An example of ridge-proximal hydrothermal mineralisation: evidence from radiolarian chert-hosted Fe-Mn-oxide mineralisation within the İzmir-Ankara Erzincan Neotethyan Ocean, Central Turkey

Abstract

Fe-Mn-oxide (oxyhydroxide) deposits are common within the late Cretaceous mélange units of the İzmir-Ankara-Erzincan Suture Zone, which marks the closure of part of the northern branch of the Neotethys Ocean in Turkey. In the Cihanpaşa region (Yozgat, central Turkey), Fe-Mn mineralisation occurs as interlayers within a sequence of mudstone and siliceous pelagic units that overlies altered pillow lavas belonging to the Artova ophiolitic complex. T-Fe-Mn mineralisations are characterised by moderate amounts of Ba (560 ppm), and low contents of Sr (243 ppm), Co (51 ppm), Zn (183 ppm), and Ni (221 ppm). Mn/Fe (0.69) and low Co/Ni (<0.40), Co/Zn (<0.50) and Y/Ho (25.7) ratios and ΣREE (233) values suggest that mineralisation formed in a submarine environment hydrothermal system. The low Ceanom. values (−0.60) are consistent with a mostly oxic depositional environment. Further, low LaSN/NdSN (<1), negative Ce anomaly (0.29), and low Al/(Al+Fe) (0.14), whereas high LaSN/CeSN (4.01) and Fe/Ti ratio (208) with moderately positive Eu anomaly (1.22), and Ti/V (1.99), LuSN/LaSN (0.89), ΣREE/Fe ratio (22.36 × 10–4) indicate that the Cihanpaşa Fe-Mn mineralisation formed in an oxygenised marine sedimentary environment with influence of a ridge-proximal (near spreading ridge) submarine hydrothermal vent system in the İzmir-Ankara-Erzincan Neotethyan Ocean. These results indicate that detailed geological and geochemical evidences determined in silicilastic rocks and submarine volcanics within mélange associations well-exposed along the suture belt could be applied to exploration studies for the discovery of ancient submarine deposits, including significant and precious metals such as polymetallic Fe-Mn deposits (Fe-Mn crust and nodules) and seafloor sulphide mineralisation.