Intraplate basaltic (IPB) lavas of twelve continental regions across the Levant, Arabian Peninsula and Ethiopia are evaluated using a dataset of 957 published analysis. Elemental and Nd-, Sr- and Pb-isotope data reveal the anomalous compositions of most of the regions in the context of global continental intraplate basalts (CIB). The analysis is performed by generating compositional profiles normalized to a recently established worldwide average IPB composition (WLD), and benchmarking the distributions using CIB, average ocean island basalts (OIB) and average Europe- Middle East and Africa (EMA) and normal mid-ocean ridge basalt (N-MORB) reference points. Representing ternary elemental and isotope values and ratio relationships in two dimensions assists in discriminating between the basalts of the studied regions. The analysis reveals that ten of the twelve studied regions have closer elemental and isotopic similarities with OIB rather than CIB, particularly so for basalts from Afar, Ethiopia, Harrat Rahat and Harrat Lunayyir. Outlying compositions suggest that some crustal contamination is involved but the established compositional distributions are indicative of the influence of an older heterogeneous, metasomatized mantle source, which has been unaffected by subduction events during the Phanerozoic. Mantle plumes have impacted several of the regions since the Oligocene causing mantle diapirism associated with crustal thinning and slow-spreading rift zones. A model is proposed involving sequential, dynamic, partial melting with melt retention in a rising variably veined mantle to explain the atypical basalt compositions. To adequately characterize these basalt compositions, it is necessary to take account of the observed decoupling in their elemental and isotopic ratio trends.
Antimony (Sb) ore mineralization, hosted in fine-grained siliciclastic sequences, represents a significant but comparatively underexplored class of Sb deposits, which is structurally controlled by major fault systems. The Sb ore deposits are typically hydrothermal in origin and are composed of stibnite-bearing quartz veins. Such vein-type deposits are present in the Pishin-Katawaz belt in the Arambi-Masezai area of the Killa Abdullah District, Pakistan, extending over several kilometers. These ore deposits are hosted in the Late Oligocene–Early Miocene Shaigalu Member of the Khojak Formation, spatially associated with the shear zones along the Chaman Transform Fault. These deposits are characterized by oxidized weathering profiles on surfaces depicting near-surface mineralization. Quartz-calcite veins have varying thicknesses and are variably mineralized. They contain ore minerals stibnite, valentinite and hematite ,and gangue minerals, quartz, muscovite, ankerite, microcline, and vaterite. The Sb mineralization is distributed along fractures, grain boundaries, within larger grains, and as veinlets or disseminated particles. The secondary mobilization of iron-leached zones, calcite veins, and Sb ore are discerned in microscopic studies suggesting multiphase mineralization and later tectonic events. Obtained results indicate high antimony content (up to 50
Hexavalent chromium [Cr(VI)] is a highly mobile and toxic contaminant that is frequently associated with iron (hydr)oxides in natural systems. Under shifts to anoxic and reducing conditions, particularly those characterized by sulfide accumulation, these Cr(VI)-bearing iron (hydr)oxides may react with dissolved sulfide and undergo sulfidation. Elucidating the fate of Cr(VI) during this transformation is essential for predicting chromium mobility and associated environmental risks; however, the mechanisms controlling its persistence, reduction, and potential stabilization remain insufficiently constrained. In this study, we investigate the transformation of Cr(VI)-bearing goethite during sulfidation at circumneutral pH under anoxic conditions, with particular emphasis on chromium repartitioning and retention associated with iron mineral recrystallization. Batch experiments were conducted across a gradient of sulfide concentrations, and reaction products were characterized using aqueous analyses combined with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM)–energy-dispersive X-ray spectroscopy (EDS). Cr(VI) was reduced to Cr(III) upon sulfidation; however, complete reduction was not achieved even under sulfide excess. Instead, sulfide-induced reduction of structural Fe(III) triggered partial recrystallization of goethite, during which chromium was progressively redistributed within the solid phase. XPS revealed that 10.4
The upper continental crust (UCC) is the principal terrestrial reservoir of antimony (Sb) and a major source of Sb to Earth-surface environments, yet its Sb isotopic composition remains poorly constrained. Here, we report high-precision Sb isotope data for representative UCC materials, including granites, granodiorites, sedimentary rocks, loess, and aquatic sediments, and integrate these results with a systematically compiled and inter-standard-normalized literature dataset. Granites and granodiorites display highly variable ε123Sb values, mainly reflecting source heterogeneity rather than fractional crystallization or fluid exsolution. Sedimentary rocks show heavier and more heterogeneous Sb isotopic composition, likely controlled by sediment provenance and depositional environments. In contrast, loess and aquatic sediments define a relatively restricted isotopic range, although aquatic sediments may be further modified by water–sediment interactions. Using two complementary approaches based on crustal rock units and sedimentary proxies, we estimate the Sb isotopic composition of the UCC and recommend a value of ε123Sb = 2.17 ± 0.44 (2SD/ √(n) , n = 56) derived from sedimentary materials. This value is slightly heavier than that of basalts but distinctly lighter than seawater, indicating significant Sb isotope fractionation during continental weathering, transport, and oceanic cycling. These results establish a robust UCC Sb isotopic baseline, providing a critical reference for tracing Sb sources, mobility, and biogeochemical cycling in continental surface environments.
Coal-bearing successions commonly contain volcanic-ash-derived tuff layers that record volcanic material input and subsequent alteration processes, and some of these layers may become enriched in critical metals. However, the mineralogical controls and enrichment mechanisms of Li, Ga, and rare earth elements and yttrium (REY) in such tuff layers remain incompletely understood. We investigated a Late Permian tuff beneath the C25 coal seam in the Mahuanggou Coal Mine, southeastern Chongqing, using major- and trace-element geochemistry, X-ray diffraction (XRD), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS). The tuff is dominated by kaolinite, chlorite, and pyrite, with minor K-feldspar, apatite, anatase, crandallite, and goyazite, and locally contains boehmite and diaspore. High Al2O3, TFe2O3, and TiO2 content, low alkali content, and chemical index of alteration values of 95.07–99.27 record intense dealkalization and Al-rich alteration. Al2O3/TiO2 ratios of 6.68–12.17, together with enrichment in high-field-strength and transition elements, indicate a predominantly mafic volcanic-ash precursor with subordinate intermediate input. The tuff contains 286–1200 μg/g Li (average 496 μg/g) and 163–1068 μg/g total REY (average 744 μg/g) and is also enriched in Ga, Nb, Ta, Zr, and Hf. The detection of Ce in apatite, crandallite, and goyazite identifies phosphate minerals as important, but not necessarily exclusive, REY-bearing phases. By contrast, the inferred associations of Li and Ga with clay minerals and Al-rich assemblages require confirmation by in situ analyses. The evidence supports a multi-stage enrichment model in which mafic volcanic ash supplied the initial metal inventory, marine and relatively oxygen-deficient depositional conditions favored preservation and early retention, and post-depositional alteration–fluid processes promoted differential redistribution and fixation. These results clarify the coupled source-to-fixation controls on critical metals in Late Permian coal-series tuffs of southwestern China.
