干旱区生态环境知识资源中心

Data integration and analyses within a geographic information system ( GIS) can improve exploration and detection of mineral deposits. We applied a GIS-based analysis and classification strategy of satellite data to the rich and well-explored Eocene-Oligocene porphyry copper province of northern Chile, attempting to recognize the distinctive signature of such giant ore deposits. Image-based favorability mapping is a supplementary exploration tool and is only applicable to exposed deposits. Additionally, favorability mapping can be used in conjunction with geophysical and geochemical data to improve exploration for buried deposits.

The study area covers part of the Central Andean Precordillera with world-class porphyry copper deposits. La Escondida mining district was selected as a training site, because Landsat satellite images are available for pre- and synmining times. Analyses of geological, structural, and optimized remotely sensed data of this mining area can help to identify some common characteristics of altered rocks and associated porphyry copper ores. To the already known geological and structural setting, optimized Landsat Thematic Mapper ( TM) and Landsat Enhanced Thematic Mapper ( ETM) data, transformed by principal component analysis, inverse principal component analysis, band "ratioing," and spectral mapping of magmatic host rocks, show typical rock alterations for the training sites at La Escondida mining district, Quebrada Blanca mining district, and other areas. These optimized data provide important surface indicators for detection and visualization of altered rocks and mineralization.

Optimized images are classified to separate target areas of altered rocks from nontarget areas without alteration. The resulting classifications of all image transformations are combined numerically in a favorability map, which shows the spatial distribution of target areas related to hydrothermally altered rocks. This approach, in combination with geological field work, provides a new impetus for exploration strategies and localization of hydrothermally altered rocks with related mineralization. On the basis of these results, mineral exploration can be improved by the use of optimized and classified satellite data in other, less examined copper provinces of similar arid-semiarid climatic conditions throughout the world.