In situ analysis of garnets from the Jingshandian iron skarn deposit, Hubei Province, and its geological implications

Abstract: This paper presents in situ microanalysis data of garnets form the Jinshandian iron skarn deposit, Hubei Province. Studies show that garnets from the Jinshandian iron skarn deposit can be divided into two stages, i.e., early Al-rich garnets mainly with grossular and grossular-andradite series, and late Fe-rich garnets dominated by andradite, with the variation implying the increase of the fluid oxidation. Compared with the early garnets, the late stage are rich in large ion lithophile elements and high field strength elements as well as REE. Early grossular shows typical HREE-enrichment and LREE-depletion features, while smaller fractionation between HREE and LREE characterizes grossular-andradite series. Total REE content, δEu and HREE/LREE fractionation degrees of Fe-rich garnet samples vary from sample to sample, and are even different in different parts of a single garnet grain, suggesting that the process of its formation was not stable, and fluid properties changed greatly, possibly due to the addition of evaporate minerals from the wall rocks. Garnet in situ microanalysis research also suggests that the evaporate minerals added into the Jinshandian skarn system had features of heterogeneity and periodicity.