Mineralogy, spread, and use of bauxites

Article abstract of DOI:10.1134/S107036321106034X

Rock-forming high-aluminous, associated, and accessory (the most common) bauxite minerals were described in detail, along with their corresponding diagnostic variables, chemical composition, and spread. A geological-economic overview of the world bauxite ore deposits and reserves was presented, and the specific features of Russian bauxite deposits and practical value of bauxites were discussed. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S107036321106034X

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 6, pp. 1277–1287. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.V. Belyaev, 2010, published in Rossiiskii Khimicheskii Zhurnal, 2010, Vol. 54, No. 2, pp. 29–37.
Mineralogy, Spread, and Use of Bauxites
V. V. Belyaev†
Institute of Geology, Komi Scientific Center, Ural Branch, Russian Academy of Sciences,
ul. Pervomaiskaya 54, Syktyvkar, Komi Republic, 167982 Russia
e-mail: institute@geo.komi.sc.ru
Received January 1, 2010
Abstract—Rock-forming high-aluminous, associated, and accessory (the most common) bauxite minerals were
described in detail, along with their corresponding diagnostic variables, chemical composition, and spread. A
geological-economic overview of the world bauxite ore deposits and reserves was presented, and the specific
features of Russian bauxite deposits and practical value of bauxites were discussed.
DOI: 10.1134/S107036321106034X
INTRODUCTION
composition Al
2
O
3
·2H O, although even in the
2
beginning of the XX century it was found that it is
comprised by several minerals and cannot be for-
mulated as an individual compound. Nevertheless,
even such a fundamental work as “The Encyclopedia
of Mineralogy” edited by K. Frye and published in the
US in 1981 [1] still attributes to bauxite the above-
mentioned composition.
Bauxite is a product of intense chemical weathering
of aluminosilicate rocks. It consists predominantly of
aluminum hydroxides and is the basic or even the
unique (in foreign countries) ore from which metallic
aluminum can be produced. Bauxites virtually
invariably contain certain amounts of iron oxides and
hydroxides, clay minerals, and other impurities; there
are also titanium and a number of valuable less-
common elements in bauxites. First discovered in 1820
by Pierre Berthier in the Fouta-Jallon region in Africa,
this rock had the following composition, wt %: 40
Al O , 33.6 Fe O , 2.0 SiO , and 24.4 H O. Berthier
At the same time, the very concept of bauxite is still
ambiguously interpreted on an international scale. The
aluminous rocks classed with bauxites strongly differ
in the composition of substances and are difficult to
compare. In terms of the content of useful, ballast, and
harmful components not all of these rocks satisfy the
requirements posed by aluminum industry, as well as
by some bauxite-consuming industries releasing
nonmetallurgical products. This necessitated classifica-
tion of bauxites by types, brands, and grades.
However, neither of the bauxite classifications avail-
able today (over ten in number) was universally re-
cognized, because they all are underlain by differently
interpreted criteria and characteristics.
2
3
2
3
2
2
believed that it does not occur elsewhere in the world,
but only after one year a rock even richer in alumina
was found in southern France, in the vicinity of the
village of Le Baux; it contained, %: 52 Al O , 27.6
2
3
Fe O , and 20.4 H O. Berthier took this rock to be a
2
3
2
mineral, with iron oxides being mechanical impurities,
and derived a chemical formula Al O ·2H O for the
2
3
2
compound that was though to be a mineral, but did not
provide it with a name. Only after half a century A.
Dufferenoy gave to this hypothetic mineral the name
of bauxite after the place of its occurrence near Le
Baux. Subsequently, this name gained wide acceptance
and is still used nowadays, though in respect to high-
alumina rocks rather than to a mineral.
The first classification proposed by J. Lapparent as
early as 1930 was based on the Al O and SiO content
2
3
2
and their weight ratio Al O :SiO , the so-called silica
2
3
2
(alumina) modulus, which were suggested as the main
criteria to be used for attribution of aluminous rocks to
bauxite. In this classification, bauxites were treated as
rocks containing >40% Al O and < 30% Fe O , the
However, bauxite has long been treated by many
foreign researchers as an individual mineral with the
2
3
2
3
modulus being over unity. Proceeding from this
modulus value, Lapparent distinguished among high-
†
Deceased.
1
277

1
278
BELYAEV
aluminous (>20), aluminous (10–20), siliceous (4–10),
and high-siliceous (1–4) bauxites, and based on the
iron content, high-iron (>25% Fe O ), medium-iron
siderite, calcite, occasionally corundum, magnetite, and
some other more rare minerals.
2
3
Aluminium Hydroxide Minerals
(
10–25% Fe O ), and low-iron (<10% Fe O ) bauxites.
2
3
2
3
Based on the dominating mineral form of occurrence
of aluminum, Lapparent recognized the gibbsite,
boehmite, diaspore, and kaolinite types of bauxites.
Aluminum hydroxides, similarly to iron hyd-
roxides, were formerly thought of as crystal hydrates
until it was found more recently that hydrogen and
oxygen occur in them as hydroxy ions (OH) and
represent a structural constituent. Below, this type of
minerals will be represented by two formulas, a
crystal-chemical and a crystal-hydrate one.
The Lapparent’s chemical classification, though in
a slightly modified form, is still used in some countries
for typization of bauxites: Aluminous rocks charac-
terized by low silica moduli (<2) are referred to as
allite, bauxite clay, or aluminous-clay rock, rather than
as bauxite. At the same time, different experts drew
different lines between bauxites and similar rocks. For
example, V.T. Allen [2] attributed to bauxite clays
even rocks containing 60–73% Al O , which clearly
Aluminum Trihydroxides
The major aluminum trihydroxide mineral in
bauxites is gibbsite, and the minor ones, bayerite,
nordstrandite and tučanite which are found oc-
casionally at the level of impurities.
2
3
fell under the category of bauxites. As to the former
USSR and Russia, GOST (State Standard) 972-74
treats as bauxites those aluminous rocks that contain
Gibbsite Al(OH) , or Al O ·3H O, aluminum hyd-
3
2
3
2
roxide mineral that is most widespread in the Mesozoic
and Cenozoic bauxites, has the following chemical
composition, %: 65.4 Al O and 34.6 H O. Gibbsite
over 37% Al O and have a silicon modulus of no less
2
3
than two.
2
3
2
was first discovered as an irregularly shaped
cryptocrystalline mass. Its crystalline varieties were
detected by I.R. Lisenko near the town of Zlatoust in
South Urals and in 1839 were submitted for examina-
tion by Gustav Rose who attributed them to hyd-
rargillite. Similar crystals were studied and identified
as gibbsite by P.I. Evreinov in 1843. In the years that
followed these two terms were used interchangeably
until the Third Session of the International Minera-
logical Association (1962) put an end to this confusing
duality and suggested that the mineral of interest be
further termed gibbsite.
The mineralogical classification suggested by
Lapparent disregards many of mixed-composition
bauxites. A much fuller classification of bauxites was
proposed in the former USSR by E.A. Rozhkova and
M.V. Solov’eva from the All-Union Institute of
Mineral Raw Materials. Depending on the forms of
occurrence of aluminum hydroxides, bauxites in this
classification were subdivided into three large groups:
monohydrate, trihydrate, and mono/trihydrate bauxites.
This classification covers virtually all the mineral
types of bauxites known in nature, as identified from
their main aluminous and aluminiferous minerals.
Main Bauxite-Forming Minerals
In bauxites, crystalline gibbsite occurs as hexagonal
tables, scaly masses, and less commonly as columnar
aggregates. As regards bauxites from South-Timan
deposit, it was found [3] that they are fairly frequently
represented by simple and polysynthetic twins and
occasionally by drusy aggregates (Fig. 1). Coarse-
grained gibbsite often occurs as a newly formed,
secondary mineral which lines the walls of cavities,
often fills entirely small pores and fractures, substitutes
quartz and other minerals, and can be easily identified
when examined under a microscope in thin sections.
Fine-grained, cryptocrystalline gibbsite in bauxites is
closely associated with other minerals and typically
can be reliably diagnosed with the use of thermo-
analytical and X-ray methods only. The DTA curve of
gibbsite contains an endothermic peak at 325–350°C,
which is associated with its dehydration, as clearly
All the mineral constituents of bauxites, with rare
exception, form very small crystals, whose analysis is
complicated by their being intimately intergrown with
one another. Their diagnostics requires the use of
special analytical techniques: X-ray phase analysis,
DTA, IR spectroscopy, electron microscopy, etc.
The main bauxite-forming minerals are aluminum
hydroxides gibbsite, boehmite, and diaspore associated
in bauxites with hematite, goethite, and less frequently
with hydrogoethite, as well as with clay minerals,
predominantly kaolinite, occasionally chamosite, and
rarely halloysite. Virtually always bauxites contain
titanium minerals rutile, anatase, ilmenite and, in some
cases (most often in sedimentary bauxites), newly
formed iron sulfides pyrite, marcasite, in places
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MINERALOGY, SPREAD, AND USE OF BAUXITES
1279
Fig. 2. Finely dispersed boehmite crystals (black) as
Fig. 1. Gibbsite crystals, intergrowths, and druses as
viewed under an electron microscope. Hollow forms
correspond to kaolinite; selective dissolution method;
×20000 magnification.
viewed under an electron microscope. Pseudoreplicas;
×
25000 magnification.
seen from the corresponding weight loss step in the
thermogravimetric curves as well. Gibbsite, in par-
ticular when mixed with other minerals, can be reliably
identified by X-ray methods, based on the charac-
teristic reflections: 4.85, 4.37, and 4.31 Å.
those from the deposits in Tikhvin, North-Onega, and
partly South-Timan (Kedva deposit) bauxite-bearing
regions of Russia.
Bayerite α-Al(OH) , or α-Al O ·3H O, was thought
3
2
3
2
of as an exclusively artificial mineral until 1950.
Native bayerite was found more recently in bauxite
deposits of Hungary, Montenegro, Greece, and
Ukraine. Though similar in the chemical composition
with gibbsite, bayerite is distinguished by lower
refractive index and birefringence, and also in the X-
ray diffraction pattern. Bayerite is represented by small
Among bauxites composed by gibbsite, the most
abundant species are those of eluvial and sedimentary
types, associated with the Mesozoic-Cenozoic crusts of
weathering and lateritic covers of the tropical belt.
Gibbsite bauxites are widely spread in Australia,
Brazil, Ghana, Guinea, India, and Venezuela, as well
as in the US (Arkansas), Indonesia, Oceania, and
Kazakhstan. They were also found in Norway,
Malaysia, Colombia, and China (Chao’an and Hainan
counties). In Russia, bauxites of gibbsite type occur in
Central and West Siberia, Middle Urals, East
Transurals, and South Timan (Upper-Ukhta deposit).
Gibbsite also has a widespread occurrence in gibbsite-
boehmite bimineral bauxites typical for a number of
Early Carboniferous-age sedimentary rocks, including
(
<1 mm) acicular, columnar, lamellar, trapezoidal, or
bladed crystals. Relatively large (up to 0.1 mm)
bayerite crystals were detected by D.P. Khorosheva [4]
in bauxite deposits of the Middle-Dnieper Region.
When heated, bayerite undergoes dehydration at
lower temperatures compared to gibbsite. This is a
two-stage process, as clearly seen from the endo-
thermic peaks in the thermograms recorded at
temperatures close to 215 and 270°C. Diagnostics of
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1
280
BELYAEV
casionally with chamosite. Boehmite typically occurs
as very small lenticular or rhomb-shaped (Fig. 2),
sometimes acicular, hexagonal crystals which are often
discernible under an electron microscope only. By
contrast to gibbsite, the secondary, newly formed
boehmite in bauxites is not widespread; it was detected
in few deposits solely. The Belgorod Ore Region
bauxites have the walls of small voids and micro-
fractures encrusted by coarser newly formed boehmite
crystals [9].
Boehmite is an ore-forming mineral of bauxites of
different ages, from Devonian to Paleogene. Boehmite
bauxite deposits, of predominantly Jurassic-Cretaceous
age, occur in some European countries: Austria,
Hungary, Greece, Italy, and France. Older bauxites of
the boehmite type were revealed in Afghanistan (pre-
Jurassic) and Turkey (Late Permian), as well as in
Belgorod and South-Timan bauxite-bearing regions
1
μm
Fig. 3. Acircular diaspore crystals in Middle-Timan bauxites.
Scanning electron microscopy.
bayerite in some cases requires an additional IR-spec-
troscopic examination. Bayerite in bauxites is often
intergrown with gibbsite.
(
Early Carboniferous) and in Middle Timan (Devo-
nian). Boehmite is also widely spread in bimineral
bauxites of the gibbsite-boehmite and boehmite-
diaspore types. The former constitutes several
European deposits, both foreign (Hungary, Mon-
tenegro) and Russian (Tikhvin, North Onega, partly
South Timan); some of the Australian and Brazilian
deposits are represented by gibbsite-boehmite bauxites.
As to the latter, they are known to occur in Greece,
former Yugoslavia, China, India, Vietnam, Pakistan,
and Central Asian region. In Russia, this type of
bauxites is most typical for North-Urals bauxite-
bearing region deposits [16] and is also found in East
Sayan (Bokson deposit). Boehmite occurs as impurity
in bauxites of many countries of the world.
Nordstrandite Al(OH) ,or Al O ·3H O, was first
3
2
3
2
detected in the natural form in association with
diaspore in West Sarawak red soils [5], and more
recently, in clays of Hungary jointly with bayerite and
gibbsite. Nordstrandite was revealed in bauxites from
Cretaceous-Paleogene deposits of Siberia [6, 7] and in
the Ozernoe deposit in Kazakhstan.
Nordstrandite is represented by colorless trans-
parent crystals up to 0.3 mm in size, which form
radiated and mosaic aggregates, polysynthetic twins. It
can be differentiated from gibbsite based on the
position of the endothermic peak in the thermogram
310°C) and the reflections (lines) at 4.780, 4.322,
.207, and 2.392 Å in the X-ray diffraction pattern.
(
4
Diaspore α-AlO(OH) with the chemical composi-
Tučanite 2Al (OH) ·H O has the following
tion, %, 85 Al
2
O
3
and 15 H O, occasionally contains
2
2
6
2
chemical composition of its air-dry species, %: 0.46
SiO , 52.94 Al O , and 46.30 H O. This mineral is still
Fe, Mn, and Cr as isomorphous impurities. Diaspore
occurs as tabular, lamellar, acircular [3], or (rarely)
prismatic columnar crystals (Fig. 3).
2
2
3
2
insufficiently studied. It should be noted that bayerite,
nordstrandite, and tučanite have no commercial value.
Diaspore in bauxites can be fairly easily identified
when viewed under a microscope in thin sections and
in immersion preparations from high refractive index
and strong birefringence. Using thermal analysis
techniques diaspore can be reliably diagnosed only in
the absence of boehmite and kaolinite, from the
endothermic peak in the DTA curve at 560–600°C and
the associated weight loss in the gravimetric curve due
to dehydration. In cryptocrystalline bauxites, fine-
grained diaspore can be unambiguously identified from
the characteristic reflections at 3.98; 2.553; 2.315; and
Aluminum Monohydroxides
Aluminum monohydroxide minerals in bauxites are
represented by boehmite and diaspore.
Boehmite γ-AlO(OH), or γ-Al O ·H O, with the
2
3
2
chemical composition, %, 85 Al O and 15 H O, is
2
3
2
contained in bauxites virtually always in finely- and
cryptocrystalline form. It is closely aggregated with
iron oxide and hydroxide minerals, as well as with
kaolinite, often with gibbsite and diaspore, oc-
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MINERALOGY, SPREAD, AND USE OF BAUXITES
.076 Å in the X-ray diffraction patterns [11].
1281
2
Diaspore is known to be an ore-forming mineral for
Paleozoic and (rarely) Mesozoic, bauxites; in the latter
case these are typically metamorphosed or hydro-
thermally altered rocks.
Diaspore in bauxites most often occurs in
paragenesis with other aluminous minerals, typically
with boehmite and rarely with corundum and gibbsite.
Monodiaspore bauxites are common in the US
(
Massachusetts), Romania, Greece, Turkey, Slovenia,
China (Xiuwen deposit), and India (Jammu and
Kashmir); they occur in Switzerland, Greenland, and
the Central Asian Republics of CIS as well.
In Russia, diaspores form (partly) North-Urals
bauxite deposits, as well as the Kukshik deposit in
South Urals, Obukhovo deposit on Salair, and Volo-
dinskoe deposit in Middle Timan [12]. Diaspore-type
bauxites were also revealed for Kizel area in North
Urals and for the Kara ore occurrences in the Polar
Urals and Pai-Khoi.
As regards anhydrous aluminum oxides, corundum
Al O occurs in bauxites from some deposits either in
2
3
the low- (microcorundum) or the high-temperature
(
macrocorundum) form. It is believed that the former
Fig. 4. Electron image of splinter-like goethite crystals.
resulted from dehydration of aluminum hydroxides
under surface conditions, and the latter, from hydro-
thermal alteration and metamorphism of bauxites.
Certain amounts of microcorundum were detected in
bauxites from Middle and North Urals, Pai-Khoi,
Middle Timan, Siberia, and Kazakhstan, as well as
from Romania, Greece, Turkey, the US (Arkansas).
Large, occasionally up to 45–50%, amounts of macro-
corundum associated with magnetite, spinel, diaspore,
chlorite, and mica occur in virtually all meta-
morphosed bauxites.
Electron transmission microscopy; suspension; ×18000
magnification.
color, respectively. It can be unambiguously identified
from X-ray reflections at 3.67, 2.69, and 2.51 Å.
Goethite α-FeООН, or α-Fe O ·H O, with the
2
3
2
chemical composition, %, 89.89 Fe O and 10.11 H O,
2
3
2
occurs as acicular, splinter-like columnar, and tabular
crystals. Bauxites contain predominantly finely dis-
persed goethite. It may form oolites and pisolites and,
occasionally, vein-like masses, splinter-like crystals,
though less commonly and in smaller amounts (Fig. 4).
It is not infrequent that red bauxites contain 30%
goethite. In mixtures with other minerals goethite can
be identified from the endothermic peak at 350–400°C
and from the weight loss due to dehydration in
thermograms and from the reflections at 4.18 and
2.69 Å in the X-ray diffraction patterns.
Iron Oxide and Hydroxide Minerals
The prevalent iron oxide and hydroxide minerals in
bauxites are hematite and goethite, whose total content
in red bauxite ores may reach 40–45%. Bauxites can
also contain magnetite, lepidocrocite, and hydro-
goethite, though much less frequently and in small
amounts.
Hematite α-Fe O occurs in red bauxites in amounts
Goethite may contain increased levels of aluminum
which isomorphically substitutes iron, in which case it
is termed aluminogoethite. The latter, along with
aluminohematite, was detected in Hungarian bauxites,
but it is not improbable that aluminum in it is a
mechanical impurity.
2
3
of 20–25%, on the average, as a typically finely-
divided impregnation; less frequently it is concentrated
in pisolites and oolites, microfractures. When viewed
in thin sections under a microscope and in reflected
light hematite has a blood-red and blue-shaded white
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BELYAEV
Hydrogoethite FeOOH·nH O, which is thought of
Thermograms of kaolinite contain a characteristic
endothermic peak at 580–620°C and a sharp exo-
thermic peak at 960–1000°C. In mixtures with other
minerals kaolinite can be reliably identified from
reflections at 7.15, 3.57 and 2.379 Å in the X-ray
diffraction patterns. Kaolinite-containing bauxites are
widespread in most of world’s deposits, which are
predominantly of sedimentary type.
2
as an independent mineral by some researchers, is
most likely essentially a kind of goethite with a high
(
up to 13%) content of water of hydration.
Lepidocrocite γ-FeOOH is a very rare mineral of
bauxites, polymorphous with goethite and isostructural
with boehmite, which in some cases occurs as an
earthy, more often as finely dispersed, mass. The
thermogram of lepidocrocite is distinguished from that
of goethite by a typical exothermic effect at 380–500°C.
Lepidocrocite can be identified more reliably from X-
ray reflections at 6.27, 3.29 and 2.473 Å.
Chamosite, iron hydroxyaluminosilicate comprised
of variable proportions of its chemical constituents,
can be approximately formulated as 3SiO ·Al O ·
2
2
3
4FeO·6(OH)·nH O [8] which formula does not
2
incorporate, however, Fe O and MgO. The chamosite
2
3
Though as negligible impurity, lepidocrocite occurs
in bauxites of France, as well as of Sokolovskoe
deposit of the Urals, Timsher deposit in South Timan,
and in some other deposits.
composition, %, is as follows: 18–33 SiO , 21–28
2
Al O , 3.2–12.3 Fe O , 19–37 FeO, 1–5 MgO, and 10–
2
3
2
3
1
1 H O. In bauxites, chamosite segregations can be
2
identified from their greenish-gray or greenish-black
color. Bauxites contain chamosite in the monoclinic
and rhombic modifications whose abundances and
chemical compositions govern the number, position,
and intensity of the reflections observed in the X-ray
diffraction patterns. The first basal interplanar spacing
for the both modifications varies within 7.04–7.11 Å,
the most typical value being 7.05 Å. Monoclinic
chamosite can be identified from the 2.40 Å reflection
which is not characteristic for the rhombic
modification, as well as from an endothermic peak at
~550°C and a not very prominent exothermic peak at
940–950°C in the thermograms.
Magnetite FeFe O , or Fe O , is abundant only in
2
4
3
4
metamorphosed and hydrothermally altered bauxites,
in which case iron often occurs in this mineral form
virtually entirely. The magnetite content in these
bauxites is 30–35% against several fractions of per
cent in original bauxites. Also, maghemite and titano-
magnetite occur in bauxites occasionally.
Regardless of the form of occurrence, iron oxide
and hydroxide minerals are treated as ballast for the
alumina refining process, which, even when in small
quantities, significantly deteriorates the quality of
diversified technical materials produced from bauxites.
Chamosite occurs as impurity in a number of
bauxite-ore deposits; it was found in bauxites of
France, Romania, and Northern Ireland and is
especially abundant in bauxites of the Belgorod region
of the Kursk Magnetic Anomaly (KMA), where it
occurs as a rock-forming mineral in many ore loci [9].
Chamosite is also abundant in the Middle-Timan
bauxite deposits, especially in the Vezhayu-Vorykvin
and Volodinskoe deposits, in which chamosite-
boehmite and chamosite-diaspore types of bauxites,
respectively, were identified [12]. Significant amounts
of kaolinite and chamosite strongly deteriorate the
quality of bauxite raw materials and limit their
commercial application.
Clay Minerals
The most abundant clay minerals in bauxites are
kaolinite and much less commonly occurring chamosite.
Kaolinite Al Si O (OH) , or Al O ·2SiO ·2H O,
4
4
10
8
2
3
2
2
with the chemical composition, %, 39.5 Al O , 46.5
2
3
SiO , and 14.0 H O, is contained in bauxites in
2
2
amounts broadly varying from 2 to 50%; it is usually
mixed with aluminum and iron hydroxide minerals.
Occasionally, kaolinite veins, stripes, and spots of a
more recent (epigenetic) origin may be found.
Restricted distribution in bauxites have relatively
coarse-crystalline occurrences ranging from pseudo-
hexagonal plates (Fig. 5) to vermiculite- and sheaf-like
aggregates and intergrowths segregating into indi-
vidual sheets. Finely dispersed kaolinite, when viewed
under an electron microscope, is represented by both
whole and chipped lamellar and thin platy crystals
ranging in size from 0.02 to 1.0 μm.
Bauxites from some deposits comprise other clay
minerals, specifically, dickite [13], nacrite, and
halloysite, though as minor impurities.
Titanium Minerals
Kaolinite can be unambiguously identified in
bauxites by thermal and X-ray diffraction analyses.
Titanium minerals in bauxites are represented
mostly by rutile and anatase and, to a lesser extent, by
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MINERALOGY, SPREAD, AND USE OF BAUXITES
1283
(
a)
(b)
(
c)
Fig. 5. Electron image of authigenic kaolinite with a chipped kaolinite impurity: (a) suspension in transmitted light, ×18000 magnifica-
tion, (b) pseudoreplica of a powder, ×20000 magnification; and (c) carbon replica of a cleaved surface, ×20000 magnification.
leucoxenized ilmenite; brookite and sphene are
observed occasionally. Leucoxene is abundant in bau-
xites; it was formerly thought of as an individual mine-
ral until it was established more recently that it is com-
prised of a mixture of rutile and quartz. The average
content of TiO in bauxites is close to 2.5%, but in
2
some deposits of Siberia (Yenisei Ridge) it reaches
9.5%, and Indian bauxites contain 17% TiO [5].
2
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BELYAEV
Rutile TiO is the most stable and widespread tita-
Carbonates
2
nium mineral occurring in bauxites, both in crypto-
crystalline and eucrystalline states. Rutile appears as
needle-like or prismatic crystals, often in the form of
geniculated twins, in a color ranging from yellow and
reddish-brown to almost black. Rutile may contain
iron, niobium, and tantalum impurities; it occurs in all
types of bauxites but mostly as part of leucoxene.
Siderite and calcite represent carbonates that are
most abundant in bauxites.
Siderite FeCO
, with a theoretical composition, %,
, occurs in bauxites as a
3
62.01 FeO and 37.99 CO
2
varigrained species and varisized crystals associated
with pores and fractures. Occasionally it forms spher-
ulites (Fig. 6), sometimes replaces oolites and pisolites,
and also may form continuous lenticular-layered masses.
Anatase TiO is a polymorph of rutile, which, being
2
one of leucoxene minerals, is also often present in
bauxites. Anatase also occurs separately in the form of
small bipyramidal, tabular, or prismatic crystals. Heat-
ing to 620°C causes the anatase–rutile conversion.
Siderite can be easily identified from thin-section
images, as well as from thermal, X-ray diffraction, and
chemical analyses data. Thermograms of siderite
contain an endothermic peak at 460–500°C and an
exothermic peak at 650–750°C, of which the former is
Ilmenite FeTiO typically occurs in bauxites as a
3
relict mineral which rarely preserves its original com-
position. It is usually leucoxenized, partially or
entirely, and undergoes a conversion to rutile and/or
anatase. Leucoxenized ilmenite contains iron that is
represented mostly or entirely by Fe O (hematite).
due to decomposition into FeO and CO , and the latter,
2
to oxidation of ferrous iron. Siderite diagnostics from
X-ray diffraction patterns is based on 2.790, 2.132 Å
reflections.
2
3
Siderite-containing bauxites have restricted dis-
tribution and occupy small areas in a few deposits.
They occur in Pennsylvania (US), as well as in
Krasnooktyabr’skoe and Kushmurunskoe deposits in
Kazakhstan and in a number of KMA and Urals
deposits. Siderite-bearing bauxites have local
distribution in South-Timan deposits.
In the bauxite-bearing weathering crust of
Verkhnyaya Shchugor deposit in Middle Timan,
I.V. Shvetsova [12] identified ilmenorutile leucoxene
with a commercial (up to 4%) content of niobium.
Sulfur-Containing Minerals
Sulfur-containing minerals are fairly common in
selected sedimentary bauxite deposits and are mainly
represented by iron disulfides: pyrite, marcasite, and
melnikovite. They occur primarily in white bauxites as
post-mineral new formations.
Calcite CaCO occurs in significant amounts as fine
3
impregnation scattered over the main ore mass, but is
mostly associated with pores and diversified small
fractures. All the above-mentioned methods are
suitable for unambiguous identification of calcite in
bauxites.
Pyrite FeS is contained in boehmite bauxites that
2
have a considerable spread in Belgorod, North-Onega,
and South-Timan deposits, as well as in North- and
South-Urals boehmite-diaspore deposits. The sulfur
content in some of the pyrite-bearing bauxite plots and
fields in these deposits exceeds that stipulated by
appropriate standards.
Calcite-containing bauxites have local distribution
in West Africa, North Kazakhstan, and Near-Angara
deposits, as well as in some fields of South-Timan and
North-Onega deposits. Bauxite ores rich in calcite are
typically discarded.
Marcasite FeS in bauxites occurs most frequently
2
Sulfides and carbonates contained in bauxites are
new formations. Also, bauxites contain a number of
other minerals, but only at the level of accessories that
do not significantly affect the crude ore quality.
as concretions, spherulites, and irregularly shaped
massive pyrite-marcasite segregations. Monomarcasite
concretions are mainly composed by druse inter-
growths. Highly characteristic for marcasite are
spherulites with a fine-grained core and a spherulitic
exterior. Also, spherulites may have pyrite in their
interior, and marcasite, in the exterior. Occasionally
the contractions have a polycentric-polyzonal structure
with a pyrite-marcasite composition. Rarely occurring
faced marcasite crystals have thick-tabular or prismatic
habit [3].
Spread, Production, and Applications of Bauxites
Published data concerning the spread and resources
of bauxites around the world are highly controversial.
Figure 7 shows how bauxite resources (in relative
terms) are broken down by continents. Different ex-
perts’ estimates of the global bauxite resources exhibit
two-threefold differences. Foreign authors typically
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MINERALOGY, SPREAD, AND USE OF BAUXITES
1285
Australia and Oceania
1.17%
1
Africa
America
29.21%
4
6.32%
Asia
1.27%
1
Europe
2
.03%
Fig. 6. Siderite spherulites. Thin section; ×20 magnification;
parallel nicols.
Fig. 7. Breakdown of bauxite resources by continents ac-
cording to [15].
take into account only already explored reserves of
high-grade bauxites, which leads to strongly under-
estimated bauxite resources availability.
increased 100 times over the period 1960–1980 and
continues to grow. Similar trends are also observed in
Guinea. By now, ca. 2 billion 750 million tons of
bauxites has been already extracted out of the ground,
with the world’s bauxite consumption rising by an
annual increase of 1.2–1.3 million tons.
Over 89% of total and ca. 86% of proven bauxite
reserves are concentrated in 11 countries only:
Australia, Brazil, Guinea, Jamaica, Venezuela, India,
Cameroon, Indonesia, Suriname, Mali, and Cote
d’Ivoire. The biggest deposits of bauxite ores exist in
Australia, Brazil, Guinea, and Jamaica.
As to Russia, it does not possess such large and
unique bauxite ore deposits as do Australia, Guinea,
and Brazil. Out of fifty bauxite deposits that were put
on Russia’s state balance sheet only one-fifth was or is
being developed. Virtually all commercially profitable
deposits are located in the European part of Russia and
in the Urals, in which area there exist seven bauxite-
ore regions [15]; among them, only three (North Urals,
Middle Timan, and North Onega) are involved in
commercial mining of bauxites. In the Asian part of
Russia, which is not involved in bauxite mining
activities as yet, bauxites are dispersed over small
deposits most of which are well off highways in hard
to develop areas.
The amount of bauxites extracted worldwide is
steadily growing, and ever widening range of countries
get involved in bauxite extraction. Before the First
World War, bauxites were extracted in five countries
solely: France, the US, Italy, India, and British Guiana,
which extracted a total of ~500 thousand tons of
bauxites. On the eve of the Second World War there
were already 12 countries involved in bauxite deposit
development with the total bauxite production of
2
1
1
.67 million tons, which level sharply increased to
2.5 million tons during the war period. In the years
955, 1960, 1970, 1980, 1990, and 2000 the amount of
Mining industry in Russia is currently unable to
satisfy the needs of Russian industry in domestic
bauxite ores of acceptable quality. The situation with
supply of bauxites to bauxite-consuming production
entities continues to deteriorate. This is due to a
dramatic decline in bauxite extraction at the North-
Urals deposit, which is of primary importance for
Russia, and to shutdown of bauxite production at the
South-Urals and Tikhvin deposits. The total amount of
bauxites extracted in Russia has declined by more than
bauxites extracted worldwide exceeded the prewar
levels by the factor of 8, 14, 34, 37, and 45,
respectively.
Currently, the major producers of bauxite ore raw
materials are Australia, Guinea, Brazil, and Jamaica,
which account for ca. 70% of the world’s total bauxite
extraction. The bauxite extraction industry in these
countries underwent very rapid development. For
example, in Australia the amount of extracted bauxites
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1
286
BELYAEV
3
5%, and the production of alumina intended for
of the above-mentioned high-technology products, in
particular of ceramic and composite materials intended
for special applications [18, 19]. The exploration,
research, and technology work dedicated to other
promising applications of low-iron bauxites is
currently under way both abroad and in Russia.
aluminum industry applications, by 30%. To satisfy its
needs Russia has to import ca. 5 million tons of
bauxites and up to 50% alumina from different
countries annually.
However, significant improvement of the situation
may be expected in the coming years through large-
scale development of Middle-Timan bauxite deposits
and construction, on their base, of an alumina refinery
in the Komi Republic. Upon completion of the second
stage of the entire complex the alumina production will
be brought to 1.4 million tons (with 7.535 million tons
of bauxites planned to be extracted in 2009 at the
currently operating mine, including 6.45 million tons
of marketable ore) [16, 17]. This will sharply reduce
Russia’s dependence on imports of these raw materials.
According to various estimates, most (80–85%) of
bauxites mined worldwide is used to produce >95% of
the world’s primary aluminum, and from 10 to 20%
goes for nonmetallurgical use, in particular manu-
facture of refractories, abrasives, alumina cement,
coagulants, and high-strength ceramics. In the US, up
to 2 million tons of bauxites is spent annually for these
purposes. In Russia, only ca. 600 thousand tons of
bauxite ores goes for such technical production, but the
amount of these products may increase substantially in
a short term. In the recent 15–20 years bauxites have
found new applications, specifically, in manufacture of
many types of advanced materials: structural, engi-
neering, electrically conductive, and armor ceramics;
composites having a wide range of performance
characteristics; and high-acid-resistant coatings and
items. The world production of special ceramics solely
is amounting to over 9 billion US dollars. Importantly,
the necessary production facilities can be established
on the basis of small deposits having from several
hundreds of thousands to the first few millions of tons
of bauxite reserves. However, this concerns a high-
quality ore to be comprised of white bauxites con-
taining no greater than 2.5–3.0% (in terms of Fe O )
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