ZONED ZN-RICH CHROMITE FROM THE NAATANIEMI SERPENTINITE MASSIF, KUHMOGREENSTONE-BELT, FINLAND

Chromite from the Archean Naataniemi serpentinite massif, Kuhmo greens tone belt, Finland, exhibits high concentrations of Zn, up to 4.4 wt% ZnO. The chromite is zoned, optically and chemically; the best-preserv ed chromite cores can be divided into two groups on the basis of their composition. Type-I chromite is interpreted as a relict core, with Cr /(Cr + Al) values from 0.58 to 0.76 and Mg/(Mg + Fe2+) values from 0.5 3 to 0.60; the core of type-II chromite has been altered to ''femitchr omit''; Mg/(Mg + Fe2+) values range from 0 to 0.37. In the core of typ e-I and -II chromite, Zn shows no correlation with the other divalent cations (Mg, Mn and Fe2+), On the basis of their Zn content, type-I an d type-II chromite resemble those examples reported from metamorphosed volcanic-type iron-nickel sulfide ores from Western Australia, though the suite of type-I chromite from the Naataniemi serpentinite massif displays higher Mg (12.1 wt% MgO) and Al (20.9 wt% Al2O3) contents.