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Geologic setting, Mineralization, and Detailed Underground Mapping of the Fire Creek Low-Sulfidation Epithermal Gold-Silver Deposit, Nevada
AdvisorMuntean, John L
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The Fire Creek mine located 8 km northwest of the town of Crescent Valley in the northern Shoshone Range in Lander County, Nevada produces high grade gold and silver ore from a series of north to northwest-striking high angle veins along the western margin of the Northern Nevada Rift (NNR). This shallow, low sulfidation epithermal vein deposit is hosted in Miocene age volcanic rocks, intrusions, and volcaniclastic sediments. It occurs in a similar structural setting as the Mule Canyon low sulfidation epithermal gold and silver deposit, which is located 15.3 km north-northwest of Fire Creek along the same structural trend. The majority of production at Fire Creek has been from high-grade, banded and brecciated, electrum-bearing quartz ± carbonate ± adularia veins (Type I ore) hosted in a Miocene basaltic andesite hypabyssal intrusive rock locally known as Tertiary equigranular basalt (Tbeq). The most recent development and mining has focused on ore associated with intense argillic alteration, fault gouge, and abundant sulfides. This refractory and somewhat disseminated ore known as Type II ore primarily occurs along faults, and to a lesser extent along subvertical dike margins and subhorizontal vesicular lava flow tops. This mineralization, north of the high-grade Type I veins is hosted in basaltic andesite flows, tuffaceous sediments, and autobreccias in the Fire Creek Sequence, a sequence of rocks similar to the Tmc “Mule Canyon Sequence” of the Mule Canyon Mine. Detailed underground mapping, construction of cross sections, reinterpretation of drill core, petrographic examinations of ore and host rocks, and electron microprobe analyses have revealed striking similarities between mineralization and host rocks at Mule Canyon and Type II ore and rocks which host it at Fire Creek. These techniques also show synchronous timing of the two differing styles of mineralization at Fire Creek along with high level of structural control to the Type II ore which was previously unrecognized. This study provides a detailed examination of host rock geology, mineralization, and alteration of a low sulfidation epithermal deposit hosted in mafic to intermediate composition igneous rocks – a rare combination that has only been studied formally at the Mule Canyon deposit. Information presented in this study may have implications for exploration of low sulfidation epithermal deposits elsewhere, particularly in the NNR.