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1.1.2 Regulatory Framework <br />• This electron microprobe analysis is a part of a larger program to address state mine <br />permitting requirements related to potential designated mining operation status and <br />preparation of an environmental protection plan for the mine. One facet of this process <br />relates to identifying any "acid- or toxic-forming materials" at the mine sites. The overall <br />program is addressed in Evaluation of Environmental Geochemistry of the Sunday Group <br />Mines (CDM 2009a) and Evaluation of Environmental Geochemistry of the Van 4 Mines <br />(CDM 2009b). This report describes one facet of the overall geochemical characterization <br />program. <br />Evaluation of the potential for ore or development rock to be toxic-forming included <br />sampling of the ore stockpiles and development rock areas, analysis of these samples for <br />total metals, and screening of the total metals data in relation to appropriate toxicity <br />screening criteria. This process is designed to evaluate potential toxicity of the ore and <br />development rock based on exposure pathways of incidental ingestion and inhalation. <br />The initial screening showed total concentrations of all metals to be below the screening <br />criteria with the exception of arsenic. Therefore a second phase of investigation was <br />initiated to further understand the potential toxicity of arsenic at the Sunday Group and <br />Van 4 mines. This program is designed to allow consideration of the bioavailability of <br />arsenic in the specific mineralogical forms present at the Sunday Group and Van 4 <br />Mines. This second phase includes in-vitro analysis of arsenic bioavailability and <br />electron microbe analyses to determine the specific mineralogical forms of arsenic <br />• present at the mines. <br />1.1.3 Deposit Type and Mineralogy <br />The Sunday Group and Van 4 uranium-vanadium deposits are roughly tabular deposits <br />that occur within the Salt Wash Member of the Morrison Formation. The deposits are all <br />located in a distinct calcareous sandstone unit called the Top Rim sandstone, which is <br />located in the upper portion of the Salt Wash Member. Uranium-vanadium <br />mineralization occurs in preferential beds within the Top Rim sandstone, and is visible <br />as dark colored disseminations in the sandstone units. Once ore or development rock <br />have been mined and exposed to surface oxidation, the uranium-vanadium minerals <br />oxidize and alter to other minerals that are recognized as yellow to greenish yellow <br />coatings on strongly mineralized rock. <br />Uranium in the Colorado Plateau occurs in two dominant oxidation states, U(IV) and <br />U(VI). The primary minerals in the deposits are thought to contain uranium in the less <br />oxidized U(IV) form. Primary minerals containing uranium as U(N) that have been <br />identified in Colorado Plateau uranium deposits include uraninite and coffinite. <br />Uraninite (UO2) is an oxide mineral. Coffinite (U(Si04)o.9(0H)o.4) is a hydroxyl silicate. <br />Uranium in uraninite and coffinite oxidizes as a result of exposure to oxygenated <br />environments and other factors to form a wide variety of U(VI) minerals (Garrels and <br />Christ 1956). <br />0 <br />2 <br />T:\64986-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.12 - Soil, Ore, Rock Data Assessment Report\Bioa"ilability\DenisonEMPText021709 (2).dm