2017-04-14_REPORT - M1974004 - Laserfiche WebLink

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Martin Marietta Materials Spec-Agg 2017 Annual Report 3.0 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, Colorado (Figure 1). The natural topography of the property increases significantly in elevation to the west, with elevations within the planned mining pit area that vary from approximately EL 6,425 ft along the mine's eastern boundary to EL 7,110 ft on the western boundary(Figures 1 and 2). This region of the Rocky Mountain Front Range was deformed during the Laramide orogeny in the late Cretaceous and early Tertiary periods. 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. 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 bedrock within the mined portions of the quarry is mapped as migmatitic quartzo-felspathic gneiss with intrusions of granitic pegmatite veins (Scott, 1972). The granitic gneiss found in the quarry is generally hard and relatively competent. The gneiss varies in color from grayish orange to dark gray, with occasional banding visible along the foliation of the rock. The term foliation refers to the realignment of minerals into a parallel orientation as a result of the intense heat and/or pressure of metamorphism. The rock mass tends to be weakest along the foliation planes, which ultimately results in a discontinuity set parallel to the orientation of the foliation. The foliation orientation is the most prominent discontinuity set identified in the quarry. The foliation undulates across rock exposures in some locations. The rock mass also exhibits several other joint sets that are locally prominent and varied with elevations as mining progress to lower elevation. However, the joints are generally not as regular or as laterally continuous at the foliation. Two regional fault orientations, trending approximately east-west and north-south, have been mapped within the property by others (Gable, 1968; Scott 1972), and multiple fault orientation measurements have been recorded in our site visits over the years, as shown in Figures 3 and 4. An approximately east-west trending fault is mapped by Gable (1968) across the northern margin of the quarry. This fault is exposed in the northern portion of the main quarry pit(Figure 3). A second approximately east-west trending fault was previously identified in Jackson Gulch (informally named the Jackson Gulch fault). However, this fault is not mapped due to the uncertainty in the orientation of the fault trace. The area has been extensively modified and fresh exposures were covered by backfill material before measurements could be made. In the Southern Expansion Area, Gable (1968) mapped a third fault that also trends roughly east-west (Figure 3). This fault was initially exposed during the 2006 investigation, and was noted by a distinct pegmatite vein that was surrounded by decomposed weak biotite rich gneiss. The fault was exposed in temporary excavation walls along the western and southern margin of the Southern Expansion Area during previous and current year site visits. GPS measurements taken along the margin of the fault exposure were registered in Google Earth to the existing fault map yielding a good match with the previously mapped trace (Figure 3 and Photo 3). At this location, it was noted in the 2012 report that the February 27,2017 Page 2 Lachel &Associates, Inc. Project 16C64003 00 ©2017 All Rights Reserved