2012-10-01_REVISION - M1977311 (12)

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overlie the massive Wingate Sandstone. The cliff forming Wingate consists of fine grain, well -sorted sand and is an important source of low to moderate quantities of groundwater. Red shales and mudstones of the Chinle Formation complete the geologic section in the immediate area of the mine. For a detailed description and map of the area geology refer to Figure T1. 8.2 Mineralization The name "Uravan Mineral Belt" is applied to a narrow, elongated area in southwestern Colorado in which carnotite deposits in the Morrison formation have a closer spacing, larger size, and higher grade than those in adjoining areas. The belt extends from Gateway through Uravan to Slick Rock. The deposits within the belt tend to be clustered in patches (Fischer and Hilpert, 1952). Cater et al. (1955) state that the most common ore minerals found in the region are carnotite and the micaceous vanadium minerals. The ore consists mostly of sandstone selectively impregnated and in part replaced by uranium and vanadium minerals and are also associated with thin mudstone partings, beds of mudstone pebbles, and carbonized fossil plant material. In general, the ore minerals were deposited in irregular layers that roughly follow the sandstone beds. In most deposits, the highest grade concentrations of ore minerals occur in sharply bounded structures called "rolls." Precipitation likely resulted from slight changes in the chemical composition of the solutions, perhaps in the environment of decaying organic material (Fischer and Hilpert, 1952). Factors of geology, geochemistry and arid climatic conditions have combined to form the Uravan Mineral Belt - dominantly sandstone deposits of uranium, vanadium and associated metals. These same conditions restrict the movement of these minerals into the environment. The only viable transport mechanism for the migration of these minerals from ore deposits located deep in geologic formations to possible exposure in the environment is via a groundwater pathway. 8.3 Regional Groundwater To understand possible exposure routes resulting from mining, the geology that forms the framework for the movement of groundwater needs to be understood. 8.3.1 Area Aquifers The Burro Canyon Formation in the Slick Rock area consists of isolated erosional remnants of resistant sandstone and pebble conglomerates that form highlands. Large areas of exposed sandstone along the top of the highland areas provide access for precipitation to collect in depressions and infiltrate into the bedrock. Compared to the available recharge areas along canyon walls, the Burro Canyon highlands provide a significant increase in the area available for recharge from the limited amount of precipitation. Across the Colorado Plateau, springs can occur at the contact of the Burro Canyon and shales of the underlying Brushy Basin member of the Morrison Formation where downward movement of groundwater in the sandstones and conglomerates is restricted by the low permeable shales. O'Connor Design Group Inc. T - 10