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Yu L.,China University of Geosciences | Wang X.-L.,China University of Geosciences | Zhou H.-R.,China University of Geosciences | Wang L.,Beijing General Research Institute of Mining And Metallurgy | And 3 more authors.
Geological Bulletin of China | Year: 2012

The Datie bauxite deposit in Qiubei County, southeastern Yunnan Province, is a recently-discovered medium-size sedimentary diaspore deposit, and its ore-hosting strata are developed in the lower member of Upper Permian Longtan Formation. Through an analysis of mineralogy and petrography, the authors conducted a systematic research on the compositions and modes of occurrence of the ore minerals. The result indicates that diaspore is the main mineral, followed by kaolinite, illite, sericite, chlorite, anatase, goethite, hematite, rutile, chalcedonite, etc., presenting a diversity of crystalline morphologies and modes of occurrence. Five main dissemination characteristics of diaspore are observed: a) unevenly disseminated in gangue minerals with euhedral or subhedral granular textures; b) in pisolitic, potato-shaped or oolitic forms; c) as aphanitic crystalline or microcrystalline aggregates or with irregular granular or microgranular texture; d) as veins, skeletal crystals; e) as aggregates of diaspore, alumina gel or gangue minerals assuming zonal patterns or concentric circles.

Qi X.X.,Chinese Academy of Geological Sciences | Zhu L.H.,Chinese Academy of Geological Sciences | Hu Z.C.,Wuhan University | Li Z.Q.,Yunnan Bureau of Nonferrous Geology
Acta Petrologica Sinica | Year: 2011

The Early Cretaceous granodiorite and quartz monzonite are the main types of igneous rocks in Tengchong block. The characteristics of I-type plutonic rocks are shown by the mineral assemblages, and high Na2O and low K2O contents and A/CNK values. Zircon SHRIMP U-Pb dating show the granodiorite and quartz monzonite emplaced at 122 ± 1.3Ma and 125 ± 1.3Ma, respectively. The zircon εHf(t) values for granodiorite and quartz monzonite range from -9. 6 to -4. 8 (average -6. 7 ±0. 7) and - 7. 8 to -4. 7 (average -6. 3 ±0. 6) , with corresponding single-stage model ages ranging from 979 to 1190Ma and 975 to 1113Ma, respectively. All samples plotted in the region between meteoritic Hf evolution line ( CHUR) and the lower crust line in the plot of εHf(t) values vs. U-Pb ages, and high Al2O 3 contents and Th/Hf ratios indicate that formed with crust-derived magma. While, the widely range of zircon εHf(t) values which are lower than those of igneous rocks produced by partial melting of crustal material, and high Th/Yb, low Ba/La and Yb/Hf ratios, show that the magmas for granodiorite and quartz monzonite are the mixing of large proportion of crust-derived magma and small proportion of mantle-derived magma. The fact of high Na2O and low K2O contents, and distribution of strongly enrichment of large-ion lithophile elements (K, Rb, Ba and K) relative to those in the primordial mantle, negative anomaly of Ba, Nd, Ta, Sr, P, Ti in the primitive mantle-normalized trace elemental spider diagram, and negative anomaly of Eu in the chondrite-normalized REE patterns, and geochemical tectonic discriminant diagrams, show the granodiorite and quartz monzonite were formed in the tectonic setting related with subduction and collision. The ages, zircon Lu-Hf isotopic compositions and corresponding single-stage model ages, and features of trace element for Early Cretaceous plutonic rocks in Tengchong block, are the same with that in the central section and southeast part of Lhasa block, suggest that the Early Cretaceous magmatic belt in Tengchong block is a part of central Lhasa magmatic belt, and resulted from subduction of middle Tethyan oceanic crust and continental collision between Lhasa-Tengchong and Qiangtang-Baoshan blocka.

Zhu L.H.,Chinese Academy of Sciences | Zhu L.H.,Geological Survey Institute of Guangdong Nonferrous Metok Geological Survey Bureau | Qi X.X.,Chinese Academy of Sciences | Peng S.B.,Wuhan University | Li Z.Q.,Yunnan Bureau of Nonferrous Geology
Acta Petrologica Sinica | Year: 2011

Daping gold deposit is a large quartz-vein gold deposit in Ailaoshan tectonic zone, made of north and south fields. Fluid inclusion homogenization temperatures range from 187°C to 329°C (average is 281°C) in north field, and from 168°C to 338°C ( average is 264°C ) in south field, respectively. Corresponding, the δDV-SMOW values range from -70‰ to -81‰ and from -71‰ to -86‰, and the δ18OH2O values rang from 2. 9‰ to 9. 8‰ and from 3. 5‰ to 5. 1‰, respectively. All samples plotted at the field between magmatic water and underground water in the plots of δD vs. δ18OH2O, and that for north field are near magmatic water area, and for south field are near underground water area. The sulfur isotopic compositions (δ34S) for north and south fields are 0.7‰ 15. 5‰ and 10. 6‰ - 15. 8‰, respectively. The vapour compositions in fluid inclusions are H2O, CO2 and N2, with a little of CH4, C 2H2, C2H4, C2H 6 and CO. The ion compositions in fluid inclusions are K+ , Na+ , Ca2+ , Cl- and SO4 2- , with a little of NO3 -, F- , Br- and Mg2+ . ESR dating data for quartz in gold-bearing quartz veins from north and south fields are 27. 2 -29. 1Ma and 17. 3 -22. 1Ma, respectively. All above show, that the ore forming fluids are mixing of postmagmatic solution and underground water, from north to south, deep to shallow fields and from earlier to later stage, the contents of the postmagmatic solution and sulfur are decreasing, and that of the underground water is increasing, and the age of minerallization is youngling, gradually.

Qi X.,Chinese Academy of Geological Sciences | Zhu L.,Chinese Academy of Geological Sciences | Zhu L.,Wuhan University | Li H.,Chinese Academy of Geological Sciences | And 2 more authors.
Acta Geologica Sinica | Year: 2010

Mylonitized granite in the Ailaoshan-Jinshajiang tectonic zone is hosted in the center of the Ailaoshan high grade metamorphic belt. LA-ICP-MS U-Pb dating of two zircon samples (08Q2-22 and 08Q2-15) shows the ages of the growth rims of zircon grains are 250. 2±2. 1Ma(MSWD=2. 5)and 247. 2±2. 3Ma (MSWD=0.15), respectively. The lattice preferred orientations by EBSD suggest that the c-axis fabrics of quartz are prism slip, and the ductile deformation formed under the condition of amphibolite facies (500 -630°C). This temperature is far lower than the zircon crystallized temperature (675-864°C) in magmatism and the closed temperature (> 800°C) of U-Pb system in zircon, so the deformation and metamorphism can not destroy the U-Th-Pb stabilization of zircon grains crystallized during magma intrusion. The features of zircon Cathodoluminescence images and the U-Pb concordia lines of zircon indicate that the LA-ICP-MS U-Pb dating (247-250Ma) for zircon rims represents the emplacement age of granite. The granite is characterized geochemically by peraluminous minerals (e. g. muscovite) , low Na and high K, A/CNK and A/NK>1.0, similar distribution of REE and trace elements geochemistry similar to those in the upper crust, as well as strong enrichment of large-ion lithophile and magmatophile elements, depletion of Sm and Y. Tectonic discrimination diagrams of (Yb+Ta)-Rb, (Y+Nb)-Rb, CaO(TFeO+MgO) and Cenozoic subducting collision of the Ailaoshan-Jinshajiang tectonic belt all suggest that the granite formed and emplaced during the stage of collision. Combined with mylonitized granites successively discovered in the Ailaoshan and Dianchangshan high grade metamorphic belt by previous workers, and ductile deformation and metamorphism of felsic rocks occurring in the middle-lower crust (deeper than 10-15km), our study shows that the Ailaoshan-Jinshajiang metamorphic belt was the early Triassic or early rocks which were squeezed out and uplifted to the crust after it was subducted to the lower crust and suffered ductile deformation and metamorphism. Therefore, the strong metamorphism might occur in Mesozoic or Cenozoic, but not Proterozoic, and is not or completely the crystalline basement rock of Yangtze block.

Qi X.,Chinese Academy of Geological Sciences | Zhao Y.,Chinese Academy of Geological Sciences | Zhu L.,Geological Survey Institute of Guangzhou Bureau of Nonferrous Geology | Li Z.,Yunnan Bureau of Nonferrous Geology
Acta Petrologica Sinica | Year: 2012

High-pressure pelitic granulite containing porphyroblasts of garnet (Grt), sillimanite (Sil), K-feldspar (Kf) and plagioclase (PI), and inclusions of spinel (Spl), kyanite (Ky), sapphirine (Spr) and rutile (Rut) have been found from the Ailaoshan orogenic belt, southeastern Tibet, regarded as a key indicator for identification of the boundary between the Indochina and South China blocks. The temperatures and pressures calculated by garnet-biotite- plagioclase-quartz geothermobarometery and high-temperature equilibrium spinel + quartz assemblage show the formation and evolution of the graunlite had experienced clockwise P-T path from high-pressure/-temperature to mid-temperature and low-pressure metamorphism. That are: 1) the high-pressure/-temperature metamorphism (HP/HT) is characterized by an assemblage of Ky + Sil + Grt 1 + Kf 1 + Pl 1 + Spr + Ter(Kf + P1) + Bt 1 + Spl + Qtz + Iln 1 + Rut 1, and the peak P-T conditions of ≥ 10.4kbar at 850 ∼ 919°: 2) the mid-temperature and low-pressure retrogressive metamorphism characterized by an assemblage of Grt 2 + Bt 2 + Pl 2 + Ms + Qtz + Ilm 2 + Rut 2, and two stage P-T conditions of 4. 9 ∼ 6. 5kbar at 664-754°C and 3. 5 ∼3. 9kbar at 572-576°C respectively. The dynamic metamorphic path was that the metapelitic rock experienced high-pressure/-temperature granulite-facies metamorphism in lower continental crust (≥ 30km) exhumated to mid-upper crust rapidly, it might be related to the continental collision and underthrusting between the Indochina and South China blocks, and exhumation and slip shearing lately.

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