Abstract At the Kidd Creek mine, massive and stringer sulfide orebodies occur within a felsic volcanic center containing both preore and postore rhyolites. These rhyolites have undergone extensive hydrothermal metasomatism, but the rare earth and high field strength elements have remained relatively immobile, except in the footwall stringer zone. Comparisons based on rare earth elements and high field strength elements indicate that least altered Kidd Creek rhyolites have a close geochemical affinity to the felsic igneous products of anomalous midocean ridge spreading centers such as the axial rift zones of Iceland, the Galapagos spreading center, and the mid-Atlantic ridge at 45° N. Rhyolites erupted from the central volcanoes Askja and Krafla in Iceland’s eastern axial rift zone are particularly close chemical analogues of the Kidd Creek rhyolites. Other similarities between Iceland’s axial rift zones and Kidd Creek include fissure-controlled eruptions, incompatible element-enriched tholeiitic basalts and gabbros, lack of terrigenous sedimentation, absence of a continental chemical component in igneous rocks, and the presence of Mg-rich volcanic rocks (picrite in Iceland, spinifex-textured komatiites at Kidd Creek). The strong similarity to Iceland suggests that the Kidd Creek rhyolites were derived by partial melting of juvenile crust, probably hydrated basalt, in response to subsidence and a steep geothermal gradient, possibly related to an upwelling mantle plume. Geochemical and volcanological similarities make it reasonable to speculate that many of the processes occurring in the central volcanoes of Iceland’s axial rift zones also occurred at Kidd Creek. The most important of these, with respect to volcanogenic massive sulfide formation, are the coupling of anomalous heat flow and subsidence in an oceanic environment. The high-temperature hydrothermal convection system that formed the Kidd Creek deposit was driven by heat derived from the mantle, either directly or by intrusion of mantle-derived magmas. Ultramafic rocks in the footwall to the Kidd Creek formation are a manifestation of high mantle temperatures. Faults bounding subsidence structures, either rift-related grabens or calderas, provided cross stratal permeability essential for focused hydrothermal discharge. Fluid discharge into volcaniclastic debris flooring the subsidence structure promoted sulfide deposition beneath the sea floor, thereby maximizing metal retention; low accumulation rates of volcanic material favored a long-lived hydrothermal system. An additional process in the formation of the Kidd Creek ore-bodies, and some other volcanogenic massive sulfide deposits in bimodal successions, may have been a shift in the location of volcanism resulting from the introduction of siliceous magma into a mafic-ultra-mafic magmatic system.

Abstract The Kidd Creek mine is an Archean volcanogenic Cu-Zn deposit with total past production and current reserves of more than 138.5 Mt at 2.4 percent Cu, 6.5 percent Zn, 0.23 percent Pb, 90 g/t Ag, and up to 0.15 percent Sn. The massive sulfides occur at the top of a locally thickened felsic volcanic pile, within and overlying a succession of massive rhyolite flows, volcaniclastic rocks, and coarse epiclastic units. The felsic volcanics occupy the core of an anomalous, S-shaped fold structure and attain a maximum thickness of approximately 300 m beneath the deposit. Massive autobrecciated rhyolite occurs at the base of the mine sequence and is interpreted to be a proximal vent facies. The local volcanic basement comprises mainly ultramafic flows, intercalated with minor rhyolite. The ultramafic rocks are interpreted to be early extrusive lavas associated with the development of an extensional rift. Basaltic pillow lavas and breccias occur in the hanging wall of the mine and are extensively intruded by gabbroic sills. South of the mine, this stratigraphy is truncated along the contact with younger, regional metasedi-mentary rocks. Kidd Creek is typical of a class of large volcanogenic massive sulfide deposits that occur within thick successions of permeable felsic volcaniclastic rocks and are dominated by large, stratiform, Zn-rich lenses with laterally extensive zones of ore-grade Cu mineralization. The deposit consists of three main ore-bodies (the North, Central, and South orebodies) that are distributed along an inferred boundary fault of a linear, grabenlike depression. The present deposits have a restored strike length of at least 2 km, indicating remarkable continuity of the hydrothermal system along the length of the graben. The main ore lenses formed by infilling and strata-bound replacement of volcaniclastic rocks, coarse volcanic breccias, and finer grained tuffs that filled the graben. Abundant relics of silicified rhyolite within the massive sulfides, gradational contacts between the massive sulfides and unmineralized fragmental rocks at the margins of the ore zones, and extensive replacement within the hanging-wall breccias confirm that a large part of the deposit formed below the sea floor. Burial of the deposits by mass flows was coincident with mineralization, and subsea-floor deposition of sulfides progressed laterally into the volcaniclastic rocks adjacent to the ore lenses. Metalliferous sediments or exhalative horizons are notably absent, and there is little evidence that widespread venting of high-temperature fluids occurred at the sea floor. Deposition of sulfides within the thick sequence of basin fill ensured that ore-forming fluids were confined to the graben and relatively little metal was lost to high-temperature discharge. The development of the three main orebodies is best explained by a long-lived, low-temperature hydrothermal system punctuated by several higher temperature pulses of Cu-rich fluid. Focusing of the fluids was caused by intense silicification of the rhyolite above and adjacent to the main upflow zone. Extensive lateral flow occurred within the bedded volcaniclastic rocks, and the highest temperature fluids appear to have occupied a number of high-level aquifers beneath the deposits. These are marked by conformable lenses of chlorite alteration, semimassive chalcopyrite, and strata-bound chalcopyrite stringer mineralization. The larger alteration envelope is broadly conformable to the ore lenses and consists of quartz and sericite, together with chlorite, Fe-rich carbonate, and minor tourmaline. Two main ore suites occur at Kidd Creek: a low-temperature, polymetallic suite enriched in Zn, Ag, Pb, Cd, Sn, Sb, As, Hg, ±Tl, ± W, and a higher temperature suite of Cu, Co, Bi, Se, In, ± Ni. The massive ores consist mainly of pyrite, pyrrhotite, sphalerite, and chalcopyrite, together with galena, tetrahedrite, ar-senopyrite, and cassiterite, in a quartz and siderite gangue. However, more than 60 different ore minerals and ore-related gangue minerals are present, including complex assemblages of Co-As sulfides, Cu-Sn sulfides, Ag minerals, and selenides. Tin is present as cassiterite in the upper part of the massive sphalerite lenses and as stannite in the underlying chalcopyrite-rich ores. Despite the high Ag content of the deposit, Kidd Creek is remarkably Au poor. The ores exhibit a close chemical affinity with their immediate felsic host rocks, including strong coenrichments of Ag, Pb, As, Sn, W, and F However, the complex metal assemblage suggests that a more primitive mafic suite may also have played a role in metal supply. The extensive metagraywackes to the south of the mine are younger than Kidd Creek and therefore could not have been a source for metals. An abundance of pyrrhotite, arsenopyrite, high Fe sphalerite, and Fe-rich chlorite indicates predominantly low fO 2 –fS2 conditions, and the abundant siderite in the ore indicates that the hydrothermal fluids were highly enriched in CO 2 . Sulfur isotope compositions range from -2.4 to +3.3 per mil, with the bulk of the massive sulfides having S 34 S values close to 0 per mil. The mineralogy and bulk composition of the Kidd Creek ores bear a closer resemblance to those of many Phanerozoic Zn-Cu-Pb deposits (e.g., Bathurst, Neves Corvo) than to other Archean Cu-Zn deposits. The predominance of Zn-rich ores (ca. 70–80 Mt) implies that most of the deposit formed at low temperatures (ca. 250°C). Solubility modeling indicates that a large hydrothermal system at relatively low temperatures would have been sufficient to account for about 75 percent of the metals. The significant enrichments in Ag, Pb, and Sn reflect not only the abundance of felsic volcanic rocks in the mine sequence but also the sustained, low-temperature venting history of the deposit. In contrast, the Cu-rich ores appear to have been introduced during relatively short-lived, hydrothermal pulses at much higher temperatures. The higher temperatures most likely coincided with discrete felsic magmatic events that occurred at several intervals during the ∼3.5 m.y. history of the volcanic complex. The late-stage introduction of Cu may indicate that the Cu-rich fluids evolved separately from the lower temperature, con-vective part of the hydrothermal system. This model is supported by the presence of a high-grade bornite zone in the South orebody, which represents a massive influx of Cu metal at peak hydrothermal temperatures late in the development of the Cu stringer zone. Kidd Creek resembles sulfide deposits that are currently forming in young, intraoceanic back-arc rifts, such as the Lau basin, and this may be an appropriate modern analogue for the Kidd Creek setting. The combination of voluminous mafic-ultramafic flows in the footwall of the deposit, punctuated by anomalous felsic volcanism, and the extensive deposits of coarse epiclastic rocks and volcaniclastic sediments suggest that Kidd Creek formed within a subsiding rift basin. The importance of a plumelike source for the ultramafic melts and the longevity of the hydrothermal system may indicate that rifting occurred above a stationary hot spot.

Abstract The bornite zone of the Kidd Creek mine is a high-grade, replacement body occupying the core of the chalcopyrite stockwork and massive chalcopyrite lens of the South orebody. The bornite zone has produced nearly 340,000 metric tons (t) of Cu-rich ore, averaging close to 19 wt percent Cu. The mineralization consists of massive and semimassive bornite that has replaced massive chalcopyrite at the base of the South orebody. Bornite stringer mineralization occurs below the massive bornite ore and has replaced chalcopyrite in the preexisting stockwork zone of the massive chalcopyrite lens. Detailed miner-alogical studies indicate that the bornite ores were part of the late-stage hydrothermal paragenesis of the South orebody, and they are interpreted to have formed from a high-temperature pulse of Cu-rich fluids, late in the history of the Kidd Creek hydrothermal system. The bornite ores contain a complex assemblage of Cu, Co, Bi, Se, Ag, As, and Ni minerals and exhibit strong geochemical enrichments in these elements compared to other Cu-rich ores. The principal ore minerals include bornite, tennantite, digenite, enargite, mawsonite, carrollite, and numerous Ag-Bi se-lenides and Bi-Pb-Cu-Se sulfides. Tennantite-rich ores are concentrated along the contact between the massive bornite and overlying massive chalcopyrite ores and define the original replacement front. Se concentrations in the bornite are up to 1 wt percent, and the main zone of bornite mineralization is surrounded by a broad halo of Se enrichment (300–1,600 ppm). Se/S ratios in the bornite ores are among the highest recorded in any volcanogenic massive sulfide deposit. Important concentrations of Sn, In, W, and Pb appear to have been inherited from preexisting Cu- and Zn-rich sulfides during emplacement of the bornite zone. Similarities in the mineralogy and bulk composition of the bornite ores and that of massive chalcopyrite and chalcopyrite stringer ores elsewhere in the deposit suggest that they formed under similar conditions at close to peak hydrothermal temperatures (ca. 350°–400°C). However, high concentrations of Cu, Co, Bi, and Se in the bornite zone suggest that these ores were products of a uniquely enriched end-member fluid. Massive bornite formed in response to increasing a Cu+ /a Fe2+ by the replacement of pyrite and chalcopy-rite. Although late pyrite porphyroblasts are present at the margins of the bornite zone, bornite + pyrite is not an equilibrium assemblage in the ores. This suggests that the bornite did not form simply by oxidation or sulfidation of preexisting chalcopyrite. Mass balance considerations also indicate that the bor-nite ores could not have formed solely by leaching of Cu metal from the massive chalcopyrite ores, as in other bornite-rich sulfide deposits. The requirement for a massive influx of Cu at close to peak hy-drothermal temperatures suggests that the bornite zone originated during a single high-temperature pulse of Cu-rich fluid, rather than by incremental addition of Cu over a sustained period of lower temperature upflow. A Cu-rich source in the deep geothermal reservoir or from a subvolcanic magma is necessary to account for the metal enrichment. The bornite ores exhibit a complex postmineralization history dominated by the effects of regional thermal metamorphism, structural remobilization, and late-stage, metamorphic hydrothermal fluids. Regional metamorphism affected the bornite ores more than any other part of the Kidd Creek deposit because of the low thermal stabilities of minerals in the Cu-rich part of the Cu-Fe-S system and their strong tendency to reequilibrate at metamorphic temperatures. Repeated heating of the Cu-rich minerals above their maximum thermal stabilities and subsequent reequilibration of complex solid solutions during retrograde cooling resulted in extensive sulfide-sulfide reactions and the widespread development of postmetamorphic textures (i.e., myrmekitic intergrowths, exsolution lamellae, reaction rims). To a large extent, the present mineralogy of the bornite ores is a product of exsolution from nonstoichiometric solid solutions formed during metamorphism. The bornite ores were also poorly buffered against metamorphic reactions between the ore minerals, owing to the absence of a stable Fe-S-O assemblage (e.g., pyrite-pyrrhotite-magnetite). The release of sulfur during retrograde cooling caused widespread sulfidation reactions among the ore minerals and the growth of abundant, large pyrite porphyroblasts in the halo of the bornite zone. The present high sulfidation assemblages (e.g., tennantite-enargite) are metamorphogenic and do not represent conditions during the hydrothermal emplacement of the bornite ores. Late-stage metamorphic fluids were strongly localized at the margins of the bornite zone and also promoted the growth of a distinctive meta-morphic assemblage of Mg-rich chlorite, phlogopite, and dolomite in the tennantite-rich ores.

Abstract Cassiterite is a minor constituent of many volcanogenic and some sedimentary-exhalative massive sul-fide deposits. For some years, it was an important by-product of mining at Kidd Creek and is a minor constituent of the remaining ores. The mineralogy and chemistry of cassiterite from a suite of Kidd Creek ore was studied and compared with cassiterite from other massive sulfide deposits, as well as from granite-affiliated Sn deposits. At Kidd Creek, cassiterite grains are colorless, subhedral to euhedral, <0.5 mm in size, and commonly occur as isolated grains within a sulfide matrix. Cassiterite is most abundant in Pb-rich, massive sphalerite ore at the top of the North orebody, less abundant but widespread in Zn-rich pyritic ore, and least abundant in Cu-rich ore. It is most commonly associated with sphalerite, regardless of the abundance of sphalerite in the ore. Grains of cassiterite often contain single inclusions or clusters of small sphalerite grains at their cores. This association suggests that cassiterite coprecipitated with and possibly nucleated on the sphalerite grains. Cassiterite grains are also found locally within massive chalcopyrite and bornite, where these minerals have replaced earlier sphalerite at the base of the orebody. The cassiterite was preserved as relict grains and commonly contains inclusions of the original sphalerite. Some of the cassiterite has clearly broken down during high-temperature replacement, and the Sn was redeposited as various Sn sul-fominerals. The Zn-Pb ore at the stratigraphic top of the North orebody may have been enriched by partial remobilization of Sn from lower parts of the orebody. Concentrations of trace elements in cassiterite from Kidd Creek are generally low, with <500 ppm Fe, <50 ppm Nb, Zr, and Ta, and <20 ppm Cu, Zn, Pb, and W. This contrasts with cassiterite in granite-affiliated Sn deposits, which is usually strongly colored, Fe rich, and may contain high Nb, Zr, Ta, and especially W contents. The low trace metal contents in cassiterite from Kidd Creek and from other massive sulfide ores may reflect differences in the ionic charge and radii of the base metals and Sn 4+ , which might inhibit substitution in the cassiterite lattice. The reduced nature of the ore-forming fluids also favors the precipitation of Cu, Fe, and Zn in cogenetic sulfides and therefore was most likely an important factor controlling the abundance of trace metals in the cassiterite.

Abstract Approximately 30 million oz (Moz) of gold has been recovered from metamorphosed terranes in Alaska. One-third of the production has come from lodes in rhe southern half of the state, predominantly from mines in the Juneau gold belt, Chichagof district, and Willow Creek district. The majority has been taken from placers in northern and interior Alaska, including those near Nome and Fairbanks, where many of the lode sources have been completely eroded. Host terranes for gold-bearing quartz veins are dominated by pelitic rocks and range in age from Precamblian(?) to Tertiary. Ore formation, however, was reshicted to a 60-m.y. interval between Albian and Eocene time. In northern Alaska, ore-forming hydrothermal systems were active in the southern Brooks Range during Albian time, on the Seward Peninsula at 109 Ma, and in the Yukon-Tanana upland between 92 and 77 Ma. In southern Alaska, seaward of the late Mesozoic to early Cenozoic Alaska Range-Coast Mountains magmatic arc, ore formation was younger; veining occurred at 63 to 57 Ma in the Valdez Creek disttict, 66 Ma in the Willow Creek district, 55 ± 2 Ma along the Juneau gold belt, and 57 to 49 Ma in the Chugach accretionary prism. Calc-alkaline plutonic rocks occur within a few tens of kilometers of most of the gold deposits in Alaska and generally were emplaced coevally with hydrothermal activity. Ore-bearing veins are composed predominantly of quartz and show brittle and/or ductile features depending on the district. Carbonate minerals, chlorite, and white mica are common gangue phases. Sulfide minerals, most commonly pyrite or arsenopyrite, compose less than 3 percent of the vein material. Silicification, carbonization, and sericitization characterize wall rocks within a few meters of most veins. This alteration is best developed adjacent to veins in igneous host rocks. Ore fluids are H 2 O dominant, with approximately 5 to 15 mole percent CO 2 and significant amounts of CH 4 , N 2 , and H 2 S. Relatively high nonaqueous gas contents in parent fluids responsible for the Alaska-Juneau deposit, deposits in the Fairbanks disttict, and many or the veins in the Valdez Creek district resulted in episodic immiscibility accompanying gold getnesis. Fluid salinities are less than 8 wt percent NaCI equiv. Vein formation temperatures rnnged from 225° to 375°C, with emplacement depths of about 3 to 10 km. In the Fairbanks district, however, some ores were more shallowly emplaced. Ore fluid values of δ 18 O (7-12‰) and δD (-15 to -55‰) for most deposits are consistent with a fluid in isotopic: equilibrium with the metamorphic terranes and one that was produced during greeuscltist to amphibolite facies devolatilization reactions. Values of δ Dchlorite between -135 and - 187 per mil for veins from the Nome disttict provide a notable exception and may be the product of postcrystallization recquilibmtion between the micas and circulating metelogic waters. A sedimentary rock origin for sulfur in most veins is favored because δ 34 S sulfide values vary with the age of host terrane according to a pattern approximating that of matine sulfate through time. Lead isotope compositions of sulfide minemls are a function of vein host lithologies and provide little input into the understanding of gold ore genesis. Gold vein formation was related to the internction among the Kula, Farallon, and North America plates. Middle to Late Cretaceous veining in northem and interior Alaska postdated initial terrane collision and obduction of oceanic rocks by 100 m.y. The veining might be a product of rising crustal temperatures associated with continued collision, accompanied by development of a major continental margin trench and the eventual subduction of the Famllon plate. Alternatively, a shift to trench retreat and slab rollback may have caused asthenospheric upwelling, crustal thinning, plutonism, and Cretaceous hydrothermal activity above the subducting Farallon plate. Veining in southern Alaska in the early Tertiaty is hypothesized to be a product of crustal thickening and shear heating in the inner fore arc and Farallon-Kula tidge subduction in the outer fore arc.

Abstract The mining of zinc in Tennessee dates back to 1854 although the presence of zinc minerals had been reported as early as 1844 by Gerard Troost, the first State Geologist. When the Mossy Creek open pit mine, in what is now Jefferson City, Jefferson County, was opened, it became the first mine in what is now known as the Mascot-Jefferson City Zinc District. In these early years, only the oxidized ore was removed, and mining stopped when the sulfide ore zone was reached because a method to treat “hard ore”, as it was called, had not yet been developed. Mining continued at the Mossy Creek operation until 1858, then ceased through the Civil War years until 1867, at which time the property was taken over by the East Tennessee Zinc Company. This company built a smelter to manufacture zinc oxide, but after only a few months of operation, the company became involved in litigation and mining ceased. In 1882, the Mossy Creek property was sold to the Eades, Mixter and Heald Zinc Company which operated intermittently until 1894, becoming the first substantial zinc mining company in Tennessee as well as the first to produce significant amounts of sulfide ore. This latter was made possible by the construction of a zinc smelter at Clinton, Tennessee, some 45 rail-miles to the west. The Mossy Creek mine was operated or prospected only sporadically thereafter, and was closed by its final owner, the American Zinc Company, in 1919. In the meantime, the discovery of lead and zinc ore in the Powell River area of Claiborne and Union Counties, some 30 miles northwest of Jefferson City, caught the attention of the mine operators. In 1883, the New Prospect mine was opened with only the lead recovered. By 1889, Eades, Mixter and Heald had taken over, erected a mill and mined the property intermittently until 1897. The lead was handpicked and shipped to New Jersey while the zinc was barged to the smelter at Clinton. There was little further activity until World War II when the very high grade pillars were robbed. The only other producing mine in the Powell River district was at Straight Creek. It operated from 1880 to 1894, the latter part of this period by Eades, Mixter and Heald Zinc Company, which also built a mill. Beyond this there was only a short period of exploration and mining from 1906 to 1908 and another effort by Universal Exploration Company in the latter part of World War II.

Abstract The Owl Creek gold mine, now closed, lies in the Archean Abitibi greenstone belt of the Superior structural province of the Canadian shield, 18 km northeast of the city of Timmins, Ontario. The major rock types observed at the Owl Creek mine are tholeiitic basalt, carbonaceous shale, arkosic graywacke, and mudstone. All rocks have been subjected to middle greenschist facies regional metamorphism. Most gold mined occurs in the form of inclusions in vein and wall-rock pyrite in steeply dipping, highly strained tholeiitic basalt and carbonaceous shale; however, considerable free gold was also mined from quartz veins located mainly within brittle, altered basalt. Most of the buff to gray basalt is high magnesium tholeiite that is massive to locally pillowed and intensely sheared. Basalt is intensely carbonatized (ankerite-dolomite; up to 16.7% CO 2 ) and the gray color is the result of postcarbonatization addition of chlorite and carbon. Sericite and pyrite alteration of basalt followed this addition. Most auriferous pyrite is between 0.1 and 1.0 mm and resides in basalt, where it forms 5 percent of the rock; such pyrite averages 58 ppm gold (n = 21). Carbonaceous shale contains as much as 14.8 percent amorphous carbon, and carbon content is highest adjacent sheared tholeiitic basalt. Carbonaceous shale contains fine-grained disseminated euhedral, nodular, and skeletal pyrite, in order of decreasing gold content. Local accumulations of larger pyrite nodules (up to 3 cm) and small lenses of massive pyrite (up to 2 m thick) occur close to shale-basalt contacts. Gold content of shale pyrite averages 3.63 ppm (n = 19). Nodules of diagenetic and hydrothermal origins are recognized. Although the former type contains low levels of gold (x = 1.72 ppm, n = 13), sporadic zone enrichment is not uncommon (up to 80 ppm). Hydrothermal nodules are significantly enriched in gold (x = 31 ppm, n = 4). Mudstone has a much lower amorphous carbon content (<2%) than shale; pyrite occurs as scattered euhedra (<1 mm) and as disseminations in bands up to 5 cm thick which may make up as much as 15 percent of the rock. However, both types are relatively devoid of gold (x = 1.47 ppm, n = 12). Two major exposures of arkosic graywackes and a 5-m-thick interflow unit within basalt make up the bulk of enveloping sedimentary rocks at Owl Creek. Individual beds range from centimeters to tens of meters in thickness. These are interbedded with mudstone laminae which are ripped up, indicating overturned strata which young to the south. Pyrite is present as well-preserved cubes up to 10 mm in size. Graywacke pyrite contains no appreciable quantities of gold. Widespread, diffuse, but sustained hydrothermal activity in the district led to accumulation of strongly arsenical and nickeliferous pyrite in sediments that bear low but significant levels of gold; however, later epigenetic activity induced pervasive carbonate, sericite, and chlorite alteration in tholeiites and introduced auriferous pyrite via myriad thin quartz veinlets. Development of a heterogeneous deformation zone was responsible for juxtaposing of altered, brec-ciated basalt against carbonaceous sediments and promoted increased permeability in these rocks. This deformation zone was the principal conduit for gold-rich fluids, and its development controlled auriferous wall-rock pyrite and gold-bearing quartz vein precipitation at Owl Creek. Quartz veins in the highly strained rocks exposed in the Owl Creek open pit are (1) subvertical; (2) south dipping, en echelon ten-sional; and (3) more shallowly dipping to subhorizontal. All three types of quartz veins contain ore-grade concentrations of gold. Subhorizontal quartz veins may themselves be brecciated, resulting in subvertical quartzose-breccia veins consisting of angular quartz fragments and a matrix of either chlorite and auriferous pyrite or goethite and chalcedony. The presence of nonfragmented auriferous pyrite confirms that there was a gold-precipitating event which postdated emplacement of gold-bearing quartz veins. Gold in altered basalt is most closely associated with pyrite, pyrrhotite, sphalerite, chalcopyrite, and ar-senopyrite in order of decreasing abundance; however, pyrite represents no less than 95 percent of the total sulfides present. With the exception of rare euhedral arsenopyrite, all inclusions in gold-bearing pyrite are anhedral. Gold grains occur as isolated blebs or as fracture fill in pyrite but may be found adjacent to chalcopyrite-pyrrhotite inclusions or at grain boundaries between arsenopyrite and pyrite. Gold was also observed as inclusions in arsenopyrite and other sulfarsenides. Altaite and rare gold tellurides were observed only with gold inclusions in hydrothermal pyrite nodules. Distinctive assemblages of accessory minerals in pyrite separates from basalt and shale suggest that there is no clear genetic relationship between gold in euhedral pyrite in carbonatized basalt, gold in crystalline pyrite nodules in carbonaceous shale, or gold in quartz veins. Rather, a succession of discrete hydrothermal events is envisaged. Sulfur isotope ratios of all types of pyrite were measured and permit the following observations. Ore-grade auriferous pyrite has a distinctive narrow range of S 34 S signatures (1.8-3.5%) which is independent of rock type. However, a narrow positive range is not exclusively indicative of auriferous pyrite (e.g., certain types of nodules). Weakly positive correlations between gold and S 34 S values for pyrite from basalt and graywacke (in contrast to negative correlations between gold and shale pyrite) support a direct hydrothermal source for epigenetic gold in the Owl Creek ore zone.