Tin-polymetallic vein type deposits are one of the major
source of metal producers in the Circum Pacific Belt. This type of deposit is of
great importance for the modem electronics and medical industries because of
their high content of rare metals (especially indium and bismuth). We have
studied two representatives, Tosham of India (Cu-In-Bi-Sn-W-Ag-Au), and Mount
Pleasant of Canada (Zn-Cu-In-Bi-Sn-W), using proton and electron microprobes in
order to delineate the distribution of medicallhigh-tech rare metals. The
electron microprobe study showed that major indium carrier in such type of
deposit are roquesite (CulnS2), sphalerite,
stannite and a Cu-Zn-Fe-In-Sn-S mineral; and that indium is incorporated in
sulfides by coupled substitution like Cu + In = 2(Zn + Fe). The proton
microprobe showed that indium at trace levels is also present in chalcopyrite
and pyrite. In addition, zinc, copper, arsenic, antimony, selenium, tin, and
bismuth are common in chalcopyrite and pyrite. Arsenopyrite contains nickel,
copper, zinc, silver, tin, antimony and bismuth. In chalcopyrite and pyrite,
zinc, arsenic, indium, bismuth and lead are higher in
Mount Pleasant
ore, but silver is higher at
Tosham. Also thallium and gold were found only in Tosham pyrite. The Tosham
deposit is genetically related to S-type magma, while the
Mount Pleasant
deposit is
related to A-type granite. Tosham ore contains zinc-bearing biotites that
coexist with chalcopyrite in ore bodies but
Mount Pleasant
ore lacks such biotite. We
propose that the difference in elemental abundance between the two deposits are
caused by the different character of source magma and different mineral
associations of the ore body.