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The Ediacaran–Cambrian Phosphogenic Episode is the Earth's first true phosphogenic event and resulted in worldwide phosphate deposits, which occurred during the processes of the Neoproterozoic Oxygenation Event. The Ediacaran Doushantuo Formation (ca. 635–551 Ma) of Weng'an area in central Guizhou, South China, contains two economic phosphorite beds (the Lower and Upper Phosphorite Beds). This paper presents a detailed stratigraphic, sedimentological and mineralogical study of multiple outcrop and drill core sections of the Doushantuo Formation across the Weng'an area, and identified 11 lithofacies and 4 types of phosphatic grains. Significant differences in lithofacies and grain types between the upper and lower phosphate deposits are observed, indicating that the two sets of phosphate deposits are the products of two distinct phosphogenic processes. The Lower Phosphorite Bed mainly consists of banded and laminated phosphorites, contains micro-oncoids formed by microbially-mediated precipitation and peloids formed by in-situ chemically oscillating reactions, indicating a biochemical and chemical enrichment of phosphorus to sediments during the Early Ediacaran Period. The Upper Phosphorite Bed is mainly composed of carbonaceous, massive, and stromatolitic phosphorites, contains bioclasts (phosphatized spheroidal fossils), and intraclasts formed by hydrodynamic agitation, suggesting that the major accesses of phosphorus to sediments were the remineralization of organic P. Deposition of the two economic phosphorite beds was controlled by two sea-level cycles. Such differences have also been documented in contemporaneous phosphate-bearing successions in Brazil and Mangolia, indicating a significant shift in global phosphogenic mechanism during the early and middle Ediacaran, which may be due to the changes in redox conditions in seawater, associated with the Neoproterozoic Oxygenation Event. These regional active P-cycle processes could produce more free oxygen, which may have contributed to the upcoming Phanerozoic global oxidation. [ABSTRACT FROM AUTHOR]

Alumina is produced from bauxite, which contains a mixture of various oxides, such as aluminum (Al), iron (Fe), silicon (Si), and titanium (Ti). Bauxite can also be considered a source of several other valuable metals, such as scandium (Sc), vanadium (V), and gallium (Ga). The composition and mineralogy of alumina determine their economic value, but their characteristics vary by locality. The physicochemical characteristics of bauxites can also be influenced largely by weathering processes, even within the same locality. For this reason, the present study was undertaken with the objective of comparing the characterization data of three bauxite samples collected, which will be referred to as D, E, and F, from the Cruz Alta do Pará plateau in northern Brazil. The samples were solubilized by multi-acid digestion and fusion with lithium metaborate to quantify their metal compositions by inductively coupled plasma optical emission spectrometry (ICP-OES). The mineralogical characterization was conducted by X-ray diffraction (XRD), and the phase changes of minerals in bauxite were detected by thermogravimetric analysis (TGA/DTG). The total organic carbon (TOC) technique was used to quantify the C in the samples, and the moisture content was also measured. Alumina was 30 wt.% on average for all samples, good for producing high-purity alumina by hydrometallurgical processes. The results, however, showed high (~20 at.%) silica concentrations in two samples and ~3 wt.% Fe in one sample, which can pose a challenge in the Bayer process. The X-ray diffraction (XRD) analysis showed that gibbsite (Gbs), kaolinite (Kln), anatase (Ant), and hematite (Hem) were the major mineral phases in these samples. The study showed that the samples from the same mine vary in their metal content, especially with regard to Si, and they, thus, need to be processed selectively to maximize their economic value. [ABSTRACT FROM AUTHOR]

In equatorial and tropical regions, supergene mineral deposits created during water/rock interactions are found. Simply put, these supergene deposits are formed through the accumulation of low solubility ions or through the preservation of primary minerals. The supergene manganese (Mn) deposits are examples of the economic importance associated with the chemical weathering processes. In Brazil, the Southern Brasilia Orogen (SBO) was generated during the collision between the Paranapanema Craton and the passive margin of the São Francisco Craton. In the southern Minas Gerais (MG), several supergene Mn occurrences are hosted in the SBO, which were originated during the chemical weathering of gondites belonging to the Amparo Complex. Here, we studied the supergene Mn occurrences in the southern MG, more specifically in the municipalities of Ouro Fino and Careaçu. The MnO contents ranged from 25.50 to 28.40 wt% at Ouro Fino and from 16.80 to 21.20 wt% at Careaçu. These supergene Mn deposits have a diverse mineral assemblage, being composed of spessartine, quartz, Mn-oxides, goethite and kaolinite. The various Mn minerals formed due to spessartine incongruent dissolution were hollandites, cryptomelanes, romanechites, pyrolusites and lithiophorites. Both study areas are relevant for the possible opening of mines for the commercialization of Mn. [ABSTRACT FROM AUTHOR]

Mining waste is a serious environmental problem in all countries where mining is carried out. Considering large amount of mining waste from the exploitation and processing of nickel laterites in Cuba and Brazil, the work takes as a hypothesis that, if it demonstrates the real possibility of using such waste as a partial substitute for aggregates in the production of asphalt concrete, the negative environmental impact caused by them in the places where they are deposited could be reduced. The objective of the work is, to demonstrate the suitability of mining waste from nickel and cobalt processing dams in the municipalities of Moa and Nicaro, in the province Holguín, Cuba. Such wastes come from Ammonium Carbonate Leaching and Pressurized Acid Leaching processes. The research methodology it has based on taking representative samples from the waste dams, their subsequent physical, chemical and mineralogical characterization, and the characterization of the aggregates and asphalt cement used in the mixtures under study. The design of the asphalt concrete mixtures was carried out using the Marshall method. Subsequently, a comparative analysis was made on the behavior of the asphalt concretes made with limestone and mining waste fillers investigated. It's demonstrated, from the results of the laboratory tests, that it is possible to manufacture asphalt concretes with the use of mining residues from the processing of nickel laterites from Moa and Nicaro, satisfactorily fulfilling the required technical parameters. [ABSTRACT FROM AUTHOR]

Interpreting the ages of supergene mineralogical phases in laterite is complex because they consist of polycrystalline mixtures of different phases at the microscopic scale that could be crystalized at different epochs. Among the geochronometers, the (U-Th)/He method on hematite and goethite is more often used, but ages can be difficult to interpret due to phases mixing. To resolve this issue, this study proposes a methodology for performing detailed mineralogical analysis of hematite and goethite single grains prior to their dating using the (U-Th)/He method. Strictly non-destructive mineralogy of single grains is not achievable by classical tools, such as conventional powder XRD (X-ray diffraction; requiring at least some milligrams of powder) or SEM (scanning electron microscopy; that can contaminate the grain by coating or fixing). Therefore, we performed X-ray diffraction patterns of single grains using high-flux X-ray beams from both a rotating anode (XRD_rotat) laboratory diffractometer and a synchrotron beamline (XRD_synch) and compared the results in order to design a method based on XRD_rotat only. For this purpose, two samples from the pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba region, Minas Gerais State, Brazil) were chosen because they presented a usual heterogeneity. Rietveld refinements of the XRD patterns obtained from both XRD_rotat and XRD_synch yielded similar results for the weight percentage ratio of the main phases and mean coherent domain sizes and less similar results for Al substitution rates, thus validating the XRD_rotat approach. No beam damage was observed when increasing X-ray exposure time, neither on XRD patterns nor on (U-Th)/He ages. Hence, sub-millimeter, undisturbed grains can be used to analyze the mineralogy of ferruginous duricrusts by XRD_rotat with a short exposure, and the same grains can subsequently be dated by (U-Th)/He geochronology analysis. The (U-Th)/He dating of pisolitic core and cortex grains also provided meaningful ages: they revealed two evolution phases of the ferruginous duricrust, which occurred at or before the Oligocene for the pisolitic core and middle Miocene for the pisolitic cortex, agreeing with the previous model for the development of pisolites. The mineralogy of single grains selected for dating is helpful for discussing the crystallization ages, and the high-flux XRD approach may be applied to other supergene mineral parageneses used for absolute dating. [ABSTRACT FROM AUTHOR]

Since the mid-nineteenth century, gold ores, mainly hosted in sulfides, have been processed at metallurgical plants located in Nova Lima, Brazil. The generated wastes have been accumulated over the years in tailings dams or in piles. These materials represent wasted from old circuits, as well as from plants still in production. In this study, geochemical, mineralogical, 3D modelling, and metallurgical analyses wastes were carried out to evaluate potential reuse of these wastes. The performed characterization detected residues of very fine grain size containing sulfides and oxides. The wastes show high grades of Au hosted in different minerals. In addition to Au, samples contain S, Fe, Zn, Pb, Sc, Si, and As. The 3D modelling for spatial definition of Au was performed using ordinary kriging with dimensional variograms. The results indicated the occurrence of Au enrichment zones and allowed to reveal the most attractive tailing deposits in terms of Au content. Metallurgical tests showed recovery of 70% of Au and suggested other potential reuse of the wastes, such as aggregates for the civil construction sector and recovery of other metals. The present work highlights the importance of an integrative characterization within the scope of the circular economy and the value of tailings in the production chain of the mineral sector. [ABSTRACT FROM AUTHOR]

Brazil has 95 million tons of Li reserves in the form of pegmatites but produces less than 1% of the global output. Historically Li production in Brazil has been low due to governmental restrictions aimed at controlling the exploitation and trade of Li in Brazil. However, as of 2022, these restrictions were revoked. The abundance of untapped pegmatite ores in Brazil complements the soaring demand for Li in energy-storage applications. This study performs process mineralogy studies on 10 samples collected from a Li pegmatite deposit in the southeastern region of Minas Gerais in Brazil. The samples were characterized by combining density separation and SEM-based automated mineralogy processing system allied with XRF, ICP OES, XRD, and LA–ICPMS. The latter was used to determine Li content in micas which allowed determining the Li deportment between Li-bearing minerals. The results show that the samples contain such Li-bearing minerals as muscovite (0.5 wt% Li2O) and lepidolite (3.1 wt% Li2O), in addition to spodumene (8.0 wt% Li2O). According to the characterization of the spodumene concentrate (d = 3.11) by density separation (at d = 2.95), two main trends were observed: (a) low Li deportment in the sink product (approximately 44% wt%) and higher Li2O grade (approximately 6.5 wt%), and (b) higher Li deportment in the sink product (58%) and lower Li2O content (approximately 4.9 wt%). The first trend is associated with higher modal content of mica since it carries Li to the light product. Lower Li grade is related to the presence of Fe-bearing minerals (e.g., epidote and amphibole) as they report to the dense product and do not contain Li. Spodumene has a high degree of liberation in all samples; therefore, it did not influence the deportment results. The findings highlight the benefit of combining scanning electron microscopy-based automated mineralogy with LA–ICPMS and other techniques from process mineralogy studies in mineral processing. In addition to the mineralogy and liberation characteristics, identifying Li-bearing minerals and determining Li deportment is crucial. [ABSTRACT FROM AUTHOR]

Mineralogical studies are incipient and necessary in the Apodi Plateau, Brazil. This study aimed to evaluate the interrelationship between the mineralogy of the clay fraction and its structural and chemical attributes and to differentiate two important pedo-environments in the semi-arid region of northeastern Brazil (Ferralsol and Cambisols of the Apodi Plateau-RN) using the multivariate technique. We evaluated the interrelationships between mineralogy and the structural and chemical attributes of the soil and differentiated between agroenvironments. We collected soil samples from six profiles in diagnostic horizons of the Ferralsols and Cambisols. In the mineralogical analysis of the clay fraction, X-Ray Diffraction was used to identify mineral peaks of clay and iron oxides. The physical and chemical properties of the soils were determined. The multivariate statistical technique was applied to process the data. The clay minerals identified were hematite, goethite, kaolinite, and illite. The principal component analysis allowed for the separation of environments according to soil density, Fed and Mg2+ for developed soils, and potassium, weighted average diameter, microporosity, total organic carbon, sodium, the sum of bases, calcium, total porosity, aeration, potential acidity, and Feo discriminated developing soils. This study revealed that the clay fraction influenced the structural attributes of the soil according to the degree of soil development. Two profiles presented atypical situations: High contents of crystallized iron in Cambisols and illite peaks in Ferralsolos. These mineralogical results are not commonly found in the literature, highlighting the potential for further studies. The answers concerning the mineralogy of semiarid soils in Brazil and the world show similarity. [ABSTRACT FROM AUTHOR]

The Piauí laterite (NE Brazil) was initially evaluated for Ni but also contains economic concentrations of Co. Our investigations aimed to characterise the Co enrichment within the deposit; by understanding the mineralogy we can better design mineral processing to target Co recovery. The laterite is heterogeneous on the mineralogical and lithological scale differing from the classic schematic profiles of nickel laterites, and while there is a clear transition from saprolite to more ferruginous units, the deposit also contains lateral and vertical variations that are associated with both the original intrusive complex and also the nature of fluid flow, redox cycling and fluctuating groundwater tables. The deposit is well described by the following six mineralogical and geochemical units: SAPFE, a clay bearing ferruginous saprolite; SAPSILFE, a silica dominated ferruginous saprolite; SAPMG, a green magnesium rich chlorite dominated saprolite; SAPAL, a white-green high aluminium, low magnesium saprolite; saprock, a serpentine and chlorite dominated saprolite and the serpentinite protolith. Not all of these units are 'ore bearing'. Ni is concentrated in a range of nickeliferous phyllosilicates (0.1–25 wt%) including serpentines, talc and pimelite, goethite (up to 9 wt%), magnetite (2.8–14 wt%) and Mn oxy-hydroxides (0.35–19 wt%). Lower levels of Ni are present in ilmenites, chromites, chlorite and distinct small horizons of nickeliferous silica (up to 3 wt% Ni). With respect to Co, the only significant chemical correlation is with Mn, and Mn oxy-hydroxides contain up to 14 wt% Co. Cobalt is only present in goethite when Mn is also present, and these goethite grains contain an average of 0.19 wt% Co (up to a maximum of 0.65 wt%). The other main Co bearing minerals are magnetite (0.41–1.89 wt%), chlorite (up to 0.45 wt%) and ilmenite (up to 0.35 wt%). Chemically there are three types of Mn oxy-hydroxide, asbolane, asbolane-lithiophorite intermediates and romanechite. Spatially resolved X-ray absorption spectroscopy analysis suggests that the Co is present primarily as octahedrally bound Co3+ substituted directly into the MnO6 layers of the asbolane-lithiophorite intermediates. However significant levels of Co2+ are evident within the asbolane-lithiophorite intermediates, structurally bound along with Ni in the interlayer between successive MnO6 layers. The laterite microbial community contains prokaryotes and few fungi, with the highest abundance and diversity closest to ground level. Microorganisms capable of metal redox cycling were identified to be present, but microcosm experiments of different horizons within the deposit demonstrated that stimulated biogeochemical cycling did not contribute to Co mobilisation. Correlations between Co and Mn are likely to be a relic of parent rock weathering rather than due to biogeochemical processes; a conclusion that agrees well with the mineralogical associations. [ABSTRACT FROM AUTHOR]

Because of their extreme heterogeneity at multiple scales, carbonate rocks present a great challenge for studying and managing oil reservoirs. Depositional processes and diagenetic alterations of carbonates may have produced very complex pore structures and, consequently, variable fluid storage and flow properties of hydrocarbon reservoirs. To understand the impact of mineralogy on the pore system, we analyzed four carbonate rock samples (coquinas) from the Morro do Chaves Formation in Brazil. For this study, we used thin sections and XRD for their mineralogical characterization, together with routine core analysis, NMR, MICP and microCT for the petrophysical characterizations. The samples revealed very similar porosity values but considerably different permeabilities. Samples with a relatively high quartz content (terrigenous material) generally had lower permeabilities, mostly caused by more mineral fragmentation. Samples with little or no quartz in turn exhibited high permeabilities due to less fragmentation and more diagenetic actions (e.g., dissolution of shells). Results confirm that carbonate minerals are very susceptible to diagenesis, leading to modifications in their pore body and pore throat sizes, and creating pores classified as moldic and vug pores, or even clogging them. For one of the samples, we acquired detailed pore skeleton information based on microCT images to obtain a more complete understanding of its structural characteristics. [ABSTRACT FROM AUTHOR]

The ability of soil to sequester carbon and reduce atmospheric CO 2 concentrations is limited and depends on the soil minerals and their interaction with the microbiota. Microbial activities are closely associated with the types and amounts of soil organic matter (SOM) and clay minerals that have functional groups that interact with energy in Vis NIR-SWIR and Mid-IR wavelengths. The main objective of this research was to determine, based on these spectral ranges, the relation between mineralogical and organic compounds, as their sequestration and specialization in soils from Brazil. It was possible to map microbiological activity by spectral transfer functions and digital soil mapping reaching R 2 from 0.77 to 0.85. Multiple regression equations were constructed to quantify enzymatic activity, microbial biomass carbon (MBC), particulate organic matter (POM), and resistant forms of carbon, and SOM associated with the mineral fraction (MAOM). All these properties were detected by specific bands obtained with the recursive feature elimination (RFE) algorithm, reaching correlations from 0.64 to 0.98 in specific ranges. The prediction model of the carbon sequestration potential was adjusted with microbiological and mineralogical variables from Vis-NIR-SWIR and the Mid-IR spectral range. A SARAR double autoregressive model was adjusted with r 0.61 and to a spatial error model (SEM) with r 0.7. The explanatory variables were associated with kaolinite, hematite, goethite, gibbsite, and the abundance of fungi, actinomycetes, vesico-arbuscular mycorrhizal fungi, enzymatic activity of beta-glucosidase, urease and phosphatase, and POM. Among the microbiological variables, the general abundance of fungi was the most important, in contrast to enzymatic activity that was the least important. The interaction between the different maps constructed and historical land use allowed the identification of areas that contribute to sequestering new carbon and could be the key to climate change mitigation strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The study presents SEM-based automated mineralogy to distinguish between natural sediments and iron ore tailings deposits from the Paraopeba River, after the failure of B1 Dam in Brumadinho, Minas Gerais, Brazil. Samples were obtained from borehole cores drilled over channel bars and banks eight months after the failure. After preliminary facies description, sediments from 54 chosen intervals were subjected to density measurement, X-ray diffraction (XRD), SEM-based automated mineralogy (QEMSCAN) analysis and determination of geochemical major components. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) revealed six main mineral associations governed by different contents and ratios of quartz, kaolinite and hematite. Natural sediments are predominantly composed of mineral associations containing kaolinite, quartz and quartz + hematite with density values ranging from 2.5 to 3.3 g/cm3. Tailings deposits have density values higher than 3.5 g/cm3 and are mainly composed of hematite with occasional occurrences of kaolinite + hematite. Because of geological complexity and historical terrain occupation and usage, geochemical anomalies are common in the Paraopeba River sediments. Our data suggests that mineralogical oriented studies should precede detailed geochemical investigations, to enhance the understanding of the source of such anomalies and the environmental jeopardy associated to the occurrence. In this sense, SEM-based mineralogy has an enormous potential in environment studies. [ABSTRACT FROM AUTHOR]

Several gold deposits display complex Bi-bearing mineralogy. Bismuth-bearing phases are generally sensitive to changes in physicochemical conditions such that the interpretation of Bi–Au associations is useful to understand these mineralizing systems. However, gaps in the physicochemical constraints given by the Bi enrichment in these systems prevent robust metallogenic models in some complex deposits. São Sebastião is a hypozonal gold deposit in the Quadrilátero Ferrífero historic mining district in Brazil, and unlike other Archean gold deposits in this area, it displays a disseminated high-temperature and high-grade sulfide overprint with Bi enrichment. The Bi-bearing mineralogy at São Sebastião is heterogeneously distributed in the BIF-hosted ore bodies. Bismuth-sulfosalts, Bi-chalcogenides, and native bismuth have crystallized in a variable set of intercalated patches, yielding different ore facies given by the fractionation of hydrothermally assisted melts. Base metal–bearing Bi-sulfosalts, electrum, and acanthite result from high-temperature (~ 600 °C) immiscible melts rich in chloride ligands, while late crystallization of high-fineness native gold associated with native bismuth at 271 °C is evidence for Au scavenging by protracted low-temperature Bi-enriched metallic melts. This mechanism has favored gold remobilization from early sulfide assemblages and the development of localized upgraded ore stringers. Rapid uplift from a reduced (low fO2) hypozonal environment to oxidized brittle conditions is suggested by crosscutting bismuthinite-bearing veins' fluid inclusion patterns and the absence of maldonite (Au–Bi alloy). Many hypozonal deposits like São Sebastião show similar mineralogy and have developed at the boundaries of Archean terrains, registering multiple tectonic overprints where partial melts may have had an essential role in the final ore formation. [ABSTRACT FROM AUTHOR]

The objective of this research was to analyze the spectral response of alluvial soils, representative of the coastal plain in the lower course of the Acaraú River, Ceará, Brazil, and to correlate with the granulometry and soil organic matter (SOM) contents, seeking to identify the best method to predict the attributes studied. In four soil profiles (n = 23 soil samples) the sand, silt, and clay and SOM contents were determined and was carried out the mineralogical characterization. Soil samples were submitted to spectral analysis using a spectroradiometer, with spectral range from visible to shortwave to near infrared (350 - 2,500 nm). It was possible to relate the soil attributes such as color, SOM contents, variation in granulometry and even mineralogy aspects, such as types of minerals in the clay fraction, with the spectral reflectance curves. Some spectral interpretations were useful in understanding aspects associated with the genesis of these soils, especially with regard to the formation environment and mineralogy. For the SOM contents, the best estimates were obtained by simple linear regression and higher correlation for the 564 nm spectrum range. Regression methods were efficient in estimating soil attributes, but the study is limited to the small sample size. [ABSTRACT FROM AUTHOR]

High-temperature conditions for ore deposition and anomalous abundances of base metals in orogenic gold deposits are frequently attributed to magmatic-hydrothermal fluids instead of metamorphic orogenic fluids. Zona Basal is a shear zone-related gold and base metals-rich mineral occurrence recently discovered in the northwestern portion of the Quadrilátero Ferrífero mining district in southeast Brazil. Mineralogical and geochemical characterization has revealed a two-stage mineralizing system. An Au-W-As stage is marked by a late- to post-tectonic arsenopyrite-pyrrhotite-pyrite assemblage (crystallized from ca. 491 to 404 °C), associated with native gold and scheelite, which was formed during the transition from the peak of greenschist facies metamorphism to retrograde metamorphism. A following, clearly post-tectonic stage comprises a pyrrhotite-pyrite-sphalerite-chalcopyrite-galena-ullmannite ± meneghinite ± fahlore ± miargyrite ± pyrargyrite assemblage crystallized from ca. 400 to < 170 °C, corresponding to the Ag and base metals stage. Fahlores from the Zona Basal mineral occurrence have been found to be sufficiently enriched in Ag, due to the Ag–Cu cation-exchange reaction 13PbS (galena) + 10AgSbS2 (in galena) = 3Ag3SbS3 (pyrargyrite) + Ag(Cu)−1 (exchange in fahlore) + CuPb13Sb7S24 (meneghinite), to jump across the (Cu, Ag)10(Fe,Zn)2Sb4S13 miscibility gap. Two mechanisms may explain the abrupt chemical change between the two mineralization stages: (1) participation of magmatic-hydrothermal fluids of relatively low temperature (acting mostly as a chemical source for fluids) associated with a syn- to late tectonic granite intrusion; or (2) local re-concentration of base metals by unmixing of an early metamorphic orogenic fluid due to fluid immiscibility after the transition from ductile to brittle conditions, generating coexisting fluids with different salinities (i.e., extremely low and moderate salinity). The findings in this paper illustrate the importance of considering retrograde or cooling reactions and mineral re-equilibrium while addressing complex ore-formation. [ABSTRACT FROM AUTHOR]

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The Gentio metagranitoid presents equigranular and porphyritic facies, modal composition ranging from tonalite to monzogranite with calculated TZr<800 °C for most samples. Its mineralogy is dominated by quartz and feldspar (77% to 95%), biotite is the only mafic mineral present (2% to 18%) and, titanite, zircon, apatite, allanite are important accessory phases. These rocks range from metaluminous to weakly peraluminous, and have large variation in major and trace elements, and high alkali contents (>6 wt.%). Zircon analyses by LA-ICP-MS and SHRIMP yielded a concordia age of 2 119±10 Ma for the porphyritic facies and an upper intercept age of 2 111±15 Ma for the equigranular facies. The whole-rock Sm-Nd TDM ages vary from 2.4 to 2.8 Ga with εNd(2.1) values between −0.7 and −5.3, indicating crustal derivation from distinct and/or heterogeneous protoliths. Field observations indicate that the Gentio metagranitoid was formed through different pulses of magma. Individual batches were subject to little or even no fractionation process after its emplacement. Although the Gentio metagranitoid crosscuts metamafic and metaultramafic rocks akin to an oceanic arc setting, this pluton is likely originated by partial melting of a more evolved quartz-feldspathic crustal igneous rock in a post-collisional environment, after the accretion of the arcs from the Mineiro belt and rocks of the Mantiqueira Complex. [ABSTRACT FROM AUTHOR]

The soil position in the landscape reveals its formation history. Landscapes combine surface features and subsurface components (parent material) of the earth, at which the soil inserts as a three-dimensional and dynamic natural body. The present research aimed to study the soil–landscape relationship in a sandstone-gneiss topolithosequence and the factors determining soil diversification in the State of Amazonas, Brazil. The study extended along a transect of 9253 m, covering the distance between the first and the last profile, for a total of five profiles opened. Profile selection considered landscape topography, from the highest to the lowest relief of the terrain. Soil profiles characterization and classification were based on morphological, chemical, and physical properties and the mineralogy of the clay fraction by X-ray diffraction (XRD). Lithological contrasts and landscape variations determined the different soil types along the topolithosequence. Morphological, physical, chemical, and mineralogical attributes also varied along the landscape. The relief and the parent material, sandstone-gneiss, were the main factors influencing the pedogenesis. Goethite (5–40 g kg–1) was the predominant Fe oxide in all the soils, reflecting the low total iron content (Fet ≤ 68 g kg–1) of the soils and parent materials. The predominance of the sand fraction in all the studied profiles reflected the alluvial nature of the parent material, with the highest values (total sand > 800 g kg–1) occurring in the convex creep slope. Knowing the geomorphic surfaces and the parent material was effective for understanding the variation of the soil attributes along the landscape. [ABSTRACT FROM AUTHOR]

Unstable soil aggregates can easily be dispersed when mechanical energy is applied, denominated as readily dispersible clay (RDC) which is usually measured by turbidimetry. Faster methods that require minimum preparation at reduced costs are needed, such as the spectroscopy technique. Nevertheless, the technique has not yet been tested on soils. Electromagnetic radiation has strong interaction with soil physical elements (sand, silt, and clay) and with selective elements of the clay fraction, such as mineralogy. Thus, this study assessed the potential of 400–16,680 nm range (visible – Vis; near-infrared – NIR; short-wave infrared – SWIR; and medium infrared – MIR) spectroscopy to estimate RDC in some tropical soils. We also evaluated the wavelengths and regions that contribute to this prediction. We collected 68 samples from the underlying horizon of three different soils from three important states in Brazil The soil analyses were performed (physical and chemical) in the laboratory. RDC quantification was compared with the Vis-NIR-SWIR and MIR wavelengths models. The random forest (RF) algorithm was used to generate the prediction in the soil database. For RDC, the Vis-NIR-SWIR and MIR configuration presented a better relationship (coefficient of correlation (r) = 0.659 and root of the mean square error (RMSE) = 0.469%), although the results were similar when the regions were evaluated separately (Vis-NIR-SWIR – 350 to 2500 nm and MIR 2500 to 16,680 nm). RDC determination is more related to bands from 1980 to 2040, 6840 to 7360, and 7750 to 9820 nm. Spectroscopy showed its importance in RDC quantification, as it is fast and does not require soil preparations. The results show that spectral wavelengths are appropriate to assist on the estimative of RDC in the studied soils and may provide a basis for future research. [ABSTRACT FROM AUTHOR]

In the Plateau of Lages, intrusions of alkaline and ultrabasic rocks occur, rocks of rare occurrence in Brazil, whose soils derived from them are practically unknown. The study aimed to evaluate the chemical composition, mineralogy, genesis, and classification of the soils developed from the rocks Nepheline Sienite (P1), Volcanic Breccia (P2), Kimberlitic Breccia (P3), Phonolitic Tephrite (P4), and Phonolite (P5). After the morphological description (field) and the collection of soil samples, chemical analyses of the soils, mineralogical of the clay fraction and the total elements of the soils and the corresponding rocks that gave rise to them were carried out. Three Humudepts (Cambissolos), a Hapludolls (Chernossolo), and a Kandiudox (Nitossolo) were identified. Except for the P3 profile, the others are acidic soils, with high levels of exchangeable aluminum, poor in basic cations, with low sum and base saturation, showing a high degree of weathering and strong leaching. In the clay fraction, the presence of 2:1 clay minerals predominated with kaolinite with interlayered hydroxy-Al polymers. The P3 profile showed a slightly acidic reaction, high sum and base saturation, and practically zero exchangeable aluminum, a situation compatible with mineralogy, where trioctahedral vermiculite predominated, revealing that it was a young, slightly weathered soil. [ABSTRACT FROM AUTHOR]

• Soil elemental composition is key to infer other soil attributes. • DSM and remote sensing can take punctual XRF information to maps. • We mapped the main chemical elements using punctual XRF information and DSM. • XRF allied with DSM can be a new and low-cost way to large areas soil mapping. • Spatial XRF information can be used to access soil variations in the landscape. Spatial soil information has significantly contributed to public policy and planning. The use of X-ray fluorescence spectrometry (XRF) in soil science, primarily in laboratory settings or for isolated point analyses, has been well documented. This study broadens the application of XRF data by integrating it with remote sensing data for a comprehensive understanding of soil patterns and processes. Focusing on a 2574 km2 area in Brazil, we utilized a lab-based XRF instrument to measure the total concentrations of key chemical elements in the soil, such as Al, Si, Ti, and Fe. These geochemical data were then spatialized using the digital soil mapping (DSM) framework. We employed a synthetic bare soil image and elevation data as covariates in the analysis. The spatial accuracy assessment yielded R2 values ranging from 0.65 to 0.81 for Fe, 0.62 to 0.78 for Ti, 0.52 to 0.63 for Si, and 0.48 to 0.63 for Al. The digital soil maps of geochemical elements aligned well with existing pedological, and geological maps as evaluated using multiple correspondence analysis. The integration of spatialized XRF data with DSM and remote sensing techniques shows significant promise in assessing soil variations across landscapes based on their chemical composition. [ABSTRACT FROM AUTHOR]

Halloysite is a 1:1 dioctahedral clay mineral that has been studied widely for applications in nanotechnology and as a mineral exploration guide for recognizing regolith-hosted heavy rare earth element (HREE) deposits. In Brazil, pegmatites from the state of Rio de Janeiro have been catalogued, but their potential to host halloysite deposits has never been studied. After a mineral exploration programme, one pegmatite with considerable halloysite contents and economic potential was discovered. This study reports the mineralogical and chemical characterization of the halloysite of this pegmatite and evaluates the possibility of clay-adsorbed HREE deposits, like that in the Zudong (China) regolith-hosted HREE deposit. Seven samples were collected in horizontal channels. Bulk samples and clay fractions (<2 µm) were analysed by quantitative mineral analysis (X-ray diffraction/Rietveld method), chemical analysis (major elements by X-ray fluorescence and Y, U, Th and rare earth elements by inductively coupled plasma mass spectrometry), scanning electron microscopy, Fourier-transform infrared spectroscopy, particle-size analysis, nitrogen physisorption and cation-exchange capacity. Mixed polygonal/cylindrical halloysite-7Å in concentrations between 6.3 and 35.4 wt.% in bulk samples and between 58.0 and 89.8 wt.% in the clay fractions were identified in the pegmatite. The clay fractions presented an average chemical composition of 45.46 wt.% SiO2, 36.10 wt.% Al2O3, 14.62 wt.% loss on ignition and 1.04 wt.% Fe2O3, as well as technological properties close to those observed in world-class halloysite deposits such as Dragon Mine (USA) and Matauri Bay (New Zealand). The clay minerals did not present significant HREE contents. [ABSTRACT FROM AUTHOR]

This work sheds light on the recent evolution (≈1915–2015 AD) of Sepetiba Bay (SB; SE Brazil), a subtropical coastal lagoon on the southwestern Brazilian coast, based on a multiproxy approach. Variations in geochemical proxies as well as textural, mineralogical and geochronological data allow us to reconstruct temporally constrained changes in the depositional environments along the SP3 sediment core collected from the central area of SB. At the beginning of the twentieth century, the substrate of the study site was composed of coarse-grained sediments, largely sourced from felsic rocks of proximal areas and deposited under moderate to strong shallow marine hydrodynamics. Since the 1930s, the study area has undergone silting and received high contributions of materials from mafic rocks sourced by river basins. The SP3 core reveals a shallowing-upward sequence due to human-induced silting with significant eutrophication since the middle of 1970, which was caused by significant enrichment of organic matter that was provided by not only marine productivity but also continental and human waste. In addition, the sediments deposited after 1980 exhibit significant enrichment and are moderately to strongly polluted by Cd and Zn. Metals were dispersed by hydrodynamics from the source areas, but diagenetic processes promoted their retention in the sediments. The potential ecological risk index (PERI) indicates that the level of high (considerable) ecological risk is in sediments deposited in ≈1995 (30–32 cm; subsurface). The applied methodology allowed us to understand the thickness of the bottom sediment affected by eutrophication processes and contaminants. Identical methodologies can be applied in other coastal zones, and can provide useful information to decision makers and stakeholders that manage those areas. [ABSTRACT FROM AUTHOR]

Purpose: Dredged sediments are often disposed on land areas and can cause adverse effects on soil biota, since these materials generally may contain toxic agents. This work examines the ecotoxicological effects on earthworms exposed to technogenic deposits formed from the deposition of dredged sediments from an urban tropical lagoon. Such evaluation supports the understanding of the ecological effects derived from dredged sediments in the tropics, as well as the influence of soil properties in the toxicity. Materials and methods: To simulate dredged sediment disposal under tropical conditions, a dredged sediment sample from the Rodrigo de Freitas Lagoon (Rio de Janeiro, RJ, Brazil) was mixed with a Gleysol (a typical organic tropical soil) to obtain the following doses: 0, 6, 12, 18, and 24%, where 0% = pure Gleysol. Acute and avoidance bioassays with Eisenia andrei were applied to these mixtures following standard protocols (ISO). Physical, chemical, and mineralogical characterization of the materials and metal determination in the test mixtures were performed to support the interpretations of ecotoxicological data. Results and discussion: Metal concentrations in the test mixtures were generally in accordance with the limits defined by Brazilian law. Earthworm mortality was significant in doses ≥ 8% (LC50 = 7.1%), while doses ≥ 2% caused avoidance responses (EC50 = 1.7%, p < 0.05). The salinity in 8% treatment is similar to the salinity levels described by the literature that cause adverse effects on earthworms, suggesting that salinity played a key role in the toxicity. Earthworm biomass increased (p < 0.05) when the organisms were exposed to non-lethal doses, and this is probably due to water bioaccumulation related to high contents of salts. When comparing the toxicity found in this work with data obtained with other tropical soils, one could suppose that Gleysol mineralogy seems to control the bioavailability of salts and metals. Conclusion: The possible formation of technogenic soils (constructed soils) due to land deposition of dredged sediments may potentially compromise natural soil fauna. In this particular case, soil mineralogy, salinity, and metals played a relevant role in the toxicity to earthworms. The development of approaches that can integrate ecotoxicological, ecological, and pedological data is urgent for better understanding the damages associated with the disposal of dredged sediments in tropical lowlands areas. [ABSTRACT FROM AUTHOR]

Increasing the recovery of the niobium metal contained in the Nelsonite rocks presents a great challenge, considering the standards and the production targets of the China Molybdenum Company (CMOC) that produces phosphate and with tailings material, concentrate niobium minerals. At Chapadão mine, located in Goiás, a mid-west Brazil's state, the weathering profile reaches up to 100 meters and the ore is subdivided into three basic types, from top to bottom: Oxidized (OX), Top Micaceous (TM) and Base Micaceous (BM). In this study, samples from these three main bodies of Nelsonite were collected and tested in laboratory scale to identify which weathering level is more favourable to niobium concentrate production. In the niobium concentration process, there can be metal losses that can jeopardize the recovery of the niobium crystals. To evaluate these losses microscopy analysis was performed using samples from industrial plant survery. The results from flotation batch tests showed that BM presented the higher mass recovery and production capacity. According to the mineralogical results the main niobium losses were identified in the barite concentrate from apatite circuit and in the screening stage in the Niobium Plant feed. The batch test results showed that adjusting the cut size of the Niobium Plant there is a potential niobium recovery upgraded to 90% from Ba-pyrochlore, and, adding the barite concentrate product as an additional mass in the tailings feed, it will result together in more than 1 t/day of niobium concentrate final product, reducing the losses and utilizing better the ore blend recovery potential. [ABSTRACT FROM AUTHOR]

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The Capoeirana emerald deposit is located near Nova Era, in the southeastern part of Minas Gerais, Brazil. Two distinct lithologies compose the geology of the zone. One consists of undifferentiated granitoid rocks and the other is formed by volcano-sedimentary rocks, both of them being strongly altered. Emeralds occur in three types of associations. The main one is a meta-ultramafic rock, and the others are quartz- and pegmatitic veins. The mineralization is located at the tectonic contact of the volcano-sedimentary sequence with the gneissic rocks. The best specimen crystallized around quartz fishes in their pressure shadows. Pegmatite veins are the Be source and granitic bodies caused the hydrothermal processes. Chemical investigations on the zoned emeralds show there was an evolution starting with low Cr and very low V concentrations. Micas, picotite, and amphibole microprobe analyses indicate at least two mafic components and a multistage process of formation. The CO2 (±CH4) - H2O - NaCl fluid inclusion type showed the CO2 density between 0.55 - 0.78 g/cm³, the aqueous phase indicated the salinity between 2 - 17 wt.% NaCl eq., the pressure between 0.8 - 2 kb, and the formation temperature between 420° and 690°C. Informally, the CO2 diad based calculation gives 0.479898 g/cm³ density. Sometimes, CO2-rich inclusions show critical homogenization. Complex carbonate/silicate primary and pseudo-secondary inclusions suggest an immiscible process at high temperature trapping conditions. [ABSTRACT FROM AUTHOR]

Heap leaching of laterites for extraction of nickel and cobalt is an attractive alternative to capital and energy intensive high pressure acid leaching, the dominant hydrometallurgical processing technology for limonitic laterites. Conventional approach for heap leaching of laterites is leaching with sulfuric acid. Consumption of sulfuric acid during heap leaching is substantial and industrial-scale operations require construction of a sulfuric acid production plant on site. In this study, heap bioleaching of laterites was simulated in laboratory scale column percolators and bioleaching of nickel and cobalt from lateritic material was successfully demonstrated for the first time. The process is based on biooxidation of the bacterially modified "wet sulfur" inside column percolators by sulfur-oxidizing acidophilic bacteria Acidithiobacillus thiooxidans. The "wet sulfur" was generated in a bioreactor with the bacterial culture, harvested, and mixed with lateritic ore before forming agglomerates to be filled in the percolator columns. Liquid was circulated with a flow rate of 8 mL/min. Maximum metal extraction was 66% nickel, 95% cobalt, 10% iron, 55% magnesium and 89% manganese from the Piauí lateritic ore after one month bioleaching. For comparison, chemical leaching with 1 M sulfuric acid with or without addition of 10 g/L of ferrous sulfate heptahydrate as reductant resulted in extraction of approximately 80% nickel, 86% cobalt, 33% iron, 50% magnesium and 81% manganese. With bioleaching a higher cobalt but lower nickel and iron extraction was achieved, i.e. a better selectivity of nickel over iron extraction, as well as a relatively higher pH of the pregnant leach solution requiring less limestone and, consequently, lower CO 2 emission and generation of iron cake waste in case of laterite bioleaching. Overall, the results are promising and show potential of laterite heap bioleaching to be further developed to application on industrial scale. • Bioleaching of laterite in percolators with acidophilic sulfur-oxidizing bacteria was tested in the lab. • Lateritic ore was agglomerated with bacterially modified "wet" sulfur. • Maximal achieved extraction of Ni and Co was 66% and 95%, respectively. • Microbially generated ferrous iron is important in order to increase bioleaching efficiency. [ABSTRACT FROM AUTHOR]

We analyzed hydrothermal silicification along the Afonso Bezerra strike-slip fault system in the Potiguar Basin, equatorial margin of Brazil, to assess the role of Si-rich fluids in fault geometry, properties, and evolution. The fault cut across the whole basin, including its crystalline basement, a late Cretaceous siliciclastic unit and a lower carbonate unit, and a Paleogene-Neogene upper carbonate unit. Intense fault-controlled silicification caused by the upward migration and diffusion of hydrothermal fluids occurred repeatedly. The fault zone is characterized by multiple events of syntectonic (dynamic) silicification with hydraulic brecciation at all scales in the fault core and static silicification, in which no or little lattice orientation or deformation occurred in the damage zone. In the carbonate units, silicification resulted in the complete replacement of the carbonate mineralogy by quartz, chalcedony and opal, and the SiO 2 content increased from 3 to 15% in the host carbonate units to as much as 94–97% in the silicified portions of the fault. The silicified fault zone presents an abrupt widening from 150 m in the siliciclastic unit to as much as 800 m in the lower carbonate unit. The matrix of the siliciclastic unit exhibits a porosity reduction from 27% to 4%. By contrast, the matrix porosity of the lower carbonate unit exhibits a primary porosity of approximately 5–10%, which is either reduced to ~ less than 1% or increased to more than 15% in the silicified zone. In the upper and lower carbonate units, centimeter-scale vuggy porosity along fractures occurs in the silicified zone. This anomalous vuggy porosity could serve as a reservoir pore space. The collective field and petrological evidence suggests that volcanic intrusion plays an important role in silicification. This work may shed light on the origin and likely geometry of the fault-controlled silica distribution causing heterogeneities within carbonate and siliciclastic reservoirs. • Hydrothermal silicification (HS) occurs in a strike-slip fault. • HS was channeled along a fault that cut across siliciclastic and carbonate units. • Multiple coeval events of silicification occurred in fault zones up to 800 m wide. • Dynamic HS affected the fault core, whereas static HS affected the damage zone. • Matrix porosity up to 14% and cm-scale vuggy porosity may provide reservoir space. [ABSTRACT FROM AUTHOR]

This research presents the mineralogical and chemical characterization and beneficiation study of two kaolin deposits from the Borborema Pegmatite Province, Brazil. Seven samples were collected and treated in two different beneficiation routes involving magnetic separation and chemical bleaching. The fractions obtained were studied by X-ray diffraction, X-ray fluorescence spectrometry, scanning electron microscopy, particle-size analyses, electron paramagnetic resonance and determination of optical properties. The samples are composed mainly of subhedral kaolinite in the form of booklets, as well as muscovite, quartz, microcline and illite impurities. The kaolinite structural formulae indicated significant replacement of Si4+ by Al3+ in tetrahedral sites and low replacement of Fe3+ by Al3+ in the octahedral sites. The first 30 min of chemical bleaching improved significantly the optical properties of kaolin, indicating that the process is more efficient than magnetic separation. [ABSTRACT FROM AUTHOR]

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Soil position in the landscape reveals its history of formation and genesis. Therefore, the landscape is the combination of features of the surface of the earth with subsurface components (parent material), while the soil is a three-dimensional, dynamic natural body inserted in the landscape. This research aimed to study the soil-landscape relationship in a sandstone-gneiss topolithosequence in Amazonas, Brazil. The study was carried out along a 9.253-meter transect from the top downwards the softer slope. Soil profiles were selected in five landscape compartments (top, upper third, lower third, transport foothill, and deposition foothill). Morphological, mineralogical, physical, chemical, and ray diffraction characterizations were performed. Soils had different morphological, physical, chemical, and mineralogical attributes due to the variations of the geological substrate and landscape position. The mineralogy of the clay fraction is composed of kaolinite, goethite, hematite, and gibbsite, with goethite being the predominant iron oxide. A sand fraction dominance was observed in relation to the other fractions in all the profiles, being related to the alluvial nature of the parent material, with the highest values occurring in the lower third. The separation of the landscape into geomorphic surfaces and identification of the parent material were effective for understanding the variation of soil attributes along the landscape. [ABSTRACT FROM AUTHOR]

Niquelândia is a nickel-lateritic ore deposit located in the State of Goiás, Brazil. This deposit is one of the best-known nickel-lateritic orebodies in Brazil and contains both oxidized and silicate ores. In the oxidized ores, nickel is essentially associated with goethite, while in the silicate ores, it is associated with clay minerals, especially smectites. Two types of smectites were found: a nickel-magnesium-rich trioctahedral and an aluminium‑iron-rich dioctahedral structure. Nickel was produced at Niquelândia by the Caron process, a reduction roasting operation followed by ammoniacal leaching; however, due to the collapse of the nickel prices, Niquelândia mine interrupted its activities in 2016. Usually, the Caron process is able to extracts over 90% of Ni from the oxidized ore and less than 60-70% from the silicate ore. At Niquelândia the nickel recoveries varied from 70 to 75% of nickel from the Run of Mine (oxidized+silicate ores). A detailed study of the mineralogy from the silicate ore residues of the Caron process was conducted in order to find out why nickel extraction is not properly performed in this type of ore. The results revealed: 1) higher nickel extraction is assigned to iron-rich dioctahedral smectites and 2) lower nickel extraction is assigned to nickel-rich trioctahedral smectites; finally, 3) the low Fe content of Ni-rich trioctahedral smectites does not allow forming Ni-Fe phases which can be dissolved by the ammoniacal leaching. • In the silicate ore, nickel is associated with di and trioctahedral smectites. • Residues from roasting and ammoniacal leaching of Ni-silicate ore were studied. • Fe-Ni phases were not formed from roasted residues of trioctahedral smectite. • High Ni recovery was noted for Fe-rich dioctahedral smectites. [ABSTRACT FROM AUTHOR]

Mineralogy, geochemistry and isotopic data for Ediacaran, Ordovician to Devonian, and Upper Triassic cordierite-bearing granitoids respectively from Brazil, Argentina and Chile are discussed here. Syn-collisional Lower to Middle Ordovician, and post-collisional Upper Devonian garnet-free granitoids from Argentina intruded greenschist-to amphibolite-facies metasedimentary rocks. Garnet-bearing and garnet-free monzogranites of the Nanuque Suite, Brazil, intruded high-grade gneisses and migmatites, and in the High Andes Belt, the Los Tilos garnet-free granite was emplaced into an early Permian batholith during an extensional event. Mineralogical, geochemical and isotopic characteristics of the granites from Argentina and Brazil, such as presence of peritectic and (±) restictic cordierite, low-magnetic susceptibility (MS) values (0.03–0.2 × 10−3 SI), negative εNd (−7.3 to −5.0) and high δ18Ozircon values (>9‰), suggest a major aluminous metasedimentary source. Data for the Chilean pluton (small volume, associated with coeval metaluminous granites, low δ18Ozircon values (6.6–7.4‰), slightly negative εNd (−4), and high MS values (1.4–2.5 × 10−3 SI) are compatible with a less-evolved source, possibly a metaluminous granitic rock. P-T magma crystallization conditions of the cordierite-bearing granites from Argentina are 2–4 kbar and 630–720 °C; and 3.6–4.0 kbar and at 670−700 °C for their cordierite. The Nanuque magma formed P > 6 kbar; T = 750–800 °C, and magma emplaced at ∼3 kbar. Their cordierite formed at P = 5.0–5.2 kbar and T = 720−740 °C. P-T conditions of the Los Tilos magma emplacement are P ∼ 3 kbar and T ∼670 °C. Cordierite-paramorph β-quartz nodules in this pluton, surrounded by leucocratic rims, have been formed by biotite dehydration reactions. This study confirms that cordierite in granites can be produced from different source rocks by a number of processes, at different P-T conditions. • South American cordierite-bearing granites formed under different P-T conditions. • Source rocks are either metapelitic rocks or metaluminous granite. • Cordierite was formed by peritectic reactions or is restitic. [ABSTRACT FROM AUTHOR]

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The Artulândia prospect area is a recently-mapped, non-auriferous VHMS mineralization within Paleoproterozoic rocks in Central Brazil. The mineralization is hosted in a felsic-dominated bimodal volcano-sedimentary sequence that formed during the onset of Campinorte Magmatic Arc. The Zn–Pb–Cu-(±Ag–Bi) VHMS mineralization occurs as massive sulfide lenses and sulfide disseminations. Surrounding the sulfide lenses, two proximal hydrothermal assemblages are identified: (i) Tremolite-spessartine (±clinochlore-epidote) assemblage, associated with the sphalerite-pyrite aggregates and (ii) Clinochlore-carbonate (±tremolite-talc-serpentine) assemblage encompassing chalcopyrite, galena, and sphalerite. Besides these two assemblages, three others are considered distal to the mineralization, and interpreted to represent the stringer zone: (i) Biotite-spessartine (±chamosite-tourmaline) assemblage, with disseminated sphalerite + pyrite + galena, (ii) Biotite-sericite-carbonate (±chamosite) assemblage, with disseminated pyrite + sphalerite and (iii) Biotite-carbonate assemblage, with pyrite and traces of sphalerite intergrown with biotite lamellae. The mineralogy of the assemblages results from the Paleoproterozoic, syn-volcanic metamorphism (Neoproterozoic, Brasiliano Orogeny) of hydrothermal alteration minerals. The mineralogy and mineral chemistry data of the assemblages show that proximal assemblages formed under great influence of Fe–Mg–Ca-rich fluids. The highest grades of base metals are restricted to the sulfide lenses: Zn (1.4% wt.), Pb (1.0% wt.%), and Cu (1.8% wt.). Anomalous contents of Mo (>180 ppm), Bi (>700 ppm) and Ag (>60 g/t) occur in the proximal hydrothermal assemblages. Gold grades as high as 270 ppb are directly related to chalcopyrite-enriched zones. The δ34S measurements in pyrite vary from +8.77‰ to +10.99‰. These values are compatible with Paleoproterozoic deposits in which the isotope composition reflects a mix of seawater and leached sulfur from host rocks. • New base metals mineralization in Central Brazil. • Polymetallic VHMS hosted in a bimodal volcano-sedimentary sequence. • The mineralogy results fromthe Neoproterozoic metamorphism of Paleoproterozoic syn-volcanic hydrothermal alteration. • Geochemical and isotopic data corroborate the volcanic exhalation origin. [ABSTRACT FROM AUTHOR]

A comparison of Rietveld refinement results for a bauxite-bearing regolith and its clayey cover in the Amazon region was made with stoichiometric calculations from chemical analysis and partly from thermogravimetric results. For this investigation a profile in the bauxite-bearing regolith occurrence in the ALCOA bauxite mine at Juruti, Brazil was studied. The different minerals, their compositions and their low crystallinity in the different horizons were investigated and the contents determined. It is evident that some minerals show several generations and some chemical composition changes that must be included in the Rietveld refinement. Al-rich hematites and goethites are common along the bauxite profile. Amorphous contents were determined with rutile added as an internal standard and shown to have gibbsite- or kaolinite-like composition. The minerals could be quantified in the different horizons and the difficulties were mainly related to variable crystalline aspects of the phases. Rietveld refinement can be a powerful tool in bauxite prospecting, quality control and during mining and beneficiation of ore minerals using the adapted refinement strategies. [ABSTRACT FROM AUTHOR]

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Fe/Mn nodules are important records of pedogenesis, weathering processes, and pedoenvironmental conditions. However, data regarding the morphology and mineralogy of Fe/Mn nodules are limited due to difficulties concerning the identification of their low crystallinity Fe/Mn oxides. The hypothesis is that nodules in calcareous soils in Northeastern Brazil present crystalline forms of Mn oxides, whose mineralogy and chemical composition are linked to slight variations in relief. This study investigated the mineralogy and geochemistry of Fe/Mn nodules of soils on different relief surfaces (convex, flat, and concave). The nodules were analyzed using sequential selective dissolution procedure (SSDP), X-ray diffraction, elemental analyses, micromorphology scanning electron microscopy, and energy dispersive spectroscopy. Improvements of the SSDP were needed to identify Mn oxide minerals (birnessite and lithiophorite) in nodules. The relief features are determinants for the distribution and formation of minerals in nodules. The occurrence of calcite silt-sized on the convex and straight surfaces indicates pedogenetic genesis. An increase in kaolinite, highly crystalline lithiophorite, and the absence of calcite in the nodules close to the concave surface also indicates synchronism with pedogenesis. Pseudo-hexagonal lithiophorite and birnessite with plate-like habits are important scavengers of Ce, Co, V, and Ba. This research represents the first record of the detailed morphology and identification of Mn minerals in Fe/Mn nodules using SSDP in semiarid calcareous soils from Northeastern Brazil. • A successive selective dissolution procedure (SSDP) was improved to distinguish Mn oxides in soils and parent material. • First micromorphological record of birnessite and lithiophorite in Fe/Mn nodules in Brazilian semiarid soils. • Slight variations in relief rules the mineralogy of Fe/Mn nodules. • Fe/Mn nodules are indicators of pedogenetic processes in calcareous soils. • Environmental control of trace elements by the nodules was revealed. [ABSTRACT FROM AUTHOR]

The estuary of the Rio Jaguaribe (NE Brazil) is filled by a sediment sequence of more than 23 m and characterised by estuarine plains that – today - extend 30 km upstream. We investigated the sedimentary dynamics in the Rio Jaguaribe estuary since the early Holocene by means of clay mineralogical analyses, as well as sediment analyses from 11 sediment cores. The clay mineralogical approach proves to provide the most robust results. A transition of the illite/kaolinite peak area ratio from 0.3 to 1.8 within the vertical depositional record suggests a change of sediment transport direction over time. Whereas in the lower sequence marine influence dominates, characterised by the relatively high kaolinite content originating from the weathered Barreira formation at the coast, in the upper sequence sediments of fluvial origin dominate, which are characterised by the relatively high illite content originating from the crystalline rocks in the source area of the Jaguaribe river. The depositional architecture of the Holocene sediments of the Jaguaribe estuary shows a seawards prograding infill, assumed to have occurred since the mid-Holocene and supports studies suggesting a stagnating or slightly falling relative sea level (RSL) since ∼7000 BP. • Within the estuary sediment infill a transition from low illite/kaolinite to high illite/kaolinite ratios is documented. • Clay mineralogy is a robust tool for defining changes of dominant sediment pathways in an estuary. • The change from marine ingression to progradation of the estuary is assumed to correlate with RSL change around 7000 BP. [ABSTRACT FROM AUTHOR]

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Specific surface area (SSA) is a key property of soils that affects nearly all soil ecological functions that involve aggregation and sorption. However, data on soil SSA are seldom reported in the literature due to time-consuming analysis or equipment constraints in most soil laboratories. Here, we measured external SSA by means of N2 sorption with the Brunauer-Emmett-Teller isotherm using fine earth samples from eight tropical soils of contrasting texture and mineralogy collected at depths of 0 to 5, 30 to 40, and 90 to 100 cm. With these and soil particle-size distribution and soil organic carbon (SOC) data, we developed a multiple linear regression for SSA description. Soil SSA varied from 2.85 to 45.37 m² g-1, generally increasing with an increase in depth for the same soil. The factor most strongly correlated with SSA was clay content, and the weakest correlations were those with SOC concentration. The best multiple regression obtained was SSA (m² g-1 soil) = 0.455(clay %) - 1.641(SOC %) (P < 0.01; n = 72). This equation explained well the observed values (r² = 0.84), including both ends of the measured range. Furthermore, the equation had the advantages of simplicity, using only textural and SOC data of routine determination, and validity for any depth within a 0- to 1-m depth interval. When oxalate-extractable Fe and especially Al data were included as inputs, the prediction power of the model increased to r² = 0.92. However, the use of equations proposed here to predict SSA for soils of other regions must be accompanied by proper validation due to unpredictable variations in soil organic matter composition and mineral crystallinity, among other factors. [ABSTRACT FROM AUTHOR]

Semiarid soils are subjected to wetting and drying cycles which influence sorption and desorption of applied phosphorus fertilizer. Phosphorus desorption was determined in soils from toposequences of two soil groups (Ferralsol and Luvisol) from a semiarid area, subjected to wetting and drying cycles. Samples from surface and subsurface horizons of upslope, midslope, and downslope positions were incubated for 4 months with phosphorus doses corresponding to 0, 5, 10, 25, 50, 75, and 100% of the maximum adsorption capacity, under constant moisture (80% water retention capacity) or 12 cycles of wetting and drying. Phosphorus desorption was lower in the Ferralsol than in the Luvisol, and lower in the subsurface than in the surface horizons, probably due to greater clay, Fe, and Al oxides contents, but they were similar among slope positions, of same mineralogy. Desorption tended to be greater in samples submitted to wetting and drying cycles but differences were small. P recovery reached 40–50% in the Luvisol, and 30–40% in the Ferralsol. The relatively low P retention capacity suggests a high residual effect of the P applied. Therefore, in relation to P losses, water retention techniques are less important than those that prevent soil erosion. [ABSTRACT FROM AUTHOR]

The Morro Preto Complex, located in the northern portion of the Cretaceous Goiás Alkaline Province, is unique in the region due to the large predominance of carbonatites and phosphate mineralization. It comprises two circular intrusions (Morro Preto North and Morro Preto South) of apatite-rich magnesiocarbonatites gradually transitioning to ferrocarbonatites. The complex also hosts fenites produced by carbonatite metasomatism at the contacts with the Neoproterozoic country rocks. Kamafugite dykes with carbonate globules suggest an immiscibility link between silicate and carbonatite magma. The magnetite-apatite-dolomite carbonatites vary in texture and modal composition from cumulates to magnesiocarbonatites with variable apatite and magnetite, with minor barite and traces of pyrochlore, phlogopite, baddeleyite and zircon. In the ferrocarbonatites, magnetite and apatite are rare or absent, and the dominant carbonate varies from Fe-dolomite to ankerite and siderite, with traces of bastnaesite, monazite, thorium-rich monazite and sulfides. SiO 2 , Fe 2 O 3 , MnO, BaO:SrO and the sum of rare earth elements (REEs) increase from magnesiocarbonatites to ferrocarbonatites, whereas the CaO, MgO and P 2 O 5 contents decrease. Four main apatite types are recognized in the complex: (i) high P-REE primary magmatic sub-euhedral apatites (type 1), (ii) fluorapatite associated with ferrodolomite-rich zones (type 2), (iii) fine-grained, Na-rich metasomatic apatite (type 3) and (iv) secondary fluorapatite filling veinlets and cavities (tuupe 4). In general, the apatite morphological and compositional variations correlate with carbonate evolution and with stable isotope data. Dolomite and type 1 apatite represent the primary group (+9.49 to +11.88‰ δ18O and −5.1 o −4.66‰ δ13C). Ferrodolomite, iron-rich carbonates, along with types 2 and 4 fluorapatite have heavier isotope compositions (up to +21.59‰ δ18O and −3.33‰ δ13C), indicating metasomatic reworking related to late-stage carbonatite-derived fluids. Geological, geochemical and mineral chemistry data are consistent with the evolution of the complex by crystal fractionation, liquid immiscibility, metasomatic overprinting and late hydrothermal events. The K fenitization and late-stage carbohydrothermal events suggest that the Morro Preto Alkaline-Carbonatite Complex represents the uppermost parts of a carbonatite magmatic system. • Outstanding carbonatite complex from the Cretaceous Goiás Alkaline Province. • Apatite-dolomite carbonatite rocks host phosphate mineralization. • Ferrocarbonatites derive from late-magmatic to carbo-hydrothermal events. • The different apatite mineral compositions correlate with the complex evolution. • The complex represents the upper-most part of a carbonatite magmatic system. [ABSTRACT FROM AUTHOR]

The Araxá Complex is a significant source of mineral deposits, including Nb, P, Ba, LREE, and Fe. These deposits are formed by weathering phlogopite-rich rocks and norsethite carbonatite in the Complex core and from the weathering of carbonatites in the surrounding ring. The main types of ore in the Complex include rust-colored, brown, and orange ore. The rust-colored ore contains over 2% CaO and MgO and is mineralized with pyrochlore, barite, and fluorapatite in the phlogopititic core and only fluorapatite in the carbonatitic ring. Brown ore has less than 2% MgO and over 2% CaO and is mineralized with pyrochlore, barite, fluorapatite, and magnetite in the core and only fluorapatite in the ring. Orange ore has less than 2% MgO and CaO and is mineralized with pyrochlore, barite, monazite, and magnetite in the core and goyazite in the ring. Pyrochlore and iron minerals were concentrated from the rock to the orange ore, while fluorapatite was concentrated from the rock to the brown ore. The weathering of fluorapatite in orange ore leads to the formation of authigenic gorceixite, goyazite, and monazite. The neogenesis of barite in the Complex occurs due to the dissolution of norsethite, followed by the chemical bonding of Ba with S from sulphuric solutions. The ore deposits are up to 200 m thick, stratiform, and horizontal, formed by meteoric water that flowed vertically downwards, then horizontally, radially, and centrifugally. The weathering of 100 m of rock resulted in the formation of approximately 33 m of orange ore, 9 m of brown ore, and 4 m of rust-colored ore in the Complex core and 35 m of orange ore, 7 m of brown ore, and 10 m of rust-colored ore in the carbonatite ring. Lake sediments accumulate on the orange regolith top surface. [Display omitted] • Araxá Complex: alkali-carbonatitic complex in Minas Gerais, Brazil. • Niobium Deposit: most considerable in the world and located in Araxá Complex. • Saprolite and Regolith: host ores of niobium, phosphorus, barium, iron, and rare earth elements. • Main Ore Minerals: pyrochlore, apatite, barite, monazite, rhabdophane, gorceixite, and goyazite. • Genetic Model: proposed for forming weathering deposits in the Araxá Complex. [ABSTRACT FROM AUTHOR]

The Morro do Engenho lateritic nickel deposit results from the action of weathering processes on the alkaline mafic-ultramafic rocks that make up the Cretaceous zoned intrusive body belonging to the Goiás Alkaline Province. Historically, the deposit is classified as a silicate one, and mineralization is present especially in phyllosilicates such as serpentine and chlorite. By identifying Ni-bearing phases and providing the lithogeochemical characterization of weathering profiles, this study aims to provide further insights into the metallogenetic processes and controls acting on the mineralization of the Morro do Engenho lateritic Ni deposit. The following methods were used: petrographic studies, SEM-EDS, XRD and lithogeochemical characterization of the weathering profiles developed on each of the parent rocks that make up the body. The Morro do Engenho intrusive massif is formed by a dunite core, surrounded by a peridotite/pyroxenite zone, an alkaline gabbro zone and more externally by a syenite-nepheline zone. The lateritic profile constitutes eight weathering horizons, stacked one upon another from the bedrock namely: (i) saprock, (ii) lower saprolite, (iii) ferruginous saprolite, (iv) ocher saprolite, (v) plasma zone, (vi) lateritic duriccrust, (vii) silcrete and (viii) topsoil. Most Ni mineralization occurs in the lower saprolite, ferruginous saprolite and ocher saprolite zones. The findings pointed to the presence of Ni in silicate mineral phases, represented by serpentine, chlorite, smectite, as well as in Fe and Mn oxyhydroxides. The depressed area, located between the two major topographic elevations, has the highest Ni enrichments, which according to mass balance calculations can account for up to 40%. Hydrodynamic factors, by dissolution/precipitation of silicates in saprolite horizons of dunite core, are suggested as possible agents in the remobilization of Ni, among other mobile elements, to topographically flat zones. The geometry of the Morro do Engenho deposit show that lateral redistribution by hydrodynamic factors could also account for the mineralization of areas peripheral to the dunite core, composed of pyroxenite and gabbro-derived lateritic profiles. The direction of regional groundwater flow, strongly influenced by topography, would also be an important factor in the remobilization of Ni, as well as the mechanical transport of lateritic materials. Silicate mineralization predominates in the Morro do Engenho deposit, concentrated in Mg hydrosilicates and clay minerals; oxide mineralization also occurs, mostly in Fe and Mn oxyhydroxides. The findings discussed in this paper can broaden the understanding of metallogenetic processes involved in the genesis of lateritic nickel deposits.. • Lateritic profiles derived from serpentinized dunite, pyroxenite and gabbro containing Ni mineralization. • Presence of oxide–silicate mineralization of Ni. • Ni concentrations affected by hydrodynamics and mechanical transport of lateritic materials. [ABSTRACT FROM AUTHOR]

Mineralogy and geochemistry of the total suspended sediment (TSS) from a granite-gneiss watershed in southeast Brazil brought light to geogenic and anthropogenic sources. TSS was sampled in 15 points along the Piabanha watershed in summer (February 2013) and winter (August 2013). The Piabanha watershed (2 × 103 km2) is located in the mountainous region of Rio de Janeiro, and it is an affluent of the Paraiba do Sul River, the most important river from the Brazilian southeastern coast. TSS mineralogical analyses were performed with X-ray powder diffraction. Geochemical analysis was done with energy dispersive X-ray fluorescence. Quartz, kaolinite and gibbsite were dominant in the TSS mineralogy, followed by feldspar and mica. Granite and gneiss rocks contribution in the TSS have a common mineralogical and geochemical source. But the alluvial deposits from river banks might have been responsible for the differences between summer and winter samples. The major features in TSS from geogenic sources were SiO2, Al2O3, MgO, Ga2O3, Nb2O5, Rb2O, K2O, SrO, ZrO2and TiO2. The good correlation on the Si:Al molar ratio suggested that the source area is intensely weathered. Pollution features (sewage source) were given by significant TSS concentration of Fe2O3, MnO, ZnO, CuO, As2O3, CaO, Na2O, P2O5and SO3. [ABSTRACT FROM PUBLISHER]

Recent studies have focused on the formation of authigenic clays in an alkaline soil system surrounding lakes of the Nhecolândia region, Pantanal wetland. The presence of trioctahedral Mg-smectites (stevensite and saponite types), which requires low Al and Fe contents in the soil solution for its formation, contrasts with the neoformation of dioctahedral Fe-mica (glauconite, and Fe-illite), which instead requires solutions relatively enriched in Al and Fe. This study aims to understand the conditions of co-existence of both, Mg-smectite and Fe-mica a common clay association in former or modern alkaline soil systems and sediments. The study was carried out along an alkaline soil catena representative of the region. The soil organization revealed that Mg-smectite occur in top soil close to the lake, whereas Fe-mica dominate in the clay fraction of deeper greenish horizons a few meters apart. We propose here that this spatial distribution is controlled by the lateral transfer of Fe and Al with organic ligands. Alkaline organic rich solutions (DOC up to 738 mg L-1) collected in the watertable were centrifuged and filtered through membranes of decreasing pore size (0.45 μm, 0.2 μm, 30 KDa, 10 KDa, 3 KDa) to separate colloidal and dissolved fractions. Fe, Al, Si, Mg and K were analysed for each fraction. Although the filtration had no influence on Si and K contents, almost 90% of Fe (up to 2.3 mg L-1) and Al (up to 7 mg L-1) are retained at the first cutoff threshold of 0.45μm. The treatment of the same solutions by oxygen peroxide before filtration shows that a large proportion of Fe and Al were bonded to organic colloids in alkaline soil solution at the immediate lake border, allowing Mg-smectite precipitation. The fast mineralization of the organic matter a few meters apart from the lake favors the release of Fe and Al necessary for Fe-mica neoformation. In comparison with chemical and mineralogical characteristics of alkaline environments described in the literature, the study suggests that the co-existence of trioctahedral Mg-smectite and dioctahedral Fe-mica should be regarded as a standard occurrence in alkaline soil systems with organic rich waters. [ABSTRACT FROM AUTHOR]