ABSTRACT
Tertiary precious-metal deposits in the Great Basin, USA, fall into two general groups, epithermal deposits (primarily volcanic-hosted) and sedimentary-rock-hosted deposits (including Carlin-type deposits). The epithermal and sedimentary-rock-hosted deposits apparently are related to three igneous assemblages, which differ with regard to petrology, geochemistry, eruptive style, and associated mineral deposits. Distribution of deposit types forms coherent patterns in time and space, but differences in grade and tonnage between the epithermal groups are minor. Most epithermal deposits have gross values between $30 million and $2 billion, but only two of them are comparable in size and value to giant porphyry Cu deposits. The origin of sedimentary-rock-hosted and some epithermal deposits is linked by their coherent pattern in time and space. Low-sulphidation deposits in the bimodal basalt-rhyolite assemblage have a different origin that is related to the inception of the Yellowstone hot spot.
