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

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

Sec 33 T32N R42E

Structure: Golconda Thrust 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 In Mine Terminology As The Front Fault.

Alteration: Contact Metamorphism, Endoskarn, Potassic Alteration, Prograde Skarn, Retrograde Skarn. See Geology Comments.

Commodity: Roberts and arnold (1965) report the presence of a vein containing pyrite and chalcopyrite 800 ft. Se of the historic workings which assays up to 2.0 oz/ton au; this is likely in the area which has been developed As an open pit. According to shipment records from 1924-1951, the Au and Ag content of the ore increases with an increase in copper.

Deposit: The orebodies mined underground associated with the front fault strike n18e and dip 40-55w. The deposit developed by open pit strikes n30 W and truncates against the front fault. Do not confuse this deposit with the buffalo valley molybdenum prospect that lies 7 km to the south at the s W tip of battle mountain in secs. 21 and 28t31n, r42e (no mrds record). This record has been merged with data from record #m233793, which has been deleted.

Deposit type: Skarn Au

Development: 214 rotary drill holes, over 3000 Au assays collected from surface, underground, and drill hole samples, surface and underground geologic mapping, and metallurigical and feasibility studies. Horizon mined the buffalo valley deposit As an open pit-heap leach operation during the period june 1, 1986 to october 1, 1990. In december, 1988, horizon formed a joint venture with chevron resources company to explore the buffalo valley property. As of november 1989, the horizon/chevron venture had discovered additional near surface Au occurrences in oxidized veins to the north, southwest, and east of the open pit and had identified an underground resource in Au-bearing oxidized veins beneath the existing pit. Total$: <1.5; mill.cap: 850 gallons/mi n.; econ.year: 1986. ; econ.com: horizon used three grade categories during open pit mining/heap leaching: number one rock (>/= 0.015 opt au) was crushed prior to loading on the heap leach pad; number two rock (>/= 0.012 and <0.015 opt au) was treated As run-of-mine material and was loaded on the leach pad uncrushed; waste was classified As anything grading <0.012 opt au. Construction and start up costs at the mine were less than $1.5 million. Cash operating costs per ounce of Au sold averaged $175 for fiscal 86/87, $250 for fiscal 87/88, $246 for fiscal 89/90, and $227 for the period june 1, 1986 to september 30, 1990 (start up to shut down). Average production cost per ounce of Au sold, including depreciation and depletion, was $321 for the period june 1, 1986 to september 30, 1990. Horizon owns a 100% working interest in the property and is operating under a lease agreement with royalties varying from 4% to 7.5% of gross proceeds, depending on realized Au prices. Most metallurgical tests have returned sodium cyanide Au leach recoveries ranging from 65%-75% of the contained Au within 60-120 days of standard heap leaching techniques, although typical recoveries at the mine were 80%. Buffalo valley mine ore was crushed to minus one inch prior to stacking on the heap leach pads. At the time of suspension of full scale operations on october 1, 1990, mining capacity was 1900 tpd. Dore bars produced at buffalo valley mine averaged 66% au, 11% ag, 19% cu, and 4% other impurities, including ni. Ore crushing was done by a contract crusher. Au recovery facilities were constructed on the property and consisted of 8 one-half-ton eduction carbon columns, 5 one-ton fixed bed carbon tanks, 2 pressurized stripping tanks, and 4 electrolytic recovery cells. These facilities were capable of treating 850 gallons of pregnant solution per minute from the heap leach pad. Prospecting in the area of the buffalo valley mine began in the 1860's with the discovery of Au placers. In 1916, buffalo valley mines co. Purchased from c. Ganser and others 28 unpatented claims 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-1960's 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,

Geology: Alteration comments: contact metamorphism: 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. Geology comments: 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 flo W 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 Au values, indicating Au deposition post-dates intrusion of the dikes. Unaltered, unmineralized intercalated ash flo W 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 Au deposition is related to the copper canyon porphyry system.

Rock formation(s): Unknown;Unknown;Unknown
Havallah Formation


Ore(s): See Comments

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Link to USGS MRDS:	10106923

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