APPLICATION OF THERMAL EMISSION SPECTROSCOPY AND REMOTE SENSING TO STUDIES OF K-METASOMATISM AND FE-CU MINERALIZATION IN THE BUCKSKIN MOUNTAINS, WESTERN AZ

Swansea, located in the Buckskin Mountains of western Arizona, is a site of intense K-metasomatism, carbonate replacement, and Fe-Cu mineralization related to Tertiary detachment faulting. Critical to our investigation of the relationship of alteration and mineralization to tectonism is accurate mapping of alteration mineralogy. The alteration mineralogy at this site is difficult to assess from field mapping alone, because many of the metasomatized rocks retain their original colors and textures despite partial or complete mineralogical replacement. In addition to more traditional analyses, such as XRD, XRF, SEM, and petrography, we applied thermal emission spectroscopy to determine the bulk mineralogy of rock samples. Thermal infrared remote sensing data from the airborne TIMS instrument are used to extrapolate the detailed spectral analyses to the whole field area.

Thermal emission spectroscopy takes advantage of vibrational absorptions present in emitted thermal radiation from minerals. For many rock types and particulate mixtures, the mineral constituent spectra add linearly, and therefore mineral abundances can be deconvolved out of whole-rock spectra. Application of this technique to rocks from Swansea indicates that Tertiary volcanics and sediments are partially to 100% replaced by secondary calcite, K-feldspar, clay, and hematite. Thermal infrared remote sensing data at 5 m/pixel can be deconvolved to map abundances of carbonate, feldspar, and clay throughout the field area. Spectral results from laboratory analyses and remote sensing analyses are consistent with mineralogical results from XRD and petrography.

Carbonate replacement is most intense within 1-5 meters above the Buckskin-Rawhide detachment fault [BRDF], but drops off rapidly in space and elsewhere occurs selectively in certain host rocks. No primary plagioclase or pyroxene remains in Tertiary basalt [K/Na ratio > 150] directly above the detachment fault, though Precambrian granitic basement rocks directly below the fault retain plagioclase [K/Na=0.1-1.2]. These early data suggest that fluid conduits along the nearly horizontal, but corrugated, BRDF are responsible for transport of the mineral-bearing fluids through permeable upper-plate rocks and above the relatively impermeable lower-plate basement rocks.