Mount Baldy-Ohio Mining District, Piute County, Utah, USAi

Regional Level Types
Mount Baldy-Ohio Mining District	Mining District
Piute County	County
Utah	State
USA	Country

This page is currently not sponsored. Click here to sponsor this page.

PhotosMapsSearchMineralogy

The Mount Baldy–Ohio mining district is situated on the eastern flank of the Tushar Mountains, approximately 8 km (5 mi) southwest of Marysvale, Piute County. It is one of Utah’s more important historic precious-metal districts, ranking roughly sixth statewide in total gold production. The camp has produced significant gold and silver with substantial zinc and lead by-products. At modern metal prices, cumulative production is estimated at approximately US$333 million. The Deer Trail underground mine, located on the eastern base of Deer Trail Mountain, has been by far the principal producer.

The district lies within the Marysvale volcanic field near the transition between the Basin and Range Province to the west and the Colorado Plateau to the east. Upper Paleozoic and Mesozoic sedimentary strata are exposed along the eastern base of the range and are unconformably overlain by volcanic rocks of the Marysvale field. These volcanic units are interpreted to be domed by an unexposed Miocene (~14 Ma) Mount Belknap alkali rhyolite intrusion beneath Deer Trail Mountain.

Mineralization shows a broad but consistent vertical zonation. Advanced argillic alteration with alunite occurs at higher elevations above about 3,300 m (10,800 ft). This is underlain by small epithermal Au–Ag veins with minor base metals above roughly 2,800 m (9,200 ft), and by polymetallic veins and carbonate replacement (manto-style) deposits at lower elevations. Approximately 80% of district production comes from precious-metal-rich polymetallic replacement ores hosted by the Permian Toroweap Formation at the Deer Trail mine (USGS Model 22c).

Average Deer Trail ore grades were approximately 12% Zn, 5% Pb, 514 ppm Ag, and 3.43 ppm Au. Common ore minerals include sphalerite, galena, tennantite–tetrahedrite, chalcopyrite, and rare native gold. Trace elements in the massive sulfide ores include fluorine (~1.5%), arsenic and antimony (~1000 ppm each), tellurium and selenium (~100 ppm), molybdenum (~50 ppm), bismuth (~10 ppm), and mercury (~3 ppm). Wulfenite has been reported from several mines. Four U.S. Geological Survey rock samples from Bullion Canyon contain strongly anomalous molybdenum (150–500 ppm), with one sample also enriched in tin (150 ppm).

The presence of molybdenum and fluorite associated with the Deer Trail replacement ores, elevated Mo and Sn values in Bullion Canyon, rhyolite dikes, and widespread alunitic alteration collectively suggest a concealed porphyry molybdenum system at depth. A buried porphyry center is inferred beneath the alunite alteration zones of Deer Trail Mountain and/or Mount Brigham, possibly represented by paired cupolas beneath the structural dome. Owing to the district’s considerable topographic relief, a deposit at depths of up to approximately 900 m (3,000 ft) could potentially be accessed by horizontal development from existing workings.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.

Mineral List

Mineral list contains entries from the region specified including sub-localities

85 valid minerals. 2 (TL) - type locality of valid minerals.

Rock Types Recorded

Rock list contains entries from the region specified including sub-localities