GEOLOGIC MAPPING AND MINERAL RESOURCE ASSESSMENT OF THE HEALY-TALKEETNA MOUNTAINS QUADRANGLES, ALASKA USING MINIMAL CLOUD- AND SNOW-COVER ASTER DATA

On July 8, 2003, ASTER acquired imagery of a 60 km-wide swath of parts of two 1:250,000 Alaska quadrangles, during a rare time of minimal cloud- and snow-cover. A variety of rock types representing eight different lithotectonic terranes are exposed within the swath of data including: Yukon-Tanana (YTT), Pingston, McKinley, Maclaren, Nenana, Kahiltna, Wrangelia and Peninsular. These terranes include a variety of lithologies ranging from oceanic crust to island-arc and flysch sequences, accreted during Mesozoic orogenic events; to parautochthonous continental margin metasedimentary and metaigneous sequences (YTT). Most of the rocks have been regionally metamorphosed to grades ranging from prehnite-pumpellyite- to amphibolite-facies, and contain Cretaceous and Tertiary plutons. Several of these lithologic sequences define permissive tracts for various mineral deposit types such as: volcanic-hosted massive sulfides (VMS) and porphyry copper and molybdenum.

Representative rock samples from 13 different lithologic units from the YTT, plus hydrothermally altered VMS, were used to produce a spectral library spanning the VNIR-SWIR (0.4 – 2.5 mm) through the TIR (8.1 – 11.7 mm). Using the five-band ASTER TIR emissivity and decorrelation stretch data, rocks from the YTT display the greatest range and diversity of silica composition of the mapped terranes, ranging from mafic rocks to silicic quartzites. Using the nine-band ASTER VNIR-SWIR reflectance data and spectral matched-filter processing, several lithologic sequences were characterized by the presence of distinct suites of minerals that exhibit diagnostic spectral features (e.g. chlorite, epidote, amphiboles and other ferrous-iron bearing minerals); whereas other sequences were distinguished by their weathering characteristics and associated hydroxyl- and ferric-iron minerals such as illite, smectite, and hematite. Smectite, kaolinite, opaline silica, and jarosite defined narrow zonal patterns around Red Mountain and other potential VMS targets.

Using ASTER we identified some of the known mineral deposits in the region, as well as mineralogically similar targets that may represent potential undiscovered deposits. Some known deposits were not identified and may have had too much vegetation- or snow-cover, or were too small to be resolved.