Spring Valley Canyon placers, Spring Valley Mining District, Humboldt Range, Pershing County, Nevada, USAi

Regional Level Types
Spring Valley Canyon placers	Group of Placers
Spring Valley Mining District	Mining District
Humboldt Range	Mountain Range
Pershing County	County
Nevada	State
USA	Country

Sec 36 T29N R34E
Commodity: Ore Materials: coarse and some fine free gold Gangue Materials: gravels; clay

Deposit: The Spring Valley Property hosts a buried vein-stockwork gold system hosted in Permo-Triassic Rochester Formation rhyolite beneath 50 to 200 feet of alluvial cover. There are several mineralized intervals within the rhyolite volcanic and volcaniclastic assemblage. Gold at Spring Valley is hosted by a buried breccia and vein-stockwork system hosted in Permo-Triassic Rochester Formation rhyolite beneath 50 to 200 feet of alluvial cover. The gold occurs in and around a volcanic breccia interpreted to be a diatreme vent, called the Pond zone. This discovery is open to the northwest, southwest, and east. Mineralization is in quartz-tourmaline stockwork veins cutting quartz-sericite altered breccias and rhyolite volcanic rock. Narrow high-grade quartz-tourmaline veins with grades of 1 ounce of gold per sort ton of ore (31g/t) have been discovered in and around the breccia pipes. Most of these zones are oxidized from a 400 to 700 foot depth. The placer gravels in the lower canyon are 20-30 feet thick and contain gold in gravel horizons underlain by clay.

Deposit type: Epithermal vein, Comstock

Development: Placer gold was discovered in 1875. Chinese miners extensively worked the deposits from 1880-1895. The gravels in the lower valley were dredged from 1910-1914, and reworked locally by hand in the 1920s and 1930s. The placers were mined by Spring Valley Dredging Co. in 1949. The placer mining area was idle when examined in Sept. 1984, but there were obvious signs of recent activity including relatively new mining equipment and trucks on property. One area of the property in sec 36 was listed as active (the Horseshoe mine) in 1984, owned by Duane E. Bender, Dan Selzer, and Walter Martin of Lovelock, NV. Since the 1970s, exploration on the Spring Valley Property by Kennecott Exploration, Ltd., and more recently, by Echo Bay Exploration, Inc., has identified several mineralized intervals within the rhyolite volcanic and volcaniclastic assemblage. To date, a total of 23 reverse circulation (RC) and two core holes have been completed on the Spring Valley Property. Echo Bay and Kennecott drilled the initial 25 holes on the property. Midway Gold has completed 31 drill holes since it acquired the project in 2003. Of the 52 reverse circulation (RC) and four core holes completed to date, forty holes have encountered gold grades greater than 0.01 oz/st (0.3 g/t) gold. Economic gold grades over significant thicknesses have been encountered in 19 drill holes. Preliminary metallurgical testing on drill cutting composites indicates gold recoveries of 75 to 95 percent. Due to the coarse nature of gold at Spring Valley, metallic screen preparation of samples is required to provide representative analyses. In addition to the Pond zone and its extensions, five new targets were identified through geologic mapping, CSAMT surveys, and geochemical sampling. These new targets have the potential to substantially increase the known gold inventory at Spring Valley. Midway began testing these targets with a 10,000 foot drill program in October, 2004. Preliminary results near the end of 2004 about halfway through this drilling project indicate the discovery of a new gold-bearing zone 500 feet east of the Pond zone, in a shallower structural block. The new zone consists of 60 feet of 0.034 ounces per ton (opt) gold (18.3m of 1.16 grams per ton (g/t) gold) in an angle hole in a rhyolite sill with quartz-tourmaline veins. A second drill hole encountered 5 feet of 0.076 opt gold (1.5 m of 2.6 g/t gold) at the alluvium-bedrock contact suggesting a nearby buried gold source. A third drill hole encountered 50 feet of 0.62 opt silver (15.2m at 22g/t) and 10 feet of 0.018 opt gold in the edge of a newly identified breccia pipe 2000 feet east of the Pond zone. Additional drilling was planned in early 2005 to test some of the thicker breccia targets, which were not then accessible.

Geology: The gravels in the lower canyon are 20-30 feet thick and contain gold in gravel horizons underlain by clay. Placer gold was derived from stringer zones in the Koipato Rhyolite.

Ore(s): Stratigraphically limited to gravel beds

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Link to USGS MRDS:	10310357

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