2009-05-19_REVISION - M1981021 (36)

Home Browse Search

Section 7 Groundwater Information 7.1.3 West Sunday Mine The local geological framework of the West Sunday Mine affected area is shown on Figure 7-4. In general, this geology of the area is similar to that previously described at the St. Jude, Carnation, and Sunday mines. However, the affected area of the mine is located in a different location in relation to the faults bounding the valley and the displaced geologic formations. The affected area of the West Sunday mine lies on the Brushy Basin Member of the Morrison Formation and the Burro Canyon Formation. Several faults are present in the general vicinity of the mine affected area; however, the faults are located upslope from the affected area. 7.1.4 Topaz Mine The Topaz Mine is located approximately 1 mile west of the other Sunday Group mines, and the local geological framework is somewhat different. The affected area of the Topaz mine is shown on Figure 7-5. This affected area directly overlies the Salt Wash Member of the Morrison Formation, which is the unit that hosts uranium- vanadium mineralization at the mine. The Salt Wash Member consists of sandstone with interbedded red shale and a few local beds of limestone. A fault is present in proximity to the Topaz Mine affected area, which displaces rock units on the north side downward as observed previously at the other Sunday Group mines. This fault juxtaposes the Brushy Basin shale on the north side of the fault against the Salt Wash member on the south side of the fault. Additional information regarding the geological framework in the area of the Topaz mine affected area is shown on the geologic map (Figure 7-1). The relative density of faults in the area west of the Topaz Mine is higher than areas adjacent to the other Sunday Group mines. This may be related to increased structural complexity associated with the intersection of the Big Gypsum Valley anticline with geologic structures associated with the Dolores River. Although the density of faults is higher, the faults show the same general pattern of displacing rock units on the north side of the fault downward towards Big Gypsum Valley. The surface geology shown in Figure 2-1 also shows that the Salt Wash Member of the Morrison Formation crops out west-northwest of the Topaz mine adjacent to the Dolores River. 7.2 Potential Aquifers in Area of Sunday Mines Group In order to better define the local hydrogeologic framework, the hydrogeologic units defined by Weir et al. have been subdivided. These subdivisions are summarized in Exhibit 7-1. • 7-2 TA64986-Denison Mines%Task Order 4 - EPP Sunday Mines GroupTINAL EPP\FINAL - Environmental Protection Plan Sunday Mines.doc