cours sur les gisements de bauxite

1. BAUXITE
DEPOSITS
PREPARED BY:
Judie Anne O. Garcia
Santiago B. Agripa Jr.

2. BAUXITE
 Bauxite is a naturally occurring, heterogeneous
material composed primarily of one or more
aluminum hydroxide minerals, plus various
mixtures of silica, iron oxide, titania,
aluminosilicate, and other impurities in minor or
trace amounts.

3. INTRODUCTION
 Continents, which possess much wider areas than limited
marine basins, accumulate most sediment, but retain
scarce geological records.
 Bauxite, as the primary source of aluminum, represents a
typical accumulation of weathered continental crust and
has been one of the most important proxies for the
reconstruction of paleoclimate.

4. MINERALOGY
The main alumina containing minerals that occur in
bauxites are:
Gibbsite
Boehmite
Diaspore
Other gangue or impurity minerals typically found in
bauxites include:
Clays, typically kaolinite
Quartz
Iron oxide and iron hydroxy-oxide (Hematite and Goethite)
Titanium dioxide in the form of anatase or rutile.
The mineralogy is very important as it dictates the refining
conditions that must be used and has a large bearing on
the economics of processing a particular bauxite.

5. SEM images of typical minerals in bauxite: (a) gibbsite as the major mineral;
(b) kaolinite as the primary subordinate mineral, (c) covelite, (d) galena,
(e) pyrite, (f) zircon, (g) calcium plagioclase, (h) orthoclase, and (i) albite
as minor minerals

6. TYPES OF BAUXITES
Bauxite deposits are commonly referred to by a number of
different terminologies relating to either their mineralogy or
geological formation.
Alternately they may be described by likening them to other
well-known deposits elsewhere around the globe.
According the to their mineralogy:
1. Trihydrate or gibbsitic bauxite: consisting chiefly of
gibbsite
2. Mixed bauxite: typically consisting of significant
proportions of both gibbsite and boehmite.
3. Monohydrate bauxite: consisting mainly of
boehmite or diaspore

7. According to their geological formation
1. Lateritic: formed in-situ from weathering of
aluminous parent rocks in tropical and temperature
regions. Consisting mostly of gibbsite or a mixed gibbsite
and boehmite content.
2. Karst: partially transformed or transformed bauxite
materials washed and accumulated in eroded limestone
cavities where further transformation can occur.
Commercially significant karst bauxites occur in Europe,
the Middle East, China and Jamaica.
3. Sedimentary: are primarily formed by the accumulation
of lateritic bauxite deposits during mechanical
transportation of surficial flows.

8. Figure 1. Distribution of the superlarge bauxite deposits in
the world (After Bogatyrev et al., 2009).

9. According to other well-known deposits:
1. Suriname type: a pseudonym for trihydrate or
gibbsitic bauxite
2. European type: composed mainly of boehmite
3. Jamaica type: applied to very fine grained
high-iron gibbsitic bauxite containing minor
quantities of boehmite.

10. BAUXITE FORMATION
Bauxite deposits are formed chiefly by weathering of
aluminous rock; some have been transported to their
present locations, but most are residual accumulations from
which most other constituents of the parent rock, other than
alumina, have been leached.
Bauxite deposits occur in rocks ranging in age from
Precambrian to Holocene.
Gibbsitic bauxite: Most deposits of this type are in the
tropics and a few occur in the temperate belts, but the
climate was probably tropical or subtropical at the time
these formed. Nearly all are of Cenozoic age.

11. Boehmitic bauxite: Deposits of this type occur chiefly in
southern Europe, the USSR and Turkey. Most are
associated with carbonate rocks of Jurassic and
Cretaceous age, but a few are of Paleozoic age. Today
most are north of the tropics, however they could have
formed under tropical conditions.
Mixed bauxites: Are associated with both the gibbsite
and boehmite types. However, they tend to be more
abundant in deposits of Paleozoic and Mesozoic ages
than in younger rocks

12. The composition of bauxite samples from a range of deposits are
tabulated below.
BAUXITE CHEMICAL
COMPOSITION
Although bauxite comprises a mixture of minerals, the composition
is normally reported as the elemental analysis, expressed as metal
oxides. This analysis is usually determined by X-Ray Fluorescence
Spectrometry (XRF), though classical methods are also available.

13. BAUXITE OCCURENCES
Based on a broad geological assessment the
potential for bauxite mineralization is quite common
across the globe. Typically deposits in the tropics
and southern temperate zones are lateritic
deposits, while those in the northern temperate
zones and beyond are monohydrate deposits,
often associated with karst systems. World Bauxite –
Key Countries Despite wide potential, most of the
world's known bauxite reserves and resources are
concentrated in only 12 countries.

15. TYPICAL ORE PICTURES FROM MAJOR
COUNTRIES
WEIPA BAUXITE
CHINESE BAUXITE

16. TYPICAL ORE PICTURES FROM MAJOR
COUNTRIES
INDONESIA BAUXITE ORE

17. The lateritic bauxite profile
A “typical” profile is really a
misnomer as there are so many
variations. The example shown
in Figure 2 is a lateritic bauxite
profile exposed in the western
coastal cliffs of Cape York
Peninsula, in northern Australia.
Elements of this “typical” profile
are seen in most lateritic
bauxite profiles in other parts of
the world.

18. Profile chart of sedimentary bauxite in Henan, China
Sedimentary bauxites

19. Schematic
stratigraphic section
of the bauxitic
horizon in the Zagros
Mountain Belt
Karst bauxites

20. Bauxite section on kaolinitic sandstone

21. Birsok Bauxite Project, Cameroon, AFRICA
EXISTING MINES

22. Bauxite in East India: The Khondalite Mountains of
Khondistan
EXISTING MINES

23. Bauxite deposits Brgy. Canliges, Paranas, Samar
EXISTING MINES

24. CONCLUSIVE STATEMENT
Bauxite, an aluminum ore, is the world's main
source of aluminum. It is widely distributed around the
world, particularly in tropical areas. It is formed by
weathering of aluminium rich rocks (clays, laterites,
etc.) and the major deposits are therefore generally
close to the surface. It consists mostly of the minerals
gibbsite, boehmite and diaspore. Bauxite takes many
physical forms including small red peas, red-yellow
“soils”, and large, pale, hard stones. The main criterion
for identification of an ore body as bauxite is that it
should contain aluminium in the form of aluminium
hydroxides, the minimum content being about 30%.

25. SOURCES
 www.geologyforinvestors.com
 www.thebauxiteindex.com
 www.sciencedirect.com
 www.geology.com