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3.0 GEOLOGY AND GEOLOGIC STRUCTURE <br /> 3.1 GEOLOGY <br /> The rocks forming the walls of the Sunnyside Pit are within the Burns Formation of <br /> the Silverton Volcanic Group, a complex accumulation of lava flows, breccias, and tuffs <br /> associated with local volcanic cones and dome-like eruptive masses. The upper member <br /> of the Burns Formation is found in Sunnyside Basin and varies from pebble-rich, welded <br /> tuffs to thick, layered lava flows. The rocks' mineral composition averages near <br /> rhyodacite, with the structural composition varying from massive to flow-layered. <br /> Locally, alteration of the rock can be severe including both intense mechanical <br /> deformation and chemical alteration. Chemically, the rocks can be silicified, epidotized, <br /> and propylitized. <br /> Most of the rock exposed in the north wall of the Sunnyside Pit is a hard, competent <br /> rhyodacite. The intact strength of NX size rock core samples is expected to be in the <br /> range of 15,000 to 20,000 psi, based upon data from other rhyodacite rocks. <br /> 3.2 ROCK STRUCTURE <br /> Excavations for Benches 1 and 2 in the north wall of the Sunnyside Pit have been <br /> mapped to characterize the existing joints and fault discontinuities. The condition of the <br /> rock following excavation is illustrated by the photographs in Figures 3.1 and 3.2 which <br /> show sections of Benches 1 and 2, respectively. The rock in the benches is quite blocky <br /> due to the presence of several sets of joints and small faults. The faults have trace lengths <br /> up to 200 ft and contain clay gouge with thicknesses up to 1 inch. <br /> 3.2.1 Bench 1 Mapping <br /> Structural mapping of Bench 1 is presented in Figure 3.3, located in the back <br /> pocket. Between the faults and joints, numerous irregular fractures have been induced <br /> into the rock by surface weathering and blast damage. Orientations of the joints mapped <br /> 4 <br />