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Geol Calavera Canyon

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Title: Geologic map of the Calavera Canyon quadrangle, Humboldt County, Nevada

Author: Christopher D. Henry, Joseph A. Laravie, William A. Starkel, Ben S. Ellis, John A. Wolff, and Stephen B. Castor
Year: 2023
Series: Open-File Report 2023-12
Format: map sheet with cross sections: 38 x 32 inches, color; text: 30 pages, b/w
Scale: 1:24,000

The Calavera Canyon 7.5-minute quadrangle covers the western margin of the 16.4 Ma McDermitt caldera, one of the oldest expressions of the Yellowstone hotspot and site of major lithium-clay deposits, and the eastern part of the adjacent Kings River Valley, a significant agricultural center. The ~800-m-high topographic scarp between the two areas exposes the caldera ring-fracture zone, extensive pre- caldera rocks, and a complete section of intracaldera tuff. The oldest pre-caldera rocks are a diverse suite of Jurassic intrusive rocks (table 1) that mostly consists of granodiorite but spans from high-Si felsite, aplite, and pegmatite to gabbro (table 2). Two major pulses of Eocene volcanism at 46–47 Ma and 39–41 Ma (table 3) produced dacite to rhyolite lavas and andesite-dacite(?) lavas, respectively (table 2). The lavas and volcaniclastic rocks coeval with the younger pulse filled a west-trending paleovalley cut into the Jurassic intrusive rocks. After a hiatus until ~17 Ma, intensive volcanic activity resumed with eruption of basalt and basaltic andesite lavas that are some of the southernmost expressions of Columbia River Basalt magmatism. Volcanism became more silicic with time, initially with anorthoclase-bearing rhyolite lavas, followed by biotite rhyolite lava domes, and peralkaline rhyolite lavas. Volcanism culminated with ~16.4 Ma eruption of ~1000 km3 of McDermitt Tuff, which is zoned from aphyric, peralkaline, high-Si rhyolite to abundantly anorthoclase-phyric trachydacite and icelandite (Fe-rich andesite). Eruption induced collapse of the ~40 x 22–30 km McDermitt caldera. Collapse along the western margin in the Calavera Canyon quadrangle was accommodated by an as much as 1 km wide zone of east-dipping, high-angle faults and monoclinal downwarps into the caldera. A lake that formed within the caldera was subsequently filled with tuffaceous sediments until ~15.7 Ma.

Normal faulting that probably began about 11–12 Ma in the McDermitt region (Colgan et al., 2006) cut through the western edge of the caldera, exposing the considerable intracaldera sequence in the quadrangle. The resulting, west-dipping Montana Mountains fault zone separates bedrock in the eastern part of the quadrangle from thick Quaternary and latest Cenozoic deposits in Kings River Valley. An as much as ~8-m-high scarp demonstrates that faulting has continued to the present. Quaternary deposits include alluvium, alluvial-fan deposits, and extensive colluvium and talus in drainages and slopes in bedrock and extending out into the valley. A pluvial lake occupied the valley into the Holocene, deposited both fine sediments in the lake bottom and gravel along shorelines and spits, and generated numerous shorelines during lake recession.

Three types of mineralization are present in the quadrangle. 1. Lithium-rich clays in the intracaldera sedimentary deposits, first recognized in the 1970s (Rytuba and Glanzman, 1979), are currently most important because of demand for Li for Li-ion batteries. The deposits also contain significant K, Rb, Mo, As, Sb, Mg, and F (Castor and Henry, 2020). The uncertain origin of these deposits involves diagenesis of the host tuffaceous sediments and possibly hydrothermal activity during the waning stages of caldera magmatism (Castor and Henry, 2020; Benson et al., 2017a, 2023). 2. U-Zr mineralization in pre-caldera volcanic rocks in and along caldera collapse faults at the Moonlight Mine and in Horse Canyon formed from hydrothermal solutions immediately following collapse (table 1; Castor and Henry, 2000). These deposits mostly consist of U-rich zircon, are accompanied by As, Sb, and Hf; minor amounts of Cu, Zn, Y, Hg, and Pb; and locally Mo, Ag, and Tl (table 4). 3. Quartz-sulfide veins in the Jurassic granitic rocks produced an unknown but probably small amount of Au and Ag in the early 1900s (Willden, 1964; Minor et al., 1988). Analyses of two vein samples for this study show minor enrichment in Co, Cu, As, Mo, Ag, Sb, Hg, and Bi (Au not analyzed; table 4).

Research supported by the U.S. Geological Survey, National Cooperative Geologic Mapping Program, under USGS agreement number G21AC10873.

Suggested citation:
Henry, C.D., Laravie, J.A., Starkel, W.A., Ellis, B.S., Wolff, J.A., and Castor, S.B., 2023, Geologic map of the Calavera Canyon quadrangle, Humboldt County, Nevada: Nevada Bureau of Mines and Geology Open-File Report 2023-12, scale 1:24,000, 30 p.

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