Discuss On The Genesis Of Magnetite-rich Ore In Gongchangling. Liaoning Province

In this paper, on the basis of detailed field geological survey, geochemistry of element and geochemsitry of iron isotope are used to analyse the geochemistry feature of iron ore and their surrounding rocks, which locate in the second district ore of Gongchangling, Liaoning province. Meanwhile, the previous research are combined to discuss the origin of the rich iron ore of the second district ore of Gongchangling, the results show that:(1)The characteristics of major elements, trace elements and REE of magnetite-rich ore and magnetite quartzite are similar. REE distribution curves are a little bit right-inclined or just flat, the bulkΣREE contents are low, the light REE enrich, and the fractionation degrees of light REE are not quite obvious, the positive Eu anomalies are both obvious. This indicates that the magnetic high-grade ore and magnetite quartzite are of consistency and continuity in their genesis.(2)The characteristics of major elements, trace elements and REE of amphibole schists and altered surrounding rocks are very similar. In addition, the amphibolites and magnetite quartzite are always interbedded, while the altered surrounding rocks and are also going with the magnetite-rich ore, these means that the altered surrounding rocks must have been formed during the metamorphic alteration from the amphibole schists.(3)Comparing the characteristics of iron isotope of magnetite-rich ore with magnetite quartzite, it is proved that the iron isotopic composition ranges of magnetite-rich ore and magnetite quartzite fall within the BIF's in different parts of the world. It implies that the magnetite-rich ore origined from the magnetite quartzite during the metamorphism, and had not reached the iron isotopic homogenization, the magnetite-rich ore remains the original deposit feature in a large scale.(4)Comparing the characteristics of iron isotope of amphibole schists and altered surrounding rocks, it is proved that altered surrounding rocks are rich in lighter iron isotopes than amphibole schists, indicating that when the regional metamorphism happened, the hydrothermal made the magnetite quartzite enriched into magnetite-rich ore, during this process, amphibole schists had the alteration,which is mainly chlorite alteration and then changed into altered surrounding rocks.(5)The iron of magnetite-rich ore originated from magnetite quartzite. During regional metamorphism, the metamorphric hydrothermal fluids in the banded iron formation, took SiO2 away by leaching, the magnetite quartzite changed into the magnetite-rich ore, meanwhile, amphibole schists had the alteration, which is mainly chlorite alteration, and then the surrounding rocks were formed.