RARE PHOSPHATES FROM THE SUROVEC TOPAZ - Li-MICA MICROGRANITE, GEMERIC UNIT, WESTERN CARPATHIANS, SLOVAK REPUBLIC: ROLE OF F/H2O OF THE MELT

Abstract

A small body of Permian high-P Li–F microgranite accompanied by medium-grained leucogranite occurs in the western Gemeric unit of the Western Carpathians; it occurs amongst other F–B-bearing specialized S-type granite massifs. Besides phenocrystic topaz and zinnwaldite, the microgranite matrix contains a characteristic assemblage of rare aluminophosphates (arrojadite, lacroixite, viitaniemiite), goyazite and gorceixite, along with late apatite. The assemblage is unusual in granitic rocks; it formed as a result of a buildup of P in the residual melt (matrix) during crystallization of mostly quartz and alkali feldspars. Topaz and lacroixite or viitaniemiite were stable instead of albite and apatite. In the absence of biotite, the increasing Fe and Mn stabilized arrojadite. Both types of granite were reworked during the Cretaceous Alpine burial, which probably resulted in the influx of Sr and Ba in low-temperature fluids. Topaz – muscovite and feldspar thermometers indicate that the temperature of fluids was below 300°C, when goyazite, gorceixite and clay overgrew earlier apatite and arrojadite. The phosphate assemblage observed in the microgranite is stable at CaO/P 2 O 5 less than 1 and Li 2 O/F less than 0.21. At higher values characteristic of other Li–F–P granite occurrences, apatite, amblygonite and lepidolite take the place of aluminophosphates and zinnwaldite.