Geological Characteristics And Genesis Of The Xilaokou Gold Deposit In The Margin Of The Jiaolai Basin, Jiaodong Gold Province

The Jiaodong area is a very famous gold deposits-concentrated area in China. Extensive studies have been carried out on the gold deposits in the northwest Jiaodong and Mouru gold metallogenic belts. However, less attention has been paid to the gold deposits in the Jiaolai basin, especially to the Xilaokou large gold deposit discovered in the northern margin of the Jiaolai basin in recent years. Based on the data in geology and ore deposit geochemistry of the Jiaolai basin, a detailed study has been completed on the geological and geochemical characteristics of the Xilaokou gold deposit, with a focus on the research of temporal and spatial distribution of alteration and mineralization and the discussion of its ore-forming material derivation and genesis.Four types of alteration exist in the Xilaokou gold deposit, including marble, granite, granulite and amphibolite series ones. A similar zonation occurs in the granite, granulite and amphibolite series, with lithologies from the hanging wall rock to the ore body varying from primary wallrock, clastic wallrock and cataclasite to quartz-sericite assemblage and quartz-sericite-pyrite (polymetallic mineralization) assemblage. In contrast, Primary marble, clastic marble, cataclastic rock (weak sericitization), and cataclastic rock (polymetallic mineralization and weak sericitization) occur in order in the marble series. The gold mineralization is related firstly to the marble series alteration, and secondly to the granite series alteration.Four stages of gold mineralization are recognized based on field investigation and microscopic observation, including coarse-grained pyrite (Ⅰ)-quartz (Ⅰ)-gold (Ⅰ), pyrrhotite (Ⅰ)-quartz (Ⅱ)-pyrite (Ⅱ)-chalcopyrite (Ⅰ)-gold (Ⅱ), pyrite (Ⅲ)-galena (Ⅰ)-sphalerite (Ⅰ)-chalcopyrite (Ⅱ)-gold (Ⅲ), and sphalerite (Ⅱ)-calcite-gold (Ⅳ)-pyrite (Ⅳ)-galena (Ⅱ)-chalcopyrite (Ⅲ) ones. The stages Ⅱ and Ⅲ are the most important for gold deposition.High precision40Ar/39Ar plateau ages of hydrothermal sericite in the quartz-sericite-pyrite assemblage and magmatic biotite in lamprophyre are116.62±0.75Ma (MSWD=0.54) and121.83±0.94Ma (MSWD=0.28), respectively. The zircon SHRIMP U-Pb age of Monzonitic granite is2125.0±7.9Ma (MSWD=1.4). These data show the formation of the Xilaokou gold deposit related not to monzonitic granite, but closely to the mafic dyke. The geochemical analyses of the surrounding rock, ore, quartz, and pyrite combined with the H-O-S-Pb isotopic and fluid inclusion data support an origin of the Xilaokou deposit via magmatic hydrothermal mineralization. The mineralization is mainly controlled by the Qingshan Group and lamprophyre, and the ore-forming material may be derivated from the lower crust. The hydrothermal ore-forming fluid may be a mixture of magmatic fluid with meteoric water or hot brine water.