Journal of the Geological Survey of Brazil

Exposure of aluminum in the Araçuaí-Itinga Lithium Pegmatite District, Minas Gerais, Brazil: Contaminant and toxicological effects on populations established nearby mining activities

Fri, 07 Mar 2025 00:00:00 +0000

This study aims to assess the geological, geochemical, and toxicological aspects of aluminum in the Araçuaí-Itinga lithium district, located in the Jequitinhonha River basin, Minas Gerais, with an emphasis on potential health risks for various population groups. Geological investigation revealed a predominance of aluminum-rich granites and metasediments, which serve as source and hosts for lithium-mineralized pegmatites. The study found that lithium levels pose no risk to human health, with maximum concentrations of the order of approximately 0.015 mg/L in water, 78 mg/kg in soil, and 33.7 mg/kg in stream sediments. However, elevated aluminum levels, where found in over 80% of the studied area, with concentrations exceeding the recommended maximum of 0.1 mg/L. Water samples exhibited aluminum levels ranging from 0.200 and 0.928 mg/L, while concentrations reached 3.1% in soil, and 0.96% in stream sediments. These values highlight the need for for further investigations into potential environmental and human health impacts. Additionally, aluminum concentrations of 1,059 mg/kg were detected in 12 vegetable samples. Plasma analyses of individuals living in the Igrejinha and Fazenda Velha communities revealed aluminum values above the normal limit of 3 µg/L in 68% of the examined individuals, and in 94% of dialysis patients, indicating significant health risks for those undergoing dialysis. . The primary route of aluminum for the sampled individuals was water, facilitated by itstransition from rock-to soil-to water-to food. It is estimated that approximately 3,200 people near tributaries of the Jequitinhonha River, particularly in the Valley of Córrego do Piauí, are at risk of aluminum exposure. These findings underscore the urgent need for further research and interventions to mitigate the health risks associated with aluminum exposure in these communities.

Geochemical and tectonic setting of mafic dike swarms of the Juruena-Teles Pires mineral province, southwestern Amazonian craton, Brazil

Gilmar Rizzotto, Cléber Alves — Thu, 10 Apr 2025 00:00:00 +0000

The present study provides a comprehensive set of whole-rock geochemical, petrographic, and mineral chemistry data on diabase dike swarms that crosscut the Archean/Paleoproterozoic basement of the Peixoto de Azevedo domain, located in the central-western part of the Juruena-Teles Pires mineral province, in the southwestern portion of the Amazonian Craton. The dike swarms are classified into two groups based on TiO₂ concentration: high-Ti (HTi, >2 wt.%) and low-Ti (LTi, <2 wt.%). In the Peixoto de Azevedo domain, LTi dikes, with an undetermined crystallization age, predominantly exhibit N30-40E strikes. In contrast, in the central-western Juruena-Teles Pires province, the ~1.8 Ga fissure-controlled HTi dikes are systematically aligned along shear zones and fault systems, with strikes varying from E-W to WNW-ESE, predominantly crosscutting Orosirian/Statherian granitic rocks. Mineral assemblages in LTi dikes are dominated by clinopyroxene (augite) and plagioclase, the latter sometimes exhibiting a Ca-rich core (An_63-74) and a Na-enriched rim (An_26-43), with minor Fe-Ti oxides, apatite, and biotite. Conversely, HTi dikes contain labradorite, augite (±olivine), magnetite, and ilmenite, with common accessory minerals such as biotite and apatite. Both groups exhibit low Ni contents, which, in conjunction with the observed CaO-MgO correlations, indicate fractional crystallization likely controlled by plagioclase and clinopyroxene. The HTi and LTi dikes are tholeiitic and classified as continental flood basalts, displaying distinct geochemical features. LTi dikes have Mg# values ranging from 0.32 to 0.58 and are enriched in Ba, K, Rb, Sr, Ce, and Y, with low to moderate MgO, Ni, and Cr contents, and moderate LREE enrichment. In contrast, HTi dikes have relatively low Mg# (31–49) and are slightly more evolved than the LTi diabase dikes. Additionally, they exhibit higher concentrations of TiO₂, P₂O₅, Ba, Rb, Sr, Th, Ce, Y, Zr, as well as both LREE and HREE. The relationship between typical crustal elements in the chemical composition of the studied diabases, such as Ba, Rb, La, Ce, and Nb-Ta, supports the presence of a crustal component in the source of both HTi and LTi dikes. These geochemical characteristics suggest that crustal contamination and fractional crystallization may have influenced their magmatic evolution. The probable occurrence of lithospheric delamination, accompanied by crustal thinning and mantle uplift followed by mantle melting, likely culminated in the generation of intraplate continental tholeiitic magmatism, often marking significant geodynamic events in the southwestern portion of the Amazonian craton.

Potential for kaolin and bauxite in the near-littoral sediments of the State of Amapá, Eastern Guiana Shield, northern Brazil

Wilson Scarpelli — Fri, 09 May 2025 00:00:00 +0000

In Amapá, northern Brazil, there is potential for large and not yet identified economical deposits of kaolin and bauxite in the Cenozoic belt of sediments that cover the margins of the Eastern Guiana Shield next to the Atlantic Ocean and the Amazon River. During geological exploration of these mineral resources, it seems adequate to consider the geological characteristics of the kaolin deposit of Morro do Felipe, at the southwest of Amapá, and the deposits of bauxite replacing Cenozoic kaolin-rich sediments at the coast of Guyana and Suriname. While the Brazilian deposits of bauxite of the Trombetas and Jari rivers occur in topographically stable plateaus, the corresponding plateaus containing bauxite in Guyana and Suriname were lowered to below seawater, and covered by younger sediments. In the southeast of Amapá, sediments similar to some that in Guyana and Suriname are guide to bauxite deposits, as the white sands, appear widespread over a large area. A few but significant exposures of high-grade kaolin suggest high tonnages of the mineral. The presence of these layers of kaolin, the mother-rock of the bauxite of the belt, and the presence of actual paleoduricrust improve the possibility of existence of hidden deposits of bauxite.

Geology and hydrothermal alteration of the Santa Bárbara polymetallic deposit (Cu, Zn, Pb, Ag, Au): Insights into the Ediacaran-Cambrian rift system evolution, Camaquã basin, southern Brazil

Wed, 11 Jun 2025 00:00:00 +0000

The Santa Bárbara deposit is a small polymetallic target (Cu, Zn, Pb, Au, Ag) located northwest of the ediacaran Caçapava do Sul granite, near the namesake city, in the Riograndense shield. It is genetically linked to other two historical cooper occurrences of the Cerro dos Andradas area, the Primavera and Andrada deposits. This study explores the Cerro dos Andradas occurrences in the context of the tectonic evolution of the ediacaran Camaquã rift system, focusing on the geological and hydrothermal characterization of the Santa Bárbara deposit. Mainly hosted in metamorphic rocks (Passo Feio Complex) these occurrences have not been considered products of Camaquã basin evolution, unlike the other major mineralizations of the region. The data were obtained by field work, petrographic analysis of thin sections, mineral reflectance spectroscopy of core samples, alongside geochemical and geological data acquired from a mineral exploration company. The mineralizations are mainly hosted in the damage zone of a master fault of the Camaquã Basin (Andradas fault). The fault’s NNE-SSW orientation is parallel to the mylonitic foliation of the footwall rocks, which comprise a sin magmatic shear belt (Passo Feio Complex or Cerro dos Andradas shear zone) developed in the western wall of the granitic pluton. The host rocks include subvolcanic and volcanic lithotypes (basalt and andesite) of the hanging wall block of the Andradas Fault, related to the Bom Jardim Group. The results indicate that the mineralized veins consist of chalcopyrite, bornite, sphalerite, galena, quartz, calcite, ankerite, gypsum, and barite, with concentrations up to 0.8% copper, 0.6% zinc, and 0.3% lead, as well as notable gold and silver concentrations. Together with the definition of hydrothermal processes near the ore (carbonatization and argilization), these findings support the interpretation of an epithermal mineral system for the Cerro dos Andradas deposits, similar to those proposed for other deposits in the Camaquã Basin.

Evolution of ichnological knowledge in the Furnas Formation of Parecis and Paraná basins, Brazil

Kevin William Richter, Elvio Pinto Bosetti, Daniel Sedorko, Luana Oliveira — Thu, 17 Apr 2025 00:00:00 +0000

Ichnology provides detailed information on the environmental parameters involved during deposition, serving as a basis for paleoenvironmental interpretations. To this end, ichnological analyses focus on the behavioral aspects represented by ichnoassociations, providing details of the interaction between organisms and the abiotic environment. Ichnological studies in the deposits of the Furnas Formation have been recorded since the early twentieth century, mentioning the presence of "worm tubes". The lack of body fossils and microfossils, except for the top of the formation and the lithological uniformity, has led to extensive discussions about its depositional origin. The palaeodepositional scenario of the Furnas Formation has been highlighted by the recognition of trace fossils, proposing a shallow marine setting for the unit. This review study aims to analysis the evolution of ichnological knowledge and its applicability to paleoenvironmental characterization in the deposits of the Furnas Formation in the Parecis and Paraná basins, Brazil, based on a review of the studies that proposed depositional scenarios for the unit.