2021-04-20_REVISION - M1983033 (20)

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Walstrum Spur Amendment, Exhibit G— Water Information April 2021 taken during the reconnaissance, and photographs are available in Appendix G-1. Figure G-6 shows the locations of the two water wells that were verified during the hydrogeologic reconnaissance. 2. A test-pit program was performed in June 2020 and included the excavation and logging of six test pits. The test pits were excavated to determine the nature and depth of the topsoil and colluvial deposits (overburden) and to determine whether groundwater was present at the overburden/bedrock contact. A description of the test-pit program and logs are presented in the Geotechnical Stability Exhibit. 3. A drilling program was performed in June 2020. This included five coreholes named CH-001 through CH- 005. Coreholes CH-001 through CH-003 and CH-005 were drilled at a vertical orientation. Corehole CH-004 was drilled at an angle of approximately 45 degrees from horizontal oriented south-southwest. The cores were logged for lithology and rock mechanic properties to support the Geotechnical Stability Exhibit, the Mining Plan (Exhibit D), and the Reclamation Plan (Exhibit E). Logs of the coreholes are presented in the Geotechnical Stability Exhibit. 3.0 PHYSIOGRAPHY The Spur Amendment is located along a topographic high bounded by the Existing Quarry to the west, Clear Creek to the south, North Clear Creek to the east, and the Tributary to North Clear Creek to the north (see Figures G-2 and G-6). North-facing slopes are covered primarily with conifer trees (see Figure G-5). South-facing slopes are generally vegetated with grass and shrubs with occasional conifers. These conditions are typical of high-altitude Precambrian-age bedrock terrain in Colorado. The topography of the Spur Amendment is steep (Figure G-4) and rocky with numerous outcrops of gneiss. Elevations range from approximately 8,100 feet above mean sea level (amsl) on the north side of the Spur Amendment along the Clear Creek-Gilpin county line to approximately 6,900 feet east of the Spur Amendment at the confluence of Clear Creek and North Clear Creek. The elevation of Clear Creek at the upstream end of the Existing Quarry is approximately 7,220 feet. The stream gradient of Clear Creek adjacent to the Spur Amendment is approximately two percent. 4.0 GEOLOGY 4.1 Stratigraphy The geology of the Spur Amendment and Existing Quarry are described in Schwochow (1989) and USGS (1975 and 1976). The geology of the Spur Amendment consists of Precambrian metamorphic gneisses and schists, dipping in a northerly direction between 40 and 60 degrees (Figure G-2). The lowest unit, stratigraphically, is a feldspar-rich gneiss, represented on the geologic map as Xf. This unit is a gray, tan or pinkish-gray fine to medium-grained gneiss which retains some of the original sedimentary structure where biotite-rich layers interlaminated with biotite-poor layers are present. Feldspars commonly are dominated by microcline. The feldspar-rich gneiss is overlain by a hornblende gneiss and amphibolite unit (Xh on the geologic map). This unit is dark gray to greenish gray and contains an elevated fraction of hornblende and plagioclase with additional mineralogy including quartz, pyroxene (clino-), biotite, and epidote. Foliation of this unit is produced by planar alignment of hornblende crystals. Overlying the hornblende gneiss is another layer of feldspar gneiss. Then above the feldspar gneiss is a second unit of hornblende gneiss (Xhcs) which generally consists of an interlayered set of hornblende gneiss with amphibolite and a calc-silicate gneiss, additionally interlayered with thinner layers of feldspar-rich gneiss and biotite-dominated gneiss. The upper-most unit, stratigraphically, is a biotite-quartz-plagioclase gneiss (Xb), which may contain fibrolitic sillimanite in laminations. The Precambrian stratigraphy is intruded locally by Cretaceous-age porphyry dikes in addition to an assembly of Precambrian quartz and granite pegmatite intrusions. The Cretaceous porphyry dikes occur as laterally continuous features which follow weaknesses associated with existing fractures and fault pathways. The pegmatite intrusions appear as discrete, elongated bodies throughout the Precambrian metamorphic units. Five exploratory coreholes were drilled in 2020 (CH-001 through CH-005) (Figure G-2). These coreholes were placed along an access road which forms a loop through the Spur Amendment. Each of these coreholes intersects a different set of the geologic units. The lithologic logs for each of these five coreholes is presented in the Geotechnical Stability Exhibit. The logs generally show occasional indication of oxidized iron staining along existing fractures or joints indicative of past hydrothermal groundwater associated with the mineralization of the Colorado Mineral Belt which is located about three miles to the west of the Spur Amendment. Given the proximity of the Spur Amendment to the Colorado Mineral Belt, core samples were analyzed for metals in solid samples, metals in leachate generated from the synthetic precipitation leaching procedure (SPLP), and acid-base � TETRA TECH P a g e 2 I 7