Abstract This contribution provides brief introductions to research on Carlin-type gold deposits completed since publication of the 2005 review paper on the deposits in the Economic Geology 100th Anniversary Volume ( Cline et al., 2005 ). Major advances in our understanding of the deposits have resulted from these studies that cover a broad range of topics, from the geology of deposits to recent discoveries and current geologic models. Studies of host rocks include expanded application of sequence stratigraphy that is refining our understanding of favorable host rocks, now known to have formed on shallow carbonate platforms during lowstands as well as in deep-water slope to basin environments. Sparse igneous dikes at the surface that were emplaced coincident with formation of deposits of the Carlin trend indicate that a batholith of about 1,000 km 2 underlies the trend. Reactivated and inverted normal Neoproterozoic faults formed anticlines and fed ore fluids into structurally prepared reactive rock types. Collaborative district studies determined that structural preparation of host rocks along the Carlin trend occurred during three discrete contractional events followed by Eocene extension and coincident mineralization. Ore and alteration studies identified systematic trace element and sulfur isotope zoning in ore-stage pyrite rims that formed from temporally discrete ore fluids fed by separate structures. Deposit-scale studies determined that ore minerals in shallowly formed deposits are similar to late ore-stage minerals of typical, more deeply formed Carlin-type gold deposits. Breccias containing high-grade ore formed both by replacement and by calcite dissolution and collapse processes. Halos useful in vectoring toward mineralization include rock quality designation values, trace elements above mineralization in premineral rock and in postmineral clay, oxygen isotope ratios, and soil, soil gas, vegetation, and groundwater chemistry. Isotopic studies have indicated relative timing of ore fluid movement through discrete structures. Deposit ages coincide with spatially related intrusion ages, from about 42 to 35 Ma, and both young from northeast to southwest. Magmatism and deposit formation are interpreted as related to Eocene delamination of subcontinental lithospheric mantle. Apatite fission track data indicate that the Betze-Post deposit, which contained >1, 240 tonnes (40 Moz) of gold, formed in <15,000 to 45,000 years. New geologic maps illustrate structural and stratigraphic relationships that will contribute to exploration efforts and potential new discoveries. Recent Nevada discoveries include South Arturo on the northern Carlin trend, the Long Canyon deposit in Cambrian-Ordovician rocks in the newly recognized Pequop district in northeastern Nevada, the giant Goldrush deposit on the Battle Mountain-Eureka trend, and the North Bullion deposit at the southern end of the Carlin trend. Two potential new districts of deposits are being actively explored in the Yukon Territory, Canada, and the Golden Triangle, southern China. Deposits in the Golden Triangle and prospects in the Yukon are currently much smaller than deposits in Nevada, and the presence of proximal coeval magmatism, now recognized in Nevada, is unclear. Studies of some of the Chinese deposits indicate that they formed at conditions intermediate to Carlin-type and orogenic deposits. Recently published geologic models propose that either shallow, basin-related processes or deep magmatic processes provided gold for the Nevada deposits. Studies evaluating the Harrison Pass pluton and the Emigrant Pass volcanic rocks, both the same age as the Carlin deposits, addressed the magmatic model and provide information about potential magmatic ore fluids and systems that may have formed the deposits.

Abstract Mining of Carlin-type gold deposits in Nevada has made the United States one of the leading gold producers in the world for almost four decades. These deposits constitute an endowment of ~255 Moz (7,931 tonnes) of gold, of which 89% occurs in four main clusters of deposits: the Carlin trend, Getchell, Cortez, and Jerritt Canyon. These four clusters share many characteristics, including (1) formation during a narrow time interval (42–34 Ma), (2) lithologic and structural controls to fluid flow and ore deposition, (3) geochemical signature of the ores, (4) hydrothermal alteration and ore paragenesis, (5) relatively low temperatures and salinities of ore fluids, (6) fairly shallow depths of formation, and (7) lack of mineral and elemental zoning. A mineral systems approach to exploring for Carlin-type gold deposits in Nevada and elsewhere is presented, in which critical processes are laid out: (1) development of source(s) for gold and other critical components of the ore fluid, (2) formation of fluid pathways, (3) water-rock interaction and gold deposition, and (4) a tectonic trigger. The critical processes are then converted into a practical targeting system for Carlin-type gold deposits within and outside of Nevada, ranging from regional to district to drill target (<~20 km 2 ) scales. The critical processes of the Carlin mineral system are translated into targeting elements and mappable targeting criteria. At the regional scale, targeting elements for magmatic sources of gold and ore fluid components include (1) intrusive centers with a mantle component to the magmas, (2) processes that could result in metasomatized subcontinental lithospheric mantle, (3) high-K, H 2 O-rich calc-alkaline magmas, and (4) evidence for fluid release. For crustal sources of gold, targeting elements include (1) carbonaceous sedimentary rocks with diagenetic/syngenetic sulfides enriched in Au-As-Hg-Tl-Sb-(Te) and sulfates and (2) a heat source to drive convection of meteoric and/or formation of metamorphic fluids. Targeting elements for fluid pathways at the regional scale include (1) basement suture zones and rifted continental margins, (2) long-lived upper crustal faults that may be linked to basement faults, and (3) a reduced crustal section to ensure long transport of gold by sulfide-rich fluids. Targeting elements at the regional scale for water-rock interaction and gold deposition include (1) passive margin dominated by carbonate rocks, (2) contractional deformation and formation of regional thrust faults and fold belts, and (3) a regional Au-As-Hg-Tl-Sb-(Te) geochemical signature. Targeting elements for tectonic triggers include (1) changes from contraction to extension, (2) periods of intense magmatism, especially related to slab rollback, and (3) plate reorganization. At the district scale, targeting elements for fluid pathways include (1) old reactivated high-angle fault zones, (2) zones of abundant low-displacement, high-angle extensional faults, (3) fault intersections, and (4) lithologic rheology contrasts, such as preore intrusions and contact aureoles. For water-rock interaction and gold deposition, targeting elements include (1) carbonate-bearing stratigraphy, (2) low-angle features that could divert upwelling fluids out of high-angle faults and into reactive wall rocks, (3) hydrothermal system of targeted age, (4) alteration consistent with wall-rock reaction with acidic, sulfide-rich hydrothermal fluids, and (5) Fe-rich rocks in the stratigraphic section, which will drive sulfidation. At the drill target scale, the targeting elements for fluid pathways are zones of increased fault/fracture permeability. The targeting elements for water-rock interaction and gold deposition include (1) zones of increased low-angle permeability in carbonate rocks proximal to high-angle faults, (2) favorable alteration, especially hydrothermal carbonate dissolution and silicification, (3) Fe-rich rocks including ferroan carbonates and mafic volcanic rocks and intrusions, (4) favorable Au-As-Hg-Tl-Sb-(Te) geochemical signature with low base metals and Ag/Au ratios, and (5) favorable mineralization, especially arsenian pyrite with textures and chemistry consistent with Carlin-type deposits.

Abstract For the last several decades, gold exploration in Nevada has been strongly focused on sedimentary rock-hosted gold deposits in the Carlin, Cortez, Independence, and Getchell trends in north-central Nevada. Accordingly, less exploration activity has been directed toward the search for similar gold deposits in the eastern Great Basin, south and east of the major trends. Deposits in the central and northern Carlin and Cortez trends are hosted primarily in Upper Devonian middle slope soft-sediment slumps and slides and base-of-slope carbonate debris flows, turbidites, and enclosing in situ fractured lime mudstones. This is in marked contrast to gold deposits in the eastern Great Basin that are hosted primarily in three chronostratigraphic horizons: (1) shallow-water, Cambrian and Ordovician carbonate platform interior, supratidal karsted horizons and shelf lagoon strata, associated with eustatic sea-level lowstands and superjacent, transgressive calcareous shale and siltstone horizons that are deposited as sea level begins to rise, (2) Early Mississippian foreland basin turbidites and debris flows overlying karsted Late Devonian platform strata, and (3) Pennsylvanian and Permian shallow marine basin strata. Stratigraphic architecture in these three horizons was influenced in part by Mesozoic (Elko and Sevier) contractional deformation, including low-angle thrust and attenuation faults, boudinage, and large-scale folds, which in turn affected the orientation and localization of synmineral brittle normal faults. A compilation of past production, reserves, and resources (including historic and inferred) suggests an overall endowment of over 41 Moz of gold (1,275 tonnes) discovered to date in the eastern Great Basin, some in relatively large deposits. Significant clusters of deposits include the Rain-Emigrant-Railroad and Bald Mountain-Alligator Ridge areas on the southern extension of the Carlin trend, the Ruby Hill-Windfall-South Lookout-Pan on the southern extension of the Cortez trend, and the Long Canyon-West Pequop-Kinsley Mountain area near Wells, Nevada. Sedimentary rock-hosted gold deposits extend to the eastern edge of the Great Basin in Utah and Idaho and include the past-producing Black Pine, Barney’s Canyon, Mercur, and Goldstrike mines. The recognition of widespread, favorable host rocks and depositional environments on the Paleozoic platform-interior shelf in the eastern Great Basin opens up vast areas that have been relatively underexplored in the past. A basic premise throughout this paper is that the better we understand the origin of rocks and the depositional and postdepositional processes under which they formed, the more accurately we can make well-founded stratigraphic, sedimentological, structural, geochemical, and diagenetic interpretations. Without this understanding, as well as the rigorous application of multiple working hypotheses to explain our observations, the advance of science and the discovery of gold deposits is problematic.

Abstract The Marigold Au deposits are located in the Battle Mountain mining district at the northern end of Nevada’s Battle Mountain-Eureka trend. The Marigold deposits currently make up the second largest Au accumulation in the district with over 320 tonnes (10.35 Moz) of Au in oxidized rock in a N-trending series of mineralized zones approximately 7.5 km long. Ore is hosted primarily in oxidized Paleozoic siliciclastic rocks between the Roberts Mountain and Golconda thrusts. Most of the ore occurs in quartzite of the Ordovician Valmy Formation. Higher grades but lower tonnages of ore are present in the overlying Pennsylvanian-Permian Antler sequence, including the Battle Formation conglomerate, the Antler Peak Limestone, and debris flows and siltstone of the Edna Mountain Formation. Sedimentary rocks at Marigold are crosscut by a series of WNW- to N-striking quartz monzonite dikes (zircon U-Pb chemical abrasion-thermal ionization mass spectrometry ages 97.63 ± 0.05–92.22 ± 0.05 Ma) and a lamprophyre (biotite 40 Ar/ 39 Ar age 160.7 ± 0.1 Ma). Marigold displays many classic Carlin-type characteristics although the deposits are predominantly hosted in relatively unreactive, carbonate-poor siliciclastic rocks. Sulfidation, minor silicification, and possibly pyritization occurred in association with Au mineralization in quartzite and argillite. Chemically reactive but volumetrically minor carbonate rocks also display these alteration styles as well as significant decarbonatization. Argillic alteration occurred proximal to faults in mudstone and siltstone and at the margins of intrusions. Gold, As, Sb, and Tl are enriched along high-angle structures and structural intersections in the sedimentary host rocks and in faulted dike margins. Gold is present in Au-, As-, and Sb-rich pyrite overgrowths on pre-gold stage trace element-poor pyrite grains. Oxidation extends to depths of 150 to 500 m below surface, and above the redox boundary Au is present natively with iron oxides in voids and fractures. In the cores and margins of the Cretaceous dikes and fault zones, a distinct geochemical association of base metal and Ag minerals is identifiable, characterized by Ag-bearing tetrahedrite-tennantite, chalcopyrite, gersdorffite, pyrite, sphalerite, stannite, and galena. Sericite 40 Ar/ 39 Ar ages of 88.0 ± 0.46 and 79.59 ± 0.16 Ma indicate that hydrothermal alteration occurred along the dike margins at least 4 m.y. after emplacement. On the basis of similarities to other deposits in the district, the base metal and Ag mineralization may have occurred at this time. The Au mineralization occurred sometime after the base metal and Ag event, possibly in conjunction with the Eocene magmatism that occurred elsewhere in the district, although this study found no definitive evidence for a magmatic-hydrothermal origin of the Au.

Abstract The Dian-Qian-Gui “Golden Triangle” area of southwest China has the second-largest concentration of Carlin-type gold deposits in the world, containing more than 800 tonnes of Au (25.7 Moz). All of the deposits are located along long-lived, deep-penetrating crustal structures inherited from Devonian rifting of the Precambrian Yangtze craton. They are hosted in Cambrian to Middle Triassic platform carbonate, transitional, and siliciclastic rocks of the Youjiang basin, and locally in Late Permian diabase intrusions or volcaniclastic rocks. These deposits have many characteristics in common with Carlin-type gold deposits in Nevada, USA, including lithology of host rocks, alteration types, elemental associations, and occurrence of gold. Our recent work has identified two episodes of gold mineralization in the Dian-Qian-Gui area that have distinct geologic settings, radiogenic and stable isotopes, and fluid inclusions. Gold deposits hosted in diabase intrusions along the southern margin of the Youjiang basin formed in the Middle-Late Triassic (232–212 Ma) and have low-salinity (~2 wt % NaCl equiv), high-temperature (~245°C) fluid inclusions with high-density CO 2 that are similar to those in orogenic gold deposits. Sediment-hosted gold deposits along the northern margin of the Youjiang basin formed in the Late Jurassic-Early Cretaceous (148–134 Ma) and have moderate salinity (~5 wt % NaCl equiv) and temperature (~210°C) fluid inclusions, with variable CO 2 , low Fe, and high As, Sb, and Au contents, based on microanalysis of fluid inclusions. Deposits on each margin contain gold-bearing arsenian pyrite and arsenopyrite that precipitated from H 2 S-rich fluids by sulfidation of Fe minerals in the host rocks. Oxygen and hydrogen isotopes indicate metamorphic fluid sources for deposits on both margins, but sulfur isotopes indicate different sources of reduced sulfur. The narrow range of high δ 34 S values for arsenian pyrite and arsenopyrite from districts along the southern margin of the Youjiang basin suggests derivation from a sedimentary source. Some of the deposits along the northern margin of the Youjiang basin have δ 34 S values near zero that permit a magmatic or sedimentary sulfur source, while others have high values indicative of a sedimentary source. We propose a model in which metamorphic ore fluids were generated by regional metamorphism of sedimentary rocks during the Indosinian orogeny along the southern margin and the Yanshanian orogeny along the northern margin of the Youjiang basin. Metamorphic ore fluids were focused into reactivated basement-penetrating rift faults and flowed upward into structural highs in response to stress relaxation during each orogeny. Gold-bearing sulfides precipitated where the ore fluids reacted with carbonaceous and Fe-rich host rocks and mixed with variably exchanged meteoric ground water. The pressure-temperature conditions and compositions of ore fluids are intermediate between those of the mesozonal orogenic and the shallow Carlin-type gold systems. The Chinese Carlin-type gold deposits may, therefore, represent a link between orogenic and Carlin-type gold deposits that formed during transitions between compressional and extensional environments.

Abstract Carlin-type Au deposits in Guizhou Province, China, have similarities to and differences from the Carlin-type Au deposits in Nevada, USA. The Shuiyindong and Jinfeng deposits, located in the Guizhou Province of southern China, are compared with the Getchell and Cortez Hills Carlin-type Au deposits of Nevada in terms of ore paragenesis and pyrite chemistry. The Guizhou deposits formed in a tectonic setting similar to Nevada with the deposition of passive-margin sequences in a rifted cratonic margin context with subsequent deformation. In both districts, orebodies are preferentially hosted in limestone and calcareous siltstone and are related to faults, gold is invisible and ionically bound in arsenian pyrite, and ore-stage minerals include quartz and illite with late ore-stage minerals, including calcite, realgar, orpiment, and stibnite. Despite major similarities, however, the Guizhou deposits have characteristics that contrast with those of Carlin-type deposits of Nevada. Significant differences include the following: Guizhou ore-stage pyrite is commonly subhedral to euhedral, and typical Nevada fuzzy ore pyrite is absent. Guizhou ore pyrite contains significantly less Au, As, Hg, Tl, Cu, and Sb than the Nevada ore pyrite. Decarbonatization in Nevada deposits is expressed by extensive removal of calcite, dolomite, and Fe dolomite. In contrast, decarbonatization in the Guizhou deposits results in loss of most primary calcite, but Fe dolomite was instead sulfidized, forming ore pyrite and dolomite. This alteration is a key process in the formation of ore pyrite in the Guizhou deposits. Silicification in Nevada deposits is characterized by jasperoid replacement of calcite, dolomite, and Fe dolomite, whereas in the Guizhou deposits jasperoid replaced mainly calcite but not Fe dolomite or dolomite. Minor vein quartz, which formed during the early ore stage in Guizhou deposits, has not been identified in Nevada deposits. Clay alteration in the Nevada deposits is characterized by formation of significant illite and variable kaolinite/dickite; however, in the Guizhou deposits, trace to minor illite is present and kaolinite is uncommon. Late ore-stage arsenopyrite and vein quartz are common in Guizhou deposit but are rare in Nevada deposits. Guizhou ore fluids contained significantly more CO 2 and were higher in temperature and pressure compared with the ore fluids in Nevada deposits. To date, magmatism spatially or temporally associated with the Guizhou deposits has not been recognized. Conversely, the Nevada deposits coincide in time and space with the southward sweep of Eocene magmatism and related extension. Dolomite-stable alteration in Guizhou formed from less acidic, CO 2 -rich ore fluids at higher temperature and pressure compared with Nevada deposits, reflecting similarities between Guizhou deposits and orogenic systems. Study results are consistent with Guizhou deposits having formed in a transitional setting between typical orogenic gold and shallow Carlin-type deposits, as indicated by estimated pressure-temperature conditions at the time of gold deposition and ore-forming fluid chemistry.

Abstract The Nadaleen trend is a 25-km-long alignment of recently discovered Carlin-type gold prospects located along the northern margin of the Selwyn basin in east-central Yukon Territory, Canada. These prospects are among the closest analogues to the large, Carlin-type gold deposits found in Nevada. The Nadaleen trend is bound structurally to the south by the regional Dawson thrust and to the north by the Kathleen Lakes fault. The Dawson thrust marks the boundary between dominantly Neoproterozoic to Paleozoic slope and basin facies carbonate, siltstone, and clastic rocks of the Selwyn basin and strata of the Mackenzie platform. The Nadaleen trend contains numerous Carlin-type prospects, with the three largest being Conrad, Osiris, and Anubis. Carlin-type prospects of the Nadaleen trend are hosted in silty limestone and calcareous siliciclastic rocks along with isolated gabbroic dikes. Gold mineralization at Nadaleen is inferred to have accompanied decarbonatization of host limestone and subsequent silicification and/or brecciation. Typically, this was followed by late, open-space calcite, realgar, and orpiment. The prospects exhibit both structural and stratigraphic controls, with zones located near prominent fault and fold features. Gold is associated with elevated As, Hg, Sb, and Tl in mineralized zones. Several types of arsenian pyrite are found in mineralized zones, typically as rims around earlier barren pyrite cores or as <10- μ m disseminations and aggregates. Evidence from the Conrad zone suggests that Carlin-type gold mineralization occurred between 74.4 and 42 Ma. The tectonic and magmatic setting in this remote part of the Yukon during gold mineralization is poorly understood, with little or no evidence for contemporaneous regional magmatism or tectonism. While deposit-scale processes responsible for gold mineralization appear very similar for Carlin-type prospects in the Yukon and Carlin-type gold deposits in Nevada, whether the crustal-scale processes that formed these systems are similar remains enigmatic.

Abstract The Bau mining district, on the island of Borneo in the southwestern Pacific, has produced gold (45.5 tonnes [t] or 1.46 Moz), antimony (83,000 tons), and mercury (1,100 t or 32,000 flasks) from calcic skarn, calcite-quartz veins, and sedimentary rock-hosted replacement deposits that are concentrically arranged around microgranodiorite intrusions with Cu-(Mo) quartz stockwork mineralization. Ores are exceptionally enriched in arsenic. Oxidized disseminated replacement ores, which are chemically, texturally, and isotopically similar to Carlin-type gold deposits in northern Nevada, have contributed the majority of the gold production of the district. The Tai Parit mine, the largest in the district, has produced about 22 t (0.7 Moz) Au at an average grade of about 7.5 g/t (0.22 oz/t) Au. Ores were mainly treated by cyanidation. The concentric zonation pattern led previous workers to propose that these and other Carlin-style gold deposits are distal manifestations of magmatic-hydrothermal systems. This investigation presents new fluid-inclusion, isotopic, and mineralogical data in the context of previously obtained geological, chemical, and other information that advance our understanding of this district, enabling comparisons with Carlin-type deposits in Nevada and distal disseminated deposits elsewhere in the world. Bau is situated on the western end of the Eocene to Miocene Central Kalimantan magmatic arc. A new K-Ar date on hydrothermal sericite of 10.4 ± 0.3 Ma from a stock with gold-bearing calcic skarns is within the age range of nearby intrusions dated at 11.6 to 9.3 Ma that form part of a NNE-trending, adakitic, magmatic belt. The subvolcanic intrusions and gold deposits are localized by NNE-striking normal faults that transect marine calcareous rocks of the Upper Jurassic Bau Formation and siliciclastic rocks of the Lower Cretaceous Pedawan Formation that are exposed along the axis of the NE-trending Bau anticline. Gold ore is best developed at the intersection of the Krian fault and the contact between these two formations. The outward zonation from wollastonite-bearing skarn, through calcite-quartz veins, to decalcified and silicified limestone and clastic rock is indicative of decarbonation and Si metasomatism of limestone as hydrothermal fluids cooled. The predominance of sericite over kaolinite shows that fluids were near neutral to moderately acidic and contained a significant amount of potassium. The spatial distribution and paragenetic sequence of native antimony, aurostibite, stibnite, sphalerite (1–7 wt % Fe), pyrrhotite, pyrite, arsenopyrite, native arsenic, and realgar is evidence for cooling and desulfidation of ore fluids. In sedimentary rock-hosted replacement deposits, mass loss due to carbonate dissolution is shown by enrichment of Ti and Al and depletion of Ca, Mg, and Sr. The strong introduction of Si, Fe, Mn, Zn, Pb, and Ag together with Au, As, and Sb is suggestive of cooling and mixing of saline and H 2 S-bearing fluids. Laser ablation-inductively coupled plasma-mass spectrometry analyses show that most of the Au resides in arsenopyrite and that Cu and Te are present in Sb and As minerals. Cooling and decompression are shown by hypersaline fluid inclusions (25–38 wt % NaCl equiv) in Cu (Mo) stockworks and calcic skarn, which were trapped between 500° and 240°C and 400 and 30 bar, while low-salinity fluid inclusions (0–6 wt % NaCl equiv) in vein and Carlin-style deposits were trapped between 350° to 100°C and 200 and 1 bar. Fluid inclusions of intermediate salinity are indicative of fluid mixing. The maximum pressure corresponds to depths of 1.6 (lithostatic) to 4 km (hydrostatic). The H, O, and C isotope compositions of sericite, wollastonite, quartz, calcite, and inclusion fluids strongly suggest that each deposit type formed from magmatic fluids that were shifted to lower δ D values by magma degassing and higher δ 18 O and δ 13 C values by exchange with marine limestone. Only fluid inclusion water extracted from late drusy quartz is shifted toward, and late calcite plots on, the meteoric water line. The isotopic composition of S in pyrrhotite and pyrite is magmatic, whereas S in Te, Sb, and As minerals was derived from country rock. The data show how readily hydrothermal fluids of magmatic origin can be modified by reaction with wall rock, mixing with other fluids, and selective loss of lighter components. In comparison to Nevada’s Carlin-type gold deposits, the Carlin-style gold deposits in the Bau district are smaller and more structurally controlled, have zonation in mineralogy and geochemistry indicative of steep thermal and chemical gradients around exposed porphyry intrusions, and formed from less acidic fluids by cooling and fluid mixing. In addition, Au resides in arsenopyrite, ore has more introduced Fe, Mn, Zn, Pb, Ag, Sb, and As and less Tl and Hg, and there is clear isotopic evidence for magmatic H 2 O, CO 2 , and H 2 S. The genetic links between magmatism and distal disseminated gold mineralization at Bau are a significant contribution to a growing body of evidence that Au and related trace elements in many Carlin-style gold deposits may be derived from magmas.

Abstract The neighboring sedimentary rock-hosted Agdarreh (~24.5 tonnes [~0.8 Moz] of Au in ore with an average grade of 3.7 g/t Au) and Zarshouran (~110 tonnes of Au [~3.5 Moz] in ore with an average grade of 4.5 g/t Au) Carlin-style gold deposits in the Takab region of northwestern Iran occur within the active geothermal field of the Miocene Urumieh-Dokhtar magmatic arc, which contains an assortment of intrusion-related deposit types (porphyry Cu, polymetallic, and epithermal Au-Ag). Although Agdarreh is hosted in early Miocene reefal limestones and is strongly oxidized and Zarshouran is hosted in exhumed metamorphosed Neoproterozoic black schist, limestone, and dolomite and is relatively unoxidized, they have many features in common. Phyllic alteration is as young as 14 Ma, and the age of local volcanic rocks is between 16 and 11 Ma. Disseminated gold ore in jasperoid occurs as replacement bodies at intersections of normal faults in decalcified and dolomitized carbonate units as well as in schists at Zarshouran. Where jasperoid is fractured or brecciated, it is cemented by drusy quartz. Precipitation of early pyrite (±pyrrhotite), abundant sphalerite, and minor chalcopyrite and galena was followed by a variety of more abundant complex sulfosalt minerals, arsenian pyrite, stibnite, late orpiment-realgar, and cinnabar, with traces of native bismuth, tellurides, and the newly discovered daliranite (PbHgAs 2 S 6 ). Most of the gold occurs as solid-solution or nanometer gold in arsenian pyrite and sphalerite and as native gold associated with late-stage As sulfides and cinnabar. Agdarreh has an abundance of barite, whereas Zarshouran contains fluorite; both deposits are crosscut by minor late calcite, and each deposit is overprinted by a younger Pleistocene to Holocene geothermal system that produced extensive travertine deposits and oxidized sulfide gold ore at Agdarreh. Whole-rock analyses indicate Al was immobile, Ca was depleted, and significant amounts of Fe, Zn, Pb, As, Sb, Hg, Tl, Ag, Au, Ba, ±F were introduced along with lesser K, W, Ni, Cd, Te, and Se. The paragenetic sequence of the ore minerals reflects a decrease in temperature and an increase in f S 2 . Geochemical data suggest that ore fluids transported base metals, trace elements, and Au together or that a saline, H 2 S-poor fluid containing Fe, Zn, Pb, and Ag mixed with an H 2 S-rich fluid containing Au and trace elements. Primary fluid (LV/LV ±CO 2 ) inclusions in drusy quartz, fluorite, and barite with salinities up to 23 wt % NaCl equiv and eutectic first melting temperatures of –19 to –10°C, are suggestive of ore-stage NaCl-KCl solutions. Secondary inclusions have low salinities (<4 wt % NaCl equiv) and higher first-melting temperatures (–13 to 0°C) suggestive of Na 2 CO 3 -Na 2 SO 4 solutions, and those with salinities close to zero and very low T fm (–56 to –30°C) suggestive of CaCl 2 -MgCl 2 -FeCl 2 solutions represent the latest population of one-phase liquid (L) inclusions. Homogenization temperatures of the primary fluid inclusions (200° ± 20°C) and calculated pressures (~150 bar) are indicative of depths around 1.5 km (assuming hydrostatic conditions). The maximum densities of the CO 2 phase present in aqueous-carbonic inclusions (0.18 g/cm 3 at Agdarreh and 0.29 g/cm 3 at Zarshouran) are indicative of pressures between 100 and 260 bar and depths around 1 km (assuming hydrostatic conditions). These data suggest mixing of immiscible brine and CO 2 -bearing vapor with dilute groundwater. Fluid inclusions in Zarshouran orpiment have δ D H 2O , Na/Cl, and Cl/Br values consistent with magmatic fluids. The δ 18 O of water in equilibrium with jasperoid and drusy quartz is either magmatic, as at Agdarreh, or extends toward meteoric water, as at Zarshouran. The δ 13 C of CO 2 in equilibrium with calcite is characteristic of the host rocks with a minor magmatic component. The δ 34 S of H 2 S in equilibrium with pyrite and sphalerite (1–6‰) is likely magmatic, whereas H 2 S in equilibrium with orpiment, stibnite, cinnabar, and getchellite (8–10‰) was derived in part from sedimentary sources. Late barite has high δ 34 S values typical of marine sulfate. These data indicate that the deposits formed in different parts of a hydrothermal system at the interface between ascending magmatic fluids and local meteoric groundwater in sedimentary or metasedimentary rocks. The characteristics of Agdarreh and Zarshouran suggest that they are shallow manifestations of intrusionrelated hydrothermal systems and, therefore, are best classified as distal disseminated deposits.

Abstract The Allchar Au-As-Sb-Tl deposit is situated in the western part of the Vardar zone, the main suture zone along the contact between the Adriatic and the Eurasian tectonic plates. It is spatially and temporally associated with a Pliocene (~5 Ma) postcollisional high-K calc-alkaline to shoshonitic volcano-plutonic center. The Allchar deposit shares many distinctive features with Carlin-type gold deposits in Nevada, including its location near a terrain-bounding fault in an area of low-magnitude extension and intense magmatism. The mineralization is mostly hosted in calcareous sedimentary rocks at intersections of high-angle faults in permeable stratigraphy. The alteration types (carbonate dissolution, silicification, and argillization), ore mineralogy (auriferous arsenian pyrite and marcasite, stibnite, realgar, orpiment, and lorandite), high Au/Ag ratios, and low base metal contents are also typical of Carlin-type gold deposits in Nevada. However, the Allchar deposit differs from Nevada Carlin-type gold deposits as follows: it is an isolated Au prospect with a close spatial and temporal relationship to a shoshonitic volcano-plutonic center in a mineral belt dominated by intrusion-related Cu-Au porphyry, skarn, and hydrothermal polymetallic deposits. The deposit is clearly zoned (proximal Au-Sb to distal As-Tl), it has a significantly higher Tl content, trace elements in pyrite and marcasite are homogeneously distributed, and synore dolomitization is a widespread alteration type. Gold mineralization is most abundant in the southern part of the deposit. It occurs mostly as invisible Au in disseminated pyrite or marcasite and as rare native Au grains. Gold mineralization is accompanied by intense decarbonatization and silicification. Fluid inclusions and the hydrothermal alteration mineral assemblage indicate that Au was deposited from hot (>200°C), saline (up to ~21 wt % NaCl equiv), moderately acidic (pH <5) fluids that carried traces of magmatic H 2 S and CO 2 . In the calcareous host rocks, mixing of such fluids with cool, dilute, near-neutral groundwater triggered deposition of Au and Fe sulfides. In Tertiary tuff, isocon analysis shows that sulfidation of preexisting Fe minerals was a critical factor for deposition of Au and Fe sulfides. Antimony mineralization prevails in the central part of the deposit, and it is mostly associated with dark-gray to black jasperoid. Stibnite, the most common Sb mineral in the Allchar deposit, occurs as fine-grained disseminations in jasperoid and as fine- to coarsely crystalline masses that fill vugs and fracture zones lined with drusy quartz. Fluid inclusions entrapped by stibnite-bearing jasperoid, quartz, and calcite crystals suggest that stibnite was deposited from more dilute and cooled fluids (aqueous-carbonic fluid inclusions: 6.0–3.5 wt % NaCl equiv, T h = 102°−125°C; aqueous fluid inclusions: 14.5 and 17.1 wt % NaCl equiv, T h = 120°−165°C). In contrast to stibnite, As sulfides (orpiment and realgar) and Tl mineralization are associated with argillic alteration. Fluid inclusions hosted by realgar, orpiment, dolomite, and lorandite record deposition from more dilute (2.6–6.9 wt % NaCl equiv) and relatively cold fluids (T H = 120°−152°C) enriched in K. Isocon diagrams show a tight link between Tl and the low-temperature argillic alteration as well as a significant correlation between Tl and K. The spatial relationship of Tl mineralization with dolomite suggests that Tl deposition was also promoted by neutralization of acidic fluids. The δ D and δ 18 O data obtained from gangue minerals and fluid inclusions indicate that magmatic fluid mixed with exchanged meteoric water at deep levels and with unexchanged meteoric water at shallow levels in the system. The δ 13 C and δ 18 O values of carbonate minerals and extracted fluid inclusions suggest mixing of carbonate rock buffered fluids with magmatic and atmospheric CO 2 . The sulfur isotope values of early disseminated pyrite and marcasite show that H 2 S was initially derived from diagenetic pyrite in sedimentary rocks. In contrast, Sb and As mineralization indicate a strong input of magmatic H 2 S during the main mineralization stage. Late-stage botryoidal pyrite and marcasite are depleted in 34 S, which indicates a diminishing magmatic influence and predominance of sulfur from sedimentary sources during the late-mineralization stage. Fractionation of isotopically light sulfide species from isotopically heavy sulfates due to oxidation under increased oxygen fugacity cannot be excluded.

Abstract Carlin, epithermal, and orogenic gold deposits, today mined almost exclusively for their gold content, have similar suites of anomalous trace elements that reflect similar low-salinity ore fluids and thermal conditions of metal transport and deposition. Many of these trace elements are commonly referred to as critical or near-critical elements or metals and have been locally recovered, although typically in small amounts, by historic mining activities. These elements include As, Bi, Hg, In, Sb, Se, Te, Tl, and W. Most of these elements are now solely recovered as by-products from the milling of large-tonnage, base metal-rich ore deposits, such as porphyry and volcanogenic massive sulfide deposits. A combination of dominance of the world market by a single country for a single commodity and a growing demand for many of the critical to near-critical elements could lead to future recovery of such elements from select epithermal, orogenic, or Carlin-type gold deposits. Antimony continues to be recovered from some orogenic gold deposits and tellurium could potentially be a primary commodity from some such deposits. Tellurium and indium in sphalerite-rich ores have been recovered in the past and could be future commodities recovered from epithermal ores. Carlin-type gold deposits in Nevada are enriched in and may be a future source for As, Hg, Sb, and/or Tl. Some of the Devonian carbonaceous host rocks in the Carlin districts are sufficiently enriched in many trace elements, including Hg, Se, and V, such that they also could become resources. Thallium may be locally enriched to economic levels in Carlin-type deposits and it has been produced from Carlin-like deposits elsewhere in the world (e.g., Alsar, southern Macedonia; Lanmuchang, Guizhou province, China). Mercury continues to be recovered from shallow-level epithermal deposits, as well as a by-product of many Carlin-type deposits where refractory ore is roasted to oxidize carbon and pyrite, and mercury is then captured in air pollution control devices.