THE CORUNDUM + TOURMALINE NODULES RELATED TO HYDROTHERMAL ALTERATION OF SPODUMENE IN THE NANPING No. 31 PEGMATITE DYKE, FUJIAN PROVINCE, SOUTHEASTERN CHINA

Abstract

The Nanping No. 31 pegmatite is a spodumene-subtype LCT granitic pegmatite in southeastern China. Spodumene mainly occurs as rock-forming mineral in the quartz – coarse albite – spodumene zone (zone III) and the quartz – spodumene – amblygonite zone (zone IV). Various alteration-induced phenomena were observed in spodumene. Spodumene in zone III is usually altered along its {110} cleavages to networks of albite + muscovite, resulting from a replacement of spodumene by an alkaline fluid, which likely begins by Na metasomatism. Extensive alteration of spodumene in zone IV to quartz and muscovite veinlets is related to replacement by K+- and H+-rich fluid. However, alteration by strongly acid fluids also affected spodumene, leading to formation of fine-grained white mica in zones III and IV. In this paper, we focus on the occurrence of nodules of corundum + tourmaline, which are typically restricted to the aggregates of white mica in zone IV. Fibrous corundum and radial tourmaline signify a hydrothermal origin. Their textural relationship with secondary muscovite suggest a close genetic relation with the latter. The corundum + tourmaline nodules arise by alteration of the secondary muscovite by late B-, Mg- and Fe-rich fluids.