Abstract

A near-vertical fracture set in Miocene Carlin Formation tuffaceous sediments occurs approximately 800 m above a deep Carlin-type gold ore zone of Eocene age at the Ren property on the northern Carlin trend, Nevada. The fractures, 0.2 to 2 cm wide, are filled with brown montmorillonite clays and contain a distinctive Carlin-type geochemical assemblage including Au, As, Sb, Hg, Tl, and S. These young, in situ geochemical anomalies are thought to originate from a paleogeothermal event that may have been seismically triggered by Yellowstone plume bulge-relaxation dynamics. The passage of the plume immediately north of the Carlin trend would have provided increased heat flow, which, coupled with crustal extension, may have allowed metal-charged geothermal vapor to be released from depth. The hydrothermal remobilization filled dilational fractures in surficial units with vapor-phase alteration clays containing the geochemical signature of the deep gold ore zone. Such fractures, if found in other areas of northern Nevada’s great mineral trends, may provide important exploration guidance for deep ore systems.

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