Lateritic Bauxite Research Articles

The geochemistry of the weathering sequences — Present and past — In and around the Pottangi and Panchpatmali bauxite-bearing plateaus, Orissa, India

The so-called East Coast Bauxite Deposits of India occur in a 30-km-wide and 400-km-long belt on the Eastern Ghats as lateritic bauxite cappings over plateau tops. The characteristics of the weathering process now active over some of these bauxite-bearing plateaus are determined by way of studying the properties of groundwater and the recent weathering profile. The groundwater is characterised by low total dissolved solids (TDS) content, feebly acidic pH and moderately high Eh-value which is promoting formation chiefly of kaolinite from the parent silicates and a minor amount of gibbsite. The results of interaction between the groundwater and the parent rock (khondalite) are registered in the recent weathering profile. A probe in the relative mobility (RM) of cations reveals the fact that out of the immobile cations Fe, Ti and Al, the least mobile is Fe and that RM of Al and Ti is higher in the kaolinitic stage than in the laterite-bauxite stage of weathering. It is concluded that bauxitisation is inoperative in the area under review during the present time. A detailed study of the ancient weathering profile comprising the laterite-bauxite duricrust has been conducted. It is established from petrographical evidence that the lateritic bauxite is an in situ derivation from the Archaean parent rock (khondalite) by direct gibbsitisation. The age of formation has been assigned to the early Eocene period. The paragenesis of mineral formation and the behaviour of the various oxides have been studied. The conditions favouring bauxitisation back in early Eocene times is discussed.

The thermal reaction of Venezuelan lateritic bauxites with glycerol

Goethite contained in lateritic bauxites or in artificial mineral admixtures is completely transformed into peculiar Fe-alkoxide compounds by reaction with glycerol at 245°C. Magnetic spinel oxides result from hydrolysis by boiling water of alkoxides obtained from the artificial admixtures. On the other hand, the production of magnetic spinel materials is not observed in alkoxides derived from natural lateritic samples. This may be caused by the high amount of Al substituting for Fe in these Venezuelan lateritic goethites.

First Co‐Operative Study on Four Tropical Soil Samples and One Lateritic Bauxite (Suriname) Proposed as Geochemical Reference Samples

Five samples from Suriname have been analysed for their chemical composition by 18 laboratories. The proposed reference samples are four soil samples and one lateritic bauxite. The samples were analyzed for major and minor elements as well as for 36 trace elements. More data are needed for better characterization of these samples, particularly for trace elements.

Petrological studies on two East Coast bauxite deposits of India, and implications on their genesis

Lateritic bauxite caps on flat-topped plateaux underlain by Precambrian khondalites along a 200–250 km stretch of the Eastern Ghats define the “East Coast bauxite province”. Studies conducted in two East Coast deposits—at Galikonda, in Andhra Pradesh, Pottangi and in Orissa—reveal a good profile differentiation, in terms of four horizontal zones of variable thicknesses, which are from top to bottom: a thin, iron-rich indurated soil cover; a lateritic bauxite zone; a lithomarge zone of partially lateritised and kaolinitised khondalite and finally, the lowermost, fresh bed-rock khondalite. Detailed and systematic mineralogical and petrographic studies have been carried out along three vertical profiles of these two deposits, using techniques of transmitted and reflected light microscopy, X-ray diffractometry, infra-red spectrophotometry, differential thermal analysis and scanning electron microscopy. These studies along with computations of quantitative mineralogical variations along the profiles confirm that the basement khondalites are the parent rocks of these East Coast bauxite deposits and that the authigenic bauxitisation was brought about by kaolinite-gibbsite transformation through desilication of the upper part of the kaolinitised lithomarge zone which formed as an intermediate stage in the weathering of the basement khondalites.

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.

Interactions between the iron and the aluminum minerals during the heating of Venezuelan lateritic bauxites. I. Infrared spectroscopy investigation

The thermal dehydroxylation of natural Al-bearing geothite was investigated by IR spectroscopy. Venezuelan lateritic bauxites (which in addition to goethite contain kaolinite, gibbsite, ilmenite and quartz), as well as chemically isolated samples of Al-goethites, were heated to 300, 600 and 1000°C. The spectral features of the iron oxides formed during the thermal treatment depend on the heating temperature, showing that the first dehydroxylation product is Al-bearing protohematite which at temperatures above 600°C is recrystallized to Al-bearing hematite. Part of the aluminum which is occuled in this hematite originates from the gibbsite and to a smaller extent from the kaolinite.

Interactions between the iron and the aluminum minerals during the heating of Venezuelan lateritic bauxites. II. X-ray diffraction study

Four samples of Venezuelan lateritic bauxites were heated to 300, 600 and 1000°C and the thermal reactions were studied by X-ray diffraction (XED) and by chemical extractability of silica and alumina. Gibbsite was converted to boehmite at 300°C, to an amorphous phase at 600°C and partly to corundum at 1000°C, with isomorphic substitution of Fe for some of the Al in the corundum structure. Goethite was converted to protohematite at 600°C and the hematite at 1000°C, with isomorphic substitution for Al for some of the Fe in both α-Fe 2O 3 varieties. Ti contributed by ilmenite is also occluded by the hematites. The occlusion of Ti takes place at 1000°C during the decomposition of the ilmenite and concomitant recrystallization of α-Fe 2O 3.

Carbonate Inhibits the Crystallization of Aluminum Hydroxide in Bauxite

Although the role of anions such as nitrate, chloride, and sulfate in inhibiting the crystallization of aluminum hydroxide in soils and geological deposits is generally accepted, the dramatic effect of the carbonate ion in maintaining aluminum hydroxide gel in the amorphous form has been overlooked by most earth scientists. Examination of bauxite occurrences suggests that the inhibiting effect of carbonate is quite apparent in the smaller grain size of gibbsite in karstic bauxite deposits as compared to that in lateritic bauxite. Scarbröite, a crystalline aluminum hydroxy carbonate, has been observed in rare instances. It is suggested that the highly reactive carbonate-containing aluminum hydroxide gels used as pharmaceutical antacids are amorphous or poorly crystalline forms of scarbröite. The effect of the sulfate anion is also apparent in certain bauxite deposits where dissolution of gibbsite by sulfuric acid has resulted from the oxidation of pyrite, with subsequent reprecipitation of gibbsite.

Scanning Electron Microscope Study of Bauxites of Different Ages and Origins

AbstractSixty-five bauxite samples of different ages and origins were studied by scanning electron microscopy. Only broken surfaces of the specimens were investigated. Size and form of individual crystals and of grain aggregates were studied as were different types of microtextures and space-fillers.Grain size varies from 0.05 μm to 1 mm. Smallest is the grain size of young karstic bauxite deposits that is explained by a physicochemical retardation effect of the carbonate environment. Significant differences were found by comparing the space-filling of karstic and lateritic bauxite deposits. High-level and low-level lateritic deposits show differences as well.A combined use of macroscopic observations, petrographie microscopy, electron microprobe, SEM, and TЕM furnishes the best clues for any genetic interpretation of bauxites. SEM studies are useful in solving technological problems of bauxite processing.

Development of bauxite in relation to parent material near Jarrahdale, Western Australia

Abstract The relationship between well‐exposed bedrock materials and lateritic bauxite developed over them was investigated in a deep railway cutting, located within the Jarrahdale bauxite mining area in southwestern Australia. Observations in the field and chemical and quantitative mineralogical analysis indicate that the bauxite developed by lateritization in place of the underlying gneissic‐granite/meta‐quartz dolerite basement complex in a leaching environment.

Investigation of bauxites with the help of electron-probe

25 representative karstic and lateritic bauxite samples from Europe, Asia and Africa were studied by a JEOL-JXA-5 electron-probe X-ray microanalyser. The main directions of the investigation were: determination of the microtextures and the distribution of the main elements in bauxite (Al, Fe, Ti, Si). Conclusions on the genesis of the textural constitution and on bauxitization are given. Further possibilities of using the electron-probe in solving different problems connected with bauxites are enumerated.

Flint Kaolins in Non-Coal-Bearing Triassic of Sydney Basin, Australia: ABSTRACT

Claystones, similar in composition, texture, and structure to the flint kaolins of the Pennsylvanian of North America, the Westphalian of Europe, and the Permian coal measures of South Africa and Australia, form a persistent marker bed in the non-coal-bearing Triassic Narrabeen Group of the Sydney basin. End_Page 538------------------------------ The claystones are indurated and characteristically possess oolitic textures, although vermicular crystals and brecciated fragments are present in most samples. Well-crystallized kaolinite is the only clay mineral present and is associated invariably with anatase and locally with abundant (> 50 percent) boehmite or siderite. Quartz, either as discrete grains or as chalcedony, is rare or absent. The unit ranges in thickness from 1 to 6 ft and can be traced for more than 50 mi along the southeastern margin of the basin. However, extensive boring downdip has shown that it thins out abruptly in that direction. The underlying sediments consist of red claystones, known locally as the chocolate shales. Apart from well-crystallized kaolinite and anatase, these claystones contain appreciable quantities of hematite (15-25 percent), but quartz and clay minerals, other than kaolinite, are sparse or absent. The overlying sediments, however, are composed of quartz, illite, and degraded illite as well as kaolinite. The chocolate shales are believed to represent a transported laterite or lateritic bauxite and the flint kaolins are considered to be the reduced equivalent, formed by the advent of swampy conditions at the close of deposition of the sedimentary sequence. End_of_Article - Last_Page 539------------

Bauxitführende laterite auf dem trappbasalt indiens als fossile, polygenetisch veränderte bodenbildung

Bauxite-bearing laterites from three regions of India are investigated: (1) Halar district (Gujerat); (2) Western Ghats near Kolhapur; (3) plateaux of the Bihar Mountains, with quantitative chemical analyses, X-rays, microscopically and as to macroscopic fabrics. These laterites have formed on trap basalts. This type of laterite originated on a low relief at low position in relation to the sea level during Early Tertiary time. Vertically, well-subdivided profiles have developed with a sharp, lower boundary preserving the macroscopic fabrics and the volume of the former basalt. In addition, the profiles show horizontal differentiation of facies into Fe- and Si-rich parts in the former center of the plateaux and Al-rich bauxites at the fossil drainage borders. This horizon which is wide-spread over large areas of India became dislocated by younger tectonics. Paleogeography and mineral paragenesis of the lateritic bauxites were preserved by marine sediments in tectonically low areas. In uplifted blocks, however, the younger erosion destroyed the primary facies pattern and the paragenesis of the deposits changed continually under the influence of later weathering processes. Thus polygenetic soils developed. A scheme of the younger history of the continent is sketched based on a combination of the facies pattern of the bauxite-bearing laterites with the morphogenesis and pedogenesis of the trap-basalt area. This scheme is compared with similar ones from Senegal and Australia.