Search Results (248)

This paper presents systematic petrological, whole-rock geochemical, and Sr-Nd-Pb isotopic studies on the mafic–ultramafic rocks of the Daaobaogou Ni-Cu sulfide deposit in the Dunhuang Block, Gansu Province. This study aims to reveal the nature of its source region, parent magma composition, and magma evolution processes. The results indicate that the parent magma of the ore-bearing intrusion in Daaobaogou originated from an enriched lithospheric mantle metasomatized by Paleozoic subduction processes. It exhibits high-magnesium characteristics and represents the product of a certain degree of evolution from a primitive magma. The magma evolution underwent significant fractional crystallization, with olivine beginning to crystallize at 1328 °C, following the crystallization sequence: olivine, clinopyroxene, plagioclase, and orthopyroxene. Sr-Nd-Pb isotopes and trace elements indicate that the magma experienced intense crustal contamination (approximately 10–20% upper crust) during its ascent. Full article

The southern margin of the Beishan orogen is a key region hosting mafic–ultramafic intrusions and Cu-Ni sulfide deposits, yet previous studies have focused mainly on the Xinjiang segment, leaving the eastern extension in Gansu Beishan poorly constrained. To constrain the emplacement age, tectonic setting and assimilation–contamination of the mafic–ultramafic intrusions in the Chengxuan area, and to address the research gaps regarding Cu-Ni sulfide mineralization and magmatic evolution, this study conducted systematic petrographic, geochronological, and whole-rock geochemical and isotopic analyses of the Chengxuanbei intrusions. The intrusions are dominated by olivine gabbro and gabbro facies, with the sulfides predominantly hosted in the olivine gabbro and gabbro; zircon U-Pb dating yields a weighted mean age of 283.5 ± 0.85 Ma, corresponding to the Early Permian. The rocks exhibit pronounced negative Nb-Ta and moderate negative Zr-Hf anomalies, indicating magma derivation from partial melting of the mantle wedge metasomatized by subduction fluids, and high-field-strength element diagrams reveal an island arc calc-alkaline basalt affinity, reflecting a subduction-related extensional setting (e.g., back-arc extension) during the Early Permian. The Sr-Nd-Hf isotopes suggest crustal contamination during magma ascent, while the δ³⁴S values indicate input of crust-derived sulfur; the olivine Fo values (79.8–81.0) and Ni contents (573–1320 ppm) indicate sulfide saturation and Ni extraction processes. A regional correlation confirms that the Chengxuanbei intrusion has favorable magmatic Cu-Ni metallogenic conditions and great exploration potential, providing pivotal theoretical support for Early Permian Cu-Ni prospecting in the southern Beishan belt. Full article

Serpentine group minerals, including lizardite, antigorite, and chrysotile, are common gangue minerals in nickel sulfide ores, and exhibit complex and often unexpected wettability that adversely affects flotation efficiency. However, how these serpentine polymorphs differ in surface hydrophobicity is still not well known, making it difficult to explain their distinct flotation behaviors. In this work, molecular dynamics (MD) simulations and experimental contact angle measurements are used to investigate the wettability of the three main serpentine polymorphs. MD simulation results reveal that the contact angles of the lizardite Si–(00$\overline{1}$) surface and Mg–(001) are 78.6° and 71.1°, respectively. Chrysotile exposes the Mg–(001) surface, with a contact angle of 74.9°. The water droplet on the antigorite surface is spread along the SiOH region. Even the Mg–OH-terminated octahedral surfaces of the three serpentine polymorphs can exhibit hydrophobicity, depending on hydroxyl orientation and oxygen bonding configuration. Contact angle measurements show that antigorite (001) is moderately hydrophobic at about 40°, while (020) is highly hydrophilic at about 10°. The combination of Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and hydrophobic interactions between antigorite and air bubbles produces a net attractive force, enabling particle–bubble adhesion. This work provides new insights for controlling serpentine behavior during flotation of copper–nickel ores hosted in ultramafic rocks. Full article

Karst bauxites represent important archives of paleoenvironmental conditions and potential sources of REE and other critical raw materials (CRMs). This study presents a multiproxy investigation of the Upper Eocene Mamutovac-1a bauxite deposit (Croatian Dinarides), integrating petrography, X-ray diffraction (XRD), magnetic susceptibility, whole-rock geochemistry, and aqua regia extractions along a 25.1 m drill core. The deposit shows clear vertical variability defined by four facies-based zones, accompanied by systematic mineralogical and geochemical changes. The bauxite is dominated by böhmite, gibbsite, hematite, and anatase, with subordinate goethite and clay minerals. ΣREE concentrations range from 276 to 670 mg/kg and increase toward the deeper zones, with consistent LREE enrichment relative to HREE, negative Eu anomalies, and variable Ce anomalies. Correlations suggest that REE are likely associated with phosphate phases, with a possible secondary contribution from clay minerals. The integrated dataset indicates a polygenetic, multi-stage evolution involving both in situ bauxitization and episodic reworking and redeposition, controlled by variable redox conditions and fluid–rock interaction. Geochemical signatures suggest a mixed provenance with contributions from intermediate to ultramafic sources. The elevated concentrations and enhanced extractability of selected elements (La, Sc, Ga, V) indicate that the deposit may represent a potential secondary source of CRMs. Full article

Ophicarbonates provide an important natural record of mineral carbonation during serpentinization of ultramafic rocks and therefore offer insight into the mechanisms and limits of CO₂ fixation in low-temperature geological environments. This paper presents a synthesis and process-oriented reinterpretation of stable-isotope published and previously unpublished data, petrographic, and mineralogical evidence for carbonate formation under fluid-limited serpentinization conditions. Using mineralogical constraints together with a compiled δ¹³C–δ¹⁸O dataset that includes legacy measurements from the 1980s–1990s, we evaluate how multi-stage carbonate precipitation reflects evolving water–rock ratio, redox state, transport limitation, and deformation-controlled permeability. Particular attention is given to systematic differences between vein-hosted carbonates and dispersed intergranular or scattered-grain ophicarbonates, as these textural–isotopic relationships help identify fluid flux, carbon source, and reaction progress in ultramafic systems. The analysis shows that carbonation does not proceed uniformly but is restricted to overlapping reactive windows controlled by fluid availability, nucleation kinetics, and permeability evolution. These constraints help explain why carbonation may either intensify or stall during progressive serpentinization. The Author further discuss why kinetic barriers and Mg–Ca partitioning may redirect carbonate mineralogy toward calcite or metastable Mg-rich phases even where dolomite or magnesite may be thermodynamically favored. The results highlight the importance of coupling isotopic signatures with petrographic context in reconstructing carbonation pathways and provide a broader framework for understanding natural mineral sequestration of carbon in heterogeneous serpentinite systems. Full article

This study quantifies the concentrations, spatial patterns, and sources of potentially toxic elements (PTEs) in Fluvisols from the Bosna River floodplain. Total As, Cr, Ni, Cu, Zn, Ba, V, and Co contents locally exceed national thresholds (e.g., As > 15 mg/kg, Cr > 80 mg/kg, Ni > 40 mg/kg), yet Ti-normalised enrichment factors mostly remain in the “no to minor” range (EF ≈ 1–3) and contamination factors in the “low to moderate” range (CF ≈ 1–3), indicating only slight to moderate enrichment even where absolute concentrations are high. Cr, Ni, Co, Ba, and V display similar spatial patterns, strong positive correlations with Mg and Fe, and consistently low EF values, confirming their predominantly geogenic origin linked to ultramafic and mafic parent rocks. In contrast, Cu, Zn, Pb, and Cd form coherent spatial clusters, share positive correlations, and show slightly elevated EF and CF values in flooded soils (typically EF and CF between 1 and 3), indicating diffuse industrial and agricultural inputs superimposed on a strong natural background. Flooding did not uniformly increase PTE concentrations but enhanced spatial heterogeneity and reorganised geochemical associations, particularly for Zn, As, and Cd, while the observed links between inorganic carbon (TIC), Ca, and Mg indicate that carbonate buffering and base cations help constrain metal mobility rather than exert a dominant control on all elements. The novelty of this work lies in integrating Ti-normalised EF and CF referenced to a local Fluvisol background with high-resolution GIS mapping and paired flooded versus control multivariate analysis, providing a quantitative, transferable framework to disentangle geogenic and anthropogenic signals and to prioritise post-flood monitoring of As, Cu, Zn, Pb, and Cd in naturally metal-rich floodplains. Full article

Weathered serpentinites are extreme lithobiontic environments characterized by oligotrophy, high heavy metal content, and desiccation stress; yet, the adaptive mechanisms of colonizing actinobacteria remain poorly understood. This study aimed to isolate and characterize xerotolerant actinobacteria from serpentinite and to profile their secondary metabolites involved in stress tolerance. Three lithobiontic strains were isolated and identified by whole-genome sequencing (dDDH and ANI) as Rhodococcus oxybenzonivorans SK11, Paenarthrobacter nitroguajacolicus SK18, and Rhodococcus qingshengii SK25. Desiccation tolerance was assessed using PEG-8000, siderophore production on CAS agar with metal substitution (Fe³⁺, Al³⁺, Cu²⁺, Ga³⁺), and biosurfactant activity via emulsification assays. Genome mining identified biosynthetic gene clusters for compatible solutes, siderophores, and biosurfactants. All strains maintained viability at 50% PEG. Compatible solute pathways included ectoine (ectABC) in SK18 and SK25, glycine betaine (gbsAB) only in SK18, and trehalose (TreYZ) and proline (ProABC) pathways in all three. Genome mining of Rhodococcus strains revealed a number of NRPS-dependent clusters, some of which are predicted to encode siderophores (rhodochelin, heterobactins), while SK18 used an NRPS-independent desferrioxamine E pathway together with a unique lanthipeptide cluster. Biosurfactant production was condition-dependent, with SK25 achieving complete emulsification (E₂₄ = 100%) in hexadecane-supplemented medium. These findings demonstrate that weathered serpentinite actinobacteria employ an extracellular molecular repertoire of compatible solutes, siderophores, and biosurfactants to survive extreme oligotrophy, desiccation, and metal stress. Full article

Panzhihua-type V–Ti magnetite deposits in the Panxi region are hosted in mafic–ultramafic intrusions, and their exploration potential depends strongly on the deep distribution of ore-bearing intrusions. High-resolution 3D magnetic inversion is an effective tool to image the geometry of these intrusions. Using 1:50,000 aeromagnetic data, we applied an unsupervised deep learning inversion to obtain the 3D magnetic susceptibility structure of related intrusions. The results show that magnetic anomalies are mainly NS and NEE trending, with minor NNW-trending features. NS-trending sources occur in the Baima–Miyi–Hongge zone between the Xigeda–Yuanmou and Anninghe faults, while NEE-trending anomalies lie west of the Xigeda–Yuanmou fault and east of the Chenghai fault. Integrated geological analysis reveals two Late Variscan rift systems: the Anninghe rift and the Panzhihua rift. Deep fault-controlled magma ascent and emplacement, forming the Emeishan large igneous province, are associated with strongly magnetic intrusions. Mantle plume-derived magmas, differentiated in shallow and deep magma chambers, generate well-differentiated layered complexes at depths < 10 km with magnetic intensities of 5–10 A/m. Shear structures within paleorifts provide favorable emplacement conditions and controlled ore localization. We propose a three-in-one ore-controlling mechanism involving rift systems, intrusive rocks, and shear structures for Panzhihua-type V–Ti magnetite mineralization. Full article

Serpentinites and associated chromitites of the Neoproterozoic Bou Azzer ophiolite (Central Anti-Atlas, Morocco) provide key constraints on mantle depletion, melt–rock interaction, and the tectono-metamorphic evolution of a supra-subduction zone (SSZ) system. This study integrates field observations, petrography, Raman spectroscopy, and whole-rock/mineral chemistry to decipher the history of this highly dismembered ultramafic suite. The mantle sequence is dominated by antigorite-bearing serpentinites derived primarily from refractory harzburgitic and dunitic protoliths. Whole-rock geochemistry and highly depleted chromite compositions (Cr# = 0.50–0.68; Mg# = 0.43–0.77; TiO₂ ≤ 0.18 wt.%) demonstrate that these peridotites represent refractory residues formed after high degrees of partial melting (~15–25%). The data delineate a clear evolutionary trend from abyssal to fore-arc and back-arc environments, where infiltrating boninitic melts drove localized podiform chromitite formation through intense melt–rock interaction. Crucially, thermodynamic and mineral–chemical constraints challenge previous models of simple greenschist-facies obduction. Equilibration temperatures exceeding 600 °C and chromite stability within the lower amphibolite to near-granulite facies indicate that the oceanic lithosphere underwent deep subduction prior to its exhumation. This high-temperature, high-pressure metamorphism was followed by multistage retrogressive serpentinization and intense CO₂-rich metasomatism (talc-magnesite alteration) during Pan-African transpressional tectonics. Ultimately, the Bou Azzer ophiolite represents a mature SSZ mantle wedge, recording a complete geodynamic cycle from deep subduction-zone metamorphism to final tectonic emplacement along the northern margin of the West African Craton. Full article

Cr-bearing clay minerals are products of hydrothermal alteration and fluid–rock interactions of ultramafic rocks that form serpentine minerals. Cr is typically observed to substitute for Al in serpentine minerals, but the crystal chemistry and environmental constraints on this substitution are unknown. Here, we synthesized endmember and Cr-substituted amesite, a typical Al-serpentine mineral, via the hydrothermal method. We found that the phase purity highly depends on the pH of the hydrothermal solution, which should be controlled at ~12.7 to avoid the formation of impurity phases. Additionally, amesite can incorporate Cr at a concentration equivalent to ~39.5% substitution of Al. The Cr-free and Cr-substituted amesite are highly defective and contain multiple polytypes, including 6R₂, 2M₁, and possibly 2H₂. However, the relative proportions of these polytypes do not change with increasing chromium substitution. Full article

Diopside–hedenbergite solid solution is the most common clinopyroxene end-member combination in mafic and ultramafic igneous rocks. The crystal structure variety caused by Mg-Fe isomorphous substitution can indicate geological processes such as Mg-Fe isotope fractionation. To explore the effect of Hubbard U correction and Fe content on iron-bearing clinopyroxene structures, we employed GGA and GGA + U to study the lattice constants, unit-cell volume, and average Fe-O bond length of the diopside–hedenbergite solid solution series. On the whole, the results by GGA + U are the increase in lattice constant a (from 9.910 Å to 10.030 Å) and volume (from 456.656 ų to 464.640 ų), the decrease in β angle (from 106.121°to 105.320°), and a slight variation in the lattice constant b (from 9.007 Å to 9.010 Å) with increasing Fe content, which is a better match with the experiment than those by GGA. The average Fe-O bond lengths and polyhedral volumes calculated by GGA and GGA + U both increase with increasing Fe content. The Hubbard U correction significantly affects the lattice constants and unite-cell volume at medium-high Fe content (Fe/(Ca+ Mg + Fe) > 2/8), the Fe-O bond at low Fe content (Fe/(Ca+ Mg + Fe) < 1/8), the bond angle variance, distortion index and quadratic elongation at relatively medium Fe content (1/8 ≤ Fe/(Ca+ Mg + Fe) ≤ 5/16). This study verifies the effectiveness of U-value correction on iron-bearing clinopyroxene and provides a theoretical basis for understanding its structural evolution. Full article

The Middle Tonian tectonic setting of the Jiangnan Orogen, South China, remains intensely debated, and is centered on two competing models: subduction–collision versus mantle plume. This study addresses this critical knowledge gap through an integrated, multi-proxy investigation of the Middle Tonian Fanjingshan Group. This region preserves a continuous volcano-sedimentary and magmatic record, offering key insights into the orogen’s full lifecycle. To test these hypotheses, we employed a synthesis of geological survey, sediment provenance analysis, detrital zircon U-Pb geochronology of clastic rocks to determine sediment provenance and basin evolution, and petrogenetic study of coeval magmatic suites (pillow lava, mafic–ultramafic sills, and granitoids) to evaluate their magmatic processes and tectonic setting. Analysis of 1736 detrital zircon U-Pb ages from Middle Tonian strata reveals a four-stage provenance evolution: (1) SW Yangtze sources in a passive margin basin before 870 Ma; (2) bidirectional sources in an 870–835 Ma arc-derived basin; (3) syn-collisional detritus during 835–820 Ma amalgamation; and (4) post-collisional and northern Yangtze inputs in an 800 Ma rifting basin. Geochemical data from ~845–840 Ma basalts and coeval sills reveal calc-alkaline affinities and marked subduction-fluid signatures. Their calculated mantle potential temperature (1404 °C) is significantly lower than that expected for plume-derived melts (1570 °C), which is consistent with melting in a subduction-modified mantle wedge, supporting a continental rear-arc basin setting. The ~845–832 Ma mafic–ultramafic sills exhibit symmetrical geochemical zoning and two-stage emplacement, recording sustained magma recharge in the rear-arc basin. Furthermore, the ~830 Ma Fanjingshan granite is identified as a crust-derived, syn-collisional S-type granite. Synthesizing these findings, we demonstrate that the sedimentary and magmatic records collectively point to plate margin setting. A four-stage tectonic model is suggested: (1) pre-870 Ma passive margin without significant magmatic activity; (2) 870–835 Ma continental arc development at an active continental margin; (3) 835–820 Ma Yangtze–Cathaysia collision; and (4) post-820 Ma post-orogenic rifting. This work provides a robust regional case study, demonstrating that integrating records of deep magmatic processes with coeval shifts in sedimentary provenance and basin architecture is essential to reconstruct the complete evolution of ancient orogens. Full article

Platinum group elements (PGE) are six rare highly siderophile metals which have similar chemical characteristics and occur together in mineral deposits: platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os). In nature, they tend to exist in a metallic state or bond with sulfur and arsenic and occur as trace accessory minerals predominantly in mafic and ultramafic rocks. High industrial demand together with their scarcity in crustal rocks has been reflected in their inclusion in 2025 US Government’s List of Critical Minerals, European Union’s List of Critical Raw Materials and Mongolian List of 11 Critical Minerals. Although Mongolia is not currently a producer, it hosts four types of potentially economic PGE deposits: (1) Podiform chromitites associated with ophiolites; (2) Ni-Cu-PGE sulfide mineralization of rift-related mafic–ultramafic intrusions; (3) Alaskan–Uralian type arc related zoned mafic–ultramafic intrusions; and (4) Placers. Particularly promising are Permian Ni-Cu-PGE sulfide bearing mafic–ultramafic intrusions of the Khangai large igneous province which bear resemblance to mineralized Permian intrusions in Russia (e.g., Norilsk-Talnakh) and N.W. China (e.g., Kalatongke; Tarim basin). In addition, sub-economic ophiolite-hosted PGE mineralization can be extracted as a by-product during chromite mining. There is also the potential for PGE recovery as a by-product in existing gold placer operations in areas hosting ophiolitic massifs and Alaskan–Uralian type intrusions. Mongolia is a promising frontier for PGE exploration and mining. Full article

The Wailukum area in North Maluku Province, Indonesia, is an ultramafic rock complex with a high degree of serpentinization. The mineral composition of ultramafic and mafic rocks strongly influences the distribution and enrichment of scandium (Sc) during lateritization. In this study, we aim to analyze three types of geological materials in a lateritic profile that contains Sc, specifically bedrock, saprolite, and limonite, in terms of element distribution, mineral composition, and rock identification. We used the analytical methods of petrography, X-ray diffraction (XRD), X-Ray Fluorescence (XRF), and Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP-OES). The results show that Sc in bedrock is mainly associated with clinopyroxene minerals such as augite and diopside. In saprolite, Sc content decreases due to higher mobility but remains partly associated with clinopyroxene, and in limonite zone, Sc reaches maximum enrichment. Among rock types, gabbro contains the highest absolute Sc concentration (23.25 ppm in bedrock and up to 58.5 ppm in limonite), while wehrlite records the greatest enrichment ratio, with a 9.18-fold increase from bedrock to limonite. By contrast, gabbro shows the lowest enrichment ratio (2.52-fold) despite its high initial Sc content. These patterns indicate that Sc enrichment is controlled by clinopyroxene as the primary host in bedrock, affecting its relative stability during weathering. Full article

Mylonitic mantle peridotites exposed at the Tosa Megamullion in the Shikoku Basin, Philippine Sea, provide direct evidence for amagmatic ductile shear deformation of the upper mantle beneath a back-arc spreading center. Oceanic core complexes (OCCs), or megamullions, are dome-shaped structures formed by detachment faulting and occur locally along slow-spreading mid-ocean ridges and back-arc basins, where they expose fault rocks derived from ductile shear zones in the lower crust and upper mantle. The Shikoku Basin hosts several OCCs, including the Tosa Megamullion, which formed during the early stage of back-arc spreading. In this study, nine ultramafic rocks were collected from the Tosa Megamullion using the submersible Shinkai6500 during cruise YK23-05S. Although all samples were highly serpentinized, several preserved primary peridotitic textures were composed mainly of olivine, orthopyroxene, with subordinate clinopyroxene, plagioclase, and spinel. Seven samples exhibit well-developed foliation and porphyroclastic textures dominated by orthopyroxene porphyroclasts, ranging from rounded to strongly elongated forms, commonly showing microkinks and undulose extinction. Crystallographic preferred orientations (CPOs) of three representative samples, analyzed using SEM-EBSD, reveal E-type-dominant olivine fabrics characterized by the (001)[100] slip system, with a subordinate contribution from C-type (100)[001] slip. These CPOs suggest deformation under non-dry conditions involving moderate hydration and/or elevated differential stress. These results indicate that the ultramafic rocks from the Tosa Megamullion represent mantle-derived mylonitic peridotites formed by ductile shear beneath the spreading axis and subsequently exhumed under strongly magma-poor, amagmatic conditions. The Tosa Megamullion thus represents an amagmatic end-member of the OCC formation in back-arc basins, dominated by tectonic strain localization rather than by magmatic accretion. Full article