Field Trip Day Four: Buena Vista Hills, Humboldt Mafic Complex, Western Nevada
David A. Johnson, Mark D. Barton, 2000. "Field Trip Day Four: Buena Vista Hills, Humboldt Mafic Complex, Western Nevada", Part I. Contrasting Styles of Intrusion-Associated Hydrothermal Systems: Part II. Geology & Gold Deposits of the Getchell Region, John H. Dilles, Mark D. Barton, David A. Johnson, John M. Proffett, Marco T. Einaudi, Elizabeth Jones Crafford
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The purpose of this portion of the field trip is to examine the spatial and temporal distribution of sodium-rich hy-drothermal alteration and iron oxide mineralization generated by a saline hydrothermal system driven by the Middle Jurassic Humboldt mafic complex. The Humboldt system is of particular interest because it represents a basaltic mag-matic end member of intrusion-driven hydrothermal systems and, in this case, one where the fluids are largely, perhaps entirely, externally derived brines. Outcrops of Jurassic rocks within the complex record multiple, mutually crosscutting magmatic and hydrothermal events at different structural levels as exposed by mid-Tertiary extension. Mapping of selected areas across this large igneous complex allows definition of the relationships among the magmatic, structural, and hy-drothermal features. In turn, these enable an interpretation of the overall temporal and spatial evolution of a large intrusion-driven hydrothermal system (Johnson and Barton, 2000). From geology and geochemistry, one can estimate that upwards of 15 billion tonnes of iron and 35 million tonnes each of copper and zinc were moved by the hydrothermal system (Johnson, 2000). What happened to these metals and what are the implications for other systems? These are among the issues to consider.