Bauxite Formation Research Articles

Geochemistry of trace elements in Paleozoic bauxite profiles in northern Russia

The data on trace-element distribution in eight Paleozoic bauxite deposits of the North of the East-European Platform are presented. Statistical methods are used in analyzing the data. The distribution and behavior of trace elements in bauxites are controlled by the following factors: 1. (1) Composition of parent rocks. Bauxites after acidic rocks are relatively enriched by felsiphile elements. On the contrary, iron-rich bauxites after ultrabasic rocks contain high amount of femaphiles. Bauxites after alkali rock can contain very high amount of Th, Nb, Zr and some other elements. 2. (2) Physico-chemical conditions of bauxite formation (pH, E h , drainage intensity etc.) have a significant effect on the mineral composition of bauxites and content of rock-forming elements. 3. (3) Mineral forms of elements in parent rocks. The same element can be concentrated in relatively insoluble accessory minerals and also dispersed in the main rock-forming minerals. The behaviour of elements during bauxitic weathering is determined by relative proportions of these different mineral phases. 4. (4) Chemical properties of elements, e.g. solubility, pH of hydroxide precipitation, possibility of complex formation etc. Sometimes very mobile element can become immobile in the presence of other elements (Sr in the presence of P). 5. (5) Diagenetic, epigenetic and recent transformations of bauxites. The redistribution of elements during such processes under reducing conditions or during hydrothermal alteration are considered. 6. (6) A carbonate footwall plays an important role, acting as a geochemical barrier to the removal of certain elements, resulting in the formation of hypergene carbonates or other minerals within a bauxite profile. The problem of temporal evolution of bauxite formation is also considered.

Foreland Sedimentation and Plate Interaction During Closure of the Tethys Ocean (Tertiary; Hellenides; Western Continental Greece)

ABSTRACT Microplate Apulia, partly represented by rocks in western continental Greece, was part of the Gondwana foreland during closure of the Tethys Ocean in the Tertiary. In the earliest Tertiary, Greek Apulia was partitioned into carbonate shoals and intervening pelagic troughs. As Eurasia overrode and flexurally deformed Apulia, a forebulge developed that migrated toward an Apulia carbonate shelf at a rate of 0.5-1 cm/yr. Forebulge uplift led to subaerial exposure of platform, carbonates, karstification, and bauxite formation. Related flexural extension fractured the foundering neritic carbonates, giving rise to carbonate breccias that intermingled with flysch mud as the bulge migrated away toward the shelf. Flysch sand influx was initially restricted to a Pindos pelagic trough, but later, through foundering of the carbonate shoals, the flysch basin widened to span the region between the Apulia shelf margin and the Eurasia hinterland. The Greek flysch is dominantly muddy but contains abundant sand and gravel at certain stratigraphic intervals. A coarsening-up trend in basal strata reflects encroachment of the source areas on the Eurasia plate. The flysch accumulated in two main depositional systems: (1) submarine slopes of fan deltas and (2) elongate basins joining the toes of the fan deltas and constricted by the carbonate highs. Paleocurrents indicate longitudinal input from the north and lateral input from the east (present coordinates). Shallow-marine and terrestrial remnants of the f ysch feeder systems are exposed east of the flysch outcrop belt, in the Mesohellenic Trough.

Oxygen-isotope fractionation in gibbsite: Synthesis experiments versus natural samples

The following oxygen-isotope fractionation factors for the gibbsite-water system ( α g-w ) have been obtained from a series of twenty-two synthesis experiments: 1.0119 ± 0.0005(51 ± 2°C); 1.0144 ± 0.0003(25 ± 0.1°C); 1.0139 ± 0.0003(22°C ± 2°C); and 1.0162 ± 0.0012(8 ± 2°C). Isotopic equilibrium is considered to have been reached in the majority of cases because of the coincidence of results for syntheses using several different techniques. All three polymorphs of Al(OH) 3, namely, gibbsite, bayerite and nordstrandite, were identified in the synthesis products. Partial dissolution techniques have been applied to samples from twelve bauxite deposits to obtain the δ 18O value of both gibbsite and kaolinite. These data, plus previously published results, have been used to calculate α g-w values, using two independent methods: 1. (1) by comparison with the δ 18O value of associated kaolinite and 2. (2) by comparison with the δ 18O value of local meteoric waters. The results show a spread of values from those obtained by synthesis experiments to values up to ~6%. higher. It is concluded that the spread of values is real and that the δ 18O value of gibbsite is dependent upon its formation mechanism. It is suggested that the gibbsite samples which exhibit high α g-w values have either obtained their isotopic signature by inheritance during the desilication of kaolinite, or from exchange with oxygen-bearing anions such as sulphate, during the transport of aluminum as Al-OH complexes. The possibility that the high values are the result of evaporative modification of the fluid prior to gibbsite precipitation cannot be ruled out, but is unlikely, given that humid conditions are required for bauxite formation. Such conclusions suggest that the oxygen isotope composition of gibbsite is unsuitable as a palaeoclimatic indicator but may prove useful in providing genetic information on bauxite formation.

Geochemical differentiation in laterite and bauxite formation

The geochemical differences between laterite and bauxite formation are discussed under the aspect that both weathering products are predominantly formed by residual enrichment of iron and aluminium. Residual enrichment is corroborated by various arguments and clearly proved for laterite formation on ultramafic rocks. Tropical weathering of the most widespread acidic rocks leads, in spite of their high Al/Fe ratio, generally to formation of laterites showing a high enrichment of iron whereas aluminium is not or only slightly enriched. This chemical variation indicates that high amounts of Al are removed additionally to Si in soil solutions when saprolites on acidic rocks are transformed into laterites containing goethite, hematite and kaolinite as main constituents. Dissolved free aluminium exist in equilibrium with kaolinite only in minimal contents, hence the removal of Si and Al probably takes place in form of freshly formed colloidal or subcolloidal, X-ray amorphous particles with kaolinitic or similiar composition. The frequently observed occurrence of two generations of secondary kaolinite in laterites corroborates this conclusion. There is general agreement that bauxites are formed by stronger leaching compared with laterites. Increased leaching lowers the concentration of dissolved silica, thus enabling gibbsite instead of kaolinite stability. The concentration of dissolved free aluminium, however, is increased in equilibrium with gibbsite. Free aluminium shows in contrast to iron an effective solubility atpH= 5, giving rise to downward leaching and re-precipitation at higher pH below a laterite crust which covers the bauxite zone in most of the bauxite deposits. In spite of the stronger leaching, bauxite formation implies a lower mass loss (mainly Si) during weathering than the formation of laterites (loss ofSi + Al) related to their highly increased iron content.

Carbonate Platform Emergence and Bauxite Formation: ABSTRACT

Carbonate Platform Emergence and Bauxite Formation: ABSTRACT

Bauxite development in the North Apuseni mountains, western Romania

The stratigraphic and palaeogeomorphologic conditions of bauxite formation in the North Apuseni mountains are related to the geotectonic evolution of western Romania during the Late Jurassic and Early Cretaceous. Bauxitization, accumulation and preservation of the bauxites were directly associated with karst development in the area under study. The petrographic and mineralogic nature of the bauxite deposits reveal superimposed aliagenetic, catagenic and, locally, metamorphic features. A comparative analysis of the principal chemical components of the different bauxite-bearing zones of the North Apuseni mountains are used to show similar development.

CARACTERIZAÇÃO MINERALÓGICA E QUÍMICA DAS BAUXITAS DE NAZARÉ PAULISTA (SÃO PAULO)

Weathering on metabasic sequence of the Serrado Itaberaba amphibolites led to bauxite formation in top and upper slopes topographic positions. This article deals with mineralogical and geochemical aspects of the fresh rock and its weathering products: bauxite and clay. Microscopic and X-ray diffraction studies indicate that the fresh rock is formed mainly by hornblende, plagioclase and quartz and that gibbsite, kaolinite and goethite are the main phases present in weathered products. The relationship between primary and secondary minerals is discussed. From a geochemical point of view, the bauxitization led to a depletion in Fe, Si, Ca, K, Mg, Mn, P, B, Ba, Be, Cu, La, Li, Mo, Sr, Sn, V, Y, Zn and Zr and an enrichment in Al, Pb, Co, Cr. REE except Ce, are generally depleted in weathered products. The similarities and differences in the elements behaviour during lateritization was investigated by factor analysis.

Geochemistry of waters associated with current karst bauxite formation, southern peninsula of Haiti

Geological and petrographical observations have led to the hypothesis that there is current formation of bauxitic deposits in the southern peninsula of Haiti. The kaolinitic products of the lateritic alteration of the basalts are trapped in karst. It is then proposed that they are transformed into gibbsite by the flushing out of dissolved silica. The study of waters percolating the different outcrops show that the formation of gibbsite takes place during the rainy season; during the dry season kailinite is not significantly altered. The geochemistry of Al, Si, Ca and ΣCO 2 is in agreement with the reaction: kaolinite → gibbsite + dissolved silica. The resulting gibbsite remains trapped in karst. Geochemical budgets show that the formation of such bauxitic deposits of 1.3 m thick can take place in only 100,000 a.

Geochemical behaviour of trace elements during bauxite formation at Belgaum (Karnataka) and Yercaud (Tamil Nadu), India

Trace elements like Cu, Ni, Co, Zr, Cr, V Ba, Sr, Ga, Be, Y and Nb were determined for bauxites derived from different parent rocks, viz. basalts and charnockites, clays, laterites and bauxites, from Belgaum (Karnataka) and Yercaud (Tamil Nadu). The behaviour of these trace elements during the lateritization process unravels that in Belgaum: (1) Zr and Nb are strongly enriched, along with Al, Fe and Ti; (2) Ga is slightly enriched; (3) Cr is slightly depleted; and (4) Cu, Ni, V, Y, Co, Ba and Sr are strongly depleted whereas in Yercaud no trace element seems to be enriched but: (1) Al and Fe are strongly enriched; (2) Ti is slightly enriched; (3) Ga is slightly depleted; and (4) V, Cr, Co, Ba, Sr, Cu and Zr are strongly depleted. Be remains unchanged in both regions. The geochemical significance of the above is discussed.

Thermodynamic and kinetic aspects of formation of bauxites

Experiments in which cleavage nepheline samples were reacted with aqueous solutions at fixed pH's and temperature were carried out in the laboratory. The chemistry of the solution as a function of time was monitored, as well as the chemistry of the nepheline surfaces. At 25°C, Al derived from the nepheline stays in solution due to slow precipitation kinetics of Al(OH) 3. At 60° and 80°C, precipitation of Al(OH) 3 is so rapid that Al concentration in solution is below 0.05 ppm. This indicates that precipitation kinetics favour the formation of bauxite deposits in tropical regions (i.e. T⩾25°C), but not in temperate regions. Precipitation products on the surface of the nepheline fragments at 60° and 80°C depend on the pH. At pH 3.0, an amorphous aluminium silicate (proto-kaolinite?) is formed. At pH>7.0, the precipitated phase contains, in addition to Al and Si, high amounts of Na and K (proto-muscovite?). The optimum pH for the formation of bauxite is in the range 5–7. These results are in agreement with thermodynamic calculations.

Genesis of certain bauxite profiles from India

An attempt is made to reveal a geochemical compatibility with paleoenvironment to understand the genesis of bauxite deposits that are derived from two different parent rocks. For this purpose two in situ bauxite profiles, one developed over basalt and another over sandstone, have been taken. Gibbsite is the major mineral in all these bauxites with minor occurrences of goethite, hematite, anatase, kaolinite, etc. From the study it is evident that the paleoenvironment and geochemical processes are vital factors that could lead to the formation of bauxites. The significance of this is fully discussed.

Palaeoenvironment of lateritic bauxites with vertical and lateral differentiation

Summary Formation of lateritic bauxites of the type described in this paper occurs world-wide in Cretaceous and Tertiary coastal plains. The bauxites form elongate belts, sometimes hundreds of kilometres long, parallel to Lower Tertiary shorelines in India and South America and their distribution is not related to a particular mineralogical composition of the parent rock. The lateral movement of the major elements Al, Si, Fe, Ti is dependent on a high level and flow of groundwater. Varying efficiency of subsurface drainage produces lateral facies variations. Interfingering of marine and continental facies indicate a sea-land transition zone where the type of sediments also varies with minor tectonic movements or sea-level changes. A typical sediment association is found in India, Africa, South and North America. It consists of (i) red beds rich in detrital and dissolved material of reworked laterites, (ii) lacustrine sediments and hypersaline precipitates, (iii) lignites intercalated with marine clays, layers of siderite, pyrite, marcasite and jarosite, and (iv) marine chemical sediments rich in oolitic iron ores or glauconite. A model is developed to account for element distributions in lateritic bauxites in terms of groundwater levels and flow. Finally it is shown that many high-level bauxites are formed in coastal plains and that they are subsequently uplifted to their present altitude.

A review of the early Tertiary bauxite event in South America, Africa and India

Extensive and thick lateritic bauxites are found in South America, Africa and India. Since Cretaceous times there have been four phases of chemical weathering alternated with erosion phases. It can be shown that the early Tertiary phase generated the thickest soil profiles and the most extensive bauxite deposits; this phase is defined as bauxite event and it relates to a temperature and humidity maximum. The early Tertiary bauxite event also relates to an accumulation maximum of leached elements precipitated in newly formed minerals in basins on the continent, the continental shelf and the deep sea in and around Africa. Using sections from Cutch and Rajasthan/India and South America the event is dated as late Early to early Middle Eocene. The regional distribution pattern of bauxite deposits in South America, Africa and India, when the latter is moved to its early Tertiary plate position, is comparable to known climaticzones. Although it seems that the uplift of the East African Rift Valley has interfered with formation and preservation of extensive bauxites and other lateritic mineral deposits, they may still be discovered when the region is better known geologically.

A low level laterite profile from Uganda and its relevance to the question of parent material influence on the chemical composition of laterites

Summary A 78 foot (24 m) ‘low level’ laterite profile from Tira, in Busia District, Uganda, is described. Mineral and chemical progressions, from the parent rock through saprolite and into the laterite, indicate its residual development. The chemical compositions of the residuum and the parent material are compared with further data from Uganda and other published results in order to assess the importance of the Fe, Al and quartz content of parent rocks in determining the chemical composition of a laterite. Quartz-richness of parent material does not appear to be disadvantageous for bauxite formation. Neither is Al-richness advantageous. This leads to the conclusion that the absence of bauxite in Uganda may be attributed to unfavourable leaching conditions rather than, as formerly believed, to the absence of suitable parent rocks.

Model for bauxite formation: Paragominas (Brazil)

Samples from a profile of the Paragominas bauxite (Brazil) were analyzed extensively. Principal minerals were determined as well as the concentrations of 56 elements. The major-element chemistry can be described in terms of the oxides and hydroxides of Al, Si, Ti and Fe, bound mineralogically as gibbsite, kaolinite and hematite. 30 of the 45 minor and trace elements analyzed often maintain their average crustal concentrations. Depletions are most obvious for the alkali metals, the alkaline earths and the metals of the first-row transition series. Enrichment is observed for B, Sc, Zr, Nb, Sn, Sb, I, Hf and Th. Differences in concentration patterns for some refractory metals (Al, Ti, Zr, Hf, etc.) lead to the suggestion that some (e.g., Ti, Zr, Hf) of these metals may be participating in biological reactions. The economic bauxite zone is bracketed above and below by kaolinitic horizons, and this succession of alteration could be explained by extraordinarily high flow rates of meteoric waters for millions of years through highly permeable terrains. The formation and preservation of these highly leached profiles also require a quiescent tectonic setting for 10–100 Ma. Such a model is consistent with conditions which may have prevailed in eastern Amazonia for at least 100 Ma.

Évolution minéralogique et chimique des bauxites au cours de leur genèse dans les gisements de l'Ariège (France)

The beds of bauxite of Ariège are schematically constitued, from lying wall to hanging wall, of clays with kaolinite and hematite, red bauxites with prevailing diaspore and hematite, white bauxites with prevailing boehmite and little hematite. Few red bauxites contain poorly crystallized diaspore which deshydrates at lower temperature than normal diaspore. This diaspore was synthetized by grinding gibbsite and goethite at 150 °C. The infrared spectrum suggests a hydrogen bond relatively weak which explains the lower temperature of dehydration. The different varieties of diaspore and goethite presently known are compared. The mineralogical and chemical data suggest the transformation of clays in red bauxites by leaching of only silica and crystallization of gibbsite, then the formation of white bauxite by leaching of only iron. After hiding, at approximatly 100 °C and 800 bars, diaspore forms in red bauxites and boehmite in white bauxites. In bauxites of Ariège, the iron concentration is one determinating factor in the formation of either monohydrate.

Features of distribution of radioactive elements in bauxite-bearing deposits

The distribution of Th and other radioactive elements in bauxite-bearing deposits was examined in detail, and the deposits were classified into three groups on the basis of the Th content. Tabulated data show the U content in ppm, Ra in ppm equivalent U, Th in ppm, K, and Th/K ratio. The significant detail revealed is that during bauxite formation potassium was extensively depleted, Th accumulated, and U remained unchanged, resulting in a Th/K ratio tens and hundreds of times greater in the bauxite than in the country rock. (JSR)

Some coordination effects in orebody formation

The most common coordinating ligands present in groundwaters are water itself, carbonate, chloride, fluoride and some organic acids. It is possible to account for the formation of bauxite, malachite, azurite, many other copper ores, and other deposits using just these complexes as starting materials and active compounds.

Island-Arc Evolution and Related Mineral Deposits

In ensimatic arcs, initial submarine eruptions of island-arc tholeiites are succeeded by subaerial and submarine volcanism which is either calcalkaline or island-arc tholeiitic. Besshi-type massive stratiform sulfides develop in deep water on the submarine flanks of islands. Pluton emplacement beneath waning volcanoes is accompanied by mercury, porphyry copper, and gold mineralization. Renewed calc-alkaline or island-arc tholeiitic volcanism commonly follows arc reversal or splitting; Kuroko-type massive sulfides form in shallow-water clastic dacitic rocks and gold is concentrated around monzonites and in meta-andesites. Reef limestone deposition, block faulting, and uplift may be followed by formation of bauxite on karstic limestones, and of stratiform manganese deposits near the limestone base. Upper mantle and ocean crust rocks, emplaced as ophiolites in melanges on the arc side of the trench and as obducted slices during arc-arc collision, contain Cyprus-type stratiform massive sulfides, podiform chro...

Laterite and Bauxite Formation

Simplified model, preferential solubilities of elements over given pH range, availability of oxygen in ground water