A Study Of Geological Characteristics And Ore-Controlling Factors Of The Zhanghe Magnetite Deposit In Xuanyangcounty, Shaanxi Province

Located on the passive continental margin of the northern part of the Yangtze plate, belonging to Niushan stratum zones , Diebu- Xunyang , South Qinling stratigraphic division , The Zhanghe magnetite deposit is a recently discovered deposit in Xunyang county, Shaanxi province. It extends in a E—W direction, about 20m long in a E—W direction and 45m wide in a S-N direction,and40square kilometers.This paper based on the lastest achievements of 1:50000 regional geological and mineral resources surveys in Xunyang-Baihe from 2006 to 2008.By analysising the Strata structur and Magmatic Rocks of magnetite deposit we can grasp the geological characteristics of the deposit. Then we analyze the ore-controlling factors from three respects: Strata factors and metamorphic factors structure factors. Finally we could discuss the metallogenic regularity and metallogenetic type by studying ore-bearing srtata,rock association characteristics and petrochemistry and trace elements and so on.According to field investigation and indoor comprehensive study,we could draw a conclusion that the Zhanghe magnetite deposit primarily hosted in strata named Shijiagou Formation , Middle Devonian period which including the next three measures section : D2s1 , D2s2 , D2s3.The main lithology in the third measures section of Shijiagou Formation , Middle Devonian is Grey the sericite—phyllite with thin-layer limestone ; the second one of that is grey-celadon - grey black limestone with thin-layer sericite—phyllite Containing magnetite Seam; the first one of that is grey black calcareous slate with grey black thin-layer limestone Containing magnetite Seam.According to the system summary of the past research, we analyzed the geological background of region metallogenic and metallogenic geological conditions. Then we got a conclusion that Zhanghe magnetite deposit formed in rift environment during the middle Devonian period ,early Paleozoic with hydrothermal metasomatism by which forming the mineralization mother rock : marbles and albitites.On the basis of studying the space distribution law of orebodies, we think the Zhanghe magnetite orebodies are mainly controlled by stratigraphic horizon and geological structure factors, especially the ore-bearing strata and fold-fault geological structure. Geological structure-controlling factors include basin margin and tectonic level and structure style .They respectively controlled the shape and Spreading of ore field and deposit and orebody.We preliminarily think Zhanghe magnetite deposit is a type of sedimentary metamorphism with hydrothermal reformation deposit. Its main host rocks is albite- marbles with magnet mineralization formed in rift environment, during the middle Devonian period ,early Paleozoic. Its formation was associated with hydrothermal metasomatism. The original rock was clastic limestone whose recrystallization was associated with hydrothermal activity. Albite- magnetite - Siderite formed in the same period .The late hydrothermal activity of host rocks formed albite, magnetite deposit and chlorite exsiting now. The host rocks (clastic limestone) and magnetite undergone low regional metamorphism with slight crushing image. The metamorphism was associated with recrystallization ,but without hydrothermal metasomatism.