2010-12-17_REVISION - C1981019 (153)

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Geologic setting 11 S Given that the drainage pattern subparallels the secondary joint orientation, it is suggested that jointing has influenced the erosion course and ultimate formation of the valleys. 2.3.2 Faulting Colowyo Mine staff have reportedly never encountered faults during mining operations. Based on comparable local structural settings, faults should be absent at the Collom Mine as well. However, a few faults have been identified in the region, some of which exhibit considerable vertical displacements. The Mt. Streeter Fault occurs north of the Colowyo mining operations and became the northern barrier of the underground workings of the abandoned Streeter /Redwing Mine. This normal fault trends N55 0 W to N75 0 W, is downthrown on the north side, and exhibits up to 280 ft of vertical displacement in Good Spring Creek. Previous workers had difficulty projecting the fault much past Taylor Creek. An additional fault with comparable orientations and 25 ft of vertical displacement occurs south of the Streeter Fault and just north of Colowyo's surface facilities. It has not been traced much further westward than Taylor Creek. North of the Collom Mine and within the confines of the Collom synclinal axis, faults have been identified and published on various geological maps (Reheis, 1981, and Hardy and C Zook, 1997). Reportedly, drilling within the axis area shows strata to be highly fractured and consequently drilling conditions are difficult. Deformation within.the axis area is also evident at the Gossard Fee Tract located northwest of the Collom study area. Exploration in that area has revealed several reverse faults having vertical displacements up to 25 ft. These faults also occur within the vicinity of the Collom synclinal axis that traverses the northern part of the study area. It is suggested that the synclinal axis area absorbed much of the compression and behaved as a locus for subsequent deformation. Faulting is evident within Chokecherry Gulch, located southwest of the Collom Mine (Collom Geologic Team, 2005). Reportedly, the fault exhibits 12 ft of vertical displacement and is downthrown on the west side. The fault could not be traced beyond the confluence of Collom Gulch. However, drilling difficulties at some 2004 holes in the Phase 3 area in the Collom study area could be the result of fractures emanating northward from the Chokecherry Fault. No direct evidence of faulting has been found during the various exploration programs conducted within the proposed Collom Mine (Phases 1 through 4). Continuous and spot core holes drilled during 2004 did not reveal any evidence of faulting. Coal seam structure maps also do not reveal obvious anomalous elevation shifts indicative of faulting. Although limited, geological reconnaissance has not revealed any definite displaced strata where exposures occur in West Fork Jubb Creek, Little Collom Gulch, and Upper Collom Gulch. 2572 -R2 Colowyo Coal Company Water Management Consultants