Distribution of Rare Earth Elements in the Ore-Bearing Sediments in the Nameless Uplift, Central Basin of the Sea of Japan

The rare-earth element (REE) composition of pyrolusites, todorokites, birnessites, and ferruginate sediments raised during dredging of a mound in the Central Basin of the Sea of Japan was studied. The age of ore formation is Late Cenozoic. The REE content in the studied samples ranges from 18 to 133 ppm. Europium anomalies Eu{ₒ₍}^* (0. 99–1. 18) may indicate the low temperatures of hydrothermal solutions. In the monomineral pyrolusite and todorokite samples, Ce{ₒ₍}^* ranges from 0. 54 to 0. 94. An unusual REE distribution (1. 21–1. 78 Ce{ₒ₍}^* and 1. 04–1. 18 Eu{ₒ₍}^*) was found in the manganese crusts containing birnessite (Ce{ₒ₍}^* – 1. 21, 1. 23) and in the ferruginate sediments (1. 38, 1. 78 Ce{ₒ₍}^*). The main REE source is presumed to be post-volcanic gas-hydrothermal solutions transporting REE in the form of complex compounds with ligands (Cl–, F–, SO₄^{2 - }). Accumulation of Ce upon contact with seawater is possible if birnessite, which has the high sorption capacity, is present among manganese minerals. Some differences in the REE composition of the studied samples compared to the ferromanganese deposits of the World Ocean may be related to the geochemical features of the sea-margin basalts and the prolonged and pulsed manner of volcanism in the Sea of Japan.