Gold and base metal exploration project generation using Landsat TM data and spectral angle mapping for specific alteration styles in the Peruvian Andes

Exploration project generation in the Peruvian Andes typically used Landsat TM data to focus on clay-iron anomalism. This led to most first order color-alteration anomalies being under claim. However, subsequent field investigations have not led to significant discoveries and recent major discoveries have weak Landsat clay-iron anomalism. The work program described aimed to optimize the use of Landsat TM data by using geological controls to reduce the size of target areas and the volume of data to be processed allowing subtle anomalies to be recognized. The target was epithermal and porphyry style gold and base metal mineralization. Research on the time and space constraints of such mineralization in the Andes were applied to parts of Andean Peru using public domain geologic data. A regional structural fabric analysis of edge enhanced Landsat data was integrated with geologic and topographic data to generate individual target zones ranging in size from approximately 20-40 km square. Landsat TM data over these target zones were processed to generate hydroxyl (clay) and FeOx (iron) mineral indices that were evaluated according to the time-space and structural constraints of the working model. Where Landsat clay-iron anomalisin was located in unclaimed ground and in optimal sites within the structural and geological framework of the model, they were selected for spectral angle mapping to determine probable alteration styles of the mineralizing hydrothermal system. High priority targets so generated were then visited in the field. Fieldwork consistently verified the interpreted alteration style and revealed the presence of sulfide mineralization in several targets over which new mineral claims were lodged. The method was successful for both epithermal gold and porphyry copper-gold targets and proved a rapid, cost effective means of project generation which identifies more subtle yet nonetheless significant mineralized systems