Lateritic Profiles Research Articles

Clay mineralogy and texture of deep-sea hydrothermal mudstone associated with the Cerro Matoso peridotite in accreted oceanic crust from Colombia

New outcrops at the Cerro Matoso open-pit nickel mine permitted to sample sediments found on top of the peridotites to study the textural relationships and composition of phyllosilicates that make up what we propose is a deep marine succession. The appearance and color of mounds and tabular layers divided them into two lithofacies formed by green claystone and black mudstone. The chemical, mineralogical, and petrographic analysis allowed the identification of berthierine and greenalite as the main components of the clay fraction of these rocks. Both phyllosilicates show sharp peaks in the X-ray diffractometry (XRD) diagrams, which show a high degree of “crystallinity”. These peaks are produced when the phyllosilicates are formed under ideal conditions of temperature, alkaline pH, and reducing environments, which differ from the supergene and oxidizing environments in which they are now found. The fossiliferous content, in which bivalves, gastropods, and polychaetes predominate, together with the fissured and brecciated textures in the sediments, accompanied by a network of microcracks and open ducts are indicative of marine environments with fluid exhalation that can be related to hydrothermal systems and serpentinization of ultramafic rocks. This work allows us to redefine some units previously described as part of the lateritic profile of Cerro Matoso, i.e., ¨black saprolite and ¨canga mona¨ and to report what would be the first discovery of fauna associated with hydrothermal vents hosted in mantle rocks that were posteriorly accreted during the Cretaceous to the continent. These were recently exposed to humid tropical environmental conditions, where they developed weathering lateritic profiles.

Multiscale physical–chemical analysis of the impact of fracture networks on weathering: Application to nickel redistribution in the formation of Ni-laterite ores, New Caledonia

Supergene processes related to downward water migration and dissolution of primary minerals in the New Caledonian peridotites result in Ni enrichment at the bottom of the lateritic profile near bedrock. However, the combined effects of relief, lateral fluid flow, and complex inherited discontinuity networks filled by serpentine generate a more complex Ni distribution than a simple flat horizon. In surficial environments, fluid flow and mass transfer are not limited to the vertical scale; they can also be related to lateral fluid circulation and local drainage along damage zones in the vicinity of faults. In this study, we present new structural, petrophysical and geochemical data for core samples to shed light on the impact of a fracture network on the alteration and progression of the Ni-enrichment front during weathering. The analysis of element redistribution by XRF mapping coupled with fracture extraction from computed tomography (CT) establishes that the serpentine fracture network comprises sets of sub-orthogonal fractures whose orientations are potentially determined by pre-existing magmatic foliation. The progression of the olivine dissolution front leads to the redistribution and concentration of Ni into the serpentine fracture network as secondary Mg-Ni talc-like phases. The increase in porosity from < 1 % in the bedrock to > 10 % in the saprock is mainly driven by the formation of nanopores. Nanoporosity may control the development of the weathering front and the redistribution of Ni by small-scale diffusion. Structural and geochemical characteristics identified at the sample scale are analogous to those observed on the larger scale of the outcrop and deposit. Scale invariance in the structural organization and geochemical evolution indicates the potential upscaling of the processes involved in the redistribution of Ni.

New insights into the distribution and speciation of nickel in a Myanmar laterite

Because ferromanganese oxides can host significant amounts of Ni during the weathering, the Fe- and Mn-oxide are resultantly considered as the important Ni-bearing minerals. However, little is known about the role of Mn species to influence the Ni behavior during this process. In this study, we employed the techniques of ICP-MS, XRF, XRD, XAFS (XANES and EXAFS), and μ-XRF to interpret the Ni behavior along a laterite profile in Myanmar. Nickel concentrations in the saprolite developed on peridotites can reach up to 11 wt% Ni mainly because of Ni precipitation as fracture-fillings and thin coatings on joints, which produce a promisingly and importantly economic mineral resource of this territory. In the peridotites, Fe and Mn species predominantly consisted of olivine (96%) and biotite (74%), respectively. Nickel XANES spectra indicated that Ni was primarily hosted by olivine (86%) in the protolith under reduction condition, lizardite (90%) and Ni-bearing goethite (10%) in the lower garnierite vein under strong oxidation condition, and lizardite (37%) and Ni-bearing goethite (63%) in the upper saprolite under medium oxidation condition. Accordingly, minerals of Fe and Mn were progressively oxidized toward Fe3+ and Mn4+, which occurred primarily as Fe3+-bearing goethite and Mn4+-bearing birnessite. The occurrence of Fe- and Mn-oxide plays an important role in Ni species and suggests that birnessite maybe facilitate the formation of Fe oxide precipitations by means of the oxidation of Fe2+ in the olivine to Fe3+ in the goethite. The results are of relevant importance, as it fills a gap in the knowledge of ore-formation processes occurring in Myanmar

Constraints on the Genesis of Cobalt Deposits: Part II. Applications to Natural Systems

AbstractIn a companion paper in this issue, the authors reviewed the properties of cobalt, its mineralogy, and the processes that concentrate it to exploitable levels. Using this information and knowledge of the geology of the principal types of cobalt deposits, the present paper assesses the conditions and controls of cobalt transport and deposition and develops/refines plausible models for the genesis of these deposits. Economic cobalt deposits owe their origins to the compatible nature of Co2+, which causes it to concentrate in the mantle, mainly in olivine, and to be released to magmas only after high degrees of partial melting (i.e., to komatiitic and basaltic magmas). Thus, there is a very close association between cobalt deposits and mafic and ultramafic rocks. Magmatic deposits, in which Co is subordinate to Ni, develop through sulfide-silicate liquid immiscibility as a result of the very strong preference of these metals for the sulfide liquid. Predictably, these deposits reach their highest grades where hosted by olivine-rich ultramafic rocks. Approximately 60% of the world’s cobalt resource is of hydrothermal origin and is contained in sediment-hosted copper deposits in the Democratic Republic of the Congo. Using a combination of thermodynamic data and geologic information, we have refined a model in which Co is leached from mafic and ultramafic rocks by oxidized, chloride-rich hydrothermal fluids, derived from evaporation, and deposited in response to decreasing fO2 in carbonaceous sediments that accumulated in intracratonic rift basins. Economic Co deposits also develop as hydrothermal vein systems, in which Co is the primary ore metal. In the only deposits of this type that are currently being exploited (Bou Azzer, Morocco), the source of the Co was an adjacent serpentinized peridotite. The ore fluid was an oxidized, high-salinity brine derived from evaporites, and deposition occurred in response to pH neutralization by the felsic to intermediate igneous host. The final major class of Co deposits is laterite-hosted and develops on olivine-rich ultramafic rocks or their serpentinized equivalents. Our thermodynamic modeling shows that Co is leached from an ultramafic source by mildly acidic fluids as Co2+ and is transported down the laterite profile, eventually concentrating by a combination of adsorption on Mn oxides, incorporation in the structure of absolane (an Mn oxide), and precipitation as heterogenite (HCoO2). The dissolution of cobalt at the surface and its deposition at depth are controlled mainly by pH, which decreases downward; oxygen fugacity, which also decreases downward, has the opposite effect, inhibiting dissolution of cobalt at the surface and promoting it at depth. It is our hope that this introduction to the economic geology of cobalt and the processes responsible for the formation of cobalt-bearing ores will help guide future studies of cobalt ore genesis and strategies for the exploration of this critical metal.

Nd and Sr Isotopes and REE Investigation in Tropical Weathering Profiles of Amazon Region

The exceptional development of lateritic profiles make the Amazon one of the best places to conduct a refined study on the effects of long-term tropical climate on the Earth's surface rocks. Concentrations of Nd and Sr isotopes, as well as rare earth elements (REE), Sr, and other trace elements were determined in six profiles in order to shed new light into element behavior and into the processes controlling the geochemistry and the transfer of these elements among the different compartments of the critical zone. Our investigation indicates natural isotope regional pulse transformations in the Oxisol at the top of all profiles. The ƐNd(t=0) values of the parent rock, mottled horizon, and lateritic duricrust are radiogenic similar to the Amazon craton signature. The thick Oxisol has ƐNd(t=0) values which are much more radiogenic and less variable, whereas it has Zr, Th, Y, and REE in higher concentrations. These issues highlight a complex process for the Nd system, and the following possibilities are proposed to explain this behavior: formation of authigenic cerianite and/or kaolinite, penetration of low-temperature weathering solutions along zircon fractures, and some vegetation uptake. These possibilities allow keeping the more radiogenic Nd isotopes, whereas the less radiogenic Nd is released especially in the Oxisol after REE mineral(s) weathering. The Sr system contrary to that of Nd became less radiogenic along the profiles and relatively to the parent rocks content, because nearly all Sr was removed after K-Rb feldspar and mica weathering. However, a mixture return of less radiogenic Sr from plant, biogenic aerosol, and rainwater may have helped let the weathering profiles become less radiogenic. These characteristics let the Oxisol even less Sr radiogenic but still permitting to identify the general parent rocks signature. In contrast, Nd is highly fractionated in the Oxisol relative to the parent rock. Thus, the REE and Sr behavior, similar in the six profiles, does not necessarily reflect only the parent rock geochemistry, but it also depends on the multiple surficial processes typical of the critical zone: weathering, pedogenesis, plant root activity, and rainwater composition which change the inherited primary minerals isotope signatures.

The Problem of the Formation of Boehmite and Gibbsite in Bauxite-Bearing Lateritic Profiles

The study of a large amount of factual material about the formation conditions of gibbsite or boehmite and their mutual transformations in lateritic bauxites allowed us to solve the problem of boehmite formation and its spatial and genetic relationship to gibbsite. The boehmite formation occurred only during the formation of sedimentary-lateritic bauxites from alluvial and lacustrine sediments that underwent bleaching and resilification at the stage of sediment flooding, as well as on bleached bedrock under sedimentary-lateritic bauxites. The most intense boehmite formation occurred at a depth of 20–30 m from the surface and was accompanied by an alumina input, which was realized here in the form of boehmite along with the gibbsite formation due to the hydrolytic decomposition of kaolinite and partially due to the input alumina. In the upper profiles, the recrystallization of bauxites occurs with the replacement of dissolving boehmite with gibbsite, with a decrease in the total Al2O3 content and an increase in the amount of crystallization water. In classic lateritic bauxites, the boehmite content is highly insignificant; that is, its formation in them practically does not occur or is very much inhibited.

Geochemical study of Al–Fe–Ti enrichment in rock weathering: Implications for the recognizing of igneous protolith and the enrichment of REE in soil profile

Chemical weathering of rocks has been investigated since 1960, and lithogeochemistry has commonly been used since 1980 to determine the protoliths of heavily weathered igneous rocks. However, it is still quite difficult to uniquely identify the laterite originating from a potassic basaltic rock, which formed in the anorogenic/within-plate environment (e.g., low silica trachytic rock, phonolite, and tephri-phonolite). These difficulties occur because the within-plate basaltic rocks contain a relatively high Zr concentration; therefore, laterites with high Zr/Ti ratios are often identified as dacite or rhyolite. Besides that, using Zr/Ti is also difficult to distinguish between ultramafic and basaltic rocks. This study has developed the “overlaid ternary DOS (Degree of Saprolitization)" to solve those problems by overlaying the existing ternary DOS to recognize the igneous rock lithology on lateritic profiles released from ultramafic, mafic/basaltic, intermediate, and felsic rocks.The study of drill core laterites from Western Sulawesi/WS (Mamuju district) in hole-A and hole-B characterized by high Zr (1170–2553 ppm), relatively high TiO2 (1.68–2.99%), and high Zr/Ti ratio values (Zr/Ti > 0.0833); and they are recognized as weathering of basaltic rock. While laterite from West Java (Dago Atas Bandung/DAB) released from weathering of andesitic rock (Zr: 148 ppm; TiO2: 1.49%; Zr/Ti: 0.0167). The enrichment of REE (rare earth element) in the hole-B laterite profile occurred on the surface of topsoil (1st meters) to a depth of the 3rd meters (TRE2O3(avg): 2359 ppm; TREY: 2005 ppm), and a slight enrichment in the 5th to 7th meters (TRE2O3: 1688–1933 ppm; TREY: 1437–1647 ppm). This study shows that the enrichment of REE in the soil horizon does not directly correspond to the Ce-anomaly.

Mineralogical and Geochemical Characterization of the Sta. Cruz Nickel Laterite Deposit, Zambales, Philippines

In this study, we present mineralogical and geochemical characterization of samples systematically collected from a nickel laterite profile at the Sta. Cruz nickel laterite deposit, Zambales, Philippines. Wavelength-dispersive X-ray fluorescence spectroscopy (WDSXRF), mass-balance element mobility calculations, transmitted and reflected light microscopy, and previously reported results from coupled X-ray diffraction (XRD) and Rietveld refinement analyses reveal that the laterite profile investigated is composed of two main horizons—the limonite and saprolite zones—separated by a thin transitional zone. Based primarily on the mineral assemblage and major element chemistry, the main zones are further subdivided into subzones: upper limonite, lower limonite, transitional zone, upper saprolite, and lower saprolite. Garnierite veins were observed cutting the upper and lower saprolite subzones. Investigation of the structure of goethite within the limonite zone via Rietveld refinement shows that the crystallinity of goethite decreases with increasing Ni content and increasing crystallite size. This suggests that upwards through the limonite zone, as goethite ages, its crystallinity increases, which possibly results in the removal of Ni from its crystal structure and eventual remobilization to the lower laterite zones.

Morphology, composition and dissolution of chromite in the Goro lateritic nickel deposit, New Caledonia: Insight into ophiolite and laterite genesis

The morphological and chemical composition of chromite in the partially-serpentinized harzburgite and oxide zone of two laterite profiles at the Goro lateritic nickel deposit, New Caledonia, were investigated to: (1) establish the melt conditions at the mantle-crust boundary during ophiolite formation, and (2) characterize the weathering of chromite and its role in the goethite maturation model in formation of the oxide zone at the Goro Ni-deposit. Chromite in the Goro harzburgite, despite being highly fractured, is relatively fresh. Dendritic branching of skeletal outgrowths from poikiloblastic chromite, encapsulate partially serpentinised harzburgite and is indicative of a parent melt under changing cooling conditions, varying from supersaturated to undersaturated with localised melt mixing. Compositionally, the refractory nature (Cr#>0.6) of chromite, low (predominantly < 0.05 wt%) TiO2 content and high logFe2+:Fe3+ ratio values of 14–16 indicate a highly depleted and reduced peridotite melt with boninite-type affinity of suprasubduction provenance. Furthermore, the high Cr# of Goro chromite may define a compositional end-member along a continuum of Al2O3-Cr2O3 exchange with a relatively consistent (i.e., 25–35 wt%) FeO content, from the Goro deposit (Cr > Al) in the south-east through to high-Al chromite (Cr < Al) at Poum in the north-west of New Caledonia. In the oxide horizon, extensive surface etching and development of solution channels throughout chromite grains, supports both their abiotic and biogenically mediated dissolution. Abiotic dissolution is evidenced by the tessellation of surface etching features and epitactic oxidation of chromite to Cr-substituted hematite. Extensive development of meandering dissolution channels through the grain interior and the precipitation of locally elevated Mn (to 3–4 wt%) that juxtapose areas depleted in Cr but elevated in Al, Mg and Fe support the inferred role of Mn-oxidizing bacteria in the preferential dissolution of Cr from chromite. Preferential leaching of Cr from chromite, whether by abiotic and/or biogenic means, feeds into the mineralogical evolution of the oxide zone at Goro and supports an alternative crystallisation model via a ‘green-rust-like’ precursor for the formation of poly-metallic-substituted goethite.

Geochemical and Mineralogical Characteristics of Garnierite From the Morowali Ni-Laterite Deposit in Sulawesi, Indonesia

The Morowali Ni-laterite deposit is located in the East Sulawesi Ophiolite, which is a large ophiolite belt on Sulawesi Island, Indonesia. The Morowali deposit is developed on a laterite profile due to ophiolite weathering, with saprolite, limonite, and ferruginous cap horizons from the bottom to top. Based on the occurrence of garnierite as the main ore, occurring in the saprolite horizon, it can be classified that the ore deposit is hydrous Mg silicate-type. The Ni ore is classified into different types based on color and XRD and electron probe micro-analyzer analyses. Whole-rock geochemical study was also conducted to understand the mineralization process. The Morowali Ni deposit consists of serpentine-like and talc-like phases. The serpentine-like phase consists of Ni-lizardite and karpinskite (0.76–38.26 wt% NiO) while the talc-like phase is mainly composed of kerolite (4.02–8.02 wt% NiO). The serpentine-like garnierite exhibits high Ni and Fe contents and occurrence similar to that of the serpentine observed in the saprolite horizon, suggesting the serpentine-like garnierite originated from the bedrock, and Mg-Ni cation exchange occurred during laterization. Contrastingly, the lower Fe content of the talc-like phase (0.01–0.05 wt%) than the serpentine-like phase (0.14–7.03 wt%) indicates that the talc-like garnierite is of secondary origin since Fe is immobile during weathering. The Morowali Ni-laterite deposit was mainly formed during laterization. The repetition of dry and wet cycles in each year results in the formation of secondary garnierite.

Preliminary Study of Scandium Enrichment in Lateritic Profile from Weathered Ultramafic Rock in Lapaopao Area Kolaka Regency of Southeast Sulawesi

Scandium is one of the rare earth elements which is currently widely used for various needs such as the aerospace industry, solid oxide fuel cells, electronics industry and in metallurgical applications. Generally, Scandium appears in small amounts so its structural role in the host minerals cannot be readily identified. Some studies reported the scandium extraction from lateritic nickel deposit where may contain considerable amount of scandium in addition to nickel and cobalt. Preliminary research of scandium enrichment has been investigated from the ultramafik rock indicates that an enrichment of scandium concentration was found in the red limonite. The aim of this study was to investigate the potentially enrichment of scandium mineral from nickel laterite in Lapaopao Area. There are a total of 38 samples from 1 (one) diamond drill holes which represent the limonite, saprolite and bedrock profiles have been collected and studied to investigate the distribution pattern of Sc grades within the lateritic profile. These samples are being analized by XRF for major and minor element and ICP-OES method for rare earth element assaying. The study has confirmed that scandium is enriched in limonite layer of weathered ultramafic laterite profile. The scandium content from the ultramafic bedrock is 15 ppm and has enriched until 81 ppm of scandium in the limonite layer.

Role of bedrock serpentinization on the development of nickel laterite deposit in Sorowako, Sulawesi, Indonesia

The objective of this research is to analyze the role of bedrock serpentinization on the development of Ni-Laterite deposits in Sorowako, Sulawesi Island, Indonesia. Samples were obtained from coring data in three areas, namely the West Block, East Block, and Petea, which are subject to mineralogical and geochemical analyses. Petrography of the bedrocks was conducted to analyze the mineral composition, texture, and serpentinization degree, and later correlated with the distribution of geochemical elements from X-ray fluorescence method in each laterite zone. The bedrock in the West Block is dunite which consists of predominantly olivine with low degree serpentinization. The bedrock in the East Blocks and Petea consists of peridotite in the form of lherzolite and harzburgite which have been moderate to highly serpentinized. The distribution of elements in each block shows that MgO, SiO2, and Ca elements significantly decrease towards the upper laterite profile while Fe, Al, and Cr are enriched in the limonite zone and Ni, Mn, and Co are significantly enriched in the saprolite zone. Ni, Fe, SiO2, Cr, MgO, and Mn in the West Block are relatively higher than the East Block and Petea. This study shows that Ni content is relatively higher in West Block compare to East Block and Petea in averages of 1.7%, 1.53%, and 1.3%, respectively. Olivine-rich bedrock and a low degree of serpentinization resulted in high-Ni concentration in the laterite profile, particularly in the saprolite layer. This means that bedrock characteristics and degree of serpentinization were responsible for the development of nickel.

Geochemistry and environmental effects of rare-earth elements in laterites from Yunnan province, SW China

Rare-earth elements (REEs) in soils are influenced by pedogenic processes and anthropogenic activities. To interpret the fractionation and migration of REEs during weathering in (sub-)tropical regions, the distribution, fractionation patterns and environmental effects of REEs in laterites were investigated in this study. Soil samples from two laterite profiles (labelled S1 and S2) were collected and the concentrations of REEs were measured with an inductively coupled plasma mass spectrometer. The results suggest that the Σ REEs of S2 (119 ± 10 mg kg –1 to 209 ± 10 mg kg –1 ) have a higher concentration and a wider variation than those of S1 (114 ± 5 mg kg –1 to 154 ± 8 mg kg –1 ). The REEs in both laterite profiles are enriched in the order HREEs &gt; LREEs &gt; MREEs. The distribution patterns of laterite profiles show evidence of inheritance from parent granites. The laterites preferentially incorporated HREEs, and secondary Fe 2 O 3 and clay minerals were likely to affect the fractionation of REEs in laterites. The enrichment factor of REEs varied from 11.1 to 18.9 for S1 and 10.0 to 27.6 for S1, indicating potential pollution by REEs. The accumulation of REEs in laterites by mining activity should be a concern of government environmental agencies. Supplementary material: Table S1, Reference values of REEs and Fe 2 O 3 in standard materials (GSS-18 and GSS-20); Table S2, Measurement parameters of ICP-MS; Table S3, Concentrations of REEs and Fe 2 O 3 in laterite profiles from Yunnan province, SW China; Table S4, The enrichment factor for the laterite profiles from Yunnan province, SW China are available at https://doi.org/10.6084/m9.figshare.c.5609234

Influence of parent lithology on field appearances and engineering properties of indurated laterites under same geographical conditions

Laterites derived from different parent lithologies in the same tropical area and under the same climatic condition are likely to have different engineering properties. In this study, two nearby abandoned laterite quarries at Haripur and Tengara in Dhenkanal district (in the state of Odisha, India) were investigated. The first objective of this study was to evaluate the strength and physical properties of the indurated laterites with reference to the characterization of the selected profiles. The other drive of this work was to demonstrate how different parent lithologies of these two lateritic profiles that share same geographical conditions can be related to the variation of engineering properties of the indurated laterites. In order to address these two objectives, the lateritic profiles were characterized which was followed by the determination of strength and physical properties of the indurated laterites; petrographic study; and XRD analysis.Although the variation patterns of engineering properties (i.e. uniaxial compressive, point load and Brazilian tensile strengths; effective porosity; dry density; vug volumetric percentage; and slake durability indices) of the indurated laterites with profile depths at Haripur and Tengara show prominent differences, such variations depict a good compliance with the characterized horizons of the respective profiles. Based on the analysis of the engineering properties in relation to characterized profiles, it was shown that for construction purposes, the indurated laterites of both areas can be classified based on the point load strength. From the geological investigation, it was ascertained that the difference in engineering properties between the indurated laterites of Haripur and Tengara is very much dependent on the mineralogy such as sesquioxides, clay content and other minerals altered from the parent lithologies.

Tropical Weathering History Recorded in the Silicon Isotopes of Lateritic Weathering Profiles

AbstractUnder tropical climates, mineral assemblages composing lateritic weathering profiles offer precious records of past weathering conditions. Silicon (Si) isotope signatures in the clay fractions of a deep lateritic profile in central Amazonia, Brazil, in combination with previously determined kaolinite ages, suggest that the surrounding region underwent two major weathering episodes, distinct in their intensity. The first episode (ca. 35–20 Ma) of moderate intensity produced well‐crystallized kaolinites from the parent sediment with limited Si isotope fractionation. A more recent (8–6 Ma) and shorter phase caused the replacement, from top to bottom of the profile, of the first kaolinite generation by a new population characterized by higher crystallographic disorder and stronger Si isotope fractionation, suggesting weathering under conditions of rapid water percolation. These inferences are supported by results from an isotope‐enabled reactive transport model, and they are consistent with paleoclimatic and paleogeographic evidences recorded over the Amazon Basin.

Distribution and Mobility of Platinum‐Group Elements in the Late Cretaceous Ni‐Laterite in the Northern Oman Mountains

AbstractLow‐grade Ni‐laterite deposits are irregularly developed overlying mafic/ultramafic protoliths in the northern Oman Mountains. Concentrations, distribution patterns, and mobility of platinum‐group elements (PGEs) are investigated in some Ni‐laterite profiles from the Oman ophiolite as potential unconventional PGE resource. The ultramafic protoliths display the lowest PGE contents (average total = 35 ppb) that are similar to the PGE contents in the overlying saprolite zones. The PGE content increased upward in the laterite profile, where the highest total PGE contents (∼253 ppb) are recorded in the oxide and ferricrete/clay‐rich zones. The highest PGE content corresponds to Pt &gt; Ru &gt; Pd, while the lowest PGE content mostly corresponds to Os &lt; Rh &lt; Ir. The general positive correlation between PGE contents and both Cr2O3 and Fe2O3 contents and the positive trend of the chondrite‐normalized PGE patterns in the Ni‐laterite profiles reflect the formation of PGE‐Fe nanoparticle alloys that are hosted by Fe‐rich oxyhydroxides or due to the residual accumulation of chromite in the oxide/clay‐rich zone during the lateritization process. The PGE distribution patterns and positive correlation of total PGE content with the ultramafic index of alteration indicate that PGE can be mobilized in different proportions in the surficial environment upon progressive lateritization processes. The high content of total PGE in the Oman Ni‐laterite is in good agreement with PGE‐rich laterite deposits worldwide. Consequently, the Oman deposits can be considered as an unconventional PGE resource if adequate extraction and refining processes are applied for their recovery from the possible upcoming Ni production.

Behaviors of Major and Trace Elements in Soils Developed from Weathering Basalt in Western Guizhou, China

Weathering is a crucial geochemical process for basalt and soil formation, which plays a vital role in restoring the karst region in Guizhou, southwest China. Two regolith profiles (Dougu and Shazi) were selected to investigate the behaviors of major and trace elements developed from advanced to extreme weathering of the Emeishan basalt in the western Guizhou province. These profiles are composed of surficial clay-humus, laterite, loess, and weathered basalt. The two profiles contain very high amounts of silica-alumina ratio (Sa), silica sesquioxide ratio (Saf), and chemical index alteration (CIA), with deficient concentrations of CaO, Na2O, MgO, and K2O compared to that of the fresh basalt. They are also characterized by notable depletion of Sr, K, Ba, P, and enrichment of La and Ce. In general, The two profiles showed enrichment in light rare earth elements. Ce is enriched in the laterite profile of Shazi. The variances in the mobilization of elements in these two profiles and their similar protolith nature indicate that they underwent various supergene geological processes. The Shazi and Dougu profiles have experienced a severe action of alkali dissolution, desilication, and enrichment of iron, aluminum, titanium. The variation characteristics of magnesium and calcium indicate more montmorillonite in the Dougu profile formed in the middle and late stages of weathering. The CIA index also shows that the weathering effect of the Shazi profile is more potent than that of the Dougu profile. The rare earth elements in the Shazi profile have apparent positive δCe anomalies, indicating that the Shazi profile is formed in an intense oxidation environment. The content of scandium (Sc) in the parent rock and its weathering degree limits its amount in weathering crusts. The Sc in the Shazi and the Dougu profiles is rich than the parent rock in the weathering crust, and the enrichment is most visible in the red soil layer. The degree of enrichment of Sc is prominent in the Shazi profile with higher Sc content in the parent rock and even reaches the level of mineralization.

Garnierite characterization for open mineral databases

The nickel laterite mining industry faces lower recovery rates related to low ore grades, multiple nickel carrying minerals, as well as lateral and vertical heterogeneities at ore deposit scale. Garnierite, a complex mixture of nickel-bearing phyllosilicates, occurs at the base of nickel laterite profiles. Samples of Ni-rich and Ni-poor phyllosilicates from garnierite and host saprolite, from New Caledonia and the Dominican Republic, were analyzed by laboratory X-ray diffractometry (XRD), Fourier Transform Infrared (FTIR) and Raman spectroscopies. These phyllosilicates are mainly composed of serpentine-, talc- and/or sepiolite-like phases. XRD allows clearly distinguishing the different phyllosilicate phases. Moreover, it shows a difference between Ni-rich and Ni-poor phases after refinement of the diffractograms, in particular the (060) reflection, little exploited at present. When Ni is present, the peaks are broader and the spacing corresponding to the (060) reflection tends to be less than 1.534 Å. Mg substitution by Ni also cause shifts of hydroxyl bands in FTIR (3500–3800 cm−1 and 500–800 cm−1 spectral range), and Raman spectra (3500–3700 cm−1 spectral range). Moreover, the intensities of the bands can be correlated with the Ni content. Both are reliable indicators to define the nature of garnierite. In Raman spectroscopy, the substitution of Mg by Ni generates shifts on most bands, and there is a variation in intensity ratios between several bands which are correlated with Ni content.Our results can be applied to spectra obtained by online and handheld analytical devices, in-field core scanners or XRD/X-Ray fluorescence (XRF) combined expert systems.

Geochemical constraints on the mobilization of Ni and critical metals in laterite deposits, Sulawesi, Indonesia: A mass‐balance approach

AbstractIndonesia is one of the largest Ni ore producers in the world and is also expected to be an important potential source of some critical metals (e.g., Co, Sc, rare‐earth elements, and platinum‐group elements). However, few studies have examined Ni laterite deposits in this country. In this study, we investigate Ni enrichment and the potential accumulation of critical metals in four laterite profiles with varying degrees of serpentinization and weathering intensity in the Soroako and Pomalaa mining areas of Sulawesi, Indonesia. We integrate geochemical evaluation with a mass‐balance approach and mineralogical analysis to better constrain the geochemical factors influencing the mobilization of Ni during lateritization. Nickel contents in the saprolite horizon of the profiles that are strongly weathered and developed over serpentinized peridotite are higher than those that are weakly weathered and developed over unserpentinized harzburgite. The bulk Ni contents of saprolite horizons are related to Ni contents of Ni‐bearing Mg‐phyllosilicates, which suggests that Ni remobilization is the main control on Ni enrichment in the profiles. Mass‐balance calculations reveal that the amounts of gained Fe and Ni in the profiles are positively correlated. This relationship indicates that the redistribution of Ni is likely controlled by the aging of Ni‐bearing goethite (dissolution/recrystallization) involving ligand‐promoted dissolution by organic matter and/or reductive dissolution by microbial activity near the surface. Critical metals show enrichment in specific horizons. Enrichments in Co and rare‐earth elements are strongly influenced by the formation of Mn‐oxyhydroxides in the oxide zone of the profiles. In contrast, Sc, Pt, and Pd show residual enrichment patterns, with grades influenced mainly by their initial contents in bedrock. The profiles show a positive correlation between Sc and Fe, as reported for other Ni laterite deposits. Among the critical metals, Sc, Pt, and Pd contents in the studied profiles are comparable with values reported from other Ni laterite deposits worldwide.

Determination of regolith production rates from 238U-234U-230Th disequilibrium in deep weathering profiles (Longnan, SE China)

The present study seeks to evaluate the application of the 238U-234U-230Th radioactive disequilibrium methodology for the determination of the regolith production rates in thick weathering profiles marked by long histories, encountered under various climate regimes, but still very little studied by these techniques. For this purpose, 238U-234U-230Th disequilibria have been analyzed in the top 11 m of a lateritic profile developed on a granitic bedrock in south China (Longnan, Jiangxi Province) under a subtropical climate. The results demonstrate that in such a weathering profile the determination of weathering rates from the analysis of U-series nuclides in bulk rock samples cannot be recovered by applying in one step to the entire alteration profile the modeling approach classically used to interpret the U-series nuclides, i.e. the “gain and loss” model. The modeling has to be made on subsections of relatively small size (<1 or 2 m of thickness), so that the model assumptions can be met, especially the constancy of the mobility parameters along the weathering zone. The results also confirm that the upper part of the weathering profiles marked by the vegetation/biological influences and responding to the short-term climate variations is not well adapted for applying the U-series nuclides methodology for recovering regolith production rates. Based on the data, regolith production rates were estimated independently on four different deeper zones of the profile. Similar values of ~2 m/Ma have been obtained whatever the level, suggesting that such a profile of more than 5 million years would be formed at a relatively stable long-term production rate (averaged over several thousand years). This production rate is slow compared to the production rate deduced from previous in situ 10Be data, which can be explained by assuming non steady-state erosion of the upper part of the profile. Slow denudation rates similar to the U-series derived production rates of 2 m/Ma can thus be obtained with a minimum exposure time of 60 ky, and an inherited component of 20,000 atoms/g originating from the exhumed deeper part of the profile. Altogether the data demonstrate that the combined analysis of U-series and cosmogenic nuclides, which has the potential to become a relevant approach to constrain the dynamics of continental surfaces, requires (a) dense and deep sampling for both nuclides studies, and (b) also to consider more systematically the polyphased and variable history of erosion of the continental surface during the Quaternary.