Bald Mountain mineral district

Region West, Southwest
Mineral systems
Deposit types
Other minerals

Information leading to the delineation of this focus area

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.