Magmatic conduit melt-fluid metallogenic system- A new Genetic Model for Xishimen Iron Deposit, Wuan area, Hebei province, China

Abstract:

Xishimen Iron deposit is located in Wuan city, Hebei province, China. it is a typical skarn deposit, but some geological characteristics in the deposit cannot been explained by skarn model. We will try to reveal the genetic mechanism of the iron deposit¢s in this paper.

Orebodys mainly occur along the boundary of diorite and metalimestone in the Xishimen iron deposit. Some orebodys intruded into diorites or limestones. There are vesicles in some massive ores. Magnetite from the lower part of orebody occur between diopside and tremolite as an intersititial minerals. Magnetites from upper part of the orebody are eqilibrium with calcite, apatite, Talc, pyrite and chalcopyrite. Magnetites coexisting with dioposide, tremolite and phlogopite have more than 15000 ppm TiO_{2, and riched in SiO2.} However, magnetites coexisting with calcite, talc and sulfides have 200 ppm- 400 ppm TiO_{2, and poored in SiO2}. Magnetites coexisting with talc have highest Al₂O₃, MgO, and MnO. Magnetites coexisting with calcite and sulfide have lowest Al₂O₃, MnO and MgO.

Trace element analysis results of magnetite show that magnetite coexisting with dioposide, tremolite and phlogopite are riched in Ti and Ta, and depleted Nb and Y. Magnetite coexisting with calcite, talc and sulfide are usually have poor positive or no anomaly of Ti and Ta, and have poor positive anomaly of Nb, Hf, and Y. The analysis results of Fe isotope for ores and rocks in Xishimen iron deposit show that there is a negative correlation relationship between altitude and the value of Fe isotope. The heavy Fe isotopes of ores are richer in the lower part than in the upper part.

The origin processes of Xishimen iron deposit are: (1) mafic-intermediate magma riched in iron reacted with limestone, and make the “iron magma” formation; (2) Fluids are added into the metallogenic system continuously, and “iron magma” was getting less density; (3) “iron magma” bearing fluids uplifting along magma conduit because of fluid superpressure; (4) The textures, and mineral assemblages, content of minerals and iron isotope of ores change systematicly in the conduit. The model of Magmatic conduit melt-fluid metallogenic system is suitable for Xishimen iron deposit's origin.