Investigação da alteração hidrotermal por meio de técnicas de PDI e SIG, no Distrito Fluorítico de Santa Catarina (DFSC), Brasil

Abstract

Santa Catarina Fluorite District (DFSC) is the major producer of South America, and currently production has stabilized due the ore produced cost in Brazil is equal or smaller than the imported ore price. However, DFSC needs to increase reservations. The fluorite occurs in sub-vertical veins, 3 meters width by 400 meters length. The beds are controlled by faults and fractures that extend themselves for kilometers, and the hydrothermal alteration occurs in strips up to 100 meters width from the veins. The fluorite search in DFSC should be make by integration of structural data and alteration. The work objective was developing techniques to distinguish the hydrothermal alteration by application digital image processing (DIP) and Geographic Information System (GIS) techniques on TM LANDSAT 5 data. The morpho-structures were obtained by filtering TM4 band, after digitalized and classified according to azimuth intervals related to the fluorite veins. To enhance alteration feature, 3/1, 5/1 and 5/4 band ratio was employed to discriminate iron oxide and hydroxide concentrations; 5/7 for clay mineral and 1/7 for general alteration. Grayscale images not enhanced the result and than reclassification was made based on their spectral behavior. SIG techniques crossed these data with structural vectors. It generated distance map around morphostructures and were multiplied by hydrothermal alteration images. Finally, more favorable zones were delimited, based on the pixel density of alteration around 100 meters of morphostructures.