GEOPHYSICAL SURVEY OF GOSSANS IN THE EASTERN UINTA MOUNTAINS, UTAH

When sulfide-bearing rocks are exposed to oxidizing conditions, they become destabilized, leaving behind a framework of leached, altered, and replaced host rock called a gossan. Many of these gossans form by the oxidation of ore minerals and have been known since antiquity to be associated with ore deposits. However, the extent and quality of ore mineralization beneath a given gossan cannot readily be determined through surface sampling of minerals. Work conducted by mineral exploration professionals (in Africa, Australia, India, and the Middle East) has indicated that geomagnetic and geoelectric surveys of a gossan can be useful for constraining the shape, size, and economic potential of an associated ore deposit. Although gossans are found in Utah, there have been no published studies of these rock units either in terms of their economic potential or geophysical signature. The objective of this study is to carry out geomagnetic and geoelectric surveys to determine the geophysical signature of gossans exposed about 10 miles northwest of Vernal, Utah, on the southeastern margin of the Uinta Mountains, for the purpose of estimating the grade and depth of possible sulfide mineralization. The gossans overlie a heavily brecciated wedge of Mississippian Madison Limestone and are structurally bounded by the South Flank Fault, which forms the boundary between the Permian Weber Sandstone to the south and the Neoproterozoic Uinta Mountain Group metaquartzites to the north. Surveys of the Earth’s total magnetic field are being carried out using the Geometrics G-856 Proton Precession Magnetometer. Magnetic susceptibilities of exposed rocks are being measured in the field using the SM-20 Magnetic Susceptibility Meter and in the lab using the Bartington MS3 Magnetic Susceptibility Meter. The magnetic susceptibility measurements are being used to constrain magnetic models, which are being carried out using the Interpex IX2D-GM Magnetic Interpretation Software. Geoelectric soundings and profilings are being carried out with the Iris Instruments Syscal Junior Resistivity System, which measures electrical resistivity, chargeability (induced polarization) and spontaneous potential. The geoelectric data are being inverted using the Interpex IX1D Sounding Inversion Software. Results will be reported at the meeting.