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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />The Summerville Formation overlies the Entrada Sandstone, and consists primarily of <br />sandy and silty shale. This unit also includes local sandstone and limestone layers. <br />The unit is approximately 105 ft. thick, except where it thins along the limbs of the <br />Gypsum Valley Anticline. <br />The Upper Jurassic Morrison Formation overlies the Summerville Formation. This <br />formation is important because it hosts the uranium-vanadium mineralization at the <br />Sunday Mines Group. The Morrison Formation includes two members: the Salt Wash <br />Member and the Brushy Basin member. The lowermost member is the Salt Wash <br />Member, which consist of sandstone with interbedded red shale and a few local beds <br />of limestone. The uranium-vanadium ore bodies occur within the Top Rim sandstone <br />unit, which is located in the top approximately 100 ft. of the Salt Wash Member (J. <br />Showalter personnel communication 2008). The thickness of the Salt Wash member <br />ranges from 320 to 380 ft. The Salt Wash member is overlain by shale of the Brushy <br />Basin member. The thickness of the Brushy Basin Member ranges from 350 to 430 ft. <br />The Lower Cretaceous Burro Canyon Formation overlies the Morrison Formation. This <br />formation is heterogeneous and includes conglomerate, sandstone, shale and thin <br />lenses of limestone. The Burro Canyon Member contains some massive beds of up to <br />100 ft. thick, and the total thickness of the formation is estimated to be 190 to 240 ft. <br />The Cretaceous Dakota Sandstone is a flaggy sandstone unit, which overlies the Burro <br />Canyon Formation. This formation also includes less-abundant conglomerate, <br />carbonaceous shale, and local impure coal. The sandstone ranges from fine grained <br />and thin-bedded to coarse grained and cross-bedded. The Dakota Sandstone is <br />approximately 200 ft. thick. <br />The Dakota Sandstone is overlain by the Cretaceous Mancos Slide. The Mancos Shale <br />is a homogeneous formation of fissile shale that is approximately 1,600 ft. thick. <br />Unconsolidated Quaternary deposits are also present including terrace gravels, wind- <br />deposited material, alluvium, and landslide deposits. These units are local in nature <br />and commonly form a thin veneer on unconsolidated sediments in areas where they <br />are present. <br />2.1.3 Structural Geology <br />Two major structural features are present in the area: the Gypsum Valley anticline <br />and the Disappointment Valley syncline. The Disappointment Valley Syncline is a <br />relatively simple structure consisting of a broad down-warping of stratigraphic units <br />which plunges gently towards the southeast, away from the Dolores River. The <br />Gypsum Valley anticline is a former anticline formed by tectonic intrusion of salt, <br />which has subsequently collapsed leading to formation of complex subsidiary faulting <br />and folding. Both of the major structural features play a role in defining the <br />hydrogeologic framework of the Sunday Mines Group area. Structural features <br />O present in the area are shown on the geological map attached as Figure 2-1. <br />cm 2-4 <br />7:\64988-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Report\fnal sunday hydro reporNextTINAL Sunday Hydrogeology Report.doc