2012-09-28_REVISION - M1977307 (23)

Home Browse Search

Underlying the Entrada/Carmel Formation is the Navajo Sandstone. According to Cater et al. (1955), the eastern edge of the Navajo Sandstone follows an irregular course through the western-most part of Colorado. In the Uravan quadrangle, the Navajo Sandstone is part of a large discontinuous lens that only reaches a maximum thickness of 40 feet in this area. The siliceous cemented Kayenta Formation, commonly a resistant bench - forming unit, consists of sandstones, mudstones and conglomerates that 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. 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 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. The minerals 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 formation 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 A review of well records from the Colorado State Engineers' office indicates that the UMETCO Corporation drilled numerous wells in Section 33, T48N, R17W and in the same section as the mine portal, down gradient from the CM -25 mine site. The majority O'Connor Design Group Inc. T - 10