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10 Geologic setting <br />2.3 Project area structural framework <br />2.3.1 Folding, dip and strike of strata <br />The Collom study area is adjacent to three significant folds (Figure 2.2). It occupies the <br />north limb of the Wilson Dome, located two miles south, and the Collom Syncline, that <br />occurs two miles north. The Wilson Dome contains an active petroleum field and is part <br />of a larger structure known as the Danforth Hills Anticline. The axis of the asymmetric <br />Collom Syncline trends northwest- southeast and sub - parallels the Axial Basin and <br />Danforth Hills anticlines. The axis of the Morgan Syncline trends north -south across the <br />Collom Syncline and influences the dip on the western edge of the Collom study area. <br />East of the Collom Mine are the coal seams of the Colowyo Mine, which also dip <br />northeastward. Immediately east of the Colowyo Mine, the strata dip steeply east into <br />the axis of the Elkhorn Syncline. <br />The stratigraphy of the Collom study area dips mildly northward toward the axis of the <br />Collom Syncline. Once the axis is reached the strata flex steeply upwards as the <br />southern perimeter of the Axial Basin is reached. Dips up to 30 are common north of <br />the Collom synclinal axis. <br />The structure within the Collom study area can be viewed as a broad, mildly dipping, <br />north- plunging anticline. The bulk of the coal deposit dips northeast but the dip shifts to <br />the northwest as the Morgan Syncline is approached on the western side of the deposit. <br />In the area planned for mining (Phases 1 -4) dips on the floor of the Gb Seam range from <br />3.5 to 8.5 (6% to 15 %). However, areas of steeper dips (greater than 15 %) can occur <br />within certain parts of the deposit. <br />Structural features such as faults, joints, coal cleats, and other miscellaneous structural <br />features were characterized by the Collom Geologic Team because they are often <br />factors in pit stability and mine plan optimization. These features may also have an <br />influence on the hydrogeologic conditions. <br />The primary joint orientation at the Collom study area is approximately N66 0 W versus <br />West Pit (i.e., the existing Colowyo Mine) measurements ranging from N55 °W to N60 0 W. <br />However, joint measurements in upper Collom Gulch show the primary joint direction to <br />be different and oriented essential east -west. It is interpreted that this joint orientation <br />change corresponds with the strike change as the Morgan Syncline is approached. <br />The secondary joint trend at the Collom study area appears to be approximately N19 °E. <br />At the West Pit of the Colowyo Mine it is approximately N25 0 E. <br />The conspicuously straight valleys within the region have been an item of debate for <br />many years. It has been suggested that they are fault- or fractured - controlled. <br />Structural contour maps do not support the existence of significant faulting in those <br />valleys. Since the valleys nearly parallel the secondary joint orientation, it was <br />suggested that the valleys occupy narrow zones of intense high frequency jointing. <br />Evaluation of fully -cored boreholes drilled in each of the major valleys dissecting the <br />area of interest in the Collom study area show that the joint and fracture frequency in <br />these valleys is within the average range of fracture frequency found along the ridge <br />tops. Therefore, the borehole data do not support the interpretation that the drainages <br />0 comprise zones of intense jointing. <br />2572 -R2 Colowyo Coal Company <br />Water Management Consultants <br />