The Hillside mine taps into the Hillside vein, containing a deposit of fluorite that was continuous for more than 1,600 feet. The nearly vertical vein trended in a north-south direction and varied in thickness from 5 to 35 feet (Bastin, 1931). This was one of the widest veins in the district.
A mine was operated by the Hillside Fluorspar Mines Company. In 1920, the company tapped into the Hillside vein and started full production in 1922. The shaft was 6 by 20 feet across and was sunk to a depth of 520 feet. It needed to be concrete lined to a depth of 182 feet, due to weathering of bedrock (Bastin, 1931). Major drifts were at the 170, 250, 350, 450, 550 and 650-foot levels. The 350-foot level followed the vein for 1,600 feet. A 450-foot deep 6 x 12-foot shaft was placed 900 feet north of the main shaft, connecting the 250 and 350-foot levels. It provided ventilation and ore hoisting. Operations ceased in 1937 when ores at the 500 and 650-foot levels were depleted (Weller, et al, 1952).
Vein contacts throughout the mine were said to be "firmly attached to both limestone walls" (Bastin, 1931). Slickensides were minor. Visual inspection within the mine showed little evidence of wall rock replacement. The appearance of stylolites in both ore and wall rock indicates that replacement may have been important. Silver in the galena averaged 5 ounces to the ton. [A. Goldstein, Min. Rec., 27:1, 1997, p. 9.]
Refs:
Bastin, E.S. (1931)The fluorspar deposits of Haridn and Pope Counties, Illinois. ISGS Bulletin 58.
Grogan, R.M. & Bradbury, J.C. (1967) Origin of stratiform fluorite deposits of southern Illinois, Economic Geology Monograph 3, p. 40 - 50.
Weller, J.M., Grogan, R.M. and Tippie, F.E. (1952) Geology of the fluorspar deposits of Illinois ISGS Bulletin 76.
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