Abstract Flake graphite is a critical battery material due to its role as the primary anode component in lithium-ion batteries. With the shift to electrification of vehicles, it is forecast that in the next five years flake graphite’s number-one use will be in battery applications, overtaking its traditional industrial uses. The burgeoning demand for battery anode materials is anticipated to double the current natural flake graphite market of roughly 645,000 tonnes per annum by 2025, which will require new flake graphite sources like the Molo graphite deposit to come into production. The Molo graphite deposit is world class due to its large size (NI 43–101 measured resource of 23.62 Mt at 6.32% C, indicated resource of 76.75 Mt at 6.25% C, and inferred resource of 40.91 Mt at 5.78% C), high proportion of large and jumbo flake (46.4%), and high average flake carbon purity (97.27% C). The deposit was discovered in 2011 as the result of a regional exploration program initiated by NextSource Materials Inc. following their delineation of a vanadium deposit called the Green Giant. Graphitic mineralization in the Molo is bimodally distributed, with low-grade and high-grade zones having carbon cutoff grades of 2 and 4% C, respectively. High-grade mineralization is associated with metamorphosed siltstones and mudstones, while low-grade mineralization is associated with rocks interpreted to represent metamorphosed sandstones, which are interpreted to be more favorable hosts for large- and jumbo-flake graphite. The Molo graphite deposit appears to have resulted from many mineralizing events, which extended over a period of time that may range from ca. 900 to ca. 490 Ma. These include graphitization during the emplacement of anorthosite complexes, graphitization in a high-strain regime under high-pressure and high-temperature granulite facies metamorphism during the collision of the Androyen domain with the Vohibory domain, graphite refining and recrystallization believed to have taken place during East Gondwana and West Gondwana collision, and the formation of postcollisional hydrothermal vein graphite during orogenic collapse. The superimposition of the tectono-metamorphic history of southern Madagascar on a sedimentary sequence in which the protoliths were rich in organic carbon has resulted in world-class flake graphite mineralization with high carbon purities and large flake sizes.

Abstract ARCHEAN Cu-Zn deposits are among the most important mineral deposit types in Canada. The Superior province of Canada contains nearly 80 percent of the known Archean Cu-Zn deposits in the world (about 100 of 125 deposits). These deposits are concentrated in 10 separate mining camps, including Sturgeon Lake, Manitouwadge, Mattagami Lake, Chibougamau, Joutel, Val d’Or, Bous-quet, Noranda, Kidd Creek, and Kamiskotia (Fig. 1 and Table 1). A few deposits in rocks of similar age and composition are also known in the Slave province, the Churchill province, and in the Archean of Western Australia, southern Africa, China, and Brazil. Known deposits of this age worldwide account for more than 650 million metric tons (Mt) of massive sulfides, containing 10 Mt of Cu metal, 29 Mt of Zn, 1 Mt of Pb, 33 Mkg Ag, and 750,000 kg Au. The giant Kidd Creek volcanogenic massive sulfide deposit in the western Abitibi subprovince of Canada is the largest known deposit of this age currently in production. The Superior province is the world’s largest exposed Archean craton, occupying an area of more than 1.5 million km 2 , bounded by the Trans-Hudson orogen to the west and the Grenville province to the east. A number of distinct subprovinces are recognized, assembled into east-west-trending granite-greenstone terranes and metasedi-mentary belts (Fig. 1). The granite-greenstone terranes are composed of gneissic rocks of plutonic origin,

Abstract The Kidd Creek copper-zinc-silver deposit, situated in the Late Archean Abitibi greenstone belt of northeastern Ontario, represents one of the world’s largest and highest grade volcanogenic massive sul-fide deposits. Its discovery, in late 1963, not only marks a major event in Canadian exploration history, but is also intimately linked to the ascendence and successful application of the syngenetic volcanogenic concept in Canada. Events leading up to and surrounding the discovery are documented and provide a historical background to other contributions in this volume on the geology of the Kidd Creek deposit.

Abstract Results from a comprehensive U-Pb geochronology study of the Kidd Creek deposit and the surrounding Kidd Volcanic Complex are presented. Eleven new zircon and two titanite ages are reported and integrated with U-Pb age results on five related samples, which were published in a previous study. Zircon ages for rhyolite volcanism of the Kidd Volcanic Complex range from 2717.0 + –2 2 . . 5 6 to 2711.5 ± 1.2 Ma. This age range is established on immediate footwall and hanging-wall rhyolites of the Kidd Creek orebody. Since both footwall and hanging-wall rhyolites can be linked to ore formation, the conclusion must be that the giant Kidd Creek deposit is the product of unusually long-lived, albeit episodic, sea-floor hydrothermal activity. Our most precise estimate for the age of footwall rhyolites at Kidd Creek is provided by results on two nearby rhyolites that have been dated at 2716.1 ± 0.6 and 2716.0 ± 0.5 Ma, respectively. The age of at least one large massive sulfide lens at Kidd Creek, the North orebody, has been tightly bracketed between the age of footwall rhyolites and the age of an overlying rhyolite lapillistone horizon dated at 2715.8 ± 1.2 Ma. Hence, ore formation of individual massive sulfide lenses appears to have been rapid and well within the resolution limits of current U-Pb dating techniques. Based on the large number of ages, it appears that volcanic activity of the Kidd Volcanic Complex can be divided into four general phases, each of which is supported by at least one or more high-precision ages: phase I, onset of bimodal komatiite and rhyolite volcanism, probably as early as 2717.7 ± 1.1 Ma, and extrusion of the footwall assemblage at Kidd Creek at ca. 2716 Ma; phase II extrusion of ca. 2714 Ma rhyolites; phase III, extrusion of ca. 2711 Ma rhyolite, including the quartz porphyritic hanging-wall rhyolite at Kidd Creek; and phase IV, extrusion of the hanging-wall basalt sequence and intrusion of subvolcanic gabbro sills sometime after 2711 Ma. The Kidd Creek deposit probably formed along the axial zone of a slow-spreading rift basin that developed during extension of an older volcanic-arc assemblage. This older arc assemblage, which included ca. 2723 and 2735 Ma components, is probably represented by the Deloro Group and correlative assemblages exposed to the south of Timmins. Rifting of the older volcanic substrate, and partial melting to produce the rhyolites, was induced by the arrival of a hot mantle plume that gave rise to the komatiites of the Kidd-Munro assemblage. Graywacke turbidites in the Kidd Creek area are all younger than ca. 2699 Ma and do not form the deeper stratigraphic footwall to the deposit. Instead, the graywackes probably overlie, unconformably to disconformably, all the volcanic assemblages in the region. From the sub -sequent protracted structural-metamorphic evolution in the area, two discrete events have been dated: the 2663.3 ± 3.3 Ma intrusion of the Prosser porphyry granitoid stock and a discrete 2639.1 ± 7.2 Ma metamorphic-hydrothermal event. The timing of both events corresponds closely to ages for granulite facies metamorphic events in lower crustal rocks of the nearby Kapuskasing structural zone.

Abstract Although the Late Archean Kidd Creek volcanogenic massive sulfide deposit is one of the largest and highest grade deposits of its kind in the world, a detailed documentation of its geology has hitherto not been available. This paper presents the results of a detailed and integrated investigation of the mine structure and stratigraphy and places these in a regional context of the southwestern Abitibi greenstone belt. The Kidd Creek orebody consists of a series of stacked lenses hosted by a complex, proximal volcanic stratigraphy associated with a ca. 2717 to 2711 Ma, subaqueous, high silica rhyolite complex that developed diachronously within what appears to have been a linear graben or half-graben structure. The mine stratigraphy has experienced polyphase folding and faulting and presently outlines a northwest-trending reclined fold (F 1 ) that is part of a larger interference structure involving one older and one younger regional folding event. The various ore lenses and their chalcopyrite stringer stockworks occur as variably stretched bodies on the western, steeply overturned limb of the reclined F 1 fold, which is referred to as the “Kidd Creek mine fold.” Internal deformation of the orebodies is strong but heterogeneous. Ore lenses have been tightly folded, thickened, partly transposed, and strongly elongated parallel to a steeply plunging stretching lineation that is subparallel to the axes of the Kidd Creek mine fold and its parasitic structures. On the scale of the mine, the fold interference structure is coaxial and sufficiently systematic so that the orebody can be unfolded and a semiquantitative reconstruction of the primary geometry, stratigraphy, and setting can be obtained. The resulting model is both simple and comprehensive and allows most of the detailed aspects of this giant deposit to be placed in a spatial and temporal context. A detailed stratigraphic section and description of the rock units document the entire Kidd Creek stratigraphy and provide the framework in which detailed parallel studies on the U-Pb geochronology, chemostratigraphy, and ore genesis have been carried out. Long-lived venting into the volcaniclastic fill of a relatively stable graben or half-graben structure, bounded by at least one deeply penetrating synvolcanic fault, is seen as the key control that led to a single giant deposit.

Abstract Quartz and quartz-feldspar porphyritic rhyolite (QP rhyolite) overlies a succession of bedded volcani-clastic deposits and massive sulfide lenses at the Kidd Creek mine and represents the last significant phase of felsic volcanism at the deposit. Isopach maps clearly illustrate that the QP rhyolite consists of two separate ridges, a north ridge exposed in mine workings east of the mine shafts, and a south ridge located south of the shafts. The north and south ridges have a combined volume of approximately 0.1 km 3 to the 4700 level. Aspect ratios of less than 10, the predominance of massive and flow-banded rhyolite with an intact re-crystallized spherulitic groundmass, the lack of broken phenocrysts and bedding, and the internal lobelike flow morphology indicate that the ridges are subaqueous rhyolite flows or domes and not pyro-clastic deposits. The ridgelike morphology of the QP rhyolite is best explained by eruption from two parallel fissures that are now subparallel to the northeast-trending F 1 fold axial plane. Features that support this interpretation include: (1) the parallel and linear orientation of the ridges, (2) the occurrence of distinct domes along both ridges, (3) the presence of coarse breccia flanking the domes, and (4) inferred flow direction vectors that indicate flow away from the domes. Thus, the QP rhyolite is interpreted as a fissure-fed, vent-proximal flow-dome complex that erupted from two parallel fissures located approximately 800 m apart. Passive fissure eruptions and endogenous dome growth resulted in the construction of the two ridges that extend for at least 1.9 km. Two rhyolite domes constructed above the north fissure and the one elongate dome constructed above the south are interpreted to mark specific vent sites along the ridges that had high lava extrusion rates and/or sustained eruptions. The inferred fissure beneath the north ridge may have acted as a conduit for ascending hydrothermal fluids before and after QP rhyolite volcanism and is interpreted to have controlled the location and deposition of the South orebody. Hydrothermal activity continued after QP rhyolite volcanism, as indicated by patchy to pervasive alteration, primarily sericitization, silicification, and feldspar destruction, as well as sphalerite mineralization within the QP rhyolite and lesser alteration in basalts above the north ridge. The QP rhyolite was emplaced at the end of hydrothermal activity; structures which controlled its emplacement may have controlled the location of underlying massive sulfide deposits. The QP rhyolite may be geochemically distinguished from underlying rhyolites. This may prove to be important, since QP rhy-olite volcanism marks the end of hydrothermal activity at Kidd Creek and exploration in, and outside of, the mine area should be focused on strata below the QP rhyolite or time-stratigraphic equivalent units. The Southwest orebody, initially interpreted to occur within the QP rhyolite, is now interpreted to occur within underlying volcaniclastic rocks of the Middle member.

Abstract Komatiites are the most abundant rock type in the stratigraphic footwall of the giant Kidd Creek volcanic-associated massive sulfide deposit. They comprise primitive, Al-undepleted flows with a preserved thickness of ∼0.8 km and correlate with ∼100 km 3 of ultramafic rocks within 30 km. Individual flows in the immediate footwall have mesocumulate peridotitic bases, spinifex-textured and flow-breccia tops, and contaminated margins. They have estimated prestrain cross-sectional areas of ∼10 to 200 m in thickness and ∼250 to 700 m in width. As a package, they parallel the orebody and footwall rhyolite flow lobes to a depth of at least 3 km. Their textures and geometry suggest a channel flow facies within a tectoni-cally active linear topographic depression, consistent with a paleo-graben oriented subvertically and facing west. The komatiitic rocks are intimately intercalated with massive and epiclastic rhyolite beneath the ore and the ore-hosting mine rhyolite unit. Textural relationships indicate that komatiite flows postdated and partially melted earlier formed rhyolite. These include ultramafic dikes and apophyses that cut rhyolite, partial melt textures in rhyolite adjacent to komatiitic rocks, back-veining of siliceous partial melts into ultramafic rocks, possible thermally shocked quartz in siliceous partial melt at komatiite-rhyolite contacts, and olivine spinifex textures quenched at the contacts with rhyolite fragments. Liquid compositions from least contaminated, quench-textured komatiite flow tops and flow-top breccias have Mg/(Mg + Fe) of 79 to 82, MgO = 17.7 to 24.0 wt percent, Cr = 1,940 to 2,660 ppm, Al 2 O 3 = 6.0 to 10.3 wt percent, TiO 2 = 0.33 to 0.61 wt percent, and La N /Yb N = 0.7 to 1.1 (anhydrous, n = 4). Their average composition corresponds to a primitive mantle partial melt of ∼33 to 38 percent or to higher degrees of partial melting accompanied by olivine fractionation prior to emplacement. Other komatiites and related high Mg basalts can be explained by relatively limited fractionation of average peridotite cumulate, accompanied by slight contamination using the average footwall rhyolite as the contaminant. These rocks have Mg numbers of 55 to 76, MgO = 7.0 to 15.0 wt percent, Cr = 100 to 1,900 ppm, Al 2 O 3 = 8.8 to 14.3 wt percent, TiO 2 = 0.45 to 0.56 wt percent, and La N /Yb N of 1.4 to 2.2 (anhydrous, n = 4). More highly contaminated komatiites are also present, with many samples explained by ∼20 to 40 percent fractionation accompanied by ∼20 to 40 percent assimilation of the footwall rhyolite. The volcanology of the Kidd Creek komatiitic footwall rocks can be considered in the context of the Norseman-Wiluna greenstone belt of Western Australia, where komatiite volcanic facies have been defined. The footwall komatiites are comparable to the channel flow facies at Kambalda at the southern end of the Norseman-Wiluna belt, believed to be medial or distal with respect to source vents. A medial or distal facies would suggest coeval but spatially distinct source vents for the intercalated footwall komati-ites and proximal rhyolites. However, a source vent for komatiite flows in the Kidd Creek footwall is possible, given the presence of well-preserved ultramafic dikelets; the spatial coincidence with the vent area for a giant metal-precipitating hydrothermal system, with feeder dikes to the hanging-wall basalts and gabbros, and with synvolcanic faults. Contiguous ultramafic rocks within 30 km of Kidd Creek are 10 to 100 times less voluminous than those of the Norseman-Wiluna belt, and they lack appreciable dunitic rocks which are diagnostic of proximal, sheet, or channel flow facies. If the Kidd Creek footwall represents a locus of komatiite fissure eruptions, the komatiites were less voluminous, and less magnesian, those of the Norseman-Wiluna belt.

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 Rhyolites in the vicinity of the Kidd Creek mine are altered to quartz-sericite and quartz-chlorite assemblages, with minor Fe-Mg carbonate and tourmaline. The deposit overlies a large volume of silicified rock that extends for up to 300 m below the ore lenses. The main upflow zone is centered on the thickest accumulation of massive rhyolite, which has been altered to a fine-grained, gray, highly siliceous rock known as “cherty breccia.” At the margins of the main upflow zone, the mine rhyolites are altered mainly to quartz and sericite, forming a distinctive halo around the deposit. However, the alteration extends only a few tens of meters into the hanging wall and is truncated by gabbroic sills intruded across the top of the deposit. The uppermost quartz porphyry unit of the mine sequence shows only minor sericitization and sphalerite staining. Close to the ore zones, quartz, sericite, and chlorite replace the matrix of fragmental rocks and occupy fracture networks in brecciated rhyolite. Discordant zones of chlorite alteration cut the most intensely silicified rocks immediately beneath the massive sulfide lenses and host the main chalcopyrite stringers. Chlorite-rich rocks also occur as strata-bound lenses within the footwall rhyolites where fine-grained, interflow tuffs have been replaced by conformable zones of chalcopyrite stringer mineralization. Quartz-sericite rocks marginal to the chalcopyrite stringer zones are stained by sphalerite and are host to widespread sphalerite stringer mineralization, which is interpreted to be the remnants of an earlier Zn-rich stockwork. Fe-Mg carbonates (ferroan dolomite, ankerite, and siderite) are intimately associated with the ore and occur immediately adjacent to and within the massive sphalerite lenses. Lower CO2/CaO ratios away from the ore zones reflect mainly regional-scale dolomitization of the rhyolites. Immobile element plots indicate significant mass and volume change associated with the alteration. Large mass gains of SiO in the footwall were accommodated by a substantial increase in volume associated with locally intense crackle brecciation of the rhyolite. Bulk SiO 2 contents in these rocks commonly exceed 85 wt percent. Silicification of the mine sequence is coincident with a large zone of alkali depletion that can be traced for several hundred meters laterally away from the ore lenses. The cherty rhyolite in the immediate footwall is stripped of Na 2 O, CaO, Rb, Sr, Ba, ± MgO, whereas quartz-sericite rocks at the margins of the ore lenses (and also in the deep footwall) have gained K 2 O and MgO, as well as Mn, F, Cl, and Li. These enrichments are interpreted to be part of the early synvolcanic alteration during the initial stages of low-temperature, hydrothermal circulation. The addition of MgO at the margins of the ore lenses indicates that these were most likely zones of infiltration of seawater. Quartz-chlorite rocks within these zones exhibit nearly quantitative removal of alkalies and have gained FeO, Mn, B, F, and base metals. Although depleted in the footwall rocks, K 2 O is largely conserved at the mine scale, and the local addition of K 2 O in sericitic rocks in the hanging wall of the deposit is most likely related to the leaching of potassium from immediately beneath the massive sulfides. A negative correlation between K 2 O and FeO (± MgO) confirms that much of the later chlorite formed at the expense of preexisting sericite. Rare earth element (REE) abundances approximate protolith concentrations in zones of silicification and quartz-sericite alteration, but are progressively reduced (up to 80%) in the quartz-chlorite rocks. Samples of black, chloritic rhyolite have flattened REE profiles implying significant light REE mobility at this stage. The distribution and style of alteration at Kidd Creek is a strong function of the original permeability of the volcanic pile and reflects a combination of mainly low-temperature, diffuse flow through the permeable fragmental rocks at the top of the mine sequence and more focused discharge through brecciated zones in the underlying massive rhyolites. The broadly conformable zones of silicification, sericitization, and chloritization contrast sharply with the narrow, chlorite-rich pipes associated with many smaller Archean Cu-Zn deposits. The extent of silicification is thought to be related to pervasive flooding of a large volume of rock by SiO 2 -saturated fluids during a sustained period of low-temperature (<200°-250°C) hydrothermal upflow. The interpreted paragenesis of alteration is consistent with the documented thermal history of the deposit inferred from the mineralization and whole-rock S 18 O values (i.e., sustained low-temperature discharge punctuated by higher temperature upflow) and is similar to that observed in other large, felsic volcaniclastic-hosted massive sulfides (e.g., Horne, Crandon).

Abstract The footwall to the Kidd Creek orebody comprises dominantly rhyolite volcaniclastic rocks of lapilli- to block-sized fragments and massive rhyolite flows. The deposit overlies a broad, conformable zone of alteration characterized by laterally extensive sericite and Mg-rich chlorite alteration, and locally, by strong silicification and Fe-rich chlorite alteration. Pervasive silicification of the footwall rhyolites has largely converted these rocks to fine-grained quartz. Sericite and chlorite have replaced the fine-grained, tuffa-ceous matrix of the fragmental rocks and occur as fracture fillings in the brecciated massive rhyolite flows. Mass change calculations employing the method of immobile elements delineate two broadly conformable zones of alteration: one immediately beneath the massive sulfide lenses (zone I), and the other a zone of weaker alteration 50 to 100 m stratigraphically below the lenses (zone II). Zone I is characterized by moderate to strong concentrations of SiO 2 and FeO and a decrease in K 2 O. Zone II is characterized by concentrations of MgO and K 2 O. Both zones are strongly depleted in Na 2 O and CaO. Distinct trends of Fe increase adjacent to the ore lenses (zone I) and Mg increase at depth (zone II) are interpreted to reflect zones of high- and low-temperature fluid flow beneath the massive sulfide lenses. These zones follow the orebodies downplunge for more than 2 km and define a narrow corridor of focused hy-drothermal fluid flow along the original axis of the Kidd Creek graben.

Abstract Altered rhyolites that host the Archean Kidd Creek volcanogenic massive sulfide deposit have constant Hf-Th-Ta ratios throughout the entire deposit. Such constant ratios suggest that footwall and immediate hanging-wall rhyolites represent a single batch of high silica rhyolitic magma and that fractionation of accessory minerals was suppressed during crystallization. Although extensive alteration has destroyed most primary minerals in the rhyolites and disturbed their geochemistry, high field strength elements such as Th, Ta, and Hf remained immobile during alteration and may be used to identify the protoliths and to determine the original trace element geochemistry of even the most altered rocks. Quantitative estimation of rare earth element (REE) mobility in the rhyo-lites demonstrates significant mobility, particularly in the highly altered stringer zone, in the bornite zone, and in the southernmost part of the deposit in rhyolite fragmentals. Nearly quantitative removal of light REE occurred in highly silicified rhyolite immediately underneath the massive sulfides. Furthermore, REE mobility was identified up to a distance of 2 km from the deposit. Mafic rocks at Kidd Creek, excluding footwall komatiite flows and plagioclase porphyritic pillow basalts in the uppermost hanging wall, can be separated into four groups. This classification is consistent with stratigraphic position and general field appearances of the mafic rocks. Group I consists of primitive low TiO 2 basaltic flows in the footwall of the distal Kidd Creek horizon and is characterized by concave-upward chondrite-normalized REE patterns. Group II consists of relatively low TiO 2 pillow basalts and associated gabbro sills in the immediate hanging wall. This group includes the “spotted gabbro sills” at the mine and is characterized by midocean ridge basaltlike, slightly light REE-depleted patterns. Group III consists of high TiO 2 gabbro sills that intrude both the hanging wall and footwall of the deposit and have slightly light REE-enriched patterns. Group IV represents more evolved gabbro to diorite sills and could be related to group III. The groups have distinct and relatively undisturbed REE patterns. The REE sys-tematics and incompatible element ratios such as Th/Yb versus Ta/Yb indicate that groups I, II, and III are unlikely to be related by fractional crystallization. Different parental magmas are implicated.

Abstract Oxygen isotope mapping in rhyolitic rocks hosting the Kidd Creek volcanic-hosted massive sulfide deposit indicates that the ores are associated with a zone of relatively low δ 18 O values (9.7-12‰). Zones of higher δ 18 O values (13-15.8‰) occur 300 to 500 m stratigraphically above ore and are associated with massive rhyolite bodies as the footwall to the orebodies. The δ 18 O values (7.2-11.3‰) of mafic rocks are lower than those of rhyolitic rocks from the strongly silicified zone immediately underlying the massive sulfide bodies. Mafic rocks with the lowest δ 18 O values (<9‰) occur in the core of a diorite sill stratigraphically above the ore zone. Hydrogen isotope mapping indicates that a zone of low δD values (<–40‰) extends at least 500 m stratigraphically below the orebodies. Most chlorite associated with chalcopyrite stringers has lower δ 18 O (2.7-4.1‰) and higher δD (-47 to -41‰) values than chlorite from metamorphic veins (δ 18 O = 5.7-7.8‰; δD = -59 to –45‰). Quartz-chlorite pairs from metamorphic veins indicate temperatures of 370° to 400°C and a metamorphic fluid composition of δ 18 O ∼ 6.7 to 7.0 per mil and δD 17 ± 8 per mil. The isotopic composition of ore-forming fluids is inferred to have been δ 18 O ∼ 3.8 ± 0.5 per mil and δD ∼ –8 ± 5 per mil. The Kidd Creek ore-forming fluids are best interpreted as evolved seawater that exchanged with 18 O-enriched country rock; it may have contained up to 20 percent magmatic hydrothermal water.

Abstract Isotopic studies covering some 200 km 2 of the Kidd Creek Volcanic Complex, within about 10 km of the giant Kidd Creek deposit, include the analysis of 395 whole-rock and quartz phenocryst samples for oxygen isotopes and 87 whole-rock samples for hydrogen isotopes. All of the rocks of the Kidd Creek Vol canic Complex are enriched in 18 O relative to fresh or even mildly altered equivalents elsewhere, comprising a range for whole rocks of δ 18 Owhole rock = 6.3 to 15.7 per mil. Mapped distribution of δ 18 O whole rock values indicates several prominent zones of lower δ 18 O whole rock values located in the footwall of the Kidd Creek mine sequence and in footwall-equivalent sequences at the Chance deposit. Other zones located elsewhere suggest widespread hydrothermal activity throughout the complex. Broadly conformable zones of relative 18 O increase in mafic and rhyolitic rocks, primarily in hanging wall-equivalent sequences, mark waning hydrothermal activity and cooling temperatures. These broad zones are not spatially associated with either the Kidd Creek mine or the Chance deposit, but they are nevertheless related to the evolving hydrothermal activity in the Kidd Creek Volcanic Complex. Isotopic alteration of the crust was the result of long-lived hydrothermal activity (possibly on the order of 10 m.y.) that continued past the period of sulfide mineralization at Kidd Creek. The zones of 18 O enrichment are, in many cases, associated with uneconomic but anomalous occurrences of Zn that may represent the manifestation of a cooling hydrothermal system still able to mobilize minor amounts of metal. The minimum oxygen isotope composition of rhyolitic magma in the Kidd Creek Volcanic Complex inferred from analyses of phenocrysts (δ 18 O quartz ) was ca. 8.5 per mil due to melting or assimilation of 18 O-enriched, possibly low-temperature altered igneous crust. Quartz phenocrysts with δ 18 O quartz values as high as 15.4 per mil indicate subsolidus exchange with the rock matrix during regional greenschist facies metamorphism. Hydrogen isotope studies indicate narrow ranges in δD values for all rock types except several rhyolite flows. A rhyolite flow in the footwall ultramafics, about 1,000 m beneath the Kidd Creek mine, has δD value vs. wt percent HO characteristics that mirror rhyolites emplaced and degassed in very shallow to surficial environments. At least 1 km of subsidence is inferred to have occurred over a short period of time, prior to mineralizing hydrothermal activity at Kidd Creek. An extensional (i.e., rifting) tectonic environment would promote both subsidence of the crust and deep penetration of seawater-derived hydrothermal fluids.

Abstract Primary fluid inclusions in what is thought to be syngenetic siderite preserve a record of the hy-drothermal evolution of the Kidd Creek volcanogenic massive sulfide deposit. The banded and zoned siderite is intergrown with sphalerite, chalcopyrite, and pyrite and occurs in irregular masses or in veinlike segregations. Microthermometric measurements suggest that the early, syngenetic carbonates in the ore zone crystallized from a predominantly aqueous fluid at a temperature of ca. 250° to 297°C and a mean salinity of 5.7 ± 0.5 wt percent NaCl equiv. Two distinct metamorphic fluids were identified at Kidd Creek, suggesting two distinct metamorphic events. First, albite porphyroblasts in the bornite zone, which contain numerous inclusions of xenotime and/or monazite, crystallized from aqueous fluids at about 450°C during peak metamorphic conditions. Their crystallization was probably contemporaneous with emplacement of the nearby Prosser porphyry, ca. 55 m.y. after ore deposition. Second, late subhorizontal quartz veins which crosscut the entire Kidd Creek deposit crystallized from fluids that had a similar composition and temperature to the fluids which crystallized the flat veins at gold deposits in the Timmins area. Fluid inclusion data indicate that some of the quartz veins at Kidd Creek formed at a temperature of 298° ± 31°C from CO 2 -rich fluids (with a minor CH 4 component) having a salinity of 1.9 ± 1.1 wt percent NaCl equiv. The close similarities in fluid composition, temperature, and structural characteristics between flat veins and the subhorizontal quartz veins at Kidd Creek suggest that the emplacement of these veins represents a distinct event in the tectonic evolution of the Abitibi belt.