Abstract

Sulfide ore deposits localized along thrust faults in and west of the Wasatch Mountains have produced substantial quantities of high grade lead-silver-zinc-gold-copper-cadmium ores during the past 110 years. The only significant deposits occur as elongate masses within relatively small thrusts, related to larger regional thrust plates. Silver and lead, occurring as sulfide minerals, accompanied by pyrite, quartz, carbonates and clay minerals, have been the most economically significant metals.

Production has been attained, in order of size, from the Park City, East Tintic, Alta-Cottonwood and West Tintic districts. Cambrian Ophir limestone, Mississippian Deseret limestone and the Permian Park City Formation have yielded most of the thrust-controlled ores. Some deposits at Bingham are also localized along local low-angle reverse faults. In most instances the ores formed where a near-vertical mineralized fracture intersects brecciated carbonate rocks along a thrust fault. The ores generally show association with silicic igneous intrusions which are regarded as a source for at least the sulfur. The thrust zone served either as a) the locus for precipitation by cooling, expansion, or chemical reactions of fluids, or b) the locus for mixing of two fluids, resulting in ore precipitation. Temperature changes at the thrust plane, exemplified by a modern geothermal system at Tintic, are the most probably cause of ore localization.

Utah’s first “overthrust boom” and widespread over-the-counter stock promotion, resulted when rich ore bodies were discovered along newly identified thrust planes near Alta in 1914-1925.