Henry Mining District, Antelope Range, Sevier County, Utah, USAi

Regional Level Types
Henry Mining District	Mining District
Antelope Range	Mountain Range
Sevier County	County
Utah	State
USA	Country

The Henry mining district is in the Antelope Range about 18 mi south-southwest of Richfield in southwestern Sevier County. The district was organized in 1883 and has been a modest Au-Ag producer with insignificant Fe (960 tons) and alunite (500 tons) production (Butler and others, 1920; Callaghan, 1973). Total district metal production at modern metal prices is estimated at $1.35 million. The largest producers are believed to be the Antelope Au-Ag, Yellow Jacket Au-Ag, and Krotke (Iron Cap) Fe mines.
The Henry district is located on the northeast flank of the Oligocene-Miocene Marysvale volcanic field in the transition zone between the Basin and Range Province to the west and the Colorado Plateau to the east. The district is underlain by a thick sequence of volcanic rocks and about the eastern one-third of the district is mapped within the early Miocene Monroe caldera. The intracaldera volcanic rocks strike N. 20° W. and dip moderately east. The area inside the caldera wall is mostly altered Monroe Peak tuffs and andesites recognized as a 2 sq mi, 22.5 Ma advanced argillic Yellow Jacket hydrothermal cell. The upper levels of this alteration consist of massive silica replacements (“silica cap”), alunite ±dickite, and locally hydrothermal breccias (Cunningham and others, 1984). This texturally destructive alteration gradually fades laterally outward into zones of weaker chloritic propylitic alteration. The advanced argillic alteration zone is one of several cells surrounding the 23 Ma quartz monzonitic Central intrusive (Cunningham and others, 1984). This area has been explored for volcanic-hosted, epithermal Au- Ag deposits (USGS Model 25e). Rock-chip samples in the area are extremely erratic, but in addition to Au-Ag, are anomalous in As, Bi, Cu, Hg, Mo, Pb, Sb, Te, Tl, and Zn. The highest values are typically found in or near the Antelope or Krotke mines and associated with silicified, hematitic, hydrothermal breccias. The district was unsuccessfully explored for Au-Ag in the late 1980s and early 1990s. This work included nine holes totaling 3450 ft. A 505-ft vertical hole collared at the Yellow Jacket quarry cut a 10-ft interval at 200 ft of 0.36 ppm Au and 21.5 ppm Ag within a zone of quartz veinlets and pyrite associated with argillically altered andesite. The Antelope Au-Ag mine to the west, outside of the caldera, developed a small Au-Ag quartz vein (USGS Model 25c) in altered Oligocene Mount Dutton Formation dacites (Callaghan, 1973).