Abstract

The Park City mining district is the third largest producer of non-ferrous metallic minerals in Utah. Base-and precious-metal deposits in the district were mined for more than 100 years beginning in 1871 and ending in 1978. Most production was from Ag–Pb–Zn±Cu±Au replacement and vein deposits; a low-grade porphyry Cu–Mo–Au deposit and a high-sulfidation (quartz-alunite) gold deposit also are present on the east side of the area (Elkhorn district). Recorded production in the district from major mines between 1875 and 1978 is more than 1.45 million ounces (45.1 tonnes) gold, 253 million ounces (7,870 tonnes) silver, 2.7 billion pounds (1,224,700 tonnes) lead, 1.5 billion pounds (680,390 tonnes) zinc, and 129 million pounds (58,513 tonnes) copper from about 16.8 million tons (15.2 million tonnes) of ore. Since mining and exploration ended in the district in the early 1980s, many mining properties have been turned into ski areas; Park City itself has become a year-round recreational center; and several small mines on the east side of the district were flooded by filling the Jordanelle Reservoir.

Mineral deposits in the Park City district are related genetically to the Wasatch igneous belt, a series of high–K, calc-alkaline stocks and cogenetic volcanic rocks that formed between about 41 to 30 Ma. The related mineral deposits formed between about 36 to 31.4 Ma. Most of the intrusive rocks were emplaced along the westward extension of the west-trending Uinta arch during mid-Tertiary NW–SE-directed extension. Much of the mineralization in the Park City district was controlled by ENE–striking high-angle faults that developed during this same period of NW–SE-directed extension. Mineralogical, geochemical, and alteration zoning suggests that many of the major deposits in the district may be related to a buried porphyry system near the Mayflower mine on the east side of the district.