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The purpose of this study is to describe the geology of the uranium deposits of the Cameron area, Arizona, and to establish geologic criteria which would serve as guides in exploration. The Cameron area is approximately fifty miles north of Flagstaff, Arizona, and is composed of a belt of east-dipping Triassic sediments which lie on the southwest flank of the Black Mesa Basin. Uranium deposits occur in the Chinle formation and the Shinarump conglomerate. Mineralization, found in small amounts In the upper parts of the Shinarump conglomerate, is of less economic importance than that which occurs in the Chinle. Production from the Chinle formation has come from nineteen deposits of two types: (a) bedded or lens deposits, (b) mineralized fossil trees. Bedded or lens deposits occur in the lower sixty feet of the "C" division of the Chinle formation within elongate lenses representing scour filling. Lens sediments are crossstratified, highly carbonaceous mudstones and argillaceous sandstones. Mudstones within a lens contain montmorillonite, kaolinite and illite-type clays. Colors range from black to yellow in contrast to the grays of the surrounding clays. The lenses usually possess a halo, which varies in thickness from a few inches to several feet of bleached country rock. Mineralized fossil trees are sporadically distributed throughout the "C" division and usually consist of individual logs, partly silicified, uranium-bearing, which often cap hummocks of clay. Detailed mapping of the Huskon Number 1 deposit indicates the ore-bearing lens attains a thickness of forty feet and a width of five hundred feet. Joints within the lens have no apparent relationship to ore. The richest ore is closely associated with carbonaceous material. Chemical analyses indicate the element molybdenum is more abundant in ore-bearing lenses and can be used to differentiate between barren and mineralized lenses. Vanadium, present in small amounts, shows no significant distribution pattern in the area. The ore bodies are almost completely oxidized and possess a large assemblage of gangue minerals, some of which are quartz, montmorillonite, kaolinite, gypsum, limonite, jarosite, pyrite, and cobaltian wad. The principal ore minerals are uraninite, uranophane, torbernite, metatorbernite, meta-autunite, schrockingerite and zippeite. The following features are presented as useful criteria for exploration of uranium deposits in the Cameron area. Stratigraphic position The favorable interval is the lower sixty feet of the tTC" division of the Chinle formation. Sandy lenses Sandy lenses which occur within the lower sixty feet of the "C" division generally possess anomalous radioactivity. Carbonaceous material Radioactivity is found almost always where carbonaceous debris is encountered. Color Light yellows, buff and rust colors are favorable. Molybdenum Molybdenum, present in trace amounts, is more abundant in and around ore-bearing lenses. |
