Lateritic Profiles Research Articles

The Geology, Geochemistry, and Mineralogy of the Moa Bay Ni Laterite Mining District, Cuba

Abstract The Moa Bay lateritic Ni-Co mining district (eastern Cuba) has total mineral resources of 198.54 million metric tonnes (Mt) at 1.07% Ni and 0.12% Co. Laterite profiles from this district are characterized by their oxide-dominated ore zones. Laterite profiles from the Yagrumaje Norte, Punta Gorda, and Yamanigüey deposits contain average Ni and Co concentrations in the oxide zone of 0.88 and 0.12%. Goethite is the most abundant mineral in the oxide zone and the most important Ni-Co-Sc–bearing mineral, with median NiO, CoO, and Sc contents of 0.78 wt %, 0.07 wt %, and 58 ppm, respectively, and up to 2.77 wt %, 0.26 wt %, and 117 ppm. Maghemite is also widely present (avg of 5% and up to 19% modal proportion) and represents an important but largely ignored Ni- and Co-bearing ore phase, with median NiO and CoO concentrations of 2.11 and 0.25 wt %, respectively, and maximum values of 13.9 and 1.84 wt % each. Nickel and Co substitute for ferric iron in the structure of maghemite. Manganese oxyhydroxides (lithiophorite and lithiophorite-asbolane intermediate), which are also significant Ni-Co–bearing phases, have median NiO and CoO contents of 10.6 and 6.41 wt %, respectively. Some Mn oxyhydroxides, which formed after replacing goethite, also contain significant amounts of Sc (up to 94 ppm). Although most deposits in the Moa Bay lateritic district are classified as oxide type, Yamanigüey (avg Ni grade of 1.98%) is characterized by well-developed saprolite horizons, with secondary serpentine (serpentine II) and garnierite being the main Ni-bearing phases.

Thermodynamics of the α-FeOOH (goethite)-ScOOH solid solution

Scandium (Sc) is a rare element that finds uses in modern technologies. Thermodynamic properties of Sc phases could help in the development of innovative technologies to extract Sc from mining waste. In this work, we investigated the FeOOH–ScOOH solid solution with the goethite structure. The end members and five intermediate compositions were synthesized and characterized. The lattice parameters show that the solid solution is non-ideal, with complex behavior induced by the Fe–Sc substitution. The excess unit-cell volume deviates negatively for the Sc-rich region, and positively for the Fe-rich region from the ideal behavior (Vegard’s law). Enthalpies of dissolution were determined by acid-solution calorimetry in 5 mol·dm-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\cdot \\hbox {dm}^{-3}$$\\end{document} HCl at T = 343.15 K. Enthalpies of mixing (ΔmixH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _{mix}H$$\\end{document}), calculated from the experimental data, are small and positive. The available data allow for fitting the data as ΔmixH=Wx(1-x)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _{mix}H = W x (1-x)$$\\end{document}, with the mixing parameter W=15.2±\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W = 15.2\\pm$$\\end{document}1.0 kJ·mol-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\cdot \\hbox {mol}^{-1}$$\\end{document}. Using ΔfGo\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _fG^o$$\\end{document} of ScOOH from earlier literature, we calculated a Lippmann diagram that shows that Sc should strongly partition into the aqueous phase upon goethite precipitation. The field observations from lateritic profiles show that Sc is primarily harbored by goethite via adsorption. It seems that under weathering conditions, thermodynamically driven partitioning of Sc3+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {Sc}^{3+}$$\\end{document} into the aqueous phases and its subsequent adsorption onto goethite surfaces controls the mobility of Sc in the weathering profiles.

Observações de campo nos materiais lateríticos de Mosqueiro (Belém, Pará) como potenciais pigmentos minerais naturais

Back in the 1980s, when I began exploring the cliffs of Baía do Sol (Mosqueiro, Belém, Pará), carved into immature laterite profiles derived from clayey and sandy sedimentary rocks of the Barreiras Formation, I was very impressed by the colorful tones of the mottled horizon in these profiles. With my children (they were still “children”) we played painting each other and it was really fun. When reading and studying cave paintings in the Amazon and around the world, it was evident, obviously, that these paintings were made with different materials, mainly Fe and Mn oxyhydroxides, coal, ash and organic extracts.

Application of (U-Th)/He hematite geochronology to the Çaldağ lateritic Ni-Co deposit, Western Anatolia: Implications for multi-stage weathering events during interglacial periods/segments

Lateritic Ni-Co deposits are supergene deposits that develop due to intense weathering of the underlying ultramafic parent rocks and/or their serpentinized equivalents under tropical to sub-tropical climatic conditions. These deposits provide not only important sources of valuable metals such as iron, aluminium, nickel, and cobalt, but they also provide a proxy for paleoclimatic conditions. In this regard, geochronological studies on these deposits are critical to determine the timing of the paleoclimatic conditions, which is important for a better understanding of the paleoclimate at regional scale and for identification of favourable weathering periods that can be targeted in the exploration of undiscovered lateritic deposits in a region. In this contribution, we report hematite (U-Th)/He geochronology results from a well-preserved Çaldağ lateritic Ni-Co deposit in Western Türkiye. We sampled the different parts of the lateritic profile from the different laterite zones at the Çaldağ deposit and carried out analyses of polished thin section to determine and identify the phases of hematite formation and primary hematite formed during primary lateritization. Then, we applied scanning electron microscopy (SEM) analysis and TESCAN Integrated Mineral Analyser (TIMA) mineral mapping to identify the suitable areas on primary hematites for subsequent (U-Th)/He dating.Primary hematites are detected at the base of the lateritic profiles (transition between the limonite zone and altered serpentinite) that are only in-situ parts of the laterites exposed in two different pits in the deposit. The obtained (U-Th)/He dates of ca. 502, 206, 178, and 63 ka correspond to the interglacial periods. The three youngest (U-Th)/He dates (206, 178, and 63 ka) from the weathering front of the hematite pit become younger towards the deeper parts of the profile in the direction of weathering. The ages indicate the weathering processes should have lasted until the Quaternary with some interruptions during interglacial periods/segments, despite the fact that the main intensive lateralization period is thought to be during the Middle Eocene.This study presents the first hematite (U-Th)/He dating of lateritic Ni-Co deposits and demonstrates the reliable use of this method after a careful selection of hematite samples. Our results suggest that, in contrast to the short-living lateritization model for lateritic Ni-Co deposits, they may have a multi-stage weathering history throughout their long-lasting development. In addition, the study showed that it has huge potential for the dating of lateritization and weathering processes that are related to paleoclimatic events. Finally, knowledge of the favourable paleoclimatic periods of chemical weathering in a region may help in determining the potential areas for ultramafic exposures for discovering new lateritic deposits.

Co, Sc, and Ni enrichment in the Cagdianao nickel laterite deposit, Dinagat Islands, Philippines

Abstract Nickel laterites are soils that are derived from the weathering of mafic and ultramafic rocks. These deposits are being extracted mostly for their economic Ni and Fe content. However, in recent studies, the potential of nickel laterites to hold significant amounts of critical metals such as Sc and Co are already being investigated. In the Philippines, nickel laterite deposits form through the weathering of ophiolitic units. One of these is the Cagdianao nickel laterite deposit which was derived from the weathering of the ultramafic units of the Dinagat Ophiolite Complex in Dinagat Island, Surigao Del Norte, Philippines. The bedrock of the Dinagat Ophiolite Complex is dominantly comprised of harzburgite. This harzburgite bedrock is overlain by a nickel laterite profile consisting of horizons of Mg- and Si-rich rocky saprolite, earthy saprolite, Fe-rich limonite, and an Al-rich topsoil. Drillcores and field exposures of the nickel laterite profile were observed, sampled, and subjected to petrography, whole rock geochemistry (XRF and ICPMS), and mineral chemistry (LA-ICPMS) analyses. In terms of major elements, Fe is dominant in the limonite zone (up to 59.76 wt.%). Mg and Si are more enriched in the rocky saprolite layer (up to 28.41 and 37.41 wt.%, respectively). In terms of the critical minerals, Ni is more enriched in the saprolite zone (up to 29936 ppm) while Co and Sc are more enriched in the limonite zone (up to 1080 and 86 ppm, respectively). Elemental mapping of the bedrock samples reveals the strong affinity of Ni to olivine and serpentine. Sc was revealed to have a greater affinity with orthopyroxenes. Lastly, Co is observed to have a slight affinity with olivine. These results show a relative enrichment of Co in the profile, particularly in the limonite. Co within the laterite profile also has a very strong affinity with MnO. Similarly, the highest concentration values for Sc were also observed in the limonite. It also exhibits an affinity for Fe2O3 and Al2O3. Lastly, Ni was observed to have a strong affinity with olivine and serpentine minerals in the bedrock and the rocky saprolite horizons. Within the deposit, Ni is the main commodity while Co, Sc, and REEs can be considered as by-products.

Using Soil Magnetic Susceptibility Proxies to Estimate Overburden Thickness Overlying Ore of Lateritic Soils in Sulawesi Island Indonesia

Sulawesi Island is one of the largest Ni ore producers in Indonesia. It is also expected to be a significant potential source of some critical metals (e.g., Co, Sc, rare-earth elements, and platinum-group elements). However, few studies show the post-mining impact on some heavy metal elements concentrated in this area. Therefore, improving the efficiency and effectiveness of soil organization and its effect on soil reclamation after mining is helpful. This study aimed to determine the accuracy in estimating the thickness of the overburden covering the nickel ore body profile from lateritic nickel post-mining areas by magnetic susceptibility measurements to discrepancy the overall laterite horizon, whereas χLF and χFD are used to distinguish the overburden zona and limonite and saprolite zone. The lateritic profile studied consists of soil formation of Fe-rich material in the Morowali, and Pomalaa block. We also evaluated the chemical element content of the soil and understood the relationship between the magnetic and geochemical properties of the soil. This study reveals the superparamagnetic (SP)-enriched soils indicated with the increase of the FD% values into the upward horizon, where the maximum values of FD are generally found at ranges 1 to 4m, indicating the overburden layers. Meanwhile, in the depth of 4m to 6m, the values of FD vary only slightly in the lower part initiated by the limonite layers, and then > 6m decreases sharply to the bottom, indicating the saprolite layers. The chemical element mobility trends indicate that Fe, Co, Cr, Mn, and Ti increase toward the layers, which is the same pattern as in FD. Due to this, parameters magnetics may also be a new geophysical approach for estimating the distribution of economically valued minerals on lateritic soils. The strong correlation of Co with Fe, Mn, and Cr in all layers indicates the influence of weathering o n these ultramafic rocks. This suggests an increasing trend toward prolonged pedogenesis.

Nickel enrichment during lateritization of ophiolitic ultramafic rocks: A case study from the Kelurahan Pondidrha laterite profile in Sulawesi, Indonesia

The Southeast Asia is one of the most important producers of Ni-laterite deposits in the world, attracting more and more attentions in recent years. However, the lateritization processes as well as the enrichment mechanisms of Ni have not been well constrained. Recently, a Ni-rich laterite profile (KPP) was newly found in the Kelurahan Pondidrha area, Sulawesi island, Indonesia. To better understand the lateritization and Ni enrichment mechanisms, in this study, detailed mineralogical and geochemical analyses were conducted on the KPP. The KPP can be divided into bedrock, saprolitic and lateritic layers from bottom to top. The bedrock is serpentinized harzburgite mainly composed of olivine, serpentine and pyroxene, while the saprolitic layer mainly consists of Fe oxides, olivine, serpentine and pyroxene, and the lateritic layer is dominated by quartz and Fe oxy-hydroxides. Nickel is mainly hosted by serpentine in the bedrock and saprolitic layers, but by oxy-hydroxides in the lateritic layer. From the bedrock to the lateritic layer, whole-rock MgO and CaO contents decrease continuously while TFe2O3 contents increase, with TiO2/Al2O3, Zr/Hf and Pd/Pt ratios keeping stable. Combined with whole-rock pH value deceasing from the bedrock to the weathering products, the above results indicate the decomposition of silicate minerals and the formation of Fe oxides/oxy-hydroxides through hydrolysis during in-situ weathering. This led to the release of Ni and its adsorption by secondary minerals (e.g., Fe oxy-hydroxides in the lateritic layer and serpentine in the saprolitic layer). Nickel shows the highest contents in the saprolitic layer rather than the more weathered lateritic layer, indicating the decoupling between the lateritization and the Ni enrichment degrees. This could be due to the enhanced leaching of Ni from the surface under the tropical rainforest climate and the secondary adsorption in the deeper levels. These Ni enrichment features are commonly observed in the Mg-silicate type laterites, which are distinct from the oxide-type showing highest Ni enrichment in the lateritic layer, indicating that lithology played a critical role in controlling the lateritization and Ni enrichment.

Low Mo mobility during the laterization of ultramafic bedrock: Evidence from the East Sulawesi Ophiolite, Indonesia

Mo (isotope) cycling during the chemical weathering of ultramafic bedrock remains poorly quantified, mainly as a result of the analytical challenges caused by low Mo concentration and complex matrix effects in these rock types. Here, we utilize an improved chemical separation protocol that enables the extraction of Mo while reducing Ru and Fe matrix effects. We apply this method to lateritic weathering profiles developed over ultramafic bedrock in a high-intensity tropical weathering regime. The Mo concentrations in the laterite samples are higher (0.022 to 0.58 μg·g−1) than those of the peridotite bedrock (0.006 to 0.021 μg·g−1). The concentration-weighted average δ98Mo of the laterite profiles is −0.05‰ (n = 17), which is slightly higher but very close to the average δ98Mo of the peridotite bedrock (0.17 ± 0.21‰; 2SD; n = 5). Weakly-laterized samples show somewhat low δ98Mo with a minimum of −1.03‰ and Δ98Molaterite-bedrock up to −0.86‰, possibly as a result of preferential adsorption of liberated light Mo onto Fe (oxyhydr)oxides. In contrast, strongly-laterized samples show an overall Mo concentration gain and a slight isotopic shift towards higher bulk δ98Mo, with a maximum δ98Mo of +0.12‰ and Δ98Molaterite-bedrock up to +0.42‰. This likely reflects the re-scavenging of Mo released from weakly-laterized horizons to the ubiquitous Fe (oxyhydr)oxides, with potential superimposition of additional heavy Mo from atmospheric and/or groundwater input. Overall, this suggests a small contribution of dissolved Mo derived from ultramafic bedrock weathering in tropical settings to the aquatic environment.

Weathering as a control on the triple oxygen isotopes of groundwater-associated ferromanganese deposits: lessons from the Grimlock Ni–Co–Mn prospect, Northern Territory, Australia

At the Grimlock laterite deposit (Northern Territory, Australia), Co and Ni mineralization occurs mainly in the Mn-oxide rich layers of the ferromanganese (Fe-Mn) crust overlying ultramafic bedrock. Groundwater-associated Fe-Mn crusts consist of mineral (e.g. Mn-oxide, Fe-oxyhydroxide and silicate) groups suitable for studying triple oxygen isotopes and present unique interpretative challenges (e.g. small Mn-oxide fractions relative to Fe-Mn precipitates from other formation environments and extensive weathering). We evaluate triple oxygen isotopes within the context of changes to properties (i.e. mineralogy, major and trace element geochemistry, and degree of weathering) of a lateritic profile. We use pre-existing mineral-water fractionation factors, meteoric water δ 18 O and temperature data to calculate δ 18 O values of fully altered mineralogical endmembers, then, using mass balance, discuss scenarios to elucidate measured whole-rock δ 18 O values. The δ ′ 18 O (′ denotes linearized notation) and Δ ′ 17 O of near-surface samples (0–8 m) are generally lower (mean of 8.892‰) and higher (mean of −0.141‰), respectively, than the δ ′ 18 O (mean of 12.767‰) and Δ ′ 17 O (mean of −0.176‰) of samples from greater depths (19–22 m). At 16–17 m depth, δ ′ 18 O and Δ ′ 17 O are relatively high (means of 17.509 and −0.118‰, respectively). The measured whole-rock δ 18 O values are explainable by substituting lower δ ′ 18 O values for the Mn-oxide and Fe-oxyhydroxide fractions, and higher δ ′ 18 O values for the aluminosilicate fraction, changes coinciding with greater alteration. These results suggest that mineral weathering is primarily responsible for observed variations in the triple oxygen isotopes of groundwater-associated Fe-Mn crusts, rather than variation in the initial source of oxygen incorporated into Mn-oxide. Supplementary material: Grimlock sample photographs, XRD patterns and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7071907

Identification of Lateritic Nickel Deposits Potential in the Kokoe Area, Kabaena Island, Central Buton Regency, Southeast Sulawesi Province, Indonesia

The study is situated in the Kokoe Region of Central Buton Regency, Southeast Sulawesi, specifically in the southern part of Kabaena Island. Its primary objective is to assess the potential of nickel laterite in the designated area. The research methodology involved microscopic analysis of bedrock using a polarizing microscope, examining the drilling data, including logging descriptions, and utilizing XRF geochemical analysis (Ni, Fe, Al2O3, Co, Mg, and SiO2) from 32 drilling sites. Both elementary grade and laterite profiles were visualized using Strater 5 software to simplify the representation of laterite profiles. Petrographic analysis divided the bedrock into two lithological units: serpentinized lherzolite and serpentinite. The laterite profiles in the study area were classified into four types: type A, type B, type C, and type D. Type A profiles consist of bedrock, saprolite, and limonite layers covered by clay and colluvium. Type B profiles lack limonite and instead exhibit saprolitic rock and rocky saprolite layers on top of the bedrock. Type C profiles comprise bedrock, saprolitic rock, rocky saprolite, limonite, and topsoil layers. Type D profiles contain three zones, namely bedrock, colluvium, and clay, but lack limonite and saprolite layers. Among the four profile types, type A and type C profiles show promising potential due to higher average grades of Ni and thicker saprolite zones compared to the type B and type D profiles.

New insight into genesis of the Maojun laterite Fe–Mn deposit in the Lanshan area, Hunan Province, South China: Evidence from detailed mineralogical and geochemical studies

Laterite Fe–Mn deposits are widespread in South China, with the majority of Fe–Mn ore being present in residual quaternary clay beds. However, detailed geological data on the lateritization of low-iron-content carbonate rocks are rare. In this study, we present new results on the mineralogy and geochemistry, as well as a genetic model, of the Maojun laterite Fe–Mn deposit in the Lanshan area, Hunan Province, South China. The profile sequence of laterite consists of an eroded bedrock horizon at its base, an intermediate black–brown clay layer containing earthy Fe–Mn ore, and a reddish-brown clay layer with nodular ferromanganese ore in contact with reddish-brown or yellowish-brown clay on top. Field evidence and chemical analysis indicated that during lateritization, the Mn-Fe-containing carbonate rocks of the Huanggongtang (D2h) and Shetianqiao formations (D3s) saw a more significant removal of mobile elements (Mg, Ca, and Na) whilst insoluble elements (Fe, Mn, Si, Al, Pb, and Zn) exhibited persistent enrichment in situ. Discriminative diagrams of Fe–Mn mineralization, as well as the assemblage-related enrichment of Y, U, Mo, Pb, and Zn and depletion of high-field-strength elements Zr, Nb, and Th, imply that subsequent hydrothermal circulation overprinted on the previously formed hydrogenous deposit. Mineralogical studies conducted using XRD, EPMA, HR-TEM, and TIMA indicated the predominance of iron and manganese oxides; hematite, goethite, limonite, and hollandite were identified as major oxide phases and cryptomelane, pyrolusite, and coronadite were present in minute quantities. Similar minerals constitute the upper ferromanganese nodule horizons, although they possess distinct textures and concentrations. The mineralogy, geochemical associations, and Ti mass balance show a continuous vertical evolution from top to bottom in the lateritic profile. Ferromanganese concretions from the drenching zone with poorly crystallized Al–goethite, Al–hematite, limonite, Fe–kaolinite, Fe–Mn oxides and hollandite predominate in shallow parts, and microcrystalline hematite, goethite and hollandite were found in deeper layers. Mn2+ can be rapidly oxidized and precipitated on the surface of hematite and limonite as high-valence-state (Mn4+) manganese oxides and binds strongly with mobile elements (Ba, K, Pb, Zn, Ca, and Ni). Petrographical, mineralogical, and geochemical studies show that three stages comprised the formation of the Maojun laterite Fe–Mn deposit.

REEs Prospects in Laterites Profiles of Ibra, Sultanate of Oman

REEs now days are acting as an alternative source of low- sustainable energy economy and got strategic significance in the development of most of the current high-end technologies in industries and Laterite deposits provide one of the major natural sources of REEs. Laterite soil or rock is a product of intensive and prolonged weathering of underlying parent rock formed in hot and wet tropical areas. It is mainly rich in iron and aluminum oxides. The development of laterite profiles in most of Oman Mountains is mainly related to the late Cretaceous (Coniacian to late Companion) tectonic evolution of the Oman Mountains which are part of the Alpine–Himalayan fold belt. Laterite and regolith formations can be found overlie the Samail ophiolite in Oman. Samail Ophiolite is a part of upper mantle & Oceanic lithosphere which over thrusted on to the continental crust. The Samail ophiolite is considered as one of the major features of the Oman Mountains. The present study focuses on the REEs prospects in the Ibra region of Sultanate of Oman and study area of Ibra region lies within the Samail Ophiolite. The fieldwork was carried out for geological evaluation at the Ibra region. Total 3 number of Laterite profiles were observed during the fieldwork. Samples were collected from the Harzburgite rock. All samples were analyzed for ICPMS analysis to know the REEs. Field observation and chemical analysis clearly indicates that the Ibra region might have good prospect for REEs exploration and mining based on their REEs content

The Effect of Geochemical Elements on Resistivity Values in Nickel Laterite Profiles (Case Study: Area "YL", Pomalaa District, Kolakaa Regency, Southeast Sulawesi

The Effect of Geochemical Elements on Resistivity Values in Nickel Laterite Profiles (Case Study: Area "YL", Pomalaa District, Kolakaa Regency, Southeast Sulawesi

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.

Geochemistry and Mineralogy of the Clay-Type Ni-Laterite Deposit of San Felipe (Camagüey, Cuba)

The Ni-laterite deposit at the San Felipe plateau, located 30 km northwest of Camagüey, in central Cuba, is the best example of a clay-type deposit in the Caribbean region. San Felipe resulted from the weathering of mantle peridotites of the Cretaceous Camagüey ophiolites. In this study, a geochemical and mineralogical characterization of two profiles (83 and 84) from the San Felipe deposit has been performed by XRF, ICP-MS, quantitative XRPD, oriented aggregate mount XRD, SEM, FE-SEM, and EMPA. Core 83, with a length of 23 m and drilled in the central part of the plateau, presents a notable concentration of cryptocrystalline quartz fragments and a rather poor content of NiO, averaging 0.87 wt.%. Core 84, which is 12 m long and drilled at the border of the plateau, lacks silica fragments and presents a higher NiO content, averaging 1.79 wt.%. The smectite structural formulae reveal that they evolve from trioctahedral to dioctahedral towards the top of the laterite profiles. Quantitative XRD analyses indicate that smectite is a dominant Ni-bearing phase, accompanied by serpentine and minor chlorite. Serpentine, as smectite, is enriched in the less soluble elements Fe3+, Al, and Ni towards the top of the profiles. Core 83 seems to have been affected by collapses and replenishments, whereas core 84 may have remained undisturbed.

Impact of the depth of a lateritic profile on the physicochemical, mechanical and microstructural properties of geopolymer binders

The aim of this study is to evaluate the influence of the layers of a laterite profile on the physical properties of the elaborated geopolymer cements. For this purpose, laterite soils were collected from different layers on a profile, and calcined at 650 °C. Calcined laterites were activated using alkaline solutions of 8, 10 and 12 M concentration. Raw materials and synthesis products were characterized using different analytical techniques comprising XRF, XRD, FTIR, PSD, TG/DTA, SEM/EDS and 29Si and 27Al MAS-NMR spectroscopy. Furthermore, mechanical and physical properties of 28 days old consolidated geopolymers were evaluated. The obtained results reveal that the E0-E3 specimens activated with 12 M alkaline solution developed the best characteristics than the C0-C3 and D0-D3 specimens consolidated with 8 and 10 M. Similar trends were observed in the water absorption, porosity and density values. Findings showed that the mineralogy of laterite soils varied from a layer to another one in a profile, which significantly influence the properties of the resulted geopolymer binder.

The bauxite-bearing lateritic profile of the Jequié Complex, São Francisco Craton, Brazil: potential for rare earth elements mineralization and insights on the mineral system

The bauxite-bearing lateritic profile of the Jequié Complex, São Francisco Craton, Brazil: potential for rare earth elements mineralization and insights on the mineral system

SOURCES OF SUBSTANCE AND GENETIC RELATION OF SOIL AND BAUXITE BEARING HORIZONS IN THE LATERITE PROFILE OF THE WEATHERING CRUST (OF THE FUTA JALLON-MANDINGO PROVINCE, REPUBLIC OF GUINEA)

For the first time, a granulometric analysis of lateritic soils was carried out and the sources of the substance involved in the formation of the degradation zone in the bauxite-bearing laterite profile of the bauxite-bearing province of Futa Jallon-Mandingo were identified. Throughout the province, on the stony rocks of the lateritic covers, the soil horizon occurs everywhere - the uppermost element of the vertical profile of the weathering crust. In the soil horizon, most of the components become mobile, leaching processes predominate, and laterites are mobilized and redistributed. The study of these continental formations made it possible to establish the genetic relationship between the soil horizon of the weathering crust and the underlying bauxite ores, and to determine the degree of influence of soil composition on the processes of bauxite formation.

Sources of Substance and Genetic Relation of Soil and Bauxite-Bearing Horizons in the Laterite Profile of the Weathering Crust (of the Fouta Jallon–Mandingo Province, Republic of Guinea)

For the first time, a granulometric analysis of lateritic soils was carried out and the sources of the substance involved in the formation of the degradation zone in the bauxite-bearing laterite profile of the bauxite-bearing province of Futa Jallon-Mandingo were identified. Throughout the province, on the stony rocks of the lateritic covers, the soil horizon occurs everywhere—the uppermost element of the vertical profile of the weathering crust. In the soil horizon, most of the components become mobile, leaching processes predominate, and laterites are mobilized and redistributed. The study of these continental formations made it possible to establish the genetic relationship between the soil horizon of the weathering crust and the underlying bauxite ores, and to determine the degree of influence of soil composition on the processes of bauxite formation.

Rock Magnetic and Mineralogical Properties of Lateritic Soil Profiles Developed on Two Different Parent Rocks in Northern Kerala, South-Western India

The rock magnetic and mineralogical properties of two lateritic soil profiles developed on two different parent rocks (khondalite and granite) in northern Kerala, south-western India were investigated to better understand pedogenic processes under tropical climate. Field investigations reveal the presence of various horizons in the lateritic profiles, such as saprolite, mottled zone, pebble horizon and top soil. The particle size, rock magnetic, Vibrating Sample Magnetometer (VSM), Scanning Electron Microscopy (SEM)-Energy-Dispersive X-ray Spectrometer (EDS) and X-Ray Diffraction (XRD) analyses were performed on samples collected from different horizons of the two profiles. Magnetic susceptibility (χlf) values of the lateritic profiles vary from 9.97 to 1717.04 x 10-8 m3 kg-1, with the granitic profile exhibiting overall higher values. The percentage frequency-dependent susceptibility (χ %) ranges between 0 % and 13.9 %. The XRD data reveal the presence of kaolinite, gibbsite (except for top soil layer) and quartz along with magnetic minerals like magnetite, hematite and goethite. The upper horizons (top-soil and pebble horizon) exhibit high values for concentration dependent magnetic parameters like χlf and χfd%, whereas, the lower horizons (saprock, saprolite, pallid zone horizons) exhibit low values. The tropical soils in the region have undergone a higher degree of pedogenesis with increased magnetic mineral concentration compared to temperate soils. The magnetic enhancement in the topsoil may be due to the neoformation of ultra fine-grained SP magnetite/maghemite (with minor anti-ferro magnetic component), aided by sufficient Fe supply, alternate wetting and drying cycles, dehydration, oxidation and redox conditions. Keywords: Lateritic Soils; Soil Magnetism; XRD; SEM; Magnetic Enhancement; Pedogenesis; Southern India