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Indium (In) is a critical metal in liquid-crystal displays and solar panels. The Earth's crust has low In concentration in the order of 10 ng g−1, but it may be concentrated in sulphides by up to six orders of magnitude. Although In isotope studies may improve our understanding of the behaviour of In during different geological processes, such studies are limited for terrestrial samples. Here, we report a new method for In purification and high-precision isotope analysis for chemically different standards. A one-column method was used to separate In from the matrix with a recovery of 98% ± 2% (2SD). Indium concentrations and isotopic compositions were determined using the column eluate, and the results show large In isotope fractionation on desorbing In from the resin. Based on the mass balance, no significant In isotope fractionation was observed when In recovery is >93.8%. In terms of precision and accuracy of In isotopic compositions, the Ag-doping method was likely better than the standard–sample bracketing (SSB) method for correction of instrumental fractionation, with In uptake concentration down to 1 ng g−1 during isotope analysis. To ensure the accuracy of isotope analyses, the concentration match between the sample and standard should be within ±30%. An elemental doping study indicated that Na, K, Te, Sb, Pb, and Cu have no impact on the accuracy of In isotope analysis within the designated range; however, Ca/In, Mg/In, Cd/In and Sn/In ratios of >5, >20, >0.001 and >0.1, respectively, in sample solutions have significant impacts on In isotope analyses. Four international standards (BCR-2 basalt; J-Zn-1 sulphide; NIST-2711a soil; and OU-3 granite) and three in-house igneous rocks, purified using the developed method, had negligible isobaric interferences and matrix effect during In isotope analysis, demonstrating that the method can be used for terrestrial samples with different compositions. [ABSTRACT FROM AUTHOR]

The ages of hydrothermal Hg deposits are difficult to constrain because of the lack of suitable minerals for dating. The South China low-temperature metallogenic domain hosts numerous Hg deposits, including the Jianyan Hg deposit that is composed mainly of cinnabar and calcite. There are two stages of calcite in the deposit: syn-ore calcite (Cal-I) and post-ore/barren calcite (Cal-II). Cal-I is mainly euhedral-subhedral and fine-grained, has homogeneous grey luminescence, and is associated with cinnabar. Subhedral-anhedral Cal-II crosscuts Cal-I and is relatively coarse-grained. The syn-ore Cal-I has high U contents (0.1–1.3 ppm) and U/Pb ratios (up to 4.2), and is thus suitable for U-Pb dating. Using a laser ablation-inductively coupled plasma-mass spectrometer equipped with ion counters, we obtained a U-Pb age of 426.3±5.7 Ma (MSWD=1.5) for Cal-I. This age is interpreted to represent the timing of Hg mineralisation at Jianyan and is similar to ages of 440–400 Ma reported for many carbonate-hosted Pb-Zn and Ba-F deposits in South China. Based on the present results in combination with existing geochemical and geochronological data, we infer that these deposits belong to a Paleozoic Hg-Pb-Zn-Ba-F mineralisation system that was controlled by Caledonian tectonism. [ABSTRACT FROM AUTHOR]

Although the involvement of hydrous fluids has been widely invoked in formation of podiform chromitites in ophiolites, there is lack of natural evidence to signify the role and mechanism of fluids. In this study, a new model for the genesis of podiform chromitite is proposed on basis of revisits of comprehensive petrological, mineralogical and geochemical results of the well-preserved Kızıldağ ophiolite and the well-characterized Luobusa chromite deposit. In this model, ascending magmas intruding oceanic lithospheric mantle would presumably form a series of small magma chambers continuously connected by conduits. Tiny chromite nuclei would collect fluids dispersed in such magmas to form nascent droplets. They tend to float upward in the magma chamber and would be easily transported upward by flowing magmas. Chromite-rich droplets would be enlarged via coalescence of dispersed droplets during mingling and circulation in the magma chamber and/or transport in magma conduits. Crystallization of the chromite-rich liquid droplets would proceed from the margin of the droplet inward, leaving liquid entrapped within grains as precursor of mineral inclusions. With preferential upward transportation, immiscible chromite-rich liquids would coalesce to a large pool in a magma chamber. Large volumes of chromite would crystallize in situ, forming podiform chromitite and resulting in fluid enrichment in the chamber. The fluids would penetrate and compositionally modify ambient dunite and harzburgite, leading to significant fractionations of elemental and isotopic compositions between melts and fluids from which dunite and chromitite respectively formed. Therefore, fluid immiscibility during basaltic magma ascent plays a vital role in chromitite formation. [ABSTRACT FROM AUTHOR]

Neoproterozoic igneous and metamorphic complexes occur as tectonic domes in the Longmen Mountains of the western margin of the Yangtze Block, and are important in reconstructing the Rodinian supercontinent and constraining the timing and mechanism of tectonic denudational processes. The Pengguan dome consists of granitic intrusions and metamorphic rocks of the Huangshuihe Group and is tectonically overlain by ductilly deformed Sinian to Paleozoic strata. The plutonic intrusions consist of granites with abundant amphibolite enclaves. New LA-ICP-MS zircon U-Pb dating yielded an emplacement age of 809±3 Ma and a protolith age of 844±6 Ma for the granite. The granitic rocks have geochemical signatures typical of A-type granites, indicating their formation under an extensional environment, by melting of newly formed tonalite-trondhjemite-granodiorite (TTG) rocks. A detachment fault, characterized by variable ductile shear deformation of S-C fabric and ESE-ward kinematics, separates the Pengguan dome from the Sinian-Paleozoic cover. 40Ar/39Ar dating of muscovite from the mylonite in the detachment fault of the dome demonstrates that ductile deformation occurred at ∼160 Ma. This study indicates the existence of a Neoproterozoic magmatic arc-basin system, which was denudated by a Jurassic middle crustal ductile channel flow along the Longmenshan thrust belt. [ABSTRACT FROM AUTHOR]

The Longzhoushan and Ertan basalts in the Pan-Xi area were generated by relatively low degrees of partial melting (<7%), during which Ir, Ru, and Rh are compatible while Pt and Pd are incompatible. Most of these samples have high PGE concentrations and much higher Pd/lr and Cu/Pd ratios than those of primitive mantle. A small amount of sulfides (∼0.007%) remained in the mantle source during partial melting, whereas part of the magmas reached sulfide saturation and segregated PGE-rich sulfides (∼0.020%–0.033%) during ascent period. Osmium, Ir, and Pt could form platinum-group metallic alloys hosted in chromites or sulfides during fractional crystallization process, leading to the decoupling of Pt and Pd contents and considerable variations of Pr contents. Sulfides segregated from the basaltic magmas may provide important material sources for the formation of the Cu-Ni-PGE deposits (mineralization) in the mafic-ultramafic intrusions near the magma conduits. [ABSTRACT FROM AUTHOR]

Presents a study on the kinetic modeling of diagenesis of Eogene Lacustrine sandstone reservoirs in the Jianghan Basin, Southeastern China. Diagenetic features identified in the sandstones; Simulation of the kinetics of fluid-mineral reactions and the concentrations of aqueous species; Result of the weak pore fluid during the early diagenetic stage; Cause of the precipitation of quartz, kaolinite and illite.

South China is the most important uranium producer in the country. Much of the Mesozoic-Cenozoic geology of this area was dominated by NNE-trending intracontinental strike-slip faulting that resulted from oblique subduction of the paleo-Pacific plate underneath the eastern China continent. This strike-slip fault system was characterized by transpression in the early-mid Jurassic and by transtension from the latest Jurassic through Cretaceous to early Tertiary. Most uranium ore deposits in South China are strictly fault-hosted and associated with mid-late Mesozoic granitic intrusions and volcanic rocks, which formed under transpression and transtension regimes, respectively. Various data demonstrate that the NNE-trending strike-slip faults have played critical roles in the formation and distribution of hydrothermal uranium deposits. Extensive geochronological studies show that a majority of uranium deposits in South China formed during the time period of 140–40 Ma with peak ages between 87–48 Ma, coinciding well with the time interval of transtension. However, hydrothermal uranium deposits are not uniformly distributed along individual strike-slip fault. The most important ore-hosting segments are pull-apart stepovers, splay structures, extensional strike-slip duplexes, releasing bends and fault intersections. This non-uniform distribution of ore occurrences in individual fault zone reflects localization of hydrothermal fluids within those segments that were highly dilational and thus extremely permeable. The unique geometric patterns and structural styles of strike-slip faults may have facilitated mixing of deeply derived and near-surface fluids, as evidenced by stable isotopic data from many uranium deposits in South China. The identification of fault segments favorable for uranium mineralization in South China is important for understanding the genesis of hydrothermal ore deposits within continental strike-slip faults, and therefore has great implications for exploration strategies. [ABSTRACT FROM AUTHOR]

The compositions of minerals and whole rocks of the Luobusa ophiolite in South Tibet, a fragment of Neo‐Tethyan forearc lithosphere, is used to investigate the magmatic evolution of nascent mantle wedges in newly‐initiated subduction zones. Clinopyroxenes in the Luobusa peridotites all have diopsidic compositions, and their Al2O3 contents vary from ∼ 2% in the dunites and refractory harzburgites to 2‐4% in the cpx‐bearing harzburgites. The REE of clinopyroxenes in the harzburgites have left‐sloping patterns with contents comparable to those in abyssal peridotites that have experienced 5‐15% partial melting. Chromites in the Luobusa chromitites have the highest Cr#s (∼ 80) and TiO2 contents (0.1‐0.2%), and those in the cpx‐bearing harzburgites have the lowest Cr#s (20‐60) and TiO2 contents (0‐0.1%), whereas those in refractory harzburgites and dunites have intermediate compositions. Cpx‐bearing and refractory harzburgites show spoon‐and U‐shaped REE patterns, respectively, and their HREE distribution patterns suggest at least 15%‐ 20% partial melting. The REE patterns of dunites and high‐Cr chromitites vary from spoon‐ to U‐shaped and require 15‐30% partial melting in their mantle sources to produce their parental melts. Our dataset reveals that the nascent Luobusa mantle wedge was first infiltrated by slab‐derived fluids and later refertilized by transitional lava‐like melts, resulting in cpx‐bearing harzburgites. Partial melting in the deeper cpx‐bearing mantle generated high‐Ca boninitic to arc picritic melts, which interacted with the peridotites in the uppermost mantle to generate high‐Cr chromitites, dunites and some refractory harzburgites. Lithological variation from cpx‐bearing to refractory harzburgites in forearc ophiolites is the result of multi‐stage melt events rather than increasing degrees of partial melting. Intermittent slab rollback during subduction initiation induces asthenospheric upwelling and high heat flux in nascent mantle wedges. Elevated geothermal gradients play a more important role than slab dehydration in triggering Mg‐rich magmatism in newly‐initiated subduction zones. [ABSTRACT FROM AUTHOR]

The Malani Igneous Suite (MIS) in NW India represents one of the largest and well‐preserved Precambrian felsic igneous provinces, with minor mafic volcanics and dykes. The SIMS (Secondary Ion Mass Spectrometric) zircon U‐Pb geochronology yielded 776.8 ± 4.5 to 758.5 ± 6.9 Ma ages for rhyolites from Jodhpur region and Sindreth Basin while dacite sample from Punagarh Basin was dated to 760.5 ± 10 Ma. Zircons from rhyolitic and dacitic lavas have oxygen isotopic compositions that can be grouped into low δ18OV‐SMOW (4.12 to ‐1.11‰) and high (δ18O = 8.23‐5.12‰) categoroes, respectively. The low δ18O zircons have highly radiogenic Hf isotopic compositions (εHf(t)= +13.0 to +3.6) suggesting high temperature bulk cannibalization of upper level juvenile crust as the essential process for magma generation. Older than 800 Ma xenocrystic zircons in dacite have high δ18O values whereas 795 Ma ones have mantle‐like Hf‐O isotopic compositions, reflecting a significant shift in tectono‐thermal regime in NW India during 800‐780 Ma. A synchronous transition in the South China Block and Madagascar suggests a spatially and temporally linked geodynamic system. Geochemical data in combination with the new isotopic results point towards an overall convergent plate margin setting undergoing localized lithospheric extension. The NW India and South China blocks together with Madagascar and the Seychelles lay either along the periphery of Rodinia or off the supercontinent with the age of convergent plate margin magmatism coinciding with breakup of the supercontinent. [ABSTRACT FROM AUTHOR]

The article presents a study which examined the subduction initiation for the genesis of podiform chromite deposits. It proposes a new model as of December 2015 in which chromitite formation played a part in intra-oceanic subduction zones initiated in closing oceanic basins. Also cited is the metamorphosis of oceanic and possibly continental crustal materials under greenschist, amphibolite and ecologite facies conditions.

The Kop ophiolite in NE Turkey is a fragment of Neo-Tethyan forearc. It can be mainly divided into a paleo-Moho transition zone (MTZ) in the North and a harzburgitic mantle sequence in the South. Dunites are predominant in the MTZ of the Kop ophiolite, and they are locally interlayered with chromitites and enclose minor bodies of harzburgites near the petrological Moho boundary. Large Fe isotopic variations were observed for magnesiochromite (−0.14‰ to 0.06‰) and olivine (−0.12‰ to 0.14‰) from the MTZ chromitites, dunites and harzburgites. In individual dunite samples, magnesiochromite usually has lighter Fe isotopic compositions than olivine, which was probably caused by subsolidus Mg-Fe exchange between the two mineral phases. Both magnesiochromite and olivine display an increasing trend of δ56Fe along a profile from chromitite to dunite. This trend reflects continuous fractional crystallization in a magma chamber, which resulted in heavier Fe isotopes concentrated in the evolved magmas. In each cumulative cycle of chromitite and dunite, dunite was formed from relatively evolved melts after massive precipitation of magnesiochromite. Mixing of more primitive and evolved melts in the magma chamber was a potential mechanism for triggering the crystallization of magnesiochromite, generating chromitite layers in the cumulate pile. Before mixing happened, the primitive melts had reacted with mantle harzburgites during their ascendance; whereas the evolved melts may lie on the olivine-chromite cotectic near the liquidus field of pyroxene. Variable degrees of magma mixing and differentiation are expected to generate melts with different δ56Fe values, accounting for the Fe isotopic variations of the Kop MTZ. [ABSTRACT FROM AUTHOR]

The article discusses the ophiolitic chromitites from Kop Mountain in NE Turkey which consists of Moho transition zone (MTZ) which contains high-Cr chromitites and cumulate dunite but with lower Rare Earth Elements (REE) concentrations than the primitive mantle.

The article presents a study which examined the multiphase solid inclusions within the cumulus silicates, particularly olivine, in iron-titanium (Fe-Ti) oxide ores from the Lower Zone of the Baima intrusion, Emeishan large igneous province in southwest (SW) China as of December 2015. The methods used are two-dimensional (2-D) scanning electron microscopy and 3-D high-resolution X-ray computed tomography. The composition of the inclusions include titanomagnetite and ilmenite.

The article presents a study which examined the constraints of iron (Fe) isotopic compositions on the origin of the Luobusa podiform chromite deposit in Tibet, China. In the study, the Fe isotopic compositions of mineral separates of harzburgite, dunite and chromitite from Luobusa and two harzburgites from Zedang, China were measured and compared. Also cited are the values of the olivine (Ol) and orthopyroxene (Opx) of harzburgites.

The article studies the discovery of hydrothermal baddeleyite and zircon in the Mesozoic Tengtie Iron Skarn Deposit in South China. The study depicts that Zirconium (Zr)-rich minerals such as baddeleyite and zirco are reported to form from marble skarns. The study results shows that Zr in the fluids was likely to derive from Zr-bearing minerals from the host granitic rocks by Fluoride (F)-rich fluids.

The article analyzes the disequilibrium iron isotopic fractionation during the high-temperature magmatic differentiation of the baima iron (Fe)-titanium (Ti) oxide-bearing mafic intrusion in South West China. It informs that iron isotopic compositions of olivine, clinopyroxene and titanomagnetite were used to investigate Fe isotopic fractionation during the formation of the Fe-Ti oxide ore bodies.