NEW OCCURRENCE AND CHARACTERIZATION OF NI-SERPENTINES IN THE KWANGCHEON AREA, KOREA

Pecoraite and nepouite, Ni-serpentines, occur in the serpentinized ult ramafic rocks in the Kwangcheon area, Korea, where the parent rock is classified as harzburgite and/or Iherzolite. Pecoraite was precipitate d twice from the solution; the early-formed pecoraite coexists with ma gnetite, millerite, and polydymite both in the Buk- and Nam-sites, whi le the late-formed pecoraite appears as well-grown colloform and opaqu e-free phase only in the Buk-site. The typical colloform texture of th e late-formed pecoraite strongly indicates that it was precipitated fr om the solution in supergene conditions. Pecoraite is characterized by its extremely high Ni content and the difference in Fe content betwee n the early- and late-formed pecoraite. Nepouite is distinguished from pecoraite by its prismatic morphology and the large degree of isomorp hous substitution between Ni and Mg. The phase relations among coexist ing magnetite-millerite-polydymite assemblage with the early-formed pe coraite suggest that the pecoraite might have precipitated in the extr emely limited f(O2) and f(s2) environment from the highly Ni-concentra ted solutions and is stable at 25 degrees C and 1 bar.