Application of per-pixel and sub-pixel unmixing methods on ASTER images to map hydrothermal alterations in a highly metamorphosed terrain: a case of the Musina copper deposit field

This study focuses on mapping hydrothermal alterations in Musina Copper Deposit Field which is characterized by unique concentric zonation of hydrothermal alterations from an outer zone of sericitization (phyllic) followed by inward zones of chloritization and epidotization (propylitic). Per-pixel and mixture tuned matched filtering (MTMF) sub-pixel unmixing methods were applied on ASTER data to map hydrothermal alterations. False colour composite (FCC) generated from combination of propylitic, phyllic and host rock index was effective in delineating alteration zones. The spatial distribution of alteration group minerals: chlorite–epidote and sericite–muscovite from MTMF classification correspond with their associated alteration zones. Correlation coefficient (R2) was utilized to assess accuracy of the results by comparing MF scores of alteration minerals with copper concentrations. R2 was 0.78 for chlorite–epidote and 0.69 for sericite– muscovite. Copper concentration levels increase towards chlorite–epidote region which represents the inward propylitic zone. Following the geometry and alteration zonation, follow-up targets were generated.