Mining Methods

Underground Mining

Fluorspar veins extend hundreds to thousands of feet along strike, with widths that range from a few inches to about 40 feet, separated by lateral and vertical “barren pinches” that usually contain no mineralization. Most underground mining along vein deposits in the IKFD used a stoping method of mining. Shrinkage stoping, overhead stoping with support timbers, or “stulls,” modified sublevel mining, and square set systems have all been used (Hatmaker and Davis 1938; Saxby 1973). Some mines at Spar Mountain in the Cave-in-Rock Subdistrict drove a horizontal entry, or “adit,” into the side of the hill. However, most underground mines started with a vertical shaft, usually sunk over the vein or, more commonly, in competent ground to the side of the vein. Concrete was applied to the shaft collar and in the uppermost portions of the shaft to prevent the unconsolidated ground from caving, but concrete lining was generally not necessary after solid rock was encountered. Timbering of the sidewalls was common in the upper levels of the veins and where shale sidewalls were encountered. Upon reaching ore, horizontal openings, or “drifts,” commonly 12 feet wide × 7 feet high, were driven through barren rock to intersect the ore. The drifts connected with the ore-producing levels, along which the ore was transported to the hoisting shaft (Hurst 1927). The vertical space between working levels varied but commonly was about 100 feet. In stope mining, open excavations formed by ore extraction, or “stopes,” were created by caving the rock from above downward. This method is called “overhead stoping.” The stulls were wedged diagonally between competent rock walls. Poles were then layered on top of the stulls to support the ore as it was blasted from above. The slope of the poles allowed the broken ore to gravity feed or funnel down to the ore cars below. Gates and chutes were constructed to allow the ore to be metered into the ore cars (Figure 4). Good explanations of mining practices were given by Bailie et al. (1960) and Reeder (1930). In some mines, arches were left on the bottom just above the haulage level to support the broken ore between the stopes. Upward lifts, or “raises,” on about 25-foot centers were driven upward to about 20 feet, leaving arches to support the broken ore as it caved downward (Figure 5). This arch method was a much more stable and safer method of mining. Because the broken ore took up to a 50% larger volume than ore in place, some of the blasted material had to be removed to supply headroom for the advancing raises. The broken ore was drawn off as necessary to allow the proper headroom and floor for the raises (Figure 5). Once the ore had been loaded through the stopes into the rail cars, it was transported to the shaft, where it was hoisted to the surface in skips and dumped into storage bins. In the earlier mines, the headframe was constructed of wood, but mine operators later erected steel head-frames to support the hoisting of the raw crude ore. The steel headframes at the Annabel Lee Mine in the Harris Creek Subdistrict and the Rosiclare Mine in the Rosiclare Subdistrict are still standing, but most other headframes have been demolished. Steam, electric, and gasoline engines were used to power the hoists that lifted the ore and miners to the ore levels. Mining in the horizontal bedding replacement deposits commonly utilized a modified room-and-pillar method of mining similar to that used in mining horizontal layers of coal and salt. This method removed ore from rooms and left blocks or pillars to support the overlying roof, inevitably leaving ore in the ground. The ore was generally competent enough to require blasting with explosives. Once the material was fragmented, it was loaded into small railcars pulled by mules during the early years, and later into rubber-tired mobile haulage equipment. High-grade ore was handpicked and sorted, but lower grade material was sent to a mill to be refined.

Surface Mining

Some of the ore within the veins cropped out at the surface, and some of the bedding deposits occurred close enough to the surface to enable mining in open pits. Because fluorspar is resistant to weathering, the ore formed what are termed “gravel spar” ore deposits as it was weathered or eroded. The ore was mainly angular to subrounded pieces of fluorite surrounded by clay. These gravel spar deposits were located over both bedding replacement deposits and veins. They were mined mainly through open pits and trenches and were dug by hand and with equipment of various sizes. The Hamp Subdistrict was reported to contain considerable gravel ore, as were some of the early mines in the Cave-in-Rock Subdistrict. Some of the deposits were large enough that both steam shovels and small draglines were used. The presently active Hastie Quarry extracts fluorspar and associated minerals in conjunction with limestone from an open pit.

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Circular 604 | Production History | Geology of the Illinois-Kentucky Fluorspar District | Mining Methods | Mineral Subdistricts and Individual Mines | Conclusions and Acknowledgments

References

Bailie, H., E. Powell, W. Melcher, and F.J. Myslinski, 1960, Fluorspar mining methods and costs, Ozark-Mahoning Co., Hardin County, Ill.: U.S. Bureau of Mines, Information Circular 7984, 33 p.

Hatmaker, P., and H.W. Davis, 1938, The fluorspar industry of the United States with special reference to the Illinois-Kentucky District: U.S. Bureau of Mines, Bulletin 59, 128 p.

Hurst, H.W., 1927, Fluorspar mining and milling in southern Illinois: University of Missouri–Rolla, professional degree thesis, 33 p.

Reeder, E.C., 1930, Methods and cost of mining fluorspar at Rosiclare, Illinois: U.S. Bureau of Mines, Information Circular 6294, 10 p.

Saxby, D.B., 1973, Gaskins Mine, in J. Baxter, J.C. Bradbury, and N.C. Hester, eds., A geologic excursion to fluorspar mines in Hardin and Pope Counties, Illinois: Illinois State Geological Survey, Guidebook 11, p. 21–23.