EVOLUTION OF NB,TA-OXIDE MINERALS IN THE PRASIVA GRANITIC PEGMATITES,SLOVAKIA - 2 - EXTERNAL HYDROTHERMAL PB,SB OVERPRINT

Titanite, fersmite, pyrochlore-group minerals and romeite in two small dikes of relatively poorly fractionated pegmatite, located in the par ent Hercynian Prasiva biotite granodiorite-granite, in central Slovaki a,were generated by hydrothermal alteration of primary columbite, tita nian ixiolite and niobian-tantalian rutile. The early titanite has ele vated contents of Nb, Ta, Al and Fe, and the fersmite is very REE-poor . Pyrochlore, microlite, betafite, uranpyrochlore, uranmicrolite, stib iomicrolite, stibiobetafite, plumbomicrolite and several transitional compositions were identified in the next generation, most of them Si-b earing. The late romeite is considerably enriched in Nb: Ta, U and Si. The hydrothermal fluids mobilized Nb, Ta, Ti, U, Fr, Si, and probably also Ca and Na from the primary minerals of the pegmatite, but Sb and Pb must have been imported from an external source. The hydrothermal overprint is attributed to the same metamorphic - magmatic solutions t hat caused the nearby Sb +/- Au and Pb-Zn-Sb sulfide deposits.