Geochronology, Metallogenic Model And Ore Prospecting Of The Guilaizhuang Gold Deposit, West Of Shandong Province

The Guilaizhuang gold deposit, located in the southeast of Pingyi County,LinyiCity,Shandong Province, is among the largest cryptoexplosion breccia type golddeposits in China at present. It principally occurs in the the cryptoexplosion brecciabelt which intrudes along the fault zone, and in Cambrian-Ordovician carbonaterocks distributed in both sides of it. This gold deposit, including12ore bodies, ismainly controlled by the Yangan fault which strikes in NNE．Basing on fieldobservations and experimental analysis, the master thesis discusses the source of themetallogenetic matter, the thermodynamic condition, and the mineralizationchronology. This study has significant implications for deposit genesis andmetallogenic model.The ore types mainly consist of breccia gold ore, limestone and dolomite goldore. The textures of ores are grain, euhedral, subhedral and anhedral granular.Thestructures of ores can be divided into brecciated structure, disseminated structure andvein structure. Metallic minerals are composed of electrum, pyrite, limonite,chalcopyrite and so on. Meanwhile, K-feldspar, plagioclase, calcite and quartz isnonmetallic mineral in this area. Gold mainly occurs as intergranular gold andinclusions. The mineralization stages contain quartz-pyrite stage, polymetallic sulfidesstage, gold tellurides stage and carbonate stage.The research focusing on fluid inclusions in fluorite and calcite of the depositindicates that almost all inclusions are saline gas-liquid inclusions. Homogenizationtemperature of the fluid inclusions ranges from103℃to296℃.Freezing point variesfrom-1.3℃to-14.2℃,the salinity ranges from1.05%to16.41%.The fluid densityvaries from0.78g/cm3to1.06g/cm3, and the depth of mineralization mainly between1.2km and1.6km. It demonstrates that the Guilaizhuang gold deposit is thelow-temperature and density epithermal hydrothermal breccia type gold deposit.The stable isotope data indicate that δ34S ranges from16.5‰to20.4‰,Pb206/Pb204ranges from18.207to18.908，Pb207/Pb204ranges from15.575to15.757，Pb208/Pb204ranges from38.313to39.252，δ13CPDBfrom-3.9‰to1.1‰, δ18OPDB ranges from-19.2‰to-9.3‰. These values suggest that the ore-forming matterderives from mantle and upper crust, which belongs to the crust-mantle mixed source.The ore-forming fluids mainly originate from mantle,which focus on primarymagmatic water and atmospheric water.The Rb-Sr isochron age of pyrite in the Guilaizhuang gold deposit is about180.3±2.3Ma, MSWD is1.3, and the initial87Sr/86Sr is0.712429±0.000076. Thismeans that the ore-forming process of the Guilaizhuang gold deposit is closelyassociated with the Tongshi subalkaline igneous complex.The crust of Luxi area haveuplifted on a large scale, the cover layer slided and detached with the invasion ofTongshi. The ore-forming fluids have continuous material exchange with thesurrounding rock in low temperature and shallow seated environment.Finally it hasbeen enriched mineralization with the close relationship between deposit andcrypto-explosive breccia.