Mine site mapping with hyperspectral imagery

Mine site mapping has been carried out at the Peak Hill and Copper Hill sites in New South Wales. At Peak Hill the lithology and alteration styles have been mapped within an active pit and its immediate surrounds. At Copper Hill the local geology has been mapped around an abandoned mine site and the poorly outcropping region that surrounds the mine. Image processing and analysis was performed using ENVI software. Data was calibrated using the Empirical Line method. The calibrated data was then spectrally and spatially compressed using the Minimum Noise Fraction and Pixel Purity Index techniques. Spectrally distinct pixel groups representing the image endmembers and their spectral signatures were extracted using the n-Dimensional Visualiser. Early results from Peak Hill show that image derived mineral alteration species coincide with those mapped by the mine geologists. They include the pyrophyllitic, sericitic, alunitic, kaosmectitic, hematitic, goethitic and jarosite endmembers. Mineral endmember spectra exhibit good agreement with the field-spectra and corresponding library mono-mineral equivalents. At Copper Hill field spectrometery confirms the existence of distinctive phases of altered dacite porphyry showing sericitic, argillic (kaolinitic), chloritic and carbonate alteration. HyMap has been able to accurately map the weathered rocks and soils at the ground surface. Sericitic and argillic alteration has been mapped in scattered outcrops. Illite and mica formed by igneous processes is differentiated from normal soil-forming illites. Weathering sequences of sericitic mica to illite and kaolinite to halloysite are recognized. The similarity between carbonate spectral signatures and those of chloritic rocks inhibits the reliable mapping of chloritic rocks where carbonates are also present. Mineral abundance maps are integrated with other data sets in a GIS and the complement field mapping.