© 2004 ... All rights ... ... in 1991 >> ... division We will ... 1 the volcanic solid mass of Androy, it is covered with thorny bush and meadows. 2 the gneiss
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Tranomaro in 1991 >>
Geographical division
We will distinguish:
1 the volcanic solid mass of
Androy, it is covered with
thorny bush and meadows.
2 the gneissic zone of to
Mandrarean Androy, fields
plains and hills, rare zones
of savanna on of red ground At the time
calcareous carapace. of the great
Altitude varies there from dryness in
600 meters on the hills the south.
to 250 meters at the bottom.
3 the western slope of the high Anosyans
chains which tops are staged between
1500 and 2000 meters. It is a field of
meadows.
Geological divisions.
1 Crystalline schists.
Gneiss with diopside, syenitic eysies
gneisses, arteritic injections, gneiss at
cordierite, etc.
2 Old eruptive rocks.
Pegmatites, Dissogénites, Esirians
granites , charnockites, kalambatreans
granites, late granites .
3 Recent eruptive rocks.
(Volcanic solid mass of Androy)
a) A the base, a thick basaltic
subhorizontale series .
b) Basaltic dykes. On the road to Andranondambo
c) A thick higher subhorizontale rhyolitic series.
d) Rhyolitic dykes .
4 Recent formations.
If russet-red sands are excluded, the recent
formations have only a very weak development.
It is necessary to quote the alluvial plains of
Androtsy, Esira, Sangoria and Pisopiso.
A notable calcareous carapace covers most of the area.
Metamorphized dolomitic limestone.
Near Andranondambo
The anosyans granites are regarded as synorogenes, eocambrians
formed in the androyans series to which an age higher than 2400 MY
is allotted.
The esirians granites present very variable crushings of intensity which
often give them a gneissic facies .
There is sometimes passage to orthogneisses. General foliation is sub meridian.
The occurrences of the Andranondambo area were industrially exploited since 1993 and have been
almost abandoned few years later. Actually, it is very difficult to exploit sapphire direct in
mother rock, because corundum is not concentrated enough. Furthermore, the hardness of the
rock makes its exploitation very expensive.
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