Ore-Forming Sources And Ages Of The Hekou And Rongdu Au Deposits In The Wuhe Area, Bengbu City Anhui Province

The Hekou and Rongdu gold deposits in the Wuhe County, Bengbu City, Anhui Province, are located in the adjacent area of the Bengbu uplift and Wuhe syncline along the southeastern margin of the North China Craton. In this paper, geological characteristics, fluid inclusion geochemistry, Re-Os isotopes and H-O-S isotopes of the Hekou and Rongdu gold deposits are studied to determine their ore-formation ages and to explore their metallogenic processes and the sources of their ore-forming materials. The ore bodies in both deposits are composed of veinlet-disseminated type, vein-type and reticulated vein-type ores hosted in the Paleo-Archaean Xigudui Formation. The ore-forming processes can be divided into four stages in the gold deposits : (1) quartz stage ( early stage) ; (2) quartz pyrite stage ( early stage) ; (3) quartz polymetallic sulfide stage ( middle stage) ; and (4) the carbonate stage ( late stage). Among them, the main gold mineralization occurred in the middle stage. The results of fluid inclusions from quartz studies in the Hekou and Rongdu gold deposits show that the inclusions in the early quartz stage of the Hekou gold deposit are mainly composed of gas-rich ( WG type) and liquid-rich ( WL type) with a handful of daughter minerals-bearing ( S type) inclusions. Their temperature and salinities vary from 322 degrees C to 412 degrees C , and 5. 56% to 15. 67% NaCleqv, respectively, which belong to a high temperature and medium-low salinity fluid system. The fluid inclusions in the mineralization stage of the Hekou and Rongdu gold deposits are consisted of liquid-rich ( WL type) and gas-rich ( WG type). The homogeneous temperature and salinities vary from 257 degrees C to 357 degrees C , and 3. 06% similar to 7. 45% NaCleqv, respectively. The ore-forming fluid in this stage generally belongs to a medium-high temperature and low salinity fluid system. Because the fluid temperature and salinities decrease from the early quartz stage to the mineralization stage, we proposed that the ore-forming process may be caused by the decrease of fluid temperature and salinity. In the middle mineralization stage of the Hekou and Rongdu deposits, the delta O-18 and delta DV-SMOW values of ore-forming fluids vary from 5. 01 parts per thousand to 7. 90 parts per thousand and -89 parts per thousand to - 65 parts per thousand, respectively, which indicates that the ore-forming fluid was mainly originated from magma. The delta S-34 values of pyrites from the Hekou gold deposit are from 3. 89 parts per thousand to 9. 65 parts per thousand, while the value of the galena from the Rongdu gold deposit is 0. 76 parts per thousand, which are characterized by magmatic sulfur, and the elevated delta S-34 value in the ore is due to the magma degassing or the participation of formation sulfur. Thus, the two gold deposits may be hydrothermal quartz vein type gold deposits and related to magmatic hydrothermal solution. Re-Os isochron dating of pyrites from the Rongdu gold deposit shows that the gold deposit was formed at 134 +/- 19Ma. It is inferred that the mineralization of the Rongdu gold deposit may be closely related to the 130Ma +/- magmatism in the Wuhe area.