ABSTRACT: Coal Roof-Rock Successions as an Exploration Tool For Ground Control in the Illinois Basin
PHILLIPS, MARK E., Consulting Geologist, Evansville, IN, PHILIP J. DeMARIS and HEINZ H. DAMBERGER, Illinois State Geological Survey, Champaign, IL
Identifying typical roof strata is the first step in evaluating potential roof stability and other coal mining problems for a potential mine property. Based on in-mine experience in the Herrin and Springfield Coals (Carbondale Formation, Pennsylvanian System) and examination of associated drill-hole data, seven different rock successions are recognized in the 10 ft of strata immediately above these coals. Each of the seven successions includes from one to three (rarely more) strata with distinct stability characteristics. A typical mine property may have only two or three different roof-rock successions. Interruptions in the typical roof-rock successions (abrupt vertical roof-rock changes) may indicated erosional channeling or tectonic faulting; these interruptions must be recognized nd evaluated during exploration.
Past and present mining advantages or problems associated with each succession can be linked to mining blocks in advance of development. Specific geologic features, both common and rare, are associated with each succession and some features are common to several successions. These features or characteristics include: plant debris around lithologic contacts, bedding separation planes, compactional faults ("slips"), laterally injected clay ("whitetop"), clay dikes in roof and coal seam, and coal balls in the coal. Thus many geologic risk factors for mining can be identified during the exploration stage, even though the magnitude of risk may remain uncertain.
AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)