The Chilpi Group (2050–1850 Ma) in the Bastar Craton contains Banded Iron Formation (BIF) deposited immediately after the Great Oxidation Event but before the “Proterozoic iron ore gap”. Baseline geochemical data generated from this crucial period of Earth's history representing the transition from an initial high productivity period followed by productivity collapse, thereby delaying the evolution of biota, are interpreted in terms of the redox state of the ocean and atmospheric oxygen content. Presence of chamosite, greenalite and siderite in the ironstones of the Chilpi Group, identified during present analysis, provide valuable information regarding the redox state of the shallow sea. Geochemical analyses reveal high concentrations of Fe2O3total and SiO2 (average ~ 87.85 wt%) in iron-rich bands. Trace elements commonly enriched in detrital phases (e.g. Sc, Hf, Nb, Th and Zr) show good correlation with total REE concentration, but these have concentration below the cut-off limit defined for detrital sediments (except 3 samples). Higher concentration of these elements in greenalite/chamosite-rich samples indicates accumulation of these elements in greenalite/chamosite during primary precipitation. Most of the samples have low concentrations of Al2O3 (<5 wt%) and TiO2 (<0.5 wt%), but some chamosite-bearing samples show enrichments of Al2O3 (up to ~20 wt%). Post-Archean Australian Shale normalised rare earth elements with Y (REEY) patterns, showing a superchondritic Y/Ho ratio (average 32.15) and positive La, Gd and Y anomalies, indicate the preservation of seawater like signatures. Though a low positive Eu-anomaly, and Al/(Al + Fe + Mn) versus Fe/Ti plot suggest seawater signature with possible mixing of hydrothermal fluids and/or <10 % detrital components, preservation of seawater signatures and no involvement of high-temperature hydrothermal fluids are deduced from Eu/Sm versus Sm/Yb and Eu/Sm versus Y/Ho patterns. The Eu/Sm and Y/Ho ratios lower than the seawater and a mixing trend away from oceanic hydrothermal solution indicate possible mixing of freshwater with seawater for the observed REEY patterns. Redox-sensitive trace element ratios indicate a dysoxic to suboxic-anoxic condition in the depositional basin. Presence of oolitic textures and occurrence of chamosite support the shallow water (<60 m water depth) and anoxic condition in the depositional basin. The oxygen content of 10−3–10−5 times the present atmospheric level in the atmosphere is inferred for the period during the deposition of the BIF.

To interpret the leaching rules, select suitable treatment methods, or optimize the treatment process of refractory gold ores, an in-depth analysis of ore characteristics using ore mineralogy is required. In this study, the mineralogical characteristics of a low-grade refractory gold ore were analyzed by a variety of analytical techniques and methods. The ore composition was obtained by chemical analysis, and the main minerals include gold, pyrite, arsenopyrite, feldspar, mica, and quartz. Gold exists in the form of sub-microscopic gold with a particle size of fewer than 1.7 μm, of which 56.90 % is encapsulated gold, 16.97 % is semi-coated gold, and 26.13 % is fractured gold. The content, classification, shape, grain distribution, and occurrence state of the main minerals in the gold ore were obtained by microscopic observation and statistical analysis. Based on the results, the leaching rules of the gold ore were predicted, and suggestions for optimizing the pretreatment process were put forward. These results can accurately guide the pretreatment and leaching process of the gold ore and lay a foundation for the effective utilization of comparable gold ores.

Discharge of acid mine drainage (AMD) along with heavy metals mobilization is a critical environmental concern. An urgent need is to manage or treat AMD in the minefield effectively. To this end, based on a hydrogeological investigation, the d-T (deuterium excess parameter-Tritium content) technique was adopted to trace the recharge, runoff, and discharge of AMD in the abandoned Dashu pyrite mine in China. The results reveal that AMD in the minefield originates from local precipitation and shallow groundwater and exhibits apparent seasonal runoff variations. The AMD is associated with shallow groundwater from the top of the Quaternary platform on the axis of the Dashu anticline, and protons could originate from the pyrite oxidation. Therefore, an engineering practice to purify the AMD is combined with (1) water diversion to stop AMD formation and blockage of the AMD outlets. (2) Acceleration of Fe(II) oxidation through aeration promotes the precipitation of Fe-oxide and hydroxide. (3) Neutralization of AMD using Karst water from the Maokou Formation (P2m). This study provides a new research idea and tracing method for improving hydrogeological surveys and effectively handling environmental problems related to AMD of abandoned mines.

The present study highlights the first evidence of hydrothermal mineral Thenardite (Na2SO4) from Puga geothermal area, North-western Himalayan belt in Ladakh Geothermal Province, India, which is unequivocal evidence for the presence of high-temperature hydrothermal fluid activity from one of the thickest crust areas of the Earth. The Puga geothermal belt illustrates a fault-bounded hydrothermal system with a clearly defined conductive zone, coinciding with Kiagar Tso fault typically exemplifying a shallow-level medium enthalpic geothermal reservoir. The hydrogeochemistry suggests that thermal and non-thermal waters are of Na-Cl-HCO3 and Ca-Mg-HCO3 type, respectively, with neutral to near alkaline pH. The silica and cation geothermometry reveal sub-surface temperatures around 150 °C and 250 °C, respectively, at shallow depth; however, >250 °C is anticipated at the deepest levels (~3 km). Stable isotope (δD and δ18O) studies explicate depletion of isotopic content for thermal waters over Puga river water and radiogenic isotope (3H) suggests matured thermal waters with ongoing water-rock interactions. The recharge altitude estimation and physiographic studies put forth that geothermal reservoir is recharged with the ice masses located at an altitude of 6458 m above mean sea level (msl) in the west of Puga valley, probably from the highest peak of Polokong La mountain. The two key processes participating in regulation of proportions of the dissolved salts in the thermal waters are silicate weathering and ion-exchange kinetics. The powder X-ray diffraction study reveals a major occurrence of hydrothermal mineral thenardite in the hot spring deposits for the first time along with huge encrustations of trona, borax, calcite and elemental sulfur. The high-temperature fluids encounter thenardite, pyrite, and jarosite-bearing minerals in basement rock causing enrichment of SO42− and Cl− in geothermal waters. The temperature-dependent speciation modelling (50 °C–200 °C) for major ion Na+ reveals the composition of the reservoir fluid (~150 °C): Na+ > NaCO3− > NaSO4− > NaHCO3 > NaF > NaOH. A conceptual evolution model of thermal waters involving the recharge-deep circulation-mixing-discharge of thermal springs is hence put forth in the study using various hydrogeochemical insights.

The Iju Cu porphyry is located in the NW part of the Kerman Magmatic Copper Belt (KMCB). It is related to a ~ 9 Ma granodiorite porphyry intrusion, with three main stages of hydrothermal activity. The homogenization temperatures for the fluid inclusions are in the ranges of 200–494 °C, and their salinities vary from 4.0 to 42.8 wt% NaCl equiv., which are typical magmatic-hydrothermal fluids. The δ34S values of sulfides range from −0.4 to +3.2 ‰ (V-CDT), and the δ34S values of anhydrite samples range from +11.6 to +16.8 ‰. The δ34S values of sulfides show a narrow range, implying a homogeneous sulfur source. The oxygen isotopic composition of hydrothermal water in equilibrium with quartz samples ranges from +3.4 to +6.0 ‰ (V-SMOW) consistent with the hydrothermal fluids having a magmatic signature, but diluted with meteoric waters in the main mineralizing stage. The most important factors responsible for metal precipitation in the Iju porphyry deposit are fluid boiling, oxygen fugacity decrease and cooling followed by dilution with meteoric water. The primary fluids of the Iju Cu deposit are characterized by relatively high temperature and moderate salinity, and are CO2-rich, indicating a typical post-collisional porphyry system.

Magmatic sulfide liquids are effective at concentrating a range of metals. Within magmatic sulfide systems pentlandite, an exsolution product of monosulfide solid solution (MSS), is the primary host of Ni, Co and significant concentrations of Pd. Over the last decade, LA-ICP-MS mapping has revealed non-uniform metal distributions and complexity to the metal patterns such as zonation and the linear alignment of elements. Whereas the compatibility and partitioning behavior of chalcophile elements during sulfide fractionation are well constrained, there is little knowledge on the crystallographic control exerted on metal distributions.In this study, LA-ICP-MS mapping of globular sulfides from the Crystal Lake Intrusion, Ontario (Canada), is complimented by EBSD analysis, revealing a strong crystallographic control on both the concentration of metals and pentlandite exsolutions. Elements considered incompatible in the high temperature monosulfide solid solution (MSS) phase (e.g., Cr, V, As, Pb, Ag, Bi and Pd) are preserved as a microfabric, showing preferential concentration in association with the (0001) basal plane of pyrrhotite and adjacent pentlandite. Where the [0001] axis is viewed perpendicular to the cut surface, the microfabric is considered to be an intersection lineation between the basal (0001) plane and the surface of the cut section.Pentlandite textures described in magmatic sulfide deposits include granular, fan and laths/blades. Our observations indicate that marginal pentlandite exsolutions, are in optical continuity with granular exsolutions, providing insights into the growth of pentlandite at MSS grain boundaries. We conclude that all pentlandite forms are crystallographically controlled by the hexagonal mineral system of MSS/pyrrhotite, with the [0001] c-axis of pyrrhotite corresponding to the 〈111〉 axis of pentlandite. This axis also acts as a twinning rotation axis for the two identified pentlandite orientations. Fan and lath textured exsolutions are considered geometrically equivalent structures, being reconstructed as flat disc–shapes developed parallel to the basal (0001) plane of pyrrhotite, which acts as a preferred nucleation site. A network of low-angle grain boundaries are recognized as hexagonal or rectangular structures within pyrrhotite, with the morphology shown to be dependent on the orientation of the crystals. As these features are again geometric equivalents, they can be reconstructed as intragrain hexagonal prisms. We speculate due to their localized development, that they could represent a plastic response of the pyrrhotite to accommodate the increase in volume suggested to be associated with late pentlandite exsolutions and thus are the result of static lattice recovery.The microstructural and trace element observations presented here provide new context to some of the common textural features of magmatic sulfide deposits, while importantly highlighting the strong crystallographic control on both metal distributions and sulfide textures. This study also importantly recognizes the dominance of hexagonal pyrrhotite within the ores of the Crystal Lake Intrusion and likely other magmatic sulfide deposits. This has implications for mineral processing as its non-magnetic properties can result in dilution of Ni-Cu-PGE ores and thus requires special attention for the flotation strategy.

Geochemical survey data play a critical role in geological studies, mineral exploration, and environmental applications by providing information on geological events and processes such as mineralization and pollution. A typical geochemical survey dataset contains the analysis of multiple elements. For example, the national geochemical mapping project of China comprises 39 major and trace element concentrations. Multiple geochemical maps can be generated by interpolating geochemical samples into raster maps to constitute a geochemical survey data cube in which elements are sorted by their atomic numbers. A geochemical spectrum can be created using these geochemical maps in which each pixel that records geochemical characteristics. In this study, a convolutional neural network (CNN) that considers the geochemical spectrum and spatial pattern of geological objects was employed to mine a geochemical survey data cube, aiming of geological mapping and geochemical anomalies identification associated with mineralization in the eastern part of Hubei Province of China. The results showed that (1) a geochemical survey data cube which built based on various geochemical exploration data provided vital information on mineralization process and the formation of geological features; and (2) a CNN had a strong ability to recognize high-level features in the geochemical survey data cube, and it showed excellent performance in mineral exploration and related geological studies.

Nitrogen (N) stable isotope ratio (δ15N) in coal organic matter (OM) provides information on the N source and dominant mechanisms affecting isotopic fractionation during coalification. However, published data on δ15N distribution in coal is rare. The present study is one of the first reports on the δ15N composition of peat, lignite, sub-bituminous and anthracite coals in India and one of the first attempts to understand the processes influencing δ15N composition at different stages of coalification from peat to anthracite. Peats were collected from the western coast of North Andaman Island and Lake Loktak in Manipur. Plant samples were collected from the peat sampling locations. Cenozoic lignites were collected from Panandhro, Matanomadh, Umarsar and Tadkeshwar mines in Gujarat and Neyveli in Tamil Nadu. Cenozoic sub-bituminous and Permian anthracite coals were collected from Assam and Sikkim, respectively. Variation of δ15N in plants is attributed to the differences in rainfall, plant type and N sources. Lower δ15N values in peats (mean 1.19) compared to the plant samples (mean 2.77) indicate a nonlinear response of δ15N to the relative enrichment or loss of N during peat formation in Lake Loktak and decomposition of OM under anaerobic conditions leading to selective preservation of 14N in the Andaman Islands. The δ15N composition of the studied peat (−1.4–1.6), lignite (−1.4–1.8) and coals (−2.8–5.0) retains their OM source signature. Overall higher δ15N values of Cenozoic lignites compared to the Cenozoic sub-bituminous coal reflects regional differences in climate. Meanwhile higher δ15N (1.3–5.0) values in Gondwana anthracites reflects the tectonic influence of Himalayan orogeny.

The migmatites of Chandrapur area near Guwahati, which forms a part of the Assam-Meghalaya Gneissic Complex (AMGC) in Northeast India, have preserved magnetite ocelli. Petrographic observations have revealed that magnetite crystals occurring in the ocellar rock are surrounded by partial to complete thin rims of biotite. Moreover, mineral chemical analyses, backscattered electron images, and quantitative elemental mapping have revealed that magnetite crystals occurring in the ocellar rock have been extensively replaced by manganoan ilmenite at the periphery. From field observations, textural, and mineral chemical analyses, it has been inferred that invasion of hot, volatile-bearing pegmatitic magmas into thermally rejuvenated basement gneisses of the AMGC during the late Pan-African tectonothermal episode (ca. 530–450 Ma) induced very restricted partial melting in the gneissic rocks producing neosomes. The newly formed neosomes were then infiltrated by the nearby pegmatitic melts leading to mixing between the two melts. The mixing event facilitated transformation of magnetite to manganoan ilmenite owing to diffusion of elements like Mn and Ti from the neosome to the pegmatitic domains. Moreover, formation of ilmenite released surplus Fe hosted in the magnetite that combined with in situ K and Al, and diffusing Mg from the neosome to form biotite crystals around magnetite. From this study, it can be concluded that magnetite-manganoan ilmenite transformation may be considered as one of the petrogenetic indicators to decipher magma mixing events.

In China, the lack of Li resources is in stark contrast to a large amount of coal gangue produced by coal mining. To determine the distribution patterns and existing status of lithium (Li) elements in the coal gangue, the mineralogical and geochemical analysis were formed on samples of the roof, floor, and parting of No. 02, 2, 8, and 9 coal seams, being mined in Malan mine, Xishan coalfield, Shanxi Province. The results show that the lithium content in this study area is relatively enriched, the highest content is 499 μg/g in sample 02-G, and the average content is 109.8 μg/g, which is two times that of the world average value of claystone (45 μg/g). XRD analysis shows that the mineral composition of parting samples is mainly clay mineral kaolinite, while the coal seam roof and floor samples also include quartz and some iron-bearing minerals, such as pyrite and siderite. Likewise, possible lithium-rich mineral phases and possible lithium-rich factors were investigated in this paper. A comprehensive clay separation experiment and correlation analysis between lithium and major elements indicate that lithium is likely to exist in the clay mineral kaolinite in the study area. It is also found that the content of Li adsorbed by cryptocrystalline kaolinite is generally higher than that of crystalline kaolinite. According to the mechanism of Li+ adsorption in clay minerals, the higher lithium content of cryptocrystalline kaolinite is due to its larger specific surface area, which can adsorb more lithium on the surface.

The Zvishavane Ultramafic Complex (ZUC) in the south central part of the Zimbabwe craton is comprised of coarse-grained serpentinites, metadunites and metagabbros and hosts Africa's largest reserves, and largest mine, of high-grade chrysotile asbestos. Magnesiohornblende, actinolite, plagioclase (An0.6–41.9), augite, diopside and clinozoisite constitute the mineralogy of the ZUC. Forsteritic olivine (>Fo90) was altered to form chrysotile and antigorite minerals, although some primary olivines are preserved. Contents of Al2O3 range from 2.5 wt% at TiO2 values of <0.7 wt% consistent with an island arc setting for the ZUC that originated from tholeiitic magmas. The Zvishavane Ultramafic Complex was metamorphosed at relatively high temperatures (542-779 °C) and low pressures (1.2-2kbars), consistent with contact metamorphism. Intrusion of several granitic batholiths relatively close to the ZUC likely triggered hydrothermal fluid migration which metamorphosed the ZUC. The associated asbestos deposits likely formed during hydrothermal circulation events. Zoned amphiboles, the occurrence of magnesiohornblende and actinolite, as well as cross-cutting serpentine veins are consistent with at least two stages of alteration and/or metamorphism of the ZUC. The lack of a thrust contact between the ZUC and its country rocks is consistent with the ZUC having intruded into the host Zvishavane Gneiss Complex and possibly acted as a feeder to the nearby Mberengwa greenstone belt (MGB). However, the occurrence of near end-member forsteritic olivine, the presence of zoned amphiboles, and faulting within the ZUC are all suggestive of an ophiolitic origin although forsteritic olivines also occur in intrusive layered complexes. Metamorphism of the ZUC, ascribed to intrusion of multiple batholiths and possibly the MGB, likely led to the formation of ZUC chrysotile asbestos deposits.

The Ahualulco Volcanic Complex (AVC) is situated in the north-central part of the San Luis Potosí Volcanic Field (SLPVF) that is found in the southern portion of the Mesa Central (MC). The Cúcamo, AVC is mainly composed of mafic and intermediate volcanic rocks. The present study focuses on understanding the evolution, origin, and magmatic processes and petrogenesis of mafic and intermediate rocks in the Cúcamo, AVC. The Quaternary mafic rocks have porphyritic textures with the mineral assemblage of olivine, and clinopyroxene. These volcanic rocks display high K calc-alkaline basaltic compositions with enrichment in light rare earth elements (LREEs) and incompatible elements. Geochemical modeling reveals that mafic magmas were derived through a partial melting process of a spinel lherzolite source at low degrees of melting (~2 to 15 %) in an extensional regime. The intermediate volcanic rocks show porphyritic and glomeroporphyritic textures with matrix formed by randomly oriented microlites. The main mineral assemblage consists of plagioclase, K-feldspar, and clinopyroxene. These volcanic rocks are characterized by calc-alkaline basaltic andesitic and andesite compositions with enrichment in light rare earth elements and incompatible elements. Geochemical modeling suggests that intermediate rocks were derived from high ratios of assimilation and fractional crystallization processes between mafic melts and continental crust in an extensional environment.

The Jurassic mafic to felsic magmatism affecting the older Ediacaran-to-Cambrian basement of the Sanandaj-Sirjan Zone of Iran has been traditionally interpreted as the product of arc and/or back-arc magmatism related to the early stages of Neo-Tethys subduction beneath Iran in the early Jurassic. Recent works and new compositional and geochronological data have started challenging this commonly accepted model in favor of scenarios involving continental rifting, mantle plume activity, and/or passive margin formation. In the Hamedan area of the central sector of the Sanandaj-Sirjan Zone, the Jurassic Cheshmeh-Ghasaban gabbro (ca. 165 Ma) is a key formation to better understand the tectono-magmatic framework of the whole area. Our new data, combined with the existing literature, suggest a transitional to alkaline OIB-like compositional character for this gabbro similar to the nearby but slightly younger (ca. 145 Ma) Panjeh and Ghalaylan basaltic complexes (in the Songhor-Ghorveh area). When integrated with the existing geochemical data of Jurassic mafic rocks from the central Sanandaj-Sirjan Zone, our results point to a scenario of intracontinental rifting, possibly involving the upwelling old metasomatized (by Proto-Tethys subduction?) mantle or mantle-plume activity.

The presence and nature of uranium minerals subject to high leachability is one of the most significant factors in the exploitation of low-grade ores. The detection of these minerals is a challenging task due to their small size and low abundance. This paper presents a novel method of data processing that allows distinguishing and visualization of micron-scale U minerals. For this purpose, core samples of U-bearing sandstones from the Břevniště deposit (Czech Republic) were used. After their study by inductively coupled plasma spectroscopy, optical and scanning electron microscopy (SEM-EDS) and X-ray diffraction analysis, the presence of authigenic grains of U minerals occurring in various associations and their chemical compositions were confirmed by an electron microprobe. However, the use of these conventional instruments for the analysis of heterogeneous ore material with valuable information hidden, showed the necessity for a special data treatment. Matrix transformation of raw SEM-EDS data allowed for even more accurate visualizations such as contour and point maps of elemental distribution. Then, mathematical and visual correlations of transformed data revealed relationships among some measured elements (Ca, P, U, Zr, Nb, Fe, S) and their spectral overlaps. Conditions of ore formation were predicted based on the visualizations, correlations and the paragenesis of ningyoite in uranium ore. Herein suggested approach can help to identify economically significant minerals in complex mineralizations worldwide and increase the mining potential of the deposits.

The research sheds light on the age, origin, and tectonic environment of two significant alkaline plutons, Sullya and Angadimogar, located in the Mercara Shear Zone in the Southern Granulite Terrain of southern India. The zircon U-Pb dating indicates that the plutons crystallized at 829 ± 3.7 Ma and 831 ± 4.7 Ma, respectively. The zircon geochemistry suggests that Sullya and Angadimogar plutons underwent distinct crystallization processes, with zircons from Angadimogar samples crystallizing at varying temperatures over a prolonged period with limited fO2 levels and zircons from Sullya samples crystallizing at stable temperatures variable redox conditions. Most of the zircons from both plutons have trace element characteristics indicating formation in the continental crust. In contrast, some zircons from Sullya have trace elements similar to those found in the oceanic crust. The presence of two distinct types of zircons in Sullya samples indicates that the parental melt of the Sullya pluton consisted of magma from multiple sources. The average estimated temperature for zircon crystallization in Sullya was 691 °C, while the mean temperature in Angadimogar was 802 °C. The research implies that the plutons were emplaced parallel to the shear plane during an extensional regime, reactivating the paleo shears during the late Proterozoic era. The study highlights the importance of using multiple geochemical and geochronological techniques to gain a better understanding of the complex geological evolution of the Precambrian terrains.

Although arsenic (As) contamination has been extensively investigated in the aquifers of the lower and middle Gangetic plains, less attention has been given to the distribution and fate of As in the groundwater of the upper Gangetic plain, India. In the current study, groundwater samples (n = 40) were collected from Moradabad district in the upper Gangetic plain and analyzed for several physicochemical parameters to characterize the groundwater chemistry and evaluate various geogenic and anthropogenic factors controlling the occurrence, mobilization, and fate of As in the plain. Arsenic concentrations in groundwater ranged from 0.17 μg/L to 139 μg/L, with the majority of high-As groundwater associated with high Fe, Mn, and HCO3− and low NO3−, SO42−, and negative Eh values, implying that As was released via reductive dissolution of Fe and Mn oxyhydroxides in reducing conditions under the influence of organic matter degradation. Interrelationships between various geochemical variables and the natural background level (NBL) quantification of As suggested the influence of anthropogenic processes on the mobility of As in groundwater. Piper and Gibbs diagrams and various bivariate plots revealed that the majority of groundwater was of the Ca2+ − Mg2+ − HCO3− type and that the major ions in groundwater were derived from carbonate and silicate weathering, cation exchange and reverse ion exchange processes, and anthropogenic activities. Moreover, the results of principal component analysis (PCA), and hierarchical cluster analysis (HCA) also suggested geogenic and anthropogenic sources for the ion concentration in groundwater. The health risk assessment showed a higher non-carcinogenic risk for children and a higher carcinogenic risk for adults, respectively, due to the daily intake of As contaminated groundwater. Overall, this study represents the first systematic investigation of the distribution, geochemical behavior, and release process of As in groundwater in the study area and provides a strong base for future research in the alluvial aquifers of the upper Gangetic plain.

Our combined mineral chemistry and spectroscopic studies enable us to envisage details about composition and genesis of beryl from the Eastern Desert of Egypt. Two types of beryl were investigated including emerald from ancient workings in the schist-related type whereas the other type is non-gem and granite-related. On the basis of FeOt-Cr2O3-MgO ternary classification, the Wadi El Gemal emeralds (alkali-type, sodic) are Mg-bearing while the Mikpid-Akarem beryls (normal-type) are Fe2+-bearing. Intense green colour of emerald results in a 323 cm−1 Raman shift due to ~0.77 wt% Cr22O3 derived from serpentinite. In the Mikpid-Akarem district (belonging to the granite-related type), beryls are either faint blue or white and lack Cr, Mg and AlIV. On the other hand, they are relatively enriched in Fe and AlVI compared with the Wadi El Gemal emeralds (up to 0.13 & 1.97 apfu and 0.04 & 1.68 apfu, respectively), which is a function of the peraluminous composition of the granite host. Al3+ is substituted in the Y-site by di- to tetravalent cations (Mg2++Fe2++Cr3++Ti4+) and this is paired with a vacancy substitution by Na+. The Wadi El Gemal emeralds have H2O & K+ in the 2a-site and H2O & Na+ in the 2b-site. The latter site is vacant in the Mikpid-Akarem beryls.The FTIR spectra of our beryls and emeralds show a series of stretching and bending vibrations due to the presence of type I H2O (OH-Na band at 3657 cm−1) and type II H2O (stretching at 3591–3657 cm−1 & bending at 1631 cm−1). Lacking of Li+ leads to the absence of OH-Li band that is indicative of type III H2O. Hypothetical H2O in the Wadi El Gemal emerald (green beryl) amounts 2.24–2.92 wt% whereas it amounts 1.21–1.25 wt% in the Mikpid-Akarem non-green beryl. The asymmetric stretching vibration at 2921–2923 cm−1 is related to CH due to the presence of CH4, and possibly CO2, in the fluid inclusions trapped in the analyzed crystals. Some beryls, e.g. the Um Kabu emerald, has a Raman shift at 672 cm−1, which indicates maximal cation substitutions in the octahedral sites and minimal H2O in the channel sites. An uncommon shift at 147 cm−1 can be attributed to defect structure due to presence of radioactive zircon and monazite inclusions. Fe2+ substitution in the octahedral sites is appreciable and results in an UV–Vis-NIR band at 836 nm.

The Cu-Sb-Pb polymetallic vein deposit is hosted by metavolcanics rocks of the Gawuch Formation at the Kaldom Gol area of the northwest Kohistan arc terrain in northern Pakistan. The mineralization is closely associated with the dioritic to granodioritic rocks of the Lowari pluton, which was intruded into the Gawuch metavolcanics. Details of ore characterization and processes of ore genesis of this evidently hydrothermal mineralization are not well documented. Integrating petrographic, mineral-chemical and isotopic investigations, this study aims to comprehend the source of hydrothermal fluids, geochemical evolution, mineral inclusions and physicochemical conditions of the Cu-Sb-Pb polymetallic vein deposit in Gawuch metavolcanics in the Kohistan arc terrain in northern Pakistan. The mineralization is distinguished into three types of ore-gangue associations: Type Ia, Type Ib, and Type II. The textural study revealed two pyrite generations: (i) Py1 displaying euhedral to subhedral habits and containing scarce inclusions, and (ii) Py2 occurring as anhedral grains hosting abundant inclusions. Type Ia is characterized by Py1 associated with abundant quartz (Qz) showing comb texture, sericite (Ser), and minor chlorite (Chl). Type Ib comprises Qz + Ser + Chl and Py2, chalcopyrite (Ccp), and magnetite (Mag). Type II is represented by mosaic quartz, rhombic adularia, and bladed calcite, and the ore minerals fahlore and galena. Alteration zones composed of Qz-Ser ± Chl and Qz-Ser-Chl, surround Type I (a, b) and Type II veins, respectively. Fahlore and galena mostly replace pyrite of Type Ia and chalcopyrite of Type Ib. In addition, malachite, azurite, hematite and covellite occur as secondary (supergene) minerals. The Co/Ni ratios (>1) of Kaldom Gol pyrites suggest that the ore-forming fluids were hydrothermal in origin and Py1 and Py2 solidified at 221–304 °C and 225–261 °C, respectively. The LA-ICP-MS time-resolved depth profiles confirm the existence of sphalerite, and chalcopyrite inclusions in pyrite (Py1 and Py2) and millerite, bravoite, vaesite, Au-tellurides, native Au and galena inclusions in chalcopyrite and fahlore. Sulfur isotope compositions of pyrites (δ34S = Py1, −0.58 to +2 ‰; δ34S = Py2, −0.24 to +2.04 ‰) indicate that the ore-forming fluids were derived from magmatic source (s). The mineral assemblage, hydrothermal alterations, textures, temperature and δ34S of pyrites suggest that the Cu-Sb-Pb polymetallic mineralization at Kaldom Gol represents an intermediate-sulfidation type of epithermal deposit.

Black sands in the southern Eastern Desert (SED) of Egypt contain substantial reserves of heavy minerals (up to 5 %), and are found mainly in three basins namely: Hodein, Ibib and Diit between Shalateen and Halayeeb cities. The heavy minerals in these black sands include ilmenite-leucoxene (31 %–44 %), magnetite (15–18 %), zircon (11–21 %), garnet and green silicates (11–15 %), rutile (6–12 %) and monazite (2–4 %). Cassiterite, thorite, uranothorite, gold, xenotime and chromian spinel are minor quantities (<1 %). Magnetite (FeO: 75–93.5 wt%) and ilmenite (TiO2: 42.7–56.9 wt%), hosting high Mn, V, Zr, Zn, Cr, Nb and Co, were probably derived from gabbroic rocks. The detrital chromian spinel composition (Cr#, 0.51–0.61; Mg#, 0.5–0.63; TiO2 < 1.0 wt%) and its morphology are similar to those of spinels in fore-arc peridotites from the SED of Egypt, suggesting dominance of fore-arc basins for peridotite emplacement. These basins were formed during arc-arc or arc-oceanic crust collision and encolsed ophiolites, gabbroic rocks and I-type granites as sources of the SED black sands. The studied garnets are mostly almandine in composition with few grossularite and spessartine; they might have been derived from I-type granites and gneisses sources. The rutile and monazite show enriched LREE relative to HREE, and display marked defeciency in Eu, suggesting highly fractionated granitic rocks as a main source. Two distinct types of zircon are recorded: radioactive (Hf: 1578–8770, Y: 319–1335, U: 36–114 and Th: 40–64 ppm) and non radioactive (Hf: 427, Y: 44, U: 2 and Th: 2 ppm); they were probably derived from different granitic sources. Compositions and P-T conditions (T: 655–970 °C, P: 1.18–9.53 kbar) of magmatic amphiboles are similar to those derived from I-type granitoids. Bulk analyses of the economic heavy mineral assemblages show significant concentrations of Fe (393 kg/ton), Zr (183 kg/ton) and Ti (129 kg/ton) with minor Cr (14 kg/ton), Ba (7 kg/ton), Hf (4.9 kg/ton), Th (up to 3.34 kg/ton) and U (0.29 kg/ton). The elevated contents of Th and U could be related to the occurrence of monazite and zircon with subordinate thorite, uranothorite and xenotime. The total REE contents of these bulk analyses range from 1 to 4 kg/ton, where LREEs form 80–90 % of total REEs. Monazite (ΣREEs: 443604 ppm on average), garnet, zicon (ΣREEs: 421 ppm) and rutile (ΣREEs: 309 ppm) are the main host of REEs in the investigated black sands. Tonnages of raw sands, to a depth of one meter, are estimated per 10 km2 in each basin, giving 18 million tons for Ibib basin and 19 million tons for both Diit and Hodein basins. Economic heavy minerals constitute 6–26 % of the total heavy minerals and around 1.0 % of total raw sands. Calculated reserves of these economic minerals, per 10 km2 of black sands, range from 0.1 million ton in Ibib and Hodein basins to 0.2 million ton in the Diit basin.

The origin of silicic rocks (SiO2 > 65 wt%) in Continental Flood Basalt (CFB) provinces could be attributed to complex petrogenetic processes. The 65.5–66 Ma old Deccan Traps CFB contains eight sporadic but significant silicic rock exposures that are studied here in a comprehensive framework using field observations, petrography, major oxides (n = 56), and trace element chemistry. Rhyolite and granophyre, as well as subordinate felsite, ignimbrite, trachyte, pitchstone, and microgranite coexist with volcanic and plutonic mafic rocks such as basalt, basaltic andesite, and gabbro. Multiple isolated and circular/semi-circular hills and linear dykes of silicic rocks are present in the form of lavas with prominent flow folding, rheomorphic ignimbrite, and tuffs. The ‘Rheological Agpaitic Index’ (RAI) indicates that most of the silicic rocks in the Deccan Traps are effusive in nature, except for Rajpipla, Alech, Bombay, and Osham silicic rocks, which are marked by explosive volcanism. Thermodynamic-based Rhyolite-MELTS modelling suggests that the major oxide composition of Pavagadh and Barda basalt is a likely candidate for the parental melt composition of the silicic rocks of the Deccan Traps. Ba, Sr, P, Zr, and Ti anomalies are consistent with the fractionation of K-feldspar, plagioclase, apatite, zircon, and Fe-Ti oxides, respectively. Two broad REE patterns are noticed in the Deccan Traps silicic rocks: a flat pattern for Barda, Alech, and Chogat-Chamardi silicic rocks, and a steep REE pattern for Osham, Rajula, Pavagadh, Rajpipla, and Bombay silicic rocks. Trace element modelling reveals that 5–10 % partial melting of a spinel peridotite source could produce an REE pattern and abundances similar to the associated basalts. Further extensive fractional crystallization (60–90 %) of the parental mafic melt at a deeper depth (where spinel is stable) could produce the REE composition and pattern observed in most silicic rocks except for those of Barda, Alech, and Chogat-Chamardi, which require fractional crystallization of the same parental melt at a shallower depth (where spinel is not stable). The geochemical variability of Deccan Traps silicic rocks reveals an origin from a mantle-derived parental mafic melt that evolved via the assimilation and fractional crystallization (AFC) process to form the silicic exposures, which is typical of silicic volcanism in other global CFBs.