| Basis for focus area |
The Bald Mountain mining district is about 115 km south-southeast of Elko and about 100 km northwest of Ely. The district contains 11 orebodies that cluster in and around the Bald Mountain pluton. |
| Identified resources |
Historical production of gold. |
| Production |
The Bald Mountain district produced about 1 Moz Au. |
| Status |
Past and current mining. |
| Estimated resources |
Estimated Measured and Indicated resources of 3.6 Moz Au. |
| Geologic maps |
Nutt and Hart (2004), scale 1:24,000; Nutt (2000), scale 1:24,000. |
| Geophysical data |
Inadequate Rank 4 aeromagnetic coverage. |
| Favorable rocks and structures |
Jurassic intrusive rock and Paleozoic sedimentary rocks. Gold mineralization is hosted in a quartz monzonite stock, quartz feldspar porphyry, and in limestone, argillite, and dolomites of the Ordovician Antelope Valley Formation along the margin of the Bald Mountain stock. Locally, calc-silicate skarn and recrystallized marble have developed along the contact between the intrusive rocks and the calcareous sedimentary rocks. |
| Deposits |
Top, Mahoney Canyon, and Sage Flat deposits (MRDS dep_id: 10310443), LJ Ridge deposit (MRDS dep_id: 10310447), RBM deposit (MRDS dep_id: 10310444). |
| Evidence from mineral occurrences |
MRDS. |
| Geochemical evidence |
The system exhibits a classic concentric geochemical zonation pattern; Au occurs throughout with Mo, W, Bi, and Cu near the center, Ag, Pb, and Zn at intermediate distances, and As and Sb peripheral to the intrusion (Nutt and Hofstra, 2007). |
| Geophysical evidence |
Unknown. |
| Evidence from other sources |
District established by minor placer mining. |
| Comments |
Geochemical and isotopic evidence suggest that Au at Bald Mountain was introduced by reduced S-bearing magmatic fluids derived from a reduced intrusion. The reduced character of the intrusion was caused by assimilation of carbonaceous sedimentary rocks. This mineral system is distinct from the Eocene Carlin-type deposits in the nearby Yankee-Alligator Ridge area (Nutt and Hofstra, 2007). |
| Cover thickness and description |
Alteration exposed at the surface. |
| Authors |
Laurel G. Woodruff, Albert H. Hofstra. |
| New data needs |
Updated geologic mapping, lidar, geochemistry, aeromagnetic and aeroradiometric surveys. |
| Geologic mapping and modeling needs |
Updated geologic mapping. |
| Geophysical survey and modeling needs |
High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys. |
| Digital elevation data needs |
Lidar inadequate. |
