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The data are given on the structure, chemical composition, and content of microelements in the ferromanganese and siliceous crusts of Pervenets Rise (the Sea of Japan). The crusts resulted from the cementation of small fragments of green clays (celadonite) with hydroxides of manganese (todorokite and birnessite) or silica. Initial was the formation of celadonite deposited during the eruption of ore-bearing hydrothermal solutions in the volcano caldera or on its slopes.The features of the crust structure show that they were originated through the diffusive infiltration of gas-hydrothermal solutions along the fractures or weakened zones in volcanic rocks and subsequent cementation of the celadonite already formed occurrences with manganese or siliceous oxides. The manganese and siliceous mineralization is separated in time and often in space and demonstrate more local distribution.

This paper provides information on the structure, chemical composition, and concentrations of microelements in ferromanganese crusts and siliceous crusts sampled on the Pervenets Rise, Sea of Japan. The crusts were formed by cementation of small fragments of green clays (celadonite) by manganese hydroxides (todorokite and birnessite) or by silica. The primary process involved the generation of celadonite, which was deposited as ore-bearing hydrothermal brine that was discharged in the caldera of the volcano or on its slopes. The crusts have a structure that indicates their formation during diffuse percolation of gas-charged hydrothermal brine along fissures or weakened zones in volcanic rocks and subsequent cementation of the resulting celadonite deposits with manganese or siliceous oxides. The manganese and the siliceous mineralization are separated over time, as well as, frequently, in space, and are more local.

The paper presents a comparative analysis of ferromanganese crusts and concretions (FMC) recovered during the dredging of 14 seamounts in the Central Basin, Sea of Japan. The major rock-forming elements in FMC are Mn, Fe, and Si. In terms of the Mn content, the studied 53 samples are divided into four groups: (1) less than 10% (given than concentrations of 2–8% are lacking); (2) 10‒25%; (3) 25‒42%; and (4) 42‒63%. The (Mn + Fe)/Si ratio increases from group 1 to group 4, and average value in them is 1.6, 2.5, 6.7, and 70.7, respectively. Taking Fe/Si and Mn/Si values into consideration, concretions of these groups belong to the following varieties: (1) ferrosiliceous; (2) mangano-ferrosiliceous; (3) siliceous-ferromanganese, and (4) manganiferous. The highest concentration of nonferrous metals is observed in FMC of groups 2 and 3. Their concentration is slightly lower in group 4 and very low in group 1. The internal structure of FMC in these groups is variable, suggesting their different formation settings. Crusts of group 1 were formed during the precipitation of Mn from a hydrothermal plume on the older ferrosiliceous crusts. Crusts of groups 2 and 3 were likely formed by the diffuse percolation of Mn-bearing hydrothermal solutions along fractures and weakened zones in volcanic rocks, with their subsequent cementation by manganiferous hydroxides from sedimentary or volcaniclastic deposits on seamounts. Crusts of group 4 were formed at sites of the hydrothermal solution discharge on the seafloor. FMC of different groups are recovered during the dredging of most volcanic seamounts in the Central Basin (Sea of Japan). Since the dredging is accomplished at a depth interval of a few hundreds of meters, the detection of concretions of a certain type is governed by the distance to the nearest hydrothermal source.

Based on data on the concentration of noble metals (Au, Ag, Pt, Os, Ir, and Ru) in bulk samples of ferromanganese crusts, the presence of inclusions of micro- and nanosized grains of Ag, Au, Pd, and Pt, often with impurities of other elements, as well as their chaotic distribution, three sources of incorporation of these metals into ore crusts of Far Eastern seas are suggested: seawater, postvolcanic gas–hydrothermal fluids, and hydrothermal plumes. The presence of grains of platinoids and gold in ferromanganese crusts on only some mounts may result from peculiarities in the formation of volcanic rocks on the ancient continental basement.

The electron microprobe investigation of volcanic rocks from the submarine rises of the Sea of Japan revealed for the first time numerous inclusions of small grains containing metals (Cu, Zn, Sn, Ni, Pb, As, Cr, W, Ti, Ta, Fe, and Ag), mainly as native elements, intermetallic compounds, phosphides, oxides, sulfides, and sulfates. These grains are usually confined to the walls of microscopic fractures and pores or fill microscopic cavities and interstices in the groundmass and in rock-forming minerals. Taking into account that native metals, intermetallic compounds, and phosphides are indicative of a high-temperature gaseous fluid, it can be supposed that such a fluid was the source of metals.

The examination of polished sections of ferromanganese crusts from the Sea of Japan revealed abundant inclusions of small grains of base and precious metals: Ag, Pd, Pt, Au, Rh, Cu, Zn, Sn, P, Ni, Cr, Ti, Sb, As, W, and Mo. The metals occur in the form of native elements or intermetallic compounds, subordinate sulfides, sulfates, oxides, tungstates, and phosphides. The data on contents, occurrence forms, and distribution of these metals in the ore crusts from this region are discussed.

Ferromanganese formations are among the major solid mineral resources in the World Ocean. They are characterized by high contents of Fe, Mn, and often nonferrous and noble metals. The issue of the mode of occurrence and genesis of noble and nonferrous metals in the FMS long ago attracted the attention of researchers. However, this issue remains debatable. According to some researchers, the metals mentioned above are extracted from seawater by manganese and iron hydroxides. Other researchers believe that the metals are derived from postmagmatic and hydrothermal solutions. Proponents of the extraterrestrial origin have suggested that platinum group elements (PGE) and some other heavy metals could be incorporated as cosmogenic spherules during the growth of ferromanganese formations. However, all these hypotheses remain controversial. We investigated ferromanganese crusts from the Kashevarov Bank, Deryugin Basin, and Akademiya Nauk Rise in the central part of the Sea of Okhotsk (Fig. 1). Ore crusts from this region are thin (up to 2 cm), usually homogeneous, and vaguely layered (Fig. 2a). The slope of the Kashevarov Bank also contains oolitic crusts related to the cementation of sandy sediment by ferromanganese hydroxides. However, the predominant crust type is characterized by a monolithic upper layer (3 to 4 mm thick) and an oolitic lower layer (Fig. 2b). Data on the chemical composition showed that the crusts contain almost equal contents of Mn and Fe. The total content of ore elements in them is as much as 30 wt %. The Mn content varies from 5.6 to 16.0%; the Fe content, from 3.9 to 17.7%; and the Mn/Fe ratio, from 0.18 to 1.42. Contents of nonferrous metals are very low (0. n ‐0.0 n %) relative to the oceanic ore crust. The total content of Ni, Co, Cu, Pb, and Zn varies from 0.03 to 0.46%. The content of Au and Ag is 0.01 and 0.24 g/t, respectively. In order to elucidate the mode of occurrence of noble and nonferrous metals, we prepared eight polished samples and examined them with an electron microscope and microprobe analyzer (JXA8100, Jeol, Japan). The results show that all samples contain inclusions of noble and nonferrous metals of different compositions. Native silver is the major constituent. Small grains of gold, iron, copper, tungsten, Fe‐Sb oxides, Zn‐Ag‐Cu sulfides, phosphates of rare earth elements, and intermetallic (Cu‐Zn, Cu‐Ni, Sn‐Pb‐Cu‐Ni, Ni‐ Cr‐Mo, Fe‐Cr‐Ni, and Au‐Cu‐Ag) compounds are the subordinate components (Tables 1, 2; Fig. 3).

This paper reports the results of an investigation of the chemical composition and distribution of manganese-rich metalliferous sediments in the Deryugin Basin. They compose an upper sedimentary layer up to 30 cm thick within a strip up to 40 km wide and 180 km long in the central part of the basin along the East Deryugin suture zone bounding the Deryugin sedimentary basin to the east. The sediments are enriched relative to the regional background composition in Mn (by a factor of 35); Au; Ni; Zn; Co (by a factor of 3–5); and, locally, in Mo, V, Ba, Cu, Pb, and Hg. It was supposed that their formation was controlled by several processes: precipitation of Mn and some other trace elements from hydrothermal plumes of seawater that occasionally form above submarine hot vents in the northern part of the basin, precipitation from anoxic bottom waters at the eastern boundary of the Deryugin sedimentary basin, and early diagenetic migration of Mn into the surface sediments.

Although barite nodules are extremely rare in the World Ocean, they are rather widespread in the Japan Sea. They were first discovered by Japanese scientists in the Honshu Island borderland (Okada et al., 1971; Sakai, 1971). They were later reported from the North Yamato Rise (Lipkina and Tsoi, 1980) and Okushiri Ridge (Astakhova et al., 1990) (Fig. 1, Table 1). All barite nodules in the Japan Sea are confined to Miocene marine sediments.