Metalogenia em terrenos de alto grau: Contexto geológico e propostas para o modelo de geração das mineralizações sulfetadas de Rio Claro, RJ

Abstract

The region of Rio Claro has been the target of economic studies since the 30 s, when there was were the discovery of the occurrences of pyrite in the area. Mineral exploration conducted by Riofinex in the mid 70 s, determined bodies of sulfides of zinc-lead, however of subeconomic character. The proposed model for the Rio Claro deposits corresponded to the Mississippi Valley type of higher grade metamorphic (RIOFINEX, 1977). In academic terms, two dissertations were carried out in the area, with the first one with a focus on the sulphide deposits (CHAVES, 1987), and the other focusing on geological mapping of the region (DIOS, 1995). However, it was found that for a better characterization of the type of sulphide mineralization is necessary to discuss the depositional environment of host rocks. For this, was characterized in detail of rock types by geological mapping of the region 1:50,000, and the stratigraphic relationship between them. The field campaign developed at the start of this work showed the base map prepared by the company Riofinex as the proposed goal. However, from the ten geological units defined by Riofinex, it was decided to detail only the the Valadão, San Roque and Lídice units, the latter hosting the mineralization, by considering that they would express the paleogeography of depositional basin. The rocks present in the Valadão unit besides different types of quartzites are also comprised thin layers of stratiform magnetite quartzite, interpreted as ironstone or metamorphosed banded iron formations. This unit was considered to be associated with turbiditic processes. The São Roque unit is mainly composed by metapelitic rock types which exhibit sedimentation characteristics of deeper environment with possible exhalative influence, probably related to formation of thick bundles of pellites deposited at the foot of slope paleotopography. The Lídice unit comprises metapsamitic and metapelitic rocks, whose most important lithotype corresponds to carbonate quartzite,which hosts the sulfide mineralization. This unit was interpreted as having been deposited in shallow platform with influence from tide variations. The proposal is that the host rock of the mineralization is part of a sabkha environment