Midway Mine, Tonopah Mining District, San Antonio Mountains, Nye County, Nevada, USAi

Regional Level Types
Midway Mine	Mine
Tonopah Mining District	Mining District
San Antonio Mountains	Mountain Range
Nye County	County
Nevada	State
USA	Country

Structure: Minor east-northeast trending faults with minimal displacements are mapped in the area. Midway lies east of the Walker Lane, a prominent zone of parallel and sub-parallel right lateral strike slip faults,a major structure that separates the Sierra Nevada batholith from the Basin and Range Province; regional extensional Basin and Range type faulting

Alteration: Rhyolite host rock is altered, silicified. Northwest-trending, sub-vertical rhyolite porphyry dikes that intrude the Palmetto Formation and overlying Rye Patch Formation at Midway are pervasively propylitized with local sericitic and phyllic hydrothermal alteration . Small amounts of pyrite and chalcopyrite occur in the dike rock.

Commodity: Ore Materials: gold Gangue Materials: calcite, quartz, chalcedony

Deposit: The deposit covers a mineralized strike length of almost 5 miles. Prior work on the property identified four zones of low sulfidation, quartz adularia, epithermal gold mineralization, the Discovery, SP, 121, and 63-77 zones. Mineralization is found in quartz-calcite vein stockworks within altered Tertiary rhyolite and underlying Ordovician sedimentary rocks. In high-grade intervals, the gold occurs as dendritic intergrowths with quartz-calcite crystals, and as bands within quartz-chalcedony veins and lining vugs within the siliceous rhyolite host rock. These veins typically contain higher-grade gold mineralization, such as 23 gpt gold over 17.5 feet in MW222. High-grade gold intercepts commonly occur within a strong quartz vein stockwork system developed in the main Discovery Zone.

Deposit type: Epithermal vein, quartz adularia

Development: Early production from the Midway (Rye Patch) District is unknown, but evidence of past exploration activity is shown by numerous pits and a shaft. Houston Oil and Minerals held the property from the 1970's through to 1984. In 1986 the present claim owners, Thomas Patton and Paul Schmidt, staked claims to cover the Midway prospect area and mineralization located to the north and east. Several companies reviewed and sampled the property and obtained locally anomalous concentrations of gold: in 1988 Coeur d'Alene Mines optioned the Midway Property and conducted preliminary geological, geochemical and geophysical surveys on it. Followed by a three hole reverse circulation drill program to test mineralization in the prospect areas. Results of this initial test were inconclusive and Coeur d'Alene dropped their option. Rio Algom optioned the property in 1989 and conducted a 42-hole reverse circulation drill program on the SP Prospect area. Results of this drill program were also inconclusive and Rio Algom dropped the option. In 1992, Kennecott Exploration optioned the Midway property and conducted extensive exploration of the known prospect areas and elsewhere on the property. Detailed geophysical programs including airborne, gravity and CSAMT surveys were completed. A large, 132-hole drill program, including four core drill holes was undertaken in 1996. This resulted in a preliminary resource estimation on the project area of 270,000 ounces of gold. Tombstone Exploration entered into a joint venture with Kennecott and in 1997 completed a 14-hole drill program on the Midway Property. Kennecott dropped their option in the fall of 1997 and the property was returned to the vendors. Between May and September 2002, Midway Gold Corp. completed more than $1.5 million of exploration drill testing the main areas of interest on the property. The property has increased in size to include 1,649 unpatented mineral claims for a total of 13,250 hectares. As operator of the project, Newmont has conducted extensive geophysical surveys including EM, magnetics and radiometric airborne surveys, ground radiometrics, gravity and CSAMT, detailed geological mapping in the Northwest and Thunder Mountain areas and rock and stream sediment geochemistry. Two major drill campaigns were completed since the July 23, 2002 report was issued. These campaigns consisted of 43 core holes totaling 22,364 ft and 77 reverse circulation holes totaling 37,690 ft. The Thunder Mountain gold property is located adjacent to and southeast of the Midway property. In 2002, Castleworth Ventures Ltd. acquired a 50% interest in the Thunder Mountain property from Pacific Intermountain Gold Corp. The 228-claim property has been mapped and sampled by Pacific Intermountain Gold to define targets for drill testing. Permitting for drill testing is in progress, and drilling was anticipated to begin in the first quarter of 2003.

Geology: Regional Geology: the Midway Property is underlain by northwest striking, easterly-dipping chert and argillite of the Ordovician age Palmetto Formation and interbedded siltstone and limestone of the Cambrian- Ordovician age Emigrant Formation the Midway Hills to the west, north and south of the property are composed of Miocene age Red Mountain trachyandesite flows (Jonson, 1988). The eastern portion of the property is covered in Quaternary fan and pediment alluvial deposits with mixed playa-dune deposits locally The Midway property is covered by alluvium, underneath which lie the favourable tuffaceous rhyolites of the Tombstone formation and older sedimentary rocks of the Palmetto formation. Subvertical dikes emplaced during the Upper Cretaceous intrude the Palmetto units. Hills to the east, north and south represent trachyandesite flows left over from the Miocene. The average thickness is 3-4 meters, though beds can thicken to as much as 300 metres.

Ore(s): Regional extensional faulting provided the conduits for the hydrothermal fluids, but mineralization is pervasive.

Other Databases

Link to USGS MRDS:	10310416

Other Regions, Features and Areas containing this locality