Geology Reference
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a
b
Generalized laterite profile
Profile of Ni laterite
Depth (m)
Vermiform and
pisolitic duricrust
Iron crust
Plasmic horizon
Red laterite
soil
Fe laterite - Lateritic gravel
Residuum - Lateritic duricrust
0
Mottled zone
(kaoline matrix)
10
Plasmic zone, mainly
kaoline and goethite
(Primary fabric
destroyed)
Ferruginous saprolite
Yellow-red laterite
Mg-discont.
20
garnierite
Earthy ore
Soft saprolite
Saprolite
>20% weatherable
minerals altered
(Primary fabic
preserved)
30
Saprolite
Ore with boulders
Coarse saprolite
Rocky ore
40
Saprock <20% weatherable
minerals altered
Harzburgite
Unaltered bedrock
50
c
d
Sample of bauxite
Variations in element abundances (%)
0
FeO
-10
-20
-30
-40
-50
0 0 0 0 0 0 0
Fig. 5.9 Profiles through lateritic profiles (a) bauxite (From Butt et al. 2000 ); (b) nickel laterite
(From Freyssinet et al. 2005 ); (c) chemical profile through the laterite, plotted from data of
Freyssinet et al. ( 2005 ); photo of pisolitic bauxite
composed entirely of clays, Al and Fe oxides and hydroxides, and minor amounts of
residual quartz. The original texture is completely lost and the rock has a pisolitic or
nodular structure that results from repeated episodes of dissolution and accretion.
The uppermost pedolith consists of unconsolidated or cemented Fe-oxide-rich
gravels and duricrust.
Most laterites in equatorial regions have the iron contents which makes them
unsuitable for the recovery of aluminium. The purest bauxites form through a
combination of processes; (1) the presence of Al-rich (and Fe-poor) parent rocks
such as alkali granite, syenite, tuff or clay-rich sediment and their metamorphosed
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