Hyperspectral image analysis for mineral exploration in Pulang, Yunnan province, China

Recent mineral exploration in Yunnan Province, China has revealed a promising alteration zone characterised by predominantly copper, gold and lead minerals in the Pulang area. This high altitude mountainous area is difficult to access and the ability to map the mineralization using remote sensing technology is thus of great interest. The launch of the first spaceborne hyperspectral instrument, Hyperion, in 2000 has provoked further research into its capabilities with regards to mineral exploration. A Hyperion scene covering the Pulang area in north west Yunnan Province, was complemented by Landsat and ASTER scenes in an attempt to highlight the advantage of using this hyperspectral dataset despite its limited application thus far for detailed mineralogical mapping. Whilst also suggesting a suitable methodology using standard image processing techniques for this area of limited geological information.
A two-step progressive approach was employed to firstly locate target areas of high potential of mineralization using broad band imagery and then detailed mineral mapping was attempted using Hyperion data. The assessment of regional geology base on Landsat-7 ETM and ASTER image visualization using colour composites, band ratios and principal components analysis led to the detection of two areas of interest, one to the north (~28° 11 20.86N, 100° 4 55.39E) and one to the south (~28° 3 47.25N, 99° 59 31.46E) of the scene. ASTER provided a detailed spectral analysis of these areas and suggested ferric and argillic minerals in what appears to be areas of weak alteration. This enabled a more focused hyperspectral analysis on the Hyperion data of the two target areas using Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) for mineral mapping. Typical hydrothermal minerals correlating with some of the minerals located at the nearby Pulang deposit were identified using these two techniques, including kaolinite and muscovite in addition to jarosite, goethite and limonite. The mineral assemblage found indicates a low temperature alteration event. Between the two techniques used, the MTMF with an appropriate feasibility value is able to distinguish subtle differences in spectra for more accurate mineral mapping and its results suggest that the extent of alteration in the two target areas is small.
Despite some uncertainties in the minerals derived, the results exceeded expectations in terms of quality. The study demonstrates Hyperion’s ability to map specific minerals as a significant advantage over the broad band imagery. The broad band and hyper-spectral combined approach used is feasible and advantageous for mineral exploration in remote areas where primary information is limited or unavailable.