Laserfiche WebLink
<br />' 2.0 Location and Geologic Setting <br />The Spec-Agg Quarry is located to the north of Interstate 70 near Jackson Gulch on the <br />east flank of the Rocky Mountain Front Range, approximately 3 miles south of <br />downtown Golden (Figure 1). The natural topography of the property increases <br />significantly in elevation to the west, with elevations varying from approximately 6,250 <br />' feet along the eastern boundary to 7,110 feet on the western boundary. <br />' For this investigation, we have defined the quarry consisting of two distinct mining <br />areas: the main pit and the southern expansion area. In past years we accounted for <br />' three regions, in addition to the two mentioned above the middle level in the main pit <br />was also evaluated. This area has almost completely been removed and the remnant of <br />this level is included in the main pit area structural geology evaluation. <br />At the time of inspection the majority of the floor of the main pit was at elevation 6,340 <br />feet with a remnant of the middle level being excavated along the southeastern margin <br />' of the main pit at an approximate elevation of 6,370 feet. Also noted was a recently <br />excavated sump located along a deepened portion of the northern margin of the main <br />pit that is now at an approximate surface elevation of 6,325 feet (Photo 1). The <br />southern expansion area is the area of excavation that initiated subsequent to the 2003 <br />geotechnical investigation and best estimates of the current elevations of the working <br />benches range in elevation from approximately 6,870 to 6,900 feet (Figure 2). In the <br />' southern expansion area the sixth and seventh benches are currently being advanced <br />' to approximately the 6,870 foot elevation (Figure 2) with reclamation occurring in stages <br />following excavation along bench six (Photo 2). <br />1 This region of the Rocky Mountain Front Range was formed structurally during the <br />' Laramide orogeny in the Late Cretaceous and early Tertiary period. The gneissic <br />bedrock within the quarry is believed to have undergone two to three episodes of <br />' deformation during Precambrian time (Gable, 1968). During this time, the bedrock <br />material was intruded by several distinct igneous bodies and dikes that have been <br />mapped up to 2 feet wide and can be fairly continuous over long distances. The <br />