REMOTE SENSING EVALUATION OF ELEMENT DISPERSION CHARACTERISTICS OF PORPHYRY COPPER DEPOSITS IN THE SILVER BELL MOUNTAINS, ARIZONA

Porphyry copper deposits in southeastern Arizona belong to a cluster of 36 mineralized centers covering a region extending from northern Mexico to western New Mexico and southern Arizona. Presently, some of these deposits are being actively mined and the rest are prospects or abandoned mining sites. As a result of the large number of porphyry copper deposits in this region, research on the interaction between mineralized centers and the environment is important, in particular, the dispersion characteristics of acid-generating-metals-enriched materials at the shallow alluvial (surficial) margins of these centers. The present research uses remote sensing techniques to evaluate element concentrations around porphyry copper deposits in the Silver Bell Mountains, Pima County, Arizona. Hyperspectral images obtained by the Airborne Visible Infrared Spectrometer (AVIRIS) are used to map supergene minerals by analyzing their spectral profiles in the visible and short wave infrared region of the electromagnetic spectrum. Reflectance profiles are characteristic for each mineral and shifts in absorption features within one mineral composition are result of differences in cation content. Image reflectance profiles are compared to stream sediment mineral assemblage and reflectance spectral profiles to better outline concentrations of Fe, S, K, Na, Ca, Mg, Cu, and Al. In addition, groundwater modeling in the Silver Bell Mountains is considered for various flow paths within shallow aquifers in the region and compared to actual groundwater chemistry and surface lithology. The broad areal distribution of dissolved sulfate stands in contrast to the aerially restricted, low pH, anomalous dissolved metal concentration patterns, and viewed in light of buffering reactions with the regional aquifer suggest limited metal dispersion potential. The Silver Bell Mountains serve as a case study for element mobility and concentration distribution in other areas where natural deposits, historic and present-day excavation activity occurs where semi-arid climate and deep vadose zone are variables that influence element mobility and concentration.