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Zhang Z.Q.,China University of Geosciences | Chen M.H.,China University of Geosciences | Chen M.H.,Chinese Academy of Geological Sciences | Mo J.M.,Guangxi Academy of Geophysical Exploration | And 4 more authors.
Acta Petrologica Sinica | Year: 2014

Shedong large scheelite molybdenite polymetallic deposit in Cangwu County of Guangxi, located in the south of Dayaoshan uplift, is a porphyry-skarn-quartz vein type deposit related to granitoids. The mineralizing process of the quartz vein type deposit can be divided into four stages, namely I quartz-pyrite stage, II quartz-scheelite-molybdenite stage, III quartz-polymetallic sulfide stage and IV quartz-calcite-fluorite stage. The second and third stages are main metallogenic stages. The homogenization temperatures from I to IV stage gradually decrease (550°C→370°C, 370°C→330°C, 330°C→240°C, 190°C→140°C). Instead, the density keeps increasing (0.61g/cm3 →0.72g/cm3→0.82g/cm 3→0.94g/cm3). The salinities (NaCl) increase from I stage to III, then decrease to the end (5.86% ∼ 8.55% NaCleqv, 4.49% ∼ 43% NaCleqv, 0.53% ∼ 46.37% NaCleqv, 0% ∼ 12.85% NaCleqv). The ore-forming fluid belongs to NaCl-H20 system, however, the composition changes during the metallogenic procedure, which is indicated by Laser Raman composition analysis. The ore-forming fluid evolved from magma, and mixed by the meteoric water later. This was implied by the isotopic composition of H-0 isotopes from the quartz veins of all stages and S isotopes from sulfides (-3.8%‰∼ + 1.7%‰, -0.46%‰ for the average). The primary reason for deposition is mixture of fluids. In a word, the ore-forming fluid of the Shedong quartz vein type deposit belongs to the NaCl-H2O hydrothermal system with medium-high temperature, midium-low salinity, and low density. And the metallogenesis is closely connected with Caledonian magmatism.

Chen M.H.,Chinese Academy of Geological Sciences | Huang Z.Z.,Guangxi Academy of Geophysical Exploration | Li B.,Guangxi Academy of Geophysical Exploration | Huang H.W.,General Academy of Geological Survey of Guangxi
Acta Petrologica Sinica | Year: 2012

The Shedong tungsten and molybdenum deposit in Cangwu County, Guangxi is a quartz-skarn type deposit related to granitoids.Major granitoids are comprised of Caledonian granodiorite, granodiorite-porphyry and Late Yanshanian granite porphyry in mineral district. Caledonian granodiorite and granodiorite-porphyry dominantly exhibit low Si, K, high Na, Al and basic components, thus can be classified to the normal calc-alkaline granite with strongly peraluminous. The rocks are characterized by low REE contents, high LREE/HREE ratios, weakly Eu depletion (SEu =0.62 ∼0.70) , depletion of Ti, Nb, Ta, enrichment of Th, U, Pb, Zr, Hf, low Rb/Sr ratio (0.78) , obviously enrichment of W, Mo, Cu.Geochemical evidences indicate that early Caledonian granodiorite ( -porphyry) are I-type granite, and formed in compression tectonic setting of early collision stage in intra-continent orogenic belt, and associated with W, Mo, Cu mineralization. Late Yanshanian granite porphyry dominantly exhibit high Si, K, low Na, Ca and basic contents, can be defined as the high-moderate potassium calc-alkaline granite with strong peraluminous. The rock is characterized by relative high REE contents, low LREE/HREE ratios, strong Eu depletion (δEu = 0.03 ∼0.06) , depletion of Ti, Ba, K, Eu, more enrichment of Th, U, Sm, Dy, Y, Ho, Yb, Lu, high Rb/Sr ratio (7.56) , clearly enrichment of Sn, Bi, thus it is assigned to Late Yanshanian S-type granite evolved well, and formed in intraplate extension tectonic setting of post-collision, and is related to Sn, Au mineralization.

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