Ti-bearing Minerals Research Articles

Tracking HFSE associated with high salinity fluid during HP metamorphism in the Zavkhan Terrane, Western Mongolia

Garnets often exhibit high concentrations of heavy rare-earth elements, which provide crucial insights into element mobility and fluid dynamics during metamorphism. This research reports on the distributions of trace and major elements in garnets from the Khungui eclogite of the Zavkhan Terrane in Western Mongolia. Within the eclogite sample, two types of garnets were identified, featuring dissimilar microstructures and compositional zoning: aggregate-type garnet with asymmetric zoning (Grt1) and euhedral garnet with concentric zoning (Grt2). Previous studies determined that Grt2 formation occurred in the pre-eclogite stage to eclogite facies (2.1–2.2 GPa and 580–610 °C), associated with the infiltration of high-saline fluids. The hexagonal-shaped pseudomorphs of Ti-bearing minerals associated with Grt1 suggest that the nucleation of titanite and garnet was simultaneously accelerated by the destabilization of Ti-augite during pre-eclogite metamorphism. This process could have contributed to the formation of aggregation textures, where Ti-bearing minerals are closely associated with Grt1 in the Khungui eclogite. Based on major divalent elemental composition zoning and trace element characteristics, both Grt1 and Grt2 in the Khungui eclogite are formed simultaneously from the pre-eclogite to eclogite stages. The cores (high Fe + Mg + Mn; Y + REE) of Grt1 and Grt2 are attributed to Rayleigh fractionation or a diffusion-limited uptake process. In contrast, the growth mechanisms of the Grt1 rim and Grt2 rim are distinct during the eclogite stage. The Grt1 rim is explained by a dissolution–reprecipitation, which resulted in the atoll texture observed in Grt1. The Grt2 rim (high Ca; low Y + REE) grew through a mechanism consistent with that of the Grt2 core. The major and trace element zonings of these garnets provide insights into element mobility related to Ti-bearing minerals and infiltration of high salinity fluids at different stages: (1) the mobilization of Ti and V increased under eclogite facies conditions (growth stage of garnet) compared to the pre-eclogite stage, with the mobility of Ti, Nb, Ta elements being pronounced under the exhumation stage (Rt–Ilm–Ttn2), possibly because of the infiltration of high-saline fluids and an increase in temperature, and (2) post-growth compositional modification of Grt1 was induced by a localized transport of Fe, Mg, Mn, and Ca elements in response to the replacement of ilmenite by titanite during decompression (0.1–0.5 GPa and 421–534 °C). The contrasting zoning of garnet in Khungui eclogite indicates dissimilar scales of element mobility under eclogite facies conditions (over a thin-section scale) and during decompression (up to several centimeters or beyond).

New insights into the metallogenic genesis of the Xiadian Au deposit, Jiaodong Peninsula, Eastern China: Constraints from integrated rutile in-situ geochemical analysis and machine learning discrimination

The genesis of the Mesozoic Au deposit within the Jiaodong Peninsula is debated, with vague connections to magmatism, deep-source metamorphic devolatilization, or the involvement of mantle materials over the long term. This study presents an integrated investigation involving textures, in-situ geochemical analysis, and machine learning discrimination of the rutile of the Xiadian Au deposit at the northwest Jiaodong Peninsula, aiming to provide metallogenic insights. Rutile is distinguished into three types: Type 1 rutile formed in the pre-ore stage is fine-grained and replaces and coexists with relict titanite, with euhedral crystal and being homogeneous and dark BSE response. Type 2 and type 3 rutile exhibit subhedral and anhedral crystals and are associated with quartz-sericite-pyrite alteration. The former has low W contents and is dark BSE response, while the latter is brighter in BSE and exhibits pronounced fragmentation and erosion. Chemical trends indicate the elemental substitution mechanism within rutiles from early to later stages: (Nb, Ta)5+ + (V, Fe, Al, Cr)3+ ↔ 2Ti4+ to 2(V, Fe, Al, Cr)3+ + W6+ ↔ 3Ti4+. Elevated concentrations of trivalent iron ions due to elevated oxygen fugacity of the ore-forming fluids are more likely to have contributed to this change, rather than the increment of W content. This may induce the destabilization of gold-sulfur complexes and contribute to gold mineralization. Machine learning models, including Extreme Randomized Tree (ET), Support Vector Machine, and Naive Bayes classifiers, were trained using a collected dataset containing 6598 rutile geochemistry data. These models consistently classify Xiadian rutile as the hydrothermal origin and having affinity to orogenic Au deposit. The SHapley Additive exPlanation (SHAP) framework was used to explain the discrimination criteria for the best-performing ET models. It revealed that elements such as Y, Ta, Mo, Sn, W, and Nb significantly contribute to classifying Xiadian rutile as affiliated with orogenic Au deposit. Further mass balance calculations with titanite, the predominant precursor Ti-bearing mineral of rutile, suggest that the W content in rutile is controlled by ore-forming fluids, likely having a deep source. In contrast, elements like Y, Mo, Cr, Nb, and Ta are influenced by leaching or re-equilibration with host rocks. Collectively, deep geodynamic processes likely provide major Au mineralization-related materials and fluids, while elemental leaching or re-equilibration with shallow crust rocks near fluid pathways influences the geochemical characteristics of the Xiadian gold system.

Distribution and modes of occurrence of Nb in subbituminous coal: A case study from the Jungar Coalfield, Ordos Basin, China

Niobium has been considered to be enriched in high-Al-Ga in north China coal and coal-hosted Nb(Ta)-Zr(Hf)-REY-Ga polymetallic deposits in the southwestern region of China. However, modes of occurrence and influencing factors of Nb in Al-Ga-rich coal in North China are rarely reported. This study investigated the distribution characteristics of Nb in the No.6 high-Al-Ga coal of the Jungar Coalfield in North China. The in-situ Nb concentration of selected minerals, including kaolinite, Ti-oxides, boehmite, and zircon, is further quantitatively characterized based on multiscale in-situ elemental analyses, including SEM-EDS and LA-ICP-MS spot and mapping analyses. The results showed that Nb is rich in the tonstein and mudstone partings among bulk samples and is highly concentrated in Ti-oxides, followed by zircon among the minerals. A certain amount of Nb is associated with kaolinite and boehmite with different modes of occurrence: vermicular kaolinite (65.94 ppm) > clastic kaolinite (25.43 ppm) > altered K-bearing kaolinite (18.11 ppm) > cryptocrystalline kaolinite (17.03 ppm) > clastic boehmite (9.08 ppm) > cryptocrystalline boehmite (7.97 ppm). The Nb-Nb/Ta and Zr/Hf-Nb/Ta ratios suggest that the primary source of Nb in the No.6 coal is the altered felsic volcanic ash and bauxite deposit. The high-Fe concentration in Ti-bearing minerals indicates that anatase may originate from the alteration of ilmenite with a process of Fe depletion and Nb enrichment. The enrichment of Nb in coal is attributed to the substitution of Nb for Ti in isomorphism in all Ti-oxides, high-Ti, and Ti-bearing minerals.

Modern River-Sand Geochemical Mapping in the Manufahi Municipality and Its Surroundings, Timor-Leste: Implications for Provenance

A geochemical mapping of regional modern river-sand is performed to clarify geological information in the study area of Timor-Leste. Several areas of Timor-Leste including the study area in particular have limited geological information due to limited accessibility and dense vegetation coverage, and deformed, weathered, and erosion-covered materials. A total of 53 modern river sand samples were collected and analyzed. Ten major elements were determined by using wavelength-dispersive X-ray fluorescence. Areas characterized by clastic sedimentary rocks are recognized clearly by elevated concentrations of SiO2, Al2O3, and K2O. Meanwhile, areas covered by carbonate sedimentary rocks are detected by significant concentrations of CaO and MnO. The occurrences of the altered clastic and carbonate sedimentary rocks of the Wailuli and Aitutu Formations due to metamorphic, silicification and other alteration processes were responsible for the elevated concentrations and positive correlation between SiO2, CaO, K2O, and MnO, and CaO, TiO2, and MnO in the midstream and near the downstream areas of the Clerec and Sahe River catchments. The positive correlation observed between TiO2, CaO and MnO may be ascribed to the presence of carbonate components associated with secondary Ti-bearing minerals, which are potentially formed through hydrothermal alteration processes.

Structure and equation of state of Ti-bearing davemaoite: new insights into the chemical heterogeneity in the lower mantle

Abstract Davemaoite (CaSiO3 perovskite) is considered the third most abundant phase in the pyrolytic lower mantle and the second most abundant phase in the subducted mid-ocean ridge basalt (MORB). During the partial melting of the pyrolytic upper mantle, incompatible titanium (Ti) becomes enriched in the basaltic magma, forming Ti-rich MORB. Davemaoite is considered an important Ti-bearing mineral in subducted slabs by forming a Ca(Si,Ti)O3 solid solution. However, the crystal structure and compressibility of Ca(Si,Ti)O3 perovskite solid solution at relevant pressure and temperature conditions were not systematically investigated. In this study, we investigated the structure and equations of state of Ca(Si0.83Ti0.17)O3 and Ca(Si0.75Ti0.25)O3 perovskites at room temperature up to 82 GPa and 64 GPa, respectively, by synchrotron X-ray diffraction (XRD). We found that both Ca(Si0.83Ti0.17)O3 and Ca(Si0.75Ti0.25)O3 perovskites have a tetragonal structure up to the maximum pressures investigated. Based on the observed data and compared to pure CaSiO3 davemaoite, both Ca(Si0.83Ti0.17)O3 and Ca(Si0.75Ti0.25)O3 perovskites are expected to be less dense up to the core-mantle boundary (CMB), and specifically ~1-2 % less dense than CaSiO3 davemaoite in the pressure range of the transition zone (15-25 GPa). Our results suggest that the presence of Ti-bearing davemaoite phases may result in a reduction in the average density of the subducting slabs, which in turn promotes their stagnation in the lower mantle. The presence of low-density Ti-bearing davemaoite phases and subduction of MORB in the lower mantle may also explain the seismic heterogeneity in the lower mantle, such as large low shear velocity provinces (LLSVPs).

Experimental investigation of the CaO-Al2O3-TiO2 system: Isothermal section of 1500 °C and liquidus projection

The CaO-Al2O3-TiO2 phase diagram is of great guiding significance for the comprehensive utilization of Ti-bearing mineral resources and the design of metallurgical slag for Al-Ti alloy steel. In this paper, the high-temperature phase equilibrium experimental method was adopted; the types and compositions of phases were identified by Electron Probe Micro Analysis (EPMA) and X-ray diffraction (XRD). A total of 12 equilibrium phases were determined, including CaO, Al2O3, TiO2, 3CaO2TiO2, 4CaO3TiO2, CaOTiO2, Al2O3TiO2, 3CaOAl2O3, CaOAl2O3, CaO2Al2O3, CaO6Al2O3, and Liquid; they formed a total of 16 phase equilibrium relations. The isothermal section of CaO-Al2O3-TiO2 system at 1500 °C in atmosphere was constructed for the first time. There are 10 three-phase fields (Liquid+CaO+3CaO2TiO2, Liquid+3CaO2TiO2+4CaO3TiO2, CaOTiO2+CaOAl2O3+CaO2Al2O3, CaO2Al2O3+CaOTiO2+CaO6Al2O3, Liquid+CaOTiO2+ CaO6Al2O3, Liquid+CaO6Al2O3+Al2O3, Liquid+Al2O3+Al2O3TiO2, Liquid+TiO2+Al2O3TiO2, Liquid+CaOAl2O3+4CaO3TiO2, 4CaO3TiO2(ss)+CaOTiO2(ss)+CaOAl2O3), 13 two-phase fields (Liquid+CaO, CaO+3CaO2TiO2, Liquid+3CaO2TiO2, Liquid+4CaO3TiO2, Liquid+TiO2, Liquid+CaOTiO2, Liquid+Al2O3TiO2, Liquid+Al2O3, Liquid+CaO6Al2O3, Liquid+CaOAl2O3, CaOTiO2(ss)+CaO2Al2O3, 4CaO3TiO2(ss)+CaOTiO2(ss), 4CaO3TiO2(ss)+3CaO2TiO2(ss)), 2 single-phase solid solution fields (4CaO3TiO2(ss), 3CaO2TiO2(ss)), and 2 disconnected single liquid phase fields. On this basis, the liquidus projection of the CaO-Al2O3-TiO2 system was revised. The types of relevant invariant reactions were identified by the Lever Rule; the types of relevant univariant reactions were determined by the original method proposed in this paper.

Weathering co-mineralization of placer type ilmenite and ion-adsorption type rare earth elements in Guangxi, China: Nature, origin and exploration implications

The placer type ilmenite and ion-adsorption type rare earth elements (iREEs) deposits are two important weathering-related mineral resources in South China, a global supplier of Ti and REEs critical metals. It was believed that these two deposits are not linked to each other because of their different ore-forming conditions and mechanisms. However, many studies have reported that parts of placer ilmenite deposits, especially for those developed by weathering of intermediate igneous rocks, also contain abundant iREEs resources that have not been noticed before. To elucidate the origin of this interesting co-mineralization phenomenon that is of both scientific and economic significance, we conducted a comparative study of three deposits, including Qinghu (QH), Madi (MD), and Tangcun (TC) from Guangxi Province in the western segment of South China. Investigations showed that although the ore-forming parent rocks from the QH, MD, and TC deposits are intermediate igneous rocks, their corresponding regolith profiles are significantly different in their mineralization characteristics. The diorite-derived QH and tonalite-derived MD deposits showed co-mineralization of ilmenite with iREEs, whereas the pyroxene diorite-derived TC deposit only showed independent mineralization of ilmenite. Evidences from systematic mineralogical and geochemical examinations indicated that the occurrence of ilmenite and iREEs co-mineralization, besides the impact of weathering, may principally regulated by the nature of accessory mineral assemblage in the parent rocks. Specifically, both Ti-bearing (ilmenite, anatase) and REEs-bearing (apatite, titanite) accessory minerals were largely identified in the QH diorite and MD tonalite. Analysis of degree of saprolitization (DOS) and weathering index of granite (WIG) revealed that they have experienced strong weathering, which gave rise to residual accumulation of Ti-bearing minerals (mainly ilmenite) at upper horizons of the regolith profiles, and simultaneously, secondary enrichment of iREEs by eluviation-illuviation process at lower horizons. It explained the ore horizons of placer ilmenite and iREEs developed symbiotically but show somewhat dislocation within the regolith. In contrast, the TC pyroxene diorite was found to be rich only in Ti-bearing minerals but poor in REEs-bearing minerals. It is conductive to develop weathering mineralization of ilmenite rather than iREEs in terms of ore source. Also, there is rich iron oxides and hydroxides in the pyroxene diorite-derived regolith, which might has inhibited REEs eluviation-illuviation and act as the other reason for absence of iREEs mineralization in the TC profile. This study not only provides a genetic model to understand the co-mineralization of placer ilmenite and iREEs ores developed by weathering of intermediate igneous rocks, but also highlights the importance of a comprehensive evaluation in future prior to exploration and resource utilization.

A New Route of Roasting-Flotation-Leaching for the Beneficiation of Ti-Bearing Minerals from Altered Vanadium Titanomagnetite

In this work, a complete beneficiation technical route combining physical and chemical methods, namely a roasting-flotation-leaching scheme, is proposed to produce a qualified grade Ti-concentrate from altered Vanadium titanomagnetite (VTM) ore. Based on the character of the ore sample, it is recommended to recover the Ti-bearing minerals, ilmenite and anatase, as composite mineral. Pretreatment experiments indicate that the oxidation roasting (800 °C) and acid washing methods increase the flotation indexes significantly. Flotation condition tests show that the optimal conditions are a grinding fineness of −0.045 mm 83%, sulfuric acid dosage of 2000 g/t, water glass dosage of 1500 g/t, oxalic acid dosage of 200 g/t, and EM328 dosage of 1500 g/t. An open flotation circuit test obtains a flotation concentrate with a TiO2 grade and recovery of 38.30% and 25.99%, respectively. A leaching exploration test shows that the TiO2 grade of the flotation concentrate can be improved to 53.90%. XRD analyses reveal that the ilmenite in the VTM ore is converted into anatase and rutile during the roasting process at 600–800 °C, but pseudobrookite begins to form at 900 °C. Compared to the flotation concentrate, it is confirmed that the content of Ti-bearing minerals is increased significantly in the leaching residue.

Geochemical Characteristics and Geological Significance of the Shangsu Mafic Dikes in Jiangxi

Mafic dikes are developed in the Shangsu region of Jiangxi, including Nanyuan Mountain and Mianhuaao. These dikes intrude into the Upper Triassic Anyuan Formation and are primarily composed of pyroxene, plagioclase, and opaque minerals, exhibiting a dolerite texture. The mafic dikes were found to have an SiO2 content ranging from 48.38% to 50.53% and the (K2O + Na2O) content ranging from 2.88% to 4.16%. The Na2O/K2O ratio was found to be between 2.56 and 3.99. The Eu anomaly was absent (δEu = 0.91–0.95), suggesting no influence of plagioclase fractionation during the rock formation process. The Ce anomaly was found to be absent (δCe = 1.04–1.08). The Mg# was found to range from approximately 40.06 to 45.06, indicating minimal crystal fractionation within the magma. The mafic dikes are enriched in light rare earth elements and large ion lithophile elements (LILE) and Th, while they showed significant depletion of high field strength elements (Nb, Ta, Ti). The Ti depletion may be related to the separation and crystallization of Ti-bearing minerals such as amphibole and ilmenite. Zr and Hf anomalies were evident, likely due to the contamination of zircon minerals in the samples. The mafic dikes were most likely products of the Middle–Late Yanshanian magmatic intrusion, formed in an extensional setting within the intracontinental rift environment caused by the collision of the Pacific Plate and the Eurasian Plate. The lithospheric mantle source was influenced by subduction zone fluid, and the magma source region exhibited mixed crustal materials.

Ti-Bearing Minerals: from the Ocean Floor to Subduction and Back

Abstract Rutile, titanite, and ilmenite are the most common Ti-bearing minerals in metamorphic rocks. Experimental constraints have shown that titanite is stable at low-grade metamorphic conditions, rutile at high pressure (HP), and ilmenite at high temperature, low pressure (HT-LP) conditions. Yet, petrological evidence suggests that titanite can also be stable at low temperature, HP (LT-HP). This implies that both titanite and rutile can be used to develop proxies to track HP metamorphism, which can have interesting applications. In this study, we have investigated the natural occurrence and chemistry of Ti-bearing minerals in gabbroic rocks and basalts that record different degrees of metamorphism, including LP amphibole-bearing gabbros from the ocean floor (Mid-Atlantic and Indian ridge IODP LEGs) and from an obducted ophiolite (Chenaillet) and HP Alpine metagabbros and metabasalts, including blueschist and eclogite facies rocks from the Western Alps and Corsica. We have performed detailed petrography, Raman spectroscopy and analyzed major and trace elements mineral chemistry using EPMA and LA-ICPMS. We found that rutile is stable at low pressure (< 2 kbar) in ocean-floor amphibole-bearing gabbros, lower than experimental constraints had previously suggested. Rutile is also found in eclogitic metagabbros from the Western Alps and can be chemically distinguished from LP rutile. Blueschist metagabbros from the Western Alps and eclogitic metabasalts from Corsica have titanite stable instead of rutile. While the titanite to rutile transition is pressure- and temperature-dependent, we demonstrate how small variations in bulk-rock Ti/Ca and Ca/Al values within the NCKFMASHTO chemical system may shift their stabilities. High-pressure titanite from these metamafic rocks exhibits La depletion and low La/SmN values in comparison to titanite from amphibolite-facies mafic rocks. La/SmN or Nb together with Yb and V can be used to distinguish HP titanite from titanite formed under other P–T settings. These new systematics can be useful in studies using detrital Ti-bearing minerals to probe the HP metamorphic record through time.

The adsorption behavior of niobium (V) on kaolin clay and kaolinite

Niobium (Nb) in kaolin clay usually occurs in the Ti-bearing minerals, such as rutile and anatase. However, the low Ti-bearing minerals contents for some kaolin clay rocks were insufficient to explain the high Nb concentrations. Thus, Nb was widely considered to be adsorbed by clay minerals. However, the adsorption behavior of niobium (V) on clay minerals has not been fully understood. In this study, a series of batch adsorption experiments were carried out on kaolin clay (Kclay) and pure kaolinite (Kaol) using niobium oxalate solutions. The effects of contact time, initial niobium (V) concentration, solution pH, and temperature on the adsorption were investigated. The results showed that Kclay exhibited a higher adsorption capacity than Kaol under the same conditions. The niobium (V) adsorptions on Kclay and Kaol were pH-dependent, and both of them showed declining adsorption capacities from pH 2 to 4. The adsorption behaviors of niobium (V) on Kclay and Kaol conformed to the pseudo-second-order model. The adsorption isotherm of Kclay was a better fit with the Freundlich isotherm model, while the Langmuir isotherm model was a better fit for Kaol. The Langmuir maximum adsorption amount of Kclay and Kaol were 5.42 and 2.25 mg/g, respectively. These results demonstrated that niobium (V) can be adsorbed by kaolin clay and kaolinite.

The use of titania polymorphs as indicators of mesodiagenesis during hydrocarbon charge

Authigenic titania (TiO2) minerals are observed in the Upper Jurassic-Lower Cretaceous pro-deltaic reservoir sandstones of the Scotian Basin. Although diagenetic rutile is rare, relatively large amounts of diagenetic anatase and brookite are present. Anatase is mostly early diagenetic whereas brookite is usually late diagenetic and is abundant in reservoir sandstones above the free-water level. The availability and mobility of Ti during late diagenesis is attributed to the dissolution of Ti-bearing minerals enhanced by Ti complexes formed from hydrocarbon-rich and highly saline fluids. This study suggests that the precipitation of late diagenetic brookite, rather than anatase or rutile, may be due to the incorporation of Fe and V during hydrocarbon charge and the presence of Cl− in circulating fluids. In addition, the chemical composition, timing and distribution of the diagenetic titania polymorphs relative to other diagenetic minerals further constrains the overall paragenetic evolution of the basin, and thus illustrates the relationship between titania minerals, hydrocarbon charge and fluid conditions in the basin.

Mineralogical and geochemical characteristics of coal from the Southeastern Qinshui Basin: Implications for the enrichment and economic value of Li and REY

Comprehensive assessment of the critical elements in coal is vital for understanding the geological processes affecting element enrichment allowing full utilization of coal in an economical and environmentally friendly manner. This study reports the latest data on the petrology, mineralogy, and coal geochemistry of the No. 15 coal seam in the southeastern Qinshui Basin. The enrichment mechanism of lithium (Li) and rare earth element and yttrium (REY) was analyzed. The result indicates that Li is significantly enriched (CC is 19.55) and mainly occurs in Ti-bearing minerals (e.g., clay minerals). REY mainly occurs in phosphate minerals, such as goyazite. The sedimentary provenance is the dominant factor influencing the mineralogical composition and elevated trace element concentrations of No.15 coal seam. Furthermore, hydrothermal fluids and marine environment also affected the mineral composition. After the high-temperature combustion process, the Li and REY have a higher enrichment ratio in the coal than that in the carbonaceous mudstone, parting the roof and floor samples. The REY contents of coal, roof and floor samples are higher than the marginal grade for industrial deposits. The evaluation results indicate the No. 15 coal seam has a potential to provide raw materials for the comprehensive processing and utilization of Li and REY.

Reconstruction of magma chamber processes preserved in olivine-phlogopite micro-ijolites from the Oldoinyo Lengai, Tanzania

A detailed petrographic and mineralogical investigation of olivine-phlogopite micro-ijolite xenoliths from Oldoinyo Lengai, Tanzania indicates a complex evolutional history. These xenoliths consist of diverse textural subdomains characterized by minerals ranging from early-formed olivine, through diopside-hosted perovskite and phlogopite, to evolved aegirine-augite and titanite. Thermometry and mineral compositions in the subdomains suggest crystallization temperatures from 1070–970 °C to 850–700 °C at plutonic pressures and SiO2-activities controlled by perovskite-titanite equilibria. Double coronas are a characteristic textural feature of the olivine-phlogopite micro-ijolite, consisting of olivine cores surrounded by an inner clinopyroxene corona and an outer phlogopite corona. These double coronas might have formed during early magma chamber processes, including magma movement to a subsequent chamber resulting in dissolution of olivine with subsequent crystallization and accumulation of diopside and phlogopite. Diopside−aegirine-augite compositional zonation indicates several magma injections followed by cooling periods, during the formation of micro-ijolite groundmass. Mg# (80–83) and Ca (0.1–0.3 in wt%) contents of olivine together with the presence of primary melt inclusions in clinopyroxene, phlogopite, and nepheline indicate a magmatic origin from a possible parental olivine-nephelinite melt. There is evidence for subsolidus, or near-solidus, re-equilibration processes as indicated by the reaction of olivine with titanite forming symplectitic textures of ilmenite and diopside with minor zirconolite. Ti-exchange between phlogopite phenocrysts and other Ti-bearing minerals (perovskite, titanite, magnetite) resulted in ∼750 °C equilibrium temperatures for phlogopite, which are much lower than mafic magmatic (>900 °C) conditions. Calculated subsolidus temperatures suggest crystallization of olivine-phlogopite micro-ijolites over a 10–20 km depth interval.

Batholith recorded mesozoic multistage tectonic evolution of the South china block: A case study of the guandimiao intrusions

South China is a well-known grand felsic igneous rocks province. However, it is still controversial and not well understood whether the Mesozoic tectono-magmatic pattern is dominated by the subduction of the paleo-Pacific oceanic plate. In this study, we address this question by concentrating on the long-term evolutionary Guandimiao batholith, which has complex lithofacies with different formation ages and can be a superb record of the Mesozoic tectonic evolution in South China. Geochronologically, four stages of magmatism can be identified combined with previous reports: granodiorite (G1, 239 Ma), biotite monzogranite (G2-1) and two-mica monzogranite (G2-2) (230–203 Ma), granite porphyry (G3, 211–190 Ma), and lamprophyre (L4, 121 Ma). G1 and G2-1 have an affinity with I-type granite and were derived from metabasaltic to metatonalitic sources, whereas G2 and G3 show S-type granite characteristics and were derived from the para-metamorphic basement of the Cathaysia block. The L4 was derived from partial melting of garnet and spinel lherzolite and underwent mixing between Mesoproterozoic pelagic and/or terrigenous sediments and the subcontinental lithosphere mantle (SCLM) of South China. The granitoids of the Guandimiao batholith underwent intensely fractional crystallization of feldspar, Ti-bearing minerals, allanite and monazite. The zircon U–Pb dating of L4 in the Guandimiao batholith completely records the six stages of pre-Mesozoic tectonic events in the SCB. During the Mesozoic, the main body of the Guandimiao batholith (G1, G2-1 and G2-2) recorded the closure of the paleo-Tethys Ocean in the Triassic and the subsequent regional extension of the postcollision. G-3 and L4 of the Guandimiao batholith documented the transition of tectonic and dynamic regimes in the early Yanshanian and the rollback and steep subduction of the paleo-Pacific Ocean in the late Yanshanian.

Hydrothermal fluid signatures of the Yulong porphyry Cu-Mo deposit: Clues from the composition and U-Pb dating of W-bearing rutile

AbstractHydrothermal rutile (TiO2) is a widely distributed accessory mineral in hydrothermal veins or alteration assemblages of porphyry deposits and provides important information for further understanding hydrothermal fluid signatures. This study determines the geochemical composition and U-Pb dates of hydrothermal rutile from the Yulong porphyry Cu-Mo deposit in east Tibet, China. Three types of TiO2 polymorphs have been identified based on their Raman spectroscopic, textural, and chemical characteristics. (1) Brookite and anatase pseudomorphs after titanite in a fine-grained matrix, indicating low-temperature hydrothermal fluids destabilizing primary Ti-bearing minerals during argillic alteration (type-I). (2) Elongated and prismatic rutile present in hydrothermal veins or in clusters in accompanying alteration envelope characterized by weak zoning (type-II). And (3) rutile intergrown with sulfides in hydrothermal veins, characterized by well-developed patchy and sector zoning (type-III). In contrast to the type-I and type-II TiO2 polymorphs, tungsten is enriched in backscattered bright patches and sector zones in type-III rutile, which is due to the substitution of W6+ in the Ti4+ octahedral site. The mechanism of the enrichment of tungsten is effectively driven by the halogen-rich (F, Cl) aqueous fluids during hydrothermal mineralization. In situ U-Pb dating of the type-III rutile yields a lower intercept age of 41.8 ± 1.2 Ma, which brackets the timing of the Cu-Mo mineralization. The relationship between rutile textures and composition indicates that W-bearing rutile can serve as a recorder of hydrothermal processes in porphyry Cu deposits.

Continental arc-derived eclogite in the Zavkhan Terrane, western Mongolia: Implications for the suture zone in the northern part of the Central Asian Orogenic Belt

We report here our investigations into the petrology and geochemistry of the Khungui eclogites and metamorphosed continental crust in the Central Asian Orogenic Belt (CAOB), Western Mongolia. The eclogites consist mainly of garnet, omphacite, amphibole, Ti-bearing minerals, phengite, quartz, epidote, and plagioclase. Two types of garnet occur: Grt1 in aggregates > 500 µm and discrete Grt2 crystals > 100 µm in size. The omphacite occurs in the matrix and as inclusions in the rims of the garnets and has a jadeite content (Xjd) ranging from 0.32 to 0.44. The phengite also occurs both in the matrix and as inclusions in the garnet rims, and its Si content is homogeneous. Amphibole in the matrix shows compositional zoning from barroisite to taramite. The mineral assemblage of the eclogite-metamorphism is found in the garnet rims and includes omphacite, rutile, phengite, epidote, and barroisite. Geothermobarometry indicates eclogite P–T conditions of 2.1–2.2 GPa and 580–610 °C. In contrast, the matrix mineral assemblage of taramite, epidote, and symplectite (hornblende + plagioclase) was formed during decompression at T = 575–635 °C and P = 0.1–0.5 GPa. Interestingly, the Khungui eclogite shows a geochemical signature of continental arc basalt (Nb/La vs La/Yb ratios), which contrasts with the MORB compositions of most other eclogite terranes in the CAOB. The geochemical and petrological features of the Khungui eclogite indicate that the collision of the continental and island arcs causes Precambrian continental crust thickening in the CAOB.

Transformation of the Sub-Continental Lithospheric Mantle Beneath the North China Craton (NCC): Constraints from the Geochemical Characteristics of Olivine Websterite Xenoliths and Their Minerals in the Cenozoic Basalts from Hannuoba

The sub-continental mantle beneath North China Craton (NCC) has attracted extensive attention in the past decades because of its dramatic transformation from an old, cold, thick, and refractory mantle to a juvenile, hot, thinner, and fertile mantle. However, the transformation mechanism remains largely controversial. The mantle xenoliths entrapped in basalts, as petrogenetic indicators, can provide an important window to reveal the evolution of the sub-continental lithospheric mantle. In this study, we present a systematical study on the geochemical characteristics of the olivine websterite xenoliths and their minerals in the Cenozoic basalts in the Hannuoba region located at the central orogenic belt of the NCC. The results, compared with the geochemical data of Paleozoic and Meosozic peridotites, the Cenozoic composite pyroxenites as well as the global cumulate pyroxenites, demonstrate that: (1) The source of the websterite is probably the lithospheric mantle, which is mainly newly accreted, but with small amounts of ancient mantle residues. The source may be contaminated by different degrees of crustal materials. The high Nb/Ta ratios (11.36–20.57) of the websterite indicate that the Ti-bearing minerals (such as rutile) are probably involved in the source; (2) The websterite is more likely to be produced as a result of interaction of mantle peridotite with the silica-rich melts that are mainly derived from the asthenospheric mantle and also contributed by the crustal materials; (3) The metasomatic crustal melts might be derived from the subducted Paleo-Pacific plate. These melts interacted with the lithospheric mantle can significantly transform the chemical composition of the lithospheric mantle, and consequently play an important role in the destruction of the NCC. An important implication for the destruction of the NCC is further discussed.

Petrogenesis and Tectonic Setting of the Madeng Dacite, SW Sanjiang Indosinian Orogen: Evidence from Zircon U-Pb-Hf Isotopes, and Whole-Rock Geochemistry and Sr-Nd Isotopes

The Sanjiang Indosinian orogen, located in the eastern part of the Paleo-Tethys tectonic domain, is a critical region to study the Paleo-Tethyan Ocean evolution. Middle Permian–Late Triassic magmatic rocks are widespread in the Deqin–Weixi–Madeng area of southwestern (SW) Sanjiang Indosinian orogen, yet their petrogenesis and tectonic setting remain disputed. In this study, LA-ICP-MS zircon U-Pb age and Hf isotopes, and whole-rock elemental and Sr-Nd isotope geochemistry of Madeng dacite were studied. The Madeng dacite was dated at ca. 241.7 and 243.4 Ma. The samples had high Al2O3 (12.91 to 14.39 wt.%) but low MgO (0.62 to 1.76 wt.%) contents, and were alkali-rich (Na2O + K2O = 6.97 to 8.66 wt.%) with A/CNK > 1.1, strongly resembling peraluminous S-type granites. The rocks were enriched in Rb, K, Th, U and LREE, but depleted in Ba, Sr, Nb, Ta, P and Ti, and showed obvious negative Eu anomalies, suggesting fractionation of Ti-bearing minerals (e.g., rutile and ilmenite) and plagioclase. The dacite had an initial 87Sr/86Sr value of 0.705698 to 0.710277, and negative εNd(t) (−11.28 to −10.64) and εHf(t) (−13.99 to −8.60), indicating a continental meta-sedimentary source. Their average Nb/Ta (12.24) and Th/U (4.65) were also consistent with continental crust. According to the lithological assemblage and geochemical features, we propose that the Deqin–Weixi–Madeng area intermediate-felsic magmatism was generated in a subduction-related tectonic setting.

Geochemical and Geochronological Constraints on a Granitoid Containing the Largest Indosinian Tungsten (W) Deposit in South China (SC): Petrogenesis and Implications

Chuankou tungsten (W) ore field, with an estimated WO3 reserve exceeding 300,000 tonnes, is so far the largest Indosinian (Triassic) granite-related W ore field in South China. However, the precise emplacement ages, sources of granitoids, and their relationship with W mineralization are still not well understood. In this research, four main magmatic stages (G-1 to G-4) have been identified in the Chuankou ore field, including G-1 (phase I, biotite monzogranite), G-2 (phase II, two-mica monzogranite), G-3 (phase III, fine-grained granite), and G-4 (phase IV, granite porphyry). LA-ICP-MS U-Pb dating of zircon grains from granitoids of the Chuankou W ore field yields emplacement ages of 230.8 ± 1.6 Ma, 222.1 ± 0.56 Ma, 203.1 ± 1.6 Ma, and 135.5 ± 2.4 Ma, respectively. Granitoids from the Chuankou ore field contain a large amount of peraluminous minerals such as biotite, musvite, garnet and tourmaline. Geochemically, the granitoids have high Si and Al (A/CNK > 1.1) content but low alkali, Fe, Mg, Mn, and Ca content. Moreover, there is enrichment of Rb, Zr, Hf, Th, and U, but depletions of Ba, Sr, P, and Ti. The granitoids have especially low Zr + Nb + Ce + Y and high Rb/Ba ratios, further indicating a highly fractionated S-type granite affinity with a significant crystal fractionation process in regard to K-feldspar, plagioclase, biotite, Ti-bearing minerals (except rutile), zircon, apatite, allanite, and monazite. Whole-rock εNd(t) and TDM2 values are −10.77 and 2090 Ma for G-1, −9.09 to −7.47 and 1764–1684 Ma for G-2, −10.07 to −6.53 and 1669–1471 Ma for G-3, respectively, indicating that the Chuankou granitoids were derived from two episodes of partial melting of the Paleoproterozoic to Mesoproterozoic metamorphic basement. Trace elements within the zircons and whole-rock geochemistry yielded evidence of the close relationship between W mineralization and G-1 and G-2 granitoids of the Chuankou ore field. The batholith of the Chuankou ore field was formed 20–10 Ma later than the peak age of the collisions orogeny and formed in a post-collisional setting.