La Sal Mountain Mining District, Grand County, Utah, USAi

Regional Level Types
La Sal Mountain Mining District	Mining District
Grand County	County
Utah	State
USA	Country

The La Sal Mountain mining district is located about 16 mi east of Moab in southeasternmost Grand County. The district was organized in 1897 and became a modest Au producer. None of the individual mines in the district have had notable production. Total district metal production at modern metal prices is estimated at $1.9 million.
The La Sal Mountains are situated in the Paradox Basin on the Colorado Plateau in southeastern Utah. The La Sal Mountains are a series of three Oligocene (about 27 Ma) stocks (North, Middle, and South) and adjoining laccolithic complexes. The stocks are aligned in a northwest direction along the trend of the pre-existing Castle Valley salt-cored anticline. The intrusive rocks range from calc-alkaline diorite to alkaline syenite to peralkaline granite. The laccoliths are typically diorite porphyry and the stocks are syenite or granite. Unlike the laccoliths, the syenite and granite stocks have dike swarms and large associated igneous (?) explosion breccias or breccia pipes (Hunt, 1958; Mutschler and others, 1997). The breccias contain angular syenite porphyry fragments in a quartz-carbonate-rock flower matrix.
Nearly all mineralization in the La Sal Mountains is associated with the North stock near Mineral Mountain, immediately east of Miners Basin. Mineral Mountain is cored by an irregular alkaline syenite porphyry intruding a larger diorite porphyry. The primary ore deposits consist of narrow, glassy, coarsely crystalline, smoky quartz veins or small quartz vein stockworks carrying a little Au-Ag and locally some Cu cutting the intrusive porphyry stocks. The primary minerals are pyrite, chalcopyrite, and bornite with some calcite, siderite, magnetite, quartz, hematite, actinoite, and occasionally fluorite (Hill, 1913; Hunt, 1958; Mutschler and others, 1997). Minor placer gold is reported from Placer Creek below Miners Basin.
Utah International, Cyprus, Exxon, and Freeport Exploration explored the Miners Basin area of the La Sal Mountain district for deep porphyry Cu and porphyry Mo deposits in the late 1970s and early 1980s. Early Freeport work concentrated on porphyry Cu exploration on Mineral and Green Mountains and later porphyry Mo exploration on Pilot Peak (southeast of Miners Basin). The holes ranged from several hundred to 2000 ft deep. However, mineralized intercepts only showed modest intervals of Cu or Mo (e.g., 10 ft of 0.23% Cu and 10 ft of 0.01% Mo). Freeport also conducted some shallow drilling for Au in the Indiana- Tornado area and encountered some wide zones of low grade (e.g., 160 ft of 0.34 ppm Au).