SPECTRAL DISCRIMINATION OF CONTACT METAMORPHIC ZONES AND ITS POTENTIAL FOR MINERAL EXPLORATION, PROVINCE OF SALAMANCA, SPAIN

In the mineralized contact aureole of Los Santos, Spain, contact metam orphic grade of rocks and the mineralogical composition of overlying s oils correlate systematically. From the exocontact towards the granite intrusion the proportions of kaolinite, illite and free iron in soils increase, while the proportions of chlorite and smectite decrease. La boratory reflectance spectra of soil samples demonstrate that with the increase of the proportion of kaolinite, illite, and free iron and th e decrease of chlorite, ratios of Band 2 / Band 3, Band 2 / Band 5, an d Band 2 / Band 7 decrease while ratios of Band 3/Band 4, Band 4 / Ban d 7, and Band 5 / Band 7 increase. Soil reflectance is significantly a ffected if more than 1. 5 % organic carbon is present. A procedure is presented that enables mapping of soils overlying contact metamorphic rocks in Thematic Mapper (TM) imagery, using these variations. In the TM image, pixels that correspond with kaolinitic soils are identified by elimination of other pixels during a process of stepwise masking va rious band ratio images. The first step was to eliminate the effect of vegetation and organic material, by masking high values of the ratio of [(TM5 / TM7) / (TM3 / TM4)]. The second step was to eliminate chlor itic soils by masking the ratio of TM2 / TM7. The third step was to is olate the most kaolinitic and limonitic soils using the ratio of TM3 / TM4. Finally, a maximum likelihood classification was performed on or iginal band ratio images, using the result of the masking as training set, in order to optimize the classification results.