Other
Scientific paper
Nov 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53.2915m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 11, pp.2915-2924
Other
4
Scientific paper
Hydrogen and oxygen isotope and X-ray analyses were performed on kaolin minerals (kaolinite, dickite, and nacrite) and pyrophyllite from the Minamishiraoi and Inarizawa deposits of northern Japan. Dickite, nacrite, and mica-rich mica / smectite mixed-layer minerals occur as envelopes around barite-sulfide orebodies in the footwall alteration zones of the Minamishiraoi and Inarizawa deposits, while kaolinite and smectite-rich mica / smectite mixed-layer minerals occur in the outer alteration zones away from the orebodies. The hydrogen and oxygen isotope ratios of kaolin minerals from the Minamishiraoi and Inarizawa deposits fall in a narrow range of -24 to -32%. for hydrogen and 7.8 to 9.9%. for oxygen. These isotope ratios indicate that the hydrothermal fluid responsible for kaolin formation was the same as that which caused mineralization. The 18 O values of kaolin minerals of the Minamishiraoi deposit increase in order of nacrite < dickite < kaolinite. This trend indicates that nacrite formed at the highest temperature among the three kaolin polytypes. The oxygen isotope ratio of monoclinic pyrophyllite ( 18 O = 5.2%.) from the Inarizawa deposit is lower than that of nacrite ( 18 O = 7.5%.). The difference of 18 O values between the pyrophyllite and nacrite may be explained by a higher temperature of formation for the pyrophyllite. The mineralogie and isotopic data of the footwall alteration halos are useful as indicators of the size and metal contents of Kuroko orebodies. The footwall alteration halo of the Minamishiraoi deposit (small size and barite-rich deposit) contains kaolin and mica / smectite mixed-layer minerals, while those of the larger polymetallic Kuroko deposits contain seriate and chlorite. Thermodynamic data of these clay minerals indicate that the Minamishiraoi deposit formed at relatively lower temperature and farther from the heat source than larger polymetallic deposits. The chemical data for hydrothermal solutions from the 13°N East Pacific Rise hydrothermal site, as presented in the literature, plot in the kaolinite stability field at 150°C or less. Therefore, active submarine hydrothermal systems such as 13°N East Pacific Rise should form kaolin minerals in the alteration halo, as long as the temperature of the hydrothermal fluid is below sericite and chlorite stability.
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