519318319-BAUXITE-DEPOSITS PRESENTATION cours

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: Trihydrate or gibbsitic bauxite: consisting chiefly of gibbsite Mixed bauxite: typically consisting of significant proportions of both gibbsite and boehmite . Monohydrate bauxite: consisting mainly of boehmite or diaspore

7. According to their geological formation 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. 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 . 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 : Suriname type: a pseudonym for trihydrate or gibbsitic bauxite European type: composed mainly of boehmite 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: A re 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.

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

15. TYPICAL ORE PICTURES FROM MAJOR COUNTRIES INDONESIA BAUXITE ORE

16. 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.

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

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

19. Bauxite section on kaolinitic sandstone

20. Birsok Bauxite Project, Cameroon, AFRICA EXISTING MINES

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

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

23. 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%.

24. SOURCES www.geologyforinvestors.com www.thebauxiteindex.com www.sciencedirect.com www.geology.com