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West Elk Mine <br />• Seven major structural faults aze known or are projected to occur in the MCC lease holdings and <br />South of Divide permit revision area. Analysis of these faults has identified them as normal <br />faults formed by a deep pluton in the Mancos Shale displacing existing fractures. The faults <br />vary greatly in offset from inches to 22 feet depending on their relative location to the pluton. <br />The faults are known to diminish vertically toward the surface as strain is partitioned into the <br />weaker strata as horizontal slip planes. Surface expression of the faults is found at the <br />sandstone cliff faces along Minnesota Creek but is covered with alluvium and colluvium <br />elsewhere. E Seam displacement is acknowledged to be 60 to 70 percent of the displacement <br />of the B Seam along the same fault trace. <br />Within the West Elk Mine coal lease area, the major cleat orientation within the F and B Seams <br />trends approximately north 65 to 70 degrees east. This face cleat direction is prominent and <br />consistent throughout the existing F and B Seam workings. Fracture sets and cleat orientations of <br />the E Seam should generally be the same. Further to the north and west, the major cleat direction in <br />the neazby Bear and Somerset mines is from north 70 to 75 degrees east. This direction is <br />representative of the face cleat direction in the Jumbo Mountain azea. The South of Divide permit <br />revision areas, however, will likely have cleat orientations more neaz north 65 degrees east. <br />Geologic Surface Features <br />Prominent Fault and Fracture Zones <br />• In-mine geologic mapping, seismic surveys, low altitude air-borue magnetic surveys, and <br />exploration drilling have been used to delineate the main fault and fracture systems within the <br />West Elk Mine coal lease area. The effect of faults and fractures in roof rock is most serious <br />when it is coincident with other geologic factors contributing to bad mining conditions. <br />Prominent faulting, when coincident with weak roof shales, large damage zones, and roof <br />and floor water, are important factors to consider in mine design and planning. These <br />pazameters were taken into consideration in the panel design for the West Elk Mine B and E <br />Seams. <br />Several fault and fracture studies have been conducted within the coal lease area at West Elk <br />Mine. Aerial photography, LandSat imagery, and photogrammetric mapping have proved to <br />be of limited success in revealing the major fault systems present in the coal bearing strata. <br />The use of aerial photo mapping of drainages and topographic lineaments, and the common <br />assumption that these features directly relate to the distribution and orientation of joints and <br />fractures on the surface and in the subsurface, may not be true in this area. While it is true <br />that most photo lineaments correspond to drainages and erosional features, the assumption <br />that the drainages and erosion features are controlled by joint and fracture patterns, may or <br />may not be true. Most major drainages in Western Colorado were established several million <br />years ago in the Pliocene or Miocene in beds many hundreds, and possibly, thousands of feet <br />stratigraphically higher and younger than the Mesaverde beds that are now exposed. Stress <br />patterns and lithology at that time were significantly different than current conditions. As the <br />younger beds were eroded, most drainages maintained established patterus. <br />• <br />1.044 4 Revised November 2004 PRIO <br />