Gamaespectrometriaaplicada à prospecção de fosfatos lateríticos na Região do Gurupi –NE do Pará e NW do Maranhão

Abstract

The growing demand for food due to increasing population growth and the poor quality of Brazil soil hasaccelerated the search for new occurrences of phosphorus. Also, the feasibility of research projects on existing areas since phosphorus is an essential element in the production of fertilizers. The occurrences ofaluminous phosphates in the NE region of Pará and NW of Maranhão have been known since the beginning of the 20th century when they were considered as guano deposits. Since then several authors have presented results on the mineralogy, geochemistry, and genesis of these occurrences, defining them aslateritized metassedimentary mineralization. Ground and airborne gamma-ray data analysis aim to evaluate how radioelements behave on the mineralized bodies in aluminous phosphates, and in most cases, phosphate minerals have traces of uranium in their structure. The ground survey was carried out in the Sapucaia and Serrote depots, with the RS-230BGO device, the airborne geophysical used corresponds to the Gurupi airborne geophysical survey, with a spacing of 500 meters between the flight lines and 10,000 meters between the control lines, with height flight set at 100 meters. The ground data processing showed a positive correlation with the airborne surveys in the Sapucaia and Serrote deposits, being the mineralizedbody delimited by the ground gamma spectrometric method. The occurrence of phosphate laterite known throughout NE of Pará and NW of Maranhão included in the airborne geophysical survey have well-defined contours in the eU, eTh, total and ternary image channels. The ferruginous laterites, with significant occurrence in the region, have a geophysical signature that is almost coincident with the phosphate laterites, presenting differences only in the absolute values of eU and total count, besides presenting the same geomorphological context. The delimitation of the known phosphate laterite occurrences through the detailed airborne survey can contribute with correlations about the mineralogy of the superficial horizons of the phosphate laterites. Gamma-ray spectrometry (ground or airborne) demonstrated for other phosphate occurrences in Brazil, discriminates the laterite bodies enriched in aluminum phosphates, being an indirect method that can contribute to the exploration of phosphate laterites in the NE of Pará and NW of Maranhão.