2012-03-06_REPORT - M1974004 - Laserfiche WebLink

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Martin Marietta Materials Spec -Agg Project 2.0 LOCATION AND GEOLOGIC SETTING The Spec -Agg Quarry is located to the north of Interstate 70 near Jackson Gulch on the east flank of the Rocky Mountain Front Range, approximately 3 miles south of downtown Golden (Figure 1). The natural topography of the property increases significantly in elevation to the west, with elevations varying from approximately 6,250 feet along the eastern boundary to 7,110 feet on the western boundary. For this investigation, we have defined the quarry consisting of two distinct mining areas: the main pit and the southern expansion area. In past years we accounted for three regions; in addition to the two mentioned above, the middle level in the main pit was also evaluated. This area has almost completely been removed and the remnant of this level is included in the main pit area structural geology evaluation (Figure 2). At the time of inspection the majority of the floor of the main pit was at an overall approximate elevation of 6,242 feet with excavation along the northern margin of the main pit continuing at an approximate elevation of 6,210 feet (Photo 1) including the temporary sump located on the main pit floor. The southern expansion area is the area of excavation that initiated subsequent to the 2003 geotechnical investigation and best estimates of the current elevations of the working bench is approximately 6,790 feet (Figure 2). In the southern expansion area the current temporary benches are being advanced to approximately the 6,770 foot elevation (Figure 2) with reclamation occurring in stages following excavation along bench nine. This region of the Rocky Mountain Front Range was formed structurally during the Laramide orogeny in the Late Cretaceous and early Tertiary period. The gneissic bedrock within the quarry is believed to have undergone two to three episodes of deformation during Precambrian time (Gable, 1968). During this time, the bedrock material was intruded by several distinct igneous bodies and dikes that have been mapped up to 2 feet wide and can be fairly continuous over long distances. The gneisses are mapped as a series of folds, which are oriented roughly east -west and have been broken and displaced by faults believed to range in age from Precambrian to Tertiary. The two regional fault orientations that have been mapped within the property, trend approximately east -west and north -south (Figure 3). A notable geologic feature near the site is the Golden fault, which runs approximately north -south and forms the eastern margin of the north - northwest trending hogback immediately east of the quarry property. A mapped reverse fault trending roughly north -south is located within the quarry property and constitutes the boundary between the metamorphosed Precambrian bedrock (to the west) and the Pennsylvanian sedimentary rocks (to the east) (Smith, 1964; Scott, 1972). The quarry property straddles this boundary, with the majority of the processing plant and the entire asphalt plant located east of the fault (Figure 3). The bedrock material east of the fault is dominantly composed of upturned sandstones and shales of the Fountain Formation (Scott, 1972). West of this fault, the material is typically mapped as migmatitic, quartzo- felspathic gneiss with intrusions of granitic pegmatite veins (Scott, 1972). February 13, 2012 Page 2 Lachel & Associates, Inc. Project 11361017.00 ©2012 All Rights Reserved