Promontory Mining District, Promontory Mountains, Box Elder County, Utah, USAi

Regional Level Types
Promontory Mining District	Mining District
Promontory Mountains	Mountain Range
Box Elder County	County
Utah	State
USA	Country

The Promontory mining district is located about 25 mi west of Ogden in eastern Box Elder County. The major orebodies of the Promontory district were not discovered until 1914 and its most productive periods were 1915 to 1919 and 1942 to 1947. The district is a moderate Zn-Pb producer with minor Cu and Ag. Total district metal production at modern metal prices is estimated at $8.4 million. The district is unusual for the eastern Basin and Range in that it is Zn dominant over Pb and has only trivial precious metal credits. The Lakeview Zn-Pb underground mine is the largest producer.
The Promontory district lies on the southern end of the Promontory Mountains in the Basin and Range Province. The Promontory Mountains extend southward as a peninsula into Great Salt Lake. The major mines in the Promontory district occur on the west flank of Lead Mountain in a homoclinal, moderately northeast-dipping sequence of interbedded Cambrian-age quartzites, shales, and carbonate rocks (Doelling, 2006).
Mineralization in the Promontory district is localized at the intersection of north-trending, steeply west-dipping fissures and favorable, northeast-dipping Middle Cambrian carbonates (Perry and McCarthy, 1977; Doelling, 2006). The bulk of the mineralization in the district occurs in a north-trending swath parallel to the fissures less than 1 mi wide and over 3 mi long. The district is zoned from Cu-Ag ore on the south, through Pb-Zn ores on Lead Hill, to Zn-dominant ores on the north. The most important class of ores is the Zn-dominant vein/replacement deposits hosted in a section of interbedded carbonate and shale (Middle Cambrian Dome Limestone equivalent). This host carbonate is a 40- to 100-ft-thick, cliff-forming, light-gray, very fine grained, oolitic limestone. The small disseminated Cu deposit in the south is hosted in the Lower Cambrian Geertsen Canyon Quartzite (Tintic Quartzite equivalent). No intrusive igneous rocks are reported in the district (Perry and McCarthy, 1977; Doelling, 2006). Only the Zn-dominant replacement ores have had significant production.
The Promontory district is almost entirely on private land except for some BLM-administered tracts to the northeast of the major mines.