Harco Quadrangle

Mining in the Harco Quadrangle

Mining began in the Harco quadrangle in 1902 and has continued to the present, with two mines active at the time of this writing – the Liberty Mine (mine index 1029) and the Millennium Portal (mine index 1032), both in the Springfield Coal. Most of the mining in the Harco Quadrangle was of the Herrin and Springfield Coals. The Herrin Coal ranged from 60 to 350 feet deep. Consequently, this seam was both surface- and underground-mined. The Springfield Coal was 100 feet or more below the Herrin Coal, and was only underground-mined in this area. This coal was generally 4 to 5.5 feet thick, with a maximum local thickness of 10 feet. The Danville and Womac Coals were also surface-mined locally.

Faulting and roof falls were the main problems of the abandoned mines. The Cottage Grove Fault System extends through this quadrangle, with the master fault running generally east-west between Peabody No. 47 Mine (mine index 124) and Peabody No. 43 Mine (mine index 751). An associated fault zone curves southward along the western limit of Peabody No. 43 Mine. The indications of these faults can be seen on the accompanying map of the Springfield Coal. Subsidiary faulting also occurs, and some traces of this can be seen in the mining patterns. In many areas, the displacements are relatively small and do not represent a serious obstacle to mining. For more detailed information on the Cottage Grove Fault System, see ISGS Circular 522, The Cottage Grove Fault System in Southern Illinois (Nelson and Krausse, 1981).

The Galatia Channel is about a mile east of the Harco Quadrangle. Associated with the channel is the Dykersburg Shale Member, a unit of light to dark gray shales, siltstones and sandstones deposited directly on the Springfield Coal. The Dykersburg Shale Member makes a stable mine roof, except where abrupt changes of thickness occur and in certain facies near the Galatia Channel. The sandy gray Energy Shale over the Herrin Coal causes similar difficulties.