Geological And Geochemical Characteristics And Genesis Of Baixiangshan Iron Deposit In Ningwu Basin

The Ningwu Mesozoic volcanic basin is located in the north margin of the Yangtze Block. It extends from the Tan-Lu fault zone to the east. There are abundant of iron ore resources in it. A total of more than 30 iron ore deposits. Baixiangshan iron deposit is one of the important large deposits in this basin. Now the times of diagenesis and mineralization yet to be determined. The genesis of the deposit remains controversial.This paper takes Baixiangshan iron deposit as the main research object, discusses the periods of Mineralization, Geochemical Characteristics, the age of the diagenesis and iron mineralization, the model of mineralization have been investigated through petrography, electron probe analysis, LA-ICP-MS analysis and 40Ar-39Ar isotopic dating. The following conclusions are reached. Mineralization is divided into one period: the hydrothermal period. Hydrothermal is the main mineralization period, it is can be further divided into two stages: the high-temperature stage and the low-temperature hydrothermal mineralization stage. There are types of magnetite ore in the high-temperature stage. We can see magnetite-phlogopite-pyroxene mineral assemblages. In low-temperature hydrothermal stage, the main mineral assemblage are hematite, sulfides, quartz and carbonate.The chemical composition of magnetite is consistent. It is the hydrothermal metasomatism. The sulfur isotope geochemistry results show that mineral come from contact metasomatism and volcanic hydrothermal.Analysis of the Baixiangshan iron deposit intrusive rock-diorite porphyry for LA-ICP-MS zircon U-Pb geochronology. We obtain the exact age of diagenetic is 131.1±1.9Ma.Through chronological study of Baixiangshan iron deposit, the 40Ar-39Ar age of phlogopite that coexisted with magnetite shows that the main metallogenic stage occurred around 130.7±1.1 Ma, mineralization formed in the early Cretaceous. Further showed that the main minerlization occurs in rocks after emplacement, but not completely cooled before freezing. Magnetite and a series of alteration are formed tightly after the formation of the rock.The formation time of the Baixiangshan iron deposit is belong to the outbreak of diagenesis and mineralization of Mesozoic in the Yangtze River metallogenic belt. It is the major period 135-120Ma of mineralization.Baixiangshan iron deposit is the type of skarn deposit. It provides an effective tool for iron deposits exploration in the study area.