Volcanic‐hosted sulfide‐barite deposit from the Kita‐Bayonnaise submarine caldera, Izu‐Ogasawara arc, northwestern pacific

Publisher Website
Google Scholar
Abstract
Volcanic‐hosted sulfide and barite mineralization with high Au content (19.3 ppm) was discovered by submersible study (Shinkai 2000) on the eastern floor of the Kita‐Bayonnaise submarine caldera on the Shichito‐Iwojima Ridge, Izu‐Ogasawara Arc, northwestern Pacific. The hydrothermally mineralized rhyolitic tuff is partly coated by Mn oxyhydrox‐ide, and associated with hydrothermal Mn crusts and debris of mussel shells in the vicinity of the hydrothermally altered tuff‐breccias. The minearlized rhyolitic tuff occurs as a fragment of a large block (about 2 ×1 ×1 m) on talus, while the crusts occur on the caldera floor as a few thin patches several meters across or smaller. Ore‐mineral composition of the mineralized rhyolitic tuff consists mainly of sulfides and barite. Randomly interstratified seriate and montmorillonite is the only hydrothermal clay mineral from glass shards in the mineralized rhyolitic tuff. The mineralized tuff is significantly enriched in Zn, Fe, Cu, Ba, Au, Ag, and As, and has high Au /Ag ratio (0.036 to 0.071) compared with other marine volcanogenic sulfides. Au is probably present as submicrometer‐sized particles within sulfide minerals or is contained within the crystal lattice of the sulfide minerals. The δ34S values of sulfides of subsamples from the mineralized rhyolitic tuff indicate a fairly narrow range between +3.4 and +4.8% but are characterized by lighter isotopes in a drusy cavity compared with vein and disseminated sulfides. The sulfide sulfur is mainly from volcanic rocks of the caldera basement. A single barite sulfur isotopic value (+20.7%o) and salinity of fluid inclusions in barite are close to modern seawater values, suggesting a major contribution of seawater sulfate to the barite precipitation.