Mixed Hydrogenetic-Hydrothermal Genesis of Quaternary Ferromanganese Nodules in a Tectonically Active Lacustrine Basin, Eastern Türkiye

Abstract

This study presents a detailed investigation of the mineralogical, geochemical, and rare earth element (REE) characteristics of ferromanganese nodules found within Quaternary lacustrine sediments in the Agri region of Eastern Anatolia, T & uuml;rkiye. These nodules, primarily composed of goethite and manganite with minor quartz, exhibit botryoidal and colloform textures typical of low-temperature diagenetic environments. Raman and XRD analyses identified significant iron and manganese mineral phases, while SEM-EDX revealed trace amounts of Co, Ni, and Zn associated with these phases. Chondrite-normalized REE patterns demonstrate light REE enrichment, a weak negative europium anomaly (EuN/Eu* = 0.69-0.84), and variable cerium anomalies (CeN/Ce* ranging from 0.74 to 1.95, corresponding to both weak negative and positive Ce anomalies), indicating a mixed hydrogenous and hydrothermal origin under fluctuating redox conditions. These geochemical signatures, together with sedimentological evidence, suggest formation within a restricted lacustrine environment characterized by episodic anoxia and limited detrital input. The results contribute to a broader understanding of Fe-Mn mineralization in continental settings and underscore the influence of volcanic and tectonic processes on nodule genesis.