Mineral Resources Potential - Geothermal Resources

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52 Mineral Resources Potential of Ethiopia
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Volcdc-associated massive sulphide (VMS) deposits qdi .
throughout the-world and throughout the geological time col4 in:-"r
nic domain that has submarine volcanic ~ cks
uent. VMS deposits we major sources of Cu
significant quantities of Au, Ag, Pb, Se, Cd, Bi,
Sn qq We11 as minor amounts of other metals. As a group, VMS
dap6% consist of massive accumulations of sulphide minerals
(&o* than 60% sulphide minhs) which occur in lens-like or
tai6ulm bodies parallel to the vofcanic stratigraphy or bedding.
@ey are usually underlain by a footwall stockwork of vein and
s&r sulphide mineralization and hydrothermal aheration. They
my occur in any rock type, but the predominant hosts are volcanic
rocks and fme-med, clay-rich sediments. The deposits consist of
ubiquitous iron sulphide (pyrite, pyrrhotite) with chalmpyrite,
sphalerite, and galena as the principal economic minerals. Barite
and cherty silica are common gangue accessory minerals.
As to the origin, at divergent boundaries, water from the
ocean floor flows though fractures in the oceanic crust. The
waters are heated by the nearby magma source, producing a
seawater convection cell which reacts with neighboring rocks to
leach out metals. These dissolved metals are transported to the
ocean floor where they mix with cold bottom waters. The sudden
decrease in temperature causes the minerals to precipitate from
solution and they are incorporated into sediments deposited ahng
the ocean ridge system. In Ethiopia, this type of mineralization
warrants further investigations.
III Epithermal gold deposit
Epithermal precious metal mineralization is commonly associated
with Cenozoic or Quaternary geothermal systems in areas of calc-
alkaline volcanism. Much of this voIcanism typically occurs above
subduction zones along continental margins and in Island Arcs as
well as along spreading Mid-Ocean Ridges. Less commonly,