Hydrothermal manganese crusts from Enarete and Palinuro seamounts in the Tyrrhenian Sea

Manganese crusts were recovered from Enarete and Palinuro Seamounts in the Tyrrhenian Sea. The crusts consist of porous, black, layered Mn oxides up to 45 mm thick. In some cases, the surface has a black metallic sheen similar to that observed in crusts from the Tonga‐Kermadec Arc. The crusts overlie substrates such as calcareous sediment, siltstone, and oyster shells. They consist dominantly of 10‐A manganate and 7‐A manganate, with minor quartz, calcite, aragonite, illite, mont‐morillonite, plagioclase, and goethite. The sample having the highest Mn content contained 52.8% Mn, 0.15% Fe, 46 ppm Ni, 84 ppm Cu, 26 ppm Zn, 6 ppm Pb, and 2,130 ppm Ba, with a Mn/Fe ratio of 347. It also had a low rare‐earth element (REE) abundance (La 2.7 ppm) and a negative Ce anomaly (Ce/La ratio 0.5). A TV profile on Palinuro showed the occurrence of yellow (Fe oxyhydroxide or nontronite), black (Mn oxide), and white (sulfate) halos in the sediment and opaqueness in the overlying water. Nontronite and massive sulfides were...