Airborne hyperspectral mineral mapping in regolith and variably weathered high-grade metamorphic sequences of the mineralized West Pinnacles area, Broken Hill, Australia

The Palaeoproterozoic high-grade metamorphic Broken Hill Block, New South
Wales (NSW), Australia, is host to the world-class Broken Hill Pb-Zn-Ag orebody. To
assist mineral exploration in the Block, the NSW Department of Mineral Resources
commissioned a 4,000 km² HyMap airborne hyperspectral survey in 2002 to provide
industry with data capable of mapping the spectrally identifiable surface mineralogy.
This paper reports on an evaluation of five HyMap flight-lines at 3 m spatial resolution,
covering 48 km² of mixed outcrop and regolith in the West Pinnacles area, 15 km
southwest of the Broken Hill orebody. A new ‘multi MNF adapted ENVI-Hourglass’
method was used to process the multiple HyMap flight-lines. Thirteen minerals were
identified from the processing and analysis of the airborne data and their distribution
and relative abundance were mapped in the regolith and in outcrop.
Mineral map products generated from the HyMap data proved potentially useful
for mineral exploration in several ways. Many bedrock units were able to be delineated,
including retrograde shear zones. The prospective garnet- and gahnite-bearing
rock units were not uniquely identified, possibly due to surface weathering and/or
small outcrop size, however, detrital garnets in stream sediments were identified. Ferich
facies within prospective lithological units were detected and mark potential sites
of concealed mineralization. Regolith mineral distribution, relative mineral abundance,
provenance, and dispersion pathways were revealed for the first time. In situ
and transported regolith were distinguished based predominantly on the spectrally
determined kaolin crystallinity index. Potential sampling media for geochemical analysis
were mapped, including goethitic lag for Pb-Zn exploration and pedogenic calcrete
(calcite) for Au exploration.