Complex Mineral Assemblages Research Articles

Tracing the Oxidizing State and Element‐Mobilizing Fluids in Continental Subduction Zones: Insights From the Granitic Melt‐Eclogite Interface

AbstractFluids in subduction zones significantly influence element mobility, isotope fractionation, and mass transfer. However, unraveling the source, composition, and redox state of fluids in continental subduction zones poses a significant challenge. This study focuses on a granitic melt‐eclogite contact interface, along with adjacent granite and eclogite from the Sulu ultrahigh‐pressure metamorphic belt in East China. The interface exhibits complex mineral assemblages, enriched rare earth elements (REEs), and high field strength elements (HFSEs). Zircon grains from the interface show an age of ∼217 ± 9 Ma, slightly later than peak metamorphism, along with the presence of coesite inclusions. These findings suggest that the interfacial fluid likely formed from the mixing of granitic anatectic melt and aqueous fluid from the eclogite during the initial exhumation of the Sulu terrane. The interaction resulted in the eclogite acquiring substantial REEs and HFSEs, suggesting the interfacial fluid's effective element‐transporting capability and potential supercritical fluid properties. Zircon Ce anomaly and Fe3+/Fe2+ oxybarometer data indicate a highly oxidizing interfacial fluid, analogous to arc magmas in oxygen fugacity. This led to the preferential loss of isotopically heavier Cr from the eclogite during fluid‐eclogite interaction, evidenced by heavier Cr isotopic compositions in the interface (δ53Cr = −0.04 to −0.05‰) compared to adjacent eclogite (δ53Cr as low as −0.11‰). In summary, our results highlight the presence of strong oxidizing and element‐mobilizing fluids in continental subduction zones, offering insights into supercritical fluid recognition and the genesis of oxidizing arc magmas in subduction zones.

Shallow storage of the explosive Earthquake Flat Pyroclastics magma body, Okataina Volcanic Center, Taupo Volcanic Zone, New Zealand: evidence from phase-equilibria experiments

Rhyolitic tuffs range widely in their crystal contents from nearly aphyric to crystal-rich, and their crystal cargoes inform concepts of upper crustal magma reservoirs. The Earthquake Flat pyroclastics (Okataina Volcanic Center, Taupo Volcanic Zone, New Zealand) are 10 km3 of rhyolitic tuffs with abundant (~ 40 vol.%) plagioclase and quartz, minor biotite, hornblende, and orthopyroxene, and accessory Fe-Ti oxides, apatite, and zircon, set in high-silica rhyolitic glass. Major minerals form large, euhedral phenocrysts and abundant glomerocrysts with few disequilibrium textures excepting some faintly resorbed quartz. Plagioclase phenocrysts have thick rims of nearly constant composition near An30, and hornblende is weakly zoned or unzoned. The abundant and texturally complex mineral assemblage contrasts with the nearby (~ 25 km), nearly synchronous, but more voluminous and crystal-moderate rhyolite tuffs from Rotoiti caldera. New H2O-saturated phase-equilibria results on the erupted Earthquake Flat melt (glass) determine its co-saturation with the partial phenocryst assemblage of plagioclase, quartz, biotite, and Fe-Ti oxides at: 140 MPa, 755 ºC. These closely approximate the conditions of the pre-eruptive magma body assuming it was saturated with nearly pure H2O and at an fO2 of ~ Ni–NiO. Absence of hornblende and orthopyroxene from the synthesized assemblages may result from those minerals being in a peritectic reaction relation with melt to produce biotite, so they would not grow from the liquid used as starting material. Experimental results on Rotoiti rhyolite (Nicholls et al. 1992) show that the two bodies resided at similar pressures, temperatures, and fO2s. Lower crystal abundance of the Rotoiti tuffs may result from slight compositional differences. We interpret that the Earthquake Flat pyroclastics were sourced from the crystal-rich periphery of a mushy reservoir system with the Rotoiti occupying a more melt-rich central location. Uncertain is whether this was a single intrusion zoned continuously in crystallinity, or discrete adjacent intrusions, but our results illustrate and quantify complexities of magma storage across relatively short distances.

Origin and thermal evolution of Cr-V-Ti magnetites (lodestones) from Coorg massif, southern India

This study deals with petrology, textural, thermometry, and geochemical characterization of naturally magnetized Cr-V-Ti magnetite deposits within the layered mafic-ultramafic intrusions in Coorg massif of southern India using ore petrography and mineral/whole rock geochemistry. These deposits, also known as ‘lodestones’, occur as rhythmic layers within the lateritized host rock, with the underlying basement distinguished by the presence of charnockites and layered gabbro-anorthosites and pyroxenites, delineating a stratified intrusive setting. Lodestones exhibit complex mineral assemblage involving magnetite, ilmenite, ulvöspinel, spinel, corundum, hematite, goethite, pyrite, pyrrhotite, and amphiboles. The bulk rock chemistry of the lodestone is analogues to Fe-Ti magnetite iron ore deposits with elevated vanadium and chromium contents. Their resemblance to tholeiitic magma-type suggests their formation in a layered intrusive setting, evolved through multiple fractional crystallization under oxidizing conditions. Thermometric and fugacity calculations using different textural associations estimate the magmatic fractional crystallization stage at elevated temperatures (601–704 °C) and low fO2 (−18.6 to −15.3), succeeded by the exsolution stage during subsolidus cooling at lower temperatures (379–540 °C) and high fO2 (−38.2 to −22.1). The whole sequence of formation and evolution of lodestone encompasses primary magmatic crystallization, subsolidus re-equilibration, metamorphism, and secondary weathering. The study also suggests a genetic linkage of lodestone with the associated mafic-ultramafic units, depicting two possible magmatic processes either through slab melting and fractional crystallization associated with subduction or due to plume magmatism and associated rifting.

Geochemical biosignature formation in experimental Martian fluvio‐lacustrine and simulated evaporitic settings

AbstractTo assess whether life existed on Mars, it is crucial to identify geochemical biosignatures that are relevant to specific Martian environments. In this paper, thermochemical modeling was used to investigate fluid chemistries and secondary minerals that would have evolved biotically over geological time scales in Martian fluvio‐lacustrine and evaporitic settings, and that could be used as potential inorganic biosignatures for life detection on Mars. Modeling was performed using fluid and rock chemistries relevant to Gale crater aqueous environments. Potential inorganic biosignatures were identified investigating alteration deposits found at the surface of a simulant exposed to short‐term bio‐mediated weathering and comparing experimental and modeling results. In a fluvio‐lacustrine setting (water/rock of 2000–278), models suggest that less complex mineral assemblages form during biotic basalt dissolution and subsequent brine evaporation compared to what would happen in an abiotic system. Mainly nontronite, kaolinite, and quartz form under biotic conditions, whereas celadonite, talc, and goethite would also precipitate abiotically. Quartz, sepiolite, and gypsum would precipitate from the evaporation of fluids evolved biotically, whereas nontronite, talc, zeolite, and gypsum would form in an abiotic evaporitic environment. These results could be used to distinguish products of abiotic and biotic processes, aiding the interpretation of data from Mars exploration missions.

Magma storage conditions over the past 4 Ma on Martinique Island, Lesser Antilles

We constrain, for the first time, the storage conditions beneath recent (<5 Ma) volcanic edifices in Martinique Island, combining petrography, geochemistry, and thermobarometry. Specifically, we investigate Morne Jacob volcano (5.2–1.5 Ma), Pitons du Carbet complex (998 ka – 322 ka), Trois Îlets Volcanic field (2.35 Ma – 346 ka), and Mt. Conil – Mt. Pelée system (<550 ka). Lava samples range in composition from basalt to dacite, and in age from 4.1 Ma (Morne Jacob) to 1929 CE (Mount Pelée). For the last ∼5 Ma, the volcanoes in Martinique were fed by andesitic to dacitic magma stored in the upper 6 km of the crust, at temperatures between 900 and 1100 °C. These shallow reservoirs were frequently replenished and remobilized by basaltic and basaltic-andesite magmas originating from the lower crust with temperatures as high as 1200 °C. Erupted products contain simple to more complex mineral assemblages, and plagioclase phenocrysts exhibit textures and compositional profiles typical of antecrysts, identified as (1) normal, (2) oscillatory, (3) sieved, (4) resorbed core, and (5) resorbed rim. All complexes also show a crystallization gap in the middle crust (10–18 km). Trois Îlets, a distributed volcanic field, is the only complex that shows continuous crystallization through the entire crust, distinct magma batches and storage regions for each individual volcano. More importantly, we see drastic changes in terms of rock composition, storage conditions, and crystal populations in pre - and post – collapse lavas. Large flank collapse (> 5 km3) can induce decompression as large as 5 MPa in the upper crust and as low as 0.1 MPa down to 10–12 km. Such decompression magnitudes might be sufficient to enhance ascent of basaltic magma from depth, initiate dike intrusions in the mid to upper crust, and remobilize shallow silicic reservoirs. Such events are likely to initiate magma mixing in shallow reservoirs. This noteworthy eruption-triggering mechanism may lead to the incorporation of distinct crystal populations and subsequently contribute to heightened rates of eruption. In summary, the magma storage conditions and plumbing system architecture for the recent volcanoes in Martinique closely resemble those observed in other volcanoes within the Lesser Antilles Island Arc, such as Soufriere Hills Volcano or La Soufriere de Guadeloupe. These newly established correlations offer valuable insights that can aid in the assessment of potential future volcanic eruptions.

Composite Collectors for the Flotation of Refractory Alkaline Rock-Type Rare-Earth Ores

Alkaline rock-type rare-earth (RE) ores have significant utilisation value. However, the exploitation of such resources faces great challenges owing to the complex mineral and element assemblages. Composite collectors exhibit excellent performances, which may provide solutions to the flotation problem of alkaline rock-type RE ores. Therefore, 16 collectors typically used in RE ores flotation were selected. Flotation tests were performed to identify collectors with high selectivity and collection ability for RE minerals, then nine composite collectors were prepared by combining the satisfactory collectors. The flotation performances of single and composite collectors for RE minerals were examined, and the composite collector FA301 with different carbon chain lengths was identified as the best one. When FA301 was applied in optimal conditions of slurry temperature, grinding size, collector and inhibitor dosage, RE concentrate yield of 6.29%, REO grade of 32.013%, and recovery of 59.02% were achieved. According to the results of the zeta potential, FTIR, and XPS test, the functional groups (dominated by carboxyl groups) in FA301 chemically adsorbed onto the main active sites (La, Ce, Y, etc.) on the surface of RE minerals. The findings can provide scientific basis for the development of efficient collectors to facilitate the exploitation of RE resources.

Impact of deformation and metamorphism on sphalerite chemistry – Element mapping of sphalerite in carbonate-hosted Zn-Pb sulfide deposits of the Kootenay Arc, southern British Columbia, Canada and northeastern Washington, USA

Sphalerites from the Kootenay Arc in British Columbia and Washington State were selected to represent three types of carbonate-hosted massive sulfide deposits, including Mississippi Valley-type (MVT), Irish-type, and fracture-controlled replacement type (FCR). These deposits were variably deformed and metamorphosed during the Cordilleran orogen. Laser ablation inductively coupled plasma mass spectrometric (LA-ICP-MS) analyses of the trace element distributions within the sphalerites are combined with petrography and sulfur isotope analyses to evaluate the influence of primary trace element signatures, along with the variable influence of post-ore metamorphism and deformation on sulfide remobilization and trace element redistribution.Mississippi Valley-type (Josephine orebodies) and Irish-type (Yellowhead orebodies) at Pend Oreille mine are only weakly deformed and recrystallized, so their sulfide minerals commonly retain primary ore textures. The sphalerite from the Irish-type deposit has positive narrow range of δ34S values (17.9–20.5‰, mean 19.2‰), and it is enriched in Ge, Tl and Pb, but depleted in Cd, Mn, and Cu relative to MVT and FCR deposits. Germanium is concentrated in dark-brown acicular-colloform bands where micro-inclusions of a germanium oxide mineral (argutite (GeO2)) and galena have been detected. Other MVT deposits of the Kootenay Arc (Reeves MacDonald, Jersey-Emerald, HB, Jackpot-Lerwick, Duncan) are more deformed and metamorphosed than the Irish-type deposit of the Pend Oreille mine and primary ore textures are only locally preserved. There is a progressive increase in deformation and degree of recrystallization from Reeves MacDonald, located away from intrusions, to deposits within the contact metamorphic aureoles of intrusions (HB, Jersey-Emerald, Jackpot-Lerwick). Sphalerite from the least metamorphosed Reeves MacDonald deposit has high Cd, Ga, Pb, and Tl contents, high Cd/Ge and Ga/In values, and the lowest δ34S values (7.4 to 11.1‰, mean 8.8‰). In contrast, sphalerites from contact metamorphosed HB, Jersey-Emerald and Jackpot-Lerwick deposits have higher δ34S values (13.3 to 28.5‰, mean 19.2‰), are enriched in Mn and Fe, with higher Zn/Cd and Mn/Fe values relative to Reeves MacDonald deposit. These enrichments and fractionations correspond to the breakdown of pyrite and pyrrhotite and the thermal annealing of sphalerite caused by contact metamorphism. Sulfide minerals from the FCR deposit (Abbott-Wagner) are undeformed (except for microfractures) and only weakly recrystallized. Sphalerite from the FCR Abbott-Wagner deposit is enriched in Cu, Ga, In, and Sn as primary source signatures relative to sphalerite from MVT and Irish-type deposits. This reflects the more complex mineral assemblage of galena, sphalerite, pyrite, chalcopyrite, and tetrahedrite in this deposit. The presence of chalcopyrite and tetrahedrite is consistent with a higher-temperature origin of the FCR deposit relative to the lower-temperature MVT and Irish-type deposits.This study demonstrates that the high spatial resolution of in-situ LA-ICP-MS analyses of trace element within sphalerites, in combination with petrography and other analytical techniques (e.g., electron microprobe, secondary ion mass spectrometry, field emission scanning electron microscopy) characterizes the behavior and distribution of trace elements in sphalerite for three deposit types and variable conditions of regional and contact metamorphism. Understanding the effects of metamorphism and deformation on trace elements can be very useful in exploration for deposits rich in critical metals.

An Unusually Warm Upper‐Crust in the Late Paleozoic North China Continental Arc: Implications for the Thermal Modification of the Giant Bayan Obo REE Deposit

AbstractThe genesis and timing of formation of the giant Bayan Obo deposit, the world's largest rare earth element (REE) deposit in the western part of the late Paleozoic northern North China continental arc (NCA), are highly controversial due to complex mineral assemblages and reported ages of mineralization. We conducted new zircon U‐Pb and40Ar/39Ar dating of metamorphic and igneous Neoarchean to Permian mid‐to upper‐crustal rocks exhumed along a north−south corridor across the western NCA and its retroarc foreland. The results show that the mid‐ to upper‐crust of the western part of the NCA has been strongly affected by thermal modifications during arc construction in the late Paleozoic, while the retroarc foreland remained thermally stable. Our results first reveal an unusually warm upper‐crust around Bayan Obo during the late Paleozoic with high geothermal gradients of 50.0 ± 8.3 to 88.3 ± 8.3°C/km and strong thermal modification of the upper‐crust during arc construction. This unusually warm upper‐crust and high geothermal gradients resulted in intensive thermal perturbations and recrystallization of REE‐bearing minerals in the Bayan Obo deposit, as well as formation of high‐grade REE ores and complete or partial resetting (U‐)Th‐Pb isotopic systems of REE minerals. Our identification of the unusually warm upper‐crust and high geothermal gradients in the western part of the NCA provides important constraints on genesis, timing and thermal modification of the giant Bayan Obo deposit, as well as other REE deposits with complex isotopic ages.

The ephemeral fumarolic mineralization of the 2021 Tajogaite volcanic eruption (La Palma, Canary Islands, Spain)

The present work aims to characterize the ephemeral mineral assemblage related to the fumarolic fields of the Tajogaite volcano, formed in 2021 in La Palma Island (Canary Islands, Spain). A set of 73 samples was obtained after two sampling campaigns in different fumarole sectors of the studied area. Mineralization related to these fumaroles formed efflorescent patches located at variable distance from the main volcanic craters. Distal patches are predominantly whitish, while in the vicinities they typically show yellowish to orange colours. Field observations also revealed that fumaroles usually occur in elevated topographic areas as well as over fractured and porous volcanic pyroclastic materials. The mineralogical and textural characterisation of the Tajogaite fumaroles unfolds a complex mineral assemblage, comprising cryptocrystalline phases related to low (< 200 °C) and medium temperature (200–400 °C) conditions. In Tajogaite, we propose a classification of three different fumarolic mineralization types: (1) fluorides and chlorides located in proximal fumarolic areas (~ 300–180 °C); (2) native sulphur associated with gypsum, mascagnite and salammoniac (~ 120–100 °C) and (3) sulphates and alkaline carbonates typically occurred in distal fumarolic areas (< 100 °C). Finally, we present a schematic model of the formation of Tajogaite fumarolic mineralization and their compositional evolution developed during the cooling of the volcanic system.

Fate and Transport of Pharmaceuticals in Iron and Manganese Binary Oxide Coated Sand Columns.

Predicting the fate and transport of pharmaceuticals in terrestrial environments requires knowledge of their interactions with complex mineral assemblages. To advance knowledge along this front, we examined the reactivity of pipemidic acid (PIP), a typical quinolone antibiotic, with quartz particles coated with a mixture of manganese oxide (MnO2) and goethite (α-FeOOH) under static and dynamic flow conditions. Batch and dynamic column experiments showed that PIP binding to MnO2 proceeded through a heterogeneous redox reaction, while binding to goethite was not redox-reactive. Mixed columns of aggregated goethite-manganese particles however enhanced redox reactivity because (i) goethite facilitated the transport of dissolved Mn(II) ion and increased the retention of PIP oxidation products, and (ii) MnO2 was protected from passivation. This mobility behavior was predicted using transport models accounting for adsorption and transformation kinetics of PIP on both goethite and MnO2. This work sheds new light on reactivity changes of mixtures of Fe and Mn oxides under flow-through conditions and will have important implications in predicting the fate and transport of redox-active organic compounds as well as development of new geomedia filters for environmental remediation.

Geochemical bio-signatures in Martian analogue basaltic environments using laboratory experiments and thermochemical modelling

The identification of geochemical bio-signatures is important for assessing whether life existed on early Mars. In this paper, experimental microbiology and thermochemical modelling were combined to identify potential inorganic bio-signatures for life detection on early Mars. An analogue mixed microbial community from an analogue terrestrial fluvio-lacustrine environment similar to an ancient lacustrine system at Gale Crater was used to study microbial dissolution of a basalt regolith simulant and the formation of bio-signatures over a short time frame (1°month) at 14°C, 2 bar. Microbial growth influenced element dissolution (Mg, Fe, Mn, Ca and K) and the formation of morphologies and Fe-Si amorphous layers on mineral surfaces. Thermochemical models were performed at 14°C, 2 bar; the results were compared with experimental data to predict bio-signatures that would occur over geological timescales. The pH was varied to simulate abiotic and biotic experimental conditions. Model results suggest that, at water to rock ratios of 100 to 38, a less complex secondary mineral assemblage forms during biotic dissolution compared to abiotic weathering. Carbonates, quartz, pyrite and hydroxyapatite form under biotic conditions, whereas in the abiotic system magnetite and phyllosilicates would also precipitate. These results could be used to distinguish between abiotic and biotic basalt weathering processes, aiding the interpretation of data from Mars exploration missions.

Emission and transformation behaviors of trace elements during combustion of Cd-rich coals from coal combustion related endemic fluorosis areas of Southwest, China

Long-term combustion of low-quality coal may release hazardous elements into the environment causing serious environmental problems. This phenomenon is particularly prevalent in the Three Gorges Region of Southwest (SW), China. Cadmium (Cd), as well as other harmful elements are found to be highly enriched in coals and supergene environments in this area. In the existing literature, the behavioral issue of emission and transformation of the elevated trace elements during simulated household stove combustion from Cd-rich inferior coal remains unknown. This study investigated the emission of toxic elements, mineral assemblages, and provided technical guidance for reducing pollution by means of optimization combustion tests on inferior coals. The research may improve the understanding of geochemical characteristics from toxic elements emission in coal combustion endemic diseased areas. For this purpose, a series of simulated coal combustion experiments were conducted to reveal the release, mobility, and distribution of elevated elements in Cd-rich coal combustion products. The results showed that Cd, Mo, Cr, Cu, Zn, As, and Sb were significantly enriched in the inferior coals of the study area. Furthermore, large amounts of toxic elements were released as fly ash into the environment during the combustion process. In particular, combustion conditions played an important role in the emission and transformation of elevated elements. For example, higher temperatures promoted the release of Cd, Sb, Zn, and Tl into the environment. Oxygen-deficient combustion was found to liberate more Cd, Sb, and Tl to the atmosphere and generated complex mineral assemblages of lizardite, calcite, dolomite, forsterite, and enstatite. Moreover, toxic elements were found to be absorbed in the fine particle matter of fly ash from the endemic fluorosis area of SW, China. The findings of this work may aid to control the emission of toxic elements from inferior coals and mitigate the effect of toxic elements in the environment to protect human health.

The Extraordinary Variety and Complexity of Minerals in a Single Keokuk Geode from the Lower Warsaw Formation, Hamilton, Illinois, USA

We performed an extensive optical and chemical analysis of a single Keokuk geode using electron microscopy (SEM) with energy dispersive X-ray (EDX) spectroscopy that revealed an extraordinary array of minerals and multiple, complex cycles of mineralization. We identified at least 15 minerals including 5 that, to our knowledge, have not been reported in previous studies of these geodes. Along with bitumen we have described the occurrence of REE’s, and other unidentified phases containing metals such as chromium, nickel, molybdenum, tin, copper, zinc, and lead. Additionally, preliminary thin-section analysis reveals the occurrence of the tentatively identified minerals zircon, rutile, and xenotime as well as grains containing gold and silver within the chalcedony shell. The presence of these potentially economically valuable minerals warrants further investigation into the micro-minerology of Keokuk geodes. Our SEM/EDX analysis reveals an array of complex mineral assemblages, intergrowths, and inclusions that help chronologically link multiple stages of paragenesis occurring in different locations within the geode. Consequently, morphology and intricate microstructures provide a window into the extreme complexity of mineral crystallization. The majority of micro-minerals we have observed correspond with the later stages of geode paragenesis, thus providing a detailed record of the secondary mineralization processes which occurred over thousands to millions of years.

Origin of metasomatic fluids in the Bayan Obo rare-earth-element deposit

The Bayan Obo REE–Fe–Nb deposit is the largest light rare earth element (REE) deposit in the world, and it has undergone serious hydrothermal reworking processes. However, the origin and nature of metasomatic fluids in this deposit remain controversial. To determine the origin of metasomatic fluids, we conducted a detailed mineralogical and geochemical investigation on the apatite from the ∼ 1.8-km drill core in the Bayan Obo deposit. The textural and geochemical variations of the apatite could trace the hydrothermal metasomatism during REE mineralization. Four types of apatites were identified according to their cathodoluminescence characteristics, including turbid euhedral apatite (Ap-0), rounded pinkish–violet apatite veinlets (Ap-1), yellowish–green apatite aggregates (Ap-2), and apatite with a pinkish–violet core and a yellowish–green rim (Ap-3). According to the in-situ Sr isotopic compositions, these apatites were classified into two groups. Ap-0, Ap-1, and Ap-2 display constant and low 87Sr/86Sr ratios (0.7030–0.7035), whereas Ap-3 displays various Sr isotopic compositions (0.7047–0.7105). The in-situ Th–Pb age of the bastnäsite associated with the Ap-0 ranges from 390 to 425 Ma. The Sr isotopic compositions and geochronological study indicate that metasomatic fluids in the Bayan Obo deposit were obtained from different sources, including the Silurian Bainaimiao arc plutons and sedimentary materials. The four apatite types display various REE distribution patterns, which could account for hydrothermal fluid properties. F-rich and Na-poor fluids metasomatized the precursor Ap-0, releasing REEs from apatites and resulting in low REE contents of Ap-0. Ap-1 and Ap-2 were derived from the same fluid but were characterized by different trace element compositions, which could be attributed to the evolution of hydrothermal fluids with changes in the Na content and F/Cl ratio. The primary Ap-3 was derived from a REE-rich source and was altered by Na-poor and Cl-rich fluids. Metasomatic fluids with different origins and variable chemical compositions result in complex mineral assemblages and geochemical features in the Bayan Obo deposit.

Accurate hyperspectral imaging of mineralised outcrops: An example from lithium-bearing pegmatites at Uis, Namibia

Efficient, socially acceptable and rapid methods of exploration are required to discover new deposits and enable the green energy transition. Sustainable exploration requires a combination of innovative thinking and new technologies. Hyperspectral imaging (HSI) is a rapidly developing technology and allows for fast and systematic mineral mapping, facilitating exploration of the Earth's surface at various scales on a variety of platforms. Newly available sensors allow data capture over a wide spectral range, and provide information about the abundance and spatial location of ore and pathfinder minerals in drill-core, hand samples and outcrops with mm to cm precision. Conversely, the complex geometries of the imaged surfaces affect the spectral quality and signal-to-noise ratio (SnR) of HSI data at these very narrow spatial samplings. Additionally, the complex mineral assemblages found in hydrothermally altered ore deposits can make interpretation of spectral results a challenge. In this contribution, we propose an innovative approach that integrates multiple sensors and scales of data acquisition to help disentangle complex mineralogy associated with lithium and tin mineralisation in the Uis pegmatite complex, Namibia. We train this method using hand samples and finally produce a three-dimensional (3D) point cloud for mapping lithium mineralisation in the open pit. We were able to identify and map lithium-bearing cookeite and montebrasite at outcrop scale. The accuracy of the approach was validated by drill-core data, XRD analysis and LIBS measurements. This approach facilitates efficient mapping of complex terrains, as well as important monitoring and optimisation of ore extraction. Our method can easily be adapted to other minerals relevant to the mining industry.

Burbankite and pseudomorphs from the Main Intrusion calcite carbonatite, Lofdal, Namibia: association, mineral composition, Raman spectroscopy

AbstractThe Neoproterozoic Lofdal alkaline carbonatite complex consists of a swarm of carbonatite dykes and two plugs of calcite carbonatite known as the ‘Main’ and ‘Emanya’ carbonatite intrusions, with associated dykes and plugs of phonolite, syenite, rare gabbro, anorthosite and quartz-feldspar porphyry. In the unaltered Main Intrusion calcite carbonatite the principal rare-earth host is burbankite. As burbankite typically forms in a magmatic environment, close to the carbohydrothermal transition, this has considerable petrogenetic significance. Compositional and textural features of Lofdal calcite carbonatites indicate that burbankite formed syngenetically with the host calcite at the magmatic stage of carbonatite evolution. The early crystallisation of burbankite provides evidence that the carbonatitic magma was enriched in Na, Sr, Ba and light rare earth elements. In common with other carbonatites, the Lofdal burbankite was variably affected by alteration to produce a complex secondary mineral assemblage. Different stages of burbankite alteration are observed, from completely fresh blebs and hexagonal crystals through to complete pseudomorphs, consisting of carbocernaite, ancylite, cordylite, strontianite, celestine, parisite and baryte. Although most research and exploration at Lofdal has focused on xenotime-bearing carbonatite dykes and wall-rock alteration, this complex also contains a more typical calcite carbonatite enriched in light rare earth elements and their alteration products.

Study on Corrosion Mechanism of Different Concentrations of Na2SO4 Solution on Early-Age Cast-In-Situ Concrete.

The deterioration of early-age concrete performance caused by SO42− internal diffusion in concrete is a critical factor of concrete durability. In this study, the mechanical properties, heat of hydration, and pore structure of early-age cast-in-situ concrete with different sodium sulfate (Na2SO4) concentrations were studied. The mechanism of SO42− internal corrosion was evaluated by measuring the dynamic elastic modulus, compressive strength, and heat of hydration rate. Scanning electron microscopy, energy dispersive spectroscopy, X-ray computed tomography, X-ray diffraction, thermogravimetry-derivative thermogravimetry, and differential scanning calorimetry were applied to analyze microstructural variations and complex mineral assemblages of concrete samples. The results indicated that during the hardening process of cast-in-situ concrete, Na2SO4 first promoted and then hindered the hydration rate of cement, and also hindered the early strength development of the cement. As the concentration of Na2SO4 solution increases, the corrosion products of ettringite (AFt) and gypsum (Gyp) gradually increase, causing cross cracks in the concrete. The proportion of small and medium pores first increases and then decreases, and the large pores first decrease and then increase. The mechanical properties of concrete gradually decrease and diminish the mechanical properties of the concrete (thereby accelerating the damage to the concrete).

High spatial resolution Raman mapping of complex mineral assemblages: Application on phosphate mineral sequences in pegmatites

AbstractPhosphates are a group of complex minerals widespread on Earth that can crystallize in several environments. Changes in environmental conditions during crystallization are reflected in the formation of a sequence of phosphate minerals, termed paragenesis. Accordingly, analyses of textural and chemical properties of complex mineral assemblages are essential to reconstruct the history of rocks and solid materials. Raman mapping can detect those mineralogical changes in complex assemblages with high spatial resolution, successfully determining the paragenetic sequence. Specifically, Raman spectroscopy is more advantageous than conventional methods because it requires little sample preparation, it is nondestructive, and it is capable of identifying hydrated minerals and phases composed of light elements (e.g., H and Li). In this study, the parageneses of two phosphatic assemblages from the Buranga pegmatite, a P–Li–Nb–Ta‐rich magmatic rock, are reported in detail. The first case shows the replacement of primary F‐rich montebrasite [LiAl(PO4)(OH,F)] by secondary F‐poor montebrasite [LiAl(PO4)OH]. Mapping of the OH‐stretching peak position and width identifies the mineral phases, illustrates their spatial relations, and allows to estimate the F content distribution. The second case investigates a sequence of phosphate minerals in a complex assemblage (trolleite + rosemaryite ➔ lazulite–scorzalite ➔ samuelsonite ➔ wardite). The application of multivariate analysis methods to characterize complex assemblages is assessed, and the classical least squares method is identified as the best suited for this setting. An analysis of Raman images shows that Buranga samples experienced a progressive hydration process during cooling, followed by fluid‐assisted mineral reactions with remobilization of elements, such as Ca and Na.

The occurrence of Hg, Se, S, Ni, Cr, and Th in Talc Ore: A scanning electron microscopy (SEM) study of historical samples from the Willow Creek Mine, Montana

Due to short timeframes over which small-scale talc mines operate (approximately 1 to 10 years), detailed characterization of their mineralogy and geochemistry in the peer-reviewed literature is limited. Investigation of sample 1497 of the Willow Creek Mine, Montana by scanning electron microscopy using back scatter detection (SEM-BSD) indicates a complex minor mineral assemblage. Hg-Se-S minerals are associated with graphite whereas Zn-Cr-Ni minerals and Th minerals are dispersed in the talc matrix. Notably, Hg, Se, Zn, Cr, and Ni are of human health concern. Minerals with these elements are ~ 20 to 0.4 µm in diameter, and all have examples in the PM10 or PM2.5 size fraction. These minerals would likely not be separated out during processing of talc ore and would be inhalable. Results indicate a need for detailed SEM-BSD investigations of historic talc products from the Willow Creek Mine and for investigating ore from similar settings in Montana.

From Ore Body to High Temperature Processing of Complex Ores: Manganese—A South African Perspective

Manganese is considered a relatively rare metal as concentrations of it in ore of commercial importance are geographically limited. In nature, manganese is found in the form of oxides, carbonates, and silicates. Manganese ores are complex in the sense that they not only consist of a complex oxide mineral assemblage but these minerals are also very finely inter-grown. South Africa accounts for 74% of the world’s identified manganese resources and 32% of the world’s reserves. The paper presented here describes in more detail the resource and the complex mineralogy of the ore body, as well as the existing and potentially new processing technologies available from minerals processing and pyrometallurgical perspectives.