By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
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Utah County, in north-central Utah, is bounded on the east by the crest of the Wasatch Range, on the north by the Traverse Mountains, on the northwest by the Oquirrh Mountains, and on the southwest by the East Tintic Mountains.
Several mining districts were organized in the county, but only the American Fork and East Tintic districts yielded substantial amounts of gold. The East Tintic district, which is geologically contiguous with the Tintic district in Juab County, was described in the discussion of Juab County. The total gold production of Utah County cannot be determined, because much of the output of East Tintic was combined with that of the Tintic.
AMERICAN FORK DISTRICT
The American Fork district, in the northeastern part of Utah County in the Wasatch Range, is about 5 miles southeast of the Cottonwood district.
After the major discoveries at Bingham Canyon, miners prospected in the Wasatch Range and found silver-lead lodes in Cottonwood Canyon and in the American Fork area. The district was organized in 1870, and the Miller mine soon became its chief producer. By 1880, however, most of the mines were idle.
Production remained small until 1904, when a large new ore body in the Miller mine was found; this ore body was mined until 1908 (V. C. Heikes, in Calkins and Butler, 1943, p. 80-85). From 1923 until 1935 the district experienced considerable activity, but from 1936 through 1959 its was largely dormant. Total gold production of the district through 1959 was about 45,000 ounces.
The geology of the American Fork district is similar to that of the Cottonwood district discussed under "Salt Lake County." In general, the rocks consist of a thick section of sedimentary units ranging in age from Precambrian to Mississippian. These rocks were folded along north-trending axes, cut by thrusts and high-angle faults, and intruded by the Little Cottonwood stock, a mass of quartz monzonite of Late Cretaceous or Tertiary age (Calkins and Butler, 1943, p. 38-71).
The major ore deposits of the district are replacement bodies in limestones adjacent to faults and fissures. A few deposits occur in fissure veins in quartzite beds of Precambrian and Cambrian age. The most common ore minerals of the replacement deposits are galena, pyrite, tetrahedrite, bornite, enargite, and sphalerite; chalcopyrite is locally present, and jamesonite occurs rarely. Gangue minerals are quartz, barite, and dolomite (Calkins and Butler, 1943, p. 94-95).
The replacement deposit at the Miller mine, the largest producer in the district, is in shattered beds of the Maxfield Limestone. The ore was oxidized and contained silver-rich galena, cerussite, gold, and hydrous iron oxides. Some ore contained as much as 2.45 ounces of gold per ton, but more commonly the gold content ranged from 0.1 to 0.5 ounce per ton (Butler and others, 1920, p. 279-280).
