Mapping geology associated with manganese mineralisation using spectral sensing techniques at Woodie Woodie, East Pilbara

Abstract

Mineralogical and geological maps are now possible through a new generation of airborne and satellite systems including the 126-band airborne HyMap and 14-band satellite-borne ASTER imaging sensors. Data from both these imaging technologies were tested for their ability to map geological host rock and mineralogies associated with the Woodie Woodie manganese (Mn) mineral deposits. A detailed study was conducted over the deposits using processed ASTER and HyMap data in conjunction with field and laboratory data. In addition, processed ASTER products were also generated for other prospective mineralised terrains over a larger area within the surrounding Bangemall Basin. Seamless maps were generated in this study from ASTER and HyMap imagery to represent surface abundances of either mineral groups or specific mineral identities. The ASTER imagery, at 15 to 90 m resolution, enabled the generation of maps designed to represent the abundance of broad mineral groups, including MgOH/carbonate, quartz/silica, ferric, and ferrous iron (within silicate or carbonate). However, the accuracy of these products was observed to be limited, mainly by the broad spectral resolution of the ASTER bands. Narrower spectral bands are generally required to discriminate and map specific minerals, and separate the effects of vegetation and the atmosphere. In contrast, 5 metre resolution HyMap data demonstrated accurate mapping of abundances of minerals such as ferric iron and dolomite/calcite, as well as dry and green vegetation. Image products representing ferrous-rich carbonate units and opaques (including manganese) were also generated. The results of this study showed that the best products for mapping the Carawine Dolomite and Pinjian Chert Breccia units hosting the Mn mineralisation are obtained by using HyMap data and included: carbonate abundance; ferrous iron content within carbonate units; and ferric iron abundance. The ASTER quartz map product also proved useful to identify silicified dolomite. The geological interpretation of these mineral maps was aided by the comparison and integration with digital elevation model (DEM) and Thorium information from detailed airborne radiometric surveying.