ACCESSORY MINERALS IN THE XIHUASHAN Y-ENRICHED GRANITIC COMPLEX, SOUTHERN CHINA: A RECORD OF MAGMATIC AND HYDROTHERMAL STAGES OF EVOLUTION

Abstract

The Xihuashan granitic complex (southern China) is mainly composed of coarse-grained porphyritic biotite granite (G-a), medium-grained porphyritic biotite granite (G-b), and medium-to fine-grained porphyritic biotite granite (G-c).The G-a granite is characterized by monazite-(Ce) and xenotime-(Y), in addition to commonly observed zircon and uranoan thorite.In the G-b and G-c intrusive units, monazite-(Ce) becomes very scarce, whereas Y-bearing minerals, including Y-bearing spessartine, xenotime-(Y), gadolinite-(Y), fergusonite-(Y), and yttrian fluorite (up to 15 wt% Y 2 O 3 ), are concentrated to various extents.Spessartine exhibits chemical zoning, which is displayed, in the core, by elevated contents of Y and heavy REE (HREE) (up to 2.32 wt% Y 2 O 3 and 1.51% HREE 2 O 3 ) and micrometric inclusions of Y-bearing minerals.Similarly, zircon from the G-b and Gc granites contains polymineralic micro-inclusions in the core.Overall, the accessory minerals point to a magmatic environment of crystallization for the G-a granite.In contrast, the crystallization of the G-b and G-c granites involved magmatic and hydrothermal stages.The late-to postmagmatic fluid is enriched in F and CO 2 , and appeared as a result of the final oversaturation of the granitic melt in a fluid phase.