ABSTRACT

Collaborative Research: Magmatism and mineralization in the Owyhee Mountains, ID: A case study of mid-Miocene Au-Ag ores and the emergence of the Yellowstone Hotspot

Intellectual Merit. Voluminous Columbia River-Steens flood basalt volcanism in eastern Oregon and Washington, southwestern Idaho, and northern Nevada occurred during the proposed ~16.7 Ma initiation of the track for the nascent Yellowstone hotspot. This magmatic event coincided with three phenomena that affected the southern portion of the flood basalt province (e.g. the Oregon Plateau): [1] region-wide development of focused zones of extensional tectonism ± eruption of flood basalt magmas (e.g. the northern Nevada rift and Oregon-Idaho graben); [2] development of numerous silicic dominated magmatic systems (e.g. the McDermitt and Santa Rosa- Calico volcanic fields); and [3] abundant epithermal Au-Ag mineralization, (e.g. Buckskin-National, Sleeper, DeLamar). Recent work by the lead PI suggests that the combination of dominantly bimodal basalt-rhyolite magmatism and focused extension resulted in magmatic systems that were not just caldera-forming, but instead were characterized by multiple discrete eruptive loci and a diversity of eruptive products and styles. It is hypothesized that the eruptive products and styles locally included Au-Ag ores that were transported from the mantle with mafic magmas and emplaced locally in epithermal systems. The validity of this model will be tested in two focus regions, the Owyhee Mountains (ID) and the Jarbidge district (Jarbidge Mountains, NV), where there are excellent exposures of mid-Miocene flood basalt lava flows and shallow intrusive bodies, silicic volcanic and hypabyssal products, and Au-Ag mines that are economically and historically significant. Field, petrographic, geochemical, isotopic, and geochronologic data will be obtained to evaluate the relation of epithermal Au-Ag mineralization to the associated magmatic activity. The proposed research will specifically examine whether local mineralization and silicic magma production was stimulated by periods of enhanced mafic magmatism. The field, geochemical, and geochronologic results will provide additional constraints on the poorly understood spatial-temporal pattern(s) and styles of mid-Miocene Oregon Plateau volcanism, which are needed to fully understand how this magmatic event affected the North American lithosphere.

Broader Impacts. This project addresses a fundamental question, namely, in what Earth reservoir do precious metals originate? The hypothesis that epithermal precious metal mineralization is intimately related to mafic magmatism (specifically, flood basalts) has worldwide economic implications, and could guide global precious metal exploration efforts. The proposed research will expose students from two EPSCoR institutions to basic geologic field work as well as detailed, laboratory-based analytical work. Additionally, this work will provide the basis for a dynamic digital map of the Owyhee field area that will be used in undergraduate and graduate courses, as well as a series of laboratory exercises regarding volcanology, petrology, and ore genesis. Finally, this project will provide invaluable mentoring aspects to a young scientist (lead PI).

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