| Description |
The area discussed comprises approximately 200 square miles and includes the West Tintic Range and part of the Sheeprock Range. The area is near the eastern boundaries of Tooele and Juab Counties, Utah, and is less than ten miles west of the Tintic mining district. Utah Highway 36 forms the northern boundary, and the Jerico Road forms the southern boundary. The eastern and western boundaries are defined by longitudes 112° 15' and 112° 25' 15" West respectively. Sedimentary and metasedimentary rqcks exposed within the area, include from older to younger: at least 13,000 feet of Precambrian schist, banded and unbanded phyllite, tillite, quartzite, argillite, and conglomerate of the Sheeprock series, and the Mutual(?) formation; at least 11,500 feet of Paleozoic carbonates and elastics which represent parts of all periods except the Permian; Tertiary strata, thought to represent all of the Tertiary epochs, and possibly being several thousand feet in thickness; several hundred feet of Pleistocene pediment gravels, recent alluvium and aeolian deposits. Mesozoic sediments, with the possible exception of an unnamed greenstone, are absent from the area. Igneous rocks include the West Tintic monzonite intrusive and a younger granite intrusive. Extrusive rocks are abundant in the area and include from the oldest to the youngest: a diabasic rock, which may represent a Precambrian flow; a rhyolite sequence, tentatively correlated with the Packard latite of the East Tintic Range; an andesite and agglomerate sequence which unconformably overlies the granite is inter¬calated with beds of known mid-Eocene Green River age, and is correlated with the latite and agglomerate sequence of the East Tintic Range; a few remnants of basalt flows, probably of late Tertiary or early Quaternary age. Three orogenic episodes are recognized and attributed to Cretaceous, earliest Tertiary, and later Tertiary phases of deformation. These episodes are tentatively considered to correlate in time with the Cedar Hills, Laramide and Basin and Range orogenies which are more specifically recognized in nearby areas. More precise dating of pre-Tertiary deformation is not possible because of the absence of Mesozoic sediments critical to such dating. Structures considered contemporaneous with the Cedar Hills orogeny include the West Tintic anticline, the Brown's Ridge homocline, and the monocline north of Little' Valley. Structures assigned to the Laramide orogeny include the Sheeprock thrust system and recumbent folds and tear faults in the allochthon. The Basin and Range structural features consist of range-defining high-angle faults such as the Vernon Creek fault and flexures and folds in the Green River-Salt Lake strata. The West Tintic and Blue Bells mining districts are in the Sheeprock portion of the area. The West Tintic district has a history of sporadic production since 1870, with production of minor amounts of gold, silver, lead, copper, tungsten, and iron ores. Nearly all production came from the Scotia mine. At present (1957), there is no mining activity in the West Tintic district. The Blue Bells mining district contains the only current operation in the area, the Blackhawk properties, which have produced several thousand dollars in high-grade silver ores in recent years. There are no records of production of metallic minerals from the West Tintic Range. However, large deposits of jasperoid may be an indication of possible mineralization at depth. Barring this possibility, the prospects of important mineral development in the West Tintic Range is considered unlikely. |
