Magmatic-Tectonic History and Component Sources of Major Precious Metal Deposits in the Southern Walker Lane

Science Center Objects

We conducted linked investigations to address the magmatic-hydrothermal evolution, post-mineralization structural histories, and sources of host rocks and hydrothermal mineral components of three significant, subduction-related, Au-Ag districts in the Walker Lane structural zone in the western Great Basin. 

Science Issue and Relevance

geologic map of study area

Location map showing regional geologic setting of the Bodie Hills and major physiographic features. Mina deflection and outline of the Walker Lane modified from Faulds and Henry (2008), Busby (2013), and Carlson et al. (2013). Figure 1 from du Bray and others, 2016, doi:10.2138/am-2016-5440.

(Public domain.)

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, the specific magmatic-hydrothermal processes and structural regimes that controlled formation (and concealment) of these often juxtaposed deposits are not precisely known. In order to identify additional resources in the districts and to predict concealed deposits (the future supplies of most mineral resources), it is necessary to conduct detailed stratigraphic, structural and geochronologic investigations of these districts and apply modern concepts of magma generation, magmatic-hydrothermal transitions, volcanic stratigraphy, and regional tectonism.

Project Relevance: The geologic and isotopic characterization 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 that have been linked to a mantle plume and continental rifting. 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.

Methodology to Address Issue

Project objectives: We conducted linked investigations to address the magmatic-hydrothermal evolution, post-mineralization structural histories, and sources of host rocks and hydrothermal mineral components of three significant, subduction-related, Au-Ag districts. Two of the districts we 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 we characterized is the Bodie Hills volcanic field, CA-NV, which contains two 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.