Mapping known and potential mineral occurrences and host rocks in the Bonnifield Mining District using minimal cloud- and snow-cover ASTER data: Chapter E in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and

On July 8, 2003, the Advanced Spaceborne Thermal
Emission and Reflection Radiometer (ASTER) sensor
acquired satellite imagery of a 60-kilometer-wide swath
covering a portion of the Bonnifield mining district within
the southernmost part of the Tintina Gold Province, Alaska,
under unusually favorable conditions of minimal cloud and
snow cover. Although rocks from more than eight different
lithotectonic terranes are exposed within the extended swath of
data, we focus on volcanogenic massive sulfides (VMS) and
porphyry deposits within the Yukon-Tanana terrane (YTT),
the largest Mesozoic accretionary terrane exposed between the
Denali fault system to the south of Fairbanks and the Tintina
fault system to the north of Fairbanks.
Comparison of thermal-infrared region (TIR)
decorrelation stretch data to available geologic maps indicates
that rocks from the YTT contain a wide range of rock types
ranging in composition from mafic metavolcanic rocks to
felsic rock types such as metarhyolites, pelitic schists, and
quartzites. The nine-band ASTER visible-near-infrared
region--short-wave infrared region (VNIR-SWIR) reflectance
data and spectral matched-filter processing were used to map
hydrothermal alteration patterns associated with VMS and
porphyry deposit types. In particular, smectite, kaolinite,
opaline silica, jarosite and (or) other ferric iron minerals
defined narrow (less than 250-meter diameter) 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 been obscured by
vegetation or snow cover or were too small to be resolved.