Big Mike Mine, Tobin and Sonoma Range Mining District, Pershing County, Nevada, USAi

Regional Level Types
Big Mike Mine	Mine
Tobin and Sonoma Range Mining District	Mining District
Pershing County	County
Nevada	State
USA	Country

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Sec 23 T31N R39E.
Volcanogenic massive sulfide deposit.
Discovered in the 1930s, mining was done from the late 1960s to the 1970s.

Commodity: Ore Materials: chalcopyrite, bornite, digenite, tenorite, cuprite, sphalerite; Gangue Materials: pyrite, iron oxide

Deposit: Big Mike is a high-grade, low tonnage, cupriferous pyrite volcanogenic stratiform massive sulfide deposit. It consists of a massive lens that occurs entirely within a thin cherty carbonaceous argillite. A stringer zone occurs in the footwall pillow basalt, and a minor stringer zone occurs north of the massive lens in the hanging wall pillow basalt. Much of the dump material and pit wall consists of pillow lava, chert, and argillite with varying amounts of limonite gossan and oxide copper minerals. The main deposit is volcanogenic massive sulfide of the hot springs type, which occurs in the Havallah sequence. This is a thick greenstone complex in the Pumpernickel formation. When discovered, the deposit consisted of a secondarily enriched pod of nearly massive copper and iron sulfides enveloped by altered rock containing zones and disseminations of secondary copper mineralization. The mineralogy is complex, as various secondary effects are apparent. The structure of the area is also complex, though the deformation of the Big Mike area is not so severe as other parts of the Havallah sequence. A shear zone runs through the Big Mike pit and extends approximately 1,000 feet in the southeast and northwest directions away from the pit. This is also the general strike of the area with dips 40 to 60 degrees to the northeast. This shear zone may be an indicator of further deposits. Five target areas have been identified for additional exploration on and adjacent to the Big Mike property. These targets show potential to extend the existing ore zone and for additional ore bodies.

Deposit type: Massive sulfide, Cyprus

Development: Copper occurrences were known in the area at about the turn of the last century. The project area was claimed in the early 1900s by the Foster family, but very little exploration was done and no development work was done. In 1966, Mr. Clair Chamberlain optioned the property and undertook a sampling program. As a result of the sampling, some copper oxide ore was shipped to ASARCO in Tacoma, Washington. From this work the Big Mike Corporation was formed to develop and exploit the copper oxide ore by heap leaching. A small pad was developed, and copper precipitate was produced. In 1967, the Big Mike Corporation entered into a joint venture with Cerro Corporation to explore the property further, and this led to the discovery of a high-grade copper sulfide ore body. By 1970, Ranchers Exploration and Development Corporation acquired the property from Cerro Corporation and confirmed the sulfide orebody, which was rapidly developed via an open pit. In fact, all the high-grade ore was mined and directly shipped to smelters in 1970. The remaining oxide ore and the mixed and low-grade sulfide ore were crushed for heap leaching. In the pit, similar low-grade ore was blasted from the walls of the pit for leaching in the bottom of the pit. Heap leaching was carried out during two periods, from 1971 to 1974 and then 1978 to 1979. Both periods were curtailed by low copper prices. In 1979, Ranchers abandoned the claims. The claims were subsequently staked and reclaimed by WR & A. Big Mike Limited Partnership (BMLP) purchased the claims from WR & A. in 1988. During the period from 1988 to 1992, BMLP undertook project studies to establish reserves, identify a treatment method, and gain environmental permits to develop the project. A considerable amount of work was done, but the project did not get underway. John Cook and Dan Mackie examined data from the project in the spring of 1997 and concluded that it would be suitable for continuous vat leaching with the EcoVat. After this work an option agreement was entered into. GoldSpring, Inc. acquired 100% of this project. The current Big Mike project is an oxide copper recovery project with the copper oxides remaining from a previous rich sulfide operation. The property also has exploration potential for further copper oxides and copper sulfides. In 2005, GoldSpring Inc. signed a memorandum of understanding with MBMI Resources Inc. to acquire a 50% interest in the 310-acre Big Mike copper property located 32 miles south of Winnemucca. Big Mike is a volcanogenic massive sulfide deposit that consists of a secondarily enriched pod of massive copper and iron sulfides enveloped by altered rock containing zones and disseminations of secondary copper mineralization. Ranchers Exploration and Development Co. produced 25 million pounds of copper from direct-shipping, high-grade copper sulfide ore from this property in 1970. Five target areas have been identified for additional exploration on and adjacent to the Big Mike property.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

29 valid minerals. 1 (TL) - type locality of valid minerals.

Rock Types Recorded