Pine Grove Mining District, Beaver County, Utah, USAi

Regional Level Types
Pine Grove Mining District	Mining District
Beaver County	County
Utah	State
USA	Country

The Pine Grove mining district is located in the Wah Wah Mountains of western Beaver County, Utah, approximately 32 miles west of Milford. Historically, the district was a small producer of zinc, lead, and silver, with total output equivalent to about US$871,000 at modern metal prices. The Tasso (Wah Wah) underground mine was the district’s largest producer. Exploration focus shifted in 1975 when Phelps Dodge Corporation drilled the first deep exploration hole into molybdenum-bearing rocks, intersecting porphyry-style mineralization at a depth of approximately 3,300 feet.

Geologically, the district lies within the eastern Basin and Range Province and hosts a large Climax-type porphyry molybdenum system. Mineralization is genetically related to a subvolcanic, silicic–alkalic, high-silica rhyolite porphyry plug of Oligocene age (~24 Ma), which intrudes more than 6,000 feet of Upper Proterozoic to Lower Cambrian quartz-rich clastic sedimentary rocks. The Pine Grove rhyolite porphyry forms a steep-sided, oval intrusion covering roughly 0.4 square miles at the surface. Molybdenum mineralization is concentrated primarily along the margins of the porphyry, beginning at depths of about 3,000 feet.

Evidence supporting classification of Pine Grove as a Climax-type porphyry molybdenum deposit includes multiple phases of high-silica rhyolite intrusion, a large tonnage of relatively high-grade molybdenum mineralization, the presence of accessory fluorite, topaz, and huebnerite, and the notable absence of significant copper. Additional diagnostic features include accessory monazite, xenotime, and ilmenorutile within the intrusive rocks. Published reserve estimates commonly cite approximately 125 million tons grading 0.17% Mo at a minimum mining width of 300 feet and a cutoff grade of 0.12% Mo, within a broader geological resource exceeding 300 million tons at similar grades. No significant exploration or development has occurred since the early 1980s, though the tendency for porphyry molybdenum deposits to occur in clusters suggests potential for additional undiscovered resources within the district.

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