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The present study provides multidisciplinary research on the alteration of petrographic, mineralogical, geochemical characteristics, and physical properties of Himachal gneiss due to weathering. Three different weathering grades fresh, slightly, and moderately weathered gneiss are collected from Kullu, Himachal Pradesh, India. The petrographic and mineralogical analyses are done by thin section and XRD analyses. The microstructural and geochemical studies of gneiss samples were performed using scanning electron microscopy (SEM) and X-ray fluorescence (XRF) respectively. The petrographic images revealed a large amount of alteration in the plagioclase due to weathering. The pervasive sericitization of plagioclase is observed in moderately weathered gneiss samples. The quartz grains are intact and only minor fracturing in some quartz grains is observed in moderately weathered gneiss samples. The SEM images indicate that the inter-granular and intra-granular micro-cracks increase with the weathering grades. The XRF results are used to obtain the different chemical weathering indices and their suitability for Himachal gneiss. Among twenty-five chemical weathering indices, the CIA, CIW, alkaline ratio, PIA, LOI, and WI show a suitable trend and can be used for assessing the weathering of Himachal gneiss. In addition, alterations in the physical properties of gneiss are observed due to weathering. The bulk, dry, saturated densities and slake durability index decrease while the porosity increases with the progressive weathering of gneiss. The progressive weathering significantly reduces the gneiss's uniaxial compressive strength (UCS). For all three weathering grades of gneiss, the maximum and minimum values of UCS were observed at 90˚ and 30˚ foliations, respectively. [ABSTRACT FROM AUTHOR]

The mafic-ultramafic intrusion in the XV anomaly area, contains magmatic Fe-Ti ox-ides±(p) ore, is located in the Bafq mining district in the Central Iran. It consists of cumulate and layered Fe-Ti-bearing gabbros and pyroxenites. The mineral assemblages include clinopyroxene, Fe-Ti oxides, plagioclase, amphibole, apatite and sulfides (pyrite and chalcopyrite). The Fe-Ti oxides mainly consist of magnetite-titanomagnetite and ilmenite, which occurred as disseminated, intergrowth, lamellae (trellis and sandwich textures) and inclusions. Magnetite in the gabbroic rocks is from the near end-member of Fe3O4 (<1 wt.% TiO2) to titanomagnetite containing up to 8 wt.% TiO2 (about 3.73 wt.% to 26.84 wt.% Ulvospinel (XUsp)). Magnetite in pyroxenite rocks is characterized with TiO2 range from 0.46 wt.% to 3.14 wt.% (XUsp varied from 1.76 wt.% to 10.46 wt.%). The abundances of V2O3 range from 0.03 wt.% to 1.29 wt.% and 0.24 wt.% to 1.00 wt.% for gabbro and pyroxenite, respectively. XUsp contents of magnetite show insignificant correlations with Al2O3 and MgO. The average XIlm in the ilmenite of gabbro is 92%, whereas it is 90.37% in the pyroxenite rocks. The MgO and V2O3 contents show a slightly positive correlation with TiO2 in ilmenite. The composition of clinopy-roxenes in gabbro and pyroxenite rocks fall in the diopside to augite field with Mg# ranging from 67 to 98 and 74 to 96, respectively. In both rock types, amphiboles are mainly pargasite and rarely actin-olite. Plagioclase in pyroxenite rocks is clustered in the labradorite to andesine fields with a compositional ranges of An46–69 and in gabboic rocks fall in two fields with compositional ranges of albite with An0.65–5.95 and labradorite with An50–63. The δ 34S isotopic values cover a limited range from +3.15‰ to +4.10‰ V-CDT consistent with magmatic origin. Fe-Ti mineralization is formed in two stages, minor inclusions of Fe-Ti oxide minerals in the pyroxene and plagioclase crystallized in the early magmatic stage, whereas interstitial oxides formed by fractional crystallization processes that accumulated by gravitational settling in the later stage as intercumulus phase. Gravitational settling process is supported by the observation of decreasing the amount of Fe-Ti oxides from Fe-Ti oxide-rich pyroxenite to weak mineralized gabbro (base to top). The high contents of H2O, phosphorate and high initial Ti-Fe in parental magma are the crucial factors controlling the Fe-Ti oxides enrichment and mineralization. [ABSTRACT FROM AUTHOR]

The elastic modulus is one of the important parameters for analyzing the stability of engineering projects, especially dam sites. In the current study, the effect of physical properties, quartz, fragment, and feldspar percentages, and dynamic Young's modulus (DYM) on the static Young's modulus (SYM) of the various types of sandstones was assessed. These investigations were conducted through simple and multivariate regression, support vector regression, adaptive neuro-fuzzy inference system, and backpropagation multilayer perceptron. The XRD and thin section results showed that the studied samples were classified as arenite, litharenite, and feldspathic litharenite. The low resistance of the arenite type is mainly due to the presence of sulfate cement, clay minerals, high porosity, and carbonate fragments in this type. Examining the fracture patterns of these sandstones in different resistance ranges showed that at low values of resistance, the fracture pattern is mainly of simple shear type, which changes to multiple extension types with increasing compressive strength. Among the influencing factors, the percentage of quartz has the greatest effect on SYM. A comparison of the methods' performance based on CPM and error values in estimating SYM revealed that SVR (R2 = 0.98, RMSE = 0.11GPa, CPM = + 1.84) outperformed other methods in terms of accuracy. The average difference between predicted SYM using intelligent methods and measured SYM value was less than 0.05% which indicates the efficiency of the used methods in estimating SYM. [ABSTRACT FROM AUTHOR]

Gold-platinum mineralization was discovered in ultramafic–mafic rocks of the Ariadne massif of the Sikhote-Alin orogenic belt. In this article, we show that ultramafic (peridotite and pyroxenite) and mafic (ilmenite and hornblende gabbro) rocks form a single series with gradual accumulation of rare and rare earth elements of more differentiated varieties. New age determinations for zircon from ilmenite gabbro are given (164 ± 0.48 Ma). We distinguished four varieties of gold differing in the Au, Ag, Cu, and Hg contents. Platinum-bearing minerals are isoferroplatinum and cuprite. The isotopic composition of sulfides from ultramafic rocks suggests a mantle source, while sulfides from ilmenite gabbros are characterized by isotopically light sulfur, indicating the possible involvement of crustal rocks in ore genesis. Carbon isotope analysis of the carbon-bearing matter of mafic–ultramafic rocks showed the presence of mantle fluids and isotopically light biogenic matter from sedimentary rocks. The data indicate the influence of mantle and crustal processes on the formation of ore-bearing mafic and ultramafic intrusions. [ABSTRACT FROM AUTHOR]

New mineralogical–petrographical and isotope-geochemical data, as well as numerical simulation results, suggest that high-magnesian basalts and basaltic andesites of the eastern block of the Talmi volcanic structure formed as a result of crystallization differentiation during the rapid ascent of mantle magmas to a depth of ∼7.5 km, under conditions of relatively low oxygen fugacity and water content. We consider acid volcanics (SiO2 ∼76–78 wt %) of the central block as crustal melts, the mixing of which with mantle melts in shallow peripheral chambers leads to the appearance of andesites with numerous mineralogical and geochemical signs of hybridism. The geodynamic position of Triassic volcanism is governed by a transtensional regime under conditions of regionally manifested submeridional compression. [ABSTRACT FROM AUTHOR]

The slake durability and the related deterioration mechanism of carbonaceous rocks exposed to adverse external environment are of a great importance to the stability of infrastructure. A series of laboratory tests were conducted to determine their slake durability index Idi, fractal dimension D, total organic carbon (TOC) content, and mineralogical characteristic. The results demonstrated that Idi value decreased rapidly within the first 4 cycles, and then reached a relatively stable state as the test cycle further increased, indicating that effective protective measures should be conducted at the earlier stage of wetting-drying process to minimize the durability deterioration of carbonaceous rock. The discrepancy of carbonaceous rocks in terms of mineralogical characteristic accounted for different slake durability responses at a given cycle. Carbonaceous rock with lower clay minerals content wc possessed superior slake durability performance, and a power correlation between Id6 and wc was obtained. Fractal dimension D was found to be an indicator to indirectly describe the durability characteristic of carbonaceous rock. The organic matter imposed negative impact on the slake durability, which was manifested by the carbonaceous rock with higher TOC content exhibited inferior disintegration resistance. The microstructure changes, including an increase in pore volume, pore size, layer spacing, and the presence of new crystalline-like substances, demonstrated the minerals/salts dissolution and chemical reactions within the rock matrix occurred during the slake durability test. These changes were mainly attributed to the hybrid influence of mineralogy and microstructure of carbonaceous rock. [ABSTRACT FROM AUTHOR]

The Khangalas orogenic gold deposit is located in the central part of the Yana–Kolyma metallogenic belt. The structure of the deposit is defined by several mineralized fracturing zones up to 70 m thick and up to 1400 m long in the arch and the southwestern limb of a NW-trending anticline. The Upper Permian terrigenous rocks host ore bodies with massive, banded, veinlet, disseminated, and brecciated textures. The major gangue minerals include quartz, carbonates, and rare sericite. The major ore minerals are pyrite and arsenopyrite, the subordinate minerals are galena, sphalerite, chalcopyrite, and native gold, and Fe-gersdorffite, tetrahedrite, and argentotennantite are rare minerals. Supergene minerals (sulfates, phosphates, arsenates, and hydrooxides) are abundant in a linear oxidation zone. The mineral formation occurred in two stages: gold–sulfide–quartz and silver–quartz. Quartz veins with visible native gold formed from low-saline (~5.0 wt % NaCl-equiv.) CO2-bearing hydrocarbonate fluids at a temperature of 330–280°C and a pressure of ~0.8 kbar. Disseminated Au-bearing pyrite-3 (up to 39.3 ppm Au) and arsenopyrite-1 (up to 23.8 ppm Au) from sericite–carbonate–quartz metasomatites are characterized by nonstoichiometric composition, a Fe excess, and a deficit of S (in addition to As in Apy), and Fe/(S + As) ratios of 0.47–0.52 (Py2) and 0.47–0.50 (Apy 1). Structurally bound Au+ is the dominant mode of occurrence of invisible gold in Py3 and Apy1. The isotopic composition of oxygen of quartz (+15.2 to +16.1‰ δ18O) and fluid (+8.4 to +9.2‰ δ18OH2O), as well as sulfur of sulfides (–2.1 to 0.6‰ δ34S), in addition to the 187Os/188Os ratios (0.2212–0.2338) of native gold and Pb of galena (206Pb/204Pb = 18.0214, 207Pb/204Pb = 15.5356, and 208Pb/204Pb = 38.2216) and geochemical features of Py3 and Apy1, allow us to suggest that sources are involved in ore formation that are mainly from the subcontinental lithospheric mantle and, to a lesser extent, crustal reservoirs. The formation of gold-bearing ore bodies of the deposit is related to the final progressive reverse-thrust deformations of stage D1 of the Valanginian period of the Early Cretaceous (~137 Ma), which occurred during postorogenic processes in the Yana–Kolyma belt upon regional southwestern transportation of rocks. Our results are important for forecasting metallogenic and prospecting works directed for the discovery of large-volume gold mineralization of orogenic belts. [ABSTRACT FROM AUTHOR]

The Libyan territory is made of a heterogeneous geologic bodies including intrusive igneous, metamorphic, volcanic rocks, and marine and continental sedimentary formations, Archean to Quaternary in age. It makes part of the "Saharan Metacraton" built up by the pre-Neoproterozoic continental crust between the Hoggar to the west, the Congo Craton to the South, and the Arabian–Nubian Shield to the East. This territory includes heterogeneous mineralogies and lithologies engendered by various geological processes that established appropriate conditions for geo-resources occurrence. Libya has indeed an interesting hydrocarbon potential and the potential to enhance the production and the development of many others geological resources. Unfortunately, trusted official data describing the true state of the geo-resources sector in Libya including production, demand, and market balance are missing for the post 2010 period due to the no effective governance resulting from the political-military instability. Accordingly, this short report is mainly based on the analysis of relevant multisource data and information from published research and available documentation. It constitutes a general diagnosis and a synthesis of the state of the art of the geo-resources of Libya from a combined geological and economic point of view and exposes the opportunities and the challenges their future development faces. [ABSTRACT FROM AUTHOR]

Reliable reconstructions of tephrostratigraphy and emplacement mechanisms of Early to Middle Miocene volcaniclastic deposits across the Alpine-Mediterranean region may yield important clues as to the nature, spread, volume, magnitude and frequency of large silicic eruptions of the Carpathian-Pannonian Region. Here we report on a sequence of Middle Miocene volcaniclastic deposits intercalated with lacustrine strata from the Livno-Tomislavgrad Basin, part of the Dinaride Lake System. We applied a multi-proxy approach to elucidate their source, decipher their emplacement mechanism, and evaluate their basin-scale and regional correlativity. New high-precision zircon geochronology (~ 14.32 Ma) reveals their simultaneity with numerous volcaniclastic deposits (and their alteration products) widely spread across the Alpine-Mediterranean region. Additionally, their correlativity is confirmed at the scale of the Livno-Tomislavgrad Basin, based on similar lithostratigraphy, mineralogy and volcanic glass geochemistry. Newly obtained zircon Hf isotope data imply that Livno-Tomislavgrad Basin distal volcaniclastic deposits and ~ 14.36 Ma Harsány ignimbrite of the Carpathian-Pannonian Region had shared a parental eruptive center. However, different volcanic glass geochemistry, bolstered by the high-precision geochronology, suggests distinct eruption events, implying more frequent explosive volcanism of the Carpathian-Pannonian Region during Middle Miocene than previously recognized. We suggest that the ~ 14.32 Ma fine fallout tephra, deposited in the distal basin in the Dinarides (> 400 km from the source), was likely re-mobilized by water-driven hillside erosion from the extensive paleo-relief, and further transported via land-derived gravity flows. Upon entering the lake, the gravity flows likely transformed into subaqueous sediment density flows. These deposited ~ 1 to 7-m-thick overall graded volcaniclastic turbidites, thinning away from the presumed source of tephra re-mobilization. Although over-thickened, the ~ 14.32 Ma Livno-Tomislavgrad Basin volcaniclastic deposits can still serve as a reliable tephro- and tectono-stratigraphic markers due to their rapid mode of accumulation. Schematic illustration of the formation of studied ~14.32 Ma volcaniclastic successions of the SE Livno-Tomislavgrad Basin, Dinaride Lake System [ABSTRACT FROM AUTHOR]

The Koum Basin is a North Cameroonian intracontinental basin that is part of the upper Benue Trough, notably the Yola arm. The sediments of this basin were examined to determine paleoenvironmental and paleoclimatic interpretations, which were based mostly on sedimentology and mineralogical evolution in its central part. The examined materials are dominated by claystone and siltstones of varied colours, which are, for the most part, carbonated, and a few layers of fine to medium sandstone and conglomerate. The bulk organic geochemistry enabled the designation of type III kerogen, indicating a terrestrial origin of organic matter, which shows predominantly immature issues. The bulk mineralogy development exhibits no significant changes and is dominated by phyllosilicate (25.66%), calcite (24.5%), plagioclase (19.36%), and quartz (19.31%). Smectite, illite, and vermiculite dominate clay mineral fraction, with only low quantities of kaolinite and chlorite. The diagenesis influence is low to moderate, as shown by moderate illitization and chloritization as well as Tmax values. The deposition occurred in a globally semi-arid climate, as evidenced by the permanent occurrence of smectite, punctuated by short periods of drier and humid weather. [ABSTRACT FROM AUTHOR]

Strongly peraluminous (SP) leucogranite typical of Himalayan-type collision orogen is reported from Kottayam, the western Madurai block, Southern Granulite Terrane (SGT). Low concentration of mafics (average ≈ 5%), consistently high A/CNK (≥1.1), and invariable presence of garnet and normative corundum (1.24–2.12 wt.%) qualify Kottayam granite (KG) as SP leucogranite. Geochemically, KG is ferroan to magnesian (F* = 0.79–0.90), alkali-calcic to calc-alkali (MALI = 6.64–7.54), peraluminous (ASI = 1.19–1.26) and plot in peraluminous leucogranite field. Further, all the KG samples fall within the 'SP granite quadrilateral,' defined by the Al2O3/TiO2 and CaO/Na2O ratios of SP granites from orogens around the world. The REE pattern is akin to SP granites from the Himalayas and the Hercynides. Various tectonic discrimination criteria and plots indicate that KG formed in a Himalayan-type collisional orogeny. Source discrimination norms, together with zircon εHf values (−6.62 to −4.02), strongly point to a crustal source comprising an admixture of metapelites and meta-greywacke. U–Pb analyses of zircons define a concordia age of 741 ± 12 Ma, which coincides with the timing of the breakup of the Rodinia supercontinent. Mineralogical, geochemical, and isotopic evidence, thus, demonstrate that KG exemplifies crustal recycling during the Tonian period. Research highlights: Strongly peraluminous (SP) leucogranite distinctive of Himalayan-type collision orogens is reported from Kottayam, Kerala, which forms part of the western Madurai block, Southern granulite terrane (SGT), southern India. Mineralogy, geochemistry, and isotope data substantiate that this SP leucogranite formed in Himalayan-type collision orogeny. Geochemical and isotope indices show that present SP leucogranite formed from a pelite-psammite mixed source, signifying crustal recycling, during the Tonian period in SGT. Chemical proxies and geochronology data suggest that this SP leucogranite is probably associated with the post-collisional phase of collision orogeny, contemporaneous with Rodinia rifting. [ABSTRACT FROM AUTHOR]

The varicoloured compacted black shale of the Duwi Formation at Mohamed Rabah, Wasief, and Umm El-Huwitat mines is part of the huge black shale belt extending from the Egyptian western desert to the Red Sea coast in the east. Egypt’s black shale has been the focus of multiple studies to investigate its potential as a future energy resource due to its organic content. However, in the this study, the focus has been on the mineralogy and geochemistry of the inorganic content of these bearing shale mines, investigated to determine their chemical characteristics. These shales mainly comprise clay minerals, calcite, quartz, orthoclase, gypsum, and anhydrite. The studied clay fraction reveals that the clay minerals are represented by montmorillonite, kaolinite, and illite. Analysed black shales are recognized by their total organic carbon (TOC) content (0.14–2.52 wt%) and are rich in SiO2 (50.83 wt%), followed by Al2O3 (14.7 wt%) and CaO (2.04 wt%). The chemical composition of these shales shows general enrichment of immobile elements and is associated with terrigenous influx, such as SiO2, Al2O3, and TiO2. Due to the oxidation and weathering of the organic matter, the geochemical composition shows that the studied black shales have high concentrations of V (1400 ppm), Sr (389.8 ppm), Zn (325.8 ppm), and Zr (258.3 ppm). The geochemical classification revealed that the studied black shale samples were related to siliceous and aluminous rocks due to the high SiO2 and Al2O3 contents and were deposited in marine environment. The studied black shale is enriched in V, Sr, Zn, and Zr and is an important source of these elements. U at Wasief exists in high concentrations due to the richness of its black shale in organic matter. These black shales were deposited in a marine environment, derived from felsic igneous as source rocks, and affected by intense chemical weathering. [ABSTRACT FROM AUTHOR]

The Jiadi and Damaidi gold deposits in southwest Guizhou Province are the largest basalt-hosted Carlin-type gold deposits recently discovered in China. This study uses the Tescan Integrated Mineral Analyzer, supported by detailed field investigations, regional geological data, and extensive sample collections, including mineralized ore, altered wall rock, and unaltered basalt samples, for ore-bearing and geochemical analyses. Comparative analysis between altered and unaltered basalt samples revealed a mineral assemblage of sericite, quartz, and pyrite. This mineral composition forms through the hydrothermal alteration of unaltered basalt, originally containing feldspar, pyroxene, and ilmenite. The wall rock primarily features sericite, quartz, and hematite. During the alteration process, major, trace, and rare earth elements notably migrate. In the Jiadi deposit, K2O, Rb, Au, and REE significantly increase, while Na2O, CaO, MgO, and MnO decrease. SiO2, Al2O3, and Fe2O3 levels remain relatively stable. In the Damaidi deposit, K2O, Rb, and Au enrich, contrasting with the depletion of Na2O, CaO, MgO, and MnO, while SiO2, Fe2O3, Al2O3, TiO2, and REE show no significant changes. In the wall rock, TiO2, Al2O3, K2O, and REE increase, while Na2O, CaO, MgO, and MnO decrease; SiO2 and Fe2O3 content remains unchanged. The mineralization process likely originated from mid- to low-temperature, reductive magmatic hydrothermal fluids rich in CO2, CH4, N2, H+, S2−, HS−, H3AsO3, and [Au(HS)2]−. These fluids migrated to tectonically weak zones in the Lianhuashan area, where Emeishan basalts are present. They reacted with Fe-bearing minerals in the basalt, such as ferro-hornblende and ilmenite, forming pyrite, arsenic-bearing pyrite, and arsenopyrite, thus enriching Au in these minerals. Additionally, K+ and H+ in the fluid reacted with plagioclase in the basalt, forming sericite and quartz. As the fluid entered the wall rock from structural weak zones, its oxidation increased, leading to the complete or partial reaction of Fe-bearing minerals in the wall rock, resulting in the formation of hematite or magnetite. This mineralization process is similar to that observed in carbonate-hosted Carlin-type gold deposits in southwest Guizhou, with the primary distinction being the iron source. In carbonate deposits, iron originates from ferridolomite within the wall rock, while in basalt-hosted deposits, it derives from ferripyroxene and ilmenite. [ABSTRACT FROM AUTHOR]

Bauxite, the primary economic raw material for aluminum production, is extensively used due to its affordability. The Al Ba'itha mine in Az Zabirah, Saudi Arabia, contains bauxite deposits with varying textures, including pisolitic, oolitic, and oolitic-conglomeratic forms. Predominant minerals within these deposits include gibbsite, boehmite, and diaspore. These deposits have elevated concentrations of Al2O3 and Fe2O3, with average values standing at 53.59 wt% and 12.12 wt%, respectively. Minor constituents such as goethite, hematite, and boehmite contribute to these compositions. The presence of SiO2 (average: 7.59 wt%) and TiO2 (average: 2.94 wt%) suggests the existence of rutile, anatase, and kaolinite. To assess the grade and mineralogical composition of bauxite, spectra were obtained using the GER 3700 spectroradiometer across low, medium, and high-grade samples. Notable features in the spectra include strong Al–OH vibrations at wavelengths approximately 1.5, 2.2, and 2.3 µm, indicative of bauxite's presence. The presence of hematite, goethite, and gibbsite is discerned through absorption features at 0.48 and 0.88 µm. Furthermore, absorption properties near 2.3 µm suggest the existence of calcite, attributed to the CO3 molecule. Analysis of the Fourier-transform infrared (FTIR) spectrum of bauxite reveals absorption bands associated with kaolinite, hematite, quartz, and gibbsite. Integration of X-ray diffraction (XRD), FTIR, and reflectance spectroscopy was useful in determining bauxite grade and mineralogical composition. These methods serve as efficient tools in the exploration and characterization of bauxite deposits, facilitating informed decision-making in aluminum production processes. [ABSTRACT FROM AUTHOR]

The results of detailed mineralogical and geochemical studies of precious metals from ultrabasic rocks of the Ariadnoe massif (Sikhote-Alin orogenic belt) are presented. The presence of several varieties of gold with different ratios of Ag, Cu, and Hg has been revealed. Isoferroplatinum predominates among platinum minerals. The isotopic composition of ultrabasite sulfides corresponds to the mantle source, while basites are characterized by isotope–light sulfur, indicating the possibility of participation in the oreogenesis of crustal rocks. Isotope-carbon analysis of igneous rocks indicates that they contain derivatives of deep fluids and isotope-light biogenic matter of sedimentary rocks. The presented data show that mantle and crustal processes were involved in the formation of ore-bearing intrusions of ultrabasic–basic rocks. The association of ilmenite, gold, and platinum in ultrabasites and basites, a derivative of these processes, can serve as a search criterion for the detection of industrially promising sources of strategic metals. [ABSTRACT FROM AUTHOR]

Hot spring environments encompass broad physicochemical ranges, in which temperature and pH account for crucial factors shaping hot spring microbial community and diversity. However, the presence of photosynthetic microbial mats adjacent to boiling hot spring vents, where fluid temperatures extend beyond photosynthetic capability, questions the microbial profiles and the actual temperatures of such adjacent mats. Therefore, this study aims to characterize thermophilic microbial communities at Pong Dueat Pa Pae hot spring using next-generation sequencing, including investigating hot spring mineralogy. Results suggest that Pong Dueat Pa Pae hot spring precipitates comprise mainly silica which also acts as the main preservative medium for microbial permineralization. Molecular results revealed the presence of cyanobacterial and Chloroflexi species in the thick, orange and green subaerial mats surrounding the vents, suggesting the mats would be at least 30 °C cooler than source vents despite constantly receiving geyser splashes. Bacterial abundance was considerably higher than archaeal (97.9% versus 2.1%). Cyanobacterial (mainly Synechococcus and Leptolygbya) and Chloroflexi species (mainly Roseiflexus) accounted for almost half (40.04%) of the bacterial community, while DHVEG-6 and Thaumarchaeota comprised dominant members (> 90%) of the archaeal fraction. This study updates and provides insights into thermophilic microbial community composition and mineralogy of hot springs in Thailand. [ABSTRACT FROM AUTHOR]

The supergene zone of the Cap Garonne mineral deposit (Provence, France) hosts one of the most remarkable mineralogy in the world with no less than 150 minerals, 16 of which are type locality. Such mineral diversity offers a detailed view of mineral and geochemical changes during weathering processes. The stratabound epigenetic primary mineralization occurs within a few meters-thick fluvial conglomerates resting above the Permian–Triassic transition and is probably related to Late Triassic–Early Jurassic hydrothermal events. The Cu–As mineralization in the lower part of the conglomerates is locally overlapped by a thin Pb–Zn-rich layer in the northern mine. The results show that the weathered part is significantly enriched in Cu, Pb, As, Zn, Ag, Ba, Sb, and Bi. The evolution of the supergene fluid is traced in an Eh–pH diagram by the succession of sulfides I (tennantite, galena), sulfides II (covellite), arsenates (olivenite), sulfates and sulfo-arsenates (brochantite, anglesite), and carbonates (malachite, azurite, cerussite). The primary sulfide oxidation acidified the host conglomerate and enabled the crystallization of secondary sulfides and arsenates. Efficient and rapid neutralization by the calcite cement of the host conglomerate and chlorite in the matrix caused successive precipitation of arsenates, sulfates, and carbonates. The supergene processes could be related to major periods of weathering in Western Europe (Early Cretaceous–Late Oligocene/Early Miocene). Erosion-prone periods may have contributed to the stripping of the Pb–Zn-rich layer in the southern mine. [ABSTRACT FROM AUTHOR]

The contemporary scientific investigations delves into the mechanisms of migration, distribution, and fractionation of rare earth elements and yttrium (REE + Y) in aqueous environments characterized by humid and arid sedimentogenesis. This particular facet has been employed to solve numerous fundamental inquiries pertaining to lithology and paleolimnology. The manner in which REE + Y behave in water bodies within the cryolithozone remains largely unexplored. By evaluating the concentration levels and distribution patterns of REE + Y in the waters and sediments of the lakes situated in the Ukok Plateau and the Ulagan depression, under the prevailing conditions of cryolithogenesis as the primary geochemical process transforming rocks, soils, and sediments, we were able to augment the existing comprehension of nival sedimentation. In all the lakes examined, the content of REE + Y in the water exhibits a similar magnitude as that of small lakes in other landscape zones of the southern Western Siberia, while the content level of REE + Y is greater in the bottom sediments. The concentrations, distribution and fractionation of REE + Y vary from lake to lake and are determined by several factors: the chemical properties of REE + Y in solutions, the intensity of transformation of host rocks and the mineral forms of the REE + Y in the rocks (minerals). The concentrations, distribution and fractionation of REE + Y in bottom sediments vary slightly from lake to lake except for the contents of Eu, Y, La. The content of Eu, Y, La in the bottom sediment of the lake is influenced by a combination of factors, including their concentrations in the water, the redox conditions of diagenesis, and the mineral composition of the bottom sediment, particularly the amount of accessory minerals. [ABSTRACT FROM AUTHOR]

The material from which an archaeological piece is made provides a great deal of information regarding the society in which it was made; thus, any misidentification can lead to erroneous conclusions. The uniqueness of many of these pieces hinders their mineralogical analysis because the pieces cannot be damaged for sampling; therefore, errors in the classification of these materials are common. In the present study, we evaluate the suitability of the spectroradiometry technique in the analysis of two archaeological talc pieces. Both came from the Iron Age archaeological site of Peña del Castro (La Ercina, León) in the northwestern Iberian Peninsula. We compared the spectral curves of these 2 pieces with the spectral curves from 50 talc geological samples from different geographical sources, combining bulk and powdered samples. Our results show that spectral curves enabled the identification of the talc material in the powdered and bulk samples. Moreover, the absence of the talc characteristic features in other soft materials also used in antiquity enabled the detection of incorrect identification of the classified pieces. Even though our results cannot be used to define any absorption feature characteristic to establish the provenance of the material, in the present study, spectral analysis has been shown to be suitable as a nondestructive technique to mineralogically identify archaeological pieces. [ABSTRACT FROM AUTHOR]

The Galim-Legalgorou area, located along the north-western branch of the Cameroon Volcanic Line (CVL), is known for artisanal gold mining and primary gold exploration, but the style and origin of the mineralization has not been fully described in the scientific literature. The close spatial association of the mineralization with Tertiary volcanic rocks raises the question of whether or not this is an epithermal system in a region where all previously studied gold occurrences have been classified as orogenic. In this contribution, we use ore mineral and alteration assemblage and mineral microchemistry to constrain the origin and evolution of the mineralization. Gold is alloyed mainly with Ag (max. 53.1 wt%) and show fineness values that vary 379 and 721 with an average of 455. A cumulative percentile plot of Ag concentrations in the cores of all electrum particles, and the observed step-change from Au-rich cores to more Ag-rich mantles in zoned electrum particles, suggest that the mineralization was deposited by two distinct hydrothermal fluid influxes. The observed ore mineral association-electrum, Se/Tl-acanthite, pyrite, Fe-rich sphalerite, ± galena; the measured FeS contents of sphalerite (average 23.1 mol%), and the presence of colloform banded chalcedony and hydrothermal breccia are all consistent with features of low sulfidation epithermal deposits. This study, therefore, demonstrates for the first time, the presence of significant low sulfidation epithermal Ag–Au mineralization on the CVL, an intracontinental rift region only previously known for orogenic gold mineralization. [ABSTRACT FROM AUTHOR]

We report whole-rock chemistry, mineral chemistry, and volatile content from Villarrica volcano's major recent paroxysms and background activity. Composition of the volcanic products are basalt to basaltic andesite with whole-rock SiO2 content between 50 and 56 wt%, and a mineralogy dominated by olivine (Fo71-80), clinopyroxene (Mg# ~ 50) and plagioclase (An60–80). Volatile contents in melt inclusions are up to 1.5 wt% H2O, 500 ppm CO2, 1230 ppm sulfur and 580 ppm chlorine. Regardless of the type of activity, there are no substantial variations in whole-rock composition or the volatile content when the activity switches from background activity to a major paroxysm, strongly suggesting that this shift does not just depend on the arrival of new magma in the shallow magmatic system. Geothermobarometry constrains crystallization of the major mineral phases at various depths between 3 and 12.7 km, suggesting that degassing of a volatile-rich recharge magma occurs deeper than 12 km, producing efficient mixing throughout the whole system, and sustaining the lava lake activity in Villarrica's summit crater. The occurrence of a permanent lava lake also suggests that the magma recharge must be close to continuous and therefore sudden changes between background and paroxysmal volcanic activity are likely controlled by relatively small changes in the rate of recharge and/or the volatile release rate in the magmatic system. This has important implications for the understanding of eruption triggers and the forecasting of volcanic eruptions. [ABSTRACT FROM AUTHOR]

The global gold ore grade has been decreasing, and the mineralogy is now more diverse and complex. This has necessitated the utilization of low-grade ores previously not used. During the cyanidation process of such ores, copper cyanide complexes form that are competitively adsorbed with gold onto activated carbon. Therefore, to decrease the amount of copper in the pregnant electrowinning electrolyte, a series of copper adsorption experiments were done to limit the amount of copper that adsorbs onto activated carbon. Tests on selective copper cold stripping were also conducted to selectively elute copper from loaded head carbon before the elution process. The results showed that increasing the solution pH from 9 to 11 decreased the copper adsorption from about 15.1% to 8.2%, but on the other hand the gold adsorption decreased from 98.7% to 95.1%. The optimal determined cold stripping parameters were 2% cyanide strength, 1% sodium hydroxide, 27 g/L carbon concentration and 4 h residence time. This experimental procedure effectively reduced the amount of copper in the gold leaching process and has potential to be used in large-scale applications. [ABSTRACT FROM AUTHOR]

Labuan, Miri, Kundasang and Raub regions of Malaysia have very different geological formations and settings that could result in different levels of natural radioactivity. Hence, this study determines the influence of different geological formations on radioactivity in these locations using field measurements, petrology and geochemistry. A total of 141 gamma dose rates and 227 beta flux measurements were collected using Polimaster survey meters (PM1405) in these four regions. The gamma dose rate values range from 0.37 to 0.05 µSv/h with a mean value of 0.11 µSv/h. Beta flux values range from 3.46 to 0.12 CPS with a mean value of 0.57 CPS. Mineralogy and elemental composition of the different rock types were analysed using thin-section petrography, XRD, ICP and pXRF methods. Felsic igneous rocks such as syenite and granite have higher natural radioactivity and contain more radionuclide-bearing minerals such as apatite, zircon, allanite, K-feldspar, titanite, muscovite and biotite. Metamorphic rocks have the second highest natural radioactivity and contain fewer radioactive minerals. The natural radioactivity of sedimentary rocks mostly depends on their clay content. The gamma dose rate maps show that igneous and metamorphic regions around Raub have higher radioactivity compared to the sedimentary-dominated regions around Miri and Labuan. Annual effective dose (AED) and excess lifetime cancer risk (ELCR) were calculated to evaluate the potential health risk for inhabitants of these regions. Labuan and Miri are considered to be safe zones with respect to natural radioactivity as the results show little to no risk for the public, compared with the Raub region, which is medium to high risk. [ABSTRACT FROM AUTHOR]

Clay-type Li deposits are poised to play a pivotal role in addressing the surging global demand for Li. The McDermitt clay-type Li deposit, located in Nevada, is the largest Li deposit in the United States, with Li hosted by a clay-rich sequence of smectite-dominated intervals and illite-dominated intervals, respectively. However, the occurrence of Li and the genesis of Li-bearing minerals within smectite-dominated intervals have not been thoroughly investigated in previous research. Here, we studied the mineralogy, the in-situ Li distribution, and the bonding environments of Li within the smectite intervals using a combination of instrumental techniques including scanning electron microscope, transmission electron microscope, time-of-flight secondary ion mass spectrometry, and nuclear magnetic resonance. Our results indicate that the smectite exhibits low crystallinity characteristics of lacustrine clay authigenesis and is commonly found to fill the interstices among volcanic minerals or envelop them; Li is mainly hosted by Mg-smectite rather than the volcanic minerals. Within the tuffaceous sediment samples, the volcanic glass has undergone a transformation, resulting in its complete disappearance and alteration into clay minerals. Owing to the octahedral sites of Mg-smectite bounded in Li, it is referred to be hectorite. We interpret that the hectorite's precipitation occurs in a high saline-alkaline water environment, a result of McDermitt tuff dissolution. This conclusion can be supported by the coexistence of spherulitic calcite and hectorite. Overall, this study confirms hectorite as the main Li-bearing mineral and increases the understanding of the genetic model of hectorite formation in intracontinental caldera basins. [ABSTRACT FROM AUTHOR]

New data favor the view previously substantiated by geological, geochemical and isotopic data that the orebodies of the Belogorskoe deposit are the Triassic erosion products of the laterite weathering crust after gabbroids, which were metamorphosed and partially regenerated in the Late Cretaceous–Paleogene. The source for the formation of the Belogorskoe deposit was shown to be the products of exogenic destruction of rocks, the isotopic and geochemical characteristics of which are close to those of Cambrian gabbroids of the Vladimiro-Aleksandrovsky massif (southern part of the Okrainsko-Sergeevsky terrane). It has been found that the Belogorskoe deposit consists of rocks and ores, the primary (magmatic) REE distribution in which was variably modified as a result of interaction between sediments (protoliths) and seawater (presumably during the Late Jurassic–Early Cretaceous accretion), as well as between their metamorphosed analogues and hydrothermal solutions (in the Late Cretaceous–Paleogene). The influence of gabbroids (as a source of material) on the chemical and mineral composition of the Belogorskoe deposit agrees with the data reported in a paper on the enrichment of orebodies in such elements as Fe and Mn characteristic of ultramafic rocks and the presence of Au–Ag–Pd–Pt, Ni–Co, and Bi mineralization in them. The orebodies of the Belogorskoe deposit contain accessory minerals and mineral varieties that are rare in nature and poorly studied. They include an unusually Th-rich variety of zircon, baddeleyite, gudmundite, a large group of bismuth compounds, including Bi2Te, (Ag,Pb)BiS2, as well as coloradoite, lafossaite, sanbornite, perovskite, and the compound InPO4. There is also a large group of rare and unusual noble metal compounds: copper gold, platinum gold, jonassonite, disordered solid solutions of Cu, Ag and Au (Au-based), Pt–Pd, Pt–Ag intermetallides, and other rare minerals and mineral varieties. [ABSTRACT FROM AUTHOR]

The mineralogy of some carbonate rocks from the Abakaliki Basin has been investigated to determine the depositional environment classification and assess the suitability of the rocks for application in geotechnical construction and industrial process systems. The method of investigation included field mapping and petrographic and geochemical techniques to characterize their field characteristics, mineral types and texture and chemical contents. Mapping revealed two lithologic units of sandstone and shale that associate with the carbonates in a similar sequence. The carbonates contain fossils and are composed of calcite, quartz and rockclasts. The grains have angular to sub-rounded sphericity and are dispersed in hetereolithic groundmass. The major oxide composition shows average value of 32.30wt% SiO2, 26.37wt% CaO, 7.23wt% MgO, 6.56wt% Fe2O3, 4.38wt% Al2O3, and 3.23wt% K2O + Na2O in decreasing order of abundance. Concentrations of trace elements are significantly higher (> 100 ppm) for V, Cr, Sr, Zr, Cu, Ba, Pb and Zn and comparatively lower for Sb, Ge, Ce, Y, As, Hg, Tiand Au. The studied rocks qualify as biomicrite or wackestone and range from dolomitic, through carbonaceous to siliceous limestone deposited in a wide spectrum of environment from shallow marine to transitional setting. The rocks are marginally suitable for use as aggregates due to the presence of deleterious contents of quartz and organics. For cement production, their low content of CaO, relatively high SiO2, comparatively high LOI and elevated abundances of contaminant heavy elements are major limitations. Similarly, in paper, plastic, paint, metallurgy and pharmaceutics, the rocks are unsuitable due to the constituent minerals. [ABSTRACT FROM AUTHOR]

The depositional ages and provenance of the Paleozoic Araba and Naqus Formations along the northern Gondwanan margin in Egypt have remained uncertain due to a lack of index fossils. Resolving this issue is crucial for understanding regional geology during deposition and subsequent tectonic development. We integrate detailed facies analysis, anisotropy of magnetic susceptibility (AMS), paleomagnetism, and mineralogical data to elucidate the genesis and depositional ages of the Araba and Naqus Formations. Petrographic analyses identified seven distinct facies types, providing insights into sedimentary textures, maturity, and sources, with contributions from igneous and metamorphic sources indicated by heavy minerals. X-ray diffraction (XRD) analysis identified accessory minerals such as quartz, goethite, kaolinite, hematite, and anatase. Paleomagnetism isolated two magnetic components (CA and CN) providing the first robust paleo pole positions at Lat. = 70.8° N, Long. = 308.2° E and Lat. = 37.8° N, Long. = 233.1° E, indicating Cambrian and Carboniferous ages for the Araba and Naqus formations, respectively. Thermal demagnetization constrained these dates using established polarity timescales. Mineralogical data indicated that the Araba Formation originated from an igneous source, while the Naqus Formation had a mixed metamorphic-igneous provenance. The integrated AMS and paleomagnetic data reveal evidence of post-depositional deformation. Specifically, the clustering of maximum AMS axes in the NW–SE direction for both formations, suggests the initial presence of a primary depositional fabric. However, prevalent tectonic activity during the Cenozoic appears to have overprinted and modified this fabric through deformation related to rifting of the Gulf of Suez region. Through this novel multi-proxy approach, we have resolved long-standing uncertainties regarding the formations' depositional ages. Our study thereby provides the first chronostratigraphic framework for these strategically important sedimentary units, significantly advancing understanding of regional Paleozoic geology. [ABSTRACT FROM AUTHOR]

To support the role of proximal and remote sensing in geological rare earth element (REE) resource exploration, we studied the reflectance spectroscopy of synthetic single- and mixed-REE phosphate phases. Synthesis yielded monazite for the elements La to Gd, and xenotime for Dy to Lu and Y. Visible-to-shortwave infrared (350–2500 nm) reflectance spectra of synthetic single-REE monazites and xenotimes can be used to identify the ions responsible for the absorption features in natural monazites and xenotimes. Nd3+, Pr3+ and Sm3+ produce the main absorption features in monazites. In natural xenotime, Dy3+, Er3+, Ho3+ and Tb3+ ions cause the prevalent absorptions. The majority of the REE-related absorption features are due to photons exciting electrons within the 4f subshell of the trivalent lanthanide ions to elevated energy levels resulting from spin-orbit coupling. There are small (< 20 nm) shifts in the wavelengths of these absorptions depending on the nature of the ligands. The energy levels are further split by crystal field effects, manifested in the reflectance spectra as closely spaced (∼ 5–20 nm) multiplets within the larger absorption features. Superimposed on the electronic absorptions are vibrational absorptions in the H2O molecule or within [OH]−, [CO3]2− and [PO4]3− functional groups, but so far only the carbonate-related spectral features seem usable as a diagnostic tool in REE-bearing minerals. Altogether, our study creates a strengthened knowledge base for detection of REE using reflectance spectroscopy and provides a starting point for the identification of REE and their host minerals in mineral resources by means of hyperspectral methods. [ABSTRACT FROM AUTHOR]

Hybridization of the lunar mantle during the overturn (sinking) of Fe- and Ti–rich ilmenite-bearing clinopyroxenite cumulates (IBC) in the lunar interior is called upon to explain the high TiO2 abundances of lunar basalts. Chemical reactions that occur after juxtaposition of IBC and mantle peridotite are poorly constrained. We experimentally investigated these reactions in experiments that adjoin an IBC glass against presynthesized dunite in a reaction couple at temperatures of 1100–1300 °C and pressures of 0.5–2.02 GPa for 0.33–31.66 h. These conditions produced experiments near to well above the solidus temperature of the IBC. Near solidus experiments produce garnet in the IBC at 2 GPa. Supersolidus experiments exhibit dissolution of olivine material into the IBC melt and the formation of clinopyroxene at the IBC melt-dunite interface. Dunite dissolution is attributed to the olivine undersaturated composition of the IBC melt. In both near- and supersolidus experiments, compositional variations produced by solid-state diffusion across the IBC melt-dunite interface are observed. When pressure increases, temperature decreases, or IBC melts become closer to olivine saturation, dissolution slows, and the effects of solid-state diffusion in the dunite become more evident. Similar chemical exchange reactions would occur in the lunar mantle as downwelling IBC and lunar peridotites are juxtaposed by cumulate overturn. Hybridized lunar mantle sources are expected to contain 47–84% normative peridotite and 16–53% IBC. Simple numerical simulations suggest that in addition to dissolution–precipitation reactions, mechanical mixing may be required to produce volumetrically significant hybridized mantle sources over geologically-relevant timescales. [ABSTRACT FROM AUTHOR]

Understanding the characteristics of modern floodplain sediment (MFS) is important for geomorphological, paleoclimatic, sedimentation, and environmental investigations. We collected samples from present floodplain Nile sediments in Egypt's Sohag area and used mineralogical and geochemical (i.e., major and trace elements) proxies to investigate the characteristics and establish their provenances, climatic conditions during deposition, and weathering influence. The study revealed that the Nile floodplain sediments are composed mainly of silt (26–77%), clay fraction (7–44%), and sand content (3–63%), and their texture is classified as clayey silt. These sediments are classified geochemically as greywacke to shale. The mineralogical studies revealed two main assemblages of heavy minerals: the first assemblage represented by magnetite, goethite, zircon, epidote, and garnet and reflects the basement complex in the Eastern Desert and its surrounding rocks; and the second assemblage of goethite, pyroxene, hornblend, and mica of fooldplain deposits derived from the Ethiopian highlands. The geochemical studies indicate that the Nile sediments are immature and formed due to the moderate degree and nonsteady chemical weathering of the parent rocks. The geochemical studies show different mixed sources of sediments, where fine sediments are mostly mafic igneous with a partial contribution from siliscic sedimentary rocks, while the coarser ones are derived mainly from siliscic sedimentary and acidic igneous rocks. The sediments of the presented modern fooldplain reflected two different tectonic setting source areas (collision and continental rift tectonic setting for high silica and low silica samples, respectively) that were shared in supplying the sediments to the present basin. The study revealed that the investigated area may become desertified as a result of climate change and human activities such as salinity, fertiliser use, sand encroachment, and pollution. [ABSTRACT FROM AUTHOR]

Topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are referred to microtopographies. In hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physicochemical, and geochemical attributes of profiles were analyzed. The results showed that from the summit to the toeslope, soil thickness increased significantly and profile configuration changed from A–C to A–B–C. The total contents of Ca and Na decreased at the summit, backslope, and footslope, while the total contents of Al, Fe and Mg showed an opposite trend. On the summit and shoulder of the hillslope, weathered materials were transported away by gravity and surface erosion, exposing new rocks. As a result, soil development in these areas was relatively weak. In flat areas such as the footslope and toeslope with sufficient water conditions, the addition of weathered components and the prolonged contact between water, soil, and sediment led to further chemical weathering, resulting in highly developed characteristics. Microtopography may influence physicochemical properties, chemical weathering, and redistribution of water and materials, causing variations in pedogenic characteristics at different slope positions. [ABSTRACT FROM AUTHOR]

The Orne River, a tributary of the Moselle River, was highly impacted by industrial activities for more than one century. Land use along the Orne River is highly contrasted, with local specificity from its source to its junction with the Moselle River. The intense industrial activity left behind tons of steelmaking wastes (SMW) on the land surface and within the Orne riverbed. To assess the sources of particulate Zn and Pb transported as suspended sediment in the Orne River, different sets of samples from likely Zn- and Pb-bearing particle sources within the Orne watershed were collected. Three sets of samples were taken from potential sources representing detrital, urban, and inherited industrial particles. Mineralogy, element contents, and Zn and Pb isotope compositions were obtained to characterize and reveal the fingerprint of each set of samples. Soil samples were collected on distinct geomorphological areas characterized by different soil types and land uses. They all display detrital minerals assigned to the geological background. Urban dusts and steelmaking residues display specific mineral phases (sulfates and iron oxides, respectively). Element compositions present strong discrepancies between the distinct sets of samples. SMWs are particularly enriched in Fe, Zn, and Pb. Concerning isotopic composition, SMWs exhibit δ66Zn values ranging from − 0.67 to 1.66‰. Urban samples display δ66Zn values between − 0.11 and 0.13‰, and soils present δ66Zn values between − 0.24 and 0.47‰. The 206Pb/204Pb ratio was estimated to range from 17.550 to 18.807 for soils, from 17.973 to 18.219 for urban samples, and from 18.313 to 18.826 for SMWs. For each of the three sets of samples (soils, urban, industrial), variations of geochemical fingerprint were observed. For soils, the relatively large variations of Zn and Pb isotopic compositions were attributed to distinct land use and the contribution of atmospheric deposition. For industrial samples, the variations were more intense and may be attributed either to distinct industrial processes in the production of pig iron or to distinct furnace-flume treatment modes. The three sets of samples (urban, industrial, and detrital) could be distinguished based on Zn and Pb contents and isotopes. Finally, this study not only highlighted the sources that released particulate Zn and Pb into the Orne River system, it also demonstrated that urban particles are well defined in terms of Zn and Pb isotopic signatures, and those isotopic signatures could be extrapolated to other case studies. [ABSTRACT FROM AUTHOR]

Despite the wide use of greenschists as a building stone, few studies have been conducted on their resistance to both physical and chemical weathering processes. The present study investigates the petrographic and physico-mechanical characteristics of the Abrangi building greenschist from Iran. In addition, it evaluates the resistance of the stone to three simulated weathering tests, including salt crystallization, frost action, and acid solution. The loss in integrity and esthetic damage caused by simulated weathering tests are quantified using P-wave velocity and colorimetry tests. Moreover, fluorescence microscopy (crack studies) and SEM–EDX techniques are applied to investigate the evolution of stone fabric caused by salt crystallization and wetting–drying in an acid solution, respectively. The results showed the quality of Abrangi greenschist is controlled by its compositionally banded texture. Mechanical damage was localized in tremolite-rich bands. Meanwhile, chemical decay was observed in granoblastic bands, where calcite and epidote were embedded within the bands. Furthermore, it was observed that tremolite-rich bands were highly damaged when the compressive stress was applied in the direction parallel to the longitudinal axis of the fibers. However, fiber bundles were cleaved into thinner or single fibers by applying the tensile stress perpendicular to the longitudinal axis of the fibers. It is noteworthy that this tensile strength is induced by the Brazilian tensile strength tester and salt crystallization weathering test. Wetting–drying in sulfuric acid caused the formation and accumulation of gypsum crystals on etched calcite and epidote crystals or adjacent voids in granoblastic bands. Highlights: The resistance of the greenschist to physical and chemical simulated weathering tests is evaluated. Petrographic and SEM techniques were used to identify greenschist quality. Fibrous bands were more susceptible to salt decay than granoblastic bands. Chemical decay is localized in granoblastic bands. Salt crystallization has the most intense impact on color, P-wave velocity, and anisotropy [ABSTRACT FROM AUTHOR]

This research contributes to the knowledge of the geothermal area of the Nevado del Ruiz Volcano (Colombia) by analyzing the secondary permeability and connectivity of fractures at microstructural and macrostructural level. Although the Nevado del Ruiz Volcano (NRV) area has had geothermal exploration studies for power generation since 1968, there is still no exploitation of its geothermal resources. The NRV geothermal reservoir is characterized by a low primary permeability and the presence of several geological faults crossing a tectonically active and complex region. The analysis was performed comparing a zone affected by intense faulting with another one characterized by the same lithology, but with less influence of faulting and located further from the volcano. Fractures were characterized at outcrops with the window sampling method, and petrographic analysis was performed to confirm the mineralogy of samples collected. At the microstructural scale it was found that faulting does not necessarily influence the interconnectivity of fractures, but it does influence their intensity, quantity, and strike. To analyze the influence of fractures on groundwater flow, it is suggested to consider three main aspects: secondary permeability, connectivity, and fracture intensity. The lithology of major geothermal interest in the NVR area (Pes) presented greater connectivity and fracture intensity, which, combined with the high foliation observed in field, increase its effective permeability. The secondary permeability of different lithologies in the NRV area ranged between 1.15 × 10–6 and 10.32 × 10–7 m2. Most of the hot springs were in areas of high macrostructural connectivity, supporting the idea that groundwater flow is dominated by the secondary permeability of rocks. Estimation of the secondary permeability and identification of areas of high fracturing and connectivity, contributes to the understanding of the NRV geothermal area, which is a key aspect when drilling for successful well production. The methodology presented is useful in the initial exploration phase in fractured geothermal reservoirs. [ABSTRACT FROM AUTHOR]

Serpulids are the only polychaetes in which all species secrete calcium carbonate tubes. Some serpulid lineages, such as species in the genus Spirobranchus, possess a second kind of hard-calcified part—the operculum. The tube and operculum microstructure and mineralogy are highly variable among serpulid species, but this type of information is still scarce for some species. Furthermore, comparing the microstructure and mineralogical composition of species from warm and temperate waters helps to determine which are more susceptible to the effects of climate change. Therefore, the aim of this study is to determine and describe the microstructure and mineralogical composition of the tubes and opercula of three Spirobranchus species from warm and temperate waters of the Mexican Pacific. The microstructures of the two hard structures were analyzed with a scanning microscope and complemented by X-ray computed nanotomography; the mineralogy was determined by X-ray diffractometry. The tubes of the three species had two layers—inner and outer—and five microstructures were found in the tubes. Numerous pores cover the operculum of all three species and have an irregularly oriented prismatic (IOP) structure. The tubes of the three species were bimineralic but had different percentages of calcite and aragonite, whereas the opercula were only composed of aragonite. Given the mineralogical characteristics of S. spinosus and because its distribution is only in temperate waters, we may conclude it could probably be the main species negatively affected according to the climate change scenarios predicted for the end of this century. [ABSTRACT FROM AUTHOR]

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]

Portezuelo de Pajas Blancas' primary metasomatic deposits host sapphires that differ in size, colour, and colour distribution through different lithological units. The discovery of sapphire-bearing secondary aeolian placer deposits enabled a detailed analysis of sapphire types to determine the causes of this heterogeneity. Representative single sapphires from the primary and secondary deposits were analysed using various techniques, including SEM-CL, OM-CL, Micro-XRF, Raman spectroscopy, and polarised transmitted light multi-focus optical microscopy. Based on the results, seven sapphire types were identified according to their colours and colour distribution. Fe and Ti concentrations mainly contribute to the colour and micro-textures occurrence. The primary growth textures include cores, progressive, oscillatory, and diffusion zoning, whereas the secondary alteration features correspond to micro-brecciation, re-arrangement, and overgrowth. Inclusions such as euhedral andalusite, anhedral anhydrite, and anhedral rutile were identified in the sapphires. The formation of Portezuelo de Pajas Blancas sapphires can be divided into five genetic stages: (i) core growth development; (ii) chemical imbalance due to open system behaviour that produces progressive and oscillatory zoning; (iii) low-temperature deformations that produce micro-brecciation; (iv) re-arrangement of pre-formed sapphire fragments and subsequent sapphire overgrowth; (v) diffusion zoning that produce Fe- and Ti-enriched outer rims. In conclusion, the Portezuelo de Pajas Blancas' sapphires were formed through at least five stages of oxidised contact metasomatism at varying temperatures and low pressures, where a heterogeneous forming condition predominates during sapphire formation. [ABSTRACT FROM AUTHOR]

The Evevpenta ore occurrence is situated in the northeastern part of the Central Kamchatka volcanic belt (Kamchatka Peninsula, Russia), and lies among andesitic volcanic complexes of the Neogene age. The ore bodies are veins, zones of quartz streaks, and hydrothermal breccias, accompanied by aureoles of argillization which transition into propylites at the periphery. The formation of noble-metal mineralization occurred through two phases: the hypogene (hydrothermal) phase and the hypergene phase. For the hypogene phase we have identified two mineral associations related to noble-metal mineralization: the Central area contains gold—telluride–quartz mineralization, while the Northern area hosts telluride–sulfide–quartz mineralization. The hypergene mineral association with native gold occurs within the Central area only. Based on data relating to the material composition of the ores we show that the Evevpenta ore occurrence is a typical member of epithermal reduction-alkaline or low sulfidation deposits. [ABSTRACT FROM AUTHOR]

Lake Salda is considered the most similar region on Earth to search for evidence of life on Mars, and its shoreline is home to microbialites containing some of the oldest known fossilized records of life on our planet. Understanding the historical process of Mars is also crucial for predicting the future of our planet, given its transition from a watery world to an arid one. In mineralogical studies to be carried out in sensitive areas such as private protected areas, it is a priority not to damage the area, and mineralogical research using remote sensing methods is frequently used in such studies. In this study, the mineralogical characteristics of the geological formations in and around Kocaadalar Burnu peninsula, located in the southwest of Lake Salda, were examined using remote sensing techniques. Mineral studies of Lake Salda were conducted using data from the Hyperion data of the Earth Observation-1 (EO-1) satellite, which can detect in 220 bands between 357 and 2576 nm wavelengths which is capable of hyperspectral sensing. The EO-1 satellite, the first spacecraft of NASA's New Millennium Programme, which operated successfully from its launch in 2000 until the end of its mission in 2017, carried the multispectral Advanced Land Imager and LEISA Atmospheric Corrector sensors, in addition to the Hyperion hyperspectral sensor. The Hyperspectral Material Identification tool in the Tactical Hyperspectral Operations Resource module of the ENVI software, the United States Geological Survey spectral library, and the Adaptive Coherence Estimator algorithm were used in the study. According to the results of this study conducted on the shores of Lake Salda, in addition to the hydromagnesite mineral, the existence of which was previously detected by various researchers, trona, vermiculite, rivadavite and borate minerals such as ulexite, tincalconite and colemanite were also detected. The results of this study have shown that remote sensing methods can make significant contributions to research in special protected areas such as Lake Salda. It is thought that the presence of trona and boron minerals in the region will contribute positively to the understanding of the historical process of Salda Lake. [ABSTRACT FROM AUTHOR]

The geochemical and mineralogical investigations conducted on a core retrieved from a paleolake in Faiyum Depression, Egypt, reveal a variation in two precipitation patterns; these are the Ethiopian African Monsoon (EAM) at the Nile Headwaters and the Mediterranean winter rains. The heavy mineral assemblage, and the geochemical characteristics, exhibit significant shifts in clastic input to the paleolake. These variations suggest shifting in the sources of sediment, with an East African origin during the African Humid Period (AHP) and in the Late Holocene, and a White Nile source during the Late Pleistocene and Middle Holocene. Geochemical data is additionally utilized in the determination of variations in the properties of the paleo-water (paleo-salinity and paleo-productivity). The paleo-water of Faiyum Lake exhibited characteristics of a substantial freshwater body during the Early to Mid-Holocene. During the subsequent period, there was a sudden drop in the lake level, accompanied by a subsequent rise in salinity due to hydrological modifications. [ABSTRACT FROM AUTHOR]

The investigation of volcano-sedimentary rocks situated to the west of the Cretaceous Babouri-Figuil basin involved a comprehensive characterization encompassing petrography, mineralogy, and geochemistry. The sedimentary formations were classified into four distinct facies: coarse sandstones, medium sandstones, fine sandstones, and schistose marls. Additionally, post-sedimentary lava flows composed of andesitic basalts were identified. Petrographic analysis revealed quartz as the predominant constituent in the sedimentary rocks. The volcanic rocks exhibited two distinct textures: a microlitic porphyritic texture, featuring oxides, plagioclase phenocrysts, and clinopyroxenes, and a doleritic porphyritic texture, wherein the rock volume comprised 10–15% automorphic plagioclase phenocrysts (1 to 3.6 mm), 20% clinopyroxenes (1.5 mm), 2–7% oxide crystals (less than 1 mm), 2% olivines, and approximately 1% amphibole phenocrysts (> 1 mm). The identified mineral phases were categorized into two groups: primary minerals (calcite, feldspar, quartz, muscovite) and secondary minerals (kaolinite, illite, smectite), along with titanium oxides, anatase, hydrated sodium silicates, and analcime. Geochemical analysis of the basalts indicated their classification as oceanic tholeiites, suggesting a composition of andesitic basalts emplaced within an orogenic setting. The Mayo Mbota sediments were categorized as intermediate to acidic rocks associated with active continental margins, deposited in an arid to semi-arid environment. These sediments were derived from the accumulation of alteration products of felsic rocks. [ABSTRACT FROM AUTHOR]

Jinchanghe is a Zn-Pb-Fe-Cu skarn deposit in the northern Baoshan block, southwestern China. It is a typical distal skarn deposit with orebodies in the Cambrian Hetaoping Formation limestone and calcareous siltstone. The skarn minerals display a vertical zonation with garnet skarn in the lower part and pyroxene skarn in the upper part. Economic metals are also zoned with Fe at the base, Cu in the middle, and Zn-Pb in the upper part. The skarn formation and Zn-Pb-Fe-Cu mineralization is divided into four paragenetic stages: a pre-ore stage dominated by prograde garnet and pyroxene, an oxide stage represented by Fe mineralization associated with retrograde ilvaite, actinolite and epidote alteration, a sulfide stage characterized with Cu–Zn-Pb sulfides, and a post-ore stage with barren calcite, quartz and chlorite. Fluid inclusion microthermometry indicates that the hydrothermal fluids of the Jinchanghe skarn system evolved from the pre-ore stage (450–480 °C and 11.7–15.5 °C wt% NaCl equiv), through the oxide stage (230–280 °C and 6.5–12.2 wt% NaCl equiv), the sulfide stage (190–230 °C and 1.3–10.3 wt% NaCl equiv), and eventually to the post-ore stage (120–180 °C and 1.6–4.6 wt% NaCl equiv). Correspondingly, the δ18Ofluid values decrease from 1.8–7.1‰ to 1.0–6.4‰, -1.0 to 1.3‰, and -3.6 to -1.4‰. This indicates that the pre-ore fluids comprise a magmatic component but mixed with some meteoric water, and in the later stages meteoric water has become dominant in the hydrothermal system. Zinc and sulfur isotope compositions reveal that the Zn and S forming the sulfides have a dominantly magmatic origin. The coupled decreases of fluid temperature, salinity, and δ18Ofluid values during the mineralization indicate simultaneous mixing with meteoric water and ore precipitation, suggesting that fluid mixing was critical in ore deposition. The gradual increase of δ13CCO2 values in equilibrium with the hydrothermal calcite (-5.2 to -1.6‰) from the sulfide stage to the post-ore is attributed to the reaction between the fluids and the carbonate wallrocks, implying a role that fluid-rock interaction has taken in the sulfide deposition. Fluid mixing and fluid-carbonate reaction are the two major factors controlling the formation of the Jinchanghe deposit. [ABSTRACT FROM AUTHOR]

Sedimentary rock–hosted stratiform copper deposits are the world's second largest source of copper and the largest source of cobalt, with about 73% of the copper occurring in two basins: the Katangan Basin (Central African Copperbelt) and the Permian Basin (Kupferschiefer). Why these two sedimentary basins are so highly endowed in copper is puzzling because sedimentary rock–hosted stratiform copper deposits have formed since the Paleoproterozoic and they all share remarkably similar ore mineralogy, host-rock characteristics and basin settings. We suggest that this discrepancy is due to the development of these two basins close to the bases of ~ 8000-km-long supermountain belts. The supermountain belts were instrumental in raising oxygen levels in Earth's atmosphere, as well as providing a voluminous source of groundwater and a powerful and long-lived driver for the fluid-flow system. The elevated oxygen levels facilitated the diagenetic processes that converted copper-bearing labile minerals to amorphous iron-oxides and smectite and then in turn to hematite and illite. When oxidized brines flushed through the basin successions, the liberated copper was transported to units containing carbon-rich mudstone and the metals were deposited. For the Katangan Basin, development of the Transgondwanan supermountain belt along its margins between about 525 and 510 Ma explains the delay of several hundreds of millions of years between basin formation and mineralization in the Central African Copperbelt. In contrast, development of the Mid-Pangean supermountain belt formed penecontemporaneous with the Permian Basin explains the similarity in timing between basin formation and mineralization in the Kupferschiefer. [ABSTRACT FROM AUTHOR]

The current study was conducted within the context of the Holocene era in Sebkha El-Guettiate, located in southeastern Tunisia. The aim was to determine the factors influencing the geochemical and mineralogical composition of sediments and to elucidate the sedimentary characteristics of the Holocene within the Sebkha core. We examined a sediment core extending 100 cm from this Sebkha, subjecting it to comprehensive analysis to uncover its sedimentological, mineralogical, and geochemical properties. Several techniques were employed to strengthen and validate the connections between geochemical and mineralogical analyses, including X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and infrared (IR) spectroscopy, among others. Furthermore, statistical analyses utilizing principal component analysis (PCA) were applied to the results of the geochemical and mineralogical studies, aiding in the identification of patterns and relationships. A comprehensive mineralogical assessment of the core’s sediments revealed the presence and interpretation of carbonate minerals, evaporite minerals, and detrital minerals. Through the application of infrared (IR) spectrometer techniques to all sediment samples, we gained insight into the mineralogical components and the distribution of key elements such as quartz, kaolinite, calcite, feldspar, and organic carbon. The geochemical composition demonstrated a clear dominance of silica (SiO2), accompanied by fluctuations in carbonate percentages (CaCO3). The prominent major elements, primarily magnesium (Mg) and calcium (Ca) originating from dolomitization, sodium (Na) and chlorine (Cl) from halite, and calcium (Ca) from gypsum, exhibited varying levels. Results from Rock–Eval 6 pyrolysis indicated that the organic matter within the sediments is generally a mixture of terrestrial and aquatic origins. This study provides practical information that underscores the diverse origins contributing to Sebkha sediment formation, often influenced by saline systems. [ABSTRACT FROM AUTHOR]

Mineral dust is transported over long distances from desert sources, interacting with Earth environments. The mineralogy and microstructures of individual dust particles are required to understand the interactions. Here, I summarize recent findings from electron microscopy of dust particles, focusing on Asian and Saharan dust. Dust particles are heterogeneous mixtures of clay and nonclay minerals. Clay minerals account for more than half of the mass of mineral dust. Fine grains of clay minerals form their own aggregates, coat coarse nonclay minerals, or become a matrix of composite particles. The most abundant clay minerals are illite‒smectite series clay minerals (ISCMs) dominated by illite and interstratified illite‒smectite. Saharan dust is distinct from Asian dust by the high contents of palygorskite and hexagonal kaolinite. Common nonclay silicates are quartz, K-feldspar, and Na-rich plagioclase. Amorphous silica is associated with clays in Saharan dust. Calcite occurs as nanofibers as well as coarse grains, reacting with atmospheric acids to precipitate gypsum. The submicron grains of iron oxides and titanium oxides are scattered through the fine matrix of dust particles. ISCMs, chlorite, biotite, and iron oxides are iron carriers to remote ecosystems. The shapes of dust particles approximate ellipsoids whose aspect ratios increase with clay contents. The mineralogical classification of dust particles has led to the determination of the bulk mineral composition of a very small quantity of samples. The constituent mineralogy of dust particles is discussed in an environmental context with a brief introduction of the geological backgrounds of the minerals in their source areas. [ABSTRACT FROM AUTHOR]

The ABM deposit is a bimodal-felsic, replacement-style volcanogenic massive sulfide deposit (VMS) that is hosted by back-arc affinity rocks of the Yukon–Tanana terrane in the Finlayson Lake VMS district, Yukon, Canada. Massive sulfide zones occur as stacked and stratabound lenses subparallel to the volcanic stratigraphy, surrounded by pervasive white mica and/or chlorite alteration. Remnant clasts of volcanic rocks and preserved bedding occur locally within the massive sulfide lenses and indicate that mineralization formed through subseafloor replacement of pre-existing strata. Three mineral assemblages occur at the ABM deposit: (1) a pyrite–chalcopyrite–magnetite–pyrrhotite assemblage that is associated with Cu–Bi–Se–Co-enrichment and occurs at the center of the massive sulfide lenses; (2) a pyrite–sphalerite assemblage, which occurs more commonly towards lens margins and is enriched in Zn–Pb–Ag–Au–Hg–As–Sb–Ba; and (3) a minor assemblage comprising chalcopyrite–pyrrhotite–pyrite stringers associated with pervasive chlorite alteration, which occurs mostly at the sulfide lens margins. Petrographic observations of preserved primary, zone refining, and metamorphic textures in combination with in situ geochemistry show that the pyrite–sphalerite assemblage formed at lower temperatures (< 270 °C) than the other two mineral assemblages (~ 270–350 °C), and that mineral chemistry in all mineral assemblages was affected by greenschist facies metamorphism, although the effects are limited to recrystallization, small-scale remobilization (< 1 m) and trace element redistribution. [ABSTRACT FROM AUTHOR]

The full behaviour of natural clay minerals in soil organic carbon (SOC) stabilization in the presence of oxides and external C inputs is yet unknown. Thus, an incubation experiment was conducted in a sand–clay mixture with different soil clay fractions (SCFs) obtained from Alfisol, Inceptisol, Mollisol, and Vertisol in the presence of wheat residues to compare their C stabilization capacity. The C mineralization rates were higher in 1:1 type dominated SCFs (Alfisol and Inceptisol) compared to 2:1 interstratified mineral dominated SCFs (Vertisol). Wheat residues as C source altered SCFs' abilities to stabilize SOC at only moderate dosages of application (3–12 g kg−1). C mineralization and microbial biomass carbon (MBC) fell by 40% and 30%, respectively, as the amount of clay increased from 7.5 to 40%. However, removing sesquioxides from the SCFs boosted C mineralization and MBC by 22% and 16–32%, respectively, which matched with higher enzymatic activities in the sand–clay mixture. The increased C stabilization capacity of Vertisol-SCF may be attributed to its greater specific surface area (SSA) (506 m2 g−1) and cation exchange capacity (CEC) [meq/100 g]. Regression analysis revealed that SSA, CEC, and enzymatic activity explained approximately 86% of total variations in C mineralization. This study highlighted the critical role of 2:1 expanding clay minerals and sesquioxides in greater stabilization of external C input compared to its 1:1 counterpart. It also implied that the role of mineralogy or texture and sesquioxides levels in different soils (Vertisol, Mollisol, Inceptisol, Alfisol) should be prioritized while adding crop residues to reduce C footprint and enhance sequestration. [ABSTRACT FROM AUTHOR]

The Lichi volcanics are a suite of mafic-intermediate-felsic rocks and are considered coeval with the Abor volcanics (~132 Ma) of the Siang window in the Eastern Himalaya. Here, we present the first report of trachytic rocks from the Lichi volcanics, which are exposed in the Ranga valley, along the Kimin-Yazali road section in the Eastern Himalayan Region, Northeast India. The trachytes occur in close association with sandstones of the Gondwana Group of rocks and are characterised based on field, petrographical, and geochemical investigations. These fine-grained trachytes are composed of alkali feldspar, biotite, plagioclase, sodic-amphibole, apatite, illmenite, and titanite. The REE profiles of the evolved trachytic rocks (higher SiO2 content) display fractionated trends. The fractionation of accessory mineral phases, like apatite and titanite, was possibly responsible for the strongly fractionated REE patterns of the evolved samples. The trachytic rocks demonstrate high apatite saturation temperatures of 988 ± 14 °C (1σ, n = 8). The Aluminium Saturation Index (< 1.1) and binary discrimination diagrams of these peralkaline trachytes define their affinity with A-type granitoids. Elemental ratios like Y/Nb, Nb/U, and Ce/Pb signify that the Lichi trachytes are differentiated products of mantle-derived ocean island basalts. Trace elemental discrimination diagrams Th/Yb versus Nb/Yb, Y versus Nb, and Y + Nb versus Rb reflect a within-plate tectonic regime for the trachytes. From the results presented in this work, we infer that the development of rifting events during the breakup of eastern Gondwana due to the onset of Kerguelen plume activity further led to underplating of basic magma in lower crustal levels. These parental basaltic magmas underwent fractionation processes forming differentiated trachyandesites and trachytes. Taking into consideration the similarities recorded between the Lichi volcanics and Abor volcanics, this study supports the idea that Kerguelen plume activities resulted in the emplacement of these volcanics in the Eastern Himalayas. [ABSTRACT FROM AUTHOR]

In the south Eastern Desert of Egypt, two contrasting types of magmatism (mafic and felsic) are recorded in the Wadi Kalalat area, and form the Gabal El Motaghiarat and Gabal Batuga intrusions, respectively. The two intrusions post-dates ophiolitic and arc associations represented by serpentinite and metagabbro-diorite, respectively. The mafic intrusion has a basal ultramafic member represented by fresh peridotite, which is followed upward by olivine gabbro and anorthositic or leucogabbro. This mafic intrusion pertains to the Alaskan-type mafic–ultramafic intrusions in the Arabian–Nubian Shield (ANS) being of tholeiitic nature and emplaced in a typical arc setting. On the other hand, the Gabal Batuga intrusion comprises three varieties of fresh A-type granites of high K-calc alkaline nature, which is peraluminous and garnet-bearing in parts. A narrow thermal aureole in the olivine gabbro of the mafic intrusion was developed due to the intrusion of the Batuga granites. This results in the development of a hornfelsic melagabbro variety in which the composition changed from tholeiitic to a calc-alkaline composition due to the addition of SiO2, Al2O3, alkalis, lithosphile elements (LILEs) such as Rb (70 ppm) and Y (28 ppm) from the felsic intrusion. Outside the thermal aureole, Rb amounts 2–8 ppm and Y lies in the range < 2–6 ppm. It is believed that the Gabal Batuga felsic intrusion started to emplace during the waning stage of an arc system, with transition from the pre-collisional (i.e., arc setting) to post-collisional and within plate settings. Magma from which the Gabal Batuga granites were fractionated is high-K calc-alkaline giving rise to a typical post-collisional A-type granite (A2-subtype) indicating an origin from an underplating crustal source. Accordingly, it is stressed here that the younger granites in the ANS are not exclusively post-collisional and within-plate but most likely they started to develop before closure of the arc system. The possible source(s) of mafic magmas that resulted in the formation of the two intrusions are discussed. Mineralogical and geochemical data of the post-intrusion dykes (mafic and felsic) suggest typical active continental rift/within-plate settings. [ABSTRACT FROM AUTHOR]

The content of sediment-forming minerals in two cores from the eastern (ANS45-37) and western (ANS45-48) parts of the valley of the Vema Fracture Zone is studied using semiquantitative XRD analysis of bulk powder sediment samples. The mineral composition of deep-sea sediments from the Amazone Cone is also analyzed for comparison. It appeared that the average composition of the terrigenous component of both cores (according to prevailing quartz, secondary mica, plagioclase and potassium feldspar, as well as smectite, chlorite, kaolinite, illite) is quite similar and approximately corresponds to the composition of sediments from the Amazon Cone. The ratio of four clay minerals suggests supply of terrigenous material to the Amazon and Orinoco due to erosion of the Andes and humid tropical weathering in the lower courses of the rivers with further transport of the suspended load to the ocean. This material was transported to the valley of the Vema Fracture Zone due to interplay between gravitational flows from the South American continental slope and current of Antarctic Bottom Water. In addition, data on biogenic calcite (planktic foraminiferal tests, nannofossils) and opal A (radiolarians, sponge spicules) have been obtained. In the study area, several authigenic (diagenetic) minerals are identified. In particular, siderite and greigite are first found in the sediments from the Vema valley and Amazon Cone, respectively. [ABSTRACT FROM AUTHOR]