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Guo X.,Chinese Academy of Geological Sciences | Guo X.,Gold Geology Institute of CAPF | Ge L.,Chinese Academy of Geological Sciences | Ge L.,Gold Geology Institute of CAPF | And 4 more authors.
Acta Petrologica Sinica | Year: 2012

Machangqing complex is an important part of alkali-rich porphyry belt in western Yunnan. The deep-derived mafic enclaves that found in Machangqing complex are significant for studying the origin and evolution of alkali-rich porphyry, ore-forming process, and regional geodynamics. According to the geological features of the enclaves, the author analyzed the zircons from enclaves with the LA-ICP-MS and obtained a U-Pb weighted average age of 35. 13 ±0. 23 Ma (MSWD =0. 64). This age is consistent with the age of granite porphyry (35. 0 ±0. 2Ma) and porphyritic granite (33. 78 ±0. 21 Ma) which are the host rocks of enclaves. The Th/U value and Ti thermometer tempetature of zircons from enclaves and host rocks suggest that the enclaves are from magma mixing. Studies show the Machangqing alkali-rich porphyry is the mixture of crust-derived and mantle-derived magma enclaves and their host rocks have the similar magma evolution process and the injection of mantle-derived magma is a key factor to the ore-formation of this series magma. Source

Guo X.-D.,Chinese Academy of Geological Sciences | Guo X.-D.,Gold Geology Institute of CAPF | Wang Z.H.,Gold Geology Institute of CAPF | Wang L.,Gold Geology Institute of CAPF | And 3 more authors.
Geology in China | Year: 2011

U -Pb ages and trace elements of zircons from porphyritic granite of Machangqing complex were analyzed by the LA-ICP-MS method. As revealed by the cathodoluminescence (CL) images, all the zircons from porphyritic granite have the oscillatory zoning. REE patterns of the analyzed zircons are characterized by significantly high heavy rare earth elements (HREE), depleted light rare earth elements (LREE), obviously positive Ce anomaly and moderately negative Eu anomaly. In addition, nearly all the zircons have high Th/U ratios. These characteristics suggest a magmatic genesis of the analyzed zircons. The zircons from the porphyritic granite of Machangqing complex yield the U-Pb weighted average age of (33.78±0.21)Ma (MSWD=0.71), whereas zircons from syenite porphyry and granitic porphyry yield the U-Th-Pb ages of (35.6±0.3)Ma and (35.0±0.2)Ma by cumulative probability statistics. Molybdenites from the Baoxingchang ore block yield the Re-Os isochron ages of (35.8±1.6)Ma and (33.9±l.l)Ma. Muscovites of contact metasomatic gold mineralization from the Luandongshan ore block yield the 40Ar/39Ar age of (35.25 ±0.36)Ma. Muscovites of hydrothermal vein gold mineralization from the Rentouqin-Jinchangqin ore block yield the 40Ar/39Ar age of (35.35 ±0.32)Ma. These ages show that porphyry type copper -molybdenum mineralization, contact metasomatic gold mineralization and hydrothermal vein gold mineralization are products of the same tectonic-magmatic-hydrothermal ore-forming system,and that the II period magmatic combination (33̃37 Ma) of syenite porphyry +monozonite porphyry + granitic porphyry + porphyritic granite seems to have been the ore-forming geological body, which supplied materials, fluid and thermodynamic conditions for the ore -forming process. The duration of the porphyry - hydrothermal fluid-ore forming system is about 4 Ma. The ore-forming process of copper, molybdenum and gold occurred in the early-middle stage. Source

Guo X.-D.,Chinese Academy of Geological Sciences | Guo X.-D.,Gold Geology Institute of CAPF | Niu C.-Y.,Gold Geology Institute of CAPF | Niu C.-Y.,China University of Geosciences | And 2 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2011

Mafic, deep-derived and dark-colored enclaves have been discovered for the first time in the Machangqing alkali-rich porphyry in Yunnan Province, which supply more credible geologic evidence to study and reveal the property and origin of the alkali-rich magma and to understand geodynamics of the rock and ore-formation. The enclaves are mainly round or sub-round and are featured by mircogranular-fine grained texture, including acicular apatite. Some enclaves contain K-feldspar and quartz phenocrysts from host rocks. The plots of major and trace elements for both enclaves and host rocks show a linear correlation trend. In addition, their REE and trace element patterns are clearly similar, which shows their geochemical similarity and conspicuous non-cognate feature. All of the characteristics indicate the dark-colored enclaves in Machangqing intrusive are generated by mixing of mantle-derived magma and crustal magma. The injection of mixed mantle-derived magma is the key factor to the ore-formation of the magma. Source

Wang L.,China University of Geosciences | Wang L.,Gold Geology Institute of CAPF | Guo X.-D.,Gold Geology Institute of CAPF | Jia L.-Q.,China University of Geosciences | And 3 more authors.
Bulletin of Mineralogy Petrology and Geochemistry | Year: 2012

A large number of dark enclaves occur in the porphyritic granite of the Machangqing complex. Major elements, trace elements and Pb isotope compositions of enclaves and their host rocks have been analyzed. The characteristics of major and trace elements show that enclaves are genetically related to host rocks. Pb isotope results indicate that enclaves and host rocks may derive from the lower crust and EM II. Based on above results and the pe-trographical features, the magma mixing genesis of the enclaves was determined. Dark enclaves in the Machangqing complex can supply credible geological evidence to reveal the origin of the alkali-rich magma, deep geodynamics and the relationship between rock and ore-forming process. It indicates that the Machangqing complex may be the production of mixing of crust-derived and mantle-derived magmas and that the mantle-derived magma may supply the main ore-forming materials. Source

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