Journal of the Geological Survey of Brazil

Geochemical and mineralogical differences between supergene and hypogene gold mineralization and influence on gold recovery: A case study of the Faina gold deposit, Pitangui greenstone belt, Brazil

Gabriel Machado da Silva — 2025-01-07

The Faina gold deposit, located in the Pitangui Greenstone Belt, NW of the Quadrilátero Ferrífero, Brazil, has produced gold from the oxidized portion of the deposit between June 2010 and June 2013. However, the deeper hypogene (sulfide-rich) section of the deposit has shown lower-than-expected recovery rates after direct leaching, leading to the interruption of gold production. This research presents a multi-methodological approach (drill core description, multi-element geochemical analyses and mineral characterization using microscopy and X-ray diffraction) to investigate describe the Faina gold deposit and identify the cause of low recoveries from the hypogene zone. The stratigraphy at Faina consists of a sequence of meta-mafic and meta-sedimentary rocks, with a thick (>40m) saprolite horizon (oxidized portion). Both the metamafic rocks and saprolite host gold mineralization, which is identified by distinct geochemical and mineral signatures: 1) Au-As-W in the hypogene zone, with gold associated with sulfides or as disseminations in silicates and 2) Au-As-W in the oxide-rich shallower section with free-milling gold associated with quartz, iron oxide-hydroxides and clay minerals. Geochemical, mineral and textural relationships in the hypogene zone show that submicroscopic gold particles associated with minerals, that consume leaching solution minerals (arsenopyrite, pyrrhotite and berthierite) may cause refractoriness during direct leaching. Separation of gold from these mineral phases, in addition to concentration methods during ore processing may increase gold recovery. The results presented in this research emphasize the importance of a detailed geochemical and mineral characterization to reveal the contrasting mineral and chemical compositions between hypogene and oxidized zone, which may influence gold recovery.

Unveiling geological complexity in the Serra Dourada Granite using self-organizing maps and hierarchical clustering: Insights for REE prospecting in the Goiás Tin Province, Brasília Belt, Central Brazil

Guilherme Ferreira da Silva — 2025-04-02

This study explores the use of Self-Organizing Maps (SOM) combined with hierarchical clustering to provide insights into the geological differentiation and mineral prospecting in the Serra Dourada Granite (SDG), part of the Goiás Tin Province, northern Brasília Belt. After some issues on the geological cartography of the SDG based on traditional approaches, such as the interpretation of outcrops and the limited geochemistry data, often struggle to capture the complexity of high-dimensional geophysical datasets. To address this, we apply unsupervised machine learning techniques to segment airborne radiometric data, providing a more nuanced understanding of the SDG internal structure. Using airborne gamma-ray data, we employed SOM for dimensionality reduction and data segmentation, supported by hierarchical clustering. This methodology enabled us to identify distinct geological units with greater accuracy and resolution than traditional methods such as Principal Component Analysis (PCA). The SOM-based approach retained the data's original topology and revealed fine-scale patterns within the dataset, distinguishing between areas affected by magmatic processes and those influenced by post-magmatic hydrothermalism and supergene leaching. The results indicate that some clusters are mainly associated with magmatic differentiation, characterized by average concentrations of potassium (K), equivalent thorium (eTh), and equivalent uranium (eU) and others show evidence of secondary processes, including hydrothermal alteration and weathering. Notably, Cluster 4 is spatially linked to REE-enriched plateaus and the Serra Verde Mine, reinforcing its significance for mineral exploration. The SOM model proved more effective than PCA at capturing non-linear relationships within the data. While PCA provided insights into the primary variance, it did not fully account for the complex geological processes at play. In contrast, the SOM model segmented the data into clusters that reflected both broad radiometric trends and localized variations, particularly in areas influenced by hydrothermalism and supergene processes. Our findings underscore the value of machine learning techniques, particularly SOM, in geoscientific data analysis. This approach provides a robust framework for integrating multivariate radiometric data, offering valuable insights for geological mapping and mineral exploration, especially in regions with complex geological histories. The methodology presented here can be adapted to other geological settings, enhancing the accuracy of subsurface mapping and identifying areas of economic interest, such as Rare Earth Element (REE) and other critical mineral deposits.

Contribution of the Geodiversity knowledge to social, economic, and environmental health development

Cassio Silva — 2025-01-31

This article explores geodiversity within the context of Geosciences, emphasizing its central role in optimizing the generation, systematization, integration, and application of knowledge related to the physical environment and the sustainable use of natural resources. The proposed approach aligns knowledge and resource utilization with ecological constraints, incorporating environmental and social variables into territorial planning and development processes. As an integrative element of diverse geoscientific information bases, geodiversity provides essential technical and scientific support to key societal sectors, including mining, energy, agriculture, public health, urban planning, housing, civil defense, infrastructure, tourism, the environment, and territorial planning. In mining, geodiversity fosters knowledge and promotes the sustainable use of mineral resources essential for survival and quality of life. In the energy sector, its contributions encompass fossil fuels, minerals used in nuclear energy production, and renewable energy sources such as solar and wind. In agriculture, geodiversity aids in the use of fertilizers, soil remineralizers, and conditioners, while ensuring a vital water supply. In public health, the monitoring of water, soil, and air quality is directly supported by geodiversity-derived knowledge, which also informs urban planning by identifying suitable areas for sustainable development and securing construction materials. Geodiversity is equally critical in preventing natural disasters, enabling civil defense to monitor and mitigate risks associated with landslides, floods, seismic activity, and erosion. In infrastructure, whether social (schools, health posts, housing, sanitation, etc.) or economic (transportation and communication systems), geodiversity plays a pivotal role by supporting solutions that enhance societal quality of life. In tourism, geodiversity promotes culture, leisure, and entertainment through the development of geoparks in areas with notable geoscientific significance and the preservation of scenic landscapes. For the environment, geodiversity provides assessments of current and potential impacts, guiding the rehabilitation of degraded areas and the prevention of natural hazards. In territorial planning, geodiversity is indispensable for formulating regional development plans, ecological-economic zoning, and land use planning, as well as for the sustainable utilization of coastal and continental shelf environments. This intrinsic relationship between society and geodiversity is evident, as the production of minerals, water, and food is essential for human survival and socioeconomic development. As knowledge of geodiversity and its connections to land use and the environment expands, its role in shaping Public Policies and Territorial Development Plans becomes increasingly relevant. These policies encompass urban and rural occupation, infrastructure planning, and the sustainable use of mineral and water resources, guiding Municipal Master Plans, State Development Plans, and the National Territorial Planning Framework. Thus, geodiversity-as an integrative element of Geosciences and its connection to society-emerges as a cornerstone for promoting sustainable development.

Artisanal and small-scale gold mining and trade in Tanzania pre to post independence: A review

Fredrick Mangasini — 2025-03-19

Appraisal of gold production and trade via Artisanal and Small-Scale Mining (ASM) in Tanzania has been achieved through assessing the literature and onsite interviews. Authors settle on the understanding that ASM is extricated to Industrial Mining (IM) upon funding, informality, and applications of technology. However, ASM has been embraced in Tanzania pre-to post-independence based on two facts: i) its gold production in the primordial period made a gateway to export trade, and ii) ASM was a feasible means of gold production in periods of insufficient infrastructures and geo-political and economic challenges. Gold produced via ASM worth £363,084,500 equivalent to Sh. 1,194.3 billion (in present-day values) was recorded during the German colonial administration (1886-1920). For the British colonial administration (1920-1961), gold worth of £169,854,560 equivalent to Sh. 558.7 billion was produced. Smuggling and illegal markets obscured the amount of gold produced and traded immediately after independence. However, two years after the establishment of the local mineral markets (2019 – 2021), Government’s collection from ASM gold sales rose from Sh. 61.53 billion to Sh.154.49 billion making 151.08% increase. In 2021, gold ASM contributed 2.6% to the GDP implying that, ASM holds a great potential of contributing significantly to the social-economic development of the resource-rich developing countries. Tanzania has worked to formalize ASM legally, and through the establishment of demonstration centers, demarcating sites, oversight, and mineral markets. Nevertheless, lack of access to loans because of bankers’ stringent conditions deters its growth. Therefore, it is imminent for scholars to research on appropriate mechanisms of ASM financing, and for the government to institute policy changes that will recognize Primary Mining Licenses (PMLs) as assets, to help alleviate the problems with lending practices and enhance ASM’s economic contribution.

Geophysical methods in graphite exploration: A review

Debora Rabelo Matos — 2025-03-25

Graphite, with its unique thermal, electrical, and chemical properties, is crucial for technologies like energy storage and advanced materials. However, exploring graphite deposits is challenging due to the variability in crystallinity, purity, and distribution within host rocks, which complicates geophysical data interpretation. This study reviews 20 articles on geophysical methods for graphite exploration, analyzing their advantages and limitations, in addition to incorporating insights from 53 other articles to support discussions on graphite properties and geophysical techniques. Electrical methods, such as resistivity and induced polarization, effectively delineate mineralized zones but are constrained by limited spatial coverage. In contrast, magnetic and electromagnetic techniques provide broader survey coverage and greater cost-efficiency, making them valuable for regional exploration, despite their lower resolution in distinguishing graphite from other minerals. Effective exploration requires integrating regional geological surveys with high-resolution investigations by academia and industry. Understanding the geophysical signatures of different graphite deposit types — like lump, flake, and amorphous graphite — is essential for refining exploration strategies and improving discovery rates. By combining large-scale data with focused studies, exploration efforts can be optimized, enhancing the identification and assessment of graphite resources.