| The Dongxiang copper deposit in the collision orogen between Yangtze and Cathay sian blocks is one of most important copper-gold polymetallic district in China. Based on the detailed geological investigation, this paper has disscused on the tectonic setting, deposit geological characteristics, element and isotope geochemistry, diagenetic and mineralization chronology, and deposit genesis.This paper made the achievements and understandings as follows:1. The geological characteristics of the Dongxiang copper deposit show that its host rocks are carboniferous sandstone and Yanshanian granite porphyry, and the Orebodies are layered lenticular, which is controlled by fracture structure. The mineralization of sandstone presenting as massive, fine veins, disseminated. Ore structure is mainly metasomatic texture, hypautomorphic-xenomorphic granular texture, crush texture. The porphyry-hosted mineralizationis distributed in and around the granite porphyry, porphyry-hosted mineralization presenting as string vein, disseminated, star-like struture and massive. Ore structure is mainly separated structure of solid solution, hypautomorphic-xenomorphic granular texture.2. Trace elements of the Dongxiang granite porphyry are enriched in large ion lithophile element (Rb Th K U) and low high field strength elements (Nb Ta Ti P), showing that the granite porphyry may be derived from partial melting of crust, and large ion lithophile elements. Nb element shows weak negative anomaly, which may imply hybridization of crust materials. In addition, the Dongxiang copper deposit granite porphyry and ore have similar REE distribution curves which were relatively enriched with LREE and loss of the HREE. The LREE curves were steeper; while a part of the HREE curves are flat. What is more, the REE curves have europium (Eu) negative anomaly which showed that the Dongxiang copper deposit has close relationship with granite porphyry.3. The δ34S from sulfides present tower distribution type and have a narrow distribution range, indicating that the δ34S came from deep source magma. The δ65Cu of chalcopyrite has a narrow distribution range and are overall near close to zero, which is accorded with the distribution pattern of the δ65Cu in magmatic deposits. The Sr-Nd isotopes show that the initial ratio values of 87Sr/86Sr have a large variable range from 0.70002 to 0.71197 with average value of 0.70787, which is clearly different from the value of Isr in the primitive mantle and continental crust. In addition, The 143Nd/144Nd values range from0.51211～0.5122, which of both are lower than those of the primitive mantle (0.51263). All those suggest that crust-mantle mixing action occurred in the magma. The Pb isotope range from mantle Pb isotope to upper crustal Pb isotope, which suggest that the magma is derived from the mantle. However, its evolution process had experienced the assimilation of crustal material contamination.4. LA-ICP-MS zircon U-Pb ages of the Dongxiang granite porphyry ranges from 156.4 ± 1.5 Ma to 161 ±1.0 Ma, which are close to the Rb-Sr isochron age (161.8 ± 9.6 Ma) from quartz fluid inclusions, suggesting that mineralization and magmatic intrusion happened almost at the same time.5. The Dongxiang copper deposit formed in Yanshanian. The early Yanshan granite porphyry hypabyssal-ultra shallow intrusion had brought a lot of ore-forming materials, and provided sufficient thermo-motive for mineralization. Meanwhile, with the continuous evolution and differentiation of magma, hydrothermal process was further enhanced, Eventually, the deposits were formed through replacement and filling ways formation of ore deposits in the interlayer fracture zone and fracture structure. |
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