UC San Diego

Fire Creek, located in northern Nevada, is host to a low- sulfidation, epithermal Au-Ag deposit that is spatially and temporally associated with mid-Miocene volcanism. This study implements a whole-rock to mineral-scale analysis in order to evaluate the ore's paragenesis. Volcanic units at Fire Creek are a co-genetic suite of basalts to trachydacites which were subjected to three distinct pulses and possess Au-Ag in two distinct forms. Two generations of gold and Ag bearing sulfide grains are present and the average Au varies from 28.3-6.7 ppm; Ag varies from 46.6-33.0 ppm. Other studies on mid-Miocene northern Nevada low-sulfidation epithermal Au-Ag deposits have reported general conditions for deposition or have focused on rhyolitic-hosted ores. These studies lack in- situ trace- and major-element analysis in order to provide a high precision model on mid-Miocene low-sulfidation, epithermal Au-Ag deposits. This study presents the first known highly siderophile element (HSE) analysis on electrum (Au and Ag alloy) grains and has coupled textural observations with in-situ chemical analysis in order to characterize individual pulses and develop a general paragenesis for northern Nevada mid-Miocene epithermal deposits