HR: 17:15h
AN: V44A-06    [Abstracts]
TI: Diversity of Active Seafloor Hydrothermal Mineralization in the Manus Back-Arc Basin, Papua New Guinea
AU: * Gena, K
EM: kgena@cc.okayama-u.ac.jp
AF: Department of Earth Science, Okayama University, Tsushimanaka 3Chome 1-1, Okayama, 700-8530 Japan
AU: Chiba, H
EM: hchiba@cc.okayama-u.ac.jp
AF: Department of Earth Science, Okayama University, Tsushimanaka 3Chome 1-1, Okayama, 700-8530 Japan
AB: The Manus back-arc basin in the Western Pacific hosts three contrasting style of mineralization called Vienna Wood, Pacmanus and Onsen site. The three deposits have distinct geology and geochemical characteristics. The Vienna Wood site in the Central Manus Basin (CMB) is hosted by mid-oceanic ridge type basalt. The mineralization is dominated by wurtzite, marcasite, pyrite, chalcopyrite, Fe-oxide and gangue minerals of anhydrite, gypsum and quartz. The filling temperatures and salinities of the inclusion range from 200-260_E#8249;C and 4.8-6.6 NaCl equiv. wt% respectively. Bulk chemical analyses of the ores indicate that the mineralization in the Vienna Wood site can be classified into the Zn-Cu type. The simple mineral assemblage indicates simple basalt-seawater interaction and is a modern analogue of the ophiolite hosted VVMS deposits. The mineralization in the Pacmanus site is hosted by dacitic lavas is characterised by a complex mineral assemblage of marcasite, pyrite, chalcopyrite, sphalerite, bornite, enargite, covellite, chalcocite, digenite, galena, tennantite, native gold, PbAs-sulfosalts and gangue minerals of barite, rare silica, anhydrite and native sulphur. The temperature of mineralization ranges from 230-280_E#8249;C. Bulk chemical composition of the ore samples indicates that the mineralization in the Pacmanus site can be classified into the Zn-Cu-Pb-Au type. The mineral assemblage, character of the ores and tectonic setting resembles those of ancient Kuroko and currently forming hydrothermal deposits in Lau Basin and in Okinawa Trough. The Onsen hydrothermal site in the Desmos caldera is hosted by basaltic andesite. The advanced argillic alteration is characterised by both high and low temperature acid stable minerals of pyrophyllite, natroalunite, quartz, cristobalite, amorphous silica, anhydrite, gypsum, pyrite, marcasite, enargite, covellite and native sulphur. The mineralization occurs at a temperature range of 240 to 340_E#8249;C. The high sulfidation mineralization is considered to be a product of magmatic degassing and is a typical example of an acid-sulphate type of hydrothermal activity developing on the seafloor.
DE: 8135 Hydrothermal systems (8424)
DE: 4825 Geochemistry
DE: 3665 Mineral occurrences and deposits
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting