The Diagenesis And Metallogenesis Studies Of Dawan Zn-Mo Deposit In Laiyuan County,Hebei Province

The Dawan Zn-Mo deposit is one of important metal deposits in the northern Taihang Mountain metallogenic belt.The Banyukou Formation of Wutai Group and the Gaoyuzhuang Formation of Changcheng System are the main country rocks of the mineralization related intrusive rocks.The Zn-Mo ore body mainly occurs in rhyolite porphyry and the contact zones of rhyolite porphyry and its country rocks.This paper determines the era relationship of rhyolite porphyry and ore body,clarifies the source of diagenetic and metallogenic materials,analyzes the process of the diagenetic and metallogenic.It helps to further improve the theory of regional mineralization,and it is conducive to the next prospecting work.In this paper,the LA-ICP-MS zircon U-Pb analysis of the two rhyolite porphyry samples from the Dawan deposit yielded the weighted ²⁰⁶Pb/²³⁸U mean ages as(137.1±0.9)Ma and(136.8±1.2)Ma,respectively.Re-Os dating of four molybdenite samples show that the weighted mean age and isochron age are(136.5±1.0)Ma and(136.1±2.3)Ma,respectively,which indicates that the Dawan deposit was formed in the Early Cretaceous.The main trace characteristics show that the rhyolite porphyry has high silicon,alkali and potassium content,belongs to calcium alkali rocks.Combined with Hf isotope analysis,the diagenetic material mainly came from the lower crust.The w(Re)of molybdenite vary in the range of5.816?16.484?g/g,showing that they were derived from mixed crust and mantle sources.In the Early Cretaceous,the destruction of the North China Craton by subduction of the Paleo-Pacific plate caused mantle material upwelling and selective melting of the lower crust that formed the crust-mantle mixed magma.With the occurrence of diagenesis such as emplacement and concealed explosion,a complete set of mineralized alteration system was formed in the Dawan deposit which acted on different surrounding rocks,resulting in two sets of alteration combinations of porphyry hydrothermal alteration and skarn alteration,and finally formed a porphyry-skarn-hydrothermal vein type deposit.Rhyolite porphyry and porphyry-related alteration system in the Dawan deposit are the useful indication for prospecting and exploration of the same style mineralization in the region.