Genesis of the Tilkiköy (Kalecik, Ankara) Manganese deposit in the Neotethyan Ankara Melange, Central Turkey: mineralogical, geochemical, and paleoenvironmental perspectives

Abstract

The Tilkiköy manganese deposit is located within the Neotethyan Ankara Mélange, a major constituent of the Izmir-Ankara-Erzincan Suture Zone in northwestern Turkey. The deposit is hosted by radiolarites, which are part of a volcanic-sedimentary sequence formed during the closure of the Neotethyan Ocean. The ore bodies are predominantly strata-bound and occur in massive, banded, and layered forms within the radiolarites. The primary ore mineral is pyrolusite, accompanied by minor amounts of cryptomelane. Trace amounts of gangue minerals such as hematite, quartz, and pyrite have also been observed. Trace element discrimination diagram indicate a hydrothermal source is effective for mineralization. This interpretation is supported by high Mn/Fe ratios (ranging from 0.23 to 20.69), elevated Co/Zn (1.30) and Co/Ni (1.07) ratios, and low total rare earth element contents (ΣREE=34.10 ppm). Additionally, the low concentrations of Cu+Ni+Co (298.65 ppm), a pronounced negative cerium anomaly (Ce/Ce*PAAS=0.57), and a high Y/Ho ratio (26.64) all point toward hydrothermal processes. Redox-sensitive elemental ratios such as Ni/Co (0.82-5.6) and V/Mo (6.7-26.5), as well as Mn*SN (-1.18-0.20) and Ceanom. (-.18), indicate deposition under oxygenated and low-salinity seawater conditions. This interpretation is further supported by low Sr concentrations (308 ppm), a CaO/(CaO+MgO) ratio of 0.49, and a Sr/Ba ratio of 0.98. In addition, the weak negative Eu anomaly (0.70) based on chondrite-normalized REE patterns, Ce anomaly (0.57), ΣREE/Fe ratio (27.8∙10-4) values, and Ti/V (3.9) indicating a low-temperature hydrothermal fluids (<250 °C) and close to the spreading ridge environment. In conclusion, the Tilkiköy manganese deposit is interpreted to have formed from low-temperature hydrothermal fluids related to the spreading ridge of the Izmir-Ankara- Erzincan branch of the Neotethyan Ocean.