Test area; color anomalous hydrothermal alteration associated with stockwork molybdenum mineralization. Tertiary Malmbjerg molybdenum occurrence. Interactive digital image processing system combined with computerized color plots. Special ratio and factor analysis techniques. The best results with ratio techniques are obtained when band 4/band 5 is displayed as cyan (red), band 5/band 7 as magenta (green), and band 6/band 7 as yellow (blue). A characteristic pink to orange color corresponds to areas of limonitic rocks. Using factor analysis, color composites displaying F2 as magenta (green), F3 as cyan (red), and F4 as yellow (blue) with a visually determined color stretch discriminates very effectively with yellow-orange to red-orange colors representing limonitic rocks. More than 50 significant rust zones located. Ratio and factor analysis techniques were applied to reconnaissance mapping of Precambrian metamorphic and Devonian volcanic terrains covering more than 30,000 km 2 of ice-free area in a province of 500 km long by 300 km wide, resulting in the localization of 38 major (surface area > 0.5 km 2 ) rust zones in Precambrian metamorphic terrain.--Modified journal abstract.