Geochemical, stable (O, C, and B) and radiogenic (Sr, Nd, Pb) isotopic data from the Eskişehir-Kızılcaören (NW-Anatolia) and the Malatya-Kuluncak (E-central Anatolia) F-REE-Th deposits, Turkey: implications for nature of carbonate-hosted mineralization

Authors: OKAY ÇİMEN, LORETTA CORCORAN, CORINNE KUEBLER, STEFANIE SIMONETTI, ANTONIO SIMONETTI

Abstract: In Turkey, the largest fluorine (F)-rare earth element (REE)-thorium (Th) deposits are located within the Eskişehir-Kızılcaören (north-western Anatolia) and the Malatya-Kuluncak (east-central Anatolia) regions, and these are associated with Oligocene extensional alkaline volcanic and Late Cretecaous-Early Paleocene postcollisional intrusive rocks, respectively. In the Kızılcaören region, the basement units include the Triassic Karakaya Complex and the Late Cretaceous oceanic units (Neotethyan suture) that are cut and overlain by phonolite and carbonatite intrusions and lava flows. In the Kuluncak region, the plutonic rocks are mainly composed of syenite, quartz syenite, and rare monzonite, and these cut the late-Cretaceous Karapınar limestone, which hosts the F-REE-Th mineralization in contact zones. A carbonatite sample from the Kızılcaören region displays both a total rare earth element (TREE) concentration (4795 ppm) and δ¹¹B (-6.83‰) isotope composition consistent with mantle-derived carbonatite; whereas it is characterized by heavier δ¹³C (+1.43‰) and δ¹⁸O (+20.23‰) isotope signatures compared to those for carbonatites worldwide. In contrast, the carbonates which host the F-REE-Th mineralization in the Kuluncak region are characterized by lower TREE concentrations (5.13 to 55.88 ppm), and heavier δ¹³C (-0.14 to -0.75‰), δ¹⁸O (+27.36 to +30.61‰), and δ¹¹B (+5.38 to +6.89‰) isotope ratios compared to mantle-derived carbonatites. Moreover, the combined initial ⁸⁷Sr/⁸⁶Sr (0.70584 to 0.70759) and ¹⁴³Nd/¹⁴⁴Nd (0.512238 to 0.512571) isotope ratios for samples investigated here are distinct and much more radiogenic compared to those for carbonatites worldwide, and therefore indicate significant crustal input and/or hydrothermal metasomatic-related alteration. Overall, stable and radiogenic isotope data suggest that the host carbonate rocks for the F-REE-Th mineralization in both the Kızılcaören and the Kuluncak regions consist of hydrothermally metasomatized carbonatite and limestone, respectively. The mineralization in the Kızılcaören region may potentially be related to carbonatite magmatism, whereas the mineralization in the Kuluncak region, which most likely formed through interactions between the plutonic rocks and surrounding limestone at contact metamorphism zone, involved hydrothermal/magmatic fluids associated with extensive postcollisional magmatism.

Keywords: Stable and radiogenic isotopes, carbonatites, metasomatised limestone, F-REE-Th mineralization in Turkey

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