Magmatic Ore Deposits - Metals and Society: An Introduction to Economic Geology - page 57

abundant crystals prevent its segregation. In addition, because the basalt is relatively
poor in nickel and PGE (because sulfide is retained in the mantle source), the sulfide
contains only low tenors of these elements. These are the main reasons why deposits of
this type are found in komatiitic and not basaltic flows.
Why are the deposits particularly common in the Kambalda region? There are
two contributing factors. The first is the presence of the sulfur-rich sediments which
provide the sulfur; the second is the nature of the komatiites themselves. The lava
flows that host the ore deposits of the Kambalda dome are unusually thick (up to
100 m) and they consist mainly of cumulates of Fo-rich olivine. These
characteristics correspond to those of rocks precipitated from a relatively primitive
komatiite liquid, one that that was particularly hot, particularly fluid and particu-
larly capable of assimilating its wall rocks. The magma also contains a full
complement of Ni and PGE, metals that are removed during the fractional crystal-
lization that has affected the more evolved komatiitic magmas such as those that
erupted in the other areas, including the Abitibi belt in Canada.
Box 3.3: Photos of the Norilsk-Talnakh Region
The town of Norilsk is situated at 56 N, in the far north of Siberia, very close
to the Arctic circle. The deposits are fabulously rich, some comprising lenses