Bernardino Ribeiro de Figueiredo

Geology and SHRIMP U-Pb Geochronology of the Igarapé Bahia Deposit, Carajás Copper-Gold Belt, Brazil: An Archean (2.57 Ga) Example of Iron-Oxide Cu-Au-(U-REE) Mineralization

A striking feature of the Carajas region, Brazil, is the clustering of a variety of different types of Cu-Au deposits. The most abundant in the belt are the >200 million metric tons (Mt) of Fe oxide Cu-Au-(U-REE) deposits, which, despite the variety of host rocks and different orebody morphologies, share a number of diagnostic features, including (1) intense Fe metasomatism leading to the formation of grunerite, fayalite, and/or Fe oxides (magnetite and/or hematite); (2) intense carbonate alteration (mainly siderite); (3) sulfur-poor ore mineralogy (chalcopyrite and bornite); (4) quartz-deficient gangue; (5) extreme low REE enrichment, and (6) enrichment in U and Co. The Igarape Bahia deposit is perhaps the best documented Fe oxide Cu-Au-(U-REE) deposit of the belt, containing about 219 Mt at 1.4 percent Cu and 0.86 g/t Au. The Cu-Au ore consists of steeply dipping breccia bodies that are hosted by hydrothermally altered metavolcano-sedimentary rocks. SHRIMP II zircon dating of the host metavolcanic rocks gives a 207Pb/206Pb age of 2748 ± 34 Ma. This suggests a correlation between the Igarape Bahia volcano-sedimentary sequence and the Grao Para volcanic rocks, which have published ages of ca. 2.75 Ga. SHRIMP dating of monazite from the matrix of ore-bearing magnetite breccias gives a 207Pb/206Pb age of 2575 ± 12 Ma, confirming the epigenetic nature of the mineralization and placing it ~175 m.y. after accumulation of the host volcano-sedimentary sequence. The 2575 ± 12 Ma SHRIMP age of hydrothermal monazite from the Igarape Bahia mineralization is indistinguishable from published conventional 207Pb/206Pb ages for zircons from the Archean A-type granites of the Carajas belt, indicating that mineralization processes at Igarape Bahia were temporally related to these A-type Archean granites. The wide range of highly radiogenic 87Sr/86Sr ratios (0.714–0.755) of carbonates from the Igarape Bahia deposit suggests multiple crustal sources, consistent with a magmatic-hydrothermal origin. SHRIMP dating of zircon xenocrysts recovered from crosscutting diabase dikes indicates a maximum 207Pb/206Pb age of ~2670 Ma, consistent with field evidence and the age of host rocks, but does not unequivocably constrain the age of the ores. The styles of hydrothermal alteration, mineralogy, and geochemistry of the Igarape Bahia ore, as well as published fluid inclusion and stable isotope data, support its classification as a member of the world-class Olympic Dam-type Fe oxide Cu-Au-(U-REE) group of deposits, as previously argued by several authors. The SHRIMP age of 2575 ± 12 Ma for hydrothermal monazite indicates that Igarape Bahia is an Archean example of this deposit group.

Middle Proterozoic vein-hosted gold deposits in the Pontes e Lacerda region, southwestern Amazonian craton, Brazil

Structural, geochemical, and isotope studies were carried out on the gold deposits of the Pontes e Lacerda region (Mato Grosso state, Brazil), where rocks of the Aguapei and Rondoniano mobile belts (southwestern Amazonian craton) occur. The orebodies are hosted in metavolcanic, gneiss-granite, quartzite, tonalite, and granite units. Tectonics involve oblique overthrusting (from northeast to southwest), which led to the formation of recumbent folds and thrusts (pathways for the mineralizing fluids), upright folds, and faults with dominant strike-slip component. These unconformities represent potential sites for mineralization. During geological mapping, it was observed that the orebodies consist of quartz, pyrite, and gold, and that the hydrothermal alteration zone contains quartz, sericite, pyrite (altered to limonite), and magnetite (altered to hematite). Chalcopyrite, galena, and sphalerite occur only in the Onca deposit. Chemical analysis of sulfides indicates high contents of Bi, Se, and Te in sulfide...

Arsênio na água subterrânea em Ouro Preto e Mariana, Quadrilátero Ferrífero (MG)

In the Iron Quadrangle region the public supply of water is done mainly by the impound of water of watersheds. However, in some places, the population use spring water or ground water from closed mines for human consumption. The main natural sources of As in the Iron Quadrangle are related to the rocks that contain lode gold deposits. The antropic sources of As are contaminated refuse piles, soil, and sediment. It was found total As concentration varying from 2 to 2,980 µg/L and As3+ from 1 to 86 µg/L in water samples collected in underground gold mines, artesian wells, and springs in Ouro Preto and Mariana counties. Based on geological and hydrogeochemical studies of the occurrence of As in rocks and groundwater, it was found that the highest As concentrations occurred in aquifers hosted in carbonate sulphide rich rocks. The As monitoring in underground water should be done periodically, independent of its absence in a first instance, in wells and other groundwater caption sources that are used nowadays for public or private suppliers.

1.76 Ga volcano-plutonism in the southwestern Amazonian craton, Aripuanã-MT, Brazil: tectono-stratigraphic implications from SHRIMP U–Pb zircon data and rock geochemistry

Abstract Paleoproterozoic felsic and mafic volcanic rocks, extrusive and hypabyssal quartz porphyry, and high-K, A-type epizonal granites dominate the Aripuana region in the southwestern Amazonian craton in the Mato Grosso state of Brazil. The extrusive and intrusive felsic rocks display similar major and trace elements abundances and equivalent SHRIMP U–Pb ages of 1762–1755 Ma; contacts between them in the field occur gradually. The felsic volcanic activity occurred predominantly as explosive subaqueous volcanism. Various features such as absence of plate collision evidences, lack of any sign of oceanic crust, lack of complete trends of magmatic differentiation, and bimodal characteristics suggest that the magmatism was intracratonic. The characteristically undeformed felsic igneous rocks were formed by extensional events, probably triggered by mantle activation in an intracratonic ‘anorogenic’ or post-collisional environment. Throughout the Amazonian craton there are wide areas displaying similar magmatism responsible for the generation of distinctive A-type granites. These A-type granites and associated volcanic rocks yield ages of ∼1.76 Ga, suggesting that they are genetically linked and that there was a unique tectonic mechanism of widespread action in this craton.

Arsenic exposure assessment of children living in a lead mining area in Southeastern Brazil

Environmental contamination by arsenic compounds in the Ribeira River Valley, São Paulo, Brazil has already been observed. Lead mining and refining activities had been carried on since late colonial times and finished recently, at the end of 1995. The source of As in the region is known to be mainly from arsenopirite geological presence in the lead ore. Chronic exposure to arsenic compounds may cause peripheral vascular disorders, hyperpigmentation, hiperkeratosis and cancer of the skin, bladder, lung, liver and other internal organs. The purpose of this study was to assess children exposure to arsenic from environmental sources in the region. Urine samples from children between 7 to 14 years old were collected at the following localities: Cerro Azul (Paraná); urban areas of Ribeira (São Paulo) and Adrianópolis (Paraná); Vila Mota neighborhood (rural area of Adrianópolis) and Serra neighborhood (Iporanga, São Paulo), identified as groups 1, 2, 3 and 4, respectively. Group 1 was considered as non-exposed control group. Toxicologically relevant forms of As were determined by atomic absorption spectrometry with hydride generation system. The median values of urine arsenic levels obtained in groups 1, 2, 3 and 4 were respectively: 3.60, 6.30, 6.41 e 8.94 microg/L.

Evaluation of Arsenic Availability in Sulfidic Materials from Gold Mining Areas in Brazil

This study is aimed at evaluating the availability and mobility of arsenic in sulfidic materials from gold mining areas in Minas Gerais State, Brazil. Eight extraction media were employed in a sequential extraction scheme, as follows: exchangeable As; strongly adsorbed As; As coprecipitated with acid-volatile sulfide, carbonates, MnO2, and Al2O3; As coprecipitated with amorphous iron; As linked to crystalline iron oxide; As coprecipitated with silicates; As coprecipitated with amorphous FeS2 and As2S3, and residual As, which was determined by GFAAS. Results demonstrated that in spite of differences in arsenic concentrations, the availability of the metalloid was found to be low for all samples. In general, arsenic was found in less available forms. Nevertheless, most of the arsenic in the environment is retained in the fractions 3, 4, and 5 which are susceptible to dissolution in acid medium, which in turn might be due to oxidation of the sulfide present in the samples.

Experiências brasileiras e o debate sobre comunicação e governança do risco em áreas contaminadas por chumbo

This investigation focused on lead contamination case studies in Brazil. The situations studied involve communities living in Santo Amaro da Purificacao and Adrianopolis, in the north-east and south of Brazil, respectively. These communities have all had to live with environmental contamination and human exposure to lead as a consequence of industrial, mining and processing activities that were conducted by the same company for decades in a manner inconsistent with modern mining and industrial standards, with little control of environmental and human health impacts. The investigation sought to analyze the strategies of risk communication to local people, and to evaluate their engagement in risk management. The methodological approach included the analysis of newspaper articles, and interviews conducted with different stakeholders, such as residents, journalists, researchers and authorities. The results indicated the need to promote public involvement in the debate and in the decision-making process. The results also confirmed the hypothesis that associative models (represented by local neighborhood associations, for instance) are important for promoting and eliciting public participation in risk management.

O papel da mídia na construção social do risco: o caso Adrianópolis, no Vale do Ribeira

This article analyzes the influence of the media on the social construction of risk, from the different perceptions and attitudes of the residents of a community exposed to lead poisoning. The study used a combination of documental analysis and field research to build up an understanding of the role the media had taken in the social amplification of risk in this particular case and to observe how the responses to a situation of risk interacted with psychological, social, institutional and cultural processes. Aside from the direct influence of the media, this case study reveals the importance of other factors in molding the communitys risk perceptions, such as a mistrust of institutions and politicians, the relationship between risk and work activities and cultural and social values.

Rainwater major and trace element contents in Southeastern Brazil: an assessment of a sugar cane region in dry and wet period

O objetivo deste estudo foi investigar a composicao das aguas de chuva da cidade de Araraquara, Brasil, uma regiao influenciada pela queima da palha da cana-de-acucar. Variaveis quimicas e mineralogicas foram analisadas em aguas de chuva coletadas durante o periodo de safra, periodo seco de 2009 e entressafra, periodo umido de 2010. Ca2+ e NH4+ foram responsaveis por 55% dos cations e NO3- por 45% dos ânions presentes nas aguas de chuva. Al, Fe e K foram os elementos traco mais abundantes nas fracoes soluvel e insoluvel. Elevada concentracao media ponderada pelo volume (MPV) foi observada para a maioria das especies analisadas em amostras do periodo de safra, principalmente devido as atividades agricolas e condicoes meteorologicas. A quimica das aguas de chuva de Araraquara e a analise de componentes principais (ACP) indicaram que fontes naturais e antropicas, principalmente as relacionadas as atividades agricolas, sao responsaveis pelas emissoes para a atmosfera.

Arsenic mobilization from sulfidic materials from gold mines in Minas Gerais State

Acid drainage results from exposition of sulfides to the atmosphere. Arsenopyrite is a sulfide that releases arsenic (As) to the environment when oxidized. This work evaluated the As mobility in six sulfidic geomaterials from gold mining areas in Minas Gerais State, Brazil. Grained samples (<2 mm) were periodically leached with distilled water, during 70 days. Results suggested As sorption onto (hydr)oxides formed by oxidation of arsenopyrite. Low pH accelerated the acid generation, dissolving Fe oxihydroxides and releasing As. Presence of carbonates decreased oxidation rates and As release. On the other hand, lime added to a partially oxidized sample increased As mobilization.