HR: 0800h
AN: V41B-1374    [Abstracts]
TI: Geochemistry of Besshi-type Massive Sulfide Deposit at Makimine in the Shimanto Belt, Southwestern Japan
AU: * HATSUYA, K
EM: hatsuya@luna.riko.tsukuba.ac.jp
AF: Master_fs Program in Science and Engineering, University of Tsukuba, 1-1 Ten_fnodai Tsukuba, Ibakaki, 300-8572 Japan
AU: KOMURO, K
EM: komuro@arsia.geo.tsukuba.ac.jp
AF: Doctoral Program in Earth Evolution Sciences, University of Tsukuba, 1-1 Ten_fnodai Tsukuba, Ibaraki, 300-8572 Japan
AU: OGAWA, Y
EM: yogawa@arsia.geo.tsukuba.ac.jp
AF: Doctoral Program in Earth Evolution Sciences, University of Tsukuba, 1-1 Ten_fnodai Tsukuba, Ibaraki, 300-8572 Japan
AB: Many Besshi-type deposits are known to be hosted in the accretionary complexes in southwestern Japan. Most of them occur in the Sambagawa metamorphic belt, but some are also found in other weakly or non-metamorphic accretionary belts. In order to understand the genesis of Besshi-type deposits, geochemical and mineralogical studies were carried out for the ores from Makimine in the northern Shimanto belt, southwestern Japan. The Makimine deposit occurs in the Late Cretaceous Makimine Formation, which is composed of a series of clastic piles and basalts, and metamorphosed up to greenschist facies. Around the deposit, chert is absent and the clastic piles around the basalts were thermally altered. The evidence indicates that the basalts in the formation had been in situ formed in the clastic piles. The massive sulfide ores of lenticular, podiform and rod-shaped are associated closely with the basalt. The orebodies are consisting of pyrite, phrrohotite and chalcopyrite with minor amounts of sphalerite and quartz. The ores are enriched mainly in the chalcophile elements such as Cu, Fe, Cd, Ag, Bi, Zn, In, Te, Co, Mo, Pb, As, Tl and Sb, and depleted in the lithophile elements compared with the average shale. They have higher Cu/Zn and Cu/Pb ratios; lower Ba contents in comparison with those of other massive sulfide deposits. Their chondrite-normalized REE patterns are characterized by negative Ce anomaly, positive Eu anomaly and depletion of heavy-REE. The chemical properties of the ores are similar to the sulfides from modern hydrothermal ore deposits at mid-ocean ridge such as East Pacific Rise and Mid-Atlantic Ridge, especially of the Cu-rich types. These results suggest that the Makimine deposit was formed by deep sea hydrothermal activity in the clastic piles of subduction zone, which is associated with basalt formation of Kula-Pacific ridge. Their unique properties might be due to mode of hydrothermal circulation in the clastic piles. On the basis of bulk-rock compositions and the Pb isotopic ratios of the ores and associated rocks, the detailed formative environment and processes of the Makimine deposit will be discussed.
DE: 8135 Hydrothermal systems (8424)
DE: 4832 Hydrothermal systems
DE: 1749 Volcanology, geochemistry, and petrology
DE: 1065 Trace elements (3670)
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting