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Diagenetic mineral assemblages within the Wingate formation are closely associated with hydrocarbon production at Lisbon Valley, Utah. The Wingate formation, exposed along the southwestern flank of the anticline, has a relatively uniform composition and appearance over the entire Colorado Plateau, except at isolated localities such as Lisbon Valley, where it is locally bleached. Previous workers have suggested that hydrocarbon microseepage may account for bleaching of the Wingate Sandstone and the presence of uranium mineralization in outcrops overlying the reservoir at Lisbon Valley. Using broad-band, Landsat Multispectral Scanner (MSS) and airborne Thematic Mapper Simulator (TMS) data, the bleached facies was mapped on the basis of brightness and lack of ferric iron. Ex mination of the TMS data provided further discrimination of bleached facies because relative abundances of clay minerals are detectable with this sensor.
Analysis of high-resolution airborne spectroradiometric data, thin sections, and x-ray diffraction suggests that the bleached rocks overlying the reservoir at Lisbon Valley contain abundant kaolinite and minor amounts of feldspar. Unbleached exposures contain substantially less clay and abundant feldspar.
This study shows a correlation between the abundance of clay minerals, particularly kaolinite, and hydrocarbon production at Lisbon Valley. Because one of the principal differences between the bleached and
unbleached rocks is in the relative abundance of clay minerals (and the TMS is very sensitive to clays), areas of potential hydrocarbon-induced diagenetic alteration may be mapped using broad-bank sensors.
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