Geologic investigation of roof and floor strata: longwall demonstration, Old Ben Mine No. 24. Prediction of coal balls in the Herrin Coal. Final technical report: Part 2. [Mineralized peat balls]
Coal-ball areas, large deposits of mineralized peat in the coal seam, obstructed longwall mining in the Herrin Coal at Old Ben Mine No. 24. In-mine mapping located coal balls under transitional roof - areas where the roof lithology alternates between the Energy Shale and the Anna Shale/Brereton Limestone. Specifically, coal balls occur under eroded exposures or windows of the marine Anna Shale/Brereton Limestone in the Energy Shale. Two types of coal-ball areas have been identified, based on stratigraphic position in the coal seam: type I is restricted to the top of the seam, and type II occurs at midseam and below. To predict the distribution of coal balls, as well as explain their formation, a depositional model was developed: First, freshwater sediments buried the Herrin peat. Decomposition of the sealed peat continued, producing high CO/sub 2/ partial pressures; then selective erosion took place as a river removed the cover along sinuous paths, cutting through to the peat in some places. With the seal broken, CO/sub 2/ was released, and freshwaters that contained Ca and Mg ions flushed out organic acids. Later, marine mud buried both the freshwater sediments and the exposed peat, which accounts for the transitional roof over the Herrin Coal and the coal balls under the marine shale windows in the Energy Shale. The depositional model was supported by the first comprehensive set of geochemical data for coal balls. Coal balls generally contained less than 4 percent organic carbon and very low levels of detrital minerals. Although individual sites of concentrated coal balls cannot be predicted, the specific linear roof exposures associated with these coal-ball areas can be identified by mapping. Based on previously mapped areas, the trends of these linear exposures can be projected.
- Research Organization:
- Illinois State Geological Survey, Urbana (USA)
- DOE Contract Number:
- FG01-78ET12177
- OSTI ID:
- 6158912
- Report Number(s):
- DOE/ET/12177-2; ON: DE83011414
- Country of Publication:
- United States
- Language:
- English
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PEAT
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UNDERGROUND FACILITIES
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011000* - Coal
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