Incompatible Elements (REE, Th, U, Nb, Ta, Ti) Mineral Association in Altered Pegmatite from the Djurkovo Pb-Zn Deposit, Central Rhodopes: Occurrence and Geochemical Properties

Abstract

The Djurkovo base-metal vein deposit in Laki ore field, is hosted by a heterogeneous gneiss/amphibolite/marble rock sequence of the high-grade metamorphic complex of the Central Rhodopes. Mineralogical and geochemical investigation was conducted on slightly deformed, and hydrothermally altered thin pegmatite dykes intruded in the marbles. The pegmatite bodies consist mostly of K-feldspar, albite and quartz, with minor garnet present. Clear textural zonation within the bodies is absent except for the preferential crystallization of garnet in the innermost parts. The main pegmatite accessories include ishikawaite, zircon, apatite, monazite-(Ce), allanite-(Ce), and titanite. The post-magmatic hydrothermal overprint on the pegmatites resulted in the formation of the assemblage including epidote, sericite, chlorite, carbonate, quartz, hematite, and leucoxene. The accessory oxide, silicate, and phosphate minerals bearing rare earth elements (REE), actinides (ACT), Nb, Ta, and Ti have undergone partial replacement by secondary mineral phases (thortveitite, fergusonite, fersmite, uraninite, thorianite, REE-epidote, xenotime) observed as irregular grains or veinlets along fractures and dissolved zones, either inside or near the primary minerals.