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She Y.W.,Chinese Academy of science | She Y.W.,University of Chinese Academy of Sciences | Song X.Y.,Chinese Academy of science | Yu S.Y.,Chinese Academy of science | And 3 more authors.
Acta Petrologica Sinica | Year: 2014

The ∼ 260Ma Taihe layered intrusion is one of the mafic-ultramafic intrusions host giant magmatic Fe-Ti oxide ore deposit in the central Emeishan Large Igneous Province. It outcrops ∼3km long and ∼2km wide, and has a thickness of ∼ 1. 2km. According to mineral assemblages and petrography textures, the intrusion can be divided into three lithologic zones: Lower Zone (LZ), Middle Zone (MZ) and Upper Zone (UZ). The LZ comprises (olivine) gabbros and thick massive Fe-Ti oxide ores. The MZ consists of six cyclic units, which are comprised of (apatite) magnetite clinopyroxenites and (apatite) gabbros from the base to the top. The UZ is comprised of Fe-Ti oxide-poor apatite gabbros. The apatite magnetite clinopyroxenites of the Taihe MZ contain 5% ∼ 12% apatite, 20% ∼35% Fe-Ti oxides and 50%-60% silicates which occur as cumulus phases together with apatite. The magnetite compositions of the apatite magnetite clinopyroxenites are characterized by high TiO2, FeO, MnO and MgO contents and its variations are similar to those of the Panzhihua intrusion. Meanwhile, the ilmenite compositions display the negative correlations between FeO and TiO2 and MgO, respectively. The FeO of ilmenite is positively correlated to Fe2O3 and MnO, respectively. These features suggest that magnetite and ilmenite crystallized from the Fe-Ti-P-rich silicate magma rather than immiscible nelsonitic melts. It thus can be concluded that the origin of apatite magnetite clinopyroxenites is resulted from crystal fractionation associated with gravitational sorting and setting. In the LZ, magnetite inclusions in olivine contain relatively high Cr2O3 (0. 07% ∼ 0. 21%), whereas the Cr 2O3 (0. 00% ∼ 0. 03%) of magnetite inclusions in olivine from the MZ abruptly decreased. The Cr2O3 contents of magnetite inclusions in olivine are positively correlated with An content of plagioclase and Cr content of clinopyroxene. It confirms the replenished parental magmas formed the MZ rocks are different from the relatively primitive parental magmas formed the LZ rocks and ores. The MZ Fe-Ti-P-rich magma may be produced by the Fe-Ti enriched magma from a deep-seated magma chamber mixing with the extensively evolved P-rich magma in a middle level magma chamber. The relatively low Ti + V contents of magnetite of the UZ and the top of MZ suggest the compositions of these magnetites may be modified by magmatic hydrothermal resulted from late stage of magma differentiation. Source


Leng C.-B.,Chinese Academy of science | Zhang X.-C.,Chinese Academy of science | Zhong H.,Chinese Academy of science | Hu R.-Z.,Chinese Academy of science | Zhou W.-D.,Sichuan Institute of Metallurgical Geology and Exploration
Mineralium Deposita | Year: 2013

The Miocene porphyry Cu-(Mo) deposits in the Gangdese orogenic belt in southern Tibet were formed in a post-subduction collisional setting. They are closely related to the Miocene adakite-like porphyries which were probably derived from a thickened basaltic lower crust. Furthermore, mantle components have been considered to have played a crucial role in formation of these porphyry deposits (Hou et al. Ore Geol Rev 36: 25-51, 2009; Miner Deposita doi:10.1007/s00126-012-0415-6, 2012). In this study, we present zircon Hf isotopes and molybdenite Re-Os ages on the newly discovered Gangjiang porphyry Cu-Mo deposit in southern Tibet to constrain the magma source of the intrusions and the timing of mineralization. The Gangjiang porphyry Cu-Mo deposit is located in the Nimu ore field in the central Gangdese porphyry deposits belt, southern Tibet. The copper and molybdenum mineralization occur mainly as disseminations and veins in the overlapped part of the potassic and phyllic alteration zones, and are predominantly hosted in the quartz monzonite stock and in contact with the rhyodacite porphyry stock. SIMS zircon U-Pb dating of the pre-mineral quartz monzonite stock and late intra-mineral rhyodacite porphyry yielded ages of 14.73 ± 0.13 Ma (2σ) and 12.01 ± 0.29 Ma (2σ), respectively. These results indicate that the magmatism could have lasted as long as about 2.7 Ma for the Gangjiang deposit. The newly obtained Re-Os model ages vary from 12.51 ± 0.19 Ma (2σ) to 12.85 ± 0.18 Ma (2σ) for four molybdenite samples. These Re-Os ages are roughly coincident with the rhyodacite porphyry U-Pb zircon age, and indicate a relatively short-lived episode of ore deposition (ca. 0.3 Ma). In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS indicate that the εHf(t) values of zircons from a quartz monzonite sample vary from +2.25 to +4.57 with an average of +3.33, while zircons from a rhyodacite porphyry sample vary from +5.53 to +7.81 with an average of +6.64. The Hf data indicate that mantle components could be partly involved in the deposit formation, and that mantle contributions might have increased over time from ca. 14.7 to 12.0 Ma. Combined with previous works, it is proposed that the Gangjiang deposit could have resulted from the convective thinning of the lithospheric root, and the input of upper mantle components into the magma could have played a key role in the formation of the porphyry deposits in the Miocene Gangdese porphyry copper belt in the Tibetan Orogen. © 2012 Springer-Verlag Berlin Heidelberg. Source


Liang H.,China University of Geosciences | Chen X.,China University of Geosciences | Wang C.,China University of Geosciences | Zhao D.,Sichuan Institute of Metallurgical Geology and Exploration | Weissert H.,ETH Zurich
Journal of Asian Earth Sciences | Year: 2016

Methane-derived authigenic carbonates with distinctive structures and morphologies have been documented worldwide, but they are rarely found from ancient strata in the Eastern Tethys Ocean. The methane-derived authigenic carbonates found in southern Tibet are developed in calcareous or silty shales of mid-Cretaceous age in the Xigaze forearc basin and in the Tethyan Himalaya tectonic zone. The morphology, mineralogy, elemental geochemistry and composition of carbon and oxygen isotopes of these carbonates are studied in detail. The carbonates have nodular, tubular, and tabular morphologies. They are primarily composed of carbonate cement that binds and partly replaces host sediment grains; host siliciclastic sediments are composed mainly of quartz and plagioclase feldspar; a few foraminifers; and framboidal or subhedral to euhedral pyrite. Carbonate cements dominantly are micritic calcite, with minor contribution of dolomite. Nodular concretions are characterized by depleted δ13C values, commonly ranging from -30‰ to -5‰. The δ13C values show a gradual decrease from the periphery to the center, and the CaO, SiO2, Fe2O3, Al2O3, K2O, and TiO2 contents generally show a gradual change. These features indicate that the nodular concretions grew from an early-formed center toward the periphery, and that the carbon source of the nodular concretions was derived from a mixture of methane, methanogenic CO2, and seawater-dissolved inorganic carbon. The tubular concretions are characterized by δ13C values of -8.85‰ to -3.47‰ in the Shangba Section, and -27.37‰ to -23.85‰ in the upper Gamba Section. Unlike the nodular concretions, the tubular concretions show central conduits, which are possible pathways of methane-rich fluids, suggesting that the cementation of tubular concretions begins at the periphery and proceeds inward. Moreover, the tubular concretions show morphological similarity with the methane-derived carbonate chimneys, pipes and slabs reported in present-day cold seep settings. We suggest that the carbon source of the tubular concretions was derived from a mixture of seawater-dissolved inorganic carbon and oxidized methane formed by released hydrate. The tabular concretions are characterized by δ13C values of -21.87‰ to -6.67‰ in the Xiege Sections. These depleted δ13C values suggest that the carbon of the tabular concretions was derived at least in part, from AOM. The tabular concretions are characterized by δ13C values of -28.81‰ to -12.99‰ in the Gamba Section. According to the δ13C values and field observation, we infer that their carbon source was more likely to be a mixture of the oxidized methane formed by released hydrate and seawater-dissolved inorganic carbon. © 2015 Elsevier Ltd. Source


Yan B.,Chengdu University of Technology | Yan H.,Sichuan Institute of Metallurgical Geology and Exploration | Zhou L.,Chengdu University of Technology | Wang T.,Chengdu University of Technology | And 2 more authors.
Kuangwu Yanshi/ Journal of Mineralogy and Petrology | Year: 2013

Stable isotope compositions of different stages of uranium minerals in the Xiangshan uranium ore field are analyzed. The δ13C PDB and δ18OSMOW values of the calcite are in the range of 3. 2‰̃7. 4‰ and 1. 7‰̃15. 2‰ respectively. It indicates that mineralizer CO2 mainly originated from earth mantle. The negative correlation between δ13CPDB and δ18OSMOW of CO2 degassing,mixing of two fluids and fluid-rock interaction may be a major controlling factor for calcite precipitation. δ18O of water in fluid inclusions of fluorites is -1. 4‰̃-9. 0‰, and δD is -68‰̃-90‰; δ18O of quartz is 2. 4‰̃4. 4‰, and δD is -59‰̃-71‰, indicating that the fluids are meteoric in origin, and extensive water-rock reaction played an important role in the mineralization. S2 - which as a reduction agent also played an important role for uranium precipitation;the measurement of S isotope in pyrite suggests that the most of part of sulfur in ore-forming fluid may mainly came from surrounding rocks. Source


Yang L.,Hubei University | Yang L.,Sichuan Institute of Metallurgical Geology and Exploration | Zhou H.-W.,Hubei University | Zhu Y.-H.,Hubei University | And 6 more authors.
Geological Bulletin of China | Year: 2014

Intermediate to mafic dyke swarms are developed in Haxiya area which is located in the north of the Eastern Kunlun orogenic belt. The rocks are mainly composed of diabase, dioriteic lamprophyre and diorite porphyrite, which have K calc-alkaline basalt series features as shown by geochemical analyses. The REE distribution patterns suggest strong fractionation between LREE and HREE and weak negative Eu anomaly, with LREE/HREE being 4.72~8.66 (6.57 on average), and δEu being 0.81~0.98 (0.91 on average), indicating indistinct fractional crystallization of plagioclase. The intermediate to mafic dyke swarms in this area are enriched in LILEs (K, Rb, Cs, Ba, Sr) and depleted in HFSEs (Nb, Ta, Zr, Hf, Ti), showing the characteristics of intraplate basalts with some information of the subduction zone. LA-ICP-MS U-Th-Pb dating shows that zircon ages are relatively scattered, and eight magmatic zircons have yielded a weighted mean 206Pb/238U age of 411.5±7.5Ma, representing the crystallization age of the intermediate to mafic dyke swarms in Haxiya area of Golmud. That age suggests that the tectonic setting of the north of the Eastern Kunlun Block had accomplished the environment conversion from compression of colliding terranes to extension after collision, and eventually entered the intracontinental orogenic stage during Late Silurian-Early Devonian. Source

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