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Project work for Mineral Systems of the Ancestral and Modern Cenozoic Cascades Arcs and central California Coast Ranges, Western USA

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This project will construct a comprehensive metallogenic model for the Cenozoic Cascades arcs and late Cenozoic magmatism in the central California Coast Ranges and refine genetic mineral deposit models, especially for epithermal deposits that are abundant in these areas. The initial phase of the project will be the development of geologic, geochemical, geophysical, geochronologic, and mineral deposit databases for the southern Cascades arc in northeast California and western Nevada. Once completed, these databases will augment similar databases compiled for the Humboldt River Basin BLM assessment project (northern Nevada), as well as the soon-to-be completed Resources and Hazards of Hydrothermal Systems in Cascades Volcanoes project which pertains to the Western Cascades arc in Washington, Oregon, and northernmost California. Database compilation will identify high-priority data gaps, such as for the Cascades arc in northwest Nevada and northeast California, and selected new data will be collected to fill these gaps. In addition, detailed studies of selected fossil and active hydrothermal systems, both mineralized and un mineralized, will be conducted to improve mineral deposit models. The comprehensive data synthesis and interpretation phase of the project will result in products that specifically address land-use planning and scientific needs. The project will be undertaken with collaboration of the Nevada Bureau of Mines and Geology, the University of Nevada, Reno, the Great Basin Center for Geothermal Energy, and other Federal, State, and Academic organizations.

Task 1 - Metallogeny of the southern Cascades arc

Mineral deposits in continental-margin volcanic arcs are the major source of the worlds copper, gold, silver and other important byproduct trace metals. Magmatic-hydrothermal systems form episodically throughout the evolution of volcanic arcs including the waning stage of arc volcanism. The southern Cascade arc in California and Nevada, and geochemically similar, coeval volcanic rocks in the California Coast Range provide an arc setting in which to understand the major magmatic and tectonic controls on the development of ore deposits throughout the evolution of the arc and its demise as a result of establishment of a transform plate boundary. This task seeks to better characterize known mineral deposits and areas of hydrothermal alteration in the southern Cascades arc and define the magmatic and tectonic controls of ore deposit generation in the arc. Research on the metallogeny of the southern Cascade arc will be combined with previous MRP studies of the northern (Western) Cascade arc in Oregon and Washington in order to create an integrated metallogenic model for the entire Cenozoic Cascade arc. This research will provide knowledge about mineral deposit generation in a continental arc setting that will be more broadly applicable to magmatic arcs worldwide. This task also contributes to the development of quantitative models for both hydrothermal alteration and mineralization in the near surface environment and the interior parts of stratovolcanoes and flow-dome fields.

Task 2 - Young hydrothermal systems

Epithermal mineral deposits and weakly mineralized hydrothermal systems in the diverse and complex geologic settings of the Cenozoic Cascades arc, northwestern Great Basin and in the central Coast Ranges, California, are considered the products of magmatic, amagmatic (extensional, non-magmatically heated), and mixed hydrothermal systems. In addition, several types of magmatic hydrothermal systems that develop different types of epithermal mineral deposits are present in these areas. Identification of the origin of many of the epithermal deposits remains uncertain. The criteria used to discriminate among the alternate origins are poorly constrained and commonly limited to empirical observations. The implications of this uncertainty to reliable mineral resource assessments are great, because assessments need to apply appropriate occurrence and grade and tonnage models.

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