The Bunce Prospect in the Velvet Mining District encompasses several square
kilometers of altered volcanic rocks that host epithermal gold mineralization. Extensive
argillic alteration and large volumes of chalcedonic and opaline silica, documented
in outcrop and drilling samples, represent the shallow levels of one or more
epithermal gold systems. The argillic assemblage includes kaolinite, illite, and mixedlayer
clays known as kaosmectite, associated with alunite and jarosite. Drilling, conducted
by various groups over two decades, has defined several small zones of shallow
gold mineralization, with assays up to 27 g/T over short intervals. Complex intersections
of NE and NW fracture zones control the distribution of alteration within a NStrending
Miocene rift system of regional scale. Mineralization occurs in a restricted
part of a widespread sequence of felsic flows, tuffs, and epiclastic sedimentary rocks
that lie beneath a post-mineral cover of Late Miocene to Quaternary mudflows, fanglomerates,
lacustrine sediments, and basalt flows.
Exploration is guided in part by Landsat Thematic Mapper (TM) alteration
using clay and iron oxide to define zones of hypogene alteration. ASTER satellite data
are processed to help define the higher temperature zones within the broad hypogene
argillic (kaosmectite) assemblage defined by Landsat TM. SpecTIR hyperspectral
airborne remote sensing data are being processed for specific mineral species. These
data, integrated with field mapping, surface geochemistry, field spectroscopy, and
geophysics support the development of exploration targets.
Exploration targets will include feeder zones delineated by higher temperature
mineral assemblages within the broad halo of high level, low temperature argillic
alteration. The combination of TM, ASTER, and SpecTIR remote sensing data offer
nominally 30 m, 15 m, and 2 m pixel data with a concomitant increase in spectral resolution.
These data offer a rare comparison of standard remote sensing data that will
be rigorously tested in the exploration environment.