Abstract The Eocene Goldstrike system on the Carlin Trend in Nevada is the largest known Carlin-type gold system, with an endowment of 58 million ounces (Moz) distributed among several coalesced deposits in a structural window of gently dipping carbonate rocks below the regional Roberts Mountains thrust. The 3.5- × 2.5-km Goldstrike system is bounded to the east by the Post normal fault system and to the south by the Jurassic Goldstrike diorite stock and is partly hosted in the favorable slope-facies apron of the Bootstrap reef margin that passes through the system. The carbonate and clastic sedimentary sequence is openly folded, cut by sets of reverse and normal faults, and intruded by the Jurassic Goldstrike stock and swarms of Jurassic and Eocene dikes, establishing the structural architecture that controlled fluid flow and distribution of Eocene mineralization. A proximal zone of permeability-enhancing decarbonatization with anomalous gold (>0.1 ppm) extends a few hundreds of meters beyond the ore footprint and lies within a carbonate δ 18 O depletion anomaly extending ~1.4 km farther outboard. The full extent of the larger hydrothermal system hosting Goldstrike and adjacent deposits on the northern Carlin Trend is outlined by a 20- × 40-km thermal anomaly defined by apatite fission-track analyses. The bulk of the mineralization is hosted in decarbonatized sedimentary units with elevated iron contents and abundant diagenetic pyrite relative to background. Gold is associated with elevated concentrations of As, Tl, Hg, and Sb, and occurs in micron-sized arsenian pyrite grains or in arsenian pyrite overgrowths on older, principally diagenetic pyrite, with sulfidation of available iron as the main gold precipitation mechanism. The intersection of a swarm of Jurassic lamprophyre dikes with the edge of the limestone reef provided a favorable deeply penetrating structural conduit within which a Jurassic stock acted as a structural buttress, whereas the reef’s slope-facies apron of carbonate units, with high available iron content, provided a fertile setting for Carlin-type mineralization. The onset of Eocene extension coupled with a southwestward-sweeping Cenozoic magmatic front acted as the trigger for main-stage gold mineralization at 40 to 39 Ma. All these factors contributed to the exceptional size and grade of Goldstrike.

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.