Abstract Carlin-type gold deposits in Nevada account for ~5% of worldwide annual gold production, typically about ~135 metric tons (t) (~4.5 Moz) per year. They are hydrothermal epigenetic replacement bodies hosted predominantly in carbonate-bearing sedimentary rocks. They are known for their “invisible” gold that occurs in the crystal structure of pyrite. Over 95% of the production from these deposits is from four clusters of deposits, which include the Carlin trend and the Cortez, Getchell, and Jerritt Canyon camps. Despite differences in the local geologic settings, the characteristics of the deposits are very similar in the four clusters. Shared characteristics include: (1) alteration characterized by carbonate dissolution, silicate argillization, and silicification; (2) ore formation characterized by auriferous arsensian pyrite, typically as rims on preore pyrite, followed by late open-space deposition of orpiment, realgar, stibnite, and other minerals; (3) Ag/Au ratios of <1 in ore; (4) an As-Hg-Sb-Tl geochemical signature; (5) low temperatures (~160°–240°C) and salinities of ore fluids (~1–6 wt % NaCl equiv) and fairly shallow depths of formation (<~2–3 km); and (6) lack of mineral and elemental zoning around ore. The four clusters share regional geologic controls related to formation as follows: (1) along the rifted margin of a craton, (2) within the slope facies of a passive margin sequence dominated by carbonates, (3) in the lower plate of a regional thrust fault, and (4) during a narrow time interval in the late Eocene (~42–34 Ma). The geometries and ore controls of the deposits in the four clusters are also very similar. At the deposit scale, ore and hydrothermal alteration are commonly associated with high-angle faults and preore low-angle contractional structures, including thrust faults and folds. The high-angle faults acted as fluid pathways for upwelling ore fluids, which were then diverted into lower angle favorable strata and contractional structures, where fluid-rock interaction led to replacement of carbonate and formation of ore. Rheologic contrasts between lithologies were also critical in diverting fluids into wall rocks. Common rheologic contrasts include contacts between thin- and thick-bedded lithologic units and the margins of contact metamorphic aureoles associated with Mesozoic intrusions. The similarities suggest common processes. Four critical processes are apparent: (1) development of source(s) for gold and other critical components of the ore fluids, (2) formation of fluid pathways, (3) water-rock interaction and gold deposition, and (4) a tectonic trigger, which was renewal of magmatism and a change from contraction to extension in the late Eocene. Consensus exists on these processes, except for the source of gold and other components of the ore fluid, with most models calling upon either a magmatic-hydrothermal source or a crustal source, where metals were scavenged by either meteoric or metamorphic fluids. Future research should focus on Carlin-style deposits in Nevada that exhibit epithermal characteristics and deposits that appear to have a clear genetic association with magmatic-hydrothermal systems associated with upper crustal intrusions. Rather than discrete types of ore deposits, there may be continua between Carlin-type gold deposits, epithermal deposits, and distal disseminated deposits, with the four large camps representing an end member.

Abstract Detailed mapping along the east face of Oxford Ridge in the southern Bannock Range, southeast Idaho determines the stratigraphic placement and lateral extent of strata in the Scout Mountain Member of the Neoproterozoic Pocatello Formation. The lower “transitional unit” overlies the Bannock Volcanic Member and consists of 70 m of massive diamictite with argillitic and vesicular basaltic clasts up to cobble size intercalated with thin metabasalt and hyaloclastite units. Overlying the transitional unit is a 150–190-m-thick, massive, brown-green to purple sandy diamictite with dominantly quartzose cobble clasts. Interbedded with this middle unit is a 60-m-thick epiclastic volcanic interval informally named the Oxford Mountain tuffite. An upper sandstone unit up to 100 m thick lies above the diamictite at the head of Fivemile Creek in the southern portion of the map area. The volcanic interval contains plagioclase-phyric volcanic lithic sandstone, porphyritic volcanic lithic fragments and rounded cobbles in tuffaceous diamictite and a reworked stratified lapilli-tuff. It is interstratified with quartzose and volcanogenic diamictite and can be traced along 5.5 km of strike. On Oxford Mountain, laser ablation–inductively coupled plasma mass spectrometry U-Pb zircon ages presented here and additional sensitive high-resolution ion microprobe ages constrain the underlying Bannock Volcanic Member to be 717–686 Ma and require that the overlying Scout Mountain Member is younger than 685 Ma.