Worldwide distribution of submarine hydrothermal deposits and their classification

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Reviewing approximately 200 original articles on submarine and sub- seafloor hydrothermal deposits, the present study provides a classification of these deposits from several points of criteria; including geological tectonics, mineralogy, and forms of ore bodies; and a worldwide distribution map based on this classification (Figs. 1 and 2).<BR>The deposits were divided into three systems based on geological tectonics; mid-oceanic ridge system, arc-trench system, and hot spot system (Table 1), while the former two systems were sub-divided into the on-spreading and offspreading axis systems.<BR>Leaving gangue materials out of consideration, the deposits were divided into the sulfide type, oxide type, and sulfideoxide mixed type (Table 3). The sulfide type was further divided into the Cu-Zn-Pb and As-Sb-Ag-Hg sub-types, and the oxide type into the Mn and Fe sub-types. The Cu-Zn- Pb sulfide type deposits, in most cases forming mixtures with other ore types, have been discovered in both the mid-oceanic ridge system and arc-trench system, in particular on the spreading axes of the both systems (Figs. 1 and 2). The distribution of Pb minerals (mainly galena) is not so wide as Cu and Zn minerals but is rather restricted in the deposits on spreading axes near continents. The As-Sb-Ag-Hg sulfide type deposits which generally form mixtures with other ore types have been discovered near continents, regardless of the system. The As-Sb-Ag-Hg sulfide end-member type is in close relation with shallow submarine hot spring activities near coasts.<BR>The Mn oxide type deposits are widely distributed without showing clear relation to the geological setting. The Fe oxide type deposits widely occur as a rather minor constituent of mixtures with other types on the spreading axes of the midoceanic ridge system, and as an end-member in the volcanic front of the arc-trench system as well as in the hot spot system. It is probable that the volcanic exhalative Fe sediments are widely distributed along the recent plate boundaries, in particular along submarine volcanic belts in the arc-trench system of the earth.<BR>The on-seafloor deposits appear in various forms of ore bodies, e.g., massive sulfides, chimneys, mounds, and metalliferous sediments, while the beneath-seafloor deposits appear in rather restricted forms, e.g., sulfide veins and dissemination (Table 4). The forms and ore types for the on-seafloor ones have lateral variation with distance from the vents; massive sulfides and/or sulfide chimneys on the vents, sulfide and/or oxide mounds around the vents, and Fe-Mn metalliferous sediments widespread on the seafloor. This lateral change in the form and ore type may be accounted for by plume diffusion and fractionation due to the difference of the metal solubilities and the bottom seawater currents (Fig. 3). Sulfide particles formed from discharging solutions accumulate on and near the vents because of their low solubilities forming massive ore bodies, chimneys or mounds. Fe and Mn hydroxide particles, on the other hand, hardly precipitate because of their long residence time in seawater. They are widely dispersed together with some sulfide particles by seawater flow, and accumulate on the seafloor to form metalliferous sediments.
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Worldwide distribution of submarine hydrothermal deposits and their classification

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