2009-05-19_REVISION - M1977416 (37)

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Conductivity Conductivity logs measure the electrical conductivity of the soils or rock surrounding the borehole. They provide a detailed measure of changes in conductivity with depth. These logs can be very useful in identifying zones of increased conductivity • related to the presence of groundwater. Conductivity logs are also termed electromagnetic induction (EM) logs. The electrical conductivity of soil or rock (and its reciprocal, electrical resistivity) depends on the porosity, groundwater conductivity, degree of saturation, clay content, and other bulk soil properties. Hence it is a useful tool in determining the changes with depth of any of these properties. Resistivi Resistivity logging is a method of characterizing the rock or sediment in a borehole by measuring its electrical resistivity. Resistivity is a fundamental material property which represents how strongly a material opposes the flow of electric current. A fluid-filled borehole is required for resistivity logging; however the log is useful for detecting water levels during air-rotary drilling. SP (Self Potential) The SP log is a measurement taken by to characterize rock formation properties and is particularly useful in mapping sand/shale contacts. The log works by measuring small electric potentials (measured in millivolts) between depths in the borehole and a grounded voltage at the surface resulting from the flow of electrical current in the earth. The change in voltage through the well bore is caused by a buildup of charge on the well bore walls. Clays and shales (which are composed predominantly of clays) will generate one charge and permeable formations such as sandstone will generate an opposite one. There are many possible sources of these currents; the major source is the different salinity interfaces, such as the borehole fluid (drilling mud) and the formation water (connate water). Whether the mud contains more or less salt than the connate water will determine which way the SP curve will go. SP cannot be used for quantitative interpretation. SPR (Single Point Resistance) SPR measures the electrical resistance (ohms) between a surface electrode and electrode in the down-hole probe. Single- point-resistance logs record the electrical resistance between the borehole and an electrical ground at land surface. In general, resistance increases with grain size and decreases with borehole diameter, density of water-bearing fractures, and increasing dissolved-solids concentration of borehole fluid. A fluid-filled borehole is required for single-point-resistance logs. SPR cannot be used for quantitative interpretation but are an excellent source of lithologic information. • Deviation Deviation is a measurement made to determine the angle from which a hole drilled deviated from the vertical during drilling. There are two basic deviation survey, or drift survey, instruments: one reveals the angle of deviation only, the other indicates both the angle and direction of deviation. Natural Gamma Gamma-ray measurements detect variations in the natural radioactivity originating from changes in concentrations of the trace elements uranium (U) and thorium (Th) as well as changes in concentration of the major rock forming element potassium (K). Since the concentrations of these naturally occurring radioelements vary between different rock types, natural gamma-ray logging provides an important tool for lithologic mapping and stratigraphic correlation. For example, in sedimentary rocks, sandstones can be easily distinguished from shales due to the low potassium content of the sandstones compared to the shales. However, the greatest value of the gamma ray log in uranium exploration is determining equivalent ore grade. Drilling Results The lithology (Table 2) observed in the drill reports generally agrees with the analysis of the geophysical data. A sequence of alternating claystone, sandstones and interbedded siltstones typical of the Morrison Formation and underlying Summerville Formation and Entrada Sandstone is illustrated in Figures 2 and 3. The Morrison Formation comprises two members in this area; the lower is the Salt Wash (Jms) sandstone member and the upper is the Brushy Basin (Jmb) shale member. Ranging in thickness from 280-442 feet, the Salt Wash sandstone predominates and ranges in color from white to gray, light buff, and rusty red. Interbedded with the sandstones are red shale and mudstones. Most of the sandstone is fine- to medium-fine-grained, and massive; with single beds associated to the "Upper Rim" (host to extensive uranium and vanadium mineralization) attaining a maximum thickness of 120 feet. • The Salt Wash was deposited as a large alluvial fan sequence covering most of western Colorado and southeastern Utah. A complex system of braided and meander stream environments aggraded back and forth across the alluvial plain, OENISONOII MINES 2