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• the pre-Cambrian crystalline rocks. This thick stratigraphic sequence to the southwest is interrupted <br />locally by salt-cored anticlines in the Paradox Basin area, basement fault-related monoclines, and <br />Tertiary/Late Cretaceous laccolith intrusions (see Figure G1). The salt anticlines are elongated in a <br />northwest direction, as is the Uncompahgre Uplift. Flowage of the salt was erratically active from <br />Permian through late Jurassic, thereby affecting deposition of the Triassic and early Jurassic sediments, <br />including the flow of the streams that deposited the Morrison Formation in which the uranium resource <br />is located. The Uncompahgre Plateau was again faulted upward in Tertiary time and deep canyon <br />cutting occurred, continuing through the Pleistocene. Some twelve miles to the southwest of the <br />Whirlwind Mine area lay the La Sal Mountains. These consist of Tertiary laccoliths intruded into <br />several different horizons of Mesozoic sedimentary rocks. <br />The uranium deposits in the Beaver Mesa Mining District occur in the late Jurassic Morrison <br />Formation. As shown on Figure G2, the Morrison Formation has two geologic members in the <br />Gateway, Colorado area. The lower member, the Salt Wash, is the main uranium host. The upper part <br />of the Morrison is the Brushy Basin Member. The Salt Wash consists of about equal amounts of fluvial <br />• sandstones and mudstones deposited by meandering river systems. The Brushy Basin was deposited <br />mostly as a large mud flat probably with many lakes and streams. Much of the material deposited to <br />form the Brushy Basin originated from volcanic activity to the west. The majority of the uranium <br />production has come from the upper sandstones of the Salt Wash Member known as the Top Rim. In <br />addition to uranium, many of the deposits contain considerable amounts of vanadium. The primary <br />uranium mineral is uraninite (pitchblende) (UOZ) with minor amounts of coffinite (U Si04 OH). <br />Montroseite (VO OH) is the primary vanadium mineral, along with vanadium clays and hydromica. <br />4. Site Geology <br />Map G-2 shows the outcrop geology of the area around the Whirlwind and Packrat mines. The <br />structural contours on this map show the base of the Summerville Formation, immediately below the <br />Salt Wash. Also shown on this map are major faults, workings of the old mines, the extent of the <br />Whirlwind decline, and the wells and springs in the area. <br />• <br />Whirlwind Mine 07 (rev. April 08) G-3 <br />