New Geologic Map — McDermitt Caldera

Preliminary geologic map of the McDermitt caldera, Humboldt County, Nevada and Harney and Malheur counties, Oregon

Authors: Christopher D. Henry, Steven B. Castor, William A. Starkel, Ben S. Ellis, John A. Wolff, William C. McIntosh, and Matthew T. Heizler
Year: 2016
Series: Open-File Report 16-1
Format: plate: 41 x 38 inches, color; text: 8 pages, b/w, includes oversize table (15 x 13 inches)
Scale: 1:70,000

The McDermitt caldera of northern Nevada and southeastern Oregon is a large, 16.4 Ma volcanic center that is commonly recognized as the starting point of the Yellowstone hotspot, which migrated northeastward over time to the Yellowstone National Park area where volcanism continues to be intensely active (Pierce and Morgan, 1992, 2009). New geologic mapping and analytical studies by geologists with and working with the Nevada Bureau of Mines and Geology reveal the overall characteristics, dimensions, timing, and relation to mineralization of the caldera. The caldera formed when about 1000 km3 (about 250 mi3) of mostly rhyolite magma erupted from an underlying chamber. So much magma erupted that the overlying ground collapsed into the resulting void, leaving a giant depression—a caldera—that was about 40 km north-south by 22 to 30 km east-west. The giant eruption was preceded by additional volcanism that began about 16.85 Ma and was followed by volcanism that lasted episodically until about 14.9 Ma. Hydrothermal activity related to the volcanism generated numerous known and probable mineral deposits in and around the caldera, especially of the strategically important minerals lithium, uranium, and gallium. Additional, currently unknown areas and types of mineral deposits are likely.

This map was prepared with support from the Nevada Division of Minerals and the U.S. Department of Energy.

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