Combined electric, electromagnetic and gamma spectrometric methods applied to the Pariquera-Açu alkaline complex

Abstract

The Pariquera-Açu Alkaline Complex, located in the city of Pariquera-Açu (State of São Paulo), is one of the Brazilian alkaline complexes which has considerable mining potential. The combined use of several methods helped to determine possible areas for exploration. Geophysical prospecting methods were used to assess the exploration potential of these areas. The methods used in this study were gamma-spectrometry, induced polarization and electrical survey. Previous geophysical studies were carried out to better understand the structural evolution of the complex and were not limited to the study of the lithological variation. Gravimetric studies showed a zone of intense fenitization, which is consistent with alkaline complexes with carbonatites. A dipole-dipole survey conducted in the central part of the complex indicated the presence in the subsurface of a resistive lithology with high chargeability. These factors, together with other studies on the alkaline complex, suggest the presence of carbonatite in the area, which is corroborated by gamma spectrometry data, given the concentrations of Th (8 ppm) and U (3.5 ppm) and considering that the measurements were performed over a non-radioactive sedimentary cover.