Lead isotope geochemistry of Dayingezhuang gold deposit, Jiaodong Peninsula, China

The gold deposits of the Jiaodong Peninsula define the China's largest gold province. Disseminated- and stockwork-style gold deposit, which accounts for 90% of the proved reserves in Jiaodong Peninsula, is the most important deposit type. Its giant source of gold is a striking and key scientific issue. Zhaoping fault zone, whose proved reserves exceed 1500t Au, is the largest fault-metallogenic belt in Jiaodong Peninsula. Dayingezhuang gold deposit, a typical disseminated- and stockwork-style gold deposit, whose proved reserves are about 125t Au, located in the central part of Zhaoping metallogenic belt. Its exploration depth is nearly -800m. NNE-trending Zhaoping fault and NNW-trending Dayingezhuang fault are the main ore-controlling structures. The Zhaoping fault develops along the contacts between the Jiaodong Group and Linglong granite and controls the occurrence of the gold orebodies in Dayingezhuang gold deposit. Linglong granite locates in the footwall of Zhaoping fault. Generally, it underwent pyrite-sericite-quartz alteration and hosts most part of the gold orebodies. Wall rocks in the hanging wall, which underwent intensive carbonation, comprise migmatization biotite-plagioclase-granulite, carbonate schist and amphibolite of Archaean Jiaodong Group, and garnet-sillimanite-biotite schist and biotite schist in the Lugezhuang Formation of Paleoproterozoic Jingshan Group. The gold mineralization is closely related to sericitization, pyritization and silication. The gold orebodies are located in the pyrite-sericite-quartz altered rock and pyrite-sericite-quartz altered cataclasite in footwall of Zhaoping fault. The main metallic mineral is pyrite, followed by galena, sphalerite and chalcopyrite. Frequently, pyrite is symbiotic with galena and sphalerite. The No. I and II orebodies, located in the south and north of the Dayingezhuang Fault respectively, account for 85% of the proved reserves in Dayingezhuang gold deposit. Comparing with the No. II orebody, the No. I orebody possesses more galena, sphalerite and higher silver grades. Nine sulfide samples selected from ores of No. I orebody yield Pb-206/Pb-204, Pb-207/Pb-204, Pb-208/Pb-204 of 17.2638 similar to 17.3585, 15.4663 similar to 15.6116 and 37.858 similar to 38.3328 respectively. Six sulfide samples selected from ores of No. II orebody yield Pb-206/Pb-204, (207)P13/Pb-204, Pb-208/Pb-204 of 17.2157 similar to 17.3286, 15.4595 similar to 15.5084 and 37.8900 similar to 38.0004 respectively. They are radiogenic and anomalous lead, who underwent three stages of evolution. The crust-mantle differentiation occurred at about 3.4Ga when the Pb isotope between the lower crust and upper mantle mixed and formed the normal lead. At about 0.8Ga, the lead escaped from the reservoirs of the second stage. Then it mixed with a certain amount of radiogenic lead. Finally, it was trapped in the gold-bearing sulfide at ca. 130Ma. All these reveal that ore-forming material may mainly be derived from the Mesozoic remobilization of metamorphic rock of the Jiaodong Group. The No. I orebody underwent intensive water-rock reaction accompanied by the mixing of more substance of the upper crust, when the gold deposited from the ore-forming fluids in the brittle faults of upper crust. In contrast, the No. II orebody keeps more information about the initial ore-forming materials and fluids.