CHARACTERISTICS OF GARNET IN SHIZHUYUAN SKARN DEPOSIT, HUNAN PROVINCE

In the Shizhuyuan polymetallic skarn deposit in Hunan Province, China, the research for garnet is made by means of the field survey, the microscopic observation and EPMA. This skarn is classified into four zonal distributions in terms of the occurrence of the garnet and the mineral assemblages: magnetite-yroxene-arnet zone, pyroxene-arnet zone, vesuvianite-arnet zone and skarnized marble zone. The features of the garnet in various skarnized zones are discussed with changes of chemical composition and mode of occurrence. The garnet is divided into two stages: early and late stages. During the early stage, the color of the garnet is dark brown, and shows a distinctive zonal pattern with various chemical compositions. In addition, the magnetite-yroxene-arnet zone to skarnized marble zone has transformed from andradite to grossular as the content of Fe₂O₃ decreases and that of Al₂O₃ increases. The garnet crystal is characterized by the pattern of compositional changes from core to rim. During the early stage, the garnet occurred in the relatively oxidizing environment at the temperature ranging between 520 and 620 ℃ and at the pressure of 1 000×10⁵ Pa. In addition, this garnet resulted from the metasomatic reaction between the thermal liquids of Si, Al, Fe, Cl, F components and the Devonian limestone of the Shetianqiao Formation. When the temperature falls to 450-540 ℃ and the pH and Eh values decrease in the late stage, the garnet occured with sheelite. The color of the garnet crystal in the late stage is red, and is lighter than that of the early stage. Furthermore, the crystal grain size is larger, and the zonal structure can be universally observed in the late stage.