Journal of the Geological Survey of Brazil

Geotechnical viability of sand, cement, and binary stabilisation of soils in the western Niger Delta; An example of Warri City, Southern Nigeria

Enivwenaye Avwenagha — 2026-01-12

The pavement performance of superficial soils in southern Nigeria is in decline, most notably due to the use of inferior pavement materials and poor soil conditions. The study, therefore, examines the impact of sand, cement, and binary (sand/cement) stabilisation on soils in an attempt to improve road development in the City of Warri. The natural condition of sixteen (16) soil samples was subjected to consistency tests, classification tests, compaction, and soaked California Bearing Ratio (CBR) analyses as a standard for comparative analysis. The effects of sand, cement, and binary stabilisation on the engineering behaviour and suitability of natural soils were examined using specified road standards, CBR responses, and t-test analysis as bases for comparison with the natural, untreated soils. The properties of natural and treated soils were fed into machine learning predictive models, including Random Forest Models (RFM), Extreme Gradient Boosting (XGBoost) Models, and Explainable Boosting Models (EBM), for CBR prediction evaluation. Results confirmed that sand stabilisation had a significant impact on the soil grade, with a marginal impact on the natural CBR (resulting in a slight boost from the natural range of 3-17.9% to 11-28.8%), while the soil suitability remained constant. Cement-treated soils were improved to subbase/base quality (71.3-193.3%) at 7% weight of cement. Binary stabilisation resulted in base-quality soils (107-272.5%). T-test analyses confirmed that binary stabilisation is the most technically viable solution to the pavement deficiency in the City. The study presents a feasibility resource database for the stabilisation of deficient superficial soils for road development in deltaic environments.

Prospectivity maps for polymetallic skarn and orogenic gold mineralization in the Rio Piranhas-Seridó Domain, Borborema Province (NE Brazil): An aid to exploration targeting

Alan Pereira da Costa — 2026-01-14

In this study, predictive mineral prospectivity modelling (MPM) was applied to the Bodó, Serra da Umburana, Currais Novos–Santa Luzia, and Caicó–São Fernando–Jucurutu areas of the Seridó Mineral Province, Borborema Province, Northeast Brazil. The MPM was designed to target tungsten (W), molybdenum (Mo), gold (Au), and copper (Cu) mineralization associated with structurally controlled polymetallic skarn and orogenic gold deposits. The predictive models were developed through the integration of geological, geochemical, and geophysical data using the Multiclass Index Overlay (MIO) methodology. Thematic maps with different prospectivity ranges were generated and validated through cumulative curves relating predictive indices to the spatial distribution of the known mineral occurrences. The results demonstrated high model efficiency, with 62% to 88% of the occurrences concentrated in areas of high to very high prospectivity, representing 5% to 25% of the total area of each map. The high prospectivity areas include both known mineralized trends as well as areas yet to be investigated. As such, our MPM results not only confirm the potential of the known mining districts but also present new research and exploration frontiers. Geochemical signatures extracted through factor analysis (FA) revealed robust multielement patterns that support the skarn-type mineralization models. Mineralogical and lithogeochemical data from samples of mineralized zones and/or panned concentrates from prospective targets reinforce the polymetallic nature (W-Mo-Au-Cu) typical of skarn deposits in the study areas. Based on the results obtained from the validation of the prospectivity models, it is concluded that the integrated, mineral systems-based approach is effective in guiding mineral exploration in geologically complex terrain. The predictive maps constitute strategic tools that help reduce uncertainty associated with exploration targeting and attract investment to the region, which is timely given the growing global demand for critical metals.

Rare earth elements, sustainability, and ion-adsorption clay: A bibliometric study on global trends and Brazil's prominence

Anna B G Tetzner — 2026-01-08

Rare Earth Elements (REE) are critical minerals for the global energy transition and for fulfilling Sustainable Development Goals (SDGs), such as SDG 7 (Clean Energy). However, the traditional supply chain, focused on primary deposits, faces significant geopolitical and environmental challenges. In this context, ion-adsorption clay (IAC) deposits have emerged as the main research route for a more sustainable REE production, aligned with the 2030 Agenda. Despite this relevance, there has been no systematic analysis of the scientific production on this topic in an integrated manner, from the perspective of the entire 2030 Agenda. The objective of this study is to fill this gap by mapping the synergies and trade-offs between global REE-IAC research and the 17 SDGs, and contextualizing this trend with Brazil's emergence as a strategic industrial player. To this end, a bibliometric and systematic review analysis was conducted using the Scopus and Web of Science databases, covering the period from 1973 to 2024. Keyword co-occurrence analysis and thematic clustering were processed using VOSviewer. This analysis was supplemented by a survey of active exploration projects in Brazil, based on technical and governmental reports. The results demonstrate an exponential growth (R² = 0.98) in research starting from 2015, the year the SDGs were launched. This period accounts for 91.5% of all historical literature on the topic. The cluster analysis reveals that the intellectual structure of the field is dominated by two pillars: the demand for sustainability (Cluster 1, centered on sdg) and the geological solution (Cluster 2, centered on ion adsorption clay). The research field proves to be mature, actively addressing the challenges of water management (SDG 6, Cluster 8) and toxicity. On the global stage, Brazil stands out as the 5th largest publisher. More importantly, the practical survey identified 24 active IAC projects in the country, including the commercial operation of Serra Verde (GO) and the advanced projects in Poços de Caldas (MG), such as Caldeira and Colossus. It is concluded that the SDGs act as the main driver of innovation in IAC research. Brazil demonstrates a unique convergence between innovation policy (aligned with SDG 9), the global scientific trend, and industrial execution. The country is using IAC deposits as a strategic solution to overcome the environmental challenges of its traditional deposits (associated with Th/U), positioning the country as the main Western hub for REE-IAC production and a strategic supplier for the sustainable energy transition.

Assessment of sub-surface water corrosion and encrustation potentials in parts of Eastern Dahomey Basin, Southwestern Nigeria

Richard Fakolade — 2026-02-02

Understanding hydro-geochemical parameters and corrosion-encrustation tendencies in coastal aquifers is crucial for sustainable water quality management. In the eastern Dahomey Basin of southwestern Nigeria, rapid deterioration of metal pipes, surface tanks, and boreholes has been observed, leading to significant infrastructure damage and failure. This study evaluates groundwater quality and assesses corrosion and encrustation potentials using multiple geochemical indices. Twenty groundwater samples were collected and analyzed for physicochemical parameters (pH, Electrical Conductivity (EC), Temperature (°C), Total Dissolved Solids (TDS)) and chemical constituents including hardness, chloride, manganese, and iron using Atomic Absorption Spectrophotometry (AAS) and titration. Physicochemical and ions concentration analysis results were further adopted to compute corrosion and encrustation indices including; Langelier Index (LSI), Ryznar Stability Index (RSI), Larson-Skold Index (LS), and Aggressive Index (AI) were computed. Results indicate LSI values of the samples were corrosive while they exhibited higher scaling tendency. AI indicated moderately corrosive and scaling-prone; RSI results ranging from high corrosive to severely corrosive nature; LS indicated high concentration scaling-prone with mild corrosive status. Spatial analysis revealed higher corrosion tendencies near coastal zones due to seawater intrusion influences. The study highlights the need for corrosion-resistant materials and preventive measures in groundwater infrastructure development.

First in situ documentation of a fossil tooth attributed of †Otodus megalodon from the deep sea of Rio Grande Rise, South Atlantic Ocean

Marcos Cristóvão Baptista — 2026-01-12

The shark †Otodus megalodon is one of the main marine predators of the Cenozoic, with fossil records ranging from 15.9 to 3.6 Ma and a distribution considered cosmopolitan. However, some regions of the planet still lack unequivocal records of the species, including the South Atlantic Ocean. Although there are records of teeth on continental South America, this work presents the first record of a †O. megalodon tooth in the South Atlantic Ocean (offshore). The tooth was collected by the Geological Survey of Brazil (SGB), in 2012, on the Rio Grande Rise (RGR) from a dredge haul between 664–667 m depth at station 4340-IV-150-HAS and is embedded in a phosphatized ferromanganese crust. The sample exhibits a porous, botryoidal surface, with internal lamination alternating dark Fe-Mn-rich layers and light calcium- and phosphate-rich layers. The morphological description indicates a triangular tooth, with TH = 57.1 mm, CH = 45.2 mm, and CW = 36.2 mm. The cutting edges are worn due to marine abrasion. The predominant color is black (N2–N3, Munsell), reflecting Fe-Mn coating. Strontium isotope analyses performed on equivalent materials indicate ages between 21.7 and 14.5 Ma (Early–Middle Miocene). This interval coincides with the period of greatest diversity and broad distribution of †O. megalodon, supporting the interpretation that the tooth corresponds to this geological interval. The presence of the tooth in deep-sea settings and associated with Fe-Mn crusts is unusual, as most findings occur in coastal environments. The results presented suggest that the RGR may have served as a migratory route or feeding area for large pelagic predators during the Miocene, possibly associated with local productivity and regional paleoceanographic conditions. The record reinforces the scientific and strategic importance of the RGR and highlights the need to expand paleontological and paleoceanographic investigations in the deep waters of the South Atlantic Ocean.

Geological map of Brazil - 2025 (scale 1:5,000,000): Methodology and main geological compartments

Vladimir Medeiros — 2026-02-26

The Geological Map of Brazil at the 1:5,000,000 scale was recently updated by the Geological Survey of Brazil (SGB-CPRM), in view of the availability of several geological maps and datasets released after the previous version, published in 2001. In this context, the methodology applied to the preparation of the map is presented here, together with a proposed framework for representing the Brazilian territory in terms of geological compartments. The work began with the acquisition of vector datasets available from SGB-CPRM at multiple scales, followed by the definition of a set of guiding assumptions, including the minimum mappable area, the lowest stratigraphic hierarchies to be adopted (Formation, Group, Complex, and Suite), the tectonic structures to be represented, the prioritization of the most recent geological cartography, and the consistent application of a unified methodology across the entire country. Following the compilation of vector files at the 1:5,000,000 scale, it became possible to apply a consistent proposal for the geological compartmentalization of Brazil, based on the characterization of the main geological, geochronological, and structural units mapped and exposed in the country, as well as on previous conceptual frameworks. This approach allowed Brazil to be initially subdivided into cratons (23% of the national territory) and mobile belts and cratonic covers (17% of the territory) associated with the Brasiliano Orogeny (Neoproterozoic), in addition to the Phanerozoic covers and basins (60% of the territory). The cratons are represented by the Rio de La Plata, Luiz Alves, São Francisco, São Luís, and Amazonian cratons, whereas the mobile belts correspond to the Borborema, Tocantins, and Mantiqueira provinces, as well as marginal belts and Neoproterozoic cratonic covers. The main representatives of the Phanerozoic covers and basins include the Amazonas, Parnaíba, Paraná, and Coastal provinces, in addition to the Parecis, Bananal, Pantanal, Sanfranciscana, Recôncavo–Tucano–Jatobá, Araripe, and Guaporé basins.