been modified to accommodate results obtained from the lead isotope investigation of mineral deposits occurring throughout the Eagle Bay Formation. Discussion of the lead isotopic composition from these deposits, and their implications on the interpretation of the stratigraphy of the Eagle Bay Formation are presented in Chapter 4. Eagle Bay Formation is directly correlative with other stratigraphic sequence occurring on the edge of the Shuswap Metamorphic Complex. Okulitch (1979) has correlated the Formation partly with the Cambrian to Ordovician Lardeau Group, and partly with the younger Milford Group of the Kootenay Arc. Struik (1986), based on lithologic, structural and age similarities, correlates the Eagle Bay Formation with both the Barkerville and the Kootenay Arc Terranes. Similarly, Ross and 1 3 Fillipone (in press) suggest that some parts of the Eagle Bay Formation, notably the basal quartzite and the prominent meta-volcanic carbonate succession, are directly correlated with similar rocks in the Snowshoe Group near Crooked Lake (100km east of Williams Lake). Struik (1986) proposed that all three successions were deposited in a similar geological setting. Accordingly, the Eagle Bay Formation is now included by Monger (1985) in the Kootenay Terrane under "variably metamorphosed Lower Paleozoic strata comprising pellite, quartzite, grits, basic acidic rocks and Devonian and (?) older intrusions." 2.3 INTRUSIONS The Eagle Bay Formation has been intruded repeatedly. Magmatism and/or volcanism affected the area in Devonian, Cretaceous and Eocene time. 2.3.1 Devonian Intrusions Meta-biotite granodiorite, correlated with the Mount Fowler orthogneiss (Fig. 2.1), intrudes Devonian volcanic rocks of the Eagle Bay Formation. Zircons from the batholith yielded upper and lower intercept dates on concordia diagrams of Devonian and of mid-Cretaceous ages ( 372+_6Ma and 92.5Ma: Okulitch, 1975). Similar bodies of intermediate to felsic composition, ranging in age from Late Devonian to mid-1 4 Mississippian (Mortensen et a_l. , in press), occur throughout the Snowshoe meta-sediments in the Barkerville Terrane. The presence of these intrusions in both the Eagle Bay Formation and the Snowshoe Group do not prove, but support correlations between these two successions in regionally distinct areas. An extrusive phase of similar composition (meta-rhyolite) found on the Beca property also yielded zircon dates of Devonian age, 399+^1 Ma, from the upper intercept on a concordia diagram (Preto and Schiarizza, 1985). The similarities in age and rock type between the Mt Fowler orthogneiss, the felsic intrusions, and some of the meta-volcanics (e.g. unit EBA, Fig. 2.1) suggest that they are oogenetic and of Devonian age. The occurrence of these volcanic and intrusive rocks of felsic affinities on the western margin of the Shuswap Complex and the presence of volcanogenic deposits within the Devonian volcanic units (Rea Gold and Homestake deposits, Appendix A), provides evidence for subduction related processes during the Devonian. 2.3.2 Cretaceous Intrusions The Raft and Baldy batholiths are elongated bodies that intrude the Eagle Bay Formation (Fig. 2.1). In several localities, both batholiths are surrounded by a structural and metamorphic hornfelsic aureole in which regional structures are rotated parallel to the westward trend of the intrusions 1 5 (Campbell and Tipper, 1971). Small intrusive bodies, such as the Scotch Creek and the Deep Creek plutons as well as quartz porphyry dykes or sills, occur throughout the area (Fig. 2.1). They are inferred to be cogenetic with the Cretaceous Baldy batholith. Both intrusions, are equigranular granodiorite to quartz monzonite and are similar chemically. They contain chloritized biotite as the only mafic mineral. Widespread minor concen trations of sulphide minerals within the intrusions include the galena-sphalerite rich quartz veins of the Leemac property (Appendix A), and several molybdenite occurrences in the Barriere Lake area reported in unpublished provincial open file reports available at the British Columbia Ministry of Energy, Mines and Petroleum Resources. Cretaceous Rb/Sr dates were obtained for the two batholiths by Jung (1986) with a five point whole rock and mineral separate isochron. A mid-Cretaceous date of 104Ma with an initial 87sr/86sr ratio of 0.7060 was obtained from a sample from the western part of the Raft batholith. A mid-Cretaceous date of 98.5+2.2Ma with initial 87sr/86sr ratio of 0.7054 was obtained for the Baldy batholith. These similar dates and initial ratios, plus the similarity in texture and composition 1 6 indicate that the two batholiths are probably oogenetic. Furthermore two K-Ar mid-Cretaceous dates of 99+5Ma and 82+6Ma were obtained by Wanless et a^L. ( 1966) for the Baldy batholith. Since the K-Ar dates are concordant with the Rb-Sr dates, the batholiths were probably not substantially affected by any later thermal events. However, incomplete new uranium-lead data on zircons from the Raft batholith indicates some uncertainty in its assigned mid-Cretaceous crystallization age (Jung, pers. comm., 1 986 ) . The initial 87sr/86sr ratios of about 0.7060 for the Raft and Baldy batholiths are higher than those below 0.7040 from batholiths located to the west in the Intermontane Belt. Values comparatively greater than 0.7060 are reported to the east in the Shuswap Metamorphic Complex (Jung, 1986). The initial strontium isotope ratio of 0.7060 passes through the Eagle Bay Formation as shown on Figure 2.0. This line probably represents a transition at depth corresponding to the western limit of Precambrian basement rocks (Armstrong, in Jung, 1986). The relatively high initial 87sr/86sr ratios for the Raft and Baldy batholiths emphasize a genetic link between the magma and the old crustal material from which these batholiths were derived. The high ratios apparently reflect the addition of radiogenic 87sr from magma generated in, or contaminated by, a Precambrian basement underlying the Eagle Bay Formation. The initial 1 7 strontium ratios are in general agreement with the lead isotopic signature of the deposits in the Eagle Bay Formation—both indicate the presence of upper crustal material beneath the formation. 2.3.3 Lamprophyre Dykes Lamprophyre dykes are widely distributed in the Adams Plateau-Clearwater area, and commonly are noted on properties where sulphide mineralization is reported (see description in Appendix A for Mosquito King, Crowfoot Mountain, and Rexspar). These dykes commonly occur along northerly trending faults and several have yielded mid-Eocene dates (dates by the Geological Survey of Canada are summarized in Jung, 1986). The relationship between these dykes and sulphide mineralization is discussed in Chapter 4. 2.4 STRUCTURE The Eagle Bay Formation is complexly deformed. Timing relationships often are neither clear nor consistent, although it is generally agreed that all the stratified units were deformed (or re-deformed) during the Jurassic folding event related to the Columbian Orogeny (Campbell, 1973). This orogeny, associated with the accretion of a western allochthonous terrane against the Omineca belt and the craton (Monger et aJL. , 1 982), produced a pervasive foliation and 1 8 southwesterly directed thrust faults. The Eagle Bay Formation subsequently was deformed and refolded by northwesterly trending folds associated to the intrusion of the Raft and Baldy batholiths in the mid-Cretaceous. Later northeasterly trending strike-slip faults, as well as northerly striking normal faults, cut through the major units and structures of the formation. 2.4.1 Pre-Jurassic Structures The first deformation of the Eagle Bay Formation may be as old as Early Devonian as indicated by the presence of an early metamorphic foliation, which is axial planar to very rare, small isoclinal folds (Schiarizza, 1986). However, direct evidence of such a deformational event has been masked by subsequent deformation and regional metamorphism. Juxtaposition of the Fennell and the Eagle Bay Formations resulted from easterly directed thrusts. This thrusting event was post mid-Permian, since conodont bearing strata of mid-Permian age are repeated by the thrusts. Thrusting was also earlier than Jurassic because the thrusts are folded by structures related to the Jurassic Columbian Orogeny (Schiarizza and Preto, 1 984) . 2.4.2 Jurassic Structures 1 9 Units of the Eagle Bay Formation exhibit evidence of syn-metamorphic deformation characterized by: 1) pervasive shistosity sub-parallel to the original bedding and axial planar to isoclinal folds that verge westward, and 2) lack of continuity of the units along strike due to shearing that caused transposition of the layering and disruptions of isoclinal folds (Dickie, 1985). The Nikwikwaia Lake synform on the Adams Plateau (Fig. 2.1) is a large westerly trending fold related to this deformation. Redistribution of sulphide masses in the crests of folds in deposits in the synform area (Appendix A: Lucky Coon, Elsie, King Tut) is probably related to this event (Fig. 4.1). A southwesterly directed thrusting event established the present configuration of the units by creating major imbricated panels within the Eagle Bay Formation (Fig. 2.1). This thrusting probably occurred near the end of the Colombian Orogeny 2.4.3 Cretaceous Structures A prominent upright, easterly oriented set of folds, well exposed in the vicinity of the Raft and the Baldy batholiths, is related to the presence of the mid-Cretaceous intrusions. The best examples of this phase of folding are exposed in the Clearwater area where intrusions locally change 20 the predominantly northerly dip direction of bedding and shistosity (Schiarizza, 1986). On the Adams Plateau, outcrop scale folds have the same easterly orientation; these folds probably were generated during or soon after the intrusive event. Northeasterly trending strike-slip faults, such as the Barriere Lakes and Johnson Creek fault (Fig. 2.1), cut the Eagle Bay Formation and the Fennell Formation and account for some major stratigraphic truncations. In the Scotch Creek area, some of these faults were intruded by Cretaceous porphyry dykes and plugs. However, in other places similar faults extend into the Baldy batholith indicating that this faulting is Cretaceous or younger. 2.4.4 Tertiary Structures The youngest phase of deformation, affecting both the Eagle Bay Formation and the adjacent Fennell Formation, is of Eocene age and is characterized by open, northerly plunging folds with upright axial planes. This deformation is responsible for regional warping of previous structures, such as the folding of the axial surface trace of the Nikwikwaia Lake synform. The orientation of this set of folds is similar to the orientation of a set of normal faults that cut all units of the Eagle Bay Formation. These faults do not cut the overlying 21 Miocene basalts; they locally are intruded by Tertiary basaltic and/or lamprophyre dykes. These structures probably are related to the Tertiary extensional and thermal event. 22 3. LEAD ISOTOPE SYSTEMATICS 3.1 HISTORY OF LEAD ISOTOPE INTERPRETATION Houtermans (1946) and Holmes (1946) were among the first to tackle the concept of addition of radiogenic lead, derived from radioactive decay of uranium and thorium, to primeval lead and independantly derived the fundamental equations which govern the increase of radiogenic lead over time. The evolution of lead with time in source regions characterized by different uranium and thorium contents are depicted in Figure 3.0. With the increase of available data inadequacies in the model were highlighted and the term 'anomalous lead1 was introduced to categorize ore lead data which gave negative or excess model ages. Nevertheless, aside from anomalous lead, the isotopic composition of lead from several conformable ore deposits of various ages were used to construct a growth curve for con formable ore lead. Stanton and Russell (1959), therefore proposed that this curve represented the development of isotopic composition of deposits derived from a nearly homogenous source, the upper mantle, which had maintained an almost constant U/Pb and Th/Pb ratio since the formation of the earth. A summary paper (Kanasecwich, 1968) reviewed the the principles and the applicability of lead isotope models as known in the late 1960's. 23 Single-stage ~1 I 1 1 1 1 1 1 r-10 12 14 16 18 206Pb/2°4Pb Figure 3.0 Model evolution of lead with time (from Koppel and Grunenfelder, 1979). A: Diagram 207pb/204pb vs. 206pb/204pb showing single-stage growth curves with u as a parameter and single-stage isochrons. B: Diagram 208pb/204pb vs 206pb/204pb showing single-stage growth curves with u and w as parameters. 24 Refinements of the parameters used to calculate the growth curve (decay constants for U and Th, isotopic composition of primeval lead, etc.) as well as improvement in lead chemistry and analytical methods, resulted in the recalibration of the curve in the late 1 960's (Stacey et a_l. , 1 969, Cooper et al., 1969). The effects of new decay constants on calculated model ages were reviewed by Oversby (1974). These modifications emphasized the deviations of the data from a single stage curve, and demonstrated the inadequacy of such curve in characterizing the evolution of ore lead through time. Several mathematical models, involving mixing of different environments and multi-stage growth, were then devised to simulate average lead isotope evolution curves that fitted the data more closely. Doe and Stacey (1974) changed the parameters related to the age of the earth used in their calculations and explained the departure from single stage conditions by the mixing of several isotopic heterogeneous source materials. Stacey and Kramers (1975) established a two-stage model in which the departure of the second stage curve at 3.7Ga corresponded apparently to a time of major crustal differentiation, and generation of an uranium-enriched and of an uranium-depleted environment. Cumming and Richards (1975) gave an alternative interpretation to the sudden episodic model espoused by Stacey 25 and Kramers (1975) by presenting a continuous evolution model in which U/Pb and Th/Pb ratios constantly increased in the source material for conformable ore. Following development of these empirical models, Doe and Zartman (1979), following Armstrong (1968) and Armstrong and Hein (1973), presented the plumbotectonic model that incorporated, by means of computer modeling, geological processes related to plate tectonic concepts with lead evolution systematics. Their idealized model furnished a more global approach to lead evolution by simulating mixing between various distinct environments — each characterized by different concentrations and proportions of U, Th and Pb. These environments existed long enough to produce marked differences in lead evolution with time. Subsequently, Godwin and Sinclair (1982) constructed the 'shale' growth curve that was specifically applicable to the autochthonous portion of the Canadian Cordillera characterized by high u/Pb and Th/Pb ratios. This part of the Cordillera is upper crustal in lead isotope character as defined by Doe and Zartman (ibid.). This study used a remodeled 'shale' growth curve (cf. Godwin and Sinclair (1981; 1982) to obtain a better fit with the 26 lead data on galena from deposits in the Eagle Bay Formation. The reasons for these changes are discussed in section 3.4. 3.2 BASIC PRINCIPLES AND EQUATIONS The wide range in lead isotopic ratios related to time and geological setting and geochemical cycles of lead, uranium and thorium provide a useful method for estimations of the age and conditions of formation for ore material. The common lead method is based upon measurement of lead that has evolved through time in one or in successively closed systems or environments. It is assumed that these environments, characterized by distinct U/Pb and Th/Pb contents, and broadly corresponding to a major source or reservoir for magma generation (e.g. upper mantle or crust), have undergone an isolated evolution for a sufficient length of time to acquire a specific isotopic signature before mixing occurs between them. The transfer of lead from one system to another generally implies active geological processes (orogenic episodes, formation of new crustal segments, etc.) characterized by a change in the U/Pb and the Th/Pb ratio due to the preferential affinities of uranium and thorium to upper crustal rocks compared to depletion in environments involving mantle and/or lower crustal materials. 27 Age determinations on galena using the common lead method rely on the measurement of lead produced from uranium isotopes (206pb, 207pb), and from the thorium isotope (208pb) decay. Galena is used because after crystallization its lead isotopic composition is 'frozen' due to the absence of radioactive elements in its structure. The amount of radiogenic component of a sample is computed and expressed as the ratio of the radiogenic lead over 204pb, whos natural abundance does not change with time. The 206pb/204pb, 207pb/204pb, 208pb/204pb ratios will therefore increase with time from their initial ratios from the decay of uranium and thorium. The rate of decay and production of the radiogenic isotope is governed by the half-life of each parent isotope and the parent abundance. The time taken for the 238u to decay into 206pb is about the same as the age of the earth; thus about half of the 238u isotope has decayed since the earth formed. The half-life of 235rj is considerably shorter; accordingly about 75% of the primordial 235rj isotope had decayed to 207pb by 3. OGa (Doe, 1970); and subsequent generation of 207pb is small. This difference in the rate of isotopic production of lead from these two isotopes over time is reflected by the smooth flattening of the isotopic growth curve toward younger ages (Fig. 3.0). Model ages can be calculated from measured isotopic ratios 28 Schematic Evolutionary History of the Multi-stage Lead for Ore Deposits in the Eagle Bay Formation 5Ga 4Ga 3Ga 2Ga 1Ga Present 1st Stage I I I I 2nd Stage I I I 3rd Stage I I I I I I r rz T-*1 lion -*1 " h LJ I ' ion of the L / = 32.2 1 c w 5 u = w = 9.74 37. 1 9 c • -5 0 W = 12.16 w = 45.35 a> j 1 </> 1 — 1 u 1 t2 = 2.0Ga t1 = 3.7Ga T = 4.55Ga Figure 3.1 Schematic evolution of the lead in galena from the Eagle Bay Formation is as follows (modified from Faure, 1977): system 1 starts T years ago and exists for a period of time equal to T-ti. At ti the lead is transferred to system 2 and continues to evolve during interval tl-t2. At time t2 the lead is transferred to system 3 and resides there for t2-t3 years. At t3 the lead is withdraw and fixed in galena—an environment containing no uranium or thorium--so that between t3 and present no further isotopic evolution occurs. 29 Table 3.0 Equations used in lead isotope model calculat ion 1 2 (2 0 4 Pb/20 4 Pb), = (2 0 6 Pb/J 0 4 Pb)0 + u (eXs T - eX»l) (eX5T_eA5l) («'Pb/*o«Pb) t = (5 07Pb/504Pb)0 + ii ^XsT -Xst 137.88 3 (208Pb/J04Pb)t = (J08Pb/304Pb)0 +W(eX2T-eXJt) (206Pb/204Pb)0 = a0 = 9.307 primordial lead (= Pb isotopic composition (201Pb/204Pb)0 =b0 = 10.294 at timeT) (20 8Pb./204Pb)0 =c0 = 29.479 (Tatsumoto et al. 1973) T = age of the Earth (calculated with the new decay constants) = 4.57 b.v. (Tilton, 1973). (207Pb/204Pb)(-b0 , (eXsT — e X51) .*sT „X8i, (2 06Pb/204Pb)t - a0 137.88 ' (eAs 1 - e' This is the equation of a straight line, the so-called isochjon. 7Pb 204 = b0 + Pb. (eXsT _ eXst) 137.88 (eX8T..eX8t) 2 06 Pb - a0 204 Pb. /J = 2 3 8 u/204pb  W= 2 3 2 Th/204pb X8,Xs,Xj: decay constants of 2 3 8U, 23SU,and 2 3 2 Th respectively. (see Steiger and Jager, 1977: Sub-commission on Geochronology: Convention on the use of uniform decay constants in geo- and cosmochronology; EPSL, 36, 359-362). The recommended constants are: Uranium: X (238U) = 1.55125 x 10"1 °/y X(J35U) = 9.8485 x 10-'°/y atomic ratio 2 3 8U/2 3 5 U = 137.88 Thorium: X (J32Th) = 4.9475 x 10"11 /y 30 of galena by solving equations 1 to 3 for t2 in Table 3.0. To use these equations the number, and characteristics of each successive environment from which lead was derived must be known or approximated. Change of U/Pb and Th/Pb, due to fractionation in the environment from which galena was generated, is assumed to be negligible. Furthermore any model age should be interpreted within a known geologic and tectonic framework. This is because the isotopic composition of galena is directly related to the time and type of mineralizing process which formed the galena. In some cases the lead system can also be disturbed by subsequent events; marked radiogenic enrichment in vein deposits has been observed (Russell and Farquhar, 1960; Watson, 1981), and signs of re-equilibration of the isotopic composition of galena due to metamorphism have been reported in several studies (Cumming and Gurjurdis, 1973; Richards, 1981; Brevart et al.f 1982). Evolution of the lead in the deposits hosted by the Eagle Bay Formation follows a multi-stage history schematically depicted in Figure 3.1. The first two stages of the lead evolution are assumed to have followed the Stacey and Kramers (1975) model, in which the lead developed initially from a primeval composition (inferred to be that of troilite lead, Tatsumoto et a_l. , 1 973 ) at time T established at 4.57Ga, followed by a second stage that started at 3.7Ga with higher u 31 and w values—departure of the second stage corresponds to the approximate age for the isolation of the lower mantle from the mixing system. The last stage of the lead evolution for the deposits of the Eagle Bay Formation is approximated by the 'shale' curve of Godwin and Sinclair (1982). This last stage, however, appears to more closely model the lead evolution in the Eagle Bay Formation when it is anchored to the Stacey and Kramers (1975) curve at 2.0Ga. Construction of the remodeled curve is developed in section 3.4. 3.3 ANALYTICAL PROCEDURES 3.3.1 Sample Description Ore samples were collected from 37 deposits and mineralized occurrences listed in Table 4.1 and described in Appendices A and C. All samples were selected from sulphide rich horizons and/or from cross-cutting mineralized structures. In several deposits both massive ore and vein mineralization were sampled to determine the effects of different types of occurrence on isotopic composition. All the lead analysed was extracted from hand picked galena and prepared according to the methods described in Appendix B. 3.3.2 Analytical Precision Lead isotopic ratios were measured on a VG Isomass 54R 32 solid source mass spectrometer interfaced with a HP-85 computer in the Geochronology Laboratory of R. L. Armstrong at The University of British Columbia. Several blocks of data were routinely taken for each sample load. The reported results (Appendix C) represent the normalized mean of these data. Within run precision, expressed as the percentage standard deviation, is usually better than 0.05%. Repeated measurement of Broken Hill Standard (BHS-UBC1) and analyses of duplicates (Appendix C) monitored the analytical precision of the runs. Thirteen determinations of BHS-UBC1, made during the course of this study, were added to 35 previously obtained values to compute the average ratio given in Table 3.1. An empirical mass fractionation correction factor was calculated using accepted values for BHS-UBC1 established by Richards (1981 ). This factor was used to normalize the isotopic ratios of all analyses. The maximum variation observed in duplicate analysis is less than 1.0%. The averaged differences between the two sets of values are 0.023, 0.019 and 0.054 for the 206pb/204pb, 207pb/204pb and 208pb/204pb ratios respectively. Paired-t test conducted on the duplicate analyses established with 95% confidence that no systematic bias exists between the different sets of duplicate analysis. However, even under optimal conditions errors arise from fractionation processes (which TAELE 3.1: Statistics related to the calculaticn of mass f ractkinBticn factors using Broken Hill Standard (BHS-UECI). Lead Isotope ratios Z16/2D4 abs + 207/204 abs + 2D8/2D6 abs + 206/207 abs + 206/20B abs + Maximim rtinimLfn 15.962 15 .m 0.007 O.0D1 15.32^ 15.300 0.005 0.000 35.653 35.359 0.056 0.002 1 .062307 1.061636 0.020032 0.000016 0.650816 0.669966 0.000705 OD000O9 Average (n=66) Std. Dev. % Std. Dev. 15.950 0.0053 0.033 0.003 15.311 O.C060 0.Q39 0.002 35.613 0.0021 0.006 0.010 1.061732 0.00D019 0.002 0.001330 0.650609 0.0COO17 0.0C& 0.000039 BH3dJECl Error Corr. Fact Precision 16.006 0.001 1.003377 0.000112 15.330 0.007 1 .005169 0.000205 35.651 0.007 1.006734 0.000121 1.039696 0.007 0.993237 0.000013 0.66B907 0.018 0.993651 0.00D061 1. BHS:UBC standard valLEs fran double spike analyses reported by Richards 1981 . 34 cause preferential depletion of elements), and from error in the measurement of the low intensity 204pb peak. The combination of these errors generates a spread in the values. Isotopic fractionation, the main source of variations in single filament isotopic determinations (Cooper and Richards, 1966; Ozard and Russell, 1970), is mass-dependent and results in the displacement of a point from its true value along a line with slopes that correspond to the product of coordinate ratio times the ratio of the respective mass difference—e.g. a slope of 3Y/2X on the 207pb/204pb vs. 206pb/204pb diagram (Ozard and Russell, 1970; Richards et al., 1981). The 204pb error causes the spread of the values along a slope equal to the 207pb/206pb and 208pb/206pb values since for each of the ratios (206pb/204pb, 207pb/204pb and 208pb/204Pb) the error is related to the 204pb measurement (York, 1969). The slopes of the corresponding errors is depicted on each diagram (Figs. 3.3 to 3.5) . 3.3.3 Calculation of Average Values for the Deposits The average isotopic composition for each deposit (Table 3.3) are presented on conventional 207pb/ 204pb vs. 206pb/204pb, 208pb/204pb vs. 206pb/204pb, and 206pb/207pb vs. 206pb/208pb diagrams (Figs. 3.3 to 3.5). The plotted average values were obtained from the computation of repeated analyses of various samples collected at the deposit site (Table 3.2; Appendix C). TABLE 3.2: Representative calculation of average galena lead isotopic values 1 for a given deposits. Sample Number2 206/206 Lead Isotope Ratios 207/204 + 208/204 + BIRK CREEK 3050B-001 18.948 30508-001D 18.947 30508-002 18.904 30508-002D 18.882 30508-003 18.901 (3050B-0030 19.026 3050B-004 18.B96 3050B-0040 18.949 30508-005 18.893 30508-506 1B.B78 30508-506D 18.869 Olean (n=11) 18.927 Rejection level at + 2 st. dev. 0.098 Mean (n=10) 18.907 Std. Error4 0.01 0.02) 0.06) 0.03) 0.03) 0.02) 0.30) 0.02) 0.14) 0.01 ) 0.06) 0.08) 15.718 15.741 15.710 15.699 15.691 15.798 15.705 15.741 15.721 15.708 15.722 15.723 0.059 15.716 0.005 0.02) 0.08) 0.01 ) 0.03) 0.01) 0.30) 0.01) 0.05) 0.01 ) 0.13) 0.10) 38.861 38.856 38.791 38.751 38.744 39.027 38.755 38.9B7 38.829 38.893 38.834 38.848 • .186 38.848 0.03 0.03) 0.08) 0.03) 0.03) 0.02) 0.30))3 0.02) . 0.16) 0.01) 0.18) 0.18) 1. Similar calculation has been made apply to all deposits (Appendix C). 2. 30508 represents the number given to the deposit; 001, 002, etc. defines different samples taken from the deposit; D, indicates duplicate analyses of the same sample. 3. Data from this run was rejected on the basis of more than 2 standard deviations from the mean. 4. Standard error = standard deviation / square root of number of samples (n). 36 tf 003 Birk Creek Deposit Average Calculation 15.75 -CL o CVJ H 003 • • 004 O 001 -LJ CL 005 I v A • T 4 O CM 15.7 1 -500A I i, 002 av Fractionation // • 003 j 204 Error i i i 18.85 18.95 19.05 206Pb/204Pb Figure 3.2 207pb/204pD vs. 206pb/204pb diagram showing the isotopic distribution of all analyses from the Birk Creek area. Filled symbols represent individual analyses and open symbols define their average. Crossed symbols identify deleted analysis. The average value for the Birk Creek area is depicted with its associated standard error (Table 3.2). 37 TABLE 3.3: Average galena lead isotope values from ore deposits in the Eagle Bay Formation. Deposit Name Map Lead Isotope Ratios1 No2 206/204 207/204 208/204 206/207 Cluster 1 Devonian 206/208 Birk Creek Homestake Rea Gold Ford 508 511 515 53B 18.907 18.854 18.869 1B.8B3 15.716 15.700 15.699 15.698 38.848 38.626 38.755 38.676 1 .20304 1 .20085 1.20192 1.20289 0.48699 0.48845 0.4B6BB 0.4B823 Average (n=4) Std. Error Mean 1B.887 +0.010 15.703 +0.004 38.720 +0.216 1.20211 +.00047 0.48767 +.00039 Between cluster 1 & 2 Art Tuin Mountain 517 519 19.060 19.027 15.737 15.704 39.147 38.B32 1.21110 1.21164 0.4B6B7 0.49027 Cluster 2 Triassic Agate Bay 506 19.143 15.701 33.909 1.21922 0.49200 Lucky Coon 518 19.142 15.694 38.900 1 .2196B 0.4920B King Tut 523 19.045 15.688 36.835 1.21718 0.49255 Elsie 524 19.142 15.700 3B.975 1.21925 0.49197 Mosquito King 525 19.090 15.693 38.846 1.21648 0.49142 Pet 526 19.126 15.732 38.980 1.21575 0.49151 Spar 527 19.130 15.690 38.881 1.21927 0.49201 Red Top 531 19.146 15.721 38.939 1.21779 0.49170 Red Mineral 2 534 19.131 15.714 3B.069 1.21747 0.48966 Silver King A 536 19.0B1 15.708 38.899 1.21471 0.49052 Orell 5P 537 19.128 15.692 38.885 1.21902 0.49191 Sunrise 541 19.105 15.696 3B.B49 1.21716 0.49176 Enargite 504 19.096 15.690 38.9B7 1.21704 0.4B979 Fortuna 513 19.125 15.721 39.018 1.21650 0.49016 White Rock 528 19.151 15.722 39.048 1.21810 0.49046 Vavenby 542 19.191 15.703 38.846 1.21574 0.49145 Silver King-Queen 545 19.104 15.684 38.978 1.21807 0.49012 PS-85-175 54B 19.177 15.721 38.962 1.21987 0.49220 Average (n=18) 19.125 15.701 38.936 1.21775 0.49138 Std. Error Mean +0.007 +0.003 +0.016 +.00365 +.00023 38 TABLE 3.3 (continued) Deposit Map Lead Isotope Ratios'! Name No2 206/204 207/204 208/204 206/207 206/208 Between cluster 2 & 3 Fluke 532 19.223 15.703 39.361 1 .22416 0.48838 mt McClennan 539 19.269 15.698 38.967 1 .22747 0.49448 Foghorn 505 19.208 15.711 39.138 1 .22258 0.49076 Rexspar 516 19.177 15.916 38.986 1.20528 0.49273 Birch Island 540 19.335 15.820 39.235 1 .22200 0.49364 Tindal 543 19.251 15.714 39.080 1 .22509 0.49261 Rouge 547 19.260 15.744 39.156 1.22330 0.49188 Cluster 3 Leemac 546 19.391 15.729 39.336 1 .23279 0.49294 Red Mineral 1 533 19.345 15.699 39.360 1.23229 0.49149 Red mineral 3 535 19.354 15.706 39.383 1.23228 0.49142 Son ja 544 19.356 15.691 39.251 1.23353 0.49313 Beca 507 19.339 15.680 39.016 1 .23338 0.49567 Average (n=5) 19.357 15.701 39.264 1 .23285 0.49293 Std. Error mean +0.040 +0.008 +0.055 +.00026 +.00077 5ide cluster 3 June 521 19.461 15.719 39.504 1.23809 0.49263 1. Lead isotopic ratios represent calculated average values from data in Appendix C (calculation of average value is described in section 3.3.2). 2. map no. in Appendix C is prefixed by 30 and suffixed by analytical sample number. 39 Figure 3.2 represents an example of such data collected from the Birk Creek area. In the average value calculation, data falling outside two standard deviations from the mean were deleted (as were outlier values obtained from runs with poor precision. Thus means representing only the 'best' values are presented in Tables 3.2 and 3.3. Consistency between samples from massive ore and from cross-cutting structures was observed in all deposits where both types of samples were collected. This indicates that mineral showings of different habit can be cogenetic and formed from similar and/or interactive hydrothermal systems. In many cases veins may represent feeder zones to massive ore. 3.4 THE REMODELED CURVE FOR THE EAGLE BAY FORMATION The average lead isotopic composition obtained from deposits in the Eagle Bay Formation (Table 3.3) forms a coherent series of clusters characterized by high 206pfc>/204pb, 207pb/204pb, and 208pb/204pb values. The isotopic uniformity displayed by the set of data as a whole is best explained by the presence of a common ultimate source for the lead in all the deposits. Because the data plot above the average 'orogene' curve of Doe and Zartman (1979), a growth curve representing the evolution in an upper crustal environment is used to determine the model ages for the various deposits clustered along it. 40 Figure 3-3 207pb/204pb vs 206pb/204pb diagram for deposits hosted by the Eagle Bay Formation using data from Table 3.3. Filled symbols denote deposits grouped in specific clusters; open symbols are outliers. Deposits in cluster 1 to 3 are plotted with different symbols. Bars represent +_ 1 standard error around the mean of the cluster. The average growth curves shown are the "shale* curve of Godwin and Sinclair (1982) and the remodeled shale curve (t2 = 2.0Ga, u = 12.16+. 08). 15.75 42 Figure 3.4 208pb/204pb vs 206pb/204pb diagram for deposits hosted by the Eagle Bay Formation using data from Table 3.3. Filled symbols denote deposits grouped in specific clusters; open symbols are outliers. Deposits in cluster 1 to 3 are plotted with different symbols. Bars represent +_ 1 standard error around the mean of the cluster. The average growth curves shown are the 'shale1 curve of Godwin and Sinclair (1982) and the remodeled shale curve (t2 = 2.0Ga, w = 45.35). 206 pb/204pb 44 Figure 3.5 • 206pD/208pb vs 206pb/207pb diagram for deposits hosted by the Eagle Bay Formation using data from Table 3.3. Filled symbols denote deposits grouped in specific clusters; open symbols are outliers. Deposits in cluster 1 to 3 are plotted with different symbols. Bars represent +_ 1 standard error around the mean of the cluster. The average growth curves shown are the 'shale' curve of Godwin and Sinclair (1982) and the remodeled shale curve (t2 = 2.0Ga, u = 12.16+.08). Cluster 3 0.495 0.024 0 Cluster 2 JQ Q. 0.49 co o CM X) D_ (0 o CM 0.485 H Remodeled curve - 2.0 Ga 0.44 0.41 Shale curve - 1.887Ga 0.44 0.48 1.190 1.20 1.21 1.22 206Pb/2°7Pb 1.23 1.24 46 The approximate coincidence of the data from the deposits of the Eagle Bay Formation with the 'shale' curve of Godwin and Sinclair (1982) supports the utilization of such a curve for model age estimation, and indicates that the lead in the deposits of the Eagle Bay Formation evolved in an upper crustal environment characterized by high u and w values. The curve is consistent with the active continental margin setting assigned to deposition of the Eagle Bay Formation, and implies that there was a significant contribution of material from recycled and homogenized Precambrian crust to constituent rock units of the formation. However, the high 207pb/204pb isotopic signature of the galena from the Eagle Bay Formation resulted in the data plotting above the average 'shale' curve on the 207pb/204pb vs. 206pb/204pb diagram (Fig. 3.3). Similarly the plotted 208pb/204pb ratios are shifted below the 'shale' curve on the 208pb/204pb vs. 206pb/204pb diagram (Fig. 3.4). Presentation of the data on a 206pb/207pb vs. 206pb/208pb diagram (Fig. 3.5) reveals that the slight but systematic discrepancy between the data set and the 'shale' curve is real and not due to analytical error of 204pb (this diagram minimizes the effect of this error by eliminating the 204pb measurement errors). Consequently the 'shale' curve represents an approximation of the average lead 47 behavior, but does not fit the data closely enough to permit model age determinations. Remodeling of the curve (Table 3.4), by changing the parameters used to define it, resulted in a better coincidence with the data from deposits hosted in the Eagle Bay Formation—especially 208pb/204 vs. 206pb/204pb and 206pb/208pb vs. 206pb/207pb (Figs. 3.4 and 3.5). The remodeled curve as defined here applies specifically only to the deposits in the Eagle Bay Formation. It does not detract from the general validity of the 'shale' curve—especially as applied east of the Adams Plateau. The remodeled curve represent a local variation from the average 'shale' curve due to the specific geological setting characteristic of the Eagle Bay Formation. The following discussion reviews the changes in parameters made to obtain the remodeled curve. 3.4.1 Departure Time, Initial Composition, and u Values The remodeled curve is anchored to the Stacey and Kramers (1975) curve at 2.0Ga. This date has been favored because it is close to Rb/Sr whole rock dates from granitic gneiss of the Shuswap Complex (2.0 to 2.25Ga: Duncan, 1982), and to the determined age of the basement by the common lead method from three groups of stratabound deposits in terrane correlated with the Eagle Bay Formation (Duncan, 1982). The 2.0Ga date is slightly older than the homogenization time of the continental 48 TABLE 3.4: Lead isotope values for the remodeled curve. Parameters: u = 12.16, u = 45.35, t2 = 2.0Ga Age1 Time Ga1 206/204 Lead Isotope Ratios 207/204 208/204 206/207 206/208 Present 0.0 19.582 15.736 39.515 1.24440 0.49556 Neogene 0.024 19.537 15.734 39.461 1.24171 0.49510 Paleogene 0.066 19.457 15.730 39.366 1.23693 0.49426 Cretaceous 0.14 19.315 15.723 39.19B 1.22846 0.49275 Jurassic 0.21 19.180 15.716 39.044 1.22041 0.49124 Triassic 0.25 19.102 15.711 3e.953 1.21584 0.49039 Permian 0.29 19.023 15.707 38.85B 1 .21112 0.48955 Carboniferous 0.36 18.884 15.698 38.699 1.20296 0.48797 Devonian 0.41 18.7B4 15.692 38.586 1 .19704 0.48681 Silurian 0.44 1B.723 15.688 38.518 1 .19346 0.4860B Ordovician 0.51 18.581 15.678 38.354 1.18516 0.48446 Cambrian 0.57 18.458 15.670 38.218 1.17792 0.48297 Anchor point2 2.0 15.159 15.192 34.799 0.99783 0.43562 1. Time boundaries from DNAG Geologic Time Scale (Palmer, 19B3). 2. Calculated from stage 2 of Stacey and Kramers (1975) u = 9.74, ID = 37.19, ti = 3.7Ga. 49 basement by the Hudsonian orogeny. It was chosen as the departure point for the model related to galena lead isotopes in the Eagle Bay Formation. Nevertheless this starting point represents an estimated parameter which is required by the multi-stage model adopted in this study. Estimation of the initial ratio at 2.OGa is not unambiguous. However, here it is simply assumed that the environment from which the basement was generated evolved along an average curve similar to the secondary growth curve of Stacey and Kramers (1975) starting at 3.7Ga (a similar assumption was made in the construction of the 'shale' curve). The initial ratios therefore correspond to the empirical data calculated by Stacey and Kramers (1975, p. 216) and are: 206pb/204pb = 15.159, 207pb/204pb = 15.192, and 208pb/204pb = 34.799. The u value of 12.16 was used to calculate the remodeled curve because it represents the average U/Pb value for the Omineca Belt calculated for the 'shale' curve (Godwin and Sinclair, 1982). The calculated u values for the data from the Eagle Bay Formation (using equations in Table 3.0) coincidently covered a range centered around a u of 12.0. Isotopic compositions on the remodeled curve were also calculated with u = 12.08 and 12.24 (Fig. 3.3) to display the effect of a variation of u on the position of the remodeled curve. 50 Utilization of 2.OGa as a departure point generates a curve which plots above the 'shale' curve (Figs. 3.3 and 3.4). Consequently, any isotopic composition associated with any model age on the remodeled curve will be greater in both 207pb/204pb and 206pb/204pb ratios relative to the 'shale' curve. The upward displacement of the curve's position increases the coincidence between the curve and clusters 1 and 3. This aspect is significant because these two clusters, containing deposits of known Devonian and Cretaceous age, fall appropriately on the remodeled curve at 375Ma and 100Ma respectively. This better fit of the data with the remodeled curve supports the use of 2.OGa rather than 1.887Ga as the anchor point for the remodeled curve. On the other hand, the variations caused by the utilization of different u values are less significant (Fig. 3.3), and it does not appear to be advantageous to change the u value to accommodate the data. 3.4.2 w Value Utilization of a w value equal to 49.09 (value used for the 'shale' curve: Godwin and Sinclair, 1982) to remodel the thorium curve (on the 208pb/204pb vs. 206pb/204pb diagram; Fig. 3.5) is inadequate. Compared to the uranogenic curve (above section) the change resulting from the utilization of t2 equal to 2.OGa rather than 1.887Ga does not sensibly affect the 51 position of the remodeled curve relative to the distribution of the data set, since it only displaces the isochron intersections upward and to the right (depicted as points and crosses in Figure 3.4). A closer fit of the remodeled curve to the data is obtained when the w value is lowered to 45.35. This value is markedly lower than the 49.09 value used for the 'shale' curve; however this value is higher than the estimated value of 41 .86 used by Doe and Zartman (1979) to characterize the upper crustal environment for their plumbotectonic model. The geochemical behavior of thorium during the fractionation process is not as well understood as uranium and, the Th/Pb ratio is considered less specific in discriminating among various source materials (Zartman, 1974). Therefore, although a slightly lower value is required to fit the data from the deposits of the Eagle Bay Formation, it does not imply any major difference in the composition of the protolith for these rocks. 3.4.3 Summary Uniformity within deposits and the range of the lead isotopic compositions obtained on galena from the deposits hosted by the Eagle Bay Formation indicates that the protolith for the lead has an average upper crustal signature. This emphasizes the involvement of old crustal basement beneath the Eagle Bay Formation and/or sediment sources for the Eagle Bay rocks. Lead from the deposits hosted by the Eagle Bay Formation 52 has generally similar isotopic compositions to the lead in the Cariboo Gold veins (Andrew, 1982), and is significantly different (mainly higher 207pb/204pb values) from the lead in the Intermontane Belt (Andrew, 1982) and the Slide Mountain Group (Aggarwal and Nesbitt, 1984). In addition this similarity in the lead isotopic signature of deposits in the Eagle Bay Formation and in the Barkerville Terrane supports the correlations established by Struik (1986). Proximity of the data to the 'shale' curve indicates that this curve is a possible approximation to the average behavior of the lead. But the distinct remodeled curve more closely fits the data from the Eagle Bay Formation. This remodeled curve is used throughout the following discussion to assign model ages to the pulses of mineralization in the Eagle Bay Formation mainly represented by three distinct clusters of data with Devonian, Upper Triassic, and Cretaceous model ages. 3.5 MODEL AGE DETERMINATIONS Using the multi-stage model depicted in Figure 3.1, model ages for the mineralization can be derived from the measured isotopic ratios of the deposits. By combining equation 1 and 2 of Table 3.0, the equation of a family of straight lines (isochrons) passing through the anchor point of the remodeled 53 shale curve at 2.OGa on Stacey and Kramers' (1975) curve can be obtained. The slope of the appropriate isochron on which the lead isotopic composition lies can be used to determine a value of t3 and to assign a model age for the galena. Since the above equation is transcendental, t3 cannot be directly calculated by conventional algebraic methods, and computer programs use an iterative calculation to approximate the best value for t3. Calculation of the slope m, and t3 determinations were made using the average isotopic values (Table 3.3.) for each deposit. Because the 207pb/204pb, 206pb/204pb slope model ages are very sensitive to small changes in m, variations in the 207pb/204pb intercept of 0.1% (comparable to experimental error) resulted in large variations in the calculated model ages (differences of 100Ma were obtained for some of the deposits in cluster 1). Consequently, the slope model ages obtained for each deposit were not used. Instead, ages of the clustered groups of deposits were determined by where they plot along the remodeled curve. Table 3.3 lists the mean values for each cluster (calculated in the same way as averages for each deposit in section 3.3.3). These means with their associated standard error are plotted on the lead diagrams (Figs. 3.3 to 3.5). Model age for the clusters were then established from the age on the remodeled curve at which the clusters—around their mean 54 values—intersected the curve. These model ages are primarily controlled by the 206pb/204pb ratios as it is these ratios that, exhibit greater variations. The model ages for clusters 1,2 and 3 were determined from each diagram (Fig. 3.3 to 3.5) as being respectively Late Devonian, Late Triassic, and mid-Cretaceous. These model ages of corresponding clusters of deposits are discussed in Chapter 4. 55 4. LEAD ISOTOPES, MINERAL DEPOSITS AND STRATIGRAPHY 4.1 INTRODUCTION The dominant influence of an upper crustal component on the lead isotope composition in galena of deposits hosted by the Eagle Bay Formation was established in Chapter 3. This chapter focuses on the differences between these deposits as defined by the clustering of the lead data into three main groups along the remodeled curve (deposits in each cluster are in Table 4.0). Deposits sharing similar lead isotope signatures define genetic links; difference in isotopic composition between the distinct clusters allow model ages to be assigned and sometimes permits distinctions between deposits that are oogenetic with, or are markedly younger than their host rocks. Stratigraphic correlation and construction of composite stratigraphic successions within the Eagle Bay Formation has been hampered by intense deformation and metamorphism, which commonly obscures contact relationships among the units. Lead isotope data are consistent with the Devonian age for the unit EBA established by other critera (see section 2.3.1). However lead data suggest an Upper Triassic age for the structurally lower part of unit EBG, which is considered to be Cambrian by TABLE 4.0: Classification and name of deposits within discrete clusters of data defined in Figures 3.3 to 3.5 Deposit Host Deposit Map Classification Unitl Name No1 Cluster 1 Devonian Volcanogenic EBA Birk Creek 50B Oogenetic with Homestake 511 host rocks Ford 538 E8F Rea Gold 515 Between cluster 1 & 2 Veins EBS Art 517 EBG Twin Mountain 519 Cluster 2 Triassic Stratiform EBG Agate Bay 506 Oogenetic with Lucky Coon 518 host rocks King Tut 523 Elsie 524 Mosquito King 525 Pet 526 Spar 527 Red Mineral 2 534 Silver King A 536 Orell 5P 537 Replacement EBQ Red Top 531 Sunrise 54Veins EBA Enargite 504 Fortuna 513 EBG White Rock 528 Vavenby 542 Silver King-Queen 545 PS-85-175 548 TABLE 4.0 (continued) Deposit Host Deposit Map Classification Unitl Name No1 Between cluster 2 & 3 Stratiform EBG Fluke 532 Replacement EBQ Mt McClennan 539 Uranium (volcanogenic) EBA Rexspar 516 Vein Foghorn 505 Birch Island 540 Tindal 543 Rouge 547 Cluster 3 Vein Baldy Leemac 546 EBG Red Mineral 1 533 Red Mineral 3 535 EBA Sonja 544 Replacement (?) EBA Beca 507 Beyond cluster 3 Vein June 521 1. Host Unit and Map No. are on Figure 4.0. Map no. in Appendix C is prefixed by 30 and suffixed by analytical sample number. 58 Schiarizza (1986). Interpretations proposed here, although not completely unambiguous, are constrained substantially by available geological data. 4.2 CLUSTER 1: DEVONIAN COGENETIC DEPOSITS Two mineralized deposits, Rea Gold and Homestake, and two mineralized showings, Birk Creek and Ford, (Table 4.0, Fig. 4.0, Appendix A) are enclosed by cluster 1 around the Devonian isochron on the remodeled curve (Fig. 3.3 to 3.5). These four occurrences are hosted by Devonian volcanic units (EBA and EBF) of the Eagle Bay Formation. These units form a conformable succession (locally separated by orthogneiss bodies) composed of strongly foliated quartz-sericite-phyllite, chloritic phyllite, and sericite schist, within which quartz and plagioclase phenocrysts and relict igneous textures are locally visible. This succession was interpreted by Preto (1981 ) as a deformed and recrystallized felsic to intermediate volcanic sequence metamorphosed to greenschist facies. Units EBA and EBF are partly interlayered with, but mostly overlained by, a turbidite sequence composed of phyllites, argillite, sandstone, grit and minor carbonates (unit EBP). Zircons from the metavolcanic rocks (Fig. 4.0) yielded a Devonian, 372+_1lMa date (Preto and Schiarizza, 1985). Conodonts found in two limestone beds of unit EBP yielded a mid-Mississippian age (Osagien to early Devonian to Permian Fennell Formation 5g I UF I Upper structural division: pillowed and massive meta-basalt. minor chert 1 if I Lower structural division: pillowed and massive meta-basalt and ribbon chert, limestone, diorite, gabbro, quartzf eldspar, porphyry, rhyolite Mississippian I EBP I Phyllite and slate with interbedded sandstone and grits Devonian and/or Mississippian I EBF 1 Feldspathic phyllite (intermediate to felsic tuff) Devonian I EBA I Sericite-auartz-phyllite and schist (intermediate to felsic volcanics and volcanoclastics) Devonian and/or older 1 EBS I Mixed meta-sedimentary seouence (phyllites) | EBC I Calcareous chlorite-schist, fragmental schist (mafic to intermediate volcanics) | '•]. 1 Tshinakin limestone fr--^ mixed phyllite (EBCp) [ -| quartzite ( EBCq ) \ ) polymictic conglomerate (EBCcg) [ I T-EBG ( ? Triassic ) Lower Cambrian and/or older IEBQ I Chlorite-muscovite quartzite. chlorite-muscovite-quartz schist and minor meta-sediments (SDQ) I EBH I Quartzite. grit and chlorite-sericite-quartz schist Intrusives Jurassic & Cretaceous [ '• 11 \\ Raft batholith. Baldy batholith, Scotch Creek plug Late Devonian I Qgn I Granite and granodiorite orthogneiss Symbols Mineral occurrences • O Cluster 1 (Oevonian) A & Cluster 3 (Cretaceous) • • Cluster 2 (Triassic) 0 Cluster 4 (Tertiary) X Outliers Faults f^*" Thrust fault (this study) Thrust fault (Schlarizza et al, 1984) Figure 4.0 Geology of the Eagle Bay Formation showing the location of the sampled mineral deposits within the major thrust units (modified from Schiarizza and Preto, 1984). 60 61 Meramecien: Okulitch and Cameron, 1976). Based on these age determinations, a bracketed Devono-Mississippian age has been assigned to these units. Rea Gold and Homestake deposits, located on the limbs of a major overturned and northwesterly trending syncline similarly occur within or near the top of a felsic pyroclastic sequence included in a thicker more mafic pile of tuffs and minor flows. Deformation has affected the deposits and is marked by a well defined penetrative foliation. Definite folds are difficult to outline due the shistosity developed in the rocks. Both deposits, composed of massive sulphide lenses and associated barite, exhibit extensive footwall alteration zones characterized by silicification, sericitization and pyrite development. These deposits are similar in many respects to the syngenetic volcanogenic polymetallic Kuroko deposits (Hoy and Goutier, 1986; Appendix A). A Devono-Mississippian lead model age for the deposits is coincident with other age determinations from their host units (EBA and EBF), and consequently, the mineralizing solutions probably were cogenetic with the formation of the host rocks. The lead isotopic signature of cluster 1 can therefore be used to fingerprint deposits which formed under similar conditions. Thus, although the silicified pyrite-pyrrhoti-te rich occurrences 62 of the Birk Creek area and the stratiform massive sulphide zones mineralized with Pb-Zn-Cu of the Ford property (Table 4.0, Fig. 4.0, Appendix A) are not conclusively volcanogenic in origin, their lead isotopic composition suggests such an interpretation. The oogenetic and volcanogenic mineralization probably was deposited either from solutions associated with the volcanism or concentrated from the volcanic pile by circulating solutions in a convective cell soon after, or during the formation of the Devonian units EBA and EBF (Hutchison, 1973; Solomon, 1976; Lydon, 1985). The probable presence of an underlying larger intrusive mass, which may have set up the convective cell, is indicated by the occurrence of quartz porphyry intrusive bodies considered to be cogenetic with the volcanics (Preto, 1981; Goutier et aJL. , 1 985). The observed isotopic ratios represent an average of the lead leached by the mineralizing solutions from the source rocks. The lead isotopic compositions from veins associated with the deposits are statistically indistinguishable from the lead extracted from the massive deposit. This suggests that formation of the veins was contemporaneous with the formation of the massive ore; they may represent feeders to massive ore bearing horizons. Compared to Kuroko type deposits (Lambert and 63 Sato, 1974; Sato and Sasaki, 1976; Sato et al., 1980), the lead data of cluster 1 are markedly radiogenic. This enrichment in radiogenic lead suggests that the ultimate source of Devonian intrusives is underlying Precambrian basement, a conclusion in agreement with the interpretation of Armstrong (in Jung, 1986) on the western position of the basement boundary (Fig. 2.0; see section 2.3.2). 4.3 LEAD DATA BETWEEN CLUSTER 1 & 2 Two mineralized veins (Twin Mountain and Art; Table 4.0, Figure 4.0, Appendix A) have their lead isotopic compositions plotting distinctively to the right of cluster 1. The Twin Mountain vein has a lead model age of mid-Pennsylvanian, and occurs in the Cambrian unit EBG (Schiarizza and Preto, 1984). The high barite content of some of the veins at Twin Mountain makes them mineralogically more similar to the nearby Rea Gold and Homestake deposit (hosted by the Devono-Mississippian units EBA and EBF) than to any deposits of the Cambrian unit EBG. The major thrust inferred by Schiarizza and Preto (1984) which isolate Twin Mountain from the Devono-Mississippian units has not been confirmed by detailed mapping by Corporation Falconbridge (see Hoy and Goutier, 1986) or by White (1985). The mid-Pennsylvanian model age determined for the Twin Mountain vein might indicate that the inferred thrust actually represents 64 an unconformity between separated volcanic and volcaniclastic sequences, and that the host unit could be younger than Cambrian as currently interpreted. However, the mid-Pennsylvanian lead model age by itself does not refute the Cambrian age assign to the unit EBG. 4.4 CLUSTER 2: TRIASSIC STRATIFORM AND VEIN DEPOSITS Cluster 2 represents galena lead with an Upper Triassic model age (Fig. 3.3 to 3.5). Several remobilized stratiform deposits hosted by the unit EBG, and veins randomly distributed through the Eagle Bay Formation have lead isotopic compositions that plot in this cluster. The form of the stratiform deposits suggests that they could be oogenetic with their host unit. Unit EBG, however, has been defined as Cambrian (Schiarizza, 1986b). Consequently, a major discrepancy exists between the Triassic model age for apparently oogenetic mineralization and the assigned Cambrian age of the host. The following constitutes a brief geological description of the deposits of cluster 2 and provides a framework for the discussion of the lead isotope interpretations in section 4.2.2. 4.4.1 Deposit geology Stratiform deposits Remobilized stratiform deposits are represented by the Lucky Coon, Elsie, King Tut, Mosquito King and Spar deposits on 65 the Adams Plateau, and by the Sunrise and Red Top deposits in the Clearwater area (Table 4.0, Fig. 4.0, Appendix A). The term stratiform is used here to characterized sulphides rich layers conformable with the surrounding rocks (cf_. Glossary of Geology, American Geological Institute, 1979). These deposits on the Adams Plateau are hosted by unit EBG which consists mainly of massive and fragmental greenschist, of intermediate and mafic volcanic affinities, associated with sedimentary units represented by graphitic and siliceous phyllite containing layers of phyllitic limestone, calc-silicate, and phyllitic quartzites. The gangue of these deposits' is siliceous; pyrite, the most abundant sulphide, occurs with dark 'black jack' sphalerite and galena. Small amounts of arsenopyrite (absent in the Mosquito King deposit) and chalcopyrite also occur. None of these deposits exhibit clear mineral zonation, and the ratios of the different sulphides are highly variable between, as well as within, the deposits. However, the overall content of galena is greater in these deposits than in those of cluster 1. The mineralization in these deposits can either be cogenetic with the Cambrian unit EBG, or younger and of replacement type (section 4.4.2). Remobilization of the sulphides during deformation is apparent from concentration and thickening of sulphide horizons in the hinge zone of isoclinal folds. For example (Dickie, 66 1985) at the Spar deposit sulphides are concentrated in an upright slightly asymmetric fold in which sulphide apparent thickness at the crest is twice that on the limbs; similar features are observed in the Lucky Coon (Fig. 4.1). Faults also offset and/or truncate sulphide bearing strata. On a smaller scale, deformation and remobilization of sulphides are outlined by crystal deformation (steel galena, undulatory extinction in quartz), replacement of arsenopyrite by galena and sphalerite, and overgrowth of euhedral pyrite (observed in polished section from samples of the Lucky Coon and Spar deposits). The stratigraphic level of the sulphide horizons in the Nikwikwaia syncline (Lucky Coon, Elsie and King Tut) appear equivalent to the Spar deposit (Dickie, 1985) indicating that these deposits may be contemporaneous. The stratiform nature and apparent continuity of the sulphide lenses in the same stratigraphic unit over 8km suggests that these deposits are syngenetic but remobilized by later folding. Near Sqwaam Bay, close to the lake shore, mineralized carbonate swells are common in chloritic schist (Agate Bay; Table 4.0, Fig. 4.0, Appendix A). Since the isotopic composition of the lead from these swells is similar to the lead from the stratiform deposits in the plateau, the showing probably represents local concentrations of disseminated cogenetic lead. The thrust fault of Schiarizza and Preto 67 Figure 4.1 Folded mineralized layers, Lucky Coon deposit. 68 (1984), assumed to pass slightly north of this deposit, has been relocated southward so that all isotopically-related deposits are within similar thrust slices (Fig. 4.0). (Note that the existence of this fault was questioned in section 4.1.1.) Two other deposits, Sunrise and Red Top (Table 4.0; Fig. 4.0, Appendix A), plot in cluster 2. These deposits consist of semi-conformable lenses and lenticular sheets of sulphide confined to a specific stratigraphic position in unit EBQ (close to quartzitic and limy zones associated with chloritic quartz-schists that are locally graphitic). The mineralization has a discontinuous but conformable distribution. Host unit EBQ is strongly folded around an easterly trending open antiform that is partly disrupted by faulting. The sulphide zones exhibit evidence of remobilization similar to that of the Lucky Coon, Mosquito King and Spar deposits. The Sunrise and Red Top deposits are classified in old reports as replacement deposits related to the emplacement of the Baldy and/or Raft batholiths (Appendix A), implying that the sulphides were introduced by solutions emanating from intrusions. However, if the assigned Cretaceous age for the batholiths is correct then the foregoing conclusion is untenable on the basis of the lead isotope data, because it plots in the Upper Triassic cluster. However any interpretation related to the intrusive age of the Raft batholith is uncertain until new zircon dates establish a more 69 reliable crystallization age for the batholith. Vein deposits The remaining group of data with isotopic composition plotting in cluster 2 is associated with well defined vein deposits (Table 4.0, Appendix A). The lead data from the vein deposits are indistinguishable from the lead of the above stratiform deposits. The occurrence of these veins is not restricted to any particular unit of the Eagle Bay Formation, and is not spatially clustered (Fig. 4.0). However, their distribution is not totally random and can be categorized as follows: 1) The Enargite and Fortuna veins (Table 4.0, Fig. 4.0, Appendix A) trend northward and occur close to well defined faults. These faults are associated with two distinct thrusting events of post-Permian to pre-Jurassic age, and of Late Jurassic age (Section 2.3); the bracketed age of the faulting includes the Upper Triassic. 2) The Vavenby, PS-75-185, and White Rock veins (Table 4.0, Fig. 4.0, Appendix A) are hosted by the Tshinakin Limestone. The occurrence of veins in the Cambrian Limestone with Triassic model age indicates the occurrence of an epigenetic Triassic pulse of mineralization. 3) The Silver King-Queen vein is part of a major vein system cutting rocks of unit EBG. Since this unit also hosts the above 70 stratiform deposits, it demonstrates the occurrence of different types of mineralization of equivalent age in similar rocks. 4.4.2 Multiple Interpretation of Lead isotope data Three possible interpretations are examined below in an attempt to reconcile the lead data with the observed geological features. These can be summarized as: 1) the mineralization is syngenetic and Cambrian, but deformation and/or metamorphism reset the lead isotopic system to an Upper Triassic model age; 2) all mineralization is epigenetic, Upper Triassic in age, and related to an epigenetic event; and 3) the mineralization is oogenetic with its host, and unit EBG, or part of it, is Triassic in age. Remobilization model Short term growth of radiogenic lead in the host rocks from time of original deposition (assumed to be Cambrian) to subsequent remobilization (in Jurassic time) coupled with an increase in temperature (capable of starting an efficient leaching and homogenizing process) might be responsible for the resetting of the lead system and for the apparent model age obtained for the stratiform deposits. This model requires production of radiogenic components from the uranium present in the rocks. Rock lithologies which have an upper crustal 71 protolith are enriched in uranium and therefore in situ growth of uranium daughters is to be expected within rocks derived from such source. The production of radiogenic uranium isotopes generates an increase in the 206pb/204pb ratio without substantially affecting the 207pb/204pb ratio. The radiogenic lead produced would be relatively easy to extract due to its loosely held position in defect structure within the mineral lattice. Post-depositional accumulation of radiogenic lead in unit EBG is possible, but would be limited by the generally intermediate to mafic nature of the volcanics. Furthermore the processes responsible for the leaching and re-transportation of metals would have to be effective over a long period of time to permit substantial extraction of metals and relative homogenization of lead isotopes (Gulson et a_l. , 1 983 ). Could intense deformation in the Early Jurassic and/or the Cretaceous have caused remobilization of galena lead isotope ? Certainly the present configuration of the sulphide masses within the deposits (see Fig. 4.1) suggests that remobilization deeply affected the ore and controlled their current distribution. Locally derived radiogenic lead may therefore have been added to the sulphides after their initial formation. In general very little is known about the effect of metamorphism 72 upon lead isotopic composition (Richards et a_l. , 1981) and even if remobilization can account for general behavior, several inconsistencies arise when details are considered. Radiogenic isotopes released from incompatible unfitted lattice sites during metamorphism might move far enough to allow them to become incorporated into surrounding mineral during remobilization (Doe and Hart, 1963). However only a high temperature regime or extensive hydrothermal activity would permit complete homogenization of the ore. Moreover, one would expect that any remobilization mechanism responsible for such homogenization would require recrystallization to such extent that all primary ore textures would have been obliterated (Le Hurray, 1982). Such an intense process did not occur as metamorphism only reached greenschist facies, and intense hydrothermal alteration observed elsewhere (Homestake deposit, Hoy and Goutier, 1986) is not observed in the deposits on the Adams Plateau. Thus low temperature alteration processes apparently at best would leave the deposits with an inhomogeneous and scattered isotopic composition (Cumming and Gudjurdis, 1973; Slawson, 1983), but analysis of several samples from the same deposit (Appendix B) reveals that the lead isotopic composition of the deposits do not exhibit such variation (section 3.3.2). Alternatively galena lead isotope evolved in the Jurassic from 73 Cambrian source rocks with variable uranium content fall along a straight line--not close to a point as in cluster 2. Comparative evidence between major deposits also negates the hypothesis that remobilization processes caused the Triassic model age obtained for the stratiform deposits. It seems reasonable to assume that if a Mesozoic re-homogenization of the lead yielded the Triassic model age assigned to those deposits hosted by the Cambrian unit EBG, it would also have affected the age of the other deposits hosted by pre-Mesozoic units in the Eagle Bay Formation. The Homestake and Rea Gold deposits should therefore also have had their isotopic composition adjusted by the metamorphic event. This is not the case since their model age is Devonian and concordant with the age of the surrounding rocks. Furthermore the lower galena and lead content of Rea Gold and Homestake deposits should have made them more susceptible to resetting since small additions of metamorphic lead would be more easily discernable from the isotopic composition of deposits containing low amounts of lead—especially when a relatively short time interval separates deposition and metamorphism. Consequently the Triassic model age obtained for the stratiform deposits hosted by unit EBG is probably not an effect of the Early Jurassic deformational and metamorphic event. 74 Nevertheless this event, did control their spatial distribution. Epigenetic, Upper Triassic model An alternative interpretation for the Triassic model age is that all the deposits with lead composition plotting in cluster 2 are epigenetic veins, or replacement lodes emplaced in older units during an Upper Triassic event. If this is the case the sulphides in the stratiform deposits hosted by the Cambrian unit EBG would have been deposited in favorable stratigraphic horizons from solutions that leached and extracted lead from the surrounding volcanic and sedimentary rocks. Recognition of a magmatic and/or mineralizing event affecting the area in Triassic time would be significant because it might indicate a period of active hydrothermal circulation that supplied radiogenic lead to the rocks of unit EBG just before Jurassic remobilization. No direct evidence of such a major event has been identified in the Adams Plateau-Clearwater area. However the vein deposits which cut the Cambrian Tshinakin Limestone and whose lead isotopic composition fall in cluster 2 are examples of epigenetic mineralization of Triassic age. The association of the sulphide rich horizons with particular stratigraphic levels, and the1 relationship between the ore and the surrounding rocks suggests strongly that the ore masses were originally controlled by the stratigraphy. The association of the sulphide horizons with chemical sediments indicates that they were 75 probably deposited contemporanously with their host unit (EBG) even if clearly remobilized later. Triassic cogenetic deposits If the mineralization at the Lucky Coon, Mosquito King and Spar deposits is cogenetic with the host rocks, and the lead model age is accommodated, then unit EBG, or part of it, must be Triassic. Unit EBG, fault bounded on both sides by other units of the Eagle Bay Formation, consists mainly of massive fragmental greenschist of volcanic affinities associated with an heterogeneous meta-sedimentary succession containing Tshinakin Limestone, the major marker of the Eagle Bay Formation. A correlated limestone unit in the Vavenby area contains Archaeocyathids of Early Cambrian age (Norford in Schiarizza, 1986), which have been used to infer a Cambrian age for the entire unit EBG. The Tshinakin Limestone is immediately underlain and overlain by similar sequences of greenschists. Locally the limestone abruptly lenses out; these terminations reflect original margins of the carbonate bank according to Preto et al_. ( 1980). However, despite the fact that this package was mapped as a single unit representing a continuous succession, alternative interpretation are possible given the structural and stratigraphic complexities of the Eagle Bay 76 Formation. It is proposed here that the southern part of unit EBG, depicted in Fig. 4.0 as unit T-EBG, is lithologically distinct from the northern part, and represent an additional thrust slice within the Eagle Bay Formation with a bounding thrust fault on the southern side and near the base of the Tshinakin Limestone. This thrust if present would separate the limestone and the greenschist volcanic rocks to the north from the meta-sedimentary sequence to the south. As presently mapped by Schiarizza and Preto (1984), the meta-sedimentary succession, containing both the folded conglomeratic and the phyllitic quartzite member (sub-units EBGcg and EBGq), occurs only on the southern side of the Tshinakin Limestone. Furthermore, the sub-unit EBGp seems restricted to the area north of the limestone. Although the Tshinakin Limestone is interbedded with greenschist in several places, it is never in direct contact with the metasediments. Even though the metasedimentary succession appears to be in stratigraphic contact, and locally is interdigitated with greenschist, the contact relationships have been obscured by folding. Thus the apparent contact between some of these units could be structural rather than stratigraphic (i.e. deformed and transposed contact). The division between units EBG and T-EBG also is supported 77 by marked differences in deformational intensity and style between the Tshinakin Limestone the greenschist volcanics, and the meta-sedimentary sequence. Gentle warping of the Tshinakin limestone contrast with the tight Nikwikwaia Lake synform, which was formed by the Colombian Orogeny, and which repeats the phyllitic quartzitic beds (sub-unit EBGq, Fig. 4.0). Older structures within unit T-EBG have not been identified and Devonian orthogneiss has not been mapped. Therefore the T-EBG part of the unit EBG does not contain any recognizable pre-Triassic elements. Implications of the presence of a Triassic unit within the Eagle Bay Formation are numerous. Certainly more detailed mapping and better structural and stratigraphic understanding are required to resolve whether or not two thrust faulted units (EBG and T-EBG) exist within the presently defined thrust slice EBG (Fig. 4.0). Contact relationships between the Eagle Bay Formation and the Sicamous Formation (exposed on the shores of Shuswap Lake, Fig. 2.0), as well as the age of the Sicamous Formation, are further constraints on the Upper Triassic age for unit T-EBG in the Eagle Bay Formation--this is elaborated on below. The Sicamous Formation until recently was considered Upper Triassic and viewed as a facies equivalent of rocks of the 78 Slocan assemblage, but there is no direct paleontological evidence to support this correlation (Okulitch, 1979). The contact between the Sicamous and the Eagle Bay Formation therefore was assumed to be a thrust fault which juxtaposed Devono-Mississippian rocks (unit EBA) on Upper Triassic rocks of the Sicamous Formation (Okulitch, 1979). However, recent mapping and drill core from the upper contact between the Sicamous and the Eagle Bay Formation in the Blind Bay area (Daughtry in. Preto and Schiarizza, 1985) supports a gradual transition between a limestone member of the Sicamous Formation and a chloritic green calcareous schist of the Eagle Bay Formation. This conformable contact relationship between these two formations has been interpreted in two different ways: 1. The Sicamous Formation underlies Devono-Mississippian unit EBA of the Eagle Bay Formation and is therefore older (i.e. Cambro-Ordovician) than unit EBA. In this case some limestone members of the Sicamous Formation could be correlative with the Index Formation of the Lardeau Group in the Kootenay Arc (Okulitch, pers. comm., 1986). 2. The contact between the Sicamous and the Eagle Bay Formation is gradual, even though not necessarily conformable, and inverted by a synformal structure overturned to the south (Daughtry, pers. comm., 1986). The Sicamous then could be Upper Triassic and part of it could be equivalent to rocks of the Slocan Group or to some black shale of the Nicola Group. These 79 shales, which may represent a deeper depositional facies of the Sicamous Formation form a more or less continuous band down to the Vernon area where they contains conodonts of Norian age (Daughtry, pers. comm., 1986; Okulitch, 1979). However, because direct paleontological evidence is lacking near Adams Lake, and structural and stratigraphic relationships ambiguous, neither of the two interpretations above can be unequivocally favored or ruled out. Imbrication of Triassic rock sequences within a succession with peri-eratonic affinities has been documented by Ross et al. (1985) from the Crooked Lake area--100km east of Williams Lake. In this area a Triassic sequence of black phyllites, correlated to the Quesnellia terrane, were mechanically imbricated within the Snowshoe Group, which is part of the Barkerville Terrane. A similar type of imbrication could be possible within the Eagle Bay Formation. However, the lead isotopic composition of the deposits hosted by unit EBG are unlike those hosted elsewhere by Quesnellia rocks (and therefore any Nicola Group related rocks), which have lead isotopic composition that plot below the shale curve (Andrew, 1982) rather than in the position of cluster 2. Correlation of unit T-EBG with a Slocan type assemblage would be better supported by lead isotopic evidence since at least part of the Slocan Group lead was probably derived from cratonic rocks (D. Gosh, in Logan 1985). 80 4.4.3 Summary Although model ages for stratiform deposits with lead isotopic composition enclosed by cluster 2 is similar to, or close to, the orogenic and metamorphic Early Jurassic Colombian Orogeny, it is unlikely that the lead isotope composition of the stratiform sulphide ores from the Adams Plateau (hosted by the unit EBG) was affected by metamorphism to the point of complete resetting. The Triassic model age for the stratiform deposits in cluster 2 can be interpreted as follow: 1) the mineralization is of replacement type and related to a Triassic event, in which case cluster 2 can be used to fingerprint that event, or 2) the mineralization is cogenetic with unit EBG and, a structural subdivision of the unit EBG into two separate units of Cambrian and Triassic age is required. Until the origin of these stratiform deposits is more clearly defined or the suggestion that a thrust exists within the unit EBG is tested in the field, these are equally valid. 4.5 LEAD DATA BETWEEN CLUSTER 2 & 3 Model ages for deposits with lead isotopic compositions that plot between cluster 2 and 3 are not interpretable. The random distribution of some of these data probably reflects an highly radiogenic component generated by proximal uranium and thorium mineralization (i.e. Rexspar deposit Table 81 4.0, Fig. 4.0, Appendix A). The highly anomalous lead isotopic composition in galena from the Rexspar deposits is associated directly with the high uranium and thorium concentration found there. This deposit, hosted by a tuffaceous trachytic to andesitic member of unit EBA, contains two mineralized zones: an uranium bearing zone composed of abundant pyrite associated with fluorphlogopite, and a fluorite zone containing traces of galena and molybdenite but mainly barren of uranium and thorium. A K-Ar date of 236 +_ 8Ma (Preto, 1977) obtained from fluorphlogopite at Rexspar ruled out the Cretaceous Baldy batholith as a potential source for the mineralization. Preto (1977) therefore proposed that the mineralization was 'syngenetic' with the host rocks. The 207pb/204pb value for the galena at Rexspar (Table 3.3) is much greater than the average value for the other deposits hosted by the Eagle Bay Formation; it consequently plots well above the remodeled curve in Figure 3.3. The 206pb/204pb and 208pb/204pb values (Table 3.3) are not as extreme and fall within the expected range for the deposit of the Eagle Bay Formation, however, since Rexspar is likely oogenetic with the Devono-Mississippian sequence, these values should be lower and within the range of values delimited by the deposits in cluster 1. 82 The Foghorn, Rouge, Birch Island and Tindal deposits (Table 4.0, Fig. 4.0, Appendix A) are veins in an area dominated by the same felsic volcanic rocks (Devonian unit EBA--trachytic member) that host the Rexspar deposit. The lead data for these epigenetic veins fall to the right of cluster 2. The high lead ratios reflect incorporation in the mineralizing solutions of a highly radiogenic component generated by the in situ decay of uranium and thorium in the surrounding rocks, most of which was probably generated and released from uranium and thorium rich minerals like those in the Rexspar deposit. Model age determinations for these veins is ambiguous and involves consideration of a short term growth of radiogenic lead from a locally uranium and thorium rich environment. Consequently the remodeled curve cannot be used directly to estimate the model age for these veins. Because an increase in radiogenic lead would generate model ages younger than the mineralization event and the lead isotopic composition is less than that associated with the mineralization caused by the Baldy batholith (cluster 3), these veins more likely are related to the Jurassic deformation associated with the Colombian orogeny. However new older dates from the Raft batholith (Jung, pers. comm., 1986) may link the formation of these veins to its intrusion. The Fluke deposit (Table 4.0, Fig. 4.0, Appendix A) consists of discontinuous sulphide rich layers that are 83 semi-conformable with the shistosity and compositional layering of host unit EBG. The sulphide zones associated with a carbonate-rich schist member therefore appear to be a true replacement. Proximity of the deposit to granitic intrusions may indicate that the mineralization was concentrated in the limy horizons by lateral circulation of fluids emanating from the intrusion. The lead plots (Fig 3.3 to 3.5) for the Fluke deposit lie between cluster 2 and 3, but it is closest to cluster 3. The slightly lower lead isotopic composition, compared to those from veins of cluster 3, is probably related to a larger component of wallrock lead. 4.6 CLUSTER 3: CRETACEOUS VEINS The Leemac vein, two unclassified small sized occurrences, and the stratiform Beca deposit plot in cluster 3 (Table 4.0, Fig.4.0, Appendix A). The Leemac vein, in the Cretaceous Baldy batholith has a lead isotopic composition coincident with the Cretaceous isochron on the remodeled curve (cluster 3; Fig. 3.3 to 3.5) This relationship suggests a genetic link between the intrusion and the mineralization. The fact that the lead isotopic composition of the vein in the batholith plots on the remodeled curve also indicates that the lead of the batholith has evolved 84 from a similar protolith source as the surrounding rocks of the Eagle Bay Formation. Specifically, the lead isotopic composition reflects the direct influence of an upper crustal basement in the origin and generation of the intrusion; this supports the interpretation that the roots of the batholith are in the adjacent Shuswap Complex (Okulitch, 1979; see section 2.4.4) . Cluster 3, therefore, is the fingerprint for Cretaceous deposits that are cogenetic with the intrusion of the batholith. Accordingly, two small mineralized siliceous zones carrying variable values of lead, zinc and silver, sampled in the vicinity of Lichen Mountain on the Adams Plateau (Red Mineral Claim 1 and 3, Table 4.0, Fig. 4.0, Appendix A) that were previously interpreted as syngenetic exhalative deposits, seems more appropriately related to a small granitic plug in the Scotch Creek area (Fig. 4.0) which is probably a satellite of the Baldy batholith. Four other showings around Lichen Mountain on Adams Plateau: Pet, Red mineral claim 2, Orell 5P and Silver King-A (Table 4.0, Fig. 4.0, Appendix A) yielded lead isotopic signatures that were distinctly different from the two Cretaceous showings by falling in cluster 2 instead of cluster 3. The spatial relationships between these unclassified 85 occurrences and the Spar and Mosquito King, coupled with their isotopic composition, indicates that they probably represent local accumulation of oogenetic mineralization similar to the other nearby stratiform deposits. The distinction between two different types of mineralization among these six mineralized occurrences is a good example of the applicability of the lead method for discriminating different ages and origin for otherwise similar looking deposits. The Sonja vein (Table 4.0, Fig. 4.0, Appendix A) cuts through the Devonian unit EBA near Clearwater. It occurs as a discontinuous silicified zone along the side of a major dyke from geological evidence, and lead data that plots in cluster 3, the mineralization on the Sonja property is epigenetic and Cretaceous. Another deposit with lead data plotting in cluster 3 is the Beca deposit (Table 4.0, Fig. 4.0, Appendix A). However, in all lead diagrams (Figs. 3.3 to 3.5) Beca plots furthest from the mean value of cluster 3. Interpretation regarding the geological setting of the Beca property is uncertain. The deposit has been classified as a syngenetic volcanogenic deposit (Preto et al., 1985; BCDM Assessement Report no. 7040) because it contains conformable sulphide rich horizons associated with pyritic cherty bands, and because it occurs within the same 86 Devonian felsic volcanic sequence as the Homestake and Rea Gold deposits (unit EBA). However the lead isotopic signature of the Beca deposit falls in cluster 3, and is markedly distinct from the lead from the Rea Gold, Homestake and Ford deposits. These isotope data indicate that the mineralization is epigenetic and Cretaceous rather than syngenetic and Devono-Mississippian. Zircons from Beca property (Fig. 4.0), yielded a discordant chord intercepting the Concordia curve at points corresponding to 399 and 100Ma (Preto, 1981). The Devonian date is interpreted as the time of crystallization for the volcanics. A subsequent Cretaceous event is advocated to account for lead loss and resulting zircon discordance. It is interesting to note that the Cretaceous age of this subsequent event corresponds to the model age of cluster 3. Therefore lead remobilization and homogenization of the lead in the Cretaceous might have occurred. The Cretaceous intrusion of the Baldy batholith offers greater potential for generation of circulating solutions than does the Jurassic event related to deformation and metamorphism. Nevertheless the same argument against the re-homogenization process (see section 4.2.2) applies here, as the lead isotopic composition of the deposits hosted by the same Devonian unit (the cogenetic deposits of cluster 1) has not been re-homogenized to a Cretaceous age. Unfortunately, the Beca deposit is not located closer than other deposits in the area to the batholith and this cannot be used to justify why its lead 87 composition could have been more significantly affected by the intrusion. The mineralization might be an epigenetic replacement. 4.7 LEAD DATA BEYOND CLUSTER 3 Mineralization of the June vein is probably late and related to a Tertiary event since its lead data plots close to a Tertiary model age along the remodeled curve. The only uncertainty surrounding this interpretation is that, although it is based on three duplicate analysis from the same deposit, no analysis from any other deposit has a similar lead isotopic composition. Tertiary lamprophyre dykes are widespread in the map area and occur in close vicinity of the Mosquito King, Spar and Fluke deposits. The isotopic signature of lead, mineralization from cross-cutting structures, spatially related to these dykes, cannot be statistically distinguished from the lead from the massive sulphide zones (Appendix C). Consequently, the intrusion of these late dykes did not affect the overall lead isotopic composition of those deposits. If the Eocene thermal and deformational event did affected the Eagle Bay Formation, the paucity of lead of Tertiary composition is another argument against remobilization as a common process responsible for variations in the lead isotopic composition of galena. 88 4.8 SUMMARY The lead isotopic composition of deposits hosted by the Eagle Bay Formation indicates that three pulses of mineralization were responsible for sulphide concentration within the units of the Formation. The oldest mineralization identified in the Eagle Bay Formation is represented by cluster 1 with a model age of Devonian. This cluster characterized lead from polymetallic deposits which are cogenetic with felsic to intermediate volcanic rocks of Devono-Mississippian age. Therefore, cluster 1 can be used to fingerprint such type of mineralization occurring in the Eagle Bay Formation. The second period of mineralization is Upper Triassic, and is represented by cluster 2. This cluster contains almost half of the deposits — mainly veins and stratiform deposits — sampled for this study. The vein deposits indicate that there was a pulse of mineralization occurring during that period that is mainly characterized by infilling of suitable structures. The stratiform deposits within this cluster may be either replacement or cogenetic in origin. If cogenetic, the part of the unit which host these deposits must be Upper Triassic rather than Cambrian as currently mapped (Schiarizza and Preto, 1984) since ressetting of the lead isotopic composition by 89 metamorphism cannot account for the Triassic model age of these deposits. Based upon the upper crustal signature of the Eagle Bay Formation, the Upper Triassic unit would probably be equivalent to rocks of the Slocan Group. Some deposits, which have their lead isotopic composition falling outside of and to the right of cluster 2, are hosted by an uranium rich member of the formation which is probably the cause for the radiogenic signature. Finally, the last major period of mineralization recorded by the lead isotope data from this study is mid-Cretaceous and represented by cluster 3. This event is related to the intrusion of the Baldy batholith. Lead isotopic compositions, of Tertiary model age, are markedly absent and indicate that even if the Formation was affected by a thermal Tertiary event no important mineralizing processes were associated with it. 90 5. CONCLUSIONS This lead isotopic study of 37 mineralized occurrences hosted by the Eagle Bay Formation in the Adams Plateau-Clearwater area allowed evaluation of the applicability of the 'shale' curve of Godwin and Sinclair (1981) to deposits in the Adams Plateau-Clearwater area. The lead isotopic composition of these deposits plot generally along the 'shale' curve indicating that the model is substantially correct. This shows that the lead source is upper crustal in origin, was derived from autochthonous portion of the Canadian Cordillera, and involved Precambrian basement under the Eagle Bay Formation. It also reinforced the correlation of the Eagle Bay Formation with other peri-cratonic successions, particularly in the Kootenay Arc and Barkerville Terranes. The 'shale' curve was inadequate for precise model age determination from the galena-lead data from the Eagle Bay Formation. Better coincidence of the data was obtained with a remodeled curve using 2.OGa as departure time from the average growth curve of Stacey and Kramers (1975). This curve has the same u value as the 'shale' curve, but has a lower w value of 45.35. The 2.OGa departure time approximates the time of formation of the Cordilleran crust, and was chosen because it corresponds to ages determined by others for the Shuswap 91 Metamorphic Complex (c|_. Duncan, 1982). The lead isotopic composition of galena from the deposits in the Eagle Bay Formation plot in three distinct clusters along the remodeled curve. The Devonian cluster 1 encloses lead isotopic compositions which characterize oogenetic mineralization associated with Devono-Mississippian volcanic rocks. This cluster therefore can be used to fingerprint polymetallic volcanogenic deposits hosted by the Eagle Bay Formation. Similarly, the mid-Cretaceous cluster 3 can be used to distinguish vein deposits related to the intrusion of the Baldy batholith and of its satellites. The Upper Triassic cluster 2 contains deposits of various types so that a unique interpretation cannot apply to all of the deposits represented. Some of them are epigenetic veins, and their formation might be related to juxtaposition of the Fennell Formation with the Eagle Bay Formation, or to a yet undefined event which affected the area in the Triassic. The stratiform deposits on the Adams Plateau, which also plot in that cluster, also may have formed during such event, however, if the mineralization in these deposits is oogenetic with the Cambrian unit EBG, the interpretation of the lead model age imply stratigraphic reconsideration and the unit EBG should be subdivided into two distinct members of Cambrian (unit EBG), and of Upper Triassic (unit T-EBG) age to accommodate the data. 92 The galena lead isotope study developed here further illustrates the applicability of the common lead method in categorizing mineral deposits within a given region. Recognition of a lead isotopic field that 'fingerprints' the deposits hosted by the Eagle Bay Formation has important implications for exploration programs by providing a curve from which the age and general genesis of any new mineralized discoveries in the Adams Plateau-Clearwater area can be assessed. 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Volcanic massive sulphide deposits and their host rocks: A review and explanation, in Handbook on strata-bound and stratiform ore deposits, K.H. Wolf ed. Elsevier Amsterdam, Vol. 2, pp. 21-50. STACEY, J.S.,and KRAMERS, J.D. 1975. Approximation of terres trial lead isotope evolution by a two stage model. Earth and Planetary Sciences Letters, 26, pp. 207-221. STACEY, J.S.,DELEVAUX, M.H.,and ULRICH, T.J. 1969. Some triple filament lead isotope ratio measurements and an absolute growth curve for single-stage leads. Earth and Planetary Science Letters, 6, pp. 15-25. STANTON,R.L.,and RUSSELL, R.D. 19 59. Anomaleous leads and the emplacement of lead sulphide ores. Economic Geology, 54, pp. 588-607. STEIGER, R.W.,and JAGER, E. 1977. Subcommission on geochronology convention on the use of decay constants in geo and cosmochronology. Earth and Planetary Science Letters, 36, p. 359. STRUIK, L.C. 1986. Imbricated terranes of the Cariboo gold belt with correlations and implications for tectonics in southern British Columbia. Canadian Journal of Earth Sciences, Vol. 23, 1 02 pp. 1 047-1061 . TATSUMOTO, M.,KNIGHT, J.R.,and ALLEGRE C.J. 1973. Time differrences in the formation of meteorites as determined from the ratio of lead 207 to lead 206. Science, 180, p. 1279. UGLOW, W.L. 1922. Geology of the north Thompson Valley map-area, British Columbia. Geological Survey of Canada, Summary Report 1921, Part A. pp. 72-106. WANLESS, R.K, STEVENS,R.D.,LACHANCE,G.R.,and RIMSAITE, J.Y.H. 1966. Age determinations and geological studies: K-Ar isotopic ages, Report 5. Geological Survey of Canada, paper 65-17, 101 p. WATSON, P.H. 1981. Genesis and zoning of silver-gold veins in the Beaverdell area, south-central British Columbia. Unpublished M.Sc. thesis University of British Columbia, 156 p. WHEELER, J.O,and GABRIESLE, H. 1972. The Cordilleran structural provinces. In R.A. Price and R.J.W. Douglas ed. Variations in tectonic styles in Canada. Geological Association of Canada Special paper 11, pp. 1-18. YORK, D. 1969. Least squares fitting of a straight line with correlated errors. Earth and Planetary Science Letters, 5, pp. 320-324. ZARTMAN, R.E. 1974. Lead isotopic provinces in the Cordillera of the western United States and their geologic significance. Economic Geology, 69, pp. 792-805. 103 APPENDIX A ADAMS PLATEAU-CLEARWATER AREA DEPOSIT DESCRIPTIONS The following descriptions constitute a brief summary of literature review on the deposits of the Adams Plateau-Clearwater area augmented by observations, and in some case detailed work, made by the writer in the summers 1984 and 1985. The compilation map of Schiarizza et a_l.(1984) has been used to assign lithologic names to host units of the deposits. The abbreviated names for these units (and subunits) appear in parentheses. Descriptions of these units and subunits appear on Schiarizza's map (op. cit.) and in BCDM fieldwork papers from Schiarizza and/or Preto on the Adams Plateau Clearwater area between 1978 and 1986. Table A.1: Mineral deposits in the Adams Plateau-Clearwater Area Deposit Name Deposit Type ADAMS PLATEAU AREA Beca Lucky Coon Spar Mosquito king BC Zn 1 Crowfoot Mtn Ford property Silver king Silver king-Queen Pet Red Mineral Claims Stratabound Stratiform/Remobilized Stratiform/Remobilized Stratiform/Remobilized Disseminations Replacement Volcanogenic Vein Vein Vein Vein JOHNSON LAKE AREA Agate Bay Twin Mountain Art Homestake Rea Gold Mineralized pods Vein Vein Volcanogenic/polymetal. Volcanogenic/polymetal. BARRIERE LAKES AREA Birk Creek Showings Enargite Fortuna White Rock June/Kajun Broken Ridge Leemac Stratif orm/Volcanogenic Vein Vein Vein Vein Disseminations Vein VAVENBY-CLEARUATER AREA Chu-Chua Foghorn Rexspar Mt McClennan Vavenby Ps-75-185 Sonja Birch Island Tindal Volcanogenic/cyprus Vein Volcanogenic/Uranion Replacement Vein Vein Vein Vein Vein 1 05 ADAMS PLATEAU AREA: BECA: Also known as: Quest Group, Lucky Strike, Rhode Island, Lakeview-Joe, Tom Minfile number: 082M-054,055 Mineral Inventory number: 82M4-PB4 Map number: 007; Lat. 51.050N long. 119.710W Production, as listed in Minfile: 5 tonnes of ore (1926): 31 g Au 2,395 g Ag 1 , 496 kg Pb Location: The Beca property on the shore of Adams Lake, due east of Squaam Bay is directly accessible by boat. A switchback road dropping 1,800m from Nikwikwia lake on the western edge of the plateau, also leads to the property. Host rock: The area consists of a repetitive succession of andesitic to rhyolitic volcanic rocks and associated quartzitic and argillaceous meta-sedimentary rocks (EBA). The rocks are metamorphosed to greenschist facies and show a high degree of schistosity that strikes about N85W and dips 25 to 45 degrees north. The more felsic phase has clearly invaded andesitic rocks which are preserved as xenoliths in the felsic rocks. Small granitic intrusions immediatly south of the property boundary produced a thermal metamorphic aureole that overprints regional low grade metamorphism. The chemical similarity between the granitic rocks and the felsic volcanic rocks may indicate a comagmatic relationship between these two rock types. Mineralization: The two mineralized areas found on the property are associated with pyritic cherty bands. The sulphides occur as fine grained conformable lenses containing porphyroblasts of arsenopyrite and local layers of sphalerite. Locally, altered rhyolite is laced with narrow (1 to 25mm), closely spaced quartz veins which are sporadically mineralized with galena and more rarely with sphalerite. Sample description: Samples are a fine grained mixture of pyrite, chalcopyrite, galena, and sphalerite associated with calcite and minor quartz. The samples were collected from massive sulphide rich layers within the schist beside the old adits near the lake shore. References: BCDM ASS RPT 6680, 7040. BCDM GEM 1970 p. 314. 106 LUCKY COON: Also known as Mc Gillivary group, Elsie, Speedwell, King Tut. Minfile number: 082M-012 to 015 Mineral Inventory number: 82M4-PB4 to PB7 Map number: 018; Lat. 51.070N Long. 119.600W Grades, as listed in Minfile: Total deposit (indicated 1972): 68,040 tonnes, cut off used: 296.0 g/t Ag 7.1 % Pb 4.8 % Zn Production, as listed in Minfile : from Lucky Coon, 496 tonnes of ore (1976-1977): 274 g Au 228,669 kg Ag 62,03 3 kg Pb 41,367 kg Zn 114 kg Cd : from East Lehmi, 30 tonnes of ore (1956): 31 g Au 35,146 g Ag 8,330 kg Pb 2,393 kg Zn Location: Lucky Coon is on the Adams Plateau at an elevation of 1,830m. The property is accessible by logging roads either from Scotch Creek across the plateau to the old open pit, or from the south end of Adams Lake to within 2km of the property. Host Rock: The mineralization is associated with black and dark brown siliceous and graphitic phyllite, and with phyllitic limestone (EBG). Wide bands of fine-grained sericitized quartzite, interlayered with smaller chlorite-calcite rich bands occur close to sulphide-rich horizons. These metasedimentary units are folded by the Nikwikwaia Lake synform and are surrounded by greenschists that are derived from mafic flows and tuffs. Quartz feldspar porphyry dykes crosscut part of the southern limb of the synform and show evidence of subsequent folding. Basic dykes are also present but are not well exposed. Structure: Isoclinal and asymmetric folds, especially well exposed in the northern pit, demonstrate the prominent role of the structure in controlling the distribution of the sulphides. In such folds, sulphide beds 25cm thick on the limbs reach a thickness of 45cm in the hinge zone. Original texture in the sulphide horizons has been obliterated by the deformation. 107 Mineralization: Silver, lead and zinc sulphides are generally restricted to a specific stratigraphic horizon (siliceous and graphitic phyllites, phyllitic limestones) that is generally continuous along strike for 2000m. In detail, however, the sulphide zones are discontinuous due to remobilization and disruption during folding (Dickie, 1985). The sulphides are fine-grained and occur as bands, from 15cm to 1m wide separated by 30 to 90cm of siliceous phyllite, or as veins in sericitic schists. The mineralization consists of arsenopyrite, pyrite, sphalerite, galena, argentite and a little tetrahedrite. The ratio of the different sulphides throughout the deposit is variable; the arsenopyrite content varies from 1 to 25% (commonly diamond shaped grains are locally extensively replaced by sphalerite and galena). The pyrite can comprise as much as 75% of the sulphide zone but is often embayed and/or replaced by sphalerite and galena; however, euhedral unbroken pyrite crystals (probably formed by recrystallization) do occur. The sphalerite and galena are intimately associated. Embayed islands of sphalerite with cusp-shape borders are common. Sample description:Massive sulph the sericitic schist unit in the consist of small blebs of galena calcite in a fine-grained matrix and pyrite. ide samples were collected from old pit number 1. The samples associated with quartz and composed mainly of sphalerite References: BCDM ASS. RPT. 11,521. BCDM MMAR 1936 pp. D41-D43. BCDM MMAR 1930 pp. A184-A186. DICKIE, G.J. 1985. 108 SPAR: Also known as: Ex 1, Bel Minfile number: 082M-017, 018 Mineral Inventory number: 82M4-PB2, PB5 to PB7 Map number: 027; Lat. 51.060N Long. 119.540W Production, as listed in Minfile: 274 tonnes of ore, (1952, 1953, 1955, 1976): 435 g Au 249,383 g Ag 4,953,594 kg Pb 891,766 kg Zn 291 kg Cu Location: The Spar deposit is on the southeastern edge of the Adams Plateau less than 2km west of the Mosquito King deposit. It is accessible by the logging roads parallel to Scotch Creek. Host Rock: Mineralization is hosted by folded limy phyllites associated with minor sericite quarztites, limestone and chloritic meta-volcanics (EBGs). The sulphide horizons and the host rocks are enclosed within the same intermediate to mafic volcanic and volcaniclastic sequences encountered at the Mosquito King and Lucky Coon deposits. Mineralization is also cut by small fine-grained diorite and granite porphyry dykes. Structure: The rocks in the vicinity of the deposit are strongly foliated, have a general east-west strike, and dip gently northward. Strata show dragfolding and crenulation cleavage; fold axes strike S600w with low plunge (the crest plunges 100sw). Two sets of fractures cut the rocks: one dipping steeply north-south and the other dipping more shallowly dipping east-west. The north- south set seems to have acted as a channel way for mineralizing solution since fairly massive fine-grained sphalerite is found in the folded zones directly above such fractures (Dickie, 1985). The east-west set terminates abruptly some mineralized horizons and thus may be part of a late fracturing event. Mineralization: Stratiform sulphide masses occur as folded elongated bodies (extending over 400m). The mineralization distribution does not appear to be confined to only one layer. However the mineralization is apparently stratabound and was originally deposited within a siliceous unit. This unit has been folded and metamorphosed, resulting in the migration and concentration of the sulphide minerals along the crests of folds or crumpled zones in the enclosing sericitic sequence (Dickie, 1 985 ) . 109 The sulphide horizons are composed of massive layered galena bordered by a fringe zone of galena, sphalerite, pyrite, pyrrhotite and chalcopyrite. Minor amounts of tetrahedrite, arsenopyrite and argentite also occur. The bands of massive mineralization (40cm thick) are separated by sericitized argillite. Sample description: Samples were collected from the main old adits from which most of the minerals were extracted in the 1950's. Fine-grained galena is associated with sphalerite and pyrite in a quartz carbonate matrix. A vein containing abundant fluorite was also sampled. References: BCDM MMAR 1953 pp. 102-103. HAINSWORTH, W.G. 1973. Unpublished report on the Giant Metallic Mines. JAMES, D.H. 1949. 1 1 0 MOSQUITO KING: Also known as: Oro, King Tut, Garnet Minfile number: 082M-016, 140 Mineral Inventory number: 82M4-AG2, CU2 Map number: 025; Lat. 51.060N Long. 119.520W Reserves, as listed in Minfile 40,824 tonnes @ (Ind. 1981): 1.25 g/t Au 21.70 g/t Ag 10.0 % Pb 8.5 % Zn Production, as listed in Minfile 419 tonnes of ore (1972-73, 1976): 219 g Au 232,154 g Ag 22,721 kg Pb 18,328 kg Zn Location: The Mosquito King property is located at an approximate elevation of 1,750m on a ridge on the Adams Plateau. A logging road between Nikwikwain Gold Creek and Kwikoit Creek leads to the property. Host Rock: Sulphide lenses are enclosed within intensively silicified beds of argillites and quartz sericite rocks. These clastic rocks are part of a predominantly mafic volcanic succession (EBGs). These units have been metamorphosed to greenschist facies and contain abundant chlorite and sericite. Silicification and bleaching is ubiquitous in the limy argillites and in the quartzite, but not in the greenschist. The sequence is cut by andesite and hornblende porphyry dykes which are similar to those occurring on the Lucky Coon property. Structure: Folds on the property have a predominent east-west trend but axes striking north-south are not uncommon; drag-folding is ubiquitous in most exposures. Joints and small north striking faults seem to control, at least locally, the mineral distribution. Mineralization: At the main showing mineralization varies in thickness from 60cm to 3.5m (average 1.5m). It consists of several thin, closely spaced beds composed of black sphalerite, galena, pyrite, chalcopyrite and fine-grained pyrrhotite which are more or less concordant with the enclosing host. Lower in the succession, beds have been mineralized with iron sulphides (mainly pyrrhotite) and minor sphalerite. Pyrrhotite and pyrite rich lenses (up to 60cm wide) are extensive in the limy argillites. Disseminated pyrite also occurs along bedding planes and in fractures associated with silicified zones. Mineralized beds can be traced over 915m along a N700E strike 111 but they are not uniformly or continuously distributed. Veins of galena and sphalerite occur locally in the schists and in the limy beds. Magnetite and secondary copper minerals are locally abundant in the mafic volcanics. Minor mineralization also occurs associated with the porphyry dykes (James, 1949). Sample description: Well crystallized but deformed galena in a quartz and calcite matrix containing a minor amount of pyrite and sphalerite is characteristic of the main mineralization. The samples come from the main mineralized area of the deposit in the open old workings. Galena was also collected from cross-cutting veins near a dyke. References: BCDM ASS RPT 45, 7019. BCDM MMAR 1949 pp. A134-136. BCDM MMAR 1930 pp. A186-188. DICKIE, G.J. 1985. JAMES, D.H. 1949. 1 1 2 BC ZN 1: Also known as: Cu 1, Cu 5 Minfile number: 082M-138, 139 Mineral Inventory number: 82M4-CU1, ZN2 Map number: 022; Lat. 51.01 ON Long. 1 1 9.520W Grades, as listed in Minfile: Indicated: 148,000 tonnes Possible: 272,000 tonnes @ 0.19 % Cu Reserves: 326,000 tonnes @ 0.35 % Cu 38 G/t 6 % Pb 2.41 % Zn 0.19 % Cu 0.14 % Mo Location: This mineralized occurrence is about 5.5km south of the Mosquito King deposit near the locally named China Creek. It is accessible from one of the numerous logging roads on the Adams Plateau. Host Rock: Argillaceous phyllites are intercalated with limy and siliceous horizons interbedded with abundant greenstone derived from mafic volcanics and volcanoclastics (EBG). The sequence is intruded by a series of minor diabasic dykes and sills. One dyke sampled consists of hornblende, quartz, andradite and minor clinopyroxene, clinozoisite, chlorite and plagioclase. Schistosity of the host rock strikes east- northeast and dips moderately to the northwest. Mineralization: A stratiform zone contains disseminated sphalerite and galena with minor pyrrhotite and locally abundant magnetite. Some zones of high iron content yield good Cu and Au values. One zone may be continous for over 510m; it has a width of as much as 1.65m. Sample description: Fine-grained disseminated in highly chloritic mineralization. sphalerite and minor galena schist is characteristic of the References: BCDM ASS RPT 5132 BCDM GEM 1978, p. E101. BCDM GEM 1974, p. 95. 11 3 CROWFOOT MOUNTAIN: Also known as: Fluke, Saul Minfile number: 082M-104, 105 Map number: 032; Lat. 51.060N Long. 119.250W Grade: composite sample, gross average: 0.34 g/t Au (From ASS.RPT.) 170.0 g/t Ag 0.1 % Cu 5.0 % Pb 8.0 % Zn 0.18 % Sn Location: The Fluke claims on Crowfoot Mountain are approximatly 16km north of Magma Bay on the north shore of Shuswap Lake, and are accessible by forestry roads. Host Rock: Mineralization is hosted by phyllitic marble and altered limestone associated with phyllite, quartzite and greenstone similar to those found in the other deposits on the Plateau (EBG). These rocks are strongly foliated and lineated. The area is intruded by an enormous number of dykes, sills and small irregular bodies of granitic and diabasic rocks. Silicification is extensive in the vicinity of the sulphide rich zones. Structure: Intense drag folding, disruption of limy horizons and greenschist facies in the meta-volcanic rocks are indications that the area has the same deformational characteristics as the rest of the Adams Plateau. Structural details of the deformation in the vicinity of the deposit are not known. Mineralization: Mineralization has been described as sulphide replacement in bands of limestone and marble. On a large scale the sulphides are confined to horizons within the limestone, but the distribution of the sulphides is highly erratic. Galena and sphalerite occur in pods as well as in disseminations throughout the rock. Sulphides are also found in veins cutting chloritic schist. These veins strike in the same direction as the main foliation (striking N400N and dipping moderately northwestward) but dip in the opposite direction. Veins are unevenly mineralized with galena, pyrite, sphalerite and chalcopyrite. Sample description: Blebs of calcite, pyrite, galena and sphalerite plus minor quartz in laminated but contorted and discontinuous limestone lenses were sampled on the property. Vein mineralization close to a lamprophyre dyke was also sampled. References: BCDM ASS RPT 609, 3821, 4031, 6230, 6857. 1 1 4 FORD PROPERTY: Map number: 038; Lat. 51.000N Long. 119.600w Location: The Ford property is centred near the head of Woolford Creek. Access is facilitated by a network of logging roads. Host Rock: The main rock types in the area are sericite quartz phyllite and sericite felspar quartz phyllite containing abundant medium to fine-grained angular clasts (unit EBA). It is likely that these rocks are altered intermediate to felsic tuffs. The units have a fragmental and porphyroblastic appearance due to metamorphism. A graphitic limestone containing unfoliated white quartz sandstone also occurs in the area. All these rocks have undergone greenschist facies regional metamorphism and locally contain abundant chlorite. Post metamorphic intrusion of diorite and lamprophyre dykes, cut through the rocks of the property. Structure: The contact between the different units appear in several places to be planar but not continous along strike. The well developed foliation, parallel to sub-parallel with the lithologies, is gently warped; this probably indicates the presence of a large open fold plunging to the north across the property. Steeply dipping north-northeasterly trending faults truncate and offset some of the units. Mineralization: The property is the probable host of stratiform massive sulphide deposits as four zones contain mineralization: 1 ) a series of five lenses (5 to 20cm thick) of massive sulphide containing mainly pyrrhotite and small amounts of sphalerite and chalcopyrite associated with abundant silica (the mineralized lenses are conformable to the foliation), 2) a series of narrow layers (1 to 3cm thick) of massive pyrite within a chloritic quartz phyllite unit, 3) pyrite rich meta-rhyolite that may be a metamorphic equivalent of a quartz-pyrite exhalative unit, and 4) a narrow (1 to 3cm thick) silver rich, galena-chalcopyrite-quartz-calcite vein cutting through sericitic chlorite quartz schist. An alteration zone consisting of secondary quartz, muscovite, biotite and actinolite is present in the lower part of the section. This zone has characteristics similar to a thermal metamorphic aureole and is interpreted by Robinson (1986) to have been generated by a intrusive at depth. Sample Description: Samples collected consist of fine grained massive sulphides containing galena associated with abundant pyrrhotite and minor sphalerite. Reference ROBINSON, C. 1986. Geology of the Ford property Adams Plateau, south central British Columbia. Unpublished BSc Thesis, University of British Columbia. 1 1 5 SILVER KING-A: Minfile number: 082M-129 Mineral Inventory number: 82M4-AG3 Map number: 036; Lat. 50.950N Long. 119.480W Location: This small showing is less than 500m north of the Spar deposit along the logging road leading to the Lucky Coon deposit. Description: Mineralization occurs in altered limestone in close proximity to brecciated rock containing fragments of argillite (fresh and partially replaced) cemented by sugary quartz. The sulphides do not occur directly in the breccia and seem restricted to the surrounding limestone. Zones rich in calcite, fluorite and porcelaneous quartz occur adjacent to the sulphides. Sample description: Small seams of fine grained galena mixed with coarser sphalerite grains in a calcitic gangue are characteristic of the sampled specimens. Reference: BCDM GEM 1971, p. 436. SILVER KING-SILVER QUEEN: Also known as: King James Minfile number: 082L-NW044 Map number: 045; Lat. 50.950N Long. 119.480w Location: A large exposure of this vein occurs on the east side of Scotch Creek 8km north of the post office of Scotch Creek along the logging road that follows the power line. Description: Mineralization occurs in a vein system which is about 30m wide and strikes northwesterly through the chloritic schist and calcareous phyllite of unit EBG. The vein contains pockets of coarse grained galena and sphalerite in quartz-calcite gangue. References: BCDM GEM 1977, p. E85. BCDM GEM 1975, p. E55. 11 6 PET: Minfile number: 082M-143 Map number: 026; Lat. 51.050N Long. 119.530W Location: This showing is exposed in a trench, about 1km south of the main workings of the Spar deposit. Description: Small amounts of galena and sphalerite (marmate) occurs as dissemination in chloritic schist. Sample description: No description is available. Data used came from analyses by the GSC (GSC number: G79PE). Refernces: BCDM ASS RPT 5919. BCDM GEM 1976, p. E59. RED MINERAL CLAIMS: Also known as: Fox, Deer, Fir, Pat, Joe Minfile number:82M-154 Map numbers: 033 Lat. 51.080N Long. 119.380W 034 51.100N 119.380W 035 51.070N 119.380w 037 51.050N 119.540w Location: The mineralized showings are clustered around Lichen Mountain, located northwest of the Mosquito King deposit, about 3km east-southeast of the junction of Cross and Kwikoit Creeks. Host Rock: The mineralization is mostly found in carbonate layers associated with argillites and meta-volcanics (EBG). Locally manganese rich bands occur near the mineralized zones. The rocks are folded and metamorphosed, as are their equivalents elsewhere on the Adams Plateau. The main foliation in the rocks strikes northeast and dips north. Mineralization: These mineral occurrences are of small size, outcrop on surface, and do not have any known underground extent. Quartz veins containing argentiferous galena cut through both volcanic rocks and limestone. The mineralization has been described as conformable lenses of cylindrical shape; but this geometry could not be confirmed in the field. Sample description: All the collected samples contain coarse galena in quartz gangue associated with variable amounts of sphalerite and pyrite. The galena from the occurrence number 033, above, clearly shows evidence of deformation. References: BCDM Open File. BCDM Exploration in BC 1979 11 7 JOHNSON LAKE AREA: AGATE BAY: Also known as: Try Me, Rankin Group, Karen, Joe Minfile number: 082M-053 Map number: 006; Lat. 51.08ON Long. 119.75oW Location: The showing is exposed at the shore line near the northern end of Squaam Bay. Host Rock: Fine-grained quartz-sericite schists are interbedded with chloritic schist (EBAa). These greenstones are highly altered and contain swells of carbonates (calcite and ankerite). This unit, mapped as part of the felsic package of the Eagle Bay Formation, bear more resemblance to the more mafic sequence (unit EBG) found to the north, and on the other side of Adams Lake. Structure: The mineralization occurs within a highly altered schist package. The main foliation strikes in average at N70oW and dips from 22o to 55o northeast. Abundant small faults cut the schist. Mineralization: Low grade Pb-Zn-Cu occurs in quartz veins. Two types of veins cut the host rocks: 1) narrow (1 to 3cm thick) closely spaced veins more or less conformable to the schistosity, 2) discontinous larger veins (8 to 40cm thick) scattered through the schists, as pods or lenses. All the vein-like masses pinch and swell erratically and are truncated by faults. In both types of occurrences, the sulphides are erraticaly distributed and consist of pyrite and sphalerite with traces of galena and chalcopyrite in a quartz, calcite and ankerite gangue. Tourmaline has been reported in these veins (BCDM, 1961). Sample description: Euhedral galena grains in quartz-calcite veins cutting altered greenstone. References: BCDM ASS RPT 4135. BCDM MMAR 1961 pp. 53-55. 11 8 TWIN MOUNTAIN: Also known as: Star, Max, Hope Minfile number: 082M-020 Mineral Inventory number: 82M4-PB3 Map number: 019; Lat. 51.13ON Long. 119.80OW Grade: Subjective average value of 11 samples considered to be representative of the mineralized zone (BCDM ASS RPT 9882) are: Barite is also present in quantities sufficient to be of possible economic interest. Location: The showing occurs on the south-east flank of Samatosum Mountain at an elevation of 1,200 to 1,500m. The old workings are accessible via logging roads. Host Rock: Two conformable mineralized zones or veins are hosted by greenschist and chlorite schist derived from mafic to intermediate volcanic and volcaniclasic rocks (EBGq). These rocks contain abundant thin carbonaceous layers and fracture fillings, and show remnant pillow structures. Tuffaceous and more siliceous horizons occur within the greenschist. This package of rocks is overlain by the Tshinakin Limestone. Structure: Rocks in the area are moderately contorted and in places exhibit kink banding. The main foliation strikes N40OW and dips 430NW. Mineralization: The veins or mineralized zones contain pyrite, chalcopyrite, sphalerite and galena in a carbonate gangue with minor quartz, and barite; the zones locally are azurite stained. Mineralized zones range in width from 20cm to over 1m. An apparently unrelated vein lacking visible mineralization contains up to an estimated 30 percent barite. Sample description: The analysed samples are from an open trench close to the old adits. They contain blobs of sphalerite, pyrite and galena in a calcitic matrix. 0.170 8.84 0.90 2.15 0.18 g/t Au g/t Ag % Pb % Zn % Cu References: BCDM ASS RPT 9882, 2093. BCDM MMAR 1936, p. D39. 11 9 Art: Minfile number: 082M-124 Map number: 017; Lat. 51.10ON Long. 119.95ow Location: This showing is adjacent to the road between Louis Creek and Squaam Bay, near the east end of Forest Lake. Host Rock: Mineralization is hosted by a spotted quartz muscovite schist containing limy quartzitic pods. This schist is part of the subunit EBSs characterized by phyllitic sandstone, grit, phyllite, chlorite schist, and quartzite with a small amount of limestone. Mineralization: Quartz carbonate veins containing minor pyrite and galena cut the schist. Traces of fuchsite are also present. Sample description: Quartz veins in the schist contain pods of galena associated with minor carbonates. References: BCDM Minfile number 082M-124. 120 HOMESTAKE: Minfile number: 082M-025 Mineral inventory number: 82M4-AG1 Map number: 011; Lat. 51.11 ON Long. 119.83ow Reserve: proven (The Financial Post, Jan. 1973) are 1,010,800.0 tonnes of ore: 240.0 g/t Ag 2.5 % Pb 4.0 % Zn 0.6 % Cu 28.0 % barite Production, as listed in Minfile: 6,965 tonnes of ore (between 1935 to 1941) 12,400 g Au 9,565,900 g Ag 11,080 kg Cu 171,325 kg Pb 426,520 kg Zn Location: Access to the property is by a switchback road that leaves the main road 5km northwest of Squaam Bay. Host Rock: The mineralized barite lenses are overlain by sideritic phyllite that contain interbedded argillite, and by a tuffaceous chloritic schist unit (EBAa). A wide zone of altered rock occurs below the mineralized lens. Regional metamorphism and local hydrothermal alteration have obscured the primary composition of the host rocks; consequently, the following unit descriptions are based on mineral assemblages (Table ). A poorly exposed chlorite phyllite (unit 1) occurs in the southern part of the map area (Fig. A.1). It is a thinly laminated brownish green chlorite phyllite that is noticeably less foliated than the overlying schists. Unit 2 comprises dominantly sericite-quartz schist with abundant disseminated pyrite throughout. Unit 2a is a more massive phase of the "paper" schist of unit 2b and contains lenticular, silica-rich segregations up to 6 cm in length. Unit 2b, referred to as a sericite-quartz "paper" schist, is the most conspicuous unit in the map area. In outcrop, the paper schist unit is easily discernible by its fissile appearance and by its weathered coating of yellow ferric sulphate. It is the host and the footwall to the barite- sulphide lenses and is interpreted to be a highly altered, predominantly felsic tuff unit. A number of quartz veins up to a metre thick are found within the paper schist below the barite OJ nj O H-0 ua CD C W H 01 CD H > O • OJ -> a cn 3: OJ r-h M O O Ml 3 rr O fD » OJ o 3 3 D-. CD tn O rt O OJ C X n- ro (D TJ M M - O •o -» CD *X> M 00 rt cn • in M" o H-ua ua CD o 1-' o ua •<: OJ a 0N. 'IT UNIT 5. zt UNIT 2b •'C|;UNIT 4 1 1 \ \ v . UNIT 3 \ LEGEND EAGLE BAY FORMATION I 5 I TUFFACEOUS CHLORITIC SCHIST I 4 I ANKERITIC PHYLLITE. 4a — ARGILLITE [~3~| CHLORITE SCHIST I 2c j MINERALIZATION: BARITE BLUFF I 2b I SERICITE-QUARTZ PAPER SCHIST I 2o I SERICITE-QUARTZ SCHIST I I I CHLORITE PHYLLITE UNIT 2o UNIT I 122 lenses; they contain pyrite but are generally barren of other sulphides. A dark green laminated chlorite schist (unit 3) occurs stratigraphically above and laterally west of unit 2b. It consists of carbonate phenocrysts within a fine-grained chlorite-feldspar matrix. These phenocrysts, which may be pseudomorphic after plagioclase, are rimmed and partially replaced by chlorite. This unit is probably altered andesite tuff; its contact with unit 2b is in part an interfingering of felsic and intermediate tuffs but may also reflect an irregular pervasive potassic and silicic alteration boundary. A fine-grained ankeritic phyllite (unit 4) composed of interbedded layers of ankerite-bearing chloritic phyllite occurs above units 2b and 3. In outcrop limonitic pseudomorphs after iron-rich carbonate give the rocks a characteristic brown tinge. Some fine-grained pyritic argillites within the phyllite package are the most continuous and reliable marker units at Homestake. These argillite layers contain elongated quartz eyes and augen-shaped clasts up to 0.8 mm in diameter. The quartz eyes have cores of euhedral pyrite crystals and are set in a fine-grained pyritic carbonaceous matrix of phyllosilicates, quartz, and feldspar. Unit 4 is interpreted to be largely a sedimentary clastic rock with interbedded chloritic tuff layers. A tuffaceous chlorite schist (unit 5) occurs on the steep cliffs in the upper, northern portion of the Homestake area. The rock contains massive and tuffaceous zones composed of chlorite and carbonate (probably developed from regional metamorphism of rocks of intermediate compositon such as andesite). Relict flattened felsic clasts imply a pyroclastic origin for at least part of this unit. Pyritic quartz veins and calcite stringers occur throughout the schist, and in several places cut the foliation. Locally, cherty pods and argillite layers are interbedded with the schist. This unit is overlain by a thick greenstone sequence (V.A. Preto, pers. comm., 1985). Structure: A well defined penetrative mineral foliation is ubiquitous throughout the Homestake area. The foliation is outlined by the preferred orientation of platy minerals such as sericite and chlorite, and lenticular silica-rich segregations in unit 2. Foliation plotted on a stereonet (Fig. A.2), has a reasonably tight cluster around a maximum that strikes 120 degrees and dips 30 degrees northeast. Original compositional layering generally is difficult to see. Except within the argillite bands of unit 4, it has been largely obscured by either metamorphism or the intense deformation. In general, however, it strikes between 120 and 160 degrees with 123 N Figure A.2. Lower hemisphere equal area projections of structural elements Homestake deposit area: A- Poles (92) to foliation, maximun concentration-30% B- Poles (15) to compositional layering, maximum concentration -33%. Contour intervals-1, 10 (from Hoy and Goutier, 1986). 124 an average dip of 35 degrees northeast (Fig. A.2). The similarity between foliation and bedding attitudes indicates either tight or isoclinal folding or a constant facing direction. No large folds have been identified in the chlorite or sericite phyllites beneath the barite lenses. Nearly all bedding-cleavage intersections in these phyllites have a common vergence. Therefore, the succession could be a homoclinal, non-folded sequence on the lower, upright limb of a tight syncline. However, rootless tight to isoclinal minor folds throughout the succession and the presence of large folds outlined by argillite beds in overlying rocks (unit 4) suggest that larger folds also occur within the phyllites. These folds would be asymmetric, essentially confined to a single unit, with shortened or sheared-out overturned folds limbs. On a regional scale the Homestake property is located on the southern limb of a large overturned syncline (Schiarizza and Preto 1984; Preto and Schiarizza, 1985). Evidence in the Homestake area, including fold closures and vergences obtained from bedding-cleavage intersections, supports a synclinal fold closure to the northeast. Mineralization: A number of barite sulphide lenses with variable amounts of sulphide occur within the upper part of unit 2b. They are described in detail in early Ministry of Mines Annual Reports (1927, 1936) and are briefly reviewed here. At least three lenses, separated by sericite schist, are recognized. They range in thickness from less than a metre to at least 10 metres; underground some have been traced several hundred metres. Metallic minerals within these lenses include tetrahedrite, galena, sphalerite, pyrite, chalcopyrite, argentite, minor native silver, and trace ruby silver and native gold. The lenses may consist either of massive to banded barite with only scattered metallic minerals throughout, or interlayered barite, schist, and sulphides. Two lenses are exposed on surface. The largest, referred to as the "barite bluff" (unit 2c), has an exposed thickness of 5 to 6 metres. It pinches out rapidly along strike, has a sharp hangingwall contact with sericite schist, and grades downward into massive sericitic chert. A smaller lens, 1 to 2 metres thick, occurs below the "barite bluff" unit; it is banded but contains only minor sulphides. Sample description: Samples were collected from the barite bluff and are composed of erratically distributed medium grained pyrite, spalerite and galena. Galena sample from quartz vein material was also analysed. References: HOY,T.,and GOUTIER,F. 1986. 125 REA GOLD: Also known as: Hilton Minfile number: 082M-091 Map number: 015; Lat. 51.13ON Long. 119.81ow Published drill indicated reserves: 120,000 tonnes of ore. 18.2 gt Au 141.2 gt Ag 0.85 % Cu 4.11 % Zn 3.67 % Pb Location: The Rea Gold property is located west of Samatosum mountain and is accessible via logging road from Squaam Bay. Host Rock: The deposit description is from Hoy and Goutier (1986). The deposit includes two thin, laterally continuous lenses that lie stratigrafically above a highly altered sequence of dominantly mafic and minor felsic tuffs (Fig. A.3). Stratigraphically above these lenses is a thin mafic tuff sequence and a thicker sequence of argillite, siltstone, and grits (EBFf). The succession is inverted; hence, the "footwall alteration zone" or "stockwork feeder zone" now forms the hangingwall of the lenses. Rock Units: The oldest unit within the deposit area comprises predominantly mafic tuff (unit 1) that lies at the structural top of the succession. This tuff unit includes ash, crystal, and lapilli tuffs with variable amounts of disseminated pyrite. They are stongly foliated, producing green phyllites and schists; more massive "greenstone" units may be derived from mafic flows. There are thin chert bands and a noticeable increase in sericite content toward the contact with unit 2. In general, this contact is gradational and reflects, in part, an increase in alteration in the stratigraphic footwall of the deposit. Unit 2 is the footwall alteration or stockwork feeder zone of the sulphide lenses. It is very extensive in the hangingwall of the more northerly of the two lenses, but is only a few metres thick in the hangingwall of RG8, the southern lens. It includes extensively altered mafic tuffs, otherwise similar to those of unit 1, chert layers, and thin more felsic (dacite ?) ash tuff layers. These units now appear as pale tan to pale green siliceous phyllites and schists interbedded with pure to sericitic chert. Alteration increases dramatically toward the contact with the sulphide lenses. It includes: a) silicification through introduction of silica in the form of quartz veins, and of thin to relatively thick chert layers, discontinuous chert lamellae, and fragmental chert; 126 o 8 T" o s T" o I580-LEGEND UNIT 6 ARGILLITE: MINOR WACKE. GRIT WACKE. GRIT: MINOR ARGILLITE UNIT 5 | 6 | MAFIC TUFF: MINOR ARGILLITE f"c~| DARK GREY TUFFACEOUS ARGILLITE UNIT 4 BARITE: MINOR SULPHIOES UNIT 3 MASSIVE' SULPHIDES UNIT 2 | | MAFIC TUFF. SILICIFIED. CHERT MINOR DACITE (?) TUFF UNIT 1 | | MAFIC TUFF: MINOR SILICIFICATION Figure A.3 Vertical section (97+00) through the RG 8 sulphide barite lens, Rea Gold deposit (from Hoy and Goutier, 1986). 127 b) pyrite, which is disseminated, in veins, and in discontinuous streaks; it increases from 1 to 2 per cent in unit 1 to commonly 10 to 20 per cent near the stratigraphic top of unit 2; and c) sericite which becomes ubiquitous within unit 2. White (1985) noted both local soda enrichment (as massive albite and paragonite) and carbonization (as dolomite, iron-rich magnesite, and calcite). Stratigraphically overlying the sulphide or sulphide-barite lenses is a thin sequence of predominantly mafic tuffs (unit 5) that grades up into argillites. These tuffs are pale grey to brown-weathering thin-bedded chlorite phyllites. Silicified zones occur only locally and pyrite content is generally low. A dark grey tuffaceous "argillite" (unit 5c) with high Ba content (I.Pirie, pers. comm., 1985) occurs in the intermediate footwall of the RG8 lens, at the stratigraphic base of unit 5. Unit 5 is generally in fault contact with unit 6, but in some drill intersections it grades through an interval of interbedded green phyllite and argillite (Fig. ). A sequence of metaclastic rocks (unit 6) at the structural base of the succession are the yougest rocks in the deposit area. They comprises grey laminated argillite, siltstone, wacke, and local pebble comglomerate with both volcanic and sedimentary clasts. Bedding and graded beds are well preserved. Thin mafic ash tuff layers occur in the basal part of unit 6. Stucture: The deposit and host rocks are within a northwest-trending, northeast-dipping homoclinal succession that has been structurally inverted. A pronounced mineral schistosity largely masks primary bedding except in structural footwall rocks where well-bedded and commomly graded metaclastic rocks occur. The observed bedding is sub-parallel to the schistosity (Fig. A.4), indicating tight to isoclinal folding. Changes in the vergence of the bedding-schistosity intersections and the many small, roootless isoclinal folds indicate, however, that the succession is folded. Folding is asymmetrical in style and individual folds are confined to specific units since repetition of the major lithologic subdivisions is not apparent. Within unit 2, cleavage-bedding intersections indicate a synformal axis located to the northeast. Relationships between the massive sulphide, barite, and alteration zone indicate that the deposit is inverted; this suggests that the observed schistosity and associated folds are second generation structures superimposed on a previously inverted panel. Within more competent structural footwall rocks (unit 6), these folds are relatively open and the location of fold hinges can be defined. A late southeast-trending crenulation cleavage, associated with minor open folds, is superimposed on the earlier schistosity. Faults parallel to schistosity are common but only the largest N -L T Figure A.4 Equal area projections onto lower hemisphere structural elements Rea Gold deposit: A- Poles to foliation B- Poles to compositional layering (from Hoy and Goutier, 1986). 129 are shown on the map. The most prominent fault strikes northwest, juxtaposing unit 5 against unit 6. The displacement on the fault is probably not large as there does not appear to be much loss of stratigraphy across it; the fault cuts locally up into unit 5 leaving a normal stratigraphic contact between units 5 and 6. Mineralization: The sulphides, within this volcanogenic sulphide-barite bearing deposit, are contained in two main lenses. The more southern, the RG8 lens, appears to be at a slightly higher stratigraphic level than the L100 lens. It has a less extensive footwall alteration zone, and is "capped" by massive barite. Description of these sulphide lenses are based on visual examination of drill core and mapping of trenches. The RG8 lens is well exposed in two trenches. It has a relatively sharp contact with altered "footwall" rocks of unit 2 and grades stratigraphically up into massive barite of unit 4. However it is in sharp contact with tuffaceous muds or mafic tuffs of unit 5 at its fringes. The barite "cap" consists of grey to white, massive or faintly banded barite with variable amounts of disseminated sulphides. The sulphide content of the barite generally decreases away from the underlying massive sulphide (Fig. A.3). The L100 lens has a surface strike length of approximatly 50 metres and a down dip projection of at least 120 metres. A thick zone of intense silica alteration stratigraphically below the lens is abruptly overlain by mafic tuffs of unit 5a. It does not have a barite "cap". Sulphide mineralogy in both lenses includes pyrite, arseno-pyrite, sphalerite, galena, chalcopyrite, and tetrahedrite-tennantite (White, 1985). Sulphides are fine-grained and massive, crudely laminated or brecciated. Gold occurs mainly in the massive sulphides but is also found in barite, in footwall stockwork, and in fault gouge (I.Pirie, pers. comm., 1985). Silver is associated with both barite and massive sulphides, while zinc, lead, and copper occur primarily in massive sulphides. Sample description: The sample was collected from the massive sulphide zone occurring on surface and is composed of extremely fine-grained sulphide ore containing essentially pyrite, arsenopyrite, and sphalerite, with only minor galena. Vein samples containing coarser galena was also analysed. References: HOY,T.,and GOUTIER,F. 1986. 1 30 BARRIERE LAKES AREA: BIRK CREEK SHOWINGS: Also Known as: Anaconda, Lynx, Rainbow, Copper Cliff, Minfile number: 082M-067, (059, 131) Mineral Inventory number: 82M5-CU3 Map number: 008; Lat. 51.33ON Long. 119.90ow Location: The area is situated 3km west of North Barriere Lake. The showings are accessible by trail that follows the north-east side of Birk Creek. Host Rock: The area is underlain by sericite schist, chlorite schist, black phyllite, and some recrystallized limestone (unit EBAa). Two stratigraphic sections; A-A1, B-B1 and a longitudinal section D-D' crossing the section C-C', are shown on the Figures , and are described in the following paragraphs. Section A-A' A cliff section is exposed from an elevation of 970m at the creek to 1,102m up section. It consists dominantly of quartz-eye sericite schist. The strike of the foliation varies from 265 to 290 degrees and dips 5 to 20 degrees to the north. The overall minimum thickness (perpendicular to foliation, which is approximately coincident with bedding) is 175m (Fig. A.5). At the base of the section the schists contain 15 per cent phenocrysts (maximum size 2mm) of quartz and plagioclase in a quartz-muscovite-plagioclase matrix. The plagioclase is altered to calcite but up section this alteration is not apparent because the plagioclase content decreases. Autolithic fragmental units (average fragment size 1.5mm), occur locally. Disseminated pyrite with an average grain size of 0.5mm, constitutes up to 8 per cent of the rock. Trace amounts of interstitial chalcopyrite are present with the pyrite. No markedly sulphide-rich horizons were observed. Section B-B' This section (Fig. A.5) passes close to several old workings. Exposure is limited to one or two outcrops and the collars of two slumped adits. A well-developed foliation, parallel to compositional layering, trends 265 to 275 degrees and dips gently north (3 to 20 degrees). Observable bedrock is composed of quartz-sericite and chlorite schist with limonite altered pyrite-rich layers, and minor laminated black phyllites. Thin sections of the schists show zones with elongated fragments (up to 3mm) of polycrystalline quartz grains. Disseminated pyrite is present throughout much of the section. Silicified massive pyrite lenses with minor chalcopyrite were observed within an 8-metre section near the old adits. The pyrite is euhedral, but fragmented, and associated with chalcopyrite which generally is located at the borders of the pyrite grains. Material observed on a dump in the immediate area contains 1 31 Figure A.5 Detailed sections A-A1 and B-B1 from the north side of Birk Creek—sections about 350m apart (from Goutier et al., 1985). 1 32 similar mineralization, as well as a few blocks of vein quartz with blebs of sphalerite and galena. The latter type of mineralization was not observed in outcrop. Sections C-C and D-D' Sections C-C* and D-D' cross a major showing along a cliff section on the south side of Birk Creek. Three short accessible adits, about 9 metres long are parallel to a major joint direction (012 degrees). Other workings in the immediate vicinity have been flooded by the creek and are observable when water levels are low (V. Preto, pers. comm., 1984). This section is composesd of sulphide-rich sericite schist in fault contact with an impure limestone unit. Structure: A well developed foliation parallel to bedding strikes east-west and dips variably to the south and north. A superimposed north stiking, shallowly east-dipping crenulation cleavage is pronounced on outcrops near the creek. Early mesoscopic recumbent isoclinal folds with axial planes parallel to the pronounced schistosity and axes plunging parallel to the mineral lineation, probably indicate a large structure which controls the distribution of the stratiform mineralized zones (Preto, pers. comm., 1984). Mineralization: Mineral occurrences are stratiform massive pyrite deposits with minor chalcopyrite sphalerite and galena. Sulphides occur as massive pods (up to 1m thick), as layers (up to 10cm thick) and as fragments in silicified breccia. Sulphide mineralization is composed mainly of well-formed but disrupted pyrite grains (average size 2.5mm across) with minor chalcopyrite in an ankeritic quartz matrix. This unit looks like a pyrite-silica exhalite. Locally the sulphide horizons are well layered (layers are 8cm thick over an exposed thickness of 3.5m). Attitudes of layering and coincident foliation are the same as those observed in the limestone. Most mineralization appears to be stratabound and syngenetic with the host felsic schists. Sample description: Collected samples consist of fine grained galena disseminated through massive iron sulphide horizons. Vein material, also analysed, contains coarser galena and sphalerite in quartz gangue. Reference: GOUTIER et al, 1985. 133 ENARGITE: Also known as: North Star, Ace Minfile number: 082M-064, 065 Map number: 004; Lat. 51.35ON Long. 119.99ow Production as listed in Minfile: From the south showing 31 tonnes of ore (1954) 280 g Ag 1 ,561 kg Cu From the north showing 5 tonnes of ore (1972) 3,452 g AG 1,341 kg Pb 651 kg Zn Location: The property at the head of Birk Creek is at the summit between the valley of Barriere Creek and the North Thompson River. Host rock: The Enargite vein occurs at, or adjacent to, the contact between a fine grained meta-sedimentary package of the Eagle Bay Formation (composed of phyllite, slate, interbedded siltstone and sandstone, and various limestone horizons, subunit EBPl), and the meta-basalt of the Fennell Formation (lFu). Structure: The vein strikes N15ow and dips 45ow. The rocks in the area strike almost vertically; near the vein the host rocks are highly disturbed. Mineralization: The sulphides are hosted by a strong quartz vein (45cm wide) bordered by gouge material probably related to a fault between the two formations above. The sulphides, mainly galena, are irregularly distributed and occur in pockets. Locally disseminated sulphides occur in the adjacent carbonate host rocks. Sample description: Coarse galena in quartz vein was sampled; no other sulphides were present in the sample. References: BCDM EXPL. IN BC. 1978, pp. E108. BCDM GEM 1974 , p. 97. BCDM MMAR 1927, p. 190. 134 FORTUNA: Also known as: Kuno Minfile number: 082M-070 to 072 Map number: 013; Lat. 51.37C-N Long. 119.93ow Location: The property is on the flank of Fortuna hill. The aluminium roof of an old cabin on the property is visible from great distance and can be used to guide access to the workings along old trails. Host rock: Quartz lenses (or vein segments) cut through light to dark green chloritic phyllites, silstone, limestone and quartzite (EBU). The schists close to these lenses are very altered and in places silicified. Structure: The foliation in the host rocks strikes at N45ow and dips 24o to the southwest. The overall strike of the mineralized bodies parallels the foliation. Mineralization: Scattered pockets of galena occur in the quartz. The various mineralized zones are more or less parallel to each other, and although they occur at several places on the slope of the hill, their continuity has not been determined. Sample description: Well crystallized galena associated with minor amounts of pyrite was sampled from one of these bodies occuring near the old workings. References: BCDM MMAR 1927, p. 190. 135 WHITE ROCK: Minfile number: 082M-066 Mineral Inventory number: 82M5-PB1 Map number: 028; Lat. 51.30ON Long. 119.91ow Grade as listed in BCDM MMAR 1950: Composite sample: 0.3 4 g/t Au 91.80 g/t Ag 2.2 % Pb 0.8 % Zn Location: The deposit is approximatively 1.6km east, and 500 to 800 metres above Barriere River at the south end of North Barriere'Lake. Host Rock: The mineralization is hosted by the Tshinakin limestone (EBGt) which occurs interdigitated with green calcareous chloritic schist (EBG). Structure: The main fracture system which hosts the veins strikes northeasterly and cuts the limestone at high angles. These fractures have been interrupted by late faults both along and across the plane of the infilling veins (BCDM, 1950). A large number of small veins, exposed on surface, are of irregular width and of unknown length. These veins generally strike N10OS and dip steeply to the east. Mineralization: Quartz veins, clots and stringers, carrying mainly argentiferous galena, occur in a series of fractures which are probably related to the main fault zone along the Barriere River valley. In several places the contact of the limestone and the surrounding schist is also well mineralized. The veins are of irregular length; widths vary from 5cm to 45cm. Sample description: Concentric galena blebs surrounded by a quartz-calcite gangue was sampled from a vein on the property. References: ECONOMIC GEOLOGY SERIES NO. 8, GSC 1930, p. 302. BCDM MMAR 1950, pp. 111-112. BCDM MMAR 1928, p. 212. BCDM MMAR 1927, p. 189. 1 36 JUNE KAJUN: Also known as: Rennings, Kajun. Minfile number: 082M-058 Map number: 021; Lat. 51.26QN Long. 119.80OW Location: A large north-south trench (120m long) exposed a mineralized vein on the southeast side of East Barriere Lake at the mouth of Deadfall Creek. Host rock: A folded mineralized vein is hosted by grey to white limestone (EBGl) associated with black graphitic phyllite. A large fault, near the base of the exposure in the trench, is underlain by black siliceous and limy gouge and by unconsolidated breccia. Above the vein, the limestone is not disturbed and strikes from N20ow to 45ow with dips near 40OE. Structure: The mineralized vein is associated with a possible fault indicated by the presence of gouge material. The vein strikes N70ow and dips 65osw. In several places mineralization is concentrated in the crests of small drag folds. Mineralization: In the crest of a open large fold a mineralized zone, appproximatively 7m long by 4m high, is composed of siliceous calcific and dolomitic gangue contain sections up to 1.3m thick which are mineralized with galena, sphalerite and minor chalcopyrite. Patches and streaks of sphalerite, galena, chalcopyrite and pyrite extend locally into the surrounding limestone. Sample Description: Well crystallized associated with pyrite and sphalerite exposed quartz mass. The samples were and 5m away from the gouge rich zone. References: BCDM ASS. RPT. 2232, 2230. but fine grained galena was sampled from the collected both adjacent to 1 37 LEEMAC: Also known as: Boomac. Minfile number: 082M-056 Map number: 046; Lat. 51.35ON Long. 119.70ow Location: The Leemac group of claims are accessible by logging roads from the east side of the town of Barriere. The claims are along Fennell Creek. Host rock: The vein occur within the Cretaceous Baldy batholith. Near the vein the intrusion is porphyritic, reddish in color and nearly devoid of mafic minerals. Sericite is locally abundant in the vicinity of the vein structure. Narrow mafic dykes (striking parallel to the mineralized vein and dipping to the north) occur throughout the batholith. Structure: The vein strikes N25OE with a moderate dip to the northwest. It is bordered on both sides by fault gouge, indicating that the vein has been subjected to movement or that it fills a shear zone related to a faulting event. Mineralization: The mineralization is hosted by a well delineated quartz vein having an average width of 90cm. The sulphides, pyrite, sphalerite and galena, are coarse and well crystallized. This mineralized vein is surrounded by a subsidiary vein system mostly barren of sulphide minerals. References: BCDM ASS. RPT. 59 39. BROKEN RIDGE: Also known as: May. Minfile number: 082M-130 Map number: 009; Lat. 51.350N Long. 119.88ow Location: The mineralized zone occurs on Harper Creek 2km northwest of the west end of North Barriere Lake. Description: Lenses and blebs of pyrite and pyrrhotite with minor amounts of chalcopyrite, sphalerite and trace of galena occur semi-conformably with the foliation in the chloritic member of the quartz-sericite schist unit EBA. Numerous iron gossans in the area are related to abundant iron sulphides (pyrite and pyrrhotite) in the schist. Sample description: The data used come from analyses made by the Geological survey of Canada, analyse no. G79BN-001. References: BCDM EXPL. in BC 1976, p. E62 BCDM GEM 1971, p. 440. 1 38 BIRCH ISLAND-CLEARWATER AREA: CHU-CHUA: Minfile number: 092P-140 Map number: 003; Lat. 51.38ON Long. 120.07OW Location: The Chu-Chua property is approximatively 20km north-northwest from the town of Barriere, on the ridge east of Chu-Chua mountain. Host Rock: The deposit is hosted in the upper structural division of the Fennell Formation (ufb) composed mainly of basalt with alkalic affinities (Aggarwall et a_l. , 1984), in which primary textures and pillows (1 to 3m across) are still visible. The margins of the pillows are slightly chilled and are chloritized or bleached. Massive talc zones and siliceous rocks are locally abundant within this package, particularily near the sulphide rich zones. Chert and/or tuffite overlie the mineralization and are believed to be exhalative in origin (Aggarwall et al., 1984). Structure: Rocks of the Fennell Formation are generally not highly foliated. The schistosity, were developed, is axial planar to early, generally northeast plunging isoclinal folds. Two generations of later folds (easterly and northwesterly trending, Schiarizza, 1980) refolded the main schistosity and may be responsible for repetition of the mineralized horizons. Mineralization: The basalt contains two major (eastern and western), and two minor lenticular bodies of massive sulphides that appear to be stratabound. In general the deposits trend north-south, dip steeply west, and plunge gently south. The sulphides are in sharp contact with the hangingwall rocks, but the extension of the bodies down dip are irregular and in several places lens out into cherty rocks (McMillan, 1980). The mineralized zones are associated with massive talc magnetite lenses, and are composed mainly of pyrite and chalcopyrite with minor sphalerite, cubannite, stannite, and quartz and calcite. Bedding is not common and occurs only locally where it is outlined by chalcopyrite-rich layers or by alternating layers of pyrite of different sizes. The massive sulphides are cut by quartz-talc veins and, in one hole, by molybdenite stringers (McMillan, 1980). 139 The Chu-Chua deposit is believed by Aggarwall et a_l. (1984) to represent deposition from saturated solution on the sea floor and/or nearby seamounts. The different lenses formed from different vent sources. The associated magnetite and talc rich zones probably represent areas where a higher component of sea-water was involved in alteration and mineralization. Similarly the apparent lack of footwall alteration is most likely due to a lack of significant interaction between the hydrothermal solution and the host rocks. Sample description: Lead data referred to in the present study are from Aggarwall and Nesbitt (1984). Their analysed lead was extracted from pyrite and chalcopyrite rather than galena and the data are only used here on a comparative basis. References: AGGARWALL,P.K.,and NESBITT,B.E. 1984. AGGARWALL,P.K.,FUJJI,T.,and NESBITT,B.E. 1984. MCMILLAN,W.C. 1980. 140 FOGHORN: Also known as: Gopher, Shamrock Minfile number: 082M-008, 029, 030, 040, 108 Mineral Inventory number: 82M12-Cu2, Ag1 Map number: 005; Lat. 51.54ON Long. 119.93ow Production as listed in Minfile: Foghorn 73 tonnes of ore (1916-17) 88,364 g Ag 57,276 kg Pb Location: The property is at approximatively 2,000m elevation on Foghorn Mountain, 6.5km south of Birch Island. Host Rock: The property is underlain by rusty weathered feldspar-chlorite schist and sericitic quartzites (EBFq), but the mineralized veins are hosted by siliceous and limy schists. The Baldy batholith, exposed in the southern part of the property at Granite Mountain, is surrounded by fine to medium grained biotite quartz gneiss with interlayered amphibolite and pelitic hornfels. Felsic porphyry dykes occur near the mineralized zones and may be responsible for both the silicification of the host rocks and for the sulphide veins. Structure: The Foghorn showings are located on the northern limb of an east-west striking antiform in very close proximity to a major northerly striking thrust fault. The northeasterly strike of the vein is at a high angle to the thrust fault. Small scale structures, drag folds for example, indicate that original bedding has been deformed and probably transposed into tight isoclinal folds now seen as foliation (striking N30OE and dipping 80ow). Mineralization: Quartz vein segments occur throughout the schist; their distribution is not continuous and may therefore represent a system of small veins rather than a major single discontinuous vein. These vein segments are locally heavily mineralized with galena, sphalerite and pyrite. In places chalcopyrite also occurs but only in minor amounts (disseminated chalcopyrite is found in greater amounts in the nearby Lydia prospect). The width of the vein segments is approximatly 35cm; they strike about N35OE and dip in various directions —some of them are vertical. Sample Description: Samples were collected from the old workings. The galena occurs with minor amounts of sphalerite and pyrite in quartz gangue specimens. References: BCDM ASS. RPT. 11381, 3820. BCDM OPEN FILE. 141 REXSPAR: Also known as: Smuggler, Spar, Black Diamond Minfile number: 082M-021 Mineral Inventory number: 082M12-U1, FSP1 Map number; 016 Lat. 51.570N Long. 119.90OW Reserves as listed in Minfile: Rexspar, total deposit (dec. 1976): 1,114,000 tonnes @ 1.55% U cut off used. Location: The Rexspar deposit 5km, south of Birch Island, is on the south slope of the North Thompson valley between Lute and Foghorn Creeks. Host Rock: Mineralization at Rexspar is directly associated with the trachytic member of the felsic unit EBA. The trachyte is massive or brecciated and strongly foliated. The surrounding rocks, chlorite sericite schist and silvery sericite-quartzite, contain exposures of clearly recognizeable dacitic and andesitic volcanic breccia. Structure: The rocks of the trachyte suite exhibit brecciation, cataclasis and mylonitization structures. The foliation in the rocks strikes north-easterly with a 300 dip to the northwest. The mineralized zones are deformed and are near to several faults and thrusts. Mineralization: The two main mineralized zones present at Rexspar are: 1) an uranium rich zone confined to tuffaceous and argillitic lenses containing abundant pyrite associated with aggregates of uranium bearing fluorphlogopite. The lenses are discontinuous, average 20cm in thickness, and are conformable with the schistosity of the host trachyte. 2) a fluorite zone, barren of both thorium and uranium, is mineralized with celestite, pyrite, trace of galena and molybdenite. The mineralization at Rexspar has been interpreted by Preto (1978, in BCDM Geology) as resulting from deposition from a late stage deuteric volatile rich fluid evolved from the highly differentiated intrusive-extrusive igneous suite. However, because C02 apparently played an important role in the transport and deposition of uranium associated with hydrothermal solutions (Morton, 1978), then the uranium and thorium mineralization could be syngenetic with the trachyte unit. 1 42 Sample description: No samples were collected from the Rexspar deposit by the writer. The data referred to here came from analyses by the Geological Survey of Canada (sample number G79SA-001. References: GSC paper 78-1B, pp. 137-140. BCDM Geology in BC 1977-1981, pp. 44-56 CIM Bull., 71, 1978, pp. 82. MORTON, R.D., AUBUT, A., GANDHI, S.S. 1978. Rexspar Deposit. Geological Survey of Canada, Current Research, paper 78-1B, pp. 137-140. 143 MT McCLENNAN AREA Deposit names: Red Top, Mt McClennan, Sunrise (Naomi). Also known as: Mimsic Claims Minfile number: 082M-044, 046 Mineral Inventory number: 82M12-PB1 Map numbers: 531, 539, 541; Lat. 51.64QN Long. 119.78ow Location: This area comprises three old prospects near the summit of the McClennan Mountain located about 7.5km northeast of Birch Island. All the showings are accessible via forestry roads. Host Rock: The mineralized occurrences of the Mt McClennan area are hosted by greenschist and by calcareous chloritic and graphitic schist intercalated with minor quartzite siliceous schist and carbonate (EBQ). Granitic rocks crop out about 2km north of the showings; the contact between the intrusion and the schists is marked by the development of hornfelsic rocks and by skarn zones in carbonate-rich horizons. Lamprophyre dykes occur in the western end of the area. Structure: Rocks in the vicinity of McClennan Mountain are highly foliated and are folded around a strong easterly trending open antiform plunging 15OE. The south limb of the antiform has been dislocated by faulting and granitic intrusion. Mineralization: Pb-Zn-Ag and Cu occurrences are widespread in the area, the three old workings sampled for the present study are: 1) the eastern area that comprised the old Sunrise group and Naomi claims. The mineralization consists of pyrrhotite and pyrite with galena and sphalerite occuring in quartzitic rocks as lenticular sheets traceable on surface over a distance of 125m along strike. The sheets vary in thickness from .3 to 1.2m and are not totally conformable with the enclosing host. 2) the central area hosts the MT McClennan (Snow) showing. This showing contains massive and semi-massive heavily oxidized pyrite with galena, sphalerite and minor amounts of chalcopyrite in impure limy horizons. The sulphide rich layers are up to 50cm thick and parallel the schistosity and compositional layering of the schists. A magnetite bearing skarn is developed below an adjacent prominent bed of crystalline limestone. 144 3) the western area hosts the Red Top showing which consists of galena and sphalerite associated with silicified pyritic zones occuring along bedding in limestone. Chalcopyrite fills many gash-like openings. The sulphides have an erratic distribution along strike, occuring in blows and seams. Nevertheless they are stratabound to a definite stratigraphic horizon composed of calcareous quartz sericite schist adjacent to an horizon that varies from skarn to clear crystalline limestone. In general these mineralized bodies appear to occur as discontinuous lenses (more or less conformable with the schistosity) or as erratic swellings formed by limestone replacement and/or skarn development due to metasomatism probably related to the intrusion of the Raft batholith. Samples description: 1) eastern area (Sunrise): Fine grained highly altered sample containing sphalerite and galena associated with abundant pyrite. 2) central area (Mt McClennan): Coarse and fine grained galena from disseminations from an altered limy horizon. 3) western area (Red Top): Seams of fine grained sulphides disseminated in chloritic schist. References: BCDM ASS. RPT. 6931, 6603, 5813, 436. BCDM Geology in BC 1977-81, pp. 44-56. 145 VAVENBY: Map number: 042; Lat. 51.58ON Long. 119.75ow Description: Quartz vein containing narrow sulphides seam (5cm wide) cut throught the Tshinakin Limestone (EBGt). The vein is mineralized with galena and contains abundant calcite material. A syenite dyke occurs in the vicinity of the mineralized vein. References: Paul Schiarizza, pers. comm., 1985. PS-75-185: Map number: 04 8; Lat. 51.58ON Long. 119.75ow Desciption: Galena and sphalerite occur in a narrow quartz vein cutting the Tshinakin Limestone, 4km east of the fossil occurrence near Vavenby. References: Paul Schiarizza, pers. comm., 1985. SONJA: Also known as: LSD, Valentine. Minfile number: 092P-049 Map number: 044; Lat. 51.590N Long. 120.0low Location: This small mineralized showing occurs on the south bank of the North Thompson River, 1km east of the Clearwater railway station. Description: Discontinuous silicified lenses or veins carry crystalline galena and anglesite. The mineralized masses occur within a quartz sericitic schist wedge of the Eagle Bay Formation close to the contact with the Fennell Formation. The mineralization appears to follow the east side of a major dyke (3.5 to 13m wide) which cuts the rocks of the Eagle Bay formation. References: BCDM EXPL. in BC 1976, p. E132. BCDM GEM 1969, p. 230. 1 46 BIRCH ISLAND: Minfile number: 082M-023 Mineral Inventory number: 82M12-PB2 Map Number: 040; Lat. 51.56ON Long. 119.90OW Production as listed in Minfile: 14 tonnes of ore (1926): 6,566 g Ag 3,362 kg Pb Location: The old workings are located along Foghorn Creek road south of Birch Island. Description: Eratic galena mineralization occurs in a fissure vein cutting through a quartzitic member of the felsic unit (EBA). The fissure, striking north and dipping steeply west, is bordered by a zone in which pyrite, siderite and calcite are locally abundant. The presence of manganese ore was also reported from this area (1931). References: BCDM MMAR 1931, p. 107. BCDM MMAR 1929, p. C22 4. TINDAL: Map number: 043; Lat. 51.60ON Long. 119.78ow Description: Galena was collected in an old adit from a quartz vein cutting quartz sericite schist of the Eagle Bay Formation. References: none available 1 47 APPENDIX B LABORATORY PROCEDURES FOR GALENA LEAD ISOTOPE ANALYSIS B.1 GALENA LEAD SAMPLE PREPARATION Galena crystals selected from rock or ore samples are stored in plastic vials. Approximately 10 mg of grains of clean galena are picked out, using a needle and a binocular microscope, and put into a disposable 10 ml polypropylene beaker. A clean glass beaker (10 ml) is weighed, then the galena grains are emptied into the glass beaker and the container is reweighed. The weight of the sample indicates the amount of water that must be added to the lead chloride crystals prior to loading. Approximately 8 ml 2N HCl is added to the sample in the glass beaker, which is then left overnight on a hotplate. The lead sulphide is converted to lead chloride with the production of hydrogen sulphide. The dry PbCl2 crystals are rinsed in 4N HCl three times. Most of the impurities are readily dissolved in 4N HCl, but PbCl2 is least soluble at this normality. Cleaned lead chloride crystals are dried by returning the beaker to the hotplate for a few minutes. A solution containing 1 ug Pb per 2 ul aqueous solution is prepared by adding a calculated amount of quartz distilled water allowing for the loss of 30% of the sample due to non-dissolution of some of the galena and loss of lead chloride during rinsing. B.2 PREPARATION AND LOADING OF FILAMENTS Pre-cleaned rhenium ribbon 1.5 cm long is spot-welded to single filament posts. A micropipette with disposable tips is used to load 2 ul of sample onto each filament, using a new tip for each sample. Samples are dried at 1 Amp. 4 ul of silica gel-phosphoric acid solution is loaded on top of the dry sample. This is left to dry at 1.1 Amp, then the current is gradually increased until the load dissolves and reprecipitates. When recrystallization is complete, the current is slowly increased until white smoke is given off and the load turns white. The current can then be turned up to 2 Amps or higher to allow the load to glow gently for a few seconds, then off. B.3 MASS SPECTROMETRIC PROCEDURES All the reported analyses were done by Francoise Goutier in the Geochronology Laboratory at the University of British Columbia using a VG Isotopes Isomass 54R mass spectrometer linked to a HP-85 microcomputer. 1 48 Samples were loaded into the mass spectrometer, six at a time, and heated to 11500-12500. The isotopic composition is measured using 'UBCGPB1 programs. Due to the uncertainity in measuring 204pb peak, this program measured the 204pb/207pb ratio twice as often as the other two ratios, improving the statistics on the ratio. Raw data is converted to the 206pb/204pb, 207pb/204pb and 208pb/204pb ratios, then normalized to absolute values using correction factors determined by repeated analyses of the Broken Hill Standard (Table 3.1). Each analysis is reported with an associated error based on a combination of the fractionation variation between runs, the uncertainity in mass fractionation factors, and within-run precision. References: Andrew, A. Ph.D Thesis in preparation, University of British Columbia. 149 APPENDIX C Adams Plateau: Lead Sample No Deposit/Sample Name 30504-001 ENARGITE 30504-00102 ENARGITE 30504- AVG ENARGITE N=2 30504/00101 ENARGITE 30505- 002 FOGHORN (SAMPLE 011) 30505-00201 FOGHORN (SAMPLE Oil) 30505-003 FOGHORN (VEIN 007) 30505-003D1 FOGHORN (VEIN 007) 30505-AVG2 FOGHORN N=2 (SAMPLE 011) 30505-AVG3 FOGHORN N=2 (VEIN 007) 30505- AVG FOGHORN N=4 30505/001 FOGHORN (SAMPLE 007) 30505/001D1 FOGHORN (SAMPLE 007) 30506- 001 AGATE BAY 30506-00101 AGATE SAY 30506-00102 AGATE BAY 30506- AVG AGATE 5AY N=3 30505/001 D3 AGATE BAY 30507- 001 BECA (TDM) 30507-00101 BECA (TQM) 30507-001D2 BECA (TOM) 30507- AVG BECA N=3 30507/00103 BECA (TOM) 30508- 001 BIRK CREEK (SECTION X DUMP) 30508-00101 BIRK CREEK (SECTION X DUMP) 30508-002 BIRK CREEK (SECTION X) 3050B-002D1 BIRK CREEK (5ECTI0N X) 30508-00301 BIRK CREEK (SECTION 012) 30506-004 BIRK CREEK (VEIN SECT. 012) 30508-00401 BIRK CREEK (VEIN SEC.012) 30506-0C5 BIRK CREEK (NEAR BRIDGE) 30508-506 BIRK CREEK (G79BA-001 ) 30508-50601 BIRK CREEK (G79BA-002) 30508-AVG1 BIRK CREEK N=2 (SECT. DUMP) 30508-AUG2 BIRK CREEK N=2 (SECT.X) 3050B-AVG4 BIRK CREEK N=2 (SECT. X) 30508-AUG6 BIRK CREEK (G79BA-AVG) 30508-AVG BIRK CREEK N=10 30508/003 BIRK CREEK (SECTION 012) 3050S-SO1 BROKEN RIOGE (G79BN-001) 30511-001 HOMESTAKE 30511-002 HOMESTAKE 30511-002D1 HOMESTAKE 30511-502 HOMESTAKE (KAMAO 70) 30511-501 HOMESTAKE (361-G79H0-001) 30511-AVG2 HOMESTAKE N=2 30511-AVG HOMESTAKE N=5 30511/OOl D1 HOMESTAKE 30513-001 FORTUNA 30513-00101 FORTUNA 30513-AVG FORTUNA N=2 30515-001 REA GOLD (MASS. SULPH.HORZ .) 30515-002 REA GOLD (VEIN) Isotope Data Mt Anl Qual Pb6/4 J6/4 Pb7/4 J7:4 GL FG GOOO 19.101 0.01 15.692 0.01 GL FG GOOO 19.090 0.03 15.688 0.03 GL FG GOOO 19.096 0.02 15.690 0.02 GL FG FAIR 19.079 0.06 15.664 0.04 GL FG GOOD 19.190 0.03 15.708 0.03 GL FG GOOO 19.202 0.03 15.693 0.03 GL FG GOOD 19.225 0.04 15.713 0.03 GL FG FAIR 19.213 0.12 15.728 0.12 GL FG GOOD 19.196 0.03 15.701 0.03 GL FG GO/FR 19.219 0.08 1 5.721 0.08 GL FG GD/FR 19.20B 0.05 15.711 0.05 GL FG POOR 18.915 0.41 15.516 0.41 GL FC FAIR 19.073 0.21 15.680 0.20 GL FG GOOD 19.148 0.02 15.703 0.02 GL FG FAIR 19.148 0.05 15.705 0.02 GL FG FAIR 19.134 0.05 15.695 0.05 GL FG FAIR 19.143 0.04 15.701 0.03 GL FG FAIR 19.033 0.06 15.633 0.06 GL FG GOOD 19.334 0.02 15.668 0.02 GL FG GOOO 19.344 0.02 1 5.6B7 0.01 GL FG FAIR 19.339 0.01 15.684 0.01 GL FG GO/FR 19.339 0.02 15.660 0.02 GL FG POOR 19.322 0.03 15.703 0.03 CL FG GODD 18.948 0.02 15.718 0.02 GL FG FAIR 18.947 0.08 15.741 0.08 GL FG GOOD 18.904 0.03 15.71C 2.01 GL FG GOOD 18.882 0.03 15.599 0.03 GL FG POOR 19.026 0.39 15.798 0.39 GL FG GODD 18.896 0.02 15.705 0.01 GL FD POOR 18.949 0.14 15.741 0.05 GL FG GOOD 18.eQ3 0.01 15.721 0.01 GL BR FAIR 18.878 0.06 15.708 0.13 GL BR FAIR 1B.669 0.08 15.722 0.16 GL FG GD/FR 18.948 0.05 15.730 0.05 GL FG GOOD 18.893 0.03 15.705 0.02 GL FG GD/PR 18.923 0.08 15.723 0.03 GL BR FAIR IB.874 0.07 15.715 0.08 GL G/R GD/FR 18.907 0.06 1 5.716 0.05 GL FG FAIR 18.901 0.02 15.691 0.01 GL BR FAIR 19.249 0.08 15.697 0.11 GL FG FAIR 18.776 0.05 15.696 0.05 GL FG FAIR 18.8B7 0.05 15.693 0.05 GL FG GOOD 18.900 0.04 15.705 0.02 GL GSC FAIR 18.827 0.00 15.719 0.00 GL GSC FAIR 18.878 0.08 15.687 0.17 GL FG FAIR 18.894 0.05 15.699 0.03 GL FR/GO 18.854 0.06 15.700 0.10 GL FG POOR 18.B69 0.19 15.770 0.19 GL FG GOOO 19.118 0.02 15.716 0.01 GL FG GOOD 19.132 0.02 15.726 0.02 GL FG GOOO 19.125 0.02 15.721 0.02 GL FG FAIR 18.859 0.04 15.709 0.04 GL FG GOOD 18.852 0.01 15.6B0 0.01 1 50 Pb8/4 US/4 Pb6/7 *6/7 Pb6/B H6/8 38.993 0.02 1.21720 0.01 0.489849 0.01 38.981 0.03 1.216B7 0.00 0.489732 O.OO 38.987 0.05 1.21704 0.01 0.489791 0.01 3B.875 0.07 1.21799 0.04 0.490772 0.04 39.140 0.04 1.22164 0.01 0.490291 0.02 39.077 0.03 1.22356 0.01 0.491389 0.01 39.146 0.05 1.22355 0.03 0.491108 0.03 39.189 0.12 1.22156 0.01 0.490262 0.01 39.109 0.03 1.22260 0.01 0.490840 0.02 39.168 0.08 1.22260 0.02 0.490685 0.02 39.138 0.06 1.22258 0.02 0.490763 0.02 38.537 0.42 1.21908 0.07 0.490829 0.08 38.959 0.21 1.21643 0.05 0.489572 0.04 38.927 0.04 1.21938 0.01 0.491889 0.04 3B.916 0.10 1 .21916 0.05 0.492018 0.08 3B.8B5 0.05 1 .21912 0.01 0.492084 0.01 38.909 0.06 1.21922 0.02 0.491997 0.04 38.581 0.06 1.21749 0.02 0.492044 0.02 38.979 0.02 1.23393 0.01 0.496001 0.01 39.042 0.02 1.23317 0.01 0.495474 0.01 39.026 0.01 1.23300 0.01 0.495531 0.00 39.016 0.02 1.23338 0.01 0.495669 0.01 39.056 0.03 1.23049 0.01 0.494725 0.02 38.661 0.03 1 .2054 B 0.01 0.487575 0.01 38.e56 0.08 1.20368 0.01 0.487617 0.01 38.791 0.03 1.20328 0.03 0.487321 0.01 38.751 0.03 1.20275 0.01 0.487256 0.01 39.027 0.39 1.20433 0.01 0.487514 0.02 3B.755 0.02 1 .20319 0.02 0.487565 0.01 36.987 0.16 1.20384 0.13 0.486037 0.07 38.829 0.01 1.20174 0.01 0.486577 0.00 38.B93 0.18 1.20182 0.00 0.486224 0.00 38.834 0.18 1.20018 0.00 0.486737 0.00 38.859 0.05 1.20458 0.01 0.487448 0.01 38.771 0.03 1.20302 0.02 0.487289 0.01 38.871 0.09 1.20352 0.08 0.486801 0.04 3B.863 0.18 1.20100 0.00 0.486477 0.00 38.B48 0.09 1.20304 0.05 0.486692 0.05 3B.744 0.02 1.20454 0.01 0.487849 0.01 39.253 0.13 1 .22630 0.00 0.491221 0.00 3B.574 0.05 1.19619 0.01 0.4B6742 0.01 38.681 0.06 1.20350 0.00 0.488279 0.02 3B.717 0.05 1.20341 0.04 0.488150 0.01 38.621 0.00 1.19773 0.00 0.488325 0.00 38.533 0.18 1.20343 0.12 0.490766 0.12 38.699 0.06 1.20346 0.02 0.488215 0.01 38.626 0.12 1.20085 0.07 0.486452 0.07 38.779 0.19 1.19652 0.04 0.485569 0.02 39.000 0.02 1.21643 0.01 0.490196 0.01 39.035 0.02 1.21657 0.01 0.490128 0.01 39.018 0.02 1.21650 0.01 0.490162 0.01 38.766 0.05 1.20052 0.02 0.486467 0.02 3B.687 0.02 1.2022B 0.01 0.487299 0.02 1 51 Adams Plateau: Lead Isotope Data Sample No Deposit/Sample Name 30515-002D1 REA GOLD (VEIN) 30515-003 REA GOLD (BARITE HORZ.) 30515-AVG2 REA GOLD N=2 (VEIN) 30515- AVG REA GGLD N=3 30515/00101 REA GOLD (MASS. SULPH. HORZ.) 30515/003D1 REA GOLD (BARITE HORZ.) 30516- 101 REXSPAR (G79SA-001) 30517- 001 ART 30517-001 Dl ART 30517- AVG ART N=2 30518- 001 LUCKY COON 30518-00101 LUCKY COON 30518-002 LUCKY COON (PIT 1) 3051B-AVG1 LUCKY COON N=2 30518- AVG LUCKY COON N=3 30519- 001 TUIN MOUNTAIN (FALC3.SAMPLE) 30519-00101 TWIN MOUNTAIN (FALCB.SAMPLE) 30519-501 TUIN MOUNTAIN (G79TM-001 ) 30519-AVG1 TWIN MOUNTAIN (FALCB.SAMPLE 30519-AVG TUIN MOUNTAIN N=2 30521-001 JUNE KAJUN 30521-00101 JUNE KAJUN 30521- 001D2 JUNE KAJUN 30521 -AVG JUNE KAJUN N=3 30521/101 JUNE KAJUN (G79JU-0C1) 30522- 001 9C (ZN 1) 30522-001D3 BC (ZN 1) 30522- AVG BC (ZN 1)N=2 30522/00101 3C (ZN 1) 30522/001D2 BC (ZN 1) 30523- 501 KING TUT (G79LU-001) 30524- 501 ELSIE (G79LU-002) 30525- 001 M050UIT0 KING 30525-002 MOSOUITO KING (VEIN) 30525-002D1 MOSQUITO KING (VEIN) 30525-AVG2 MOSQUITO KING N=2 (VEIN) 30525- AVG MOSQUITO KING N=2 30526- 501 PET (G79PE-001) 30527- 001 SPAR 30527-00101 SPAR 30527-002 SPAR (FLUORINE SHOWING) 30527- AVG1 SPAR N=2 30528- 001 WHITE ROCK 30528/00101 WHITE ROCK 30531-001 RED TOP 30531-002 RED TOP (TRENCH) 30531-00201 REO TOP (TRENCH) 30531-AVG2 RED TOP N=2 (TRENCH) 30531- AVG REO TOP N=2 30532- 001 FLUKE 30532-00101 FLUKE 30532- AVG FLUKE N=2 30533- 001 OR ELL 1D (RED MINERAL) Mt Anl Qual Pb6/A *6/4 Pb7/4 *.7:4 GL FG GOOD 1B.862 0.02 15.6B8 0.01 GL FG GOOD 18.893 0.03 15.706 0.03 GL FG GOOD 18.857 0.02 15.684 0.01 GL FG GOOO 18.869 0.03 15.699 0.03 GL FG POOR 18.804 0.24 15.661 0.24 GL FG POOR 18.776 0.50 15.702 0.50 GL 8R FAIR 19.177 0.10 15.911 0.20 GL FG FAIR 19.079 0.10 15.750 O.OB GL FG GOOD 19.040 0.D1 15.724 0.01 GL FG GO/FR 19.060 0.05 15.737 0.04 GL FG FAIR 19.123 0.04 15.688 0.01 GL FG GOOD 19.140 0.01 15.699 0.01 GL FG FAIR 19.163 0.10 15.696 0.01 GL FG GD/FR 19.132 0.03 15.694 0.01 GL FG GD/FR 19.142 0.07 15.694 0.01 GL FG FAIR 19.013 0.05 15.704 0.02 GL FG FAIR 19.012 0.04 15.691 0.04 GL BR FAIR 19.057 0.07 15.716 0.18 GL FG FAIR 19.013 0.05 15.69B 0.03 CL FAIR 19.035 0.06 15.707 0.10 GL FG GOOD 19.472 0.02 15.724 0.02 GL FG FAIR 19.469 0.05 15.725 0.02 GL FG FAIR 19.442 0.07 15.707 0.07 GL FG FR/GD 13.461 0.05 15.719 Q.04 GL ER FAIR 19.441 0.04 15.575 0.14 GL FG FAIR 18.294 0.01 15.552 0.01 GL FG FAIR 18.232 0.06 15.554 0.06 GL FG FAIR 18.2B8 0.03 15.553 0.03 GL FG FAIR 18.403 0.02 15.578 Q.02 GL FG POOR 18.245 0.30 15.516 0.30 GL BR FAIR 19.095 O.DB 15.6BB 0.1B GL BR FAIR 19.142 0.08 15.700 0.1B GL FG GOOD 19.075 0.01 15.692 0.01 GL FG GOOD 19.071 0.02 15.692 0.02 GL FG GOOO 19.124 0.02 15.694 0.02 GL FG GOOD 19.098 0.02 15.693 0.02 GL FG GOOO 19.090 0.02 15.693 0.02 GL BR FAIR 19.126 0.06 15.732 0.15 GL FG GOOD 19.133 0.01 15.692 0.01 GL FG GOOD 19.126 0.04 15.687 0.04 GL FG POOR 19.150 0.28 15.671 0.28 GL FG GOOD 19.130 0.03 15.690 0.03 GL FG GOOD 19.151 0.04 15.722 0.04 GL FG POOR 19.227 0.64 15.801 0.62 GL FG FAIR 19.142 0.05 15.719 0.02 GL FG GOOO 19.159 0.09 15.737 0.09 GL FG FAIR 19.136 0.07 15.710 0.00 GL FG GD/FR 19.148 0.08 15.724 0.04 GL FG GD/FR 19.146 0.06 15.721 0.04 GL FG GOOD 19.219 0.02 15.702 0.02 GL FG GOOD 19.227 0.05 15.704 0.05 GL FG GOOD 19.223 0.03 15.703 0.03 GL FG GOOD 19.362 0.02 15.715 0.02 PbB/4 JIB/4 Pb6/7 JB/7 Pb6/B %6/B 3B.742 0.03 1.20232 0.02 0.4B6872 0.03 38.823 0.03 1.20292 0.01 0.486640 0.01 3B.715 0.02 1.20232 0.02 0.487086 0.03 38.755 0.03 1.20192 0.03 0.486879 0.03 38.904 0.24 1.20066 0.03 0.483341 0.01 38.708 0.50 1.19577 0.04 0.485070 0.05 3B.9B6 0.20 1.20528 0.00 0.492734 0.00 39.185 0.11 1.21132 0.06 0.486886 0.04 39.109 0.01 1.21088 0.01 0.486848 0.00 39.147 0.06 1.21110 0.03 0.486B67 0.02 38.847 0.05 1.21B97 0.04 0.492258 0.03 36.896 0.03 1.21924 0.00 0.492096 0.02 38.958 0.10 1 .22084 0.10 0.491874 0.03 3B.872 0.04 1.21911 0.04 0.492177 0.03 3B.900 0.07 1.21968 0.06 0.492076 0.03 38.B37 0.06 1.21066 0.04 0.489554 0.02 3B.B13 0.05 1 .21166 0.01 0.489B43 0.01 38.846 0.05 1.21260 0.00 0.491415 0.00 36.825 0.06 1.21116 0.03 0.489699 0.02 38.836 0.06 1.211B8 0.03 0.490557 0.02 39.525 0.02 1.23B37 0.01 0.492647 0.01 39.513 0.05 1 .23B09 0.04 0.49271B 0.03 39.473 0.07 1.237B2 0.01 0.492534 0.01 39.504 0.05 1.23309 0.02 0.492633 0.01 39.396 0.00 1.24019 0.00 0.494320 0.00 38.309 0.01 1.17631 0.00 0.477523 0.01 38.337 0.07 1.17539 0.02 0.476B89 0.03 3B.331 0.04 1 .17S85 0.01 0.477206 0.02 36.412 0.03 1.18137 0.00 0.479100 0.01 38.243 0.30 1.17594 0.02 0.477093 0.02 38.B35 0.16 1.21718 0.00 0.492547 0.00 38.97 5 0.09 1.21925 0.00 0.491974 0.00 38.335 0.02 1.21552 0.02 0.491163 0.01 38.827 0.03 1.21532 0.01 0.491186 0.02 38.877 0.03 1.21B54 0.02 0.491907 0.01 3B.852 0.03 1 .21693 0.02 0.491547 0.02 38.846 0.03 1.2164B 0.02 0.491419 0.02 38.980 0.11 1.21575 0.00 0.491512 0.00 38.902 0.06 1.21928 0.01 0.491821 0.06 38.859 0.04 1.21926 0.01 0.492191 0.01 3B.B64 0.2B 1.22197 0.05 0.492745 0.03 38.881 0.05 1.21927 0.01 0.492006 0.03 39.048 0.04 1.21810 0.01 0.490461 0.01 39.198 0.65 1.21684 0.14 0.490511 0.15 38.938 0.06 1.217B1 0.04 0.491608 0.04 38.974 0.10 1.21748 0.01 0.491598 0.04 3B.905 0.07 1.21808 0.01 0.491880 0.01 3B.940 O.OB 1.2177B 0.01 0.491739 0.03 38.939 0.07 1.21779 0.03 0.491695 0.03 39.366 0.06 1.22398 0.01 0.488203 0.06 39.356 0.05 1.22433 0.01 0.48B550 0.02 39.361 0.05 1.22416 0.01 0.48B377 0.04 39.401 0.04 1.23213 0.01 0.491419 0.04 1 52 Adams Plateau: Lead Isotope Data Sample No Deposit/Sample Name 30533-00101 OR ELL 1D (RED MINERAL) 30533-002 ORELL 1E (RED MINERAL) 30533- AVC ORELL ID N=3 (RED MINERAL) 30534- 001 ORELL 2G (RED MINERAL) 30534-00101 ORELL 2G (RED MINERAL) 30534- AVG ORELL 2G N=2 (RED MINERAL) 30535- 001 ORELL 3K (RED MINERAL) 30536- 001 ORELL 4N (SILVER KING,A) 30537- 001 ORELL SP 30537-001D1 ORELL 5P 30537- AVG . ORELL 5P N=2 30538- 001 UTAH PROSPECT (FORD) 30538-001D1 UTAH PROSPECT (FORD) 3O53B-O01D2 UTAH PROSPECT (FORD) 30538- 001D3 UTAH PROSPECT (FCSD) 30S3B-AVG UTAH PROSPECT N=4 30539- 001 MT McCLENNAN (X-CUTTIMG Mil'!) 30539-002 MT McCLENNAN 30539- AVG MT McCLENNAN N=2 30540- 501 BIRCH ISLAND (HL P45 KQ73-36) 30541- 001 SUNRISE 30541-002 SUNRISE 30541- AUG SUNRISE N=2 30542- 001 VAVENEY 30542-00101 VAVENEY 30542- AVG VAVEN9Y N=2 30543- 001 TINDALL (ADIT DUMP) 30544- 001 50NJA 30545- 001 SILVER KINC-SILVEC QUEEN 30545-00101 SILVER KING-SILVER QUEEN 30545- AVG 5ILVER KING-SILVER QUEEN N=2 30546- 001 LEEMAC 30546-00101 LEEMAC 30546- AVG LEEMAC N=2 30547- 001 ROUGE 30547-001D1 ROUGE 30547- AyG ROUGE N=2 30548- 001 PS-3S-17S 30548-0101 PS-35-175 30548-AVG PS-8S-175 N=2 Mt Anl Dual Pb6/4 J6/4 Pb7/4 *7:4 Pb8/4 *8/4 Pb6/7 5S6/7 Pb6/8 *6/8 GL FG FAIR 19.327 0.07 15.682 0.07 GL FG GOOD 19.35S 0.02 15.705 0.02 GL FG GD/FR 19.345 0.04 15.699 0.04 GL FG GOOO 19.121 0.02 15.705 0.02 GL FG GOOD 19.140 0.03 15.722 0.02 GL FG GOOO 19.131 0.03 15.714 0.02 GL FG FAIR 19.354 0.05 15.706 0.03 GL FG GOOD 19.081 0.04 15.708 0.04 GL FG GOOD 19.128 0.01 15.689 0.01 GL FG FAIR 19.128 0.05 15.694 0.05 GL FG GD/FR 19.128 0.03 15.692 0.03 GL FG GOOD ie.B93 0.02 15.704 0.02 GL FG GOOO 18.B64 0.07 15.702 0.07 GL FG GOOD 18.875 0.01 15.691 0.01 GL FG GOOO ie.8a0 0.03 15.695 0.03 GL FG GOOD 18.863 0.03 15.698 0.03 GL FG FAIR IS.249 0.05 15.680 0.05 GL FG FAIR 19.288 0.04 15.715 0.04 GL FG FAIR 19.269 0.05 15.698 0.05 GL GSC FAIR 19.335 0.00 15.820 0.00 GL FG FAIR 19.086 0.07 15.681 0.07 GL FG GOOD 19.123 0.03 15.711 0.01 GL FG FR/GD 19.105 0.05 15.596 0.04 GL FG GOOD 19.127 0.03 15.733 0.03 GL rG FAIR 19.055 0.14 15.7C3 0.13 GL FG GD/FR 19.091 0.08 15.723 0.08 GL FG GOOD 19.251 0.02 15.714 0.02 GL FG FAIR 19.355 0.06 15.E91 Q.06 GL FG GOOD 19.098 0.07 15.631 0.05 GL FC FAIR 19.110 0.06 15.635 0.06 GL FG GD/FR 19.104 0.07 15.684 Q.06 GL FG FAIR 19.406 0.04 15.741 6.04 GL FG GOOD 19.375 0.03 15.717 0.03 GL FG FR/GD 19.391 0.04 15.729 0.04 GL FG GOOD 19.267 0.01 15.750 0.00 GL FG GOOD 19.253 O.QO 15.738 0.00 GL FG GOOD 19.260 0.01 15.744 0.00 GL FG GOOD 19.180 0.00 1 5.72 5 0.00 GL FG GOOD 19.174 0.00 15.717 0.00 GL FG GOOD 19.177 0.00 15.721 0.00 39.318 0.07 1.23245 0.01 0.491567 0.01 39.377 0.03 1.23237 0.01 0.491516 0.02 39.360 0.05 1.23229 0.01 0.491493 0.02 39.044 0.03 1.21749 0.01 0.489721 0.01 39.093 0.04 1.21744 0.02 0.489604 0.03 39.069 0.04 1.21747 0.02 0.489663 0.02 39.383 0.05 1.23228 0.04 0.491420 0.02 38.899 0.04 1.21471 0.01 0.490516 0.01 38.879 0.01 1.21923 0.01 0.4919B2 0.00 3B.891 0.05 1.21881 0.02 0.491834 0.02 38.BB5 0.03 1.21902 0.02 0.491908 0.01 38.699 0.02 1.20308 0.00 0.488201 0.01 38.696 0.08 1.20267 0.01 0.488007 0.03 38.659 0.02 1.20287 0.01 0.438240 0.01 38.651 0.05 1.20292 0.01 0.488468 0.05 38.676 0.04 1.202B9 0.01 0.488229 0.03 38.932 0.06 1.22757 0.02 0.494426 0.03 39.001 0.06 1.22736 0.01 0.494536 0.05 38.967 0.06 1.22747 0.02 0.494481 0.04 39.235 0.00 1.22200 0.00 0.493642 0.00 38.BD6 0.08 1 .21715 0.03 0.491827 0.03 3B.892 0.04 1.21717 0.03 0.491691 0.02 3B.B49 0.06 1.21716 0.03 0.491759 0.03 38.889 0.03 1 .21804 0.01 0.491833 0.01 38.B02 0.16 1.21344 0.05 0.491074 0.08 38.846 0.09 1.21574 0.03 0.491454 0.05 39.080 0.05 1.22509 0.01 0.492605 0.02 39.251 0.06 1 .23353 0.00 0.493132 0.01 38.977 0.08 1.21789 0.05 0.489971 0.02 38.979 0.06 1.21826 0.01 0.490261 0.02 38.97B 0.07 1.21BC7 0.03 0.490116 0.02 39.375 0.04 1.23287 0.02 0.492849 0.01 39.297 0.04 1.23271 0.01 0.493036 0.01 39.336 0.04 1.23279 0.02 0.492943 0.01 39.172 0.03 1.22329 0.01 0.491845 0.03 39.139 0.00 1.22331 0.00 0.491910 0.00 39.156 0.02 1.22330 0.01 0.491878 0.02 38.696 0.00 1 .21977 0.00 0.492194 0.00 38.955 0.00 1.21997 0.00 0.492212 0.00 38.96 2 0.00'1 .21937 0.00 0.492203 0.00 


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