2019-06-28_REVISION - M1977004 (11)

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Homestake Mining Company May 10,2019 Regular(112d)Operation Reclamation Permit Application Package 3.0 SITE CONDITIONS 3.1. Geology 3.1.1. Geologic Setting The Mine is located on the western flank of the Sawatch Range within the Southern Rocky Mountains (SRM) physiographic province (Figure 3-1). The SRM extends from central Wyoming to north-central New Mexico and is characterized by high mean elevations, rugged upland terrain, and deeply incised drainages (Fenneman, 1931; Eaton, 1986). To the east, over the Sawatch Range, is the Rio Grande Rift Zone which at the surface is expressed as the Upper Arkansas and San Luis Valleys. To the south and southwest are the Bonanza and Cochetopa calderas of the San Juan Volcanic field (Steven and Lipman, 1976), and to the northwest is the West Elk Volcanic field. During the Laramide Orogeny' the site experienced thrust faulting which juxtaposed a basement cored uplifts against younger sedimentary bedrock (Dickinson et al., 1988; Tweto, 1980). Since the Laramide, the area has experienced epiorogenic uplift and incision, Neogene volcanism, and ongoing extensional tectonics (McMillan et al., 2006; Pazagllia and Kelley, 2006). 3.1.2. Stratigraphy The Mine stratigraphy includes Precambrian2 metamorphic and igneous rocks, PaleozoiC3 sedimentary rocks, and Cenozoic4 volcanic rocks (Olsen, 1988; Nash, 1988; Olson, 1983; Goodknight and Ludlum, 1981) (Figures 3-2 and 3-3). MesozoiC5 strata were not deposited at the site and absent in the stratigraphy. Cenozoic volcanic deposits do not overly the Mine but are believed to have covered the entire district at one time before removal by erosion (Goodknight, 1981). The Precambrian geology consists of pre-1.7 billion-year-old (Ga) high grade metamorphic rocks and younger granitic and pegmatite intrusive dikes and veins which cross-cut the older bedrock. Paleozoic sedimentary rocks unconformably overlie the Precambrian rocks and are approximately 2100 ft thick. They range in age from late Cambrian6 to Pennsylvanian'. The early (lower) Paleozoic stratigraphy includes interbedded sequences of dolomite and quartzite that were deposited during multiple phases of marine transgression. This sequence is overlain by a relatively thicker package of diverse sedimentary lithologies of fluvial-deltaic and marine origins that were deposited during Pennsylvanian time. ' The Laramide Orogeny was a period of mountain building in Western North America that occurred between 80 to 50 million years ago (Ma). 2 The Precambrian Eon is the part of earth's history that occurred before 541 Ma. 3 The Paleozoic Era occurred between 542 and 251 Ma. 4 The Cenozoic Era is the geologic time that began 66 Ma and extends through the present. 5 The Mesozoic Era occurred between 251 to 66 Ma 6 The Cambrian Period occurred between 541 and 485.5 Ma. The Pennsylvanian occurred between --323 and -299 Ma. EXHIBIT E-RULE 6.4.5(AMENDED RECLAMATION PLAN) Page 13 HOMESTAKE MINING COMPANY