Escalante Mining District, Iron County, Utah, USAi

Regional Level Types
Escalante Mining District	Mining District
Iron County	County
Utah	State
USA	Country

The Escalante district is in southwestern Iron County, about 36 mi west of Cedar City. The district was originally organized in 1896 but did not become a large Ag producer until the 1980s. Total district metal production at modern metal prices is estimated at $277 million. The only important producer is the Escalante underground mine.
The district is in the southern Escalante Desert of the Basin and Range Province of southwestern Utah. The Escalante mine was developed on a single persistent quartz-calcite ±adularia vein cutting middle Miocene rhyolitic volcaniclastic sediments of the “mine series” (690 ft thick), approximately temporally equivalent to the Steamboat Mountain Formation. The main vein is 3600 ft long, 5 to 45 ft wide (average 26 ft), strikes N. 27° E., and dips 70° NW. The main vein reportedly horsetails into multiple smaller veins to the southwest (Fitch and Brady, 1982). Adularia from the vein has been dated at 11.6 ± 0.5 Ma (Siders, 1985).
The main mineralized area is a zone of supergene Ag enrichment from about 200 to 700 ft in depth where grades average about 300 ppm Ag. The Ag is partially leached and sub-ore grade at the surface where the vein is narrower (4 to 10 ft wide) and Ag continues at depth in a primary zone, but the grade also diminishes. The vein is strongly crustiform-banded (repeated mineralizing events), vuggy, white quartz-calcite and dark gray Fe-Mn oxides with minor Cu-As-oxides (USGS Model 25c). The principal Ag minerals in the enriched zone are very fine-grained chlorargyrite and rare native silver. The main ore/sulfide minerals in the primary zone are argentite, galena, sphalerite, pyrite, hematite, jalpaite, and rare native silver and gold. Gangue minerals include several generations of quartz with subordinate calcite, fluorite, barite, and rare adularia. Calcite, fluorite, and galena appear to be increasing with depth (Fitch and Brady, 1982). The vein is surrounded by a 10- to 50-ft-wide zone of silicification having lower Ag grades next to the vein which grades outward to a weak calcitic alteration and minor sericite, calcite, chlorite, and kaolinite. Limited trace element geochemistry shows anomalous Au, Cu, Mo, Pb, and Zn associated with ore in the veins.
Although virtually all production from the Escalante mining district is derived from the Escalante vein; other smaller veins and hydrothermal alteration occur over an area of some 16 sq mi. Much of this alteration occurs on and or near The Point, a knoll some 4 mi north of the Escalante mine (Siders, 1985). At The Point, the volcanic facies of the rhyolite of Beryl Junction (13 to 10 Ma) is locally silicified and Fe-stained in spatial association with intrusives and flow domes of the rhyolite member (Siders, 1985).