Amed Bonilla

Illegal mining and the transboundary trade of poorly characterized mineral concentrates have expanded throughout the northwestern Amazonian Craton, particularly in eastern Colombia, southern Venezuela, and adjacent parts of northern Brazil. Materials marketed as “coltan” or “black sands” are commonly extracted, transported, and commercialized without adequate mineralogical characterization or radiological controls, despite the potential presence of naturally occurring radioactive materials (NORM). This study presents an integrated mineralogical, geochemical, and radiological screening assessment of confiscated mineral concentrates recovered from the Guainía and Vichada departments of eastern Colombia. A total of 24 samples, including black sands, wolframite-group minerals, iron oxides, and Nb-Ta-bearing concentrates, were investigated using field mineralogical observations, X-ray diffraction (XRD), wavelength-dispersive X-ray fluorescence (WDXRF), and gamma dose-rate measurements. The results demonstrate that materials traded as “coltan” or “black sands” are mineralogically heterogeneous and do not correspond predominantly to columbite–tantalite sensu stricto. Instead, Nb and Ta are primarily associated with Nb-rich rutile (ilmenorutile) and Ta-rich rutile (strüverite), whereas rare earth elements (REE), uranium, and thorium occur mainly within monazite–xenotime assemblages. Black-sand concentrates contain significant enrichments in REEs and NORM, with uranium contents reaching approximately 0.29 wt.% and thorium up to 0.57 wt.%. Radiometric measurements revealed a marked contrast between local background radiation and several confiscated concentrates. Background radiation averaged approximately 0.089 µSv/h under field conditions and ranged from 0.107 to 0.173 µSv/h during laboratory analyses, whereas storage areas containing confiscated materials reached approximately 4 µSv/h. Direct measurements above monazite-rich concentrates exceeded 20 µSv/h and reached up to 70 µSv/h in samples provided by indigenous communities. These findings indicate that a significant proportion of materials circulating through illegal mineral supply chains are misclassified and may contain elevated concentrations of NORM-bearing minerals. Although this study represents a preliminary radiological screening assessment rather than a comprehensive risk evaluation, the measured dose rates highlight the need for improved mineralogical characterization, radiological monitoring, and handling protocols for miners, traders, local communities, and law-enforcement personnel involved in the extraction, transport, storage, and confiscation of these materials. The results further demonstrate that illegally traded heavy-mineral concentrates from the northwestern Amazonian Craton constitute an underrecognized source of potential NORM exposure and emphasize the importance of integrating mineralogical verification and radiological screening into critical-mineral governance frameworks throughout northern South America.

Landslides constitute one of the most lethal and costly hydrometeorological hazards at the global scale. There is a growing trend associated with the increase in extreme precipitation and the expansion of urban development on unstable slopes. In the tropical Andes, this problem is intensified under climate change scenarios. The objective of this study is to develop a logistic regression model to analyze socioeconomic risk due to landslides in the Bogotá Savannah (Colombia). An integrated risk model was developed using binary logistic regression and a socioeconomic vulnerability index. A total of 12 physical–biotic variables and SSP climate projections (2021–2040) were used. A GIS-based environment was implemented to generate prospective spatial risk scenarios. The model demonstrated high robustness and predictive capability, with an improvement in statistical goodness-of-fit of 8.2% (AIC: 2574–2367), adequate probabilistic calibration (Pseudo-R²: 0.675; Brier Score: 0.084), and excellent predictive performance (AUC: 0.935; sensitivity: 84.7%; specificity: 90.0%). Simulations estimated maximum risk probabilities close to 0.600 (scale between 0 and 1), concentrated in geomorphologically critical sectors. Simulations under SSP scenarios showed a progressive increase in risk toward 2040 (up to 0.673), associated with precipitation increases between 10 and 30%. Integrated modeling constitutes a reliable technical tool for land-use planning, climate adaptation, and prospective landslide risk management in urbanized Andean regions.

Urban growth and climate change intensify urban heat islands (UHIs), altering atmospheric stability and promoting the accumulation of particulate matter ≤ 10 µm (PM₁₀) and particulate matter ≤ 2.5 µm (PM_2.5), particularly in high-altitude megacities. However, there remains a scarcity of integrated dynamic models capable of representing these interactions at the intra-urban scale. This study develops a socio-environmental dynamic model to evaluate the influence of UHIs on PM₁₀ and PM_2.5 concentrations across localities of a high-altitude Latin American megacity (Bogotá, Colombia). A dynamic simulation model was developed in Vensim^®, integrating temperature, PM₁₀, PM_2.5, and citizen perception data. Statistical and spatial analyses were conducted to represent intra-urban thermo-atmospheric interactions. The results show that the model captures the influence of UHIs on PM₁₀ and PM_2.5 concentrations. Higher PM concentrations are simulated in localities with high imperviousness (PM₁₀: 33.4–50.4 µg/m³; PM_2.5: 21.5–25.1 µg/m³) and lower PM concentrations in areas with greater vegetation cover. Sensitivity analysis of the dynamic model reveals nonlinear amplifications of up to 15–20 µg/m³ in PM₁₀ and 8–10 µg/m³ in PM_2.5 associated with small thermal variations (1–2 °C). Under scenarios with significant UHI intensity, increases reach 4–6 µg/m³ in PM₁₀ and 3–4 µg/m³ in PM_2.5. These findings confirm that UHIs act as amplifiers of pollution and that urban thermal interventions could reduce PM concentrations by up to 10–20%.

The northwestern Amazonian Craton exposed in eastern Colombia preserves a complex Proterozoic tectonothermal history. In this study, we present new zircon and apatite U–Pb geochronological data from orthogneisses of the Guaviare Complex (Termales Gneiss unit) to constrain the timing of crust formation, metamorphism, and subsequent thermal events. Zircon U–Pb data define a dominant concordant population at ca. 1.30 Ga, interpreted as the crystallization age of an igneous protolith. This age is consistent with Mesoproterozoic A-type magmatism previously recognized in the region and consistent with emplacement under intracratonic extensional conditions, as suggested by previous studies. A limited number of discordant zircon analyses indicate Pb loss and/or partial isotopic resetting between ~1.0 and 0.6 Ga, although no well-defined metamorphic zircon population is identified. Meanwhile, apatite U–Pb analyses from key samples yield consistent lower intercept ages between 633 ± 16 Ma and 543 ± 8 Ma, indicating a widespread Ediacaran thermal disturbance that may have affected the Guaviare Complex, temporally overlapping with alkaline magmatism in the northwestern Amazonian Craton, including the San José del Guaviare Nepheline Syenite. However, alternative mechanisms such as fluid-assisted Pb mobility, regional reheating, or prolonged cooling cannot be excluded. Finally, the combined zircon–apatite dataset highlights the value of multi-chronometer approaches for resolving complex thermal histories in cratonic domains.

Los resultados aquí presentados describen parte de la geomorfología única al sur de la ciudad de San José del Guaviare, donde areniscas conforman mesetas de poca elevación que han sufrido procesos kársticos en Ciudad de Piedra siguiendo estructuras (NE-SW - NW-SE) preferencialmente. Las areniscas pertenecientes al Miembro Basal Ciudad de Piedra de la Formación San José contienen icnofósiles, y petrográficamente se observa predominancia de cuarzo de grano medio redondeado y cementado por sílice que otorga mayor resistencia, sobre un 5% restante que corresponde a líticos metamórficos y volcánicos, feldespatos, micas, opacos y circones. Análisis U-Pb LA-ICP-MS en estos circones mostraron edades proterozoicas con picos entre 1000 a 1800 Ma, mientras circones extraídos de un neis cerca de Cerritos, El Capricho, revelaron una edad concordante de 1317±4 Ma, interpretada como edad del protolito. Los datos obtenidos confirman que el basamento cristalino en el área de estudio pertenece al Cratón Amazónico y que los sedimentos que dieron origen a las areniscas de la Formación San José provienen de este basamento compuesto principalmente por neises y granitoides. Posteriormente, el basamento fue intruído por la Sienita Nefelínica de San José del Guaviare (~602 Ma), la cual aflora en contacto tectónico fallado con la Formación San José en cercanías a Ciudad de Piedra.

Para resolver la pregunta si megacristales de rutilo-(Nb,Ta) en la Comunidad Indígena de Cachicamo (NE-Vichada) provienen de rocas del Granito Rapakivi de Parguaza se extrajeron rutilos de una coraza ferruginosa superficial o duricrust compuesta por (hematita, limonita, ± magnetita, ilmenita, circón, fragmentos de roca), desarrollada sobre un perfil laterítico del basamento granítico, que fueron analizados junto a suelos y concentrados. Mediciones simultáneas de densidad y FRXp de >250 rutilos revelaron variaciones fuertes desde rutilos livianos (~3,4 g/cm3), de casi puro TiO2, hasta rutilos-(Nb,Ta) de 5,9 g/cm3 enriquecidos en Nb, Ta, Fe, Mn, Sn, V y W. Metalografía, MEB-EDX, FRX y DRX revelaron inclusiones de hasta 0,2 mm compuestas de ~17% columbita-(Fe) y 4% casiterita en una matriz de ~78% rutilo-(Nb,Ta). Valores EPMA (72% TiO2, 11% Nb2O5, 9% Ta2O5, 6% Fe2O3, 1,5% SnO2) confirman junto con bajos contenidos de W y Mn una afinidad pegmatítica - pneumatolítica. Mediciones ICP-MS indicaron suficiente U para probar dataciones en la Universidad Rennes 1, donde, usando estándares R10 y R19, diez rutilos-(Nb,Ta), arrojaron edades de cristalización U/Pb concordantes de 1512±12 Ma. Estas edades coinciden con observaciones de campo, según las cuales los rutilos-(Nb,Ta) de Cachicamo cristalizaron en el Granito de Parguaza hace 1500-1550 Ma en Venezuela, donde depósitos secundarios contienen mineralizaciones comparables (sub-?) económicas de casiterita, rutilo-(Nb,Ta), columbita-tantalita y monacita. El análisis de minerales pesados (circón, ilmenita, magnetita) muestra que los rutilos-(Nb,Ta) se limitan al duricrust del horizonte A, donde circones detríticos de 1525 Ma son coetáneos al Batolito de Parguaza en Venezuela (1500-1550 Ma), mientras los circones del horizonte C (regolito) con 1415 Ma tienen edades similares al Granito Rapakivi Parguaza local (1340-1402 Ma) en estas partes distales del Batolito en Colombia. Así, los rutilos-(Nb,Ta) de Cachicamo no se pueden haber formado in-situ sino que experimentaron un transporte post-exhumación por decenas de kilómetros atravesando lo que actualmente es el valle del río Orinoco.