U-Pb dating and composition of columbite from Vishteritsa: Implication for timing of granite magmatism and rare-element granitic pegmatites in the Western Rhodopes, Bulgaria

Abstract

The economic significance of pegmatites as a source of strategic rare metals for high-tech products and green energy motivated the present study on Ta–Nb oxides from Vishteritsa rare-element beryl–columbite LCT pegmatites of the Rila–West Rhodopes Batholith in the Western Rhodopes, Bulgaria. Here, we present the first U/Pb age data from columbite with application of the LA–ICP–MS U–Pb technique and a new X36 columbite standard reference material. The obtained Concordia age of 47.57 ± 0.32 Ma with a small spread of the individual 206Pb/238U ages between 45 and 51.3 Ma argues for Early Eocene magmatism and pegmatite formation. The host granite of the rare-element pegmatites is dated 51.94 ± 0.61 Ma with LA–ICP–MS U–Pb technique on zircon and suggests a fertile Early Eocene magmatic period in the Western Rhodopes. EPMA data for the composition of the columbite is used to refine the formula of the mineral (Mn0.554Fe0.427U0.006)0.987(Nb1.826Ta0.085Ti0.116)2.03O6 and define it as columbite-(Mn). Application of the in-situ LA–ICP–MS data technique establishes a series of typical trace elements (Ti, U, Zr, Hf, Y, W, and Zn) that are usually found in content above 500 ppm. The studied columbite is enriched in heavy rare earth elements (HREE sum: 306–697 ppm) and depleted in light REE and Eu. These geochemical characteristics are collectively interpreted as evidence for crystallization from highly fractionated fluid-rich magma. High UO2 content reaching 0.89 wt. % is characteristic for the Vishteritsa columbite. The decrease of U proximal to cracks and in outer crystal zones documents U-mobility during overprinting hydrothermal processes.

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

“…Granitic magmatism in the metamorphic units of the Middle Allochthon, showing similar ages, is reported for the Pripek granites 52.8±0.89 Ma and Drangovo pluton 49.9±0.42 Ma (Marchev et al, 2013, and references therein). These events coincide with the wider range of 56-40 Ma granitoids and pegmatites in the units of the same allochthon in Central (Dolno Dryanovo granite -56 Ma; Jahn-Awe et al, 2010), Eastern (Topolovo -52.5 Ma; Marchev et al, 2013) and Western Rhodopes (Vishteritsa pegmatite -47.57± 0.32 Ma, Peytcheva et al, 2021;50±5 Ma, Arnaudov et al, 1969;and NW Rila area, Gorinova et al, 2019).…”

Efficient benchtop acid digestion of organic-rich sediments for ICP-MS analyses: testing analytical procedures on NIST 2702 standard reference material

“…In addition, two NIST 2702 aliquots were fused in a flux of lithium metaborate and lithium tetraborate, and fragments of the broken glass discs were mounted in epoxy resin and analyzed by LA-ICP-MS on the same ICP-MS instrument as acid-digested samples (for analytical details see Peytcheva et al, 2021).…”

Depositional conditions for Lower–Middle Jurassic sedimentary rocks from Northern Bulgaria inferred from whole-rock elemental composition

“…Trace elements were analyzed on broken and polished pellet pieces by LA-ICP-MS at the Geological Institute, Bulgarian Academy of Sciences. The 193 nm ArF excimer laser ATLEX-Lr and ELAN DRC-e ICP-MS instruments were operated in standard instrument conditions as described in Peytcheva et al (2021).…”