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Magmatic-tectonic history and component sources of major precious metal deposits in the southern Walker Lane

Issue: The Walker Lane structural zone in the western Great Basin contains numerous Miocene gold-silver (Au-Ag) deposits, several of which are world-class or uncommonly high-grade. These magmatic-hydrothermal deposits formed during continuous subduction-related magmatism but represent markedly different styles of mineralization. Although close temporal relationships among magmatism and hydrothermal systems have been established, specific magmatic-hydrothermal processes and structural regimes that controlled formation (and concealment) of these often juxtaposed deposits remain imprecisely known. Detailed stratigraphic, structural and geochronologic investigations of these districts, applying modern concepts of magma generation, magmatic-hydrothermal transitions, volcanic stratigraphy, and regional tectonism, are necessary for identification of additional resources in districts, and for prediction of concealed deposits, the future supplies of most mineral resources.

Project objectives: We propose linked investigations that will address in detail the magmatic-hydrothermal evolution, post-mineralization structural histories, and sources of host rocks and hydrothermal mineral components of 3 significant, subduction-related, Au-Ag districts. Two of the districts to be investigated, Tonopah, and Goldfield, NV, are among the largest or highest grade representatives of the quartz-adularia (“low sulfidation”), and quartz-alunite (“high-sulfidation”) deposit types. A third area to be characterized is the Bodie Hills volcanic field, CA-NV, which contains 2 significant quartz-adularia vein systems (Bodie and Aurora districts), and extensive areas of quartz-alunite alteration, one of which was mined for Au and Ag (Masonic district). Collectively, the districts provide age (~21-8 Ma) and size (hundreds of millions to thousands of oz. Au+Ag) diversity, in addition to varied styles of mineralization.

Relevance of this work: The thorough geologic and isotopic characterization proposed will enable comparison of source and process models for Walker Lane precious metal districts to those of Miocene precious metal deposits in the northern Great Basin (NGB) that have been linked to a mantleplume and continental rifting. We anticipate that the results of this investigation will provide new geologic and tectonic maps of important districts in the Walker Lane, reduce uncertainty in sources of elements in ore deposits, improve precious metal deposits models, and refine provincial and local scale targeting of resource exploration.

Project Staff:

Project Leader: Peter Vikre - (775) 784-5597 - pvikre@usgs.gov

Mark Bultman - (520) 670-5503 - mbultman@usgs.gov

Joseph Colgan - (650) 329-5461 - jcolgan@usgs.gov

Michael Cosca - (303) 236-4974 - mcosca@usgs.gov

Ed du Bray - (303) 236-5591 - edubray@usgs.gov

Mark Gettings - (520) 670-5507 - mgetting@usgs.gov

Al Hofstra - (303) 236-5530 - ahofstra@usgs.gov

David John - (650) 329-5424 - djohn@usgs.gov

Andrew Manning - (303) 236-1812 - amanning@usgs.gov

Richard Moscati - (303) 236-0023 - rmoscati@usgs.gov

Leonid Neymark - (303) 236-7898 - lneymark@usgs.gov

Arron Pietruszka - (303) 236-5514 - apietruszka@usgs.gov

Wayne Premo - (303) 236-7686 - wpremo@usgs.gov