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Geochemical Characteristics of the Akiyoshi Limestones, Japan and Their Bearing on Exploration for Blind Skarn Deposits
Author(s) -
Nakano Takanori,
Ishihara Shunso
Publication year - 2003
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/j.1751-3928.2003.tb00155.x
Subject(s) - skarn , geology , carboniferous , geochemistry , hydrothermal circulation , permian , carbonate , cretaceous , plateau (mathematics) , mineralogy , paleontology , fluid inclusions , mathematical analysis , mathematics , structural basin , materials science , metallurgy
. Carboniferous‐Permian limestones of the Akiyoshi Plateau, in the Inner Zone of southwestern Japan, are composed of essentially pure calcium carbonate containing only small amounts of other elements, and they are accompanied by marble and copper skarn deposits near the contact with late Cretaceous granitoids. The δ 18 O values of the Akiyoshi limestones range widely from 7.6 to 28.3% and are mostly lower than those of other areas of the same age (23–29%), whereas the differences among the δ 13 C values are small. The δ 18 O values are negatively correlated with Mn and Fe contents. Samples with high δ 18 O (>25%) and δ 13 C (>2%) values do not contain Fe, Zn, or Pb, but those with low δ 18 O values tend to be rich in these elements, indicating that these elements were introduced by interaction with H 2 O dominant fluids, possibly of magmatic origin. Potential scores for evaluating the degree of interaction with hydro thermal fluids were calculated for δ 18 O, δ 13 C, Fe, Mn, Zn, Pb, and Sr. Higher scores implying much hydrothermal interaction were evident in the Mt. Hananoyama area, where there are many skarn deposits, and along faults oriented mainly NNW‐SSE. Therefore, these are promising areas for exploring for blind deposits. It is likely that the hydrothermal fluid traveled through the limestones along fractures at the time of the granitic intrusions. However, the potential scores here are much smaller than those in the Pb‐Zn mineralized area of the Kamioka mine, so more detailed petrological and mineralogical investigations are necessary.