Prospecção de carbonatitos na Região Sul do Granito Caçapava – RS: ênfase em mapeamento geológico e química mineral para ETRs, NB E P

Abstract

Carbonatites are rocks composed of more than 50% carbonate minerals. They are relatively rare and have great economic importance due to their concentration of minerals with expressive content of rare-earth elements (REE), Nb and phosphate minerals (P2O5), which have applications in the high technology industry and fertilizers, respectively. In the region of Caçapava do Sul - RS there are 2 carbonatite complexes, known by the names of Picada dos Tocos and Passo Feio, located to the east and southeast of the granite suite called Caçapava do Sul granite. The presence of these bodies is marked by expressive gamma-ray spectrometric anomalies in the thorium equivalent channel (eTh) and by the distribution along fault structures, interpreted by magnetometry. Sets of similar geophysical anomalies are observed immediately south of the Caçapava granite in a semi-continuous zone, which may indicate the presence of carbonatite bodies. In this way, the mapping of the study areas was carried out, established according to the geophysical data, and the analysis of mineral chemistry in SEM-EDS of samples collected with the main objective of prospecting new carbonatite bodies in the region and studying their chemical concentration in REE, Nb and phosphate (P2O5).The results obtained didn’t reveal the concrete presence of carbonatite rocks, however, calcisilicate amphibolitic rocks with high biotite content, occurrence of phosphate minerals (P2O5) and minerals with REE and Nb content were observed. In addition, rocks with veins of alkaline minerals were mapped as well. Lithologies similar to these are found in the phenitized host of the CCPT and CCPF, which allowed interpreting the presence of possible zones of phenitic alteration in the amphibolites of this study and which may be related to the presence of a possible carbonatite intrusion in the subsurface.