Prospecção de Zinco e Chumbo na região de Lídice (RJ): uma campanha geoquímico-geofísica na reavaliação de horizonte mineralizado

• Autor(a) principal: Ferreira, Laís de Oliveira
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/19820
• topic: Pb-Zn; Prospecção geoquímica; Sedimento de corrente; Magnetometria; Gamaespectrometria; Geochemical prospecting; Stream sediment; Magnetometry; Gamma-ray spectrometry; CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIA

The Rio Claro region is located in the southwest of Rio de Janeiro State and comprises the Neoproterozoic metasedimentary succession of the Raposo Group of the Ribeira Belt. In the 70's, an exploration campaign was carried out in the region by Riofinex company aiming for the exploration of Zn-Pb. The mineralization was characterized as sedimentary syngenetic enclosed under intercalation of carbonate lithotypes, in the subsurface, and represented by the subunit Lídice III. The researches carried out by Riofinex resulted in average contents of 2.0% Zn, 0.3% Pb and 50 ppm Ag, which, associated with the low thickness and lack of continuity of the mineralized layers, contributed to the negative evaluation of the prospect by the company. The measured and indicated reserves were 1,600t (with 950t Zn) and 9,200t (5,500t of Zn), respectively. The possibility of a longitudinal continuity of the mineralized horizon is the aim of this research. The Lídice III subunit, with thickness of approximately 500 m, comprises impure quartzites, carbonate quartzites, and calcissilicatic rocks. The carbonate quartzite is the host lithotype of the sulfide mineralization. Mineralization control is apparently lithological, and the main ore minerals are sphalerite, pyrrhotite, pyrite, and galena. This work has utilized the techniques of geophysical prospecting (magnetometry and gamma-ray spectrometry) and geochemistry (stream sediment). Three geophysical sections were carried out, transversal to the mineralized layer, following three main drainages: Ribeirão das Várzeas, the streams of Canoas and Passa Dezoito. The samples of stream sediment, collected in first and second order drainages in the fraction of less than 80 mesh, were analyzed in 63 chemical elements through the analytical method ICP-MS (Inductively Coupled Plasma Techniques) and ICP-OES (Inductively Coupled Plasma Emission Spectroscopy) with aqua regia digestion in Actlabs (Canada). The analysis of the magnetometric data observed in the three sections indicates an increase in the average values in the Lídice III Unit justified by the presence of magnetite in the quartzites of the region. Such increase may be associated with the greater apparent thickness of this layer, a fact that was observed during the field activities. The mineralized layer exhibited a stable pattern (few spikes in magnetometric profiles), suggesting that the Lídice III subunit projects to the northeast along the Ribeirão das Várzeas. The gamma-spectrometric acquisitions and the stacked profiles of the radioelements eU, eTh and K, together with the eTh/eU, eTh/K and eU/K ratios, allowed to draw contacts among metasedimentary subunits, as well as to delimit intrusive bodies (pegmatite, dikes, gabbros and quartz veins) in the study region. The stream sediments campaign identified anomalous domains of Ba, Hg, and Mo, observed in the sections transversal to the continuity of the mineralized horizon. Therefore, the prospective campaign integrating geochemical, geophysical and lithological data showed that the region is promising for the research since there is the possibility of an extension to the east (towards the locality of São João Marcos) of the horizon enriched in zinc and lead.