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• There are numerous dikes exposed in the area, as well as some sills and plugs. Sills and <br />plugs do not occur within the mine plan area, though several vertical to near vertical dikes <br />cut through the coal. Where such dikes are indirect contact with the coal, the coal has been <br />locally coked in place. The dikes generally strike in a west to southwest and east northeast <br />direction with local off-shoots striking normal to the main dikes. The dikes appear to have <br />filled fractures in sediments as a result of tectonics relating to the synclinal fold of the basin. <br />The dikes are roughly parallel to each other, regularly spaced, and vary from 3 to 100 feet <br />thick. <br />Several faults have been mapped in the mine plan area. Structural dips in the mine plan <br />area are relatively gentle and range from two to five degrees to the west-southwest. Precise <br />directions of the dip vary along the eastern boundary of the syncline. The nose of the <br />syncline immediately north of the mine plan area contains dips of up to fourteen degrees <br />to the south-southwest. <br />The coal seams which were mined by the operations were the Lower Robinson, the Pryor, <br />the Walsen, the Lennox, and the Cameron Seam. These coal seams are found in the <br />Vermejo foundation and ]ie within a sequence of sedimentary rocks characterized by <br />sandstones, siltstones, shales and carbonaceous and silty shales. <br />Exploration test borings were conducted within the mine plan area and were utilized far the <br />following purposes. <br />• Location of Subsurface Water <br />The primary circulation medium for most exploration boreholes drilled within the mine plan <br />area was both compressed air and drilling mud. Several drill holes throughout the area that <br />encountered groundwater were left open to measure the recovered elevation of the <br />piezometric surface in each hole. Information on groundwater occurrence is set forth under <br />Section 2.04.7. <br />Physical Properties <br />The overburden material removed as a part of the mining operation consisted mainly of <br />shales, siltstones, and sandstones. Generally, the shales have a relatively high erodability and <br />compaction factor while sandstones and siltstones have low erodability factors and low to <br />moderate compaction. Because of the extremely lenticular nature of the strata in the permit <br />area, it was difficult to detetzttine an actual value for the swell of the overburden. <br />Therefore, the swell of the overburden material was estimated at 25%. <br />Chemical Properties <br />As shown in Table 3, Overburden Analysis, chemical analyses of each strata within the <br />overburden and within the strata immediately below the lowest coal seam to be mined, are <br />• availab]e for the purpose of identifying, at a minimum, those horizons which may possibly <br />2.04-11 <br />