Original paper

Complex compositional zoning in epidote from rhyodacitic tuff, Bobae sericite deposit, southeastern Korea

Choo, C.O.

Abstract

Epidote in the propylitic alteration zone of the Bobae sericite deposit, southeastern Korea, resulted from progressive hydrothermal alteration of rhyodacitic tuff. It shows complex compositional zoning patterns that include patchy zoning, multiple growth zoning, sector zoning, and oscillatory zoning. On the whole, the zoned epidote has Al-rich cores and Fe-rich rims. Remnant textures in zoned epidote indicate that the earlier zone was partially resorbed prior to growth of a later one. Al and Fe in the M-site are the most important components that control patterns of oscillatory zoning. Mn and Sr substituting Ca in the A-site show some fluctuations in the concentration amplitude, although their contribution to the oscillatory zoning is still insignificant relative to Al and Fe. A variety of zoning patterns that occur in the Bobae epidote suggest that there are disequilibrium crystallization and chemical fluctuations in the local system during multiple hydrothermal alteration processes.

Keywords

epidotebobae sericite depositcompositional zoninghydrothermal alteration