Geology
Mbomo area belongs to the « Massif granitoïde du Haut-Zaïre », which is composed of high grade
migmatitic series, typical amoeboïdal granite patches and epimetamorphic greenstone belts
The “Tele Belt”, covered by the M'Bomo permits, belongs to a NNW rosary of similar “greenstone”
terranes running from Tanzania to Central Africa Republic .
The epimetamorphic greenstones extend over several cycles, some older than 2.9 b.y. And some as
late as Lindian sediments rest on the north and south flanks of the « Massif ». Southwards the
sediments dip into the large Congo Basin.2.0 b.y.
Formations outcropping in the permit are shown in the picture extracted from the Zobia 2/25
reconnaissance map at scale 1/200,000 (BRGM 1975).
Two brown lithologies, in the SW and SE corners of the leases, belong to the Lindian cover
formations, dating from Upper Precambrian and made of arkoses, sandstones and claystones
becoming carbonaceous at the bottom of the sequence (L2, L4 and L5).
The Lindian cover rests over the granite/greenstone complex (massif) . The red and purple
features granite (G) and gneisses( ɣ ) ; the contorted orange features the lower Kibalian (KI1) and
the two brown tints the upper Kibalian( KI2), darker brown features the banded ironstones (BIF).
The typical circumscribed granites crop out inside the belt, these late, tarditectonic, granites with
two micas , are shown in red.
Recent residual sandy formations rest on lower grounds (ST).
Not drawn on this map is a ENE shear zone following the
southern edge of the BIF
click to enlarge
The banded iron formations (BIF) are sedimentary rocks with a high iron content (at least 15%).
They represent 90% of the iron ore exploited in the world. The rock is called itabirite.
The particularity of the Banalia deposit is its extremely high iron content (more than 63%)
whereas the usual content of itabirites is often less than 45% Fe.
The iron enrichment of the ore comes from an intense leaching that has taken the sterile
gangue, the ore is then porous, but very rich.
This leaching comes from its proximity to an imposing massive granite intrusive.
It
is
responsible
for
the
recovery
of
the
sedimentary
layers
which
are
found
in
a
subvertical
position.
The
last
phase
of
consolidation
of
this
granite
is
the
hydrothermal
phase
characterized
by
an
increase
in
pressure.
The
high
pressure
and
high
temperature
hyrothermal
liquids
escape
from
the
granite
massif
by
crossing
the
rocks
that
adjoin
this
granite.
The
sedimentary
layers
being
straightened,
these
hydrothermal
flows
must
cross
them,
which
explains
the
effectiveness
of
this
leaching.
This
hydrothermal
phase
is
also
responsible
for
the
gold
mineralization
caused
by
hydrothermal
flows.
It
is
therefore
logical
to
preferentially
look
for
this
gold
mineralization
in
the
fault
zones that were transport vectors of these flows.