Mineralogy And Ore-forming Mechanism Of The Chengchao Large Skarn Fe Deposit In Southeastern Hubei Ore Cluster

Chengchao Fe deposit is a typical,large-scale skarn Fe deposit in southeastern Hubei Province.Based on the results of pervious studies,this paper focus on the analysis of geologic characteristics of the deposit,ore types and skarns,and carried out the electron microprobe analysis,rare earth elements analysis,Hf isotope analysis,diagenesis chronology research.We have studied mineralization stages,mineralogy,diagenetic chronology,source of diagenetic material,ore-controlling factors and metallogenic mechanism.The main results are as follows:1)The mineralization stages of the deposit include:skarn stage,retrograde alteration stage and sulphide-carbonate stage.Retrograde alteration stage is the main stage of mineralization.The characteristics of mineralogy and rare earth element indicate that the fluid of skarn stage and retrograde alteration stage has high temperature,high oxygen fugacity,low acidity and Eu positive anomaly characteristics.2)The magnetite electron microprobe analysis shows that the depleted of Si,Al,Ca,Mg and enrichment of Fe,K in environment is conducive to the Fe enrichment in the magnetite.The results of the electron microprobe analysis show that garnets,clinopyroxenes and amphiboles in calcic skarns is dominated by andradite,diopside,and pargasite respectively.The end member components of clinopyroxenes in magnesium skarns is more than that in calcium skams.From the early skarn minerals to the vein skarn minerals,end member components in garnets and pyroxenes have a trend of the transition to the grossular end member and hedenbergite end member,respectively.3)LA-ICP-MS zircon U-Pb dating results shows that medium-fine grained syenogranite,fine grained biotite diorite and quartz monzonite porphyry occurred in early Cretaceous,in response to basaltic underplating,which was followed by lithospheric thinning.Hf isotope characteristics indicate that the diagenetic substance of the fine grained biotite diorite may mainly derived from the depleted mantle,the sources of the rest of the rocks are dominated by the old crust component.4)The quartz monzonite porphyry and moderate-fine-grained granite in Chengchao Fe deposit may play a key role in the formation of skarns and ore bodies.5)In the aspect of ore-forming mechanism,there are mainly two major ways of magnetite formation,one is through metasomatism,another is metal complex bydrolysis which lead to the mineralization.