Eocene magmatism and associated Fe-Cu mineralization in northeastern Turkey: a case study of the Karadağ skarn

ABSTRACT

The metallogenic belt containing numerous skarn mineralized systems starting from Eastern Europe continues through Turkey and Iran. The study area in the Eastern Pontides is within this metallogenic belt. The 44.39 ± 0.53 Ma Karadağ Intrusion sourced skarn mineralization is located along the granitoid-to-limestone contact. The Karadağ Intrusion is an arc-like pluton with medium–high K calc-alkaline and peraluminous–metaluminous affinity. The Karadağ Fe–Cu skarn mineralization (Gümüşhane, Turkey), an exoskarn, is hosted by Late Cretaceous limestone and consists of early garnet, clinopyroxene, and orthoclase with late epidote and chlorite. Primary ore minerals are magnetite and haematite, accompanied by minor amounts of chalcopyrite and pyrite. Pyroxene comprises mostly diopside and less hedenbergitic diopside and johannsenite. Wollastonite is very rare. Garnet is andradite and grossular–andradite. Thus, all these results imply that the Karadağ Fe–Cu skarn mineralization formed under relatively oxidized and Fe-rich conditions. The homogenization temperatures of the fluid inclusions vary from 189°C to 405°C for quartz and 186°C to 430°C for calcite. The salinity contents in the fluid inclusions are within 0.2–9 wt% NaCl equivalent for quartz and 0.4–14.8 wt% NaCl equivalent for calcite. First melting temperatures between −36.5 and −47.4°C were attained with the presence of NaCl–FeCl₂± CaCl₂ in the initial phase of fluid inclusions. The first melting in the later stage of fluid inclusions is between −3.8 and −17.2°C, thereby, supporting the existence of NaHCO₃-Na₂CO₃-KCl-type salt composition. The δ¹⁸O values of minerals are 1.7–10.3‰ for garnet, 11.1–14.6‰ for quartz, 6.4 to 6.8‰ for epidote, and 2.8–3.8‰ for magnetite in the Karadağ skarn mineralization. The δ¹⁸O value of epidote indicates magmatic fluid, whereas those of garnet, magnetite, and quartz suggest magmatic fluids together with less meteoric effect. The δ¹⁸O values in limestone (18.7 to 22.3‰), marble (8.7‰), and calcite (10.5 to 12.2‰) were depleted relative to typical δ¹⁸O contents of marine carbonates (20 to 30‰). Moreover, the C isotope values of calcite (−5.4 to −1.4‰), marble (−2.1‰), and limestone (1.0 to 1.2‰) reflect those of metamorphic rocks and skarns (−4.0 to 3‰ and −18 to 2‰). Mineral paragenesis, fluid inclusion, and stable isotopic signatures are consistent with ore mineralization caused by the interaction of magmatic fluids with carbonate host rocks. Karadağ Fe-Cu skarn mineralization, associated with Karadağ postcollisional magmatism, is an example of skarn mineralized system in the Eastern Pontides.

Graphical abstract

KEYWORDS:

• Fluid inclusion
• Karadağ Fe-Cu Skarn
• mineral chemistry
• stable isotopes
• Turkey

Acknowledgments

This research was financially supported by project number 114Y099 from the Turkish Science Foundation (TÜBİTAK). We would like to thank Dr. Lynn Heizler for mineral chemistry analysis, Dr. Keewook Yi for U-Pb zircon age analysis and Dr. Meral Kaya (Atatürk University, Turkey) for paleontological investigation. The authors also thank Meltem Yılmaz, Enes Türk, Fatih Alkan and Z. Samet Güloğlu for their help during the fieldwork. We are grateful to Catherine Yiğit (Skaian Gates English Language Editing and Translation Service) for professional English editing assistance. Also, the authors thank editor-in-chief Dr. Robert J. Stern, reviewers Dr. David Lentz and Dr. Fatemeh Sepidbar and an anonymous reviewer for their critical comments which improved our manuscript.

Disclosure of potential conflicts of interest

No potential conflict of interest was reported by the author(s).

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Funding

This work was supported by the Scientific and Technological Research Council of Turkey [114Y099].