Magnetite Characteristics Of Yushiwa Iron Deposit In Wu'An,Hebei Province And Its Indication Significance To Genesis Of Iron Deposit

Handan-Xingtai area is an important skarn type iron ore concentration area in China.predecessors have conducted a large number of systematic geologica 1 studies in this area.Wu' an area is an important part of Han-xing area.In H anxing area,the traditional skarn iron ore genesis model has two viewpoints:c ontact metasomatism origin and ore pulp origin.Jianshan rock mass is located in the northern part of Yushiwa iron deposit of Wu'an.on its profile,three types of magneTite appear from bottom to top.magnetite in the lower part of yushiwa iron deposit has high ti and high temp erature ore pulp genetic characteristics.vein magnetite in the middle monzonite mostly has hydrothermal genetic characteristics with high Si content.the occur rence of vein high Si(SiO2>1%)magnetite in the upper limestone is hydrother mal genetic characteristics,coexisting with calcite in equilibrium and self-formi ng.The continuous change of magnetite from bottom to top and elements from high Ti to high Si in space is obviously different from the metallogenic chara cteristics of traditional skarn deposits.Through the analysis of major trace ele ments of these three types of samples,it is found that magnetite in the lower jade depression massive magnetite and the upper crystalline limestone has the c haracteristics of gradually decreasing Ti content,gradually increasing Si and M g content,and gradually increasing fluid activity.The formation of high silicon magnetite(SiO2>1%)is related to fluid and is probably a fluid crystal minera 1.However,the Fe-V/Ti discrimination diagram of magnetite shows that the lo wer Yushiwa iron deposit is of ore pulp origin,the vein magnetite in monzonit e and crystalline limestone is of hydrothermal origin,and the magnetite has a continuous process of ore pulp origin transition to hydrothermal origin from th e lower part to the upper part.High silicon magnetite was first proposed by S.A.Shcheka(1977)and others.Later generations Shiga(1989)and others discovere d that there was high content of silicon magnetite in Japan's Ketishi Cu-Fe ska rn deposit.Thus Hidehiko Shimazaki(1999)defined magnetite containing more t han 1%silicon and lacking other components except Fe2+ and Fe3+,called high silicon magnetite.For the occurrence of this characteristic different from the traditional skarn genetic model,the author studies the genesis of high Si magnetite and proves that it is a mineral formed by direct crystallization of fluid.Combining with t he transition of magnetite elements from high Ti to high Si in space,the meta llogenic model of magmatic channel metallogenic system is put forward.in the late stage of magmatic evolution,the deep ore-bearing melt is mixed with the fluid rich in volatile matter,and the fluid dissolves a large amount of metal s olution as a large amount of ore-forming material due to pressure action.Whe n the volume of fluid injected into the melt is large enough,due to the drive of fluid overpressure and crustal tectonic stress,the "ore-bearing melt-fluid flo w"has the ability to rapidly invade from the deep along the magma passage t o the shallow melt crystallization of the crust to form high Ti magnetite,and t hen the fluid precipitates high Si magnetite.