Epithermal ore deposits form at shallow depth. This conclusion was initially based on geologic reconstructions, ore mineralogy and related textures (Lindgren, 1933). It has subsequently been refined withfluid inclusion data to indicate that epithermal ores form over the temperature range of <150o C to ~300o C, from the surface to as deep as 1 to 2 km. Here we highlight the general characteristics of the two principal styles of epithermal mineralization in which gold is the dominant economic metal. We base our generalizations on observations of many deposits and prospects in the circum-Pacific region. Distinguishing between the two styles is crucial for effective exploration. Although they show similar alteration mineralogies, the distribution of the alteration zones is different, and the economic mineralization is associated with different parts of the system. The alteration zoning can be used as a pointer towards the most prospective part of the system, but only when the style has been correctly recognized. In addition, the two styles of mineralization have differences in their geochemical associations. <...>

Geology and gold deposits of the Oatman district, northwestern Arizona

Geology and gold deposits of the Marysville mining district, Montana

Gold deposits of the Boulder County gold district, Colorado

The Goldfield gold district, Esmeralda and Nye Counties, Nevada

The Tonopah precious-metal district, Esmeralda and Nye Counties, Nevada

The Republic gold district, Ferry County, Washington

The Comstock Lode precious-metal district, Washoe and Storey Counties, Nevada

The gold deposit at La Josefina, in the Deseado Massif of Argentina, is a low-sulfidation epithermal deposit with some features of the intermediate sulfidation style; the Au occurs in quartz veins and hydrothermal breccias hosted by acid pyroclastic rocks produced by Jurassic bimodal volcanism. Exploration for this deposit type uses geochemical data for vectoring to mineralized rocks. Although a general suite of elements with anomalous concentrations around low-sulfidation deposits is known, that suite varies amongst individual deposits, which should be studied individually.

Epithermal gold deposits in Chile are Cretaceous to Cenozoic in age. The ores and the volcanic rocks with which they are associated were generated at a noncollisional, ocean-continent convergent plate margin. They are related to long, slightly sinuous north-northeasttrending magmatic belts roughly parallel to the Pacific coast. Most of the deposits are associated with eroded volcanic centers and subvolcanic porphyries. North-south variations in the nature, extent, and timing of magmatism control the succession of mineralization events. In the Late Cretaceous, vein districts (e.g., E1 Bronce) and hydrothermal alteration zones were formed in central Chile.

The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (
29470 S Lat., 70430 W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (þsupergene kaolinite).

Fruta del Norte is a completely concealed and extraordinarily well preserved epithermal gold-silver deposit located in the remote Cordillera del Cóndor mountain ranges of southeastern Ecuador. Currently defined resources in a single, steep, relatively small body, displaying exceptional grade continuity, contain 9.81 million ounces (Moz) of gold and 15.0 Moz of silver, with an indicated resource grade of 9.59 g/t Au and 12.9 g/t Ag. The deposit was discovered in early 2006 during a greenfields program conducted by Aurelian Resources, a Canadian junior explorer. Discovery resulted from systematic drill testing of a conceptual geologic model, which predicted that auriferous veins would be present in andesitic volcanic rocks inferred to underlie a steep silicified rib cutting a fluvial conglomerate sequence.

Тектонический контроль, реконструкция и консервация тигелонгнанского месторождения порфиров и эпитермальных отложений меди (Au), Центральный Тибет, Китай

The newly discovered Tiegelongnan Cu (Au) deposit is a giant porphyry deposit overprinted by a high-sulfidation epithermal deposit in the western part of the Bangong–Nujiang metallogenic belt, Duolong district, central Tibet. It is mainly controlled by the tectonic movement of the Bangong–Nujiang Oceanic Plate (post-subduction extension). After the closure of the Bangong–Nujiang Ocean, porphyry intrusions emplaced at around 121 Ma in the Tiegelongnan area, which might be the result of continental crust thickening and the collision of Qiangtang and Lhasa terranes, based on the crustal radiogenic isotopic signature.

The successful exploration geologist uses knowledge of geologic relationships and ore-deposit styles, tempered by experience, to interpret all information available from a given prospect in order to develop an understanding of its mineral potential. In the case of exploration for epithermal gold deposits, this understanding can be augmented by familiarity with active hydrothermal systems, their present-day analogues.

This report constitutes a new descriptive model for epithermal gold-silver deposits. It summarizes characteristics of known deposits, including their geological, geophysical, geochemical, and geoenvironmental aspects. Models concerning the genesis of epithermal gold-silver deposits are discussed. How descriptive and genetic aspects of the model can be applied to mineral exploration and resource assessment of undiscovered deposits is described.