The Gold Bar district contains five Carlin-type gold deposits and four resources for a combined gold endowment of 1.6 M oz [50 t]. The gold deposits are hosted in Devonian carbonate rocks below parautochthonous and allochthonous Paleozoic siliciclastic rocks emplaced during the Early Mississippian Antler orogeny. The district is in the Battle Mountain-Eureka trend, a long-lived structural feature that localized intrusions and ore deposits of different types and ages.
Постаккреционная металлогения Восточной Якутии характеризуется доминирующим развитием эпитермальной Au-Hg минерализации (Суплецов, 2001). Конформные металлогенические зоны золотоносного Hg оруденения, контролируемые продольными разломами, расположены в структурах Колымо-Омолонского микроконтинента и Верхоянского складчатого пояса. Данные разломы, как правило, трассируются свитами кайнотипных даек щелочных базальтоидов. Металлогенические построения позволили выделить две генетически близкие группы Au-Hg месторождений, локализованные в карбонатных и терригенных комплексах пород, отличающихся морфоструктурой, гидротермальными изменениями и масштабами оруденения. Ртути и сурьме в данных месторождениях, скорее всего, принадлежит второстепенное значение, и они выступают в качестве бипродукта.
In 1997 the British Columbia Geological Survey (BCGS) initiated a project to identify prospective areas for sediment-hosted gold mineralization. The inspiration for the project came from presentations and articles by Howard Poulsen of the Geological Survey of Canada (1996a, 1996b). He pointed out that there is potential to find hypogene, sediment-hosted gold mineralization in Canada akin to deposits found in Nevada. He mentioned that if an intrusive association is important to generate the mineralization, then two different geological environments might host this style of mineralization. Accreted terranes with a basement containing carbonate lithologies intruded by Mesozoic or Cenozic plutonism would be a prospective geological setting, specifically the Stikine and Quesnel terranes. The second favourable environment is within the sediments deposited along the continental margin of ancestral North America which have been cut by Mesozoic magmas, such as are found in the Kootenay Arc and Selwyn Basin (Figure 1).
Others have considered British Columbia as prospective territory for sediment-hosted gold. Early work by companies focused on the Insular Belt rocks exposed on Vancouver Island and the Queen Charlottes. These exploration programs were based largely on an epithermal-style model for the mineralization which was in favour at the time. The discovery of the Babe deposit (now called the Specogna or Cinola) in the Queen Charlotte Islands in 1970 increased the interest in this model because it was initially identified as a Carlin-type deposit (Richards et al, 1976; Champigny and Sinclair, 1982). <...>
The Carlin trend contains the largest concentration of Carlin-type gold deposits in the world. Two major controversies about these giant gold deposits have been their age, which is now firmly established as Eocene, and the source of heat, fluids, and metals, which remains debated. We present data that demonstrate an intense period of Eocene magmatism coincided in time and space with deposit formation and was arguably the primary heat source. Geologic studies over the last 40 years have emphasized the stratigraphy and structure of Paleozoic sedimentary rocks, which are the major ore hosts. However, four igneous episodes affected the Carlin trend, in the Jurassic, Cretaceous, Eocene, and Miocene. A Jurassic diorite-granodiorite laccolith and related dikes were emplaced at about 158 Ma in the northern Carlin trend. A Cretaceous granite intruded the northcentral part of the trend at 112 Ma. Abundant Eocene dikes intruded along most of the trend and were accompanied by lavas in a large volcanic field along the southwest edge of the trend between ~40 and 36 Ma. Miocene rhyolite lavas erupted just west of and across the southern part of the trend at ~15 Ma.
Stable isotopes from sulfates of three origins in Carlin-type deposits (CTDs) from western North America fall into distinct clusters and can be utilized to discriminate between barite of Paleozoic (sedimentary exhalative) origin, barite of hydrothermal origin related to gold mineralization, and supergene alunite and jarosite of weathering origin. Although the latter are obvious from field relations, the distinction between hydrothermal and sedex barite is not always so clear. Sedex sulfate sulfur was probably reduced and mobilized during gold mineralization, equilibrated with hydrothermal fluids, and then precipitated as sulfate during the late stages of mineralization, with a distinctly different sulfur and oxygen isotope signature. Isotopic signatures of sulfates may, therefore, be utilized as a mineral exploration tool for CTDs.
The Carlin trend in northeastern Nevada forms the largest and most productive accumulation of gold deposits in North America. Teal and Jackson (1997b) reported a gold endowment that by the end of 1996 included past production, reserves, resources, and mineral inventory of over 107 million ounces (3,330 t [metric tons]). More than 40 separate deposits have been delineated since disseminated gold mineralization in carbonate host rocks was first discovered by Newmont geologists John Livermore and Alan Coope in 1961. From their original discovery, a classification for this style of gold mineralization has come to be referred to as “Carlin-type” deposits. By early 2002, more than 50 million ounces (1,560 t) of gold had been recovered on the Carlin trend from 26 separate operating or past producing mines. Open-pit mining began in 1965 at the Carlin Mine, and underground mining began in 1993 on the same deposit.
The scope of this paper is to present a regional geologic setting of the Carlin trend. As part of the concluding discussion, a spectrum of Carlin trend deposit types is categorized to illustrate the relative influence of structural and stratigraphic controls on each deposit.
Pre-existing crustal structures are important in localising strain related to the large-scale evolution of an orogeny. Rheological contrasts between basement blocks will also influence the degree and location of faulting and relative uplift. In northern Nevada, U.S.A., basement architecture in the form of early rifted continental margins, formed during Proterozoic extension, may dictate the subsequent structural geometry of overlying sedimentary sequences during large-scale compression (Figure 1a). Within the region of the Carlin gold trend, specific anticlinal fold and thrust geometries in the sedimentary rocks, involved in various orogenies up until the Laramide, may focus fluid movement and provide effective traps to the system, resulting in the unique gold endowment of the area. Most mineralisation is situated less than 100 m below the Roberts Mountain thrust, which defines the lower boundary of the sequence of deep-water sedimentary rocks that has ridden over both the basement and younger sedimentary layers.
Muntean et al. (2003) argue that the Carlin and Battle Mountain–Eureka (BME) gold trends (Figure 1b) correspond to reactivated normal faults that likely had their origins in Proterozoic rifting. Numerical modelling offers a way to test the basic hypothesis by which “steps”, relics of continental rifting, control the subsequent location of upper crustal faults and anticlinal structures during compression.
The origin of Carlin-type or sediment-hosted, disseminated gold deposits of the Great Basin, the major source of gold in the United States, is poorly understood. We propose that Eocene magmatism was the heat source that drove the hydrothermal systems that generated these deposits in the Carlin trend and Independence Mountains in northern Nevada. This interpretation is based on a strong spatial and temporal association of Eocene intrusive-volcanic centers with the gold deposits of this region. Our new work and published 40Ar/39Ar dates indicate that magmatism was particularly intense between 39 and 40 Ma throughout northeastern Nevada, especially in and around the area of gold deposits. Carlin-type deposits may have formed preferentially during Eocene magmatism because it was (1) more intense in the area than other magmatic episodes, (2) somehow compositionally distinct, or (3) accompanied by extension that promoted hydrothermal flow. However, large-scale extension does not appear to have been a factor in generating Carlin-type deposits.
Carlin-type Au deposits in Nevada have huge Au endowments that have made the state, and the United States, one of the leading Au producers in the world. Forty years of mining and numerous studies have provided a detailed geologic picture of the deposits, yet a comprehensive and widely accepted genetic model remains elusive. The genesis of the deposits has been difficult to determine owing to difficulties in identifying and analyzing the fine-grained, volumetrically minor, and common ore and gangue minerals, and because of postore weathering and oxidation. In addition, other approximately contemporaneous precious metal deposits have overprinted, or are overprinted by, Carlin-type mineralization.
