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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />Quaternary sediments. The orientation of the rock units varies as a result of tectonic <br />displacements associated with the Gypsum Valley Anticline. The strike of the rock <br />units is generally west to northwest and the dip varies from approximately 20 degrees <br />south to 70 degrees north. Additional information regarding the structural geology of <br />the area will be provided below in Section 2.1.3. <br />The oldest rock unit that crops out in the area is the Pennsylvanian Hermosa Formation. <br />The Hermosa Formation plays an important role in controlling both the structural <br />geology and the natural geochemical characteristics of the area. The Hermosa <br />Formation includes a lower member composed of rock salt called the Paradox <br />Member, which is overlain by an upper member composed of limestone. The rock salt <br />is composed of 70 to 80 percent halite (NaCl) , potash salts such as sylvite (KCl), and <br />gypsum (Weir et al 1983, Cater 1955). The Paradox Member consists of intrusive salt <br />and gypsum, which has been tectonically emplaced to thicknesses of up to 10,800 feet. <br />The upper limestone member is a fossiliferous thick-bedded limestone, which is <br />estimated to be 2,000 to 3,000 feet thick. <br />Outcrops of the Paradox Member of the Hermosa Formation consist of cellular and <br />earthy textured gypsum, but the formation contains over 50% rock salt where <br />penetrated by drill holes in the sub-surface. This suggests that rock salt originally <br />present in the exposed portions of the formation has dissolved. This unit crops out in <br />the western portion of Big Gypsum Valley, where an ecosystem supporting salt- <br />tolerant plants is present (BLM 2008). The salt of the Paradox Member of the Hermosa <br />Formation is present in several areas of the Dolores River Basin, and contributes to <br />naturally elevated total dissolved solids content in the Dolores River (Chafin 2002). <br />A thick sequence of clastic sedimentary rocks containing various portions of <br />sandstone, siltstone, shale, conglomerate and local limestone overlies the Hermosa <br />Formation. These rock units range in age from Triassic to Cretaceous. This sequence <br />of clastic sedimentary rocks is important both with regard to the hydrogeologic <br />framework of the area and the occurrence of uranium-vanadium mineralization. This <br />sequence includes the following formations: <br />¦ Permian Cutler Formation; <br />¦ Upper Triassic Chinle Formation; <br />¦ Jurassic Glen Canyon Group; <br />¦ Mid to Upper Jurassic San Rafael Group; <br />¦ Upper Jurassic Morrison Formation; <br />¦ Lower Cretaceous Burro Canyon Formation; <br />¦ Cretaceous Dakota Sandstone; <br />w <br />cm 2-2 <br />T964986-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Report\fnal sunday hydro reporNextTINAL Sunday Hydrogeology Report.doc