--> The Use of the Rim Geophysical Method for Fault and Igneous Dike Detection: Three Case Studies, by W. A. Koontz and D. M. Pillmore; #90986 (1994).

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Abstract: The Use of the Rim Geophysical Method for Fault and Igneous Dike Detection: Three Case Studies

Wendell A. Koontz, Donn M. Pillmore

The presence of faults, igneous intrusions, and sand channel scours in coal mine longwall panels can greatly impede the recovery and quality of the

coal in those panels. Early detection of geologic anomalies can aid in the development and coal extraction of longwall panels. One of the more promising methods of investigating coal seam geologic anomalies is the Radio Imaging Method (RIM). RIM is a geophysical technique that uses electromagnetic waves in the radio frequency range. These waves are transmitted through a longwall panel at a specific frequency, using transmitter and receiver antennas placed at various locations on opposite sides of the area of interest. The strength of the signal measured at the receiver is used to calculate the rate of signal absorption (attenuation rate), which is a function of electrical conductivity which varies depending on the geology encountered. Data collected in a survey are analyzed by compari g them to data gathered through known geology and geophysical models. Additionally, data can be put into a tomographic reconstruction algorithm that produces a contour map of the attenuation rate. The tomographic image is then interpreted in a geologic context.

Three different (300-Khz) RIM surveys were conducted at an operating coal mine in the Wasatch plateau of Utah in the upper O'Connor Seam (Upper Cretaceous Blackhawk Formation) and are presented as examples. One survey was conducted through a fault zone in a longwall panel designated as 6Left A. Faults with offsets up to 12 ft were encountered in development entries (coal thickness approximately 11 ft), then extrapolated successfully through the panel with the RIM data. RIM survey data collected in longwall panel 7Left B was used to delineate the limits of an intrusive igneous body. RIM data supports and further defines geologic anomalies that have been located by underground mapping and longhole drilling. The fourth survey example is in the 7Left A panel designed to detect the locatio of and the amount of compaction or scouring in the coal seam under a sandstone channel in the roof. The analyzed RIM data clearly delineates the location of the sand body with little to no inferred scouring through the seam.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994