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Abstract

Carlin-type ores have been reported in various locations around the world, but to date, the major economic deposits have been restricted to the Great Basin of the southwestern United States. Recent discoveries in east-central Yukon have many characteristics of Carlin-type deposits, and hold promise of great potential for new discoveries of economic importance. Both regions share commonalities of geologic history, including initial deposition of Proterozoic-Paleozoic calcareous host rocks on the passive margin of the fragmented Rodinian supercontinent. This was followed by compressional tectonism and continental accretion that included thrust faulting and plutonism through the late Paleozoic and Mesozoic. Many deposits in the Great Basin are associated with post-accretionary magmatism as the tectonic environment shifted to an extensional regime. However, at this early stage of investigation, the timing of mineralization in Yukon is not clear; the deposits may be geologically related to Late Cretaceous post-accretionary plutons. Associated gold skarn-style mineralization is present in both regions. Following mineralization, both regions experienced significant right-lateral transcurrent tectonism on their western margins; no known Carlin-type mineralization is associated with this latest tectonism.

Mineralization in both areas comprises finely disseminated gold associated with arsenian pyrite hosted in calcareous siltstones-sandstones to silty carbonates, although other rock types locally host significant mineralization. Other hydrothermal minerals present in these systems include realgar/orpiment, stibnite, fluorite, barite, and quartz. Temperature of deposition appears to be near 225°C. Hydrothermal alteration consists of decarbonatization, silicification, and argillization. Gold/silver is typically high at 1:1 or higher. Trace elements that show good correlation with gold include thallium, arsenic, antimony, mercury, and to a lesser extent antimony and silver.

In general, the deposits from the two areas are quite similar in terms of their tectonic history, and the processes and geochemistry appear to be very similar. The presence of extension and ore-related magmatism in Nevada appears to be a component that is much less clear in the Yukon Territory.

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