The central Cherry Creek Range exposes a nearly intact, 8-km thick crustal section of Precambrian through Eocene rocks in a west-dipping homocline. Similar tilts between Eocene volcanic rocks and underlying Paleozoic carbonates demonstrate that tilting and exhumation largely occurred during post-Eocene extensional faulting, thus allowing for relatively simple paleo-depth determinations of Eocene intrusions and mineral deposits. The study area is cored by the Cherry Creek quartz monzonite pluton (35 km2 exposure; ~132 km 2 coincident magnetic anomaly), which was emplaced into Precambrian and Cambrian meta-sedimentary strata between 37.9–36.2 Ma and is exposed along the east side of the range. The pluton and overlying Paleozoic strata are cut by abundant 35.9–35.1 Ma porphyritic silicic dikes.
A range of polymetallic mineralization styles are hosted by the intrusive rocks along two deeply-penetrating, high-angle faults and their intersections with favorable Paleozoic units. Geochemical, geochronological, petrographic, and field mapping show progression among hydrothermal ore deposits from the mesozonal intrusion-proximal through the epizonal intrusion-distal environments. Data indicate that both the intrusions and hydrothermal deposits at Cherry Creek are exclusively Eocene, and were developed prior to the westward tilt that affects rocks above and below the Eocene unconformity. The deepest-formed and highest-temperature deposits are intrusion-related Sn-W-(Mo) greisen and Au-rich polymetallic vein mineralization that occurred at paleodepths of 7–8 km and developed during the emplacement of the Cherry Creek pluton based on 187Re/187Os and 238U/206Pb ages. Carbonate replacement deposits containing Ag-Pb-Zn-(W) occurred at intermediate depths of ~4–5 km during the Eocene, whereas distal-disseminated Au-Ag and Carlin-Type Au deposits (CTDs) formed slightly later than high-temperature deposits in shallower environments, from 1–3 km below the Eocene unconformity. The close timing and spatial associations suggest a link between all deposits and the development of the Cherry Creek intrusive complex.
These findings imply that Eocene CTDs relate to large deep-seated plutons and/or batholiths, not to shallow porphyry-type plutons, and that shallow CTDs are potentially zoned with deep Sn-W-Mo greisen and high-temperature Au-rich vein and replacement deposits. Late Eocene magmatic-hydrothermal events at Cherry Creek regionally coincided with a major metallogenic period in the Cordillera that resulted in the formation of economically important CTDs.
|Advisor:||Ressel, Michael W.|
|Commitee:||Boyle, Douglas P., Muntean, John L.|
|School:||University of Nevada, Reno|
|School Location:||United States -- Nevada|
|Source:||MAI 58/01M(E), Masters Abstracts International|
|Keywords:||Cherry Creek, Eocene, Magmatism, Mineral deposits, Nevada, Polymetallic|
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