Mineral indices from principal component analysis of Geoscan AMSS data; an example from the Chanarcillo Skarn District, Chile

Relationships between mineral deposits in the Chanarcillo district are not well understood. Ag (Chanarcillo veins), Fe-Cu-Au (Anamar) and Fe (Bandurrias) mineralization is hosted in Upper Jurassic-Lower Cretaceous volcanics and sediments that are intruded by Lower Cretaceous granites. Skarn occurs in association with the granite but has not been previously considered to be related to mineralization. Geoscan AMSS MkII data were used to produce interpretive geological and mineral alteration maps with the aim of elucidating the metallogeny of the district and developing a useful regional exploration tool for the identification of skarn. The date were processed using simple band difference algorithms and principal component analyses to generate indices for skarn minerals. Thermal infrared bands were used to create indices for silica and garnet and indicated now areas of hitherto unmapped garnet rich rock, interpreted as skarn. The skarn, as mapped from the Geoscan date and subsequently verified by field checking, is spatially associated with all known mineralization in the area. In areas interpreted as skarn and in the different ore deposits, garnet was seen to be intergrown with magnetite, galena, sphalerite, and copper oxides in varying proportions, suggesting a genetic relationship between the different ore deposits in the district and skarn forming hydrothermal processes. The potential of Geoscan thermal date as a tool for the identification of skarn related mineral deposits in regional mineral exploration programs is well demonstrated.