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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 8. (August)

First Page: 1167

Last Page: 1167

Title: Prediction of Geologic Anomalies in Advance of Mining: Three Case Studies: ABSTRACT

Author(s): Stephen K. Danner, W. John Nelson

Article Type: Meeting abstract

Abstract:

Studies at three underground mines in Illinois show great differences in the predictability of geologic anomalies that interfere with mining. Exploratory drilling can be used to detect major features of the depositional environment such as areas of thin or no coal, ancient channels, and unstable roof lithologies. Local features such as faults, jointing, clay dikes, and rolls can best be delineated and predicted by in-mine mapping. Some anomalies, however, such as unexpected stresses, some clay dikes and rolls, and faults encountered for the first time, defy successful prediction by either method.

Mine A, a small drift mine in the Herrin (No. 6) Coal, was opened with very little test drilling. It soon became apparent that the single set of main entries was confined to an 800-ft wide (240 m) trough of minable coal bounded by areas of nondeposition and erosion. When the roof rock became so unstable that further advance was impossible, the mine was abandoned. With an additional investment in exploratory drilling, the company could have been forewarned about the confining nature of the trough and the presence of unstable roof, and perhaps could have relocated to a more minable body of coal.

At Mine B, also in the Herrin Coal, the density of drill holes was well above average for Illinois. Nevertheless, abnormally hard, thin coal was encountered at several faces. While exploratory drilling failed to detect these thin coal areas, in-mine mapping delineated them as narrow, sinuous, branching features, and offered a means of short-range projection.

A thorough exploration program preceded shaft sinking at Mine C. This program and subsequent in-mine mapping failed to predict severe roof stability problems in the north-south headings. The in-mine mapping did indicate that the north-south weakness was not due to lithologic or structural changes, but to high horizontal stresses. Ultimately, the mine headings were turned 45°, with an overall improvement in roof stability.

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Copyright 1997 American Association of Petroleum Geologists