Griffon Mine, White Pine Mining District, White Pine County, Nevada, USAi

Regional Level Types
Griffon Mine	Mine
White Pine Mining District	Mining District
White Pine County	County
Nevada	State
USA	Country

Structure: The structural geology of the Griffon property includes Mesozoic contractional structures with superimposed Cenozoic extensional structures that have locally obscured, rotated, or reactivated older structures. The White Pine Range falls within the Central Nevada Thrust Belt,a zone of pre-early Cretaceous contractional structures in rocks as young as Permian. Regional structures include low amplitude, open folds with axes that strike between N-S and N15E. The Griffon property has been subjected to multiple episodes of deformation predating, concurrent with, and post-dating mineralization. The proposed sequence of deformational events at Griffon is: (1) Early high-angle normal faulting striking roughly WNW that offsets Devonian through Mississippian rocks up to 55 meters (180 ft.). (2) Upright, open folds trending N to NNE with possible thrust faulting. (3) Low-angle normal faulting which is most likely associated with the mineralizing event, since mineralized strata in the hanging-wall of this fault comprise both the Discovery Ridge and Hammer Ridge deposits. (4) Several episodes of high-angle normal faulting and possible strike-slip faulting that commonly offset mineralized strata. (5) Later movement along the Blackrock fault, a major low-angle normal fault of probable Oligocene age in the southern part of the range. At Griffon, the Blackrock Fault moved after gold mineralization had occurred and is interpreted to have been active between 31.3 and 14.3 Ma.

Alteration: Mineralized strata are variably altered with local argillization, silicification, decalcification, and jasperization. There is, however, no direct correlation between ore grade and alteration. Despite the prominent role of jasperoid in the discovery of the deposit, very little of the actual ore is strongly silicified.

Tectonics: Central Nevada Thrust Belt

Commodity: Commodity Info: Au:Ag ratios are generally > 50:1. Ore Materials: micron sized gold grains Gangue Materials: hematite, limonite, opal, barite, scorodite

Deposit: The ore occurs in two distinct deposits, the Discovery Ridge and Hammer Ridge deposits, separated by only about 100 meters at their closest point. The center of the Discovery Ridge deposit is approximately 400 meters (1300 ft.) northwest of the center of the Hammer Ridge deposit. Both deposits are hosted by Mississippian siltstone, shale, and silty limestone (the ?Griffon Member?) that occur along the contact between the Chainman Formation and the upper Joana Limestone, which is locally interpreted to be a low-angle normal fault. The mineralized zone at Discovery Ridge is elongate, trending NNW. Thickest, highest grade material occurs in the central portion of the mineralized zone, systematically decreasing to the east, west and south. The deposit is fault-bounded to the north. Within the Hammer Ridge deposit, ore occurs in several pods and lacks the continuity of the Discovery Ridge orebody.

Deposit type: Carbonate-hosted Au-Ag

Development: Although the rich deposits of Treasure Hill and Mt.Hamilton about 10-15 miles to the northwest were known as early as 1866, the area around the Griffon deposit had no historic production or exploration activity prior to the late 1980s. Billiton Minerals first staked the Griffon property and drilled the discovery holes in1988. Subsequent drilling by Billiton and Westmont Minerals defined the Discovery Ridge deposit which by itself was not an economic deposit. After this drilling program, Griffon Resources obtained the property. In 1994, Alta Gold Company entered into a lease with option to purchase agreement with Griffon Resources. A soil sampling program conducted by Alta Gold identified the Hammer Ridge anomaly which was defined as a deposit by several phases of drilling between 1994 and 1997. Site development at Griffon began in July 1997, followed two months thereafter by the commencement of mining. Also during the 1997 program, proven and probable gold reserves at Griffon were expanded by more than 40 percent to nearly 100,000 ounces of gold. In January 1998, Alta Gold Co. announced the first gold pour from Griffon Gold Mine. Alta Gold Company operated the Griffon mine between 1997 and 1999, producing 3.0 million tons of ore with an average grade of 0.03 ounce of gold per ton. Mining was suspended at Griffon in April 1999 when Alta Gold entered into bankruptcy, but production continued in declining amounts through the end of 1999. The Forest Service collected thereclamation bond. but since it was inadequate to fully complete the reclamation work at this site, the Forest Service prioritized the reclamation and closure of the heap leach facility over the reclamation of other facilities. The site was included in a 2001 proposal to the Army Corps of Engineers by the Nevada Division of Minerals for help in reclamation and revegetation of selected Abandoned Mine Lands.

Geology: Similar to other gold mines in the range such as Green Springs and Easy Junior, disseminated gold in the Griffon deposit occurs in strata on either side of the contact between the upper members of the Joana Limestone and overlying Chainman Formation. Low-angle normal faults are interpreted to have exerted considerable influence on the pattern of mineralization at Griffon, similar to Green Springs. Consistent with many disseminated, sediment-hosted gold deposits in the region, gold ore at Griffon contains elevated concentrations of arsenic, antimony, and mercury. However, the relatively high zinc and low silver concentrations in the Griffon ore are unusual in such gold deposits. Based on the geochemical similarities between Hammer Ridge and Discovery Ridge, a single event of gold mineralization probably formed both deposits. Age of mineralization is probably Late Cretaceous to mid-Oligocene It is unclear if the Griffon epithermal-style gold deposits are genetically linked to the Late Cretaceous intrusion-related silver and base metal deposits at Treasure Hill and Mt. Hamilton to the north.

Ore(s): Low-angle normal faults are interpreted to have exerted considerable influence on the pattern of mineralization at Griffon. Both the Discovery Ridge and Hammer Ridge deposits are composed of mineralized strata situated in the hanging-walls of these faults.

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Link to USGS MRDS:	10310556

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