Trace-element signatures and U-Pb geochronology of magmatic and hydrothermal titanites from the Petrovitsa Pb-Zn deposit, Madan region, Central Rhodopes (Bulgaria)

Abstract

The current study presents new geochronological and geochemical data for the Petrovitsa Pb-Zn deposit, Central Rhodopes, South Bulgaria. Based on in-situ U-Pb dating of titanites from pegmatites and skarnified mineralized marbles, it aims to provide new insights into the pegmatite formation and their relation to the hydrothermal system in the region. Titanite is an abundant accessory mineral in pegmatites and skarns within the Madan ore district. Commonly, it associates with feldspars, epidote, clinopyroxene, chlorite, hematite, zircon, apatite, allanite and monazite in both lithologies. Crystal size varies from 5 μm to 600 μm. The combined analytical approach revealed compositional and age variations of the studied titanites divided into: (i) early formed magmatic; and (ii) later hydrothermal. The magmatic crystals are characterized by mean Th/U of 1.91, Lu/Hf averaging at 0.59, and Dy/Yb of 2.03. The chondrite-normalized REE patterns show LREE dominance over HREE. The average ƩREE is 6548 ppm. The hydrothermal titanites have a mean Th/U of 0.22, Lu/Hf of 1.20, and average Dy/Yb of 1.50. HREE content slightly prevails over LREE. ƩREE is two times lower compared to magmatic titanites – 3388 ppm. Negative Eu-anomaly is common for both types. The LA-ICP-MS U-Pb geochronology shows a well-defined age distinction of magmatic and hydrothermal titanites. The calculated U-Pb weighted average age for the magmatic titanites is 48.9±2.3 Ма, while the pegmatite-hosted hydrothermal titanites are dated at 39.2±1.5 Ma. The hydrothermal titanites from skarns yield a weighted average age of 37.7±1.3 Ma. Data suggest pegmatite emplacement in the Rhodope metamorphic complex during the late Ypresian. Later hydrothermal fluids precipitated younger titanites with different signature.