2021-04-13_HYDROLOGY - M1977342 - Laserfiche WebLink

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April 2021 MNGW-I pH Memo 1 2 2.0 SUMMARY OF GEOLOGY AND HYDROGEOLOGY 2.1 SITE GEOLOGY Bedrock in the vicinity of the Henderson Mine surface facilities is shallow,generally less than 30 feet,and is composed primarily of Precambrian Silver Plume Granite and Tertiary-age stock and dike granitic intrusions. Bedrock in the vicinity of the Henderson Mine property is, in places, mineralized, and has the potential to naturally generate acidic conditions when contacted by meteoric water. Shallow colluvial and glacial deposits consisting of poorly sorted and unconsolidated sand, gravel, and cobbles, overlie the bedrock surface in drainage areas, such as near the West Fork of Clear Creek. The two monitor wells installed east of the Henderson Mine surface facilities in 2014 were drilled through the entire thickness of the colluvial sediments,which were approximately 20 to 25 feet thick.The geology consisted of colluvial sediments consisting of boulders,cobbles, gravels and sands with varying amounts of clay. Bedrock consisting of Precambrian Silver Plume Granite,was encountered below the sediments. 2.2 SITE HYDROLOGY AND HYDROGEOLOGY Groundwater in the vicinity of the Henderson Mine surface facilities occurs within colluvial deposits near and adjacent to the West Fork of Clear Creek. Groundwater flow is generally from west to east from the upper end of the drainage to the lower end. Upgradient of the confluence with Woods Creek,the colluvium pinches out and groundwater is forced to surface into the West Fork of Clear Creek (Climax Molybdenum Company, 2012). Drilling observations showed that the Precambrian Silver Plume Granite is generally impermeable and non-water bearing. o ame ulch, an unlined diversion ditch in this area, flows intermittently through the colluvial deposits less than 50 feet west of POC monitor well MNGW-1 (Figure 2). The diversion ditch routes natural runoff from the adjacent Red Mountain slopes south of the