Redistribution of incompatible elements during hydrothermal alteration of pegmatite from the Djurkovo Pb-Zn deposit, Central Rhodopes

Mineralogical and geochemical study was done on weakly deformed, relatively thin pegmatites that intruded the marbles of the Rhodope metamorphic complex in the Djurkovo Pb-Zn deposit, Central Rhodopes. The pegmatites consist mainly of K-feldspar and quartz and contain minor garnet; the pegmatites lack clear zonation except for the preferable crystallization of the garnet in the central parts. The main accessory minerals are ishikawaite, zircon, monazite-(Ce), apatite, and titanite. The textural relationships indicate later hydrothermal alteration of pegmatites which led to the formation of albite, epidote, sericite, chlorite, carbonate, quartz and leucoxene. The (REE+Y, ACT, Nb, Ta, Ti)-bearing pegmatite minerals (oxides, silicates and phosphates) are partly leached and/or replaced by secondary ones. The newly-formed phases precipitated as anhedral grains along fractures and dissolved zones onto/or close to the primary minerals due to the limited mobility of the incompatible elements in fluids conditioned by pH, ligand activity and temperature.