The Zoning Characteristic of Garnets in the Futuyu Orefield of the Northern Taihang Mountain

The Futuyu orefield is composed of seven small-middle skarn Cu-Fe deposits and Mujicun porphyry Cu-Mo deposit in the northern Taihang Mountain within the Central area of the North China Craton. Garnet is the main mineral of the skarn deposits in the Futuyu orefield, which is closely related to the mineralization and the important mineral to study the genesis of the Futuyu orefield. Combined with a geological investigation and petrographic feature study, the composition of zoning garnet from four ore deposits by using electron microprobe analysis was analyzed. Garnets in this orefield were classified into Andradite-grossularite series, and from core to rim of the crystal, andradite and grossularite show a rhythmic style change. Total content of Andradite component (78.1%-86.2%) is much larger than that of Grossularite (12.91%-16.61%). According to the zoning structure and component feature of garnet, it was generated in the weak acid, low temperature and relatively oxidation environment. According to the changes of temperature, pH, oxygen fugacity and salinity of the ore-forming fluid, garnet was not formed in a completely closed balance environment and the fluid has characteristics of multi-phases and multi-periods, which is the prerequisite and important factor of the enrichment of metal in the skarn deposit.