Thrasher

Project Summary

Tungsten skarn project on the west slope of the Selenite Range, Pershing County, Nevada, approximately 18 miles southeast of Gerlach within the Hooker–Empire–Gerlach mining districts. 11 lode claims totalling 227.3 acres covering two known prospects: Stormy Day Mine (W-Mo-Cu, past producer) and Thrasher (W-Mo). The Stormy Day produced tungsten from 1941 to 1957 at grades of 0.66–1.0% WO₃, with diamond drilling in 1953 confirming ore extends at least 100 feet below the lowest adit level. A 1942 USBM field examination reported surface cuts grading 1.5% WO₃ across 18 feet and tunnel face samples at 0.9% WO₃. The contact zone has been traced along outcrop for approximately 3 miles and remains open along strike. Mineralization is hosted in tactite at the igneous contact of granodiorite with carbonate rocks of the Auld Lang Syne Group.

Location: West slope of the Selenite Range, ~18 mi (29 km) SE of Gerlach, Pershing County, NV. BLM administrative area. Claims: 11 lode claims (THR 1–11) totalling 227.3 acres.

Geology

The project area lies on the western slope of the Selenite Range where Late Jurassic to Late Cretaceous granodiorite and diorite intrusives have contact-metamorphosed older carbonate and clastic sediments of the Auld Lang Syne Group. Mineralization follows the USGS tungsten skarn model (14a), occurring as scheelite-bearing tactite at the igneous contact of granodiorite with limestone and dolomite. The contact trends approximately north–south, dips 50–70° westerly, and has been traced along outcrop for approximately 3 miles. Metamorphism is intense, producing garnet, pyroxene, actinolite, tremolite, zoisite, epidote, and vesuvianite, with minor pyrite, chalcopyrite, and molybdenite. Ore minerals include scheelite, powellite, molybdenite, and chalcopyrite in a gangue of garnet, epidote, pyroxene, pyrrhotite, and quartz. The contact zone pinches and swells, ranging from 2 to 4 feet in thickness, with the best ore occurring at the marble edge of the garnet zone.

History

The deposit was discovered in 1941 by John J. Thrasher and first developed during World War II, with production from 1941 to 1957 by shrinkage stope methods. Between 1944 and 1957, the mine produced 19,523 tons of ore containing 1.66% WO₃. In July 1942, USBM geologist Vincent P. Gianella examined the property and reported approximately 400 feet of development work, with the main tunnel running east then turning south along the contact for a total length of about 200 feet. Gianella sampled the tunnel face at 0.9% WO₃ and noted surface cuts grading 1.5% WO₃ across 18 feet. He concluded the area was worthy of further intensive prospecting. In 1953–1954, Stanley F. O'Leary obtained a lease and option and explored the southern portion of the deposit with government assistance under the DMEA program (DMEA 4240), driving crosscuts and conducting diamond drilling that confirmed the ore extended at least 100 feet below the lowest adit level. By 1957, development included four levels of underground workings totalling approximately 610 m (2,000 ft) of drifts and crosscuts to a depth of 69 m (225 ft). The property has been inactive since the late 1950s.

Prospects

Stormy Day Mine

A past producer at 1,658 m elevation, historically known as Old Thrasher or Milky Way. Primary commodity is tungsten with secondary molybdenum and copper. The deposit is an irregular to tabular tactite body at the granite–carbonate contact, striking N–S, dipping 50–70°W, approximately 4.6 m thick and 99 m wide. Host rocks include hornfels, schist, skarn, and limestone of the Auld Lang Syne Group. Ore grades averaged 0.66% WO₃, with DMEA crosscut samples ranging from 0.01% to 1.60% WO₃. Workings include two cross-cutting adits driven beneath the mineralized outcrop, with lesser adits and pits above and along the N–S structures, totalling four levels of development. The main adit had an ore-bin and stockpiles at the portal. Produced tungsten by shrinkage stoping from 1941 to 1957.

Thrasher

A tungsten-molybdenum prospect at 1,579 m elevation, located approximately 2 km north of the Stormy Day workings on the same granodiorite–carbonate contact. Host rocks are shale, mudstone, siltstone, sandstone, and carbonate rock with local silicification alteration. The prospect lies on the northern extension of the mineralized contact traced from the Stormy Day Mine and represents additional strike length of the same skarn system that has received limited historical exploration. Gianella noted in 1942 that the Cecil B. Jeakins prospect (approximately 2 miles north of the Thrasher workings, on the same contact) also showed good values, indicating the mineralized system extends well beyond the developed area.

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