Buffalo Valley Gold Mine, Buffalo Valley mine, Buffalo Valley Mining District, Lander County, Nevada, USAi

Regional Level Types
Buffalo Valley Gold Mine	Mine
Buffalo Valley mine	Mine
Buffalo Valley Mining District	Mining District
Lander County	County
Nevada	State
USA	Country

Structure: The Havallah Sequence of the Buffalo Valley Mine has a homoclinal appearance. With certain exceptions, beds strike NW to slightly east of north and generally dip 45-65 SW or West. Buffalo Valley Mine is situated in a fault block that is bounded on the east by the western range-bounding fault of Battle Mountain and on the west by another west-dipping normal fault, which is known locally as the Front Fault. Golconda Thrust

Alteration: Contact metamorphic effects in the upper structural unit of the Havallah Sequence: non-calcareous silty lithologies are converted to biotite hornfels; slightly calcareous, siliceous and argillaceous siltstones are metamorphosed to calc-silicate hornfelses (diopside + quartz plagioclase, clinozoisite, epidote). Sulfides are restricted to later fractures. Endoskarn: sulfide-poor calc-silicate mineral assemblages which occur as alteration products of porphyry dikes are common west and southwest of the open pit, rare in the open pit, and absent east and north of the pit. In some hand specimens, endoskarn alteration can be observed as envelopes about individual quartz veins, e.g. plagioclase-quartz-pyroxene-bearing inner envelopes (hornblende destroyed) and relict hornblende-stable outer envelopes. Potassic alteration: shreddy hydothermal biotite is abundant in dikes in the open pit and the degree of biotization is independent of proximity to quartz veins. Prograde skarn: a few unequivocal but rare examples of coarse grained garnet-pyroxene skarn have been exposed in the center of the open pit, interbedded with calc-silicate hornfels. These skarns contain pyrite, although it is unclear whether it was deposited synchronous with skarn silicates. Retrograde skarn: pyroxene hornfels and less commonly basalt and biotite hornfels locally are intensely altered to dark green chlorite, pyrite, and nontronite(?). This assemblage has been reported to carry free gold.

Commodity: Ore Materials: auriferous pyrite, native gold, chalcopyrite, malachite, chrysocolla Gangue Materials: limonite, hematite, quartz, biotite, diopside, clinozoisite, epidote

Deposit: The early orebodies that were mined underground were associated with the frontal fault striking N18E and dipping 40-55W. The more recently mined deposit developed by open pits strikes N30W and truncates against the frontal fault.

Deposit type: Skarn Au

Development: Prospecting in the area of the Buffalo Valley Mine began in the 1860s with the discovery of gold placers. In 1916, Buffalo Valley Mines Co. purchased 28 unpatented claims from C. Ganser and others, which were then developed as the underground mine. Production was almost continuous from 1924 to 1941, and also in 1951. A 10-ton cyanidization plant was built in 1925 and 1196 tons of ore were treated by 1933. Total reported production through 1951 was approximately 3000 tons. Numerous independent exploration companies explored the Buffalo Valley Mine from the mid-1960s to 1985. In 1985, Horizon Gold Shares Inc. acquired a 99 year mining lease on 158 unpatented mining claims at the Buffalo Valley Mine. Horizon then expanded their land position by locating an additional 679 unpatented claims. At the time of Horizon's acquisition of the property, there existed a database collected from previous exploration efforts that consisted of over 200 short percussion drill holes, 7 diamond drill holes, 214 rotary drill holes, over 3000 gold assays collected from surface, underground, and drill hole samples, surface and underground geologic mapping, and metallurgical and feasibility studies. Horizon mined the Horizon as an open pit-heap leach operation from 1986 to 1990. In December, 1988, Horizon formed a joint venture with Chevron Resources Company to explore the Buffalo Valley property. In 1989, the Horizon/Chevron venture had discovered additional near surface gold occurrences in oxidized veins to the north, southwest, and east of the open pit and had identified an underground resource in gold-bearing oxidized veins beneath the existing pit. Fairmile Goldtech acquired the Buffalo Valley property in the early 1990s. Drilling on the property by Fairmile in 1994 established significant gold mineralization along the Front fault, a north-south striking, 40-50? west-dipping structure that has been traced for over 2,000 feet south of its intersection with the main Buffalo Valley structure. A geological resource within the Front fault zone of more than 350,000 ounces of gold was recognized. This is in addition to an underground geological resource in excess of 250,000 ounces of gold at the historic Buffalo Valley mine. At the Dore Hills prospect, about 3,000 feet north of the old Buffalo Valley pit, drilling confirmed the presence of similar mineralization with short intercepts in the 0.1 to 0.2 ounce per ton range.

Geology: Rocks of the Havallah Sequence in the Buffalo Valley Mine area can be grouped into 3 local units (and their metamorphic and metasomatic equivalents): 1) a lower structural unit consisting of chert, lesser shale and siltstone, minor pebbly sandstone rich in black chert clasts, and minor limestone; 2) a sill or lava flow of fine grained basalt; and 3) an upper structural unit consisting of non-calcareous to weakly calcareous siltstone, quartzite, and shale. The basalt and upper structural unit are exposed in the pit. Variably altered granodioritic porphyry dikes intrude the Havallah Sequence rocks throughout the mine area and are interpreted to be part of a late Eocene(?) porphyry system, inferred to be related to a larger subjacent pluton. Some dikes carry anomalous gold values, indicating that gold deposition post-dates intrusion of the dikes. Unaltered, unmineralized intercalated ash flow tuffs and alluvium overlie the Havallah Sequence rocks and dikes. Based on the spatial correspondence of au-bearing pyritic veins with the swarm of dikes in the pit and the presence of minor au occurrences associated with outlying porphyry dikes, Seedorff (1991) suggests that gold deposition is related to the Copper Canyon porphyry system. Roberts and Arnold (1965) report the presence of a vein containing pyrite and chalcopyrite 800 feet SE of the historic workings which assays up to 2.0 oz/ton gold. This is likely in the area which has been developed as an open pit. According to shipment records from 1924-1951, the gold and silver content of the ore increases with an increase in copper.

Ore(s): Larger orebodies mined underground during 1924-1951 formed in calcareous beds between strands of the Front fault; smaller orebodies were formed in calcareous beds near shear zones and small faults in the footwall of the Front fault. Oxidized, sheeted pyrite veinlets that generally parallel the axis of the open pit host a majority of the gold mined in the open pit. This veinlet zone is located in the NE part of a contact metamorphic aureole and is centered directly on a swarm of porphyry dikes. Auriferous sulfide veinlets, quartz veinlets, and dikes all have similar attitudes.

Other Databases

Link to USGS MRDS:	10310306

References