Sísmica de Refração e Eletroresistividade Aplicadas à Investigação Indireta de Depósitos Estratiformes na Chapada Diamantina

Abstract

Vertical electrical sounding and seismic refraction profiling were employed in the study of a 12 km² target area for sulfides mineralization on the northern border of the Chapada Diamantina. The work aimed at delineating in subsurface two clastic levels containing disseminated copper and lead mineralization. These levels are separated by a dolomitic horizon and, in general, are covered by meta argillite and meta-sillites, the whole sequence overlying a silicified quartzitic substratum. Eleven seismic profiles and electrical soundings were carried out along the same base lines and their results were compared with data from drill hole lithologic logs. The two clastic levels are normally characterized by low seismic velocities and electrical resistivities. Typical ranges of these properties are: 1800-330O m/s and 6O-130 Ωm for the clastics, 5OOO-550O m/s for the dolomite and 5OOO-65OO m/s for the quartzites, with the last two lithologies exhibiting, resistivity above 3OO Ωm. This strong contrast in petrophysical properties, permitted the subsurface mapping of the mineralized levels through the investigated area. New drilling locations have been selected on the basis of these results.