Vanadium Potentiality of Late Silurian-Early Devonian Black Shales in Northwestern Black Sea Region, Turkey

Vanadium (V), is primarily used in the production of metal alloys (in addition to high strength low alloy properties) and reinforcing titanium alloys, take notice in the current critical element list by organizations such as the European Union and USGS. There is no detailed study on the exploration of vanadium resources in Turkey. Recently, vanadium can be extracted from several different types of mineral deposits and from fossil fuels. Black shales can be considered as one of the vanadium resources recently. Black shales are fine-grained sedimentary rocks containing not only in organic matter but also in specific trace elements, like V, Mo, Cu, Zn, Ni, Cd, Se, Pb and U.

The study area is located in the Karabük – Kastamonu in Black Sea region of Turkey and primarily consist of Silurian aged black shales. These black shales can be described as a Hercynian continental sliver, which represents the northernmost part of the Western Pontides . This study focuses on revealing the content and major controlling factor of V of Late Silurian-Early Devonian aged black shales in the northwestern Black Sea Region of Turkey. In the end, the depositional model was established. Studied black shales have a wide range of vanadium content, varying from 74 to 400 μg/g. It can be stated that authigenic enrichments in modern suboxic settings, and likely represent the removal of dissolved V as V(IV). V(IV) was adsorped by organic matter. This result is also supported by several redox indicators such as V systematics (V/Sc, V/Ni) as well as ratios of Ni/Co, Th/U, and Mo/Mn. The reducing of V(III), is mainly associated with the excessive H₂S accumulation in sediments and bottom waters and strong reducing conditions is also a key factor. In this circumstance, the decoupling mechanism of V changes from surface adsorption to ionic substitution forming solid solution series with Al in clays. In addition, the Al−Fe−Mn discriminant diagram of siliceous rocks, show that the genesis of siliceous rocks are close to the biogenic origin. The moderate positive correlation of V vs. TOC (R²=0.52) crossplot and the lack of correlation of V vs. clay-forming elements (Al₂O₃, K₂O, Na₂O, and CaO) mean that the organic matter rather than clay minerals can play a role in V enrichments. Also, it means that water conditions were controlled by elevated organic matter flux and consequent oxygen drawdown. Nevertheless, the discreteness of data in cross-plot diagrams may imply that a portion of the V in the samples occurs in other forms in addition to occurring in relation to organic matter. More detailed investigations are necessary.

Keywords: Vanadium potential; Black shales; Depositional model; Northwestern Black Sea; Turkey