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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />10 The Disappointment Valley syncline results in down-warping of rock units in the <br />central portion of Disappointment Valley. The orientation of rock units south of the <br />topographic divide between Big Gypsum Valley and Disappointment Valley is <br />controlled by this structure. Rock units in this area dip towards Disappointment <br />Valley at approximately the same slope as the topography forming a dip slope. The <br />Salt Wash member of the Morrison Formation, which is the host to uranium- <br />vanadium mineralization in the area, dips generally south in this area. The Salt Wash <br />Member is approximately 600 feet below the surface in the mining areas south of the <br />topographic divide between Big Gypsum Valley and Disappointment Valley. The Salt <br />Wash Member occurs at a depth of approximately 1400 feet depth in Disappointment <br />Valley as a result of the down-warping of rock units associated with the <br />Disappointment Valley Syncline. The Salt Wash Member does not crop out in <br />Disappointment Valley as a result of the anticline. <br />The affected areas of the Sunday Group mines are all located within Big Gypsum <br />Valley. The geologic structures in this area are largely controlled by the Gypsum <br />Valley Anticline, which is a collapsed anticline formed by tectonic intrusion of salt <br />from the Paradox member of the Hermosa Formation, subsequent exposure of <br />portions of the salt core of the anticline, salt dissolution and plastic flow, and later <br />collapse of clastic sedimentary rocks into the central portion of Big Gypsum Valley. <br />This complex structural history has resulted in marked variations in the strike and dip <br />of the rocks, and the presence of fault bound blocks. These fault bound blocks of rock <br />are described further in Section 2.4, because they are related to understanding the <br />hydrogeologic framework of the mine affected areas. <br />2.2 Local Geologic Framework <br />This section focuses on aspects of the local geologic framework that are pertinent to <br />understanding the hydrogeologic framework of the mine areas. This discussion <br />includes descriptions of rock units underlying affected areas of the mines, and the <br />location of faults that could influence movement of water in the subsurface. Details <br />regarding the hydrogeologic framework of the areas are included in a subsequent <br />section of this document, Section 2.4. <br />The geologic framework in the affected areas of the Sunday Group mines is depicted <br />on the geologic map included as Figure 2-1 and on geologic cross-sections included as <br />figures 2-2 through 2-5. <br />2.2.1 Sunday and Carnation Mines <br />The affected area of the Sunday and Carnation Mines are shown on Figure 2-2. The <br />affected area of the mine lies on the Brushy Basin Member of the Morrison Formation, <br />which is composed primarily of bentonitic shale. Two faults are present in the mine <br />area. One of the faults is present near the northern edge of the affected area, which <br />displaces Brushy Basin Member downward towards Big Gypsum Valley. A marked <br />49 variation in the orientation of the rock units is apparent between the fault blocks, with <br />cm 2-5 <br />7:\84988-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology ReporlVinal sunday hydro reporNext\PINAL Sunday Hydmgeology Report.doc