Laterite Formation Research Articles

Evaluating groundwater potential in water-deficit laterite zones of Eastern India using RS and GIS techniques, combining an analytical hierarchical process for sustainable water resources management

Sustainable groundwater management in water-deficit, laterite-dominated regions need urgent planning, which involve accurate identification of groundwater potential zones (GWPZs). While unsustainable water extraction has exacerbated groundwater availability in laterite zones, laterite is globally known for its limited groundwater potential but has received relatively little research attention. Therefore, the present study aims to examine the role of laterite formation on groundwater potentiality and its relationship with the stage of groundwater development in Paschim Medinipur district of West Bengal in eastern India. This study integrated cost-effective and efficient time-saving tools like remote sensing, and GIS and to produce thematic map layers for overlay analysis and analytical hierarchy process (AHP) to delineate the GWPZs precisely using n = 10 parameters, while a consistency check was performed prior to the integration of these parameters to ensure low subjectivity in the GWPZ. The three identified GWPZ classes cover 30% of ‘good’, 44% of ‘moderate’ and 26% of ‘poor’ zones. The yield data and water level fluctuation analysis revealed that 70% and 60% match the delineated GWPZs. The cross-validation with the receiver operating characteristic curve also demonstrated good (75.1%) prediction accuracy. We found that hydrogeological factors like laterite formations witness around 80% of moderate to poor GWPZ, while poor GWPZ covers half of the laterite belt. However, flood plains and valley fill deposits in the lateritic parts demonstrate moderate to good GWPZ, suggesting laterite formation at variable depths that control groundwater recharge potential. The laterite regions with lower groundwater recharge potential have experienced a 17% increase in water extraction compared to non-laterite areas. Whereas four blocks within the district are partly overlapped with laterite formations and poor GWPZ, which encounter high stages of groundwater development (70–90%), leading to semi-critical to critical conditions. It is attributed to anthropogenic perturbations and hydrogeological conditions, which need urgent planning to ensure sustainable groundwater usage.

Identifying the origin of springs in weathered-fractured crystalline aquifers using a hydrogeophysical approach

Over the last few decades, important advances have been made in the development of relevant hydrogeological conceptual models for crystalline aquifers, and notably for weathered-fractured crystalline aquifers. Paradoxically and contrary to other types of aquifers, these researches never aimed at characterizing springs, the places were groundwater naturally outflows from such aquifers. With such an objective, our methodological approach consisted first of a lithological and hydrogeological description of the aquifer system based on borehole data and outcrops in a representative weathered-fractured crystalline aquifer (Daloa, Ivory Coast). Next, electrical resistivity tomography (ERT) has been used (after validating the appropriate inversion method) to provide the imagery of the weathering profile both below the plateaus and in the valleys where the springs outflow. Piezometric and river discharge data were also processed notably to determine the direction of groundwater flow. Results demonstrate unambiguously that the isalterites aquifer supplies the springs, and that the underlying fractured layer is not directly implied in this supply. ERT combined with borehole and field lithological data also shows that the lateritic formations (alloterites) present near surface below the plateaus, as well as the upper part of the isalterites, were eroded in the valleys, but not deep enough to let the fractured layer outcrop. This conceptual model for springs not only provides a basis for characterizing such complex aquifers, but also provides technical guidance for spring catchment and groundwater protection in these crystalline areas.

The role of clay minerals in the concentration and distribution of critical metals in lateritic palaeosols from NE Iberia

The intense chemical weathering processes that lead to the formation of laterites and bauxites result in the enrichment of critical metals (Sc, V, Co, Ga, Ge, Nb, In, Hf, Ta, W, and REEs), which are of great economic interest and are directly involved in the manufacture of various devices essential for the technology transition. This work focuses on combined geochemical and scanning transmission electron microscopy (STEM) studies of lateritic palaeosols developed in continental profiles (Lower Cretaceous, NE Iberia) in order to evaluate the distribution and concentration of critical metals and their possible relationship with weathering processes. In this study, we show that during the process of laterization the highest weathering produces the highest critical metal concentrations (reaching concentrations of 1914.80 ppm in the lateritic palaeosols and 926.30 ppm in the ferruginous macropisoids). Concentrations normalized to the upper continental crust (Taylor and McLennan, 1985) indicate that both the lateritic palaeosols and the macropisoids are enriched in LREEs (256.81 and 223.01 ppm, respectively) and HREEs (107.11and 110.53, respectively). In the lateritic palaeosols, the (La/Sm)c values are higher than those of (Gd/Yb)c, indicating that the LREEs exhibit higher fractionation with weathering, whereas the opposite occurs for the macropisoids, in which the HREEs have higher fractionation. These data indicate that the HREEs are less mobile than the LREEs during laterization. The critical metals present a good positive correlation with Fe, Ti, and Al, but a good negative correlation with K. STEM images and EDS analyses allowed us to identify REE-phases (including monazite, xenotime, and La, Ce and Nd oxides) and nanoparticles of gold adsorbed on the surface of kaolinite crystals. This shows not only that during the laterization process Fe and Ti oxides act as scavengers for the critical metals, but also that kaolinite controls their distribution.

Weathered ultrabasic rocks in the Lapaopao, an implication for development of nickel laterite

The research conducted in the Lapaopao area focuses on analyzing the process of serpentinization in ultramafic rocks and its impact on the formation of nickel laterite. Ultrabasic rocks containing olivine and pyroxene minerals undergo hydrothermal metamorphism, resulting in the formation of serpentine minerals. The research purposed to understand effect of serpentinization process to development of nickel laterite. Various samples were taken on location to see the correlation in both the Lapaopao sub-block and Babarina sub-block. There are two (2) types of samples were taken, including fresh rock (bedrock samples) and laterite samples (limonite and saprolite material). All samples were analyzed using methods such as XRF, thin section, and XRD. Bedrock samples were analyzed using the thin section method, while laterite samples (limonite and saprolite) were analyzed using XRF and X-RD analyzing methods. The serpentinization process in the Babarina sub-block is generally medium to high level, while in the Lapaopao sub-block low to moderate level. The enrichment of nickel (Ni) in the supergene zone is dominantly influenced by Ni’s ability to replace magnesium (Mg) in weathered serpentine minerals.

Evolution of weathering products over mylonites of the Lom series at Kissi (Bétaré-Oya Gold District, East-Cameroon): Morphological, mineralogical and geochemical mechanisms for trace and rare earth elements enrichment

Weathering and lateritization processes and their implication to the fractionation of trace and rare earth elements (REEs) in soil materials developed upon mylonites in Kissi area of the Bétaré-Oya Gold District (Lom series, East Cameroon) were assessed through morphological (position on the slopes), mineralogical (X-ray diffraction) and geochemical (X-ray fluorescence and Inductively Coupled Plasma-Mass Spectrometry) investigations. Three (03) representative soil profiles were selected and described according to the topography (upslope, mid-slope and downslope). The resulted weathering products are rich in kaolinite (16–49%), gibbsite (3–17%), goethite (5–10%) and hematite (2–10%), with quartz (30–49%) and muscovite (4–31%) as inherited minerals. Geochemical proxies and related ternary diagrams signal an intense chemical weathering (CIA: 43.3–100%; PIA: 41.9–100%), but weak lateritization (IOL: 11.3–40.8%) of parent mylonite under warm and wet tropical climate, that induce the formation of kaolinitic laterites. These processes are characterized by a weak leaching of SiO2 (79.7–52.2%), but strong one of labile elements (WIP: 48.7 to 0.8%; TRB: 228.9 to 15.1 mg kg−1). Al2O3 (16.2–22.8%) and Fe2O3 (4.2–14.0%) are the slightly enriched major oxides in the weathered materials. Some trace elements including Sc, V, Cr, Co, Ni, Cu, Ga, As, Li, Y, Mo, Cs, Hf, W, Pb, Th, Tl, U, Zr and REEs are reported as strongly enriched compared to mylonite, but weak mineralized according to their average contents in the earth's crust (Maximum Enrichment factor: 1.1–38.8). This gives rise of low mining potential of the current weathering products. Nevertheless, Ce (37.8–453.6 ppm), Ba (34.2–379.6 ppm), Cr (100.0–270.0 ppm), V (108.9–215.0 ppm), Zn (23.4–192.0 ppm), Ni (29.3–170.0 ppm) and Rb (2.5–140.0 ppm) are the most abundant in the soil profiles. Topographically, trace and REEs are preferentially enriched and mineralized at mid-slope and downslope of the interfluve. But, the overall behavior and enrichment of elements in Kissi are controlled by the dissolution of rock-forming minerals and their release in the residual soil system, their incorporation into the crystalline structure of newly formed secondary minerals and the lateral water runoff along the slope gradient.

Mechanisms leading to exceptional niobium concentration during lateritic weathering: The key role of secondary oxides

Niobium (Nb) is considered as one of the most immobile elements during supergene weathering due to its low solubility and the expected resistance of the pyrochlore mineral group (A2B2X6Y) in which Nb occupies the B site. Although the resistance of pyrochlore is challenged by direct evidence of alteration in lateritic profiles, the geochemical and mineralogical processes controlling its behavior in the critical zone remains elusive. This study uses a multiscale geochemical, mineralogical and spectroscopic approach to monitor Nb solid speciation in a thick weathering profile. The weathering of the pyrochlore-bearing core carbonatite facies from Morro dos Seis Lagos has resulted in a Fe-enriched laterite with exceptional Nb concentrations (2.91 wt% Nb2O5 on average). The preservation of the successive secondary phases (Ti-, Fe-, Ce-oxides) resulting from weathering processes along the horizons offers the opportunity to track Nb during pyrochlore alteration from the fresh parent rock to the final stages of weathering. Intense lateritization processes have led to an enrichment in Fe and Ti in the pyrochlore B-sites, resulting in the weakening of the structure and its ultimate destabilization due to weaker B-O bonds. After the release of Nb from pyrochlore, the fate of Nb is dependent on the secondary phases formed during weathering. In the lower horizons dominated by Fe oxides, goethite is the main host for Nb (1 wt% Nb2O5) due to its capacity to substitute Fe3+ for Nb5+, in contrast to hematite. In the upper horizons, where Ti oxides have formed during the reworking of the laterite, Nb5+ is preferentially incorporated into brookite and rutile (20 wt% Nb2O5), which may have formed owing to slightly acidic pH and high Nb activity during their growth. The presence of Nb in hollandite and cerianite in a vein from the manganiferous horizon involves the transport of Nb with mobile elements at the scale of the laterite. With this study, we describe a new model accounting for the formation of Nb-enriched laterites. The latter is based on the ability of Nb5+ to substitute for Fe3+, Ti4+, Ce4+ in minerals formed by lateritization processes after its release from pyrochlore. The nature of the secondary Nb-bearing oxides is dependent on the chemistry of the parent rock and the conditions of formation of the laterite. This work, evidencing the mobilization of Nb both at the scale of the mineralogical assemblage and of the entire profile questions the pervasive use of Nb as a geochemical invariant in the critical zone.

Unraveling the sedimentation environment of Marajó island: Insights from geochemical studies and implications for the origin of potentially toxic element in soils

Marajó Island, located at the mouth of the Amazon and Tocantins rivers, is the largest fluvial maritime island on Earth. Its unique location within the Amazon biome and its complex sedimentary dynamics makes it a region of great ecological and socio-economic importance. However, the island is facing significant challenges due to climate change, with projections suggesting permanent flooding of its floodplains in the coming decades. Despite numerous studies on soil geochemistry in the Amazon biome, there is a lack of research specifically focused on Marajó Island. Our study aims to investigate the soil's geochemical properties on the major parent materials in the eastern portion of Marajó Island, seeking to unravel the nature of its complex sedimentary environment, elemental relationships, origin and implications of potentially toxic elements. Samples from seven soil profiles representative of the eastern portion island were collected in a chronosequence, to conduct physical and chemical analyzes: selective dissolution of Fe oxides by sodium citrate-bicarbonate-dithionite and ammonium acid oxalate; quantification of major, trace and rare earth elements (REE) performed by multi-acid digestion and determination in ICP-OES/MS; characterization of weathering intensity by the chemical index of alteration (CIA), chemical weathering index (CWI), plagioclase index of alteration (PIA), chemical proxy of alteration (CPA), and index of compositional variability (ICV); and assessment of potentially toxic elements using enrichment factor and geoaccumulation index. The results indicated that the geochemical variation of soils reflected particularities of the parent material influenced by marine transgression events, and by the current conditions of water table oscillation and humid tropical climate. Holocene Sediments (HS) revealed enrichment by light REE. In soils on Post-Barreiras (PB), Laterite Formation (LF) and Lateritic Debris (LD), the main elements were Al, Fe, and Ti. Due to intense weathering and leaching, negative anomalies were observed in nearly all elements, including the REE. Arsenic enrichment in HS soils was due to the past estuarine influence and the current hydromorphic conditions, while soils on PB, LF and LD are naturally enriched by the parent material.

Scenario analysis of fluoride contamination in the groundwater in Kerala.

The Kerala State is a narrow strip of land in the southwest of India,with the Arabian Sea on the west and the Western Ghats in the east. Recent studies related to contaminant transport in the soil and groundwater in Kerala have reported Fluoride contamination in the aquifers. Due to the poor quality of the surface water sources in the state, the majority of the population in the state depends on groundwater resources for domestic and agricultural uses. When using groundwater for domestic purposes, it is highly important to analyzethe quality of the groundwater. This study focuses on the analysis of the Fluoride transport in the soil and groundwater intwo different lithological units(laterite and coastal alluvium)in the State. The study concluded that the aquifer in coastal alluvium formation is more susceptible to Fluoride contamination compared to the laterite formation.

Redistribution and fractionation of trace and rare earth elements during weathering and lateritization of orthogneiss in Ndokayo (Bétaré-Oya Gold District, South East Cameroon)

Ferralsols in the transitional zone between the Adamaoua and the South Cameroonian plateaus provided evidence of significant economical and scientific interests, but they have received very little attention over the last decades. Thus, macroscopic, mineral and geochemical investigations of two residual soil profiles from orthogneiss in the Bétaré-Oya Gold District (BOGD) with significant morphological differences were conducted in order to assess weathering and lateritization processes and their significance to the occurrence of mineralized trace and rare earth elements. Macroscopically, soil profile in upslope is deep weathered and thick (> 8.0 m thick), exhibiting a 5.1 m thick encrusted mineral level. Inversely, the downslope soil profile is moderately weathered and marked by a near surface water table that partly affects the mineral horizon B. These studied ferralsols result from an intense weathering but weak to moderate lateritization as revealed by the Chemical Index of Alteration (CIA: 87 to 99%), the Plagioclase Index of Alteration (PIA: 98 to 100%) and the Index of Lateritization (IOL: 31.48 to 60.83%). The two soil profiles have a similar mineralogical content characterized by the predominance of newly-formed secondary minerals such as kaolinite (12–40%), gibbsite (12–27%), goethite (7–15%), hematite (2–15%), maghemite (6–10%) and anatase (1–2%). However, a considerable amount of residual quartz (16–56%) and muscovite (3–15%) is evidenced in the weathering products. Geochemically, the weathering products of Ndokayo show weak to moderate depletion of SiO2 (77.26–31.82%), strong depletion of alkali and alkaline earths (Weathering Index of Parker or WIP: 56.73 to 1.56), and moderate enrichment of Al2O3 (12.43–29.20%), Fe2O3 (1.26–23.45%) and TiO2 (0.11–1.77%). V (64.67–210 ppm) and Cr (25.81–720 ppm) are the most enriched trace elements in this area, with their respective maximum enrichment factor of 2 and 7, and display similar geochemical patterns with Fe2O3, suggesting their adsorption or incorporation into the crystalline structure of Fe-oxides. Some others mineralized trace elements (Sc, Ga, As, Mo, Sn, Cs, Pb, Bi, Th and U) exhibit low to moderate contents, even if their mineralization indices range between 1 and 81. This is indicative of low mining potential of the Ndokayo weathering products. Finally, the deep and intense weathering of orthogneiss, coupled with weak to moderate lateritization of the weathering products in the study area is controlled by rock type involving the formation of kaolinitic laterites and bauxitious kaolins with weak mineralization indices of some trace and rare earth elements.

Geochemistry and microbiology of tropical serpentine soils in the Santa Elena Ophiolite, a landscape-biogeographical approach

The Santa Elena Ophiolite is a well-studied ultramafic system in Costa Rica mainly comprised of peridotites. Here, tropical climatic conditions promote active laterite formation processes, but the biogeochemistry of the resulting serpentine soils is still poorly understood. The aim of this study was to characterize the soil geochemical composition and microbial community of contrasting landscapes in the area, as the foundation to start exploring the biogeochemistry of metals occurring there. The soils were confirmed as Ni-rich serpentine soils but differed depending on their geographical location within the ophiolite area, showing three serpentine soil types. Weathering processes resulted in mountain soils rich in trace metals such as cobalt, manganese and nickel. The lowlands showed geochemical variations despite sharing similar landscapes: the inner ophiolite lowland soils were more like the surrounding mountain soils rather than the north lowland soils at the border of the ophiolite area, and within the same riparian basin, concentrations of trace metals were higher downstream towards the mangrove area. Microbial community composition reflected the differences in geochemical composition of soils and revealed potential geomicrobiological inputs to local metal biogeochemistry: iron redox cycling bacteria were more abundant in the mountain soils, while more manganese-oxidizing bacteria were found in the lowlands, with the highest relative abundance in the mangrove areas. The fundamental ecological associations recorded in the serpentine soils of the Santa Elena Peninsula, and its potential as a serpentinization endemism hotspot, demonstrate that is a model site to study the biogeochemistry, geomicrobiology and ecology of tropical serpentine areas.Graphical

Revealing the radiation damage and Al-content impacts on He diffusion in goethite

Over the past few decades, the (U-Th)/He geochronological method on goethite has been more and more applied to date laterite formation and evolution or ore-deposit formation. However, questions remain on possible He loss by diffusion due to the polycrystalline structure of goethite and associated underestimation of the goethite crystallization date given by the (U-Th)/He age. Prior studies estimated helium loss in goethite to range from 2 to 30%, but no relation or models have been produced to explain such values. To clarify the situation, we firstly performed a complete review of experimental He diffusion data in natural goethite, that reveals the link between activation energy and He loss with the damage dose. To understand He diffusion behavior in goethite and model the He loss, natural defect and alpha damage as well as the chemical composition and growth structure effect on He diffusion have been investigated thanks to a multi-scale study. We used numerical simulations combining the Density Functional Theory (DFT) at the atomic scale and Kinetic Monte Carlo (KMC) simulations at the macroscopic scale. We found that He diffusion is purely anisotropic along the preferential elongated axis (i.e., b-axis) and He leaks out easily in defect-free goethite and Al-goethite. The consequence of this anisotropy is that crystallographic defects and alpha damage strongly lower the He diffusivity in goethite and Al-goethite by obstructing the diffusion channel or trapping He along the b-axis. Defect and damage impact on He diffusion is even larger for Al-goethite. The obtained He diffusion parameters for goethite containing defect and damage are similar to the activation energy and He diffusional loss obtained in natural goethite from the literature. We demonstrate the systematic dependence of the diffusion coefficient with damage dose and the impact of Al on He retention. He atoms are retained only at the favor of obstructions blocking the diffusion and vacancies trapping them in the goethite structure. The consequence of the diffusive behavior is that a part of He diffuses out of the crystal until sufficient damage accumulated along the b-axis. The diffusion domain size is the channel length along the b-axis rather than the whole crystallite size. To correct the He loss this study proposes estimation of the He retention and needed corrections for different types of goethite.

Mineralogy and geochemistry of Permian–Triassic lateritic‐bauxitic horizons, eastern and central Alborz, Iran: Implications for provenance, palaeogeography, and palaeoclimate

This paper presents a survey of geological attributes on the lateritic‐bauxitic deposits to examine their provenance, palaeogeography, and palaeoclimate condition in the Permian–Triassic boundary of Alborz Mountain, north Iran. The mineralogical analysis revealed that haematite, quartz, goethite, kaolinite, diaspore, boehmite, and anatase are the major rock‐forming minerals in these deposits. The major oxide composition of samples detected that enrichment of Al2O3 (up to 31.5%) and Fe2O3 (up to 37.9%) led to the formation of laterite, kaolinitic laterite, and bauxitic kaolinite. The distribution of trace and rare elements provides information about the enrichment of deposits concerning immobile elements. Employing geochemical proxies such as Al2O3/TiO2, bivariate diagrams of Eu/Eu* versus Sm/Nd and TiO2/Al2O3, enrichment of samples relative to heavy rare earth elements, and positive Eu anomaly revealed that the deposits originated from intermediate to mafic rocks. Several factors are inferred to be responsible for the transformation of parent rock(s) into lateritic‐bauxitic deposits: The high values of CIA, CIW, and PIA (mostly above 80) and increase of kaolinite point to deep to moderate parent rock(s) weathering, which is consistent with warming and humidity around the Permian–Triassic boundary. In continuation, transportation and trapping of weathered materials above the karstified carbonate bedrock of the Ruteh Formation and environmental interactions induced the formation of new minerals in a transitional environment near the vadose zone. The deposits have a generic correspondence with Palaeotethys Oceanic crustal subduction due to tectonic uplift, exhumation of bedrock, and regional sea‐level fall at the end of Palaeozoic that offered an opportunity for lateritization process.

Lateritic processes in Madagascar and the link with agricultural and socioeconomic conditions

Madagascar hosts a youthful landscape atop old bedrock geology. Observed rapid surface uplift – possibly a consequence of sub-plate mantle plume activity – does not fit the concept of “The Red Island”, i.e. thick piles of laterite, formed by slow chemical weathering that requires prolonged periods of tectonic quiescence. Here, we document the results of a three-year field campaign in which we sought to interrogate and decouple the climatic and tectonic drivers behind laterite formation, and establish a tentative link to agricultural productivity, which may reinforce local levels of poverty. We installed 45 rain gauges and merged their data with a satellite precipitation product to develop a new high-resolution climatology. We also collected 11 sediment samples from which we established 10Be-derived erosion rates; and measured laterite/saprolite thickness at 60 localities. The thickest lateritic profiles coincide with a narrow band of annual rainfall, suggesting that laterite evolution processes co-evolved with climate changes. Laterite thickness correlates negatively with erosion rate, and strongly positively with the headcount index of poverty. In the absence of agricultural technology, we propose a direct link between the local prevalence of lateritic soil and poor agricultural productivity. We also suggest that the spatial distribution of uplift/erosion and precipitation governs the distribution and thickness of laterite. Uplift and erosion rates vary dramatically over small distances, restricting the development of thick laterite to two small patches that straddle the central Hauts Plateaux.

Reading the climate signals hidden in bauxite

The dynamics of tropical weathering through time with the formation and long-term evolution of laterite associated with climatic and geodynamic forcing is still a poorly explored issue. To better access this, we focused on lateritic-bauxitic duricrusts from the well-explored, 300 m high Kaw mountain in northeastern French Guiana. Macroscopically homogeneous Fe (oxyhydr)oxides-rich subsamples were separated from 10 bulk samples. Bulk- and subsamples were investigated by mineralogical and geochemical analyses and (U-Th)/He geochronology. The samples show a large heterogeneity on the macro- and microscopic scale reflecting different stages of duricrust formation and evolution through processes of dissolution and (re)precipitation of Fe (oxyhydr)oxides. The 284 (U-Th)/He ages obtained for goethite α-(Fe, Al)OOH and hematite α-Fe2O3 range from 30.5 ± 3.1 to < 0.8 Ma and show large variability within a sample. The oldest hematite and Al-poor goethite subsamples precipitated since 30 Ma and formed while kaolinite was stable. Precipitation of Fe-minerals increased since ∼ 14–12 Ma but still happened under ferruginous lateritic, non-bauxitic conditions. The dissolution and (re)precipitation of Fe minerals, Al-substitution in goethite, and the overall enrichment in Th, as well as gibbsite precipitation indicate an intensification of weathering and a shift towards bauxitic conditions since the end of the Miocene. The Th-, U-, and Al-rich Fe phases formed in this late episode of intense weathering partially replace the oldest, often Th- and U-poor phases leading to a considerable age spread. We claim that this episode of intensified weathering, which had its peak at ca. 6–2 Ma, corresponds to the bauxitization of the lateritic cover of Kaw mountain.Our proposed model of lateritization since at least 30 Ma and bauxitization since the late Miocene provides new constraints on the timescale and intensity of weathering at Kaw mountain. The onset of lateritization in French Guiana (Kaw region) is potentially older than ca. 30 Ma and was possibly synchronous with the development of bauxites in neighboring countries, and differences in the Paleogene weathering intensity might be due to different drainage capacities of the parental material. Late Neogene bauxitization suggests a regional increase in precipitations and drainage potentially linked to increased incision owing to local uplift.Finally, we confirm that a detailed combination of geochronological results coupled to mineralogical and geochemical analyses improves our understanding of tropical weathering processes and duricrust formation by placing mineralogical and geochemical processes into a temporal framework.

CONTRIBUTION TO THE HYDROCHEMICAL KNOWLEDGE OF AQUIFERS IN THE DEPARTMENT OF TANDJILE-EAST, SOUTHERN CHAD

The province of Tandjile is one of the 23 provinces of the Republic of Chad. The drinking water supply rate in this region remains low. Part of the population obtains its water supply through open wells and / or surface water. Climatic and anthropogenic variations in recent years have shown how much groundwater can be influenced both in terms of its quality and its quantity to be used. The objective of this study is to provide knowledge on the state of the hydrodynamic and hydrochemical parameters of the aquifer of the department of Tandjile-Est to help decision-makers in their approach. This study is based mainly on existing data collected in Chadian institutions and literary journals. The analysis of these data showed that the lithology is represented by clayey, sandy, lateritic formations and clay-sandy mixtures. The aquifers are sandy and sandy-clayey. The groundwater temperature values are in equilibrium with those of the air, the pH shows values close to neutrality and the electrical conductivity below standards (Chad, WHO). The groundwater in the study area is not very mineralized and the concentrations of elements indicating contamination (nitrates, chloride, etc.) are clearly in traces. Chemical analyzes revealed two chemical facies: calcium and magnesium bicarbonate and sodium and / or potassium bicarbonate.

Mobilization and health risk assessment of fertilizer induced uranium in coastal groundwater

Uranium (U) in groundwater is hazardous to human health, especially if it is present in drinking water. The semiarid regions of southern India chiefly depend on groundwater for drinking purposes. In this regard, a comprehensive sampling strategy was adopted to collect groundwater representing different lithologies of the region. The samples were collected in two different seasons and analysed for major and minor ions along with total U in the groundwater. Two samples during pre monsoon (PRM) and seven samples during post monsoon (POM) had U > 30 μgL−1, which is above the World Health Organization's provisional guideline value. The high concentration of U (188 μgL−1) was observed in the alluvial formation though a few samples showed the release of U near the pink granite (39 μgL−1) and the concentration was low in the lateritic formation (10 μgL−1). The uranyl carbonato complexes UO2(CO3)22− and UO2(CO3)34− were associated with high pH which facilitated the transport of U into groundwater especially during POM. U3O8 is the major form observed in groundwater compared to either UO2 or UO3 in the both seasons. The uranium oxides were observed to be more prevalent at the neutral pH. Though U concentration increases with pH, it is mainly governed by the redox conditions. The principal component analysis (PCA) analysis also suggested redox conditions in groundwater to be the major process facilitating the U release mechanism regardless of the season. The POM season has an additional source of U in groundwater due to the application of nitrogenous fertilizers in the alluvium region. Furthermore, redox mobilization factor was predominantly observed near the coastal region and in the agricultural regions. The process of infiltration of the fertilizer-induced U was enhanced by the agricultural runoff into the surface water bodies in the region. Health risk assessment was also carried out by determining annual effective dose rate, cancer mortality risk, lifetime average daily dose and hazard quotient to assess the portability of groundwater in the study area. Artificial recharge technique and reducing the usage of chemical based fertilizers for irrigation are suggested as sustainable plans to safeguard the vulnerable water resource in this region.

Geochemistry of paleokarst-hosted uranium anomalies at Abu Zarab area, southwestern Sinai, Egypt

This paper discusses the behavior of elements in the paleokarst and attempts to establish the relation between uranium and other elements in the paleokarst conditions at Abu Zarab locality. Abu Zarab is a small area within Um Bogma environ located in southwestern Sinai, Egypt, where paleokarsts are widespread, especially in carbonate rocks. One of these paleokarsts at Abu Zarab area was selected to geochemical investigation. The studied paleokarst was dissected by three excavated trenches constructed by Nuclear Materials Authority team to reveal its geologic features. It is filled with lateritic components represented mainly, by intercalation of clay with gibbsite and kaolinite, ferruginous siltstone and clay minerals.Twelve samples were collected from the walls of these trenches and chemically analyzed for this purpose in term of major oxides, traces and rare earth elements. The geochemical data of the major oxides display three important geochemical processes in the lateritic components of the paleokarst: (1) Enrichment of aluminum and iron; (2) depletion of calcium and magnesium (3) silicon experienced both depletion and enrichment. The geochemical data of trace and rare earth elements (REE) display enrichment of U, Cu, Pb, Zn, Ag, As and Cd with obvious enrichment of REE and conversely some elements were depleted such as V, Cr and Ga. It also, noticed that uranium has strong positive correlation with both iron and Aluminum.It is more likely, according to geochemical features of radioactive elements, that the uranium enrichment process was later than the laterite formation and the iron played an important role in capturing and trapping uranium.

Episodic weathering in Southwestern Amazonia based on (U[sbnd]Th)/He dating of Fe and Mn lateritic duricrust

This study presents the results of mineralogical analysis and (UTh)/He dating of micrometric grains of hematite, goethite, cryptomelane and hollandite from six samples of bauxite, Fe, Mn, Mn-Al-Fe, MnAl and Mn-Al-P duricrusts located in southwestern Amazonia (Brazil). The samples were collected at different elevations to constrain temporal epochs of lateritization and to provide insights into the cratonic landscape evolution of Proterozoic and Paleozoic terrains in Brazil. Three main phases of duricrust formation were recognized, indicating a long period of lateritic weathering: The first phase, preserved as a fragment in Fe duricrust on the Paleozoic sedimentary rocks, began in the Permian (~290 Ma) and lasted until the Late Cretaceous (~65 Ma). The second (and best preserved) phase formed Mn duricrusts on the Paleoproterozoic Apuí lateritic surface (150–250 m a.s.l.) and on the Aripuanã lateritic surface (<170 m a.s.l.) between the Late Cretaceous (~90 Ma) and Oligocene (~32 Ma). The third phase of lateritic formation occurred from Late Oligocene to Early Miocene times (~28 to ~19 Ma). A degradation process, indicated by a goethite cortex on hematite fragments, took place in the Early to Late Miocene (~23 to ~13 Ma), affected all previous lateritic duricrusts, and can be correlated to an epoch of extensive bauxite duricrust formation in the region. These Fe, Mn and Al aggradation episodes indicate strong and widespread polyphasic weathering in southwestern Amazonia since ~290 Ma, as expected on stable cratonic terrains exposed to alternating hot, humid, and dry climate conditions over time.

On detailed field-based observations of laterite and laterization: a study in the Paschim Medinipur lateritic upland of India

The term ‘laterite’ and the process ‘laterization’—both have raised perpetual scientific debates. The present study reviews the relevant scientific pieces of literature associated with tropical red lateritic and ferralitic soils and tries to justify them with the observations in the Paschim Medinipur Lateritic Upland. This particular area is practically the natural laboratory for observing the laterization process. The area exhibits a distinctive geomorphologic, hydrological, and climatic characteristic over an evolutionary geological setting. The favorable tropical climate, intense weathering, groundwater movement with seasons, and neo-tectonic upliftment exerts complex influences on the pedo-geomorphological distinctiveness of this area. Presence of planation surfaces, typical scarp development along the surface margins and exposure of deep lateritic profiles by basal sapping, accelerated erosion of the margin, and formation of rills and gullies with waxing slope development are worthy of being synced with available scientific understandings. The study is based on extensive field observations, profile studies, and soil sample analysis from different geomorphic units. The study reveals that the role of tectono-climatic evolution has had a massive influence on characteristics and development of the present lateritic formations. Transportation and deposition of Neogene ferruginous sediments over basin shelf region as paradeltaic formation, alternating wet (June–October), and dry (November–May) monsoonal climate with adequate rainfall and iron segregation and relative accumulation along with neo-tectonic modification are the important considerations regarding ferrugination process in the area under study. The justifications of the observed attributes of this particular tropical lateritic landscape may be used as a reference work for future scientific studies and model building processes on the same in this area as well as the other parts of the world.

Contribution of bacterially-induced oxidation of Fe-silicates in iron-rich ore to laterite formation, Salobo IOCG mine, Brazil

A diverse array of microorganisms, found within the uppermost lithosphere, can mediate the dissolution and precipitation of minerals and therefore contribute to the formation of laterites. The Salobo iron-oxide copper gold (IOCG) mine in Brazil is an ideal environment to examine the specific interaction between iron-oxidising bacteria and ferrous iron-bearing minerals during formation of a ~60 m thick laterite weathering profile. We identified bacteria using DNA extracted from samples in active weathering zones. Many of the identified species are capable of oxidising the ferrous iron and/or reduced sulphur that occurred in minerals associated with the unweathered rocks of the deposit. Fe-bearing phyllosilicates have been variably altered to clays along cleavage planes by bacterial iron oxidation. Accelerated weathering of fresh rocks in laboratory-scale leaching column experiments was conducted using an endemic Acidithiobacillus ferrooxidans ssp. previously cultured from the Salobo mine. There were strong similarities between field samples from the Salobo laterite zone, and experimental leachate chemistry, associated precipitates, and fossilised bacteria remnants, particularly with respect to ferric (oxyhydr)oxide formation. Groundwaters in the Salobo laterite zone have circumneutral pH, whereas some iron-oxidising bacteria thrive in, and locally create, more acidic conditions (~pH 3). The leaching experiments showed that bacterially-facilitated silicate weathering, and bornite (Cu5FeS4) oxidation, can consume acid generated by bacterial oxidation reactions, creating an effective equilibrium with ferric (oxyhydr)oxide precipitation. However, the current acid neutralisation capacity of the ferricrete horizon at the top of the laterite zone was minimal. While bacterial activity promoted mineral oxidation and decomposition within the thick laterite at the Salobo mine, related iron mobility is restricted to the micrometre scale by essentially instantaneous precipitation of ferric (oxyhydr)oxide that eventually transforms via inorganic dehydration to goethite and hematite. Similar processes to those described in this study have likely occurred during the formation of many other iron-rich laterites.