Characteristics And Origin Of Magnetite In Fushan Iron Deposit, Shexian County, Hebei Province

For a long time,Fushan Iron Mine is generally considered to be a contact metasomatic skarn-type iron deposit,but it has been accompanied by controversy.There has been a lack of a unified understanding of the source of iron materials in Fushan Iron Mine,the evolution process of ore-forming fluids and the metallogenic model.The magnetite in the interlayer ore body of Fushan Iron Mine is in sharp contact with the surrounding rocks,and almost no skarn is developed;the ore has a stomata structure;according to the geochemical characteristics of magnetite,magnetite can be divided into three categories: high Silicon magnetite,high titanium magnetite and ordinary magnetite;and ordinary magnetite can be divided into high silicon ordinary magnetite and low silicon ordinary magnetite.Moreover,it was found that high-silicon magnetite appeared near the pores,and some high-silicon magnetite showed obvious metasomatous layers.These phenomena are difficult to explain by contacting the skarn deposit model.During the evolution of the deposit,the main element trend of magnetite always evolved from titanium-rich to magnesium-rich.This process can be clearly reflected in the sample data of magnetite in Fushan mining area,which shows that the formation of Fushan iron ore includes the complete process from the early magmatic high temperature stage to the late hydrothermal stage.The genetic mechanism of the Fushan deposit may be: there is a silicon-rich fluid in the process of mineralization,which is mixed with the "ore-bearing melt-fluid flow" from the deep,transforming the high-titanium magnetite brought by the deep,A part of the high-silicon ordinary magnetite is formed,and a small amount of unmodified magnetite eventually forms a high-titanium magnetite;and the silicon-rich fluid will also transform the ordinary magnetite produced by the replacement of the rock body with the surrounding rock.Increase the Si content in it,making part of the ordinary magnetite produced by the explanation more rich in silicon,together with the transformed deep magnetite to form a high-silicon ordinary magnetite;and in this entire process,the silicon-rich fluid will also take part Iron eventually forms minerals,resulting in high-silicon magnetite.A new metallogenic process of Fushan Iron Mine is proposed: after the partial enrichment of the magnetite is reformed in the silicon-rich fluid,it is mixed with the deep ore-bearing melt-fluid flow due to fluid overpressure and the magnetic The iron ore eventually formed in place in the structurally weak zone.