Toyoha is the largest Ag-Pb-Zn vein-type deposit in Japan,
and is about 40 kilometers on road to from my office at downtown Sapporo,
the capital of Hokkaido, Japan.
The veins here are characterized by occurrence of rare elements;
Au, Sn, W, In, Bi, Mo, Co, Ni and Ga.
Moreover, recent studies detected Te, Se, V, Cr and rare-earth elements
in ores from drill cores recovered by MMAJ,
Metal Mining Agency of Japan, and by the Toyoha Mines Co. Ltd.
from southwest of the current mining area.
Average indium concentration in these veins is 150 to 250 ppm,
which is comparable to that in zinc concentrates (not in crude ore)
of some representative indium producers in central Peru.
This figure and the current production tonnage of crude ore
(about 500,000 metric tons/year) suggest that the
Toyoha mine is currently the largest indium producer in the world.
Want to know more details on this deposit?
Occurrence and chemistry of indium-containing minerals
and accompanied tin minerals were reported by Ohta (1989) and Ohta (1991),
and those of electrum by Kanbara and Kumita (1990).
Gangue and alteration minerals are described and discussed by Ohta and Marumo (1985),
and Ohta and Yajima (1988).
Deposition processes of silver and bismuth minerals,
tetrahedrite-tennantite solid solution and Pb-Sb sulfosalts from Toyoha
are discussed by Ohta (1992).
Formation models of the polymetallic veins is introduced by Yajima and Ohta (1979),
Yajima et al.(1993), Watanabe and Ohta (1995), and by Ohta (1995).
Regional setting of the ore deposits and igneous rocks in southwest Hokkaido
is discussed by Ohta et al. (1998).
Yajima, J. and Ohta, E. (1979):
Two-stage mineralization and formation process of the Toyoha deposits, Hokkaido, Japan.
Mining Geol., 29, 291-306.
Ohta, E. and Marumo, K. (1985):
Occurrence of apatite and associated gangue minerals in the Toyoha deposits, West Hokkaido, Japan.
Proc. Japan Academy 61, Ser. B, 99-102.
Ohta, E. and Yajima, J. (1988):
Magnesium to iron ratio of chlorite as indicator of type of hydrothermal ore deposit.
Mining Geol. Sp. Issue 12, 17-22.
Ohta, E. (1989):
Occurrence and chemistry of indium-containing minerals from the Toyoha mine,
Hokkaido, Japan. Mining Geol., 39, 355-372.
Kanbara, H. and Kumita K. (1990):
Mode of occurrence and chemical composition of electrum from
the Toyoha polymetallic vein-type deposits, Hokkaido, Japan.
Prof. Urashima volume, 201-210 (in Japanese with English abstract).
Ohta, E. (1991):
Polymetallic mineralization at the Toyoha mine, Hokkaido, Japan.
Mining Geol. 41, 279-295.
Ohta, E. (1992):
Silver mineralization at the Toyoha mine, Hokkaido, Japan. Mining Geol., 42, 19-32.
Yajima, J., Ohta, E., Kamiki, T. and Takeyama, T. (1993):
Formation model and exploration of the Toyoha mine,Hokkaido,
Japan. Resource Geol. Sp. Issue, 15, 451-458.
Watanabe, Y. and Ohta, E. (1995):
The relation of two-stage mineralization at the Ag-Pb-Zn Toyoha Deposit,
Southwest Hokkaido, to subduction of the Pacific Plate.
Resource Geol. Sp. Issue, 18, 197-202.
Ohta, E.(1995):
Common features and genesis of tin-polymetallic veins.
Resource Geol. Sp. Issue, 18, 187-195.
Ohta, E., Kawano, Y., Nakagawa, M. and Kagami, H. (1998):
Petrochemistry of Late Miocene to Quaternary igneous rocks and metallogenesis in southwest Hokkaido, Japan.
Resource Geol. 48, 183-195.
Growth zoninig in sphalerite from Toyoha
Vein system of Toyoha