Geochemical Characteristics and Re-Os isotopic dating of Tongde Graphite Deposit, Sichuan Province

The Tongde Graphite Deposit in Panzhihua is located in the accretionary zone on the western margin of the Yangtze plate. In this paper, the whole rock geochemical analysis, C isotope determination and Re-Os isotope dating of the ore in Tongde graphite mining area are carried out, the original rock of the ore is restored, and the metallogenic environment is discussed. Research shows that the ore SiO₂ is 55.65~61.68%, SiO₂/Al₂O₃ ratio is 4.59~5.42, and Ni/Co ratio is 6.23~12.88. It is rich in Ba, Rb, Sr and other large ion lithophile elements and Nb, Zr, Hf, Th, U and other high field strength elements. Total rare earth elements of ore ΣREE is 149.13×10^-6～195.37×10^-6, with weak Ce negative anomaly and Eu negative anomaly, representing the anoxic marine sedimentary environment. The Carbon isotope δ¹³C_V-PDB in ore is -25.0‰~-23.5‰, which is within the range of biogenic organic carbon, indicating that the ore-forming carbon mainly comes from organic matter. The Re-Os isotopic age of graphite is 983 ± 72 Ma (MSWD=1.7), belonging to the early Neoproterozoic, earlier than the intrusion age of magmatic rocks around Tongde. The content of re is between 27.66×10^-9～79.81×10^-9, the contents of ordinary Os and ¹⁸⁷Os are 0.52 ×10^-9～2.16×10^-9, 0.28 × 10^-9～0.83×10^-9,respectively ,it is significantly enriched relative to the abundance of Re and Os in the crust. The ¹⁸⁷re/¹⁸⁸os ratio is 122.9~350.5, and the initial Os isotope ratio ¹⁸⁷Os/¹⁸⁸Os=0.31±0.21. Combined with the field geological survey, the original rock of ore and ore bearing mica quartz schist in Tongde area is restored, and it is concluded that the original rock is sedimentary rock.