Carrollite from the Sazare mine, Ehime Prefecture, Japan

Abstract

Mode of occurrence and mineralogical properties of carrollite from the Sazare mine are described. The deposits of the mine are of the stratabound massive sulphide type in the Sanbagawa metamorphic terrain in Shikoku, Southwest Japan. The carrollite is found exclusively in a copper rich ore which occurs close to hanging- or footwall side of the main orebody or to apophyses, while common massive or banded ore does not contain the mineral. The mineral is usually associated with chalcopyrite and bornite, and also with pyrite, sphalerite or tetrahedrite in some cases. Under the reflection microscope, the mineral shows rather similar appearance to pyrite, but is more faint in reflection colour giving always traces of cubic cleavage. Its chemical composition analysed by EPMA was as follows: Cu=20.2, Co=38.0, Fe=0.2, Ni=0.9, S=42.0, Total=101.3 in wt. %. Atomic ratio of metals in the mineral calculated on the basis of S=4.00 is (Cu_0.97Co_1.97Fe_0.01Ni_0.05)_3.00S_4.00. a₀ by powder camera method (Ø=114.59mm) is 9.478±0.002 Å. The mineral is thought to be of metamorphic origin which was formed through recrystallization of chalcopyrite-pyrite ore during the Sanbagawa metamorphism from its mode of occurrence. Cobalt in the carrollite seems to be originally contained as a minor element mainly in primary pyrite. Chemical composition and a₀ value of carrollite from the Nkana mine, Zambia were also determined for comparison.