Low TiO2 Contents Research Articles

Sr–Nd–Hf isotopes of the intrusive rocks in the Cretaceous Xigaze ophiolite, southern Tibet: Constraints on its formation setting

The Cretaceous Xigaze ophiolite is best exposed at the central part of the Yarlung–Zangbo Suture Zone, Tibet Plateau. It consists of a thick section of mantle peridotites, but a relatively thin mafic sequence. This study presents geochronological and geochemical data for intrusive dykes (both mafic and felsic) and basalts to revisit the formation setting of the Xigaze ophiolite. The rodingites are characterized by high CaO and low Na2O contents relative to mafic dykes and show big variations in trace element compositions. Both gabbros and diabases have similar geochemical compositions, with MgO contents of 6.42–11.48wt% and Mg# of 0.56–0.71. They display REE patterns similar to N-MORB and are variably enriched in large ion lithophile elements. Basalts have fractionated compositions and display LREE-depleted patterns very similar to N-MORB. They do not show obvious enrichment in LILE and depletion in high-field-strength elements, but a negative Nb anomaly is present. The studied plagiogranites have compositions of trondhjemite to tonalite, with high Na2O and low K2O contents. They have low TiO2 contents less than 1wt%, consistent with melts formed by anatexis of gabbros rather than by differentiation of basalts. Zircons from seven samples, including three rodingites, three plagiogranites, and one gabbro, have been dated and yielded U–Pb ages of 124.6~130.5Ma, indicating the Xigaze ophiolite was formed during the Early Cretaceous. They have mantle-like δ18O values of +4.92~+5.26‰ and very positive εHf(t) values of +16~+13.3. Ages of the rodingites and less altered gabbros indicate that serpentinization was occurred at ~125Ma. Occurrence of both gabbroic and diabase dykes within the serpentinites suggests that the mantle lithosphere of the Xigaze ophiolite was rapidly exhumed. Both mafic and felsic dykes have slightly more radiogenic 87Sr/86Sr ratios relative to MORB, but depleted Hf–Nd isotpe compositions. They have a limited range of εNd(t) values of +7.9~+8.9 but variable εHf(t) values ranging from +9.9 to +16.7, which are similar to the global MORB. This indicates that the intrusive dykes within the Xigaze ophiolite were derived from a depleted mantle source, which has not been obviously affected by recycling of subducted materials. The MOR-type basalts in this study, combined with the basalts with SSZ signatures previous reported in the literature indicate the diversity of basalts in the Xigaze ophiolite. We apply the forearc hyperextension model to reconcile the occurrence of both MOR- and SSZ-type basalts in the Xigaze ophiolite. In this model, the SSZ-type basalts were produced by melting of the metasomatized mantle wedge during exhumation, whereas the MOR-type basalts were derived from the upwelling asthenosphere triggered by forearc hyperextension.

Effect of Sodium Sulfate on Direct Reduction of Beach Titanomagnetite for Separation of Iron and Titanium

The effect of sodium sulfate on direct reduction of beach titanomagnetite, followed by magnetic separation, to separate iron and titanium was investigated. Direct reduced iron (DRI) with a high Fe content, low TiO2 content and low iron recovery was obtained after adding sodium sulfate. When the sodium sulfate dosage was increased from 0 to 10 mass %, the Fe content of the DRI increased from 90. 00 mass% to 93. 55 mass% and the TiO2 content decreased from 1. 27 mass% to 0. 70 mass%. The reduction mechanism of sodium sulfate was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). Results revealed that the metallic iron grains in the reduced ore with sodium sulfate were larger than those in the ore without sodium sulfate. Sodium sulfate promoted the migration of iron as well as the accumulation and growth of metallic iron grains by low-melting-point carnegieite and troilite formed in the redox system. Low-melting-point carnegieite decreased the melting point of the system and then promoted liquefaction. Troilite could decrease the surface tension and melting point of metallic iron grains.

Geochronology and geochemistry of the Tianmugou Mo deposit, Dabie Shan, eastern China: Implications for ore genesis and tectonic setting

The Tianmugou molybdenum (Mo) deposit is a newly discovered porphyry deposit in the Dabie Shan of eastern China. The Mo-mineralization is spatially and genetically related to the Tianmushan granite batholith, and mainly occurs as thin molybdenite-bearing pegmatite dykes and numerous hydrothermal veins, with the development of potassic alteration, silicification, sericitization, propylitization, and fluoritization. The Tianmushan batholith is composed of outermost fine-grained K-feldspar granite (Phase 1), medium-grained K-feldspar granite (Phase 2), coarse-grained biotite monzogranite (Phase 3), porphyritic granite (Phase 4), and innermost fine-grained K-feldspar granite (Phase 5). Zircon crystals from the biotite monzogranite yield a weighted average 206Pb/238U age of 123.0±0.8Ma, but those from the porphyritic granite do not yield a good age because of their high contents of Th, U and Pb. Seven molybdenite samples from the ores yield individual Re–Os isotopic ages of 120.5±1.7Ma to 122.5±1.9Ma, which are slightly younger than the U–Pb age for the biotite monzogranite. These ages constrain the ore-forming magmatic-hydrothermal activity at the Tianmugou Mo deposit that took place during the post-collisional tectonism subsequent to the collision between the Yangtze and North China continents, consistent with the 142–111-Ma regional Mo mineralization event in Dabie Shan. The biotite monzogranite and porphyritic granite have high contents of SiO2, K2O and Al2O3, and low contents of TiO2, MgO and CaO, showing a metaluminous to peraluminous high-K calc-alkaline affinity, with significant depletion in Eu, Ba, Sr, P and Ti, and enrichment in Rb, Th, U, Nb, Ta, Hf and Y. The rocks have high initial 87Sr/86Sr ratios of 0.73546–0.89204, and negative εNd(t) values of −11.6 to −11.0, with TDM2(Nd) of 1.81–1.86Ga. Their (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t are 17.337–17.554, 15.450–15.465 and 37.992–38.147, respectively. The Sr-Nd-Pb isotopic signatures indicate that the causative granitic intrusions for the Tianmugou deposit mainly originated from partial melting of the Qinling Group during Early Cretaceous post-collisional tectonic extension. The Tianmugou Mo deposit belongs to a collisional- or Dabie-type porphyry Mo system.

Genesis and tectonic setting of the giant Diyanqin'amu porphyry Mo deposit in Great Hingan Range, NE China: Constraints from U–Pb and Re–Os geochronology and Hf isotopic geochemistry

The Great Hingan Range is located in the eastern sector of the Central Asia Orogenic Belt, and is the second important Mo province in China, next to the Qinling–Dabie orogenic belt. Previous studies concluded that all the Mo deposits (Mo-only or Mo-dominated polymetallic) in the area were formed in the Mesozoic, and related either to the syn- to post-collisional setting following the closure of the Paleo-Asia Ocean, or to the westward subduction of the Pacific plate. However, the fluids forming the giant Diyanqin'amu porphyry Mo deposit in the area disagree with the features of collision-type Mo deposits, but accord with those of the subduction- or continental arc-type. The Mo mineralization is hosted in the Late Jurassic volcanic rocks and genetically related to the buried porphyritic granite and aplitic granite. Two porphyritic granite samples yield LA-ICP-MS zircon weighted mean 206Pb/238U ages of 158.7±0.8Ma (MSWD=0.64, 2σ) and 158.0±0.9Ma (MSWD=0.38, 2σ), respectively. The aplitic granite yields a zircon U–Pb weighted mean 206Pb/238U age of 156.9±1.1Ma (MSWD=0.48, 2σ), slightly younger than the porphyritic granite. Seven molybdenite samples from the ores yield Re–Os isotope ages of 156.1±2.2 to 158.1±4.3Ma. These ages constrain that the Diyanqin'amu Mo system was formed in the period of 159–156Ma. The granites at the deposit have high contents of SiO2, K2O and Al2O3, and low contents of TiO2, MgO and CaO, showing a peraluminous high-K calc-alkaline affinity. These granites and the host volcanic rocks are characterized by enrichment of K, Rb, U, Pb, Th and LREE, and depletion of Nb, Ta, Ti and HREE, with negative Eu anomaly, which are similar to magmatic rocks in the Andean arc. Zircon grains from the granites show positive εHf(t) values of 4.2–9.0, with TDM2(Hf) ages of 0.63–0.94Ga. These geochemical data imply that the granites at Diyanqin'amu are highly fractionated I-type, formed in a continental arc generated by the southeastward subduction of the Mongol–Okhotsk oceanic plate.

Analysis of Crystallization Behavior of Mold Fluxes Containing TiO2 Using Single Hot Thermocouple Technique

The crystallization behavior of mold fluxes containing 0—8 mass% TiO2 was investigated using the single hot thermocouple technique (SHTT) and X-ray diffraction (XRD) to study the possible effects on the coordination of heat transfer control and strand lubrication for casting crack-sensitive peritectic steels. Time-temperature-transformation (TTT) and continuous-cooling-transformation (CCT) curves were plotted using the data obtained from SHTT to characterize the crystallization of the mold fluxes. The results showed that crystallization of the mold fluxes during isothermal and non isothermal processes was suppressed with TiO2 addition. From the TTT curves, it could be seen that the incubation and growth time of crystallization increased significantly with TiO2 addition. The CCT curves showed that the crystallization temperature initially decreased, and then suddenly increased with increasing the TiO2 content. XRD analysis suggested the presence of cuspidine in the mold fluxes with lower TiO2 content (< 4 mass%), while both perovskite and cuspidine were detected in the mold fluxes when the TiO2 content was increased to 8 mass%). In addition, the growth mechanisms of the crystals changed during the isothermal crystallization process from interface-controlled growth to diffusion-controlled growth with increasing the TiO2 content.

Structural evolution and late Carboniferous magmatism of the Zhongguai arc in the western Junggar Basin, Northwest China: implications for tectonic evolution of the Junggar Ocean

ABSTRACTThe structural evolution and late Carboniferous magmatism of the Zhongguai arc in the western Junggar Basin offer some new constraints on the tectonic evolution of the Junggar Ocean. In this study, we conducted structural analysis of seismic profiles and report new geochronological and geochemical data for the late Carboniferous borehole volcanics (basalts, andesites, dacites, and rhyolites) in the Zhongguai arc. Seismic data suggest that the upper Carboniferous lies between the lower Carboniferous and middle Permian compressional tectonostratigraphic strata. Zircon secondary ion mass spectrometry U–Pb and whole-rock Ar–Ar dating results indicate that they erupted at 309–305 Ma. The andesites are low-Fe calc-alkaline, and characterized by relatively high Mg# (3.24–6.00%), Cr (41.2–70.4 ppm), and Ni (23.3–35.6 ppm) contents, and low TiO2 contents (0.69–0.83%) and TFe2O3/MgO ratios (1.48–2.08), similar to those typical of magnesian andesites. They were likely produced by reaction between slab-derived melts and mantle wedge. The basalts show tholeiitic to calc-alkaline affinity, high εNd(t) values (7.7–8.0) and Nb and Zr contents, variable enrichment in Th, U, and light rare earth elements (LREEs), and significant depletion in Nb and Ta. The felsic rocks display arc-like geochemical features with alkaline grantite, and positive εNd(t) values (5.6–7.1). The basalts are interpreted as resulting from partial melting of a metasomatized mantle by slab-derived melt and fluids with involvement of asthenospheric mantle in an extensional setting, whereas the felsic rocks were derived from juvenile lower crust. The formation of these late Carboniferous rocks is probably related to ridge subduction. Given the widespread presence of such rock association in the area from southern West Junggar terrane to Zhongguai arc and initial southeastward-vergent thrust structures in the Zhongguai arc, we suggest that the southern West Junggar terrane and Zhongguai arc might have been amalgamated as a unified overriding plate above a northwestward ridge subduction zone of the Junggar Ocean at 309–302 Ma. The occurrences of middle Permian terrestrial sediments and thrusting reactivation in the Zhongguai arc are possibly indicative of the final welding of the Zhongguai arc and other units of the Junggar basement.

Geological, geochronological, geochemical, and Sr–Nd–O–Hf isotopic constraints on origins of intrusions associated with the Baishan porphyry Mo deposit in eastern Tianshan, NW China

The Baishan porphyry Mo deposit (0.72 Mt; 0.06 % Mo) is located in the interior of the eastern Tianshan orogenic belt in Xinjiang, NW China. The deposit comprises 15 orebodies that are associated with monzogranite and granite porphyry stocks and are structurally controlled by roughly EW-trending faults. Secondary ion mass spectrometry (SIMS) zircon U–Pb dating of the monzogranite and granite porphyry yielded the Middle Triassic age (228 ± 2 to 227 ± 2 Ma), which coincide with the molybdenite Re–Os model ages ranging from 226 ± 3 to 228 ± 3 Ma. The Triassic monzogranite and granite porphyry belong to high-K calc-alkaline series and are characterized by high SiO2 and Al2O3 and low MgO, TiO2, and P2O5 concentrations, with negative Eu anomalies (δEu = 0.55–0.91). The least-altered monzogranite and granite porphyry yield uniform e Nd(t) values from +1.6 to +3.6, and wide (87Sr/86Sr) i ratios ranging between 0.7035 and 0.7071, indicating that they were derived from the lower crust. In situ O–Hf isotopic analyses on zircon using SIMS and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) indicate that the δ18O and e Hf(t) values of zircon from a monzogranite sample vary from 6.1 to 7.3 ‰ and +8.0 to +11.7, respectively, whereas zircon from a granite porphyry sample vary from 6.2 to 6.9 ‰ and +7.3 to +11.2, respectively. The geochemical and isotopic data imply that the primary magmas of the Baishan granite were likely derived from partial melts from the lower crust involving some mantle components. The Baishan Mo deposit and granitic emplacement were proposed to be most likely related to post-orogenic lithospheric extension and magmatic underplating. An extensional event coupled with the rising of hot mantle-derived melts triggered partial melting of the lower crust, as well as provided metals (Mo).

Effective removal of anionic and cationic dyes by kaolinite and TiO2/kaolinite composites

AbstractThe present study investigated the removal of methylene blue (MB) and orange II (OII) dyes from synthetic wastewater by means of adsorption and photocatalysis using natural kaolins. ForMB adsorption, the raw kaolinite-rich samples showed the greatest adsorption capacity, with rapid uptake (90% after 20 min). The experimental results were fitted better using the Langmuir isotherm model parameters compared to the Freundlich model, suggesting that the adsorption corresponds to monolayer coverage of MB molecules over the kaolinite surface. For OII, neither the Langmuir nor the Freundlich model gave reliable results, because the adsorption of anionic dye molecules by the clayey particles is not favoured.Mixtures of kaolinite/Degussa TiO2 were also prepared, and their photocatalytic properties under UVlight exposure were investigated. Decolourization of MB solutions was observed, even in a mixture with low TiO2 content. This is related to the combined effect of adsorption and photocatalysis and, unlike the pure clay samples, the efficiency of such mixtures against OII was only slightly weaker (80–94%).For TiO2-impregnated clays, with the kaolinite layers separated by sol-gel TiO2 particles, the MB removal was slow and effective only after &gt;24 h due to the complexity of the bonding of MB molecules. On the other hand, the removal performance against OII solutions was very efficient (nearly 100%) within only 2 h. This excellent performance was attributed to morphological changes in clay particles.

Geochemistry of Tertiary sandstones from southwest Sarawak, Malaysia: implications for provenance and tectonic setting

Tertiary sandstones collected from southwest Sarawak, Malaysia, were analyzed to decipher their provenance, weathering, and tectonic setting. The studied sandstones have a sublitharenite composition and are dominantly composed quartz with little mica and feldspar, and a small amount of volcanic fragments. These sandstones were generally derived from quartz-rich recycled orogenic sources. They have relatively high SiO2 content with low Na2O, CaO, MnO, and MgO contents. Values of Chemical Index of Alteration (CIA) of these rock samples vary from 71 to 93, with an average of 81, implying intense chemical alteration during weathering. A felsic igneous source is suggested by a low concentration of TiO2 compared to CIA, enrichment of Light Rare Earth Elements, depletion of Heavy Rare Earth Elements, and negative Eu anomalies. A felsic origin is further supported by a Eu/Eu* range of 0.65–0.85 and high Th/Sc, La/Sc, La/Co, and Th/Co ratios. This work presents the first reported geochemical data of Tertiary sandstones of the Sarawak Basin. These data led us to conclude that the sandstones were dislodged from recycled orogenic sources and deposited in a slowly subsiding rifted basin in a passive continental tectonic setting.

Zircon U–Pb dating and Sr–Nd–Pb–Hf isotopes of the ore-associated porphyry at the giant Donggebi Mo deposit, Eastern Tianshan, NW China

The giant Donggebi porphyry Mo deposit is located in the Jueluotage metallogenic belt of Eastern Tianshan, Xinjiang, Northwest China. Mo mineralization mainly occurs as numerous veinlets in the altered sandstone wall-rocks, with the development of potassic, phyllic, argillic and propylitic alteration assemblages outward from a buried porphyritic granite stock. Zircon crystals from the buried porphyritic granite yield a weighted average 206Pb/238U age of 236±2.2Ma (MSWD=1.2, 1σ, n=17), slightly older than the molybdenite Re–Os isotope ages of 231–234Ma, suggesting that the Donggebi porphyry Mo deposit was formed in the Triassic, post-collisional tectonism subsequent to termination of the Paleo-Asia Ocean. The samples from porphyritic granite show high contents of SiO2, K2O and Al2O3, low contents of TiO2, MgO and CaO, and peraluminous high-K calc-alkaline to shoshonite affinity, with obvious LREE enrichment and negative Eu anomalies. They have high initial 87Sr/86Sr ratios of 0.70618 to 0.70821, εNd(t) values of 0.60 to 1.62, and TDM2(Nd) ages of 0.88 to 0.96Ga. Their (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t values are 17.122–18.577, 15.493–15.574, and 37.887–38.006, respectively. Zircons from the porphyritic granite yield εHf(t) values of −1.58 to 4.82, and TDM2(Hf) ages of 0.96–1.36Ga. These geochemical and isotopic data imply that the Donggebi porphyritic granite originated mainly from partial melting of lower continental crust derived from a depleted mantle. The Donggebi Mo deposit is unique based upon the crustal source for the causative porphyry, the distal position of mineralization, and the previously revealed CO2-rich ore-forming fluids, and thus belongs to the collisional- or Dabie-type porphyry deposits as exemplified by the Qiane'chong and Yaochong deposits in Dabie Shan, the Donggou deposit in Qinling Orogen, China.

Geochemical characteristics of hydrous basaltic magmas due to assimilation and fractional crystallization: the Ikoma gabbroic complex, southwest Japan

To clarify the processes that occur in hydrous basaltic magma chambers, we have undertaken detailed petrological and geochemical analyses of mafic and intermediate rocks from the Ikoma gabbroic complex, southwest Japan. The complex consists mainly of hornblende gabbros, hornblende gabbronorites, and hornblende leucogabbros. The hornblende leucogabbros are characterized by low TiO2 and high CaO contents, whereas the hornblende gabbronorites have high TiO2 and low CaO contents. The initial 87Sr/86Sr ratios (SrI) of the hornblende gabbronorites and hornblende gabbros are higher than those of the hornblende leucogabbros and plagioclase, and they may have resulted from a higher degree of assimilation of metasediments. The geochemical features of the hornblende leucogabbros and hornblende gabbronorites can be explained by accumulation of plagioclase and ilmenite, respectively, in a hybrid magma that formed by chemical interaction between mafic magma and metasediment, whereas the hornblende gabbros were produced by a high degree of crustal assimilation and fractional crystallization of this hybrid magma. As a result of the density differences between crystals and melt, the Ikoma gabbroic rocks formed by the accumulation of plagioclase in the middle of the magma chamber and by the accumulation of ilmenite in the bottom of the chamber. Taking into account the subsequent assimilation and fractional crystallization, our observations suggest an enriched mantle (SrI = ~0.7071) as the source material for the Ikoma gabbros.

Eocene slab breakoff of Neotethys as suggested by dioritic dykes in the Gangdese magmatic belt, southern Tibet

The Gangdese magmatic belt in southern Tibet demarcates an important boundary between the Indian and Eurasian plates. Due to its location and magmatic evolutionary history, it is key to understanding both the history of Neotethys closure and the Indo–Asian collisional process. This study presents new geochronological and geochemical data for dioritic dykes in the southern Gangdese magmatic belt in southern Tibet. U-Pb geochronological results reveal that the dykes were emplaced at ca. 41Ma and thus broadly coeval with the 40–38Ma Dazi volcanics and the 42–40Ma Gaoligong–Tengliang basaltic dykes. Geochemically, these dykes are characterized by alkaline signature, high Mg# (57–63) and low TiO2 contents (~0.9–1.0), showing notable enrichment of light rare earth elements relative to the heavy rare earth elements, enrichment of incompatible elements (i.e. Cs, Rb, Ba, Th and U), and depletion of high field strength elements (i.e. Nb, Ta and Ti). In addition, a large variation of zircon εHf(t) values (−10 to +13) was shown, implying heterogeneity of magma sources. A heterogeneous source is also suggested by the occurrence of xenocrysts in the dykes. These observations suggest that the magma source of the dykes was dominated by partial melting of lithospheric mantle and then subsequently contaminated by crustal material during ascent. In combination with other geological data in the region, we suspect that the slab slicing of the Neotethys played a key role in the formation of the lithospheric mantle-derived dioritic dykes and adakitic granite, asthenosphere-derived volcanics, basaltic dykes, as well as the recently reported strongly fractionated granites.

Multiple episodes of partial melting, depletion, metasomatism and enrichment processes recorded in the heterogeneous upper mantle sequence of the Neotethyan Eldivan ophiolite, Turkey

The Eldivan ophiolite along the Izmir–Ankara–Erzincan suture zone in north-central Anatolia represents a remnant of the Neotethyan oceanic lithosphere. Its upper mantle peridotites include three lithologically and compositionally distinct units: clinopyroxene (cpx)–harzburgite and lherzolite (Group-1), depleted harzburgite (Group-2), and dunite (Group-3). Relics of primary olivine and pyroxene occur in the less refractory harzburgites, and fresh chromian spinel (Cr-spinel) is ubiquitous in all peridotites. The Eldivan peridotites reflect a petrogenetic history evolving from relatively fertile (lherzolite and cpx–harzburgite) toward more depleted (dunite) compositions through time, as indicated by (i) a progressive decrease in the modal cpx distribution, (ii) a progressive increase in the Cr#s [Cr/(Cr+Al)] of Cr-spinel (0.15–0.78), and (iii) an increased depletion in the whole-rock abundances of some magmaphile major oxides (Al2O3, CaO, SiO2 and TiO2) and incompatible trace elements (Zn, Sc, V and Y). The primitive mantle-normalized REE patterns of the Group-1 and some of the Group-2 peridotites display LREE depletions. Higher YbN and lower SmN/YbN ratios of these rocks are compatible with their formation after relatively low degrees (9–25%) of open-system dynamic melting (OSDM) of a Depleted Mid-ocean ridge Mantle (DMM) source, which was then fluxed with small volumes of oceanic mantle-derived melt [fluxing ratio (β): 0.7–1.2%]. Accessory Cr-spinel compositions (Cr#=015–0.53) of these rocks are consistent with their origin as residual peridotites beneath a mid-ocean ridge axis. Part of the Group-2 harzburgites exhibit lower YbN and higher SmN/YbN ratios, LREE-enriched REE patterns, and higher Cr-spinel Cr#s ranging between 0.54 and 0.61. Trace element compositions of these peridotites can be modeled by approximately 15% OSDM of a previously 17% depleted DMM, which was then fluxed (β: 0.4%) with subduction-influenced melt. The Group-3 dunite samples contain Cr-spinel with elevated Cr#s (0.73–0.78) and low-TiO2 contents (<0.13wt.%), implying higher degrees of melting (21–24%) of an already depleted DMM that was triggered by infiltration of low-Ti boninite melt with fluxing rates of 0.4–4.0%. The existence of interstitial, idiomorphic Cr-spinel (high Cr# and low Ti) in the Group-3 dunites is consistent with this interpretation. The occurrence of both MOR- and SSZ-type peridotites in the Eldivan ophiolite suggests that its heterogeneous upper mantle was produced as a result of different partial melting and melt–rock reaction processes in different tectonic settings within the Neotethyan realm.

High Dielectric Constant Study of TiO2-Polypyrrole Composites with Low Contents of Filler Prepared byIn SituPolymerization

TiO2/polypyrrole composites with high dielectric constant have been synthesized byin situpolymerization of pyrrole in an aqueous dispersion of low concentration of TiO2, in the presence of small amount of HCl. Structural, optical, surface morphological, and thermal properties of the composites were investigated by X-ray diffractometer, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, and thermogravimetric analysis, respectively. The data obtained from diffractometer and thermal gravimetric analysis confirmed the crystalline nature and thermal stability of the prepared composites. The dielectric constant of 5 wt% TiO2increased with filler content up to 4.3 × 103at 1 kHz and then decreased to 1.25 × 103at 10 kHz.

Geochemistry of platinum-group elements and mineral composition in chromitites and associated rocks from the Abdasht ultramafic complex, Kerman, Southeastern Iran

The Abdasht complex is a major ultramafic complex in south-east Iran (Esfandagheh area). It is composed mainly of dunite, harzburgite, podiform chromitites, and subordinate lherzolite and wehrlite. The podiform chromitites display massive, disseminated, banded and nodular textures. Chromian spinels in massive chromitites exhibit a uniform and restricted composition and are characterized by Cr# [=Cr/(Cr+Al)] ranging from 0.76 to 0.77, Mg# [=Mg/(Mg+Fe2+)] from 0.63 to 0.65 and TiO2<0.2wt.%. These values may reflect crystallization of the chromian spinels from boninitic magmas. Chromian spinels in peridotites exhibit a wide range of Cr# from 0.48 to 0.86, Mg# from 0.26 to 0.56 and very low TiO2 contents (averaging 0.07wt.%). The Fe3+# is very low, (<0.08wt.%) in the chromian spinel of chromitites and peridotites of the Abdasht complex which reflects crystallization under low oxygen fugacities.The distribution of platinum group elements (PGE) in Abdasht chromitites displays a high (Os+Ir+Ru)/(Rh+Pt+Pd) ratio with strongly fractionated chondrite-normalized PGE patterns typical of ophiolitic chromitites. Moreover, the Pd/Ir value, which is an indicator of PGE fractionation, is very low (<0.1) in the chromitites.The harzburgite, dunite and lherzolite samples are highly depleted in PGE contents relative to chondrites. The PdN/IrN ratios in dunites are unfractionated, averaging 0.72, whereas the harzburgites and lherzolites show slightly positive slopes PGE spidergrams, together with a small positive Ru anomaly, and their PdN/IrN ratio averages 2.4 and 2.3 respectively. Moreover, the PGE chondrite and primitive mantle normalized patterns of harzburgite, dunite and lherzolite are relatively flat which are comparable to the highly depleted mantle peridotites.The mineral chemistry data and PGE geochemistry indicate that the Abdasht chromitites and peridotites were generated from a melt with boninitic affinity under low oxygen fugacity in a supra-subduction zone setting. The composition of calculated parental melts of the Abdasht chromitites is consistent with the differentiation of arc-related magmas.

Geochemical Fingerprint and Iron Ore Potential of the Siliceous Itabirite from Palaeoproterozoic Nyong Series, Zambi Area, Southwestern Cameroon

AbstractThe study area forms part of an emerging iron ore province of southern Cameroon. Geochemistry analyses reveal that the siliceous itabirite has a very simple chemical composition, with Fe2O3 and SiO2 representing more than 96 wt.% of the average composition; suggesting chemical precipitates of silica and iron. Low Al2O3 and TiO2 concentrations and a weak positive correlation between them point to a minor detrital component in the precipitated marine sediments. The Si/Al ratio (average 52.7) indicates the hydrothermal origin of the studied itabirite. The Al–Si discrimination diagram supports this interpretation through the plot of all data in the hydrothermal field. The studied samples have low iron content (about 39.32% Fe), high gangue content (40.97% SiO2 and 1.3 % Al2O3) and low concentration of the deleterious elements (0.16 % P and &lt; 0.01% S). The main gangue mineral is silica which can be efficiently removed from iron ores during preparation of raw materials for the blast furnace process. According to commercial standards for crude iron ores, it may be concluded that the Zambi iron ores are a low‐grade magnetic ore that can be profitably exploited for the production of iron for steel production.

Mineralogy, geochemistry, and geotectonic significance of the Neoproterozoic ophiolite of Wadi Arais area, south Eastern Desert, Egypt

ABSTRACTThe dismembered ophiolites in Wadi Arais area of the south Eastern Desert of Egypt are one of a series of Neoproterozoic ophiolites found within the Arabian–Nubian Shield (ANS). We present new major, trace, and rare earth element analyses and mineral composition data from samples of the Wadi Arais ophiolitic rocks with the goal of constraining their geotectonic setting. The suite includes serpentinized ultramafics (mantle section) and greenschist facies metagabbros (crustal section). The major and trace element characteristics of the metagabbro unit show a tholeiitic to calc-alkaline affinity. The serpentinized ultramafics display a bastite, or less commonly mesh, texture of serpentine minerals reflecting harzburgite and dunite protoliths, and unaltered relics of olivine, orthopyroxene, clinopyroxene, and chrome spinel can be found. Bulk-rock chemistry confirms harzburgite as the main protolith. The high Mg# (91.93–93.15) and low Al2O3/SiO2 ratios (0.01–0.02) of the serpentinized peridotite, together with the high Cr# (>0.6) of their Cr-spinels and the high NiO contents (0.39–0.49 wt.%) of their olivines, are consistent with residual mantle rocks that experienced high degrees of partial melt extraction. The high Cr# and low TiO2 contents (0.02–0.34 wt.%) of the Cr-spinels are most consistent with modern highly refractory fore-arc peridtotites and suggest that these rocks probably developed in a supra-subduction zone environment.

Reduction roasting–magnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms

Reduction roasting with sodium sulfate followed by magnetic separation was investigated to utilize vanadium tailings with total iron grade of 54.90 wt% and TiO2 content of 17.40 wt%. The results show that after reduction roasting–magnetic separation with sodium sulfate dosage of 2 wt% at roasting temperature of 1150 °C for roasting time of 120 min, metallic iron concentrate with total iron grade of 90.20 wt%, iron recovery rate of 97.56 % and TiO2 content of 4.85 wt% is obtained and high-titanium slag with TiO2 content of 57.31 wt% and TiO2 recovery rate of 80.27 % is also obtained. The results show that sodium sulfate has a catalytic effect on the reduction of tailings in the novel process by thermodynamics, scanning electron microscopy (SEM) and X-ray diffraction (XRD) and reacts with silica and alumina in the tailings to form sodium silicate and sodium aluminosilicate. Migration of elements and chemical reactions destroy the crystal structures of minerals and promote the reduction of vanadium tailings, resulting in that iron grains grow to large size so that metallic iron concentrate with high total iron grade and low TiO2 content is obtained.

Magmatic evolution of the Tuwu–Yandong porphyry Cu belt, NW China: Constraints from geochronology, geochemistry and Sr–Nd–Hf isotopes

The Tuwu–Yandong porphyry Cu belt is located in the Eastern Tianshan mountains in the eastern Central Asian Orogenic Belt. Petrochemical and geochronological data for intrusive and volcanic rocks from the Tuwu and Yandong deposits are combined with previous studies to provide constraints on their petrogenesis and tectonic affinity. New LA–ICP–MS zircon U–Pb ages of 348.3±6.0Ma, 339.3±2.2Ma, 323.6±2.5Ma and 324.1±2.3Ma have been attained from intrusive units associated with the deposits, including diorite, plagiogranite porphyry, quartz albite porphyry and quartz porphyry, respectively. The basalt and andesite, which host part of the Cu mineralization, are tholeiitic with high Al2O3, Cr, Ni and low TiO2 contents, enriched LREEs and negative HFSE (Nb, Ta, Zr, Ti) anomalies consistent with arc magmas. Diorites are characterized by low SiO2 content but high MgO, Cr and Ni contents, similar to those of high-Mg andesites. The parental magma of the basalt, andesite and diorite is interpreted to have been derived from partial melting of mantle-wedge peridotite that was previously metasomatized by slab melts. The ore-bearing plagiogranite porphyry is characterized by high Na2O, Sr, Cr and Ni contents, low Y and Yb contents, low Na2O/K2O ratios and high Sr/Y ratios and high Mg#, suggesting an adakitic affinity. The high εNd(t) (5.02–9.16), low ISr (0.703219–0.704281) and high εHf(t) (8.55–12.99) of the plagiogranite porphyry suggest they were derived by a partial melting of the subducted oceanic crust followed by adakitic melt-mantle peridotite interaction. The quartz albite porphyry and quartz porphyry are characterized by similar Sr–Nd–Hf isotope but lower Mg# and whole-rock (La/Yb)N ratios to the plagiogranite porphyry, suggesting they were derived from juvenile lower crust, and negative Eu anomalies suggest fractionation of plagioclase. We propose that a flat subduction that started ca. 340Ma and resulted in formation of the adakitic plagiogranite porphyry after a period of “steady” subduction, and experienced slab rollback at around 323Ma.

Geochemical characteristics of Carboniferous volcanic rocks from the Wulungu-Luliang area, Junggar basin: constraints on magma source and tectonic setting

The Carboniferous volcanic rocks in the Wulungu-Luliang area are mainly andesites of medium- to high-K calc-alkalic series. Volcanic rock samples have relatively high alkali (Na2O + K2O = 4.7 % to 6.8 %) and low TiO2 contents (0.7 % to 0.9 %), relatively high MgO (2.5 % to 3.4 %) and Mg# (49.9 % to 67.1 %), high rare earth element (REE) contents, and relatively high K2O contents (1.7 % to 3.1 %). Chondrite-normalized REE patterns show light REE enrichment ((La/Yb)N = 4.15 to 5.19) with weak Eu anomalies (δEu = 0.75 to 0.92). These samples are enriched in large-ion lithophile elements but relatively depleted in high field strength elements. The trace elements and REE patterns are similar to those of Setouchi and central Ryukyu high-Mg andesites, indicating a high-Mg andesite source. Relatively high Y contents (16.7 to 24.4 ppm), and relatively low Sr/Y ratios (17.2 to 38.8) and TiO2 contents (0.7 % to 0.9 %) exclude the possibility of slab melting. Low Sr/Nd (16.6 to 42.8), Ba/Th (66.4 to 266.8), and U/Th (0.2 to 0.3) indicate that the influence of slab-derived fluids is low. The ratios of Ce/Th (4.9–7.3), Ce/Pb (1.8–4.2), Ba/Rb (7.99–22.03), Ba/Th (66.4–266.8), and La/Sm (3.6–4.3) are similar to ratios found in subducting sediment melts. Relatively high ratios of K/Nb (1357–3258), Th/La (0.28–0.42), Zr/Nb (8.8–27.1), and especially Th/Nb (0.48–1.25) suggest that the magma was assimilated and contaminated by upper continental crust. These characteristics, along with the ratios of La/Yb, Sc/Ni, Th/Yb, Ta/Yb, Ce/P2O5, and Zr/TiO2, demonstrate that the earlier Carboniferous volcanic rocks in the Wulungu-Luliang area were generated in a continental island-arc setting.