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Duan X.-X.,CAS Institute of Geology and Geophysics | Duan X.-X.,University of Chinese Academy of Sciences | Zeng Q.-D.,CAS Institute of Geology and Geophysics | Yang Y.-H.,CAS Institute of Geology and Geophysics | And 4 more authors.
International Geology Review | Year: 2015

The Laojiagou Mo deposit is a newly discovered porphyry Mo deposit located in the Xilamulun Mo metallogenic belt, Northeast China. Mo mineralization mainly occurred within the monzogranite and monzogranite porphyry. Re-Os isochron dating of molybdenites indicate a mineralization age of 234.9 ± 3.1 Ma. Zircon LA-ICP-MS U-Pb analysis for monzogranite porphyry and monzogranite yield 206Pb/238U ages of 238.6 ± 1.8 and 241.3 ± 1.5 Ma, respectively, indicating that Laojiagou Mo mineralization is related to Middle Triassic magmatism. Hf isotopic compositions of zircons from both monzogranite porphyry and monzogranite are characterized by positive εHf(t) values [εHf(t) = 2.9-7.3 and 1.5-7.9, respectively] and young TDM2 model ages, which implies that the magma was derived from juvenile crust created during accretion of the Central Asian Orogenic Belt (CAOB). Identification of the Laojiagou Mo deposit adds another important example of Triassic Mo mineralization in the Xilamulun Mo metallogenic belt where most Triassic Mo deposits in northeast China cluster around the northern margin of North China Craton. Based on the regional geological setting and geochronological and Hf isotope characteristics, we propose that Triassic Mo deposits and related magmatic rocks in northeast China formed during the last stages of evolution of the CAOB. These deposits formed during post-collisional extension after the closure of the Palaeo-Asian Ocean and amalgamation of the North China-Mongolian Block with the Siberian Craton. © 2014 Taylor & Francis. Source

Duan X.X.,CAS Institute of Geology and Geophysics | Duan X.X.,University of Chinese Academy of Sciences | Liu J.M.,CAS Institute of Geology and Geophysics | Wang Y.B.,CAS Institute of Geology and Geophysics | And 8 more authors.
Acta Petrologica Sinica | Year: 2012

The Qingchengzi orefield which lies in geotectogene of Liaodong rift is an important polymetallie mineral district in northern China for its clustering several large Pb-Zn, Ag and Au deposits. A phase of Late Triassic magmalism, represented by Shuangdinggou biotite monzogranite and Xinling granite, is intimately related to polymetallie mineralization. LA-ICPMS zircon U-Pb age of 224.2 ± 1.2Ma was obtained for the Shuangdinggou intrusion. Geochemical data for the Shuangdinggou intrusion reveal SiO 2 content of 69.07% ∼71.31%, while K 2O accounts for 3.53% ∼5.22% and Na 2O for 3.87% ∼4.14%, indicating it belongs to high K calc-alkaline series. Al 2O 3 content ranges between 12.46% ∼ 14.48% and A/CNK < 1 suggest metaluminous feature. Trace element geochemistry of the biotite monzogranite displays high total REE content and demonstrate strong fractionation between light and heavy REE elements [ ( La/Yb) N = 35.43 ∼ 79.01, LREE/HREE = 23.09 ∼ 35.10 ] and minor negative Eu anomalies ( δEu = 0.68 ∼0.97). The biotite monzogranite also shows LILE (such as Rb, Th, K, Pb) enrichment and HESE (including Nb, Ta, P, Ti) depletion, with unusual high Ba and Sr, low Y and Yb abundances manefesting adakitic geochemical signature. Based on above-stated petrological and geochemical data it is inferred that the biotite monzogranilic magma might be derived Irom the partial melting of a thickened lower crust with prominent garnet and rutile retained in the residual assemblages, and magma mixing is probably involved based on the unusually high Nb/Ta ratio (18.4∼21.2). It is suggested that slab break-off during the process of Yangtze Craton and North China Craton continental deep subduction in Late Triassic may be responsible for the ore-related magmatism. Source

Liu Y.,China University of Geosciences | Yang L.,China University of Geosciences | Guo L.,China Railway Resources Exploration Company | Li R.,China University of Geosciences | And 4 more authors.
Acta Petrologica Sinica | Year: 2014

The Dayingezhuang gold deposit, located in the central section of the Zhaoping Fault Zone, northwestern Jiaodong Peninsula, within the phyllic zone in the footwall of main fault. Wall-rock alteration is intense and has a variety of types that include potash feldspathization, silication, sericitization, pyritization, chloritization and carbonatation. Amongst these alterations, silication, sericitization and pyritization are considered more closely related with the gold mineralization. Based on the cutting relations of veins and paragenesis of ore minerals, we determined three major mineralization stages: gold-quartz-pyrite, gold (silver) -quartz-polymetallic sulfides, quartz-calcite-pyrite. Employing the decrepitation thermometry to the ore quartz, we identified three concentrated ranges: 330-510°C, 240-330°C and 240-330°C, which are corresponding with each of the mineralization stage above. The ore-forming fluids in the Dayingezhuang gold deposit are characterized by medium temperature and rich in CO2content, contain a small amount of volatile gases, such as CH4, C2H6and H2S. The scheme of NaCl-H2O-CO2and the high level content of C2H6existed in all of mineralization stages indicate that the ore-forming fluids mostly are the metamorphic water. Even though the gas-liquid content from different mineralization stages are similar with each other, we still observed certain rules along the ore-forming evolution. The trend of increasing N2content indicates that the ore-forming fluids system switch to an open system in the late stage, and atmospheric water began to take part in the ore-forming fluids. The high quantity of H2S in the early gold mineralization indicates that the gold possibly was migrated as Au-S complex. The climbing ratios of C1-/SO2- 4and Na+/K+show that the ore-forming system convert from the CO2-H2O-K2SO4into CO2-H2O-NaCl system with the evolving process. The concentration of Na+, C1-, K+and SO2- 4decreased from early stage to later stage indicates that the salinity of ore-fluid declined. The higher ratio of H2O/CO2in the later stage represents that the fluid boiling may occurred in the middle stage. Overall, we think that a variety of fluid processes, including change of fluid inclusion types and fluid boiling, have been suggested for gold precipitation. Source

Zhang Z.L.,China Railway Resources Exploration Company | Zhang Z.L.,CAS Institute of Geology and Geophysics | Liu J.M.,CAS Institute of Geology and Geophysics | Chu S.X.,CAS Institute of Geology and Geophysics
Acta Petrologica Sinica | Year: 2012

The Yangchang Mo deposit is located in the Xilamulun molybdenum metallogenic belt on northern margin of North China Craton, Inner Mongolia. The mineralization is occurred within the NW- to NNW- trending faults and fractures hosted by the Yanshanian biotite monzogranite. The ore-forming hydrothennal process can be subdivided into four stages: quartz vein stage ( I ), quartz-pyrite stage ( II-1), quartz-pyrite-molybdenite-ehaleopyrite-galena- sphalerite stage ( II-2) and carbonate stage (III). Three types of fluid inclusions are observed in quartz crystals, i. e. liquid-rich ( VH2O < 50% ) inclusion, gas-rich ( VH2O =50% ∼90% ) inclusion and vapor inclusions. Homogenizalion temperatures of I, II-1, II-2 stages are 173 ∼ 280°C, 180∼467°C, 151 ∼ 366°C, respectively. From I stage to II-1 stage the temperatures become higher, suggesting the magmatic water was introduced into the mineralizing system. Salinities of I, II-1, II-2 stages are in the range of 4.03%∼10.61% NaCleqv, 2.07%∼10.36% NaCleqv, 2.41%∼9.98% NaCleqv, respectively. The composition of the hydrothennal fluids at different stages are mainly H2O ( >94.39mol% ), with minor CO2 N2, CH4, C2H6, Ar, H 2S, and Na+, HS-, Cl- ions. These suggest the Yangchang Mo deposit was formed in reduction condition and the ore-forming fluids were ot the NaCl-H2O ± CO2 system. Hydrogen and oxygen isotopes ol fluid inclusions in various mineralization stages are - 119.66‰ ∼-98.79‰ and -0.08‰ ∼1.90‰ respectively, indicating that the ore-forming fluids were the mixture of magmatic water and meteoric water. It is suggested that the mixing of different fluids with distinct natures might be responsible for the precipitation of molybdenite. Source

Yang X.,China University of Geosciences | Mingqi W.,China University of Geosciences | Yuyan G.,China Railway Resources Exploration Company | He Z.,China University of Geosciences
Geochemistry: Exploration, Environment, Analysis | Year: 2015

The ‘Metals in Soil Gas’ (MSG) survey has proven to be a useful tool for mineral exploration under exotic overburden. Tracing the source of these metals with Pb isotopes is helpful to understand the formation of MSG. Lead isotope ratios in MSG samples were determined by ICP-MS (Model HP4500); the Pb isotope ratios in loess, red soil, wall rocks and ores were measured following decomposition and separation using a VG-354 thermal ionization mass spectrometer (TIMS) for comparison. The results of the study of samples collected over the Jiaolongzhang base metal deposit show that the Pb isotope ratios of MSG background samples are markedly distinct from those ratios of any medium (loess, red soil layer, wall-rocks and ores) in the vicinity of the deposit. The Pb isotope ratios in the MSG anomalous samples (206Pb/204Pb = 18.34–18.56, 207Pb/204Pb = 15.622–15.809 and 208Pb/204Pb = 38.184–38.691) are totally different from those in the samples of background areas (206Pb/204Pb = 16.46–17.68, 207Pb/204Pb = 13.985–14.945 and 208Pb/204Pb = 34.199–36.884). The Pb isotope ratios of MSG anomalous samples scatter near the ratios of the mineralized wall-rocks (206Pb/204Pb = 18.554– 18.874, 207Pb/204Pb = 15.618–15.755 and 208Pb/204Pb = 38.629–39.126) and sulphides (206Pb/204Pb = 18.130–18.251, 207Pb/204Pb = 15.671–15.767 and 208Pb/204Pb = 38.350–38.582). It can be concluded that some of the Pb in MSG anomalous samples originates from deep sulphide mineralization and Pb isotope ratios of MSG anomalous samples indicate that an MSG survey can detect the deeply concealed mineral deposits under exotic cover. © 2014 AAG/The Geological Society of London. Source

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