Extraction of Mineral Alteration Zone from ETM+ Data in Northwestern Yunnan, China

Alteration is regarded as significant information for mineral exploration. In this study, ETM+ remote sensing data are used for recognizing and extracting alteration zones in northwestern Yunnan, China. The principal component analysis (PCA) of ETM+ bands 1, 4, 5, and 7 was employed for OH⁻ alteration extractions. The PCA of ETM+ bands 1, 3, 4, and 5 was used for extracting Fe²⁺ (Fe³⁺) alterations. Interfering factors, such as vegetation, snow, and shadows, were masked. Alteration components were defined in the principal components (PCs) by the contributions of their diagnostic spectral bands. The zones of alteration identified from remote sensing were analyzed in detail along with geological surveys and field verification. The results show that the OH⁻ alteration is a main indicator of K-feldspar, phyllic, and prophilized alterations. These alterations are closely related to porphyry copper deposits. The Fe²⁺ (Fe³⁺) alteration indicates pyritization, which is mainly related to hydrothermal or skarn type polymetallic deposits.