EOCENE MAGMATISM AND VERTICALLY ZONED POLYMETALLIC DEPOSITS IN THE CENTRAL CHERRY CREEK RANGE, WHITE PINE COUNTY, NEVADA

The Cherry Creek Range contains one of the most complete crustal sections in eastern Nevada. Along with concordantly-dipping Eocene volcanic strata, the range exposes over 7 km of Neoproterozoic and Paleozoic carbonate and clastic strata in a west-dipping monocline. This nearly intact succession is underlain by an extensive intermediate to felsic Eocene pluton, which intrudes and variably truncates metamorphosed sedimentary rocks of earliest Cambrian and older age. Abundant Eocene dikes cut virtually all stratigraphic levels, from the pluton upward to within a kilometer of the Eocene unconformity. In the central Cherry Creek Range, horizons within the Neoproterozoic and Paleozoic miogeoclinal strata exhibit distinctive styles of polymetallic mineralization that reflect diverse host lithologies and depths of formation. Progressing stratigraphically from the plutonic roof, deposit styles change from quartzite-hosted Au-rich silicic veins to bedding-controlled Ag-Pb-Zn-W metasomatic carbonate replacement bodies and finally to jasperoid-bearing Carlin-style disseminated Au deposits. The total vertical range of these ore deposits exceeds 6 km. We hypothesize that this zonation of deposit styles can be accredited to intrusion proximity and the corresponding transition from high temperature to low temperature conditions.

Fifteen new U/Pb zircon ages for representative igneous rocks are between 35.4 and 40.7 Ma, 13 of which are younger than 37.9 Ma. The ages confirm the presence of a major Eocene intrusive center in the Cherry Creek Range. These findings are temporally and spatially consistent with Eocene magmatic trends in northern Nevada that are likewise associated with the region’s Carlin-type gold deposits. Recent studies suggest that Carlin-type ore fluids separated at 7-10 km depths from plutonic sources. The exposure of both Carlin-style deposits and an underlying Eocene pluton in the Cherry Creek Range provides the ideal opportunity to test this hypothesis. By examining the range’s spectrum of distinct mineralization styles we will determine their geologic setting, age, and genetic links to magmatism. Here, we present primary results from primary field mapping, geochemical, and geochronological analyses which constitute the first phase of our study.