Pittsburg Quadrangle

Mining in the Pittsburg Quadrangle

Mines extending into the Pittsburg Quadrangle from the Johnson City Quadrangle to the west opened in 1907 and 1908. Most of the mining here began later, around 1920. The coal was not so thick here as in the large mines on the West Frankfort Quadrangle to the northwest.

The Herrin Coal is the major resource, ranging from just over 5 feet up to 9 feet thick. Limestone was found immediately above the coal in some areas, and this made a good roof. This quadrangle encompasses an area where a gray shale above the coal was of variable thickness. Where the gray shale was thick or very thin, it held up fairly well. However, where the gray shale was of intermediate or changing thickness, the roof fell readily. Several mines noted slips in the shale. These often occurred where the shale changed thickness greatly over short distance. This transitional roof facies is noted for its instability (see Treworgy and others, 2000, Availability of the Herrin Coal for Mining in Illinois). Many of the mines had much water, which exacerbated some roof problems and floor heaving. Faults related to the Cottage Grove Fault System were noted in some mines, particularly the Orient No. 4 Mine (mine index 0688) and the Zeigler No. 4 Mine (mine index 0662).

Most of the mines in the Pittsburg Quadrangle operated for 20 to 30 years, however, so these geological problems must not have been genuine hindrances to mining and did not prohibitively increase the expense of mining. The Pittsburg Quadrangle is also at the eastern edge of the thick, low-sulfur coal deposits of the “Quality Circle”. These geological factors all controlled the pattern of mining over the quadrangle, where the northeastern one-third is essentially unmined.