ÁREAS DE RELEVANTE INTERESSE MINERAL - EVOLUÇÃO CRUSTAL E METALOGENIA DA FAIXA NOVA BRASILÂNDIA, ESTADO DE RONDÔNIA (original) (raw)

2019, PROGRAMA GEOLOGIA, MINERAÇÃO E TRANSFORMAÇÃO MINERAL

The Nova Brasilândia do Oeste region since the 1980s is well-known by the presence of gold artesanal mining and occurrences of polymetallic sulphides. The Project Crustal evolution and metalogeny of the Nova Brasilândia Belt was carried out in the southeast portion of the state of Rondônia, southwest of the Amazon Craton, covering part of the municipalities of Nova Brasilândia do Oeste Rolim de Moura, Pimenta Bueno, Alta Floresta do Oeste and São Miguel do Guaporé. Eight cartographic sheets in scale 1:100,000 cover the area. These sheets are Gabriel Maciel (SC.20-Z-C-IV), Paulo Saldanha (SC.20-Z-C-V), Rio Pardo (SC.20-Z-C-VI), Pimenta Bueno (SC.20-Z-D-IV), São Roque (SD.20-X-A-I), Colorado (SD.20-X-A-II), Arara (SD.20-X-A-III) e Roncador (SD.20-X-B-I), totaling 24,000 km². The integration of previous data with the work methodologies carried out in this project allowed the description of the lithostratigraphic units present in the area, ranging from Paleoproterozoic to Cenozoic, some proposed or redefined in this work. The identified units were: Jamari Complex, Serra da Providência Suite, Alto Alegre Suite, São Felipe Complex, Rio Branco Formation, Migrantinópolis Formation, Terra Boa Formation, Rio Pardo Suite, Costa Marques Suite, Novo Mundo Suite, Pedra Redonda Formation, Fazenda da Casa Branca Formation, Salto das Nuvens Formation, Anari Formation, Undifferentiated Sedimentary Coverage and Alluvial Deposits. Some of these units have subunits described throughout this Mineral Resource Report. The region presents three distinct deformational events, in addition to three episodes of sedimentation, indicative of alternation of orogenesis processes and crustal subsidence. The statistical analysis of the geochemical prospecting data allowed the identification of 51 univariate anomalous basins and their main anomalous correlations, some of them being of great economic value, such as ETR, Zn, Pb, Cu and Cr. Eight new mineral resources were identified and cataloged, with 4 occurrences of Zn-Pb-Cu, 1 Cu occurrence, 1 Mn trace, 1 P trace and 1 limestone mine. The most economically relevant occurrences (Zn-Pb-Cu occurrences) were mapped in detail in order to better understand geometry, structuring, host rocks and chemistry. The occurrence of Zn-Pb-Cu occurs mainly as iron (70-85% Fe2O3) with anomalous concentrations of Zn (5.8%), Pb (7711 ppm) and Cu (2355 ppm). Next to these gossans were observed rocks with more than 15% of gahnite (Zn spinel), as well as the occurrence of this mineral in the concentrates of bateia. Some of these rocks have preserved structures, which indicate that the gossans were affected by the D3 deformation, during the closing of the Nova Brasilândia basin. The occurrences of copper located in the contact between the Colorado Graben and São Felipe Complex are present in carbonates and conglomerates of the Parecis Basin and orthogneisses of the São Felipe Complex, brecciated and cemented by copper minerals (chalcocite, azurite and chrysocolla). The gold artesanal mines located near the contact of the Migrantinópolis Formation with the Rio Branco Formation, are hosted in paragneisses and schists. Within the galleries was possible to observe hydrothermal alteration, with weathered zones containing sulfur. The chemical analyzes on the rocks of the goldsmiths presented levels of up to 7531 ppb Au. The manganese evidence is hosted as a tabular layer interspersed with arcosean sandstones of the Parecis Basin. The phosphorus trace is identified in a magnetiteapatite sulfide troctolite, which occurs intruding the Costa Marques Suite, west of the project area. The chemical analyzes indicated values of 3947 ppm of P and 1.25% of Ti