Mineral Resources Potential - Geothermal Resources

Metallic Minerals 97
occurrences have also been reported in Sidamo (e,g, Kilta, 2 Mt at
1.5 % Ni, Big Dubicha, Small Dubicha, Fulanto, Monissa, Burjiji
wnd Lolotu).
All these occurrences are related to ultrabasic rmks,
metamorphosed to serpentinites, almost entirely altered. These
serpentinites formed of lizardite and antigorite, with some
chrysotile stringers, are all enclosed in a "Mo" of talc and bands
of talc schists, tremolite schists, chlorite schists and actinolite
schists, ~hl: nickel mineralization, of residual type, is hosted in
Iaterites capping the serpentinite budies and is apparently mainly
held in a secondary mineral of the garnierite group (pimelite). The
average metal contents for unaltered ultrabasic source rocks are
uneconomical: nickel (0.1-0.3%), cobalt (0.02%), copper (0.998%).
Impregnations of q d t e with pyrite and cobalt with manganese
coating have been reported in Kunni valley. Other cobalt mineral
occurrences have also been reported in the area of Nejo, near Tulu
Bolio and Tula Gotel (Wollega).
The origin of the deposits seems to be similar to that of
silicate deposits in other parts of the world. Nickel concentrates in
the crystalline lattice of ferrornagnesian silicate rock forming
minerals such as olivine and pyroxene during the early cooling and
crystallization history of the magma, in the absence of sulphur.
Fractional crystallization and cumulative process such as gravityinduced
settling of these early crystals on the bottom of the magma
chamber can account for the high nickel and chrome contents in
mnulative ultramafics. Secondary adchment is attained during
iqmtinization and weathering. The following are descriptions of
m e of the beqer known deposits some of which have received
nore attentioh in recent years.