Hobbs Creek Subdistrict

The Hobbs Creek Subdistrict lies to the west of and parallel to the Stewart Subdistrict. The subdistrict lies along a fault zone called Hobbs Creek Fault Zone. Segments of this fault zone have been subdivided and named such as the Shelby Fault (Weller et al. 1952). The majority of production in this subdistrict came from the Henson Mine.

Mines in the Hobbs Creek Subdistrict

Henson Mine

Ozark-Mahoning operated this mine. Vein ore was present along a northeast-trending fault. The Henson Mine was in operation during the 1980s. It had a shaft 950 feet deep to what was called the Hobbs Creek Vein. The fault was normal, striking northeast and dipping steeply northwest. Ore from the Henson Mine was trucked to a mill and concentrator in Rosiclare, Illinois, in Hardin County. John Nelson, Donald K. Lumm, and James C. Baxter of the ISGS toured the Henson Mine in 1982. At a working level about 900 feet below the surface, the northeast-striking, northwest-dipping normal fault juxtaposed Ste. Genevieve Limestone in the footwall with Bethel Sandstone in the hanging wall. The fault surface was a clean, sharp break, and normal drag was well developed in the hanging wall. Slickensides and mullion plunged at 70°–90° (vertical), indicating a small right-lateral component. Ore veins contained white and purple fluorite in a breccia of sandstone and shale fragments. Mining procedures were much the same as in the Barnett Mine. Ozark-Mahoning files indicate that 112,000 raw tons was extracted from this complex and that mining conditions were not favorable. More Information: 10083065

Shelby (Spiller) Mine

In March of 1942, Horace G. Spiller drove an adit 56 feet into the hillside just above the level of Grand Pierre Creek and then drove a winze to a mineralized fault zone (Bishop 1947a). Spiller then commenced to sink a shaft on the hillside above the adit but halted work at a depth of 110 feet without reaching the vein. The target mineralization lay along a segment of the Hobbs Creek Fault Zone, a normal fault striking N 50° E, dipping 62° SE, and having about 250 feet of throw down to the southeast. The Hardinsburg and Golconda Formations in the hanging wall were juxtaposed with Cypress, Ridenhower, and Bethel in the footwall. About 25 tons of ore from the winze was processed at Rosiclare, where the shipment assayed about 27% fluorspar and 5% zinc. These values were deemed too low to repay the cost of mining, so further development was halted. Two years later, the U.S. Bureau of Mines drilled three angled diamond drill holes across the fault to explore for mineralization below the depths of the Shelby workings. Only small calcite veins were encountered (Weller 1943a; Bishop 1947a). Weller located the mine entrance 1,570 feet from the south line and 2,040 feet from the east line of sec. 9, T 12 S, R 7 E. This mine was also located along a northwest boundary fault (Shelby Fault) in the Hobbs Creek Fault Zone. During geologic mapping in 2008–2009, fluorite was observed in fractured sandstone scattered on the surface near this abandoned mine. Although the fault was not well exposed, nearly vertical fractures trending N 40° E could be observed in the sandstone bluff southeast of the mine (Denny and Counts 2009). More Information: 10097472

McGuire Prospect

The McGuire Prospect was located about 1,200 feet southwest of the Shelby Mine along the same vein and fault. The location from the map of Baxter et al. (1967) was 800 feet from the south line, 2,400 feet from the west line, sec. 9, T 12 S, R 7 E. Although poorly exposed near the mine site, the fault could be observed to the south in sec. 16-12 S-7 E (400 feet from the north line, 500 feet from the west line), where fractures in the limestone trend N 55° E. The rock at this prospect is moderately brecciated, and thin veins of calcite are present along vertical slickensides. Excavation and core drilling failed to locate ore of commercial grade, so no production took place at this prospect (Weller 1943a; Bishop 1947a). More Information: 10083064

The Seinor Prospects

The Seinor No. 1 and Seinor No. 2 were located along the northeasterly projection of the Shelby Fault (Weller et al. 1952). The Seinor No. 2 Prospect was a pit that exposed a normal fault trending N 60° E and having vertical slickensides on the sandstone footwall. Sandstone also composed the hanging wall, and the fault dipped to the southeast. The amount of displacement was not readily observable because sandstone was on both sides of the fault. A vein of colorless and purple fluorite 1 to 2 inches wide was observed along the fractured sandstone in this pit. This prospect may be on a fault subsidiary to the Shelby Fault. Several small shallow pits are present at the Seinor No. 3 Prospect. The pits contain gray fissile shale and porous weathered sandstone with thin layers (less than half an inch) of purple fluorite. The fluorite appears to be horizontal along bedding surfaces. The Seinor No. 3 Prospect is located along the southeast side of the Hobbs Creek Fault Zone, whereas the Seinor No. 1 and No. 2 are located along the northwest side of the Hobbs Creek Fault Zone. Brett Denny observed a trace amount of fluorite in limestone along the northeast projection of the Shelby Fault in sec. 3, T 12 S, R 7 E (1,300 feet from the west line, 200 feet from the south line) during mapping in 2008–2009 (Denny and Counts 2009). Baxter et al. (1967) mapped the Ridenhower Formation on the southeast side of the fault and the Cypress Sandstone on the northwest side of the fault. The small piece of mineralized limestone Denny found while mapping in 2008–2009 was mapped as Ridenhower. More Information: 10083025 10083026 10083027

References

Baxter, J.W., G.A. Desborough, and E.W. Shaw, 1967, Areal geology of the Illinois Fluorspar District: Part 3—Herod and Shetlerville Quadrangles: Illinois State Geological Survey, Circular 413, map, 1:24,000; report, 41 p. and 1 pl.

Bishop, O.M., 1947a, Fluorite and zinc on the J.J. Shelby and H. McGuire properties, Pope County, Illinois: U.S. Bureau of Mines, Report of Investigations 4048, 10 p.

Denny, F.B., and R.C. Counts, 2009, Bedrock geology of Shetlerville Quadrangle, Pope and Hardin Counties, Illinois: Illinois State Geological Survey, USGS-STATEMAP contract report, 2 sheets, 1:24,000; report, 6 p.

Weller, J.M., 1943a, Illinois fluorspar investigations, III. Outlying properties, A. J.J. Shelby Prospect, H.G. Spiller, lessee: Illinois State Geological Survey, unpublished manuscript, filed under J.M. Weller, ms. 12-A, 14 p.

Weller, J.M., R.M. Grogan, and F.E. Tippie,1952, Geology of the fluorspar deposits of Illinois: Illinois State Geological Survey, Bulletin 76, 147 p.