THE FIRST FIND OF MANGANESE AND CADMIUM SULFIDE MINERALS IN PLEISTOCENE-HOLOCENE DEPOSITS OF THE DERYUGIN BASIN IN THE SEA OF OKHOTSK (PACIFIC OCEAN)

We report here the results of studies on manganese and cadmium sulfide minerals first found in Pleistocene-Holocene deposits of the marginal seas of the western Pacific Ocean. Manganese sulfide minerals (alabandine-αMnS and rambergite-ᵞMnS) from sediments of the mud volcanic structure in the Deryugin Basin (the Sea of Okhotsk) are the second find in the world (after the Baltic Sea basins) in marine deposits of the present-day ocean. There is currently no evidence of the presence of cadmium sulfide minerals (greenockite) in Pleistocene-Holocene marine deposits. Manganese calcites and elemental sulfur are found in close association with these sulfides. The results of electron microscopic studies made it possible to characterize in detail the morphological types of the identified mineral phases and their chemical composition features. It has been established that among the studied sulfide minerals, isomorphic substitutions in the MnS-ZnS-CdS solid solution system are widely developed and in some cases are accompanied by the formation of intermediate mineral phases of variable composition. The existence of a periodic oxygen minimum environment in the Deryugin Basin (up to the point of hydrogen sulfide contamination), combined with the episodic influx of elision gas-fluid components with hydrogen sulfide and a number of metals (manganese, cadmium, zinc) at local sites of the seafloor within mud volcanic structures, contributed to the formation of this unusual paragenesis of authigenic sulfide minerals. A model for the formation of manganese-containing mineral phases, characteristic of anoxic environments in local depressions of the Baltic Sea with periodic hydrogen sulfide contamination, was accepted as the main working hypothesis of authigenic mineral formation.