Abstract: The genesis of skarn iron deposit has long been controversial involving mainly the contact metasomatism and ore magma genetic models. The Yushiwa iron deposit is one of the major skarn iron deposits in the Handan-Xingtai area, Hebei Province. It contains three types of magnetite ores in the Jianshan section, on which a detailed study should help to resolve the genetic controversy. Magnetite in the main ore body of the Yushiwa iron deposit in the lower part of the profile is characterized by high Ti content. However, magnetite veins in the upper crystalline limestone have high Si (w(SiO2)>1%) content. And magnetite in monzonite has a transitional composition. Through major and trace elemental analysis of the three types of magnetite, we found gradual decreasing Ti and increasing Si and Mg contents in magnetite in the main ore body in the lower Yushiwa iron deposit to magnetite veins in the upper crystalline limestone. High silicon magnetite forms euhedral crystal and coexists with calcite in equilibrium. Its formation has fluid involvement, making it possible a fluid crystal mineral. The magnetite FeV/Ti discrimination diagram shows a magmatic genesis of the iron ore body of the lower Yushiwa iron deposit, and a hydrothermal genesis of magnetite veins in monzonite and crystalline limestone. The iron deposit experienced a continuous transition from magma genesis of the lower part to hydrothermal genesis of the upper part. According to these characteristics, we believe that the iron ore slurry contains a large amount of fluid to form the “iron bearing melt-fluid”. Under fluid overpressure, the “iron bearing melt-fluid” rises rapidly from the magmatic conduit to arrive at the shallow part of the crust, forming high-temperature high-Ti magnetite in the lower part and transitioning to high-Si magnetite of fluid crystal in the upper part of the deposit. We call this metallogenic model a magmatic conduit metallogenic system.

Key words: Handan-Xingtai iron deposit, high titanium magnetite, high silicon magnetite, metal bearing melt-fluid, magmatic conduit metallogenic system