Native iron and the associated minerals from the ultramafic masses in the Sanbagawa belt, central Japan

Abstract

Native iron has commonly been found in the serpentine vein of the second stage of serpentinization of dunites from the ultramafic masses in the Sanbagawa belt, central Japan. It is nearly pure iron but contains small amounts of Ni and Co. In the dunites other metallic minerals and sulfides have not yet been found, though magnetite and primary chromite are present. In serpentinized wehrlites from the same masses native iron is almost absent, but in a few of them native cobalt-iron, CoFe₂, which is chemically different from wairauite (CoFe), has been found. In the serpentinized wehrlites awaruite and native copper have also been found with sulfides such as pyrrhotite and pentlandite, and oxides such as magnetite and primary chromite. An occurrence of ilvaite and andradite in the serpentinized wehrlites has been noted. The chemical composition and occurrence of these minerals are described. These native metals have been formed during the serpentinization of the dunites and wehrlites.