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Geologic map of the Como quadrangle, Lyon County, Nevada [MAP AND TEXT]
Geol map Como quad

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Title: Geologic map of the Como quadrangle, Lyon County, Nevada

Author: Michael C. Say and Andrew V. Zuza
Year: 2022
Series: Open-File Report 2022-09
Format: 1 sheet: 39.5 x 27.5 inches, cross section, color; text: 7 pages, color
Scale: 1:24,000

This 1:24,000-scale geologic map of the Como 7.5-minute quadrangle covers part of the northern Pine Nut Mountains in Lyon County, Nevada. The northern Pine Nut Mountains consist of Mesozoic plutonic and sedimentary rocks unconformably overlain by west-tilted Oligocene tuff and a thick-package of Miocene volcanic and sedimentary strata. The range was tilted westward by Miocene east-dipping normal and left-oblique faulting along the middle and eastern flanks of the Pine Nut Mountains.

The map area consists mostly of parallel and conformable west-tilted Miocene volcanic and sedimentary rocks that are ~2 km thick. The volcanic sequence consists of mostly dacite to andesite, with some basaltic andesite. Some dacite-andesite dikes intrude the volcanic rocks. New 40Ar/39Ar dates bracket main volcanic sequence to 14.2–6.8 Ma, with most dates between 8.2 and 6.8 Ma. Miocene strata were deposited on sparse Oligocene ash-flow tuff and the Jurassic Gardnerville Formation. The Miocene sequence was tilted 30°–36° west by several north-striking east-dipping normal faults that must have initiated after ca. 6.8 Ma based on the parallel nature of the volcanic section. Restoration of the faulted strata suggests >14% extensional strain.

The Como mining district is located in the northern Pine Nut Mountains and hosts gold and silver mineralization. Active exploration projects are currently underway throughout the range including the Hercules project. Mineralization is thought to be a low-sulfidation volcanic-hosted epithermal gold and silver deposit. Abundant northeast-striking quartz veins are exposed throughout the Como, Hercules, and eastern flank areas. Large halos of hydrothermally altered volcanic rock envelope quartz veins. Alteration is not observed in the hanging wall of the main eastern fault block.

This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G21AC10873, 2021.

Suggested Citation:
Say, M.C., and Zuza, A.V., 2022, Geologic map of the Como quadrangle, Lyon County, Nevada: Nevada Bureau of Mines and Geology Open-File Report 2022-09, scale 1:24,000, 7 p.

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