REE geochemistry and origin of skarn garnets from eastern Inner Mongolia

Abstract: Eastern Inner Mongolia, as the most important skarn-type tin-silver-copper-lead-zinc polymetallic metallogenic province in northern China, is characterized by not only well-developed Mesozoic magmatic plutons and their related skarn mineral deposits but also a great variety of mineral deposit types. Based on the mineralogical study of garnets of different stages from the Huanggangliang iron-tin mineral deposit, Baiyinnuo lead-zinc-silver polymetallic deposit and Haobugao skarn lead-zinc-tin deposits, two kinds of garnets are recognized. The early-stage garnet is mainly andradite, which is light-colored, fine-grained, anhedral and isotropic and in most cases forms the core of a grain; the late-stage garnet is mainly grossular, which is dark-colored, medium- to coarse-grained, subhedral and slightly anisometric and mostly forms the rim of a grain. In addition, rare earth element (REE) concentrations in garnet separates from the Huanggangliang and Haobugao skarn mineral deposits were determined using ICP-MS. The results suggest that the early-stage garnet in the area shows the character of magmatic origin, while the late-stage garnet indicates a hydrothermal metasomatic origin. So, there are both early-stage magmatic skarn and late-stage hydrothermal metasomatic skarn in eastern Inner Mongolia.