Lone Tree/Stonehouse Mine Area, Lone Tree Mine, Buffalo Mountain Mining District, Humboldt County, Nevada, USAi

Regional Level Types
Lone Tree/Stonehouse Mine Area	Area
Lone Tree Mine	Mine
Buffalo Mountain Mining District	Mining District
Humboldt County	County
Nevada	State
USA	Country

Alteration: Dominant alteration types affecting the host rocks are silicification, argillization, and pyritization.

Commodity: Ore Materials: Gold, arsenopyrite, pyrite. Gangue Materials: chalcopyrite, marcasite

Deposit: At Lone Tree, the Power Line Fault is the principal ore host and is equivalent to the NW-1 structure identified at the Stonehouse Deposit to the south. Gold mineralization at Lone Tree occurs in all three rock units (Valmy Formation, Antler Sequence, and Havallah Sequence) and is largely confined to a N-S trending zone of intense fracturing and faulting known as the Wayne Zone. The Wayne Zone dips steeply to the west and has been traced for nearly a mile along strike on the lone tree property. Major cross structures offset and pinch the Wayne Zone at the northern and southern ends of Lone Tree Hill.In sulfide ore, gold is associated mainly with arsenopyrite and to a lesser extent with one or two generations of pyrite. Overburden ranges from 1 foot to 200 feet thick. At Stonehouse, the NW-1 structure is the most economically important structure. Gold mineralization occurs in three main areas: the main NW-1 structure has been defined over almost 1.5 miles, strikes NNW, and dips 70-75 west. East Zone mineralization lies east of NW-1, in its footwall. The east zone is a series of horsetail structures that strike approx. N-S and have steep west to almost vertical dips. The Southeast zone is offset approximately 1000 feet from the NW-1 structure. Gold values have been encountered over a broad area in the Southeast zone with some suggestion of a relatively flat-lying ore body. Mineralization in the Southeast zone tends to be erratic, low grade, and refractory.

Deposit type: Distal disseminated Ag-Au

Development: Drilling at Lone Tree was conducted near the completion of a much larger drilling program in the South Valmy Area. Holes at Lone Tree were sited in part on drilling results at the Stonehouse Deposit immediately to the south and in part on geologic factors considered since 1987. The discovery hole, TH-79, was drilled in July, 1989. It intersected 35 feet of ore grading 0.12 ounces of gold per ton starting at a depth of 140 ft. A follow-up reverse circulation drilling program of 10 holes was begun in August, 1989. These were angle holes drilled mainly as east-west fences in the vicinity of TH-79. Of these 10 holes, only 1 failed to intersect significant au mineralization. By December, 1989, the known strike length of the au-bearing structure extended nearly 0.5 mile on Santa Fe Pacific property. An accelerated drilling program beginning in January, 1990, used as many as 17 drill rigs simultaneously. The goal was to delineate an oxide resource by June, 1990. The presence of power lines on the property was a hindrance to the siting of the drill holes. Prior to mine development, these power lines were moved at a cost of $4 million. The production decision was made May, 1990, construction began in December, 1990, full scale mining began April, 1991, and the first dore was poured august, 1991. Over 400 drill holes had been completed at Lone Tree as of April, 1992. The project capital cost was $52.9 million, excluding initial exploration. Cash costs in 1991 were $103.45/oz. Au. A mill equipped with a low temperature, low pressure autoclave to treat sulfide ore was built in 1994 at an estimated cost of $67 million. Newmont acquired Santa Fe Pacific Gold Corporation in 1997, adding Lone Tree and other deposits near Winnemucca to its portfolio.

Ore(s): The Power Line Fault is the principal ore host and is equivalent to the NW-1 structure identified at the Stonehouse Deposit to the south. Gold mineralization at Lone Tree occurs in all three units (Valmy Formation, Antler Sequence, Havallah Sequence) and is largely confined to a N-S trending zone of intense fracturing and faulting known as the Wayne Zone. The Wayne Zone dips steeply to the west and has been traced for nearly a mile along strike on the Lone Tree property. Major cross structures offset and pinch the Wayne Zone at the northern and southern ends of Lone Tree Hill.

Other Databases

Link to USGS MRDS:	10310324

References