Deposit Types & Mineralization
Deposit Types
Quartz veins in the Andramasina region consist of linear and lenticular systems containing
mesothermal mineralization over-printed by intense thermal metamorphism. Veins are similar
to gold systems found worldwide but the high metamorphic grade, comparable to that of the
Homestake mine in South Dakota, is a distinguishing feature.
Geological conditions at the Kolar Mine in Karnataka State, India closely resemble
those seen in Precambrian rocks in the Andramasina region. Gold at the Kolar mine is
associated with persistent, tabular gold-quartz veins that form ore-shoots at the
intersections of cross-cutting structures. The Kolar Mine was about 300km off the east
coast of Madagascar before the Indian land mass split from Madagascar.
Proximity to the Angavo Tectonic Belt places the B7 Project on the flank of a major
tectonic suture where faulting controls gold mineralization. Gold deposits would generally
form where the combination of fault structures and favorable host lithology focus
mineralizing fluids along fracture systems and dilation zones.
Mineralization
Gold is found in stream placers and associated eluvial accumulations in saprolite throughout
a region extending northward from the headwaters of the Mania River to beyond the Onive River.
Placer alluvial and eluvial deposits were worked from about 1885 to 1950 by several companies
and entrepreneurs. The extent of workings suggests that a large but unrecorded amount of
gold was recovered.
Visual evidence, supported by government reports, indicates that most operations focused
on readily treatable alluvial deposit. Mines often worked the banks of small to medium sized
streams and appear to have also recovered mineralization from faults that control drainage
patterns. There are no records showing detail production from individual properties, and it
is not possible to determine how much historical production came from ground presently held
by PAMM.
The three abandoned placer sites examined by Christopher exposed zones of quartz
stringers and veinlets in saprolite. The sites were leached of sulphides and the potential
in underlying bedrock must be inferred.
Quartz stringers in a series of parallel shears exposed in active workings at Site #5
are intensely weathered and erratically mineralized. Gold recovered from manganiferous pockets
being mined by informal miners has been remobilized but should reflect primary mineralization
in underlying veins and stringers.
Boulanger describes Site #4 as an exposed series of quartz veins in limonite-rich
lateritized pegmatite and stated that the material yields significant gold. This showing was
a 'recent find' at the time of Boulanger's visit and no record of the production or development
has survived.
Gold is associated with quartz veins and stringers. However, vein selvages composed of
high-grade metamorphic minerals are often weakly mineralized with gold though there is no
suggestion of hydrothermal alteration. Gold appears to have been an original constituent of
the pre-metamorphosed strata and Lacroix, referring to gold bearing gneissic rocks at Sahofa,
stated "… gold is found as if it were a primary rock constituent no different from any
other mineral".
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