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Mining and Reclamation Permit Amend.-M-1988-112 <br /> Groundwater Management Plan Battle Mountain Resources,Inc. <br /> was backfilled with waste rock composed of Santa Fe Fm and Precambrian gneiss-granite <br /> materials. The general surficial geology was mapped by the U.S. Geological Survey <br /> (Wallace and Soulliere, 1996) and is represented in Figure G-2. <br /> The Precambrian gneiss-granite complex forms the core of the Sangre de Cristo range <br /> and hosts the ore body that was mined out of the West, East, and Pink Granite Pits of the <br /> San Luis Mine Project. The upper surface of the gneiss-granite complex within and to the <br /> south of the West Pit is truncated by a low-angle thrust fault that trends northwest and <br /> plunges to the southwest. The fault zone is identified by a fault gouge that has been <br /> altered to a green clay. The green clay was originally exposed at the ground surface <br /> within the West Pit but was mined out. The green clay separates the Precambrian gneiss <br /> from the overlying Santa Fe Fm and averages 5 to 10 feet thick across the portions of the <br /> mine site where it is present. <br /> The Santa Fe Fm was deposited on an erosional surface during a period of rapid uplift of <br /> the Sangre de Cristo Mountains. This unit consists of alternating sequences of fluvial <br /> gravel, sand and silt, and eolian sand. In the West Pit, prior to being mined out, the Santa <br /> Fe Fm was 60 to 90 feet thick and consisted of predominately fine- to very fine-grained <br /> cemented sandstones. This unit is very competent (Water Management Consultants, Inc., <br /> 1994). The Santa Fe Fm is generally absent above 8,800 ft amsl (CSPS NGVD29) over <br /> much of the property. <br /> The most recent depositional unit includes Quaternary alluvial sediments that have been <br /> deposited along the Rito Seco Valley, generally south of the West Pit. This unit consists <br /> of silty sands with some gravelly clay, and organic-rich zones and can be over 60 feet <br /> thick in the project area. Along the south side of the West Pit, the alluvium is in direct <br /> contact with the backfill material, in an area that has been historically referred to as the <br /> "alluvial window". Alluvial sediments are generally absent within a few hundred feet to <br /> the east of the West Pit, where the Rito Seco is incised into the Precambrian bedrock. <br /> 4.0 SITE HYDROGEOLOGY <br /> 4.1 Hydrologic Units <br /> The Precambrian rocks within the mine area contain an aquifer of unknown extent. <br /> Groundwater in the unit occurs within interconnected fractures in the crystalline rock. <br /> Prior to mining, the bedrock aquifer was at least partially under artesian conditions in <br /> areas where the green clay provided a confining layer at the top of the unit. Pre-mining <br /> groundwater flow direction was to the south and west. Recharge to the Precambrian <br /> aquifer is believed to occur to the north where the green clay is eroded away and the <br /> fractured rocks are exposed at the surface. During active mining, the Precambrian aquifer <br /> was dewatered using a single well (DW-1). The well ran continuously at between 150 <br /> and 250 gallons per minute and lowered the potentiometric head in the vicinity of the <br /> West Pit between 100 and 200 feet to an elevation of approximately 8,492 ft amsl <br /> (NGVD29) (Water Management Consultants, Inc., 1994), over 60 feet below the bottom <br /> of the pit. Exploration drilling data suggest that the Precambrian aquifer may be <br /> April 2025 3 Engineering Analytics,Inc. <br />