Late Devonian–Mississippian(?) Zn-Pb(-Ag-Au-Ba-F) deposits and related aluminous alteration zones in the Nome Complex, Seward Peninsula, Alaska (original) (raw)
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Economic Geology, 2016
The Glacier Creek volcanogenic massive sulfide (VMS) deposit, Alaska, is hosted within Late Triassic, oceanic back-arc or intraarc, rift-related bimodal volcanic rocks of the allochthonous Alexander terrane, known as the Alexander Triassic metallogenic belt. The Alexander Triassic metallogenic belt is host to the world-class Greens Creek Zn-Pb-Ag VMS deposit near Juneau in the south and the giant Windy Craggy Cu-Co VMS deposit in British Columbia, about 250 km to the north. The Glacier Creek deposit, located ~80 km southeast of Windy Craggy, consists of four tabular massive sulfide lenses within a bimodal mafic volcaniclastic and rhyolitic sequence. The mineralization-hosting stratigraphy is folded by a deposit-scale anticline and offset by a thrust fault near the axial surface of the fold. A resource of 8.13 Mt has been inferred from drilling, with grades of 1.41% Cu, 5.25% Zn, 0.15% Pb, 0.32 g/t Au, and 31.7 g/t Ag. Six main mineralization types are recognized, dominated by massive barite-sphalerite-pyrite, which is replaced at the base and center of the main lenses by massive and semimassive chalcopyrite-pyrite-quartz. The flanks and tops of the lenses are carbonate rich and consist of interbedded calcite-dolomite, barite and sulfide, resedimented massive barite-sulfide, and mineralized massive carbonate rocks. Tuffaceous hydrothermal sediment, with a distinct positive Eu anomaly, overlies the massive sulfide. Pyrrhotite and chalcopyrite in stringers constitute the main "feeder zone." Stringer-style sphalerite-pyrite mineralization occurs above and below the lenses. Fe-poor sphalerite is dominant throughout the lenses, whereas Fe-rich sphalerite occurs at the stratigraphic top and bottom of the lenses in pyrrhotite-rich zones. Galena, tennantite-tetrahedrite, and arsenopyrite are the most important trace minerals within massive barite-sphalerite-pyrite mineralization, which is generally enriched in Sb, Hg, and Tl. Mineralization-related gangue minerals include barite, quartz, barian muscovite, calcite, dolomite, albite, chlorite, hyalophane, and celsian. Four types of alteration are recognized in the dominantly basaltic host rocks: pervasive muscovite-rich alteration, quartz-pyrite alteration associated with sulfide stringers, stratabound carbonate-bearing alteration, and background epidote-bearing alteration. Mass balance calculations indicate gains of S, Fe, Si, and K with coincident losses of Ca, Na, and Mg in all of the alteration types. Trace elements, Tl, Sb, Hg, Ba, Zn, Cu, and As were added to the rocks, whereas Sr was lost. Short wavelength infrared (SWIR) spectroscopy shows an increase in the wavelength of the AlOH absorption feature toward mineralization at a scale of 30 to 50 m, coincident with a general decrease in the Na, K, and Al and increase in the Fe, Mg, and Ba content of muscovite. The Glacier Creek deposit is transitional in character between Greens Creek, which is more Zn, Pb, and precious metal rich, and the Windy Craggy deposit, which is more Cu and Co rich, reflecting differences in the basement rocks and depositional settings within the Alexander Triassic metallogenic belt. Mineral-chemical studies and sulfur isotope data suggest that the Glacier Creek deposit formed under initially oxidized and sulfate-rich conditions that evolved to more reduced conditions in the latest stages of mineralization. The abundant argillite and presence of hyalophane rather than barite in the immediate hanging wall of the deposit may be an indication of a deepening basin and development of local anoxia, similar to Greens Creek. Alexander Triassic metallogenic belt remains underexplored in many parts, owing to difficult access, and many questions remain concerning the origins of these two very different VMS systems within the same belt. Recent drilling at the Glacier Creek VMS deposit, southeast of Windy Craggy, has revealed an important style of mineralization that is intermediate in character between the Zn-Pb-Ag-rich ores at Greens Creek and the Cu-Co-rich ores at Windy Craggy and may reflect the transition from a mature back-arc or intraarc rift setting in the north to a basin-margin setting in the south. Base metal sulfides and barite were initially discovered at Glacier Creek by local prospector Merrill Palmer in 1969. Exploration carried out at what would later be called the Palmer property initially focused on the Upper, Lower, and Main zone prospects, which are now known to be surface
American Mineralogist, 2017
The key magmatic processes that lead to the formation of large magmatic-hydrothermal porphyry copper mineral deposits remain uncertain, and a particular question is why a few of these deposits, such as the Pebble porphyry Cu-Au-Mo deposit, are strongly enriched in both gold and molybdenum. This study investigated the igneous rocks of the Pebble district and obtained major and trace element compositions, Sr and Nd isotopic compositions, and zircon age and trace element data to model the origin of the ore-forming magmas. The Pebble porphyry Cu-Au-Mo deposit, one of the world's largest Cu-Au resources, formed during the final stages of regional Late Cretaceous arc magmatism (101-88 Ma) in the Southwest Alaska Range. Local pre-mineral intrusions (99-95 Ma) are dominated by alkaline compositions including monzodiorite stocks, shoshonite dikes, and monzonite porphyries, but also include lesser volumes of high-K calc-alkaline diorite and granodiorite sills. The occurrence of early alkaline magmas has been noted at other gold-rich porphyry systems, including Bingham and Kerr-Sulfurets-Mitchell. Mineralization at Pebble is associated with granodiorite to granite porphyry dikes related to the >165 km 2 high-K calc-alkaline Kaskanak granodiorite batholith (91-89 Ma). Over a period of 10 m.y., Late Cretaceous melts evolved from high temperatures (930-730 °C) and modestly hydrous and oxidized conditions to relatively low temperatures (760-680 °C) and very hydrous and oxidized conditions. Collectively, all Late Cretaceous igneous rocks at Pebble contain magnetite and little or no ilmenite, are metaluminous to weakly peraluminous, and have typical arc trace element enrichments and depletions. They have moderate Sr/Y ratios (20-55) and gently sloped REE profiles (La/Yb = 5-20) that are not adakitic, which supports a source area lacking garnet that is consistent with a thin crust in southwest Alaska. Radiogenic isotopes for Late Cretaceous intrusions at Pebble have a restricted range of primitive Sr and Nd isotopic compositions (87 Sr/ 86 Sr i = 0.70329-0.70424; εNd i = 4.9-6.1), which overlap with volcanic and plutonic basement rocks of the Jurassic Talkeetna Arc along the Alaska Peninsula. The Kaskanak batholith intrudes the Late Jurassic-Early Cretaceous Kahiltna flysch, and mixing models using Sr and Nd isotopes indicate that the Kaskanak batholith assimilated ≤10 wt% Kahiltna flysch in amounts that did not likely affect magma fertility. Xenocrystic zircon samples are abundant in Cretaceous pre-mineral intrusions and have U-Pb ages similar to detrital zircon samples in the Kahiltna flysch. These data support some assimilation of upper crustal Kahiltna flysch, but the dominance of Devonian-Mississippian xenocrystic zircon populations in some intrusions suggests derivation from unexposed older basement. The extraordinary endowment of Cu and Au at Pebble is inferred to result from primitive calcalkaline and alkaline arc magmas and the hydrous and strongly oxidized conditions that suppressed the formation and fractionation of Cu-and Au-enriched sulfide melts. Furthermore, differentiation to silicic compositions was a product of extensive crystal fractionation of parental melts accompanied by minor crustal assimilation. The trace element content of the intermediate composition intrusions indicates that both hornblende and titanite fractionation processes in the mid-to shallow-crust were both required to produce the more evolved granodiorite and granite porphyry compositions. Despite the apparent lack of Mo-enriched continental crust in the region, primitive hydrous melts were produced by protracted arc magmatism and were modified by minor crustal assimilation including early alkaline magmatism, periodic recharge of mafic hydrous basalts and hybrid andesites, and fractional crystallization, which was apparently sufficient to enrich Mo in late stage felsic melts.
Contributions to the Au …, 1998
Sedimentary platform rocks in northern Nevada serve as hosts for the bulk of the gold in Carlin-type gold deposits. These deposits largely account for this region comprising the most significant gold province in North America. The most prolific part of the Carlin trend is the northern half, which extends from the Gold Quarry Mine on the south to the Dee Mine on the north. Although sedimentary rocks constitute a fundamental element of genetic models for Carlin-type deposits, the implications and impacts of Paleozoic sedimentary fabrics and diagenetic processes on deposit genesis have not been investigated as thoroughly as have the associated alteration, chemistry of the mineralizing fluids, and structural setting(s) of the deposits. Five Silurian-Devonian rock units below the Roberts Mountains thrust are the principal gold-hosting units in the Carlin trend; these are the Hanson Creek Formation, Roberts Mountains Formation, Bootstrap limestone, Popovich Formation, and the Rodeo Creek unit. Of these units, only the Roberts Mountains and Popovich Formations have the mineralogy and porosity which favors gold mineralization. In both the Roberts Mountains and the Popovich Formations, the sedimentary rocks are typically calcitic dolostones with primary intercrystalline vug porosity resulting essentially from diagenetic crystallization of dolomite. The Roberts Mountains and Popovich Formations thus had an inherent porosity due to primary early crystallization of dolomite in lime mud (micrite) and an abundance of intercrystalline sulfur-rich carbon has subsequently enhanced its reactivity to gold-bearing fluids that circulated there during the Cretaceous and (or) Tertiary. The sequence of rocks discussed in this report lies below the regionally extensive Roberts Mountains thrust. They include a number of structurally autochthonous units: (1) The Ordovician to Silurian Hanson Creek Formation, which is composed of arenaceous dolostones, is the lowest unit studied. These sedimentary rocks were deposited as arenaceous, pellet, peloid, ooid, packstone, and grainstone in a shallow water, shoaling environment as the final phase in a thick, upward shoaling sequence. (2) The Silurian and Devonian Roberts Mountains Formation, lying
Economic Geology, 2008
The Blake River Group of the Abitibi greenstone belt is host to the well-known volcanogenic massive sulfide (VMS) deposits of the Noranda camp, Québec, Canada. In the Noranda camp massive sulfide deposits are spatially associated with the coeval Flavrian-Powell intrusive complex, which is interpreted to have driven hydrothermal circulation that formed the deposits in the camp. In the western Blake River Group in Ontario there are also abundant intrusive rocks, yet relatively insignificant accumulations of VMS deposits. These intrusive rocks are younger (2686.9 ± 1.2 and 2688.5 ± 2.3 Ma) and are associated with porphyry-style Cu-Mo-Au mineralization with Re-Os molybdenite ages of 2682.4 ± 5 Ma. The intrusions are also smaller in areal extent and do not have a temporally extended, polyphase history like the Flavrian-Powell intrusive complex. The intrusions of the western Blake River Group can also be distinguished by lithogeochemical attributes and a distinct petrological history compared to the Flavrian-Powell intrusive complex.
Economic Geology, 2014
The Kennecott district, Alaska, contained three important copper-(silver) orebodies, Bonanza-Mother Lode, Jumbo, and Erie, and numerous other small occurrences. From 1911 to 1938, the Kennecott Copper Corporation recovered some 1.18 billion pounds (Blbs) of copper and around 9 million ounces (Moz) of silver from these deposits. The host rocks for the Kennecott deposits are part of the type section Wrangellia terrane. Ore was hosted in the Triassic (Carnian) Chitistone Limestone, most of it located 20 to 40 m above the contact with the native copper-bearing Triassic (Ladinian) Nikolai Greenstone. The Bonanza-Mother Lode and Jumbo orebodies are upward-tapering veins having wide bases controlled by one or more, often subtle, bedding-parallel fault(s); they plunge downdip to the northeast with long axes approximately parallel to the direction of regional shortening. The veins hosting the orebodies occupy NE-striking oblique-slip faults with dextral and normal kinematics that were probably formed between 155 to 110 Ma during the docking of Wrangellia with North America.
Atlantic Geology, 1999
Cu-Ag deposit occurs within a ca. 1 m wide quartz vein characterized by comb, cockade, crustiform, and breccia textures. The mineralized vein, NW-trending and steeply dipping, has a medium-to coarsegrained, biotite-muscovite±cordierite monzogranite phase of the 370 Ma Musquodoboit batholith as its hanging wall and a fine-grained felsic dyke rock as its footwall. Silicate mineralogy in the vein is dominated by quartz with trace amounts of Kfeldspar (Or86.l00), muscovite (<2 wt. % FeO, <0.8 wt. % F), chlorite, and kaolinite, whereas sulphides include Fe-poor sphalerite (<4 wt. % Fe), galena, chalcopyrite, and a variety of secondary Cu sulphides. Dating (40Ar/39Ar) of vein muscovite and the footwall dyke rock indicate similar ages of 370 Ma; therefore, vein formation and dyke injection are interpreted to be coincident with emplacement of the 370 Ma Musquodoboit Batholith. Fluid inclusion studies of aqueous, L-V inclusions indicate homogenization temperatures of ca. 140 ± 5°C and salinities of 20 ± 2 wt. % eq. NaCl, but minor amounts of inclusions with higher (24 to 27 wt. %) and lower (8-16 wt. %) salinities occur. First melting temperatures and analysis of decrepitate mounds indicate two fluid types, a more abundant NaCl-H20 fluid and a less abundant NaCl-CaCl2-KCl-H20 fluid. Sulphur isotopes for hypogene galena, chalcopyrite, and sphalerite are uniform and equate to 834Sh 2s of +4.2 to +6.6%o (at 300°C), which is similar to data for other granite-related sulphide mineralization in the Meguma Zone. Vein quartz has an 8lsO value of +15.3 ± 1.2%o (n=10), which equates to Sl8Owater of +9 to +11.5%o at 300°C, whereas fluid inclusion extracts indicate 5D values of-90 to-113%o (n=6). Collectively, the timing of mineralization (i.e., 370 Ma) and the dominantly magmatic isotopic and geochemical signature for the vein-forming fluid suggest a genetic association with the Musquodoboit Batholith. However, the Ca-rich nature of some fluid inclusions and low 5D values of fluid extracts suggest involvement of another reservoir, possibly reflecting a fluid that equilibrated with the country rock of the Meguma Group. La mineralisation au depot de Pb-Zn-Cu-Ag Dunbrack se produit dans une veine de quartz d'une largeur c. 1 m caracterisee par des textures de peignes, cockade, crouteuses et de breches. La veine mineralisee en direction nord-ouest a un pendage i pente forte, et une phase a grain grossier, de biotite-muscovite+cordierite monzogranite provenant du batholite Musquodoboit de 370 Ma en tant que 16vre superieure et a un dyke a grain fin de roche felsique en tant que sa 16vre inferieure. La mineralogie de silicate dans la veine est dominee par le quartz avec des traces de K-feldspath (Or86.10o): muscovite (<2 poids en pour-cent de FeO, <0.8 poids en pour-cent de F), chlorite, et kaolinite, tandis que les sulfures incluent la sphalerite pauvre en Fe (<4 poids en pour-cent de Fe), la gal&ne, la chalcopyrite, et une varidte de sulfures secondaires de Cu. La datation (40Ar/39Ar) de la veine de muscovite et du dyke de roche a levre inferieure indiquent des ages semblables de 370 Ma ; done, la formation de veine et l'injection de dyke sont interpretees pour etre coi'ncidentes avec la mise en place Batholite Musquodoboit de 370 Ma. Les etudes d'inclusions fluides « L-V » et aqueuses, indiquent les temperatures d'homogeneisation de c.140 ± 5°C et salinites de 20 % equivalent poids en pour-cent ± 2 NaCl, mais a des quantity mineures d'inclusions avec plus haut (24 a 27 poids %) et abaissement (8-16 poids %) des salinites produites. Les premieres temperatures et analyse de fonte des monticules decrepites indiquent deux types de liquides, un fluide plus abondant de NaCl-HO et un fluide moins abondant de NaCl-CaCl2-KCl-HO. Les isotopes de souffe pour la gaiene hypogee, la chalcopyrite, et la sphalerite sont uniformes et egalisent 4 834Sh 2s of +4.2 to +6.61 (e 300°C), semblable a des donnees pour d'autre mineralisation de sulfure jumeler au granite dans la zone de Meguma. Le quartz de veine a une valeur de 8lsO +15,3 ± 1.21 (n=10), qui egalise k 8l8Oeau de +9 a +11.51 a 300°C, tandis que les extraits liquides d'inclusion indiquent des valeurs de 8D de-90 a-1131 (n=6). Collectivement, la synchronisation de la mineralisation (c.-ad ., 370 Ma) et la signature isotopique et geochimique principalement magmatique pour le fluide provenant de veine suggerent une association g6netique avec le Batholite de Musquodoboit. Cependant, la nature riche en calcium de quelques inclusions liquides et valeurs basses 8D d'extraits liquides suggerent la participation d'un autre reservoir, refietant probablement un fluide qui a equilibre avec la roche de la region du Groupe de Meguma. [Traduit par la redaction]
Professional Paper, 1999
The north-central and northwestern Brooks Range of Alaska hosts widespread Zn-Pb-Ag shale-hosted massive sulfide (Sedex), vein-breccia, and disseminated sulfide deposits. The vein-breccia and disseminated occurrences show no obvious igneous association and are hosted by a deformed, but only weakly metamorphosed, package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group). The Sedex deposits (i.e., Red Dog, Drenchwater) are hosted by black siliceous carbonaceous shale and mudstone of the Mississippian to Pennsylvanian Kuna Formation. Previous studies have suggested that the vein-breccia zones are either Carboniferous or were formed along Mesozoic or post-Mesozoic faults. This study documents a Mississippian age for the Kady vein-breccia prospect and investigates the physical and chemical controls on ore formation. Early diagenetic and hydrothermal features at the Kady Zn-Pb-Cu-Ag vein-breccia prospect provide insights into Carboniferous basinal dewatering of the Upper Devonian to Lower Mississippian Endicott Group in the northern Brooks Range, Alaska. Sulfides at Kady occur in several subparallel, quartzdominated, linear vein-breccia zones (1-35m wide, with a minimum strike length of about 800 m), which are offset by Mesozoic structures, and as permeability-controlled, strata-bound disseminated cements in gray sandstone in a 5-km by 3-km area. Sphalerite ((Znsi.S-99. 7 , Feo.J-t 7. 9 , Cd 0. 1 _ 0. 9)S) is the dominant sulfide mineral, followed by galena, chalcopyrite, minor pyrite, trace bravoite and Ag+Sb±Pb sulfosalts, and extremely rare pyrrhotite. The relative proportion and volumetric abundance of the primary minerals varies widely within and between veinbreccia zones. Main stage quartZ+sulfide (±late calcite) veinbreccia zones cut rare early ankerite and siderite veins. Sulfides and quartz precipitated during a steep drop in temperature, possibly during the change from lithostatic to hydrostatic pressure during extensional faulting, from a relatively low temperature (::; 250°C), slightly acidic, carbon-destructive hydrothermal fluid. Textural and mineralogical data indicate that sulfides and quartz were deposited under evolving chemical conditions (i.e., increasing pH, fugacity of oxygen, and fugacity of sulfur). The lack of known Sed ex mineralization in the northcentral Brooks Range suggests that Kady represents the hydrothermal fluid pathway below a failed or nonexistent Sedex system. Although early diagenetic processes within the Endicott Group were favorable for the mineral-destructive release of base metals from detrital minerals, base metals were not transported and deposited in overlying shales but, rather, were deposited within the Endicott Group. Unfavorable conditions may have existed for Sedex deposit formation above the Kady prospect including one or more combinations of the following: boiling above the level of the vein-breccia system leading to rapid precipitation of base metal sulfides in the vein-breccias; dispersion of buoyant, low-salinity, metal-bearing fluids (if they reached the sea floor) such that metals would not be deposited and accumulated in massive amounts; and a short-lived, lowtemperature system. 1 Killik River (A-4) quadrangle, Townships 32 N. and 33 N., 1 Range 17 E., section numbers shown on map !!!.
Economic Geology, 1995
The Blende zinc-lead-silver deposit, 60 km northeast of Keno City, Yukon Territory, is spatially associated with a mid-Proterozoic fault zone that crosscuts stromatolitic dolostones of the Middle Proterozoic, upper Gillespie Lake Group. It is the largest known strata-bound, carbonate-hosted, zinc-lead deposit in the Yukon Territory. Mineralization, largely epigenetic, consists of sphalerite and galena, with lesser pyrite and chalcopyrite, and trace friebergite in quartz-carbonate veins and veinlets. Veining is zoned from copper-and silver-rich mineralization at the base of the deposit, through lead-and zinc-rich, to zinc-dominated at the top. Detailed cross-section mapping indicates that controls on the deposit are both stratigraphic and structural. Many of the stromatolite beds are mineralized and are especially rich in lead and zinc close to normal faults. Fluid inclusion studies indicate that mineralizing fluids were about 285øC during main-stage mineralization. Sulfur isotope analyses of unmineralized whole-rock samples cluster tightly around an average •i34S value of 23.6 _+ 0.4 per mil. The source of sulfur is apparently seawater sulfate, probably from minor anhydrite in the host dolostone. Sulfide sulfur isotope ratios define three populations. Local blebs of pyrite associated with stromatolites have markedly negative ratios (-15.1%) that are probably bacteriogenic in origin. Vein sulfides in tight dololutites have ratios between 19.0 and 26.3 per mil, with an average •i34S value of 23.2 _+ 0.9 per rail. This is virtually identical to the whole-rock sulfur isotope ratio. Veins that crosscut stromatolitic beds have sulfur isotope ratios between 18.3 and 7.4 per mil with a mean of 15.0 _+ 1.2 per mil. Intermediate sulfur isotope ratios apparently reflect a mixed sulfur source of both whole-rock sulfate and biogenic sulfide. Carbon and oxygen isotopes in host rocks and ore-stage dolomite spar are related genetically; both are related to ancient seawater. The calculated isotopes for mineralizing fluids are characteristic of basinal brines. Galena lead isotopes, interpreted using the shale model, indicate an age of 1.4 to 1.5 Ga for the deposit. This is older than, or penecontemporaneous with, regionally extensive diorite sills (1380 _+ 4 Ma, U-Pb zircon) that occur below the upper Gillespie Lake Group. However, a close spatial association of mineralization to upper parts of sills and the high temperature of ore fluids from fluid inclusion homogenization temperatures supports a genetic relationship between the sills and mineralization. During the winter the property can be reached by the Wind River trail, an established winter road. The Blende is centered near Mount Williams, a distinctive peak in the southern Wernecke Mountains. Pleistocene to Recent glaciation has modified the terrain; slopes are mostly oversteepened and cirques are common above 1,370 m. Property at the Blende was first staked in 1975 as the Will claims by the Cyprus Anvil Mining Corporation to cover a geochemical stream sediment anomaly. Archer, Cathro and Associates (1981) Ltd. restaked the prospect as the Blende claims in 1981. Work continued sporadically until 1986 when NDU Resources Ltd. acquired the claims and initiated a drill program in 1988 consisting of three holes totaling 718 m. In 1989 the deposit was optioned to Billiton Metals Canada, Inc., for a 50 percent interest. Drilling programs in 1990 and 1991 were operated by Billiton with field management by Archer, Cathro and Associates. Reserves currently outlined by 20,000 m of diamond drilling are 20 Mt of ore grading 6 percent Zn q-Pb. This paper presents the results of detailed geologic section mapping and sampling. Petrographic, fluid inclusion, and stable isotope analyses were done on many hand and drill core samples. Galena lead isotopes were used to date mineralization. U-Pb analysis of zircons from a coarsegrained diorite sill determined the age of spatially and probably genetically related intrusions. Regional Stratigraphic Setting The Blende deposit is hosted by the Wernecke Supergroup (Fig. 1), a Middle to Late Proterozoic shelf assemblage deposited during periodic extension at the margin of ancestral North America (Thompson et al., 1986).
Results of sulfur and oxygen isotopic studies of sedimentary-exhalative (SEDEX) Zn-Pb(-Ag-Au-Ba-F) deposits hosted in metamorphosed Paleozoic clastic and carbonate rocks of the Nome Complex, Seward Peninsula, Alaska, are consistent with data for similar deposits worldwide. Stable isotopic studies of the Nome Complex are challenging because the rocks have undergone Mesozoic blueschist-and greenschist-facies metamorphism and deformation at temperatures estimated from 390 to 490 °C. Studies of sulfur and oxygen isotopes in other areas suggest that, in the absence of chemical and mineralogical evidence for metasomatism, the principal effect of meta-morphism is re-equilibration between individual minerals at the temperature of metamorphism, which commonly leads to a narrowing of the overall range of isotope values for a suite of rocks but generally does not signifi cantly modify the average whole-rock value for that suite. Sulfur isotopic studies of the stratabound and locally stratiform sulfi de lenses at the Aurora Creek–Christophosen deposit, which is of possible Late Devonian–Early Carboniferous age, show a large range of δ 34 S sulfi de values from –9.7‰ to 39.4‰, suggesting multiple sulfur sources and possibly complex processes of sulfi de formation 235 *Current address: 7309 W.