Lehi Mining District, Utah County, Utah, USAi

Regional Level Types
Lehi Mining District	Mining District
Utah County	County
Utah	State
USA	Country

The Lehi (Long Ridge) mining district is in extreme northwestern Utah County, about 27 mi south-southwest of Salt Lake City. The district was organized in 1894 and became an insignificant Pb-Ag producer. The Old Mayflower underground mine is the only known metal producer.
The Lehi district is situated on the east flank of the Oquirrh Mountains in the easternmost Basin and Range Province. The district is aligned along the north-northwest-trending Long Ridge anticline. The Long Ridge anticline is the next major anticline east of, and parallel to, the Ophir anticline. The Long Ridge anticline, like the Ophir thrust-cored anticline, is a closed, asymmetrical fold with a steep northeast limb (30°–70°) and a gentle limb on the southwest (20°–40°). The anticline has a gentle to moderate plunge to the north-northwest (Gilluly, 1932; Laes and others, 1997). Quartz monzonite porphyry dikes occur intermittently near the axis of the anticline from the Old Mayflower mine south to Iron Canyon.
The main mineralized area is in West Canyon and includes the Old Mayflower Pb-Zn-Ag mine in its upper reaches (USGS Model 19a). The Old Mayflower mine occurs in bleached hornfels associated with quartz monzonite porphyry dikes in the Upper Mississippian Manning Canyon Shale, just above the top of the Great Blue Limestone. Minor pyrite, galena, sphalerite, and boulangerite are disseminated along narrow veinlets (Gilluly, 1932).
To the south of the Old Mayflower, sedimentary rock-hosted precious metal mineralization occurs near the crest of the Long Ridge anticline in the Mississippian Great Blue Limestone (USGS Model 19c). The strongest known outcrop of Au mineralization occurs just southeast of Oak Grove in the Left Hand Fork of West Canyon. Alteration includes strong silicification (jasperoid), decalcification, Liesegang banding, and locally argillized/sericitized siltstone. Strong clay alteration and a completely argillized feldspar porphyry dike are noted in the upper Great Blue Limestone near the crest of the anticline in Iron Canyon. The southern zone of alteration and mineralization (south of the Left Hand Fork of West Canyon) lies in the Mercur member just below the Long Trail Shale Member. Gold Fields drilled 14 holes totaling about 7484 ft on the south side of the Left Hand Fork of West Canyon in 1990. Geochemical Au was present in the silty limestones of the Mercur member of the Great Blue Limestone with the best intercept being 15 ft of 0.3 ppm Au (James Lunbeck, 2008, written communication).