Sedimentary Kaolin Research Articles

Rare-earth element (REE) remobilization and fractionation in bauxite zones from sedimentary kaolin deposits, western Georgia (USA), Upper Coastal Plain

Rare-earth elements (REE) are critical minerals that are indispensable for high-tech products and technologies. Significant efforts have been focused on the exploration and identification of new and domestic reserves of REE. This study reports geochemical and mineralogical occurrences of accumulated REE with significant fractions of ion-adsorption clays (IAC) within bauxite-kaolin ore, hosted within sedimentary strata. This deposit type can be found throughout portions of Georgia and eastern Alabama (USA) in the Southeast Upper Coastal Plain. These deposits were developed by high degrees of chemical weathering of older, kaolinite-rich sedimentary strata. Several major changes in whole rock mineralogy and geochemistry occurred, leading to the development of zones of REE depletion, fractionation, and accumulation. Depletions of REE in the bauxite zone were significant, with whole rock contents of ∼50% ΣREE relative to average upper continental crust (UCC). Fractionated REE were observed by low La/YbN values (La/YbN = 0.2) due to depletion in LREE (<40% UCC) with concomitant HREE retention (∼1.1–1.3 times UCC). Strongly positive Ce/Ce* anomalies (Ce/Ce* = 1.3), very low ion-exchangeable Ce contents (Ce/LREE = 0.1), and low solubility of Ce (0.9–1.2%) under reducing conditions compared to all other LREE (4.5–9.9%) were further observed. These characteristics were strong indications of REE fractionation that occurred during formation of the bauxite zone. Underlying the bauxite zone, accumulations of the remobilized REE were substantial. At the base of the lower kaolin zone, elevated ion-exchangeable REE contents were notable (11–33% for total REE), and more specifically 11–12% for LREE, ∼28% for ΣTb-Lu, and ∼ 33% for Y. The elevated ion-exchangeable contents coincided with whole rock contents that were ∼ 250% ΣREE relative to UCC. These REE accumulations occurred within organic-rich strata at the base of the section. This setting represents a significant difference relative to the REE accumulations in profiles for the granite-regolith deposit type. These findings highlighted the movement of dissolved REE, accumulation as sorbed species, as well as the potential role that organic ligands play during REE precipitation and sorption processes. These results permit consideration for further research into REE occurrences in clay deposits of sedimentary origin, which have been underexplored compared to granite-regolith REE deposits.

Analysis of the microstructure and morphology of disordered kaolinite based on the particle size distribution

The defected kaolinite is common in sedimentary kaolin, but its structure and disorder mechanism remains unclear. In this paper, three different size distributions of kaolinite particles: 0–300 nm, 200–1000 nm, and 500–2000 nm, were separated and classified from high-defect sedimentary kaolin, collected from Quaternary sedimentary kaolin in Guangxi Zhuang Autonomous Region of China. The three particle sizes of kaolinite have been monitored by particle size analyzer, high-resolution magic-angle spinning NMR (MAS NMR), small and wide-angle X-ray scattering (SAXS and WAXS), X-ray diffraction (XRD), BET surface analyzer, nitrogen gas-adsorption, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The results revealed that the smallest particle size of kaolinite exhibited high degrees of broken Al-O-Al and Si-O-Si bonds, more disordered structure, and elevated specific surface area. The degree of the structural disorder of kaolinite increases as the particle size decreases, which can be attributed to the more aluminum substituted for silicon in tetrahedron sheet in the finer kaolinite crystal, compared to the coarser kaolinite crystals.

Microbial nitrification and acidification of lacustrine sediments deduced from the nature of a sedimentary kaolin deposit in central Japan

Kaolin deposits in the Seto-Tono district, central Japan, were formed by intense kaolinization of lacustrine arkose sediments deposited in small and shallow inland lakes in the late Miocene. Based on mineralogical and stable isotopic (Fe, C, N) studies of Motoyama kaolin deposit in the Seto area, we concluded that it was formed by microbial nitrification and acidification of lacustrine sediments underneath an inland lake. Small amounts of Fe–Ti oxides and Fe-hydroxide in the kaolin clay indicated that iron was oxidized and leached during the kaolinization. The field occurrences indicate that leached ferric iron precipitated on the bottom of the kaolin deposit as limonite crusts, and their significantly fractionated Fe isotope compositions suggest the involvement of microbial activity. The C/N ratios of most of the kaolin clay are distinctly higher than those of modern lacustrine sediment. Although, the possibility of a low-temperature hydrothermal origin of the kaolin deposit cannot be completely ruled out, it is more likely that acidification by dilute nitric acid formed from plant-derived ammonia could have caused the kaolinization, Fe oxidation and leaching. The nitrate-dependent microbial Fe oxidation is consistent with dilute nitric acid being the predominant oxidant.

Geochemical Evidence for Rare-Earth Element Mobilization during Kaolin Diagenesis

This study investigates how saprolization influences inherent rare-earth element (REE) source rock signatures and how depositional environment(s) and diagenetic reactions ultimately impact the REE signature within sedimentary kaolin bodies. Rare-earth element geochemistry signatures are particularly useful for tracking element sources and mobility and are, therefore, powerful tools in the investigation of clay mineral formation and diagenesis. Rare-earth element and bulk chemical compositions were determined using discrete chemical analyses and chemical imaging. Saprolitic materials show an enrichment in the light and heavy REEs, compared with the parent material, with enhanced Ce/Eu anomalies. Light REEs within sedimentary kaolins are associated with phosphate mineralogy and have experienced variable degrees of diagenetic fractionation and mobilization. Cretaceous kaolins display more light REE mobility compared with Tertiary kaolins, which show very little REE fractionation. Degrees of REE fractionation...

MINERAL CONTAMINANTS OF THE SEDIMENTARY KAOLIN ORE FROM IPIXUNA MINE, BRAZIL

Minerais contaminantes do minério de caulim sedimentar da Mina Ipixuna, Brasil. O minério de caulim sedimentar da mina Ipixuna, na Amazônia brasileira, contém minerais contaminantes, tais como anatásio, hematita e goetita, entre outros, cujas ocorrências alteram a cor branca original de blocos de caulim para vermelha, cinza e roxa. O principal objetivo do presente estudo foi identificar os minerais contaminantes do minério ROM de caulim, as texturas e suas relações com o ambiente de deposição. Análises por estereomicroscopia binocular e difração de raios-x permitiram definir a paragênese mineral dos contaminantes em diversas áreas do corpo de minério, bem como caracterizar as condições de deposição. Os minerais contaminantes alteram a cor branca do minério para vermelha, amarela, cinza e roxa. A cor vermelha é associada com goetita e hematita disseminada no minério de caulim. A cor amarela é associada com quartzo, muscovita e anatásio disseminados no minério de caulim. A cor cinza é associada com finas multicamadas de caulinita contendo baixas e altas concentrações de anatásio. A cor roxa resulta da disseminação de hematita no minério de caulim.

Kaolin deposits and their uses: Northern Brazil and Georgia, USA

Kaolin mineral-bearing rocks are classified by their mineralogy and texture, which delineate their potential use. Refractory clay products are made from a continuum of ores comprising fire clay, bauxitic kaolin and bauxite. Ceramic clay products are made from a range of ores comprising near pure kaolin, ball clays, plastic clays, kaolinitic sandstone and china clays along with some other clay minerals that impart plasticity and having some other non-clay minerals such as quartz and feldspar that allow a white-burnt appearance at a specified melting temperature. Pigments and additives are beneficiated from kaolinitic rocks that have textures which permit particle dispersion for size classification and for removal of impurities. The diverse mineralogy and texture found in Georgia, USA sedimentary kaolin deposits explain their range of beneficiation processes and uses. Capim [Brazil] soft kaolins are mostly used for pigment applications because of their mineralogical purity, ease of dispersion and geological homogeneity, which permits large-scale production of products having consistent quality.

Genesis and mining potential of kaolin deposits in Patagonia (Argentina)

Kaolin occurs in Patagonia as residual (weathering or hydrothermal) deposits at the surface of an extended Jurassic rhyolite province or in the upper sedimentary Cretaceous or Danian–Paleocene layers. On the same paleogeographic surface, numerous epithermal Au–Ag lodes occur, making kaolin genesis a crucial point in mining exploration. The weathering or sedimentary genesis of some deposits (Puma, Súper, FPS, Espingarda and Marta) was confirmed through clay isotope results. The origin of some corrective clays (Bajo Grande and White Bentonite) was analyzed and compared with that of one sample from Ukraine and one from a hydrothermal deposit in Furtei, Sardinia, Italy. In Patagonia, the residual and sedimentary kaolin deposits have resources of over 12 million tons. The identified hydrothermal deposits have more limited resources, due to their strong mineralogical zonation, which requires their selective “pocket” kaolin exploitation. The Patagonian region is the southernmost part of a continent where a Gondwana paleosurface of Late Mesozoic age developed on Jurassic rhyolite volcanic units. This surface is exposed along tens of thousands square kilometers in the cratonic units of northern and southern Patagonia, having a strong potential for finding new kaolin or epithermal precious metal deposits.

Mineralogy and geochemistry of clay fractions from different saprolites, Egypt: implications for the source of sedimentary kaolin deposits

The clay fractions of saprolites from granites, basalt, and schists in Egypt were subjected to mineralogical and geochemical investigations to examine the effect of source rock on the composition of the saprolites and the possibilities of these saprolites as a source of the nearby sedimentary kaolin deposits. The clay fractions of the studied saprolites show mineralogical and geochemical variations. Saprolites from the granites consist of kaolinite, while saprolites from the basalts are composed entirely of smectite. Schists-derived saprolites are composed of kaolinite in some cases and of a mixture of kaolinite, illite, and chlorite in the other. Saprolite from the basalt is characterized by relatively higher contents of TiO2 and Ni compared to the saprolites from granites. Saprolites from granites have higher contents of Ba, Li, Pb, Sr, Th, Y, and Zr compared to those of the saprolites from the basalts and schists. Saprolites from different schists show variations in the distributions of many constituents, such as TiO2, Cr, Ni, Ba, Y, and Zr. Although chondrite-normalized rare earth elements (REE) patterns are characterized by relative enrichments in the light rare earth elements (LREE) compared to the heavy rare earth elements (HREE) in all saprolites, granitic saprolites show negative Eu anomalies, while saprolite from basalt has no Eu anomaly. REE patterns of the saprolites from schists exhibit slight positive Ce anomalies and slight to moderate negative Eu anomalies. Weathering of saprolites from the basalt and metasediments is classified as the bisiallitization type, while weathering of saprolite from the granite is allitization type. Saprolites from schists vary from the bisiallitization (Aswan and Abu Natash) and allitization (Khaboba) types. Saprolites from the Khaboba schist can be considered the possible source of the Carboniferous kaolin deposits in the Hasber and Khaboba areas of Sinai, based on the similarity in the mineralogy and geochemistry of major, trace, and REE between the saprolites and the deposits. On the other hand, Carboniferous sedimentary kaolin deposits in the Abu Natash area, as well as the Cretaceous kaolin deposits in all areas of Sinai, might have been derived from the nearby schist saprolites, based on the similarity in the mineralogy and geochemistry between the saprolites and the kaolin deposits. Granites from the Arabian-Nubian Shield (ANS) and East Sahara Craton (ESC) are the possible sources of the pisolitic and plastic kaolin deposits in the Kalabsha area (Aswan), as indicated by the similarity in the mineralogy and geochemistry of the granitic saprolites and the kaolin deposits.

Ti-bearing minerals in sedimentary kaolin deposits of Egypt

Titanium (Ti) is a major impurity in the economic Carboniferous and Cretaceous sedimentary kaolin deposits in Egypt. The current study clarifies the distribution of Ti and its modes of occurrence in these deposits through petrographic, mineralogical, and geochemical investigations. It is found that Ti is present as an independent mineral phase rather than in the crystal structure of kaolinite. Ti occurs mainly as uniform very fine-grained and rounded anatase crystals in pockets within the kaolin mass of all deposits. Traces of rutile, leucoxene and ilmenite are present in the sand fractions. Average anatase content ranges between 1.4% and 3%. Cretaceous kaolin deposits show a homogeneous distribution of anatase regardless of the location (1.8 and 2.8%), while Carboniferous deposits are heterogeneous with the highest anatase content in the Abu Natash deposit (3%) and the lowest (1.4%) in the Khaboba deposit. The positive correlations between TiO2 and some trace elements such Cr, Nb and Zr in the clay fractions, where anatase is the only Ti-bearing mineral, suggest the occurrence of most of such elements in the anatase structure.The occurrence of anatase as uniform very fine-grained crystals as pockets within the kaolin mass, together with the presence of ilmenite and/or leucoxene in the sand fractions of the studied kaolin samples suggests an authigenic origin for the anatase as a result of post-depositional alteration of ilmenite precursor to leucoxene. The positive correlations between TiO2 and trace element contents probably support this assumption. The higher trace element contents in the anatase from different deposits compared to the associated leucoxene and ilmenite are considered to result from relative enrichment of the immobile trace elements during the alteration of ilmenite and leucoxene to anatase.

Provenance of sedimentary kaolin deposits in Egypt: Evidences from the Pb, Sr and Nd isotopes

This work reports, for the first time, the Pb, Sr and Nd isotopes of the clay fractions (<2μm) from sedimentary kaolin deposits in Egypt of different ages (Carboniferous and lower Cretaceous), localities (Sinai, Red Sea and Aswan), lithologies (flint and plastic) and clay minerals composition (pure kaolinite and mixture of kaolinite, illite and chlorite) to determine their source area compositions and examine the effect of provenance on their isotopic compositions.Measured (present day) and age-corrected Pb isotopes data (100 and 300My for the Cretaceous and Carboniferous deposits, respectively) are more or less homogeneous in all deposits regardless of their ages, localities, and compositions. This, therefore, suggests that the Pb isotopes cannot be used as a tracer for source area compositions of these kaolin deposits. On the other hand, the studied kaolin deposits show variations in their measured and age-corrected Sr and Nd isotopes regarding to their ages and compositions. The Carboniferous illite-rich kaolin deposits in the Khaboba and Hasbar areas, Sinai have higher measured and age-corrected 87Sr/86Sr ratios (average of 0.715742 and 0.711156 for measured and age-corrected, respectively) compared to the non-illitic Carboniferous deposit at Abu Natash area (average of 0.70772 and 0.70769 for measured and age-corrected, respectively) and the lower Cretaceous deposits in all areas (average of 0.70827 and 0.70821 for measured and age-corrected, respectively). The Carboniferous kaolin deposits in the Khaboba and Hasbar areas also have lower 143Nd/144Nd ratios (average of 0.51206 and 0.51180 for measured and age-corrected, respectively) compared to the Carboniferous Abu Natash deposit (average of 0.51253 and 0.51231 for measured and age-corrected, respectively) as well as the lower Cretaceous deposits in all areas (average of 0.51248 and 0.51239 for measured and age-corrected, respectively). Initial εNd values are negative in the Carboniferous kaolin deposits in the Khaboba and Hasbar areas (average of −8.8) and lower Cretaceous deposits (average of −2.3), while the initial εNd values are positive in the Carboniferous Abu Natash deposit (average of 0.95).The comparison of radiogenic isotopic compositions of the studied sedimentary kaolin with those of the Arabian Nubian Shield (ANS) and East Sahara Craton (ESC) basement rocks indicates that the source of these kaolin deposits is not a simple source but rather a mixture of different rock types represent the composition of the ANS and ESC basement rocks. The 87Sr/86Sr ratios and εNd values suggest an old crustal source (ESC) for the Carboniferous kaolin deposits in the Khaboba and Hasbar areas but younger and more juvenile crustal sources (ANS) for the Carboniferous kaolin deposit in the Abu Natash area as well as the lower Cretaceous deposits in all areas.The homogeneity of the Pb isotopes in the studied kaolin deposits indicates that the Pb isotopes cannot be used as tracer for source area composition of kaolin deposits, while the systematic variations of both Sr and Nd isotopes among the studied deposits suggest their possible use to differentiate between sedimentary kaolin deposits based on their source rock compositions.

Spectrophotometric characterization of iron and titanium minerals in sedimentary kaolin deposit

The northern region of Brazil produces kaolin for paper industry. Ipixuna Mine, located in the Pará State, exploits important sedimentary kaolin deposits, which are extracted ROM material blocks that vary in color depending on both the paragenesis and concentration of mineral contaminants. Samples were collected from different mining fronts, which represented the different varieties of ore. Samples were processed in a pilot plant. Both products and tailings were analyzed to define the mineral paragenesis and color data. Specific studies on the iron and titanium minerals and spectrophotometry were performed on the samples. The results indicated that the proportion of goethite, hematite and anatase and the particle size of the last two minerals in the blocks of ore affect their color and mineral processing efficiency. This study defined seven spectral groups of kaolin ore, the relationship of the groups with the paragenesis of mineral contaminants, varieties of ore that can be economically processed and the best blending options between ore varieties to improve the processing operations.

Geochemistry and origin of the Cretaceous sedimentary kaolin deposits, Red Sea, Egypt

This work reports, for the first time, the mineralogical and geochemical characteristics of the Cretaceous sedimentary kaolin deposits in the Red Sea area, Egypt and sheds the light on their source. Mineralogical and geochemical analyses of both bulk deposits and the sand and clay fractions of these deposits indicated that they are composed of kaolinite (average of 75wt.%) and quartz (average of 22wt.%). Traces of anatase (average of 1wt.%) were identified in all kaolin samples, while traces of halite (average of 2wt.%) and hematite (average of 1wt.%) were reported in the majority of the analyzed samples. The clay fractions show relatively high contents of TiO2 (average of 2.1%), Ni (average of 103ppm), Nb (average of 98ppm), Y (average of 67ppm), and Zr (average of 630ppm). Sum of the rare earth elements (ΣREE) in the clay fractions varies between 193 and 352ppm. Chondrite-normalized REE patterns show enrichment of the light REE relative to the heavy REE ((La/Yb)N=9) and negative Eu anomaly (Eu*/Eu=0.67).Major, trace, and rare earth elements geochemistry of the clay fractions from the studied kaolin deposits suggested that these deposits were derived from a mixture of more than source rocks probably a mixture of mafic, granitic, and alkaline rocks. The contribution of granitic rocks was proposed based on the REE pattern and negative Eu anomaly as well as the high Zr and Y contents, while the contribution of mafic rocks to the source was suggested based on the relatively high TiO2 and Ni contents. The abnormally high Nb contents in the clay fractions of the Red Sea kaolin deposits indicated a contribution of alkaline rocks to the source of these deposits. Igneous and metamorphic rocks of different composition belonging to the Arabian-Nubian Shield are located very close to the studied deposits.The monomineralic nature of the Red Sea kaolin deposits as kaolinite, abundance of organic matter, and absence of any marine fossils suggested a non-marine depositional environment of these deposits. Occurrence of halite in the studied deposit is probably due to sea breezes since the studied deposits are located close to the Gulf of Suez.

Hydrogen and oxygen isotopic compositions of sedimentary kaolin deposits, Egypt: Paleoclimatic implications

The clay fractions of sedimentary kaolin deposits representing different ages (Carboniferous and Cretaceous), types (pisolitic flint and plastic), and localities (Sinai and Aswan) from Egypt were analyzed for their H and O isotopic compositions to examine the paleoclimate conditions during their formation. The δD values of the Carboniferous deposits in Sinai range between −67‰ and −88‰, while the values for the Cretaceous deposits in Sinai range between −59‰ and −75‰. The δ18O values of the Carboniferous deposits range from 17.9‰ to 19.4‰ and the values for the Cretaceous deposits range between 19.2‰ and 20.4‰. The relatively low δD and δ18O values of the Carboniferous deposit at the Abu Natash area (−67‰ and 17.9‰, respectively) compared to other Carboniferous deposits (averages of −83.3‰, and 18.8‰ for δD and δ18O, respectively) could be due to isotopic exchange between this deposit and the adjacent dolomite and/or the enclosed hydrothermally-formed Mn ores of the Carboniferous Um Bogma Formation. The δD and δ18O values of the Cretaceous pisolitic flint kaolin deposit from Aswan (averages of −65‰ and 20.3‰, respectively) and plastic kaolin from the same area (averages of −66‰ and 19.5‰, respectively) are almost identical. The differences in the δ18O values between the clay fractions of the pisolitic flint kaolin (20.3‰) and the previously analyzed bulk kaolin of the same deposit (average of 17.5‰) suggest a significant effect of non-clay minerals on the isotopic compositions of the kaolin deposits.The H and O isotopic compositions plot close to the kaolinite line that marks the isotopic composition of kaolinite in equilibrium with meteoric water at 20°C. This indicates that the kaolinite from both the Carboniferous and Cretaceous deposits in Egypt formed by meteoric water weathering of the source rock(s). The δD and δ18O values also suggest that kaolinite of these deposits formed under warm-temperate to tropical conditions. The slight deviations of some samples from the kaolinite line suggest post-depositional modifications of the isotopic compositions of studied deposits probably due to the interaction between earlier-formed kaolinite and downward percolating meteoric water.The δD and δ18O values of the Cretaceous and Carboniferous deposits from all localities suggest that both deposits formed under similar climatic conditions due to the location of Egypt at almost the same distance from the equator either to the south during the Carboniferous or to the north during the Cretaceous.

Mineralogy and Geochemistry of the Sedimentary Kaolin Deposits from Sinai, Egypt: Implications for Control by the Source Rocks

AbstractMineralogical and geochemical variations among the Carboniferous and Cretaceous sedimentary kaolin deposits from Sinai provided an opportunity to examine the effect of the source area on compositions of the deposits. The Carboniferous kaolin deposits are mineralogically and geochemically heterogeneous. The Khaboba and Hasbar deposits consist of kaolinite, quartz, anatase, illite, chlorite, zircon, and leucoxene. The shale-normalized rare earth element (REE) patterns of the Khaboba deposit showed a slight LREE over HREE enrichment ((La/Yb)SN = 1.19–1.51) with a MREE depletion (Gd/Gd*SN = 0.51–0.75), while the Hasbar kaolin had a MREE enrichment. The Abu Natash kaolin deposit consisted of kaolinite, anatase, and a little quartz with larger TiO2, Cr, and V and smaller Zr and Nb contents compared to other Carboniferous deposits. The shale-normalized REE patterns of the Abu Natash deposit exhibited a positive Eu anomaly (Eu/Eu*SN = 1.28–1.40) and a MREE enrichment (Gd/Gd*SN = 1.41–2.05). The Cretaceous deposits were relatively homogeneous in terms of mineralogical composition and geochemistry and are composed of kaolinite, quartz, anatase, rutile, zircon, and leucoxene. The Cretaceous kaolin deposits showed mostly flat shale-normalized REE patterns with a variable LREE depletion.The presence of illite and chlorite, the absence of rutile, large Zr and Nb contents, and the REE patterns suggested a component of weathered low-grade metasediments as a source for the Carboniferous deposits in the Khaboba and Hasbar areas, while the large Ti, Cr, and V, and small quartz contents indicated mafic source rocks for the Abu Natash deposit. The abundance of high-Cr rutile and the absence of illite and chlorite, and large Zr, Ti, Cr, and V contents suggested a mixture of medium- to high-grade metamafic and granitic rocks as source rocks for the Cretaceous kaolin deposits. The occurrence of alkaline rocks in the source of the deposits studied was identified by high-Nb contents and the presence of bastnaesite. The mineralogical and geochemical heterogeneity and lesser maturity of the Carboniferous deposits suggested local sources for each deposit and their deposition in basins close to the sources. The mineralogical and geochemical homogeneity and maturity of the Cretaceous deposits, on the other hand, indicated common sources for all deposits and their deposition in relatively remote basins.

Advances in selective flocculation processes for the beneficiation of kaolin

Selective flocculation enables the production of high-brightness kaolin products from kaolin ore once considered too poor in quality for beneficiation into paper-coating pigments. Anatase, Ti(1−X)FeXO2, with X = 0 to 0.05, is a common iron-bearing impurity in sedimentary kaolin that can be unresponsive to kaolin beneficiation processes, such as magnetic separation, due to its extremely fine particle size (<0.3 µm), or chemical bleaching, because of its chemical stability. Described here are selective flocculation technologies that separate anatase by flocculating anatase or flocculating kaolinite from dispersed slurries. Applying the advances in the chemical and mechanical dispersion of ultrafine particles and the selective aggregation of kaolinite or anatase particles have resulted in the selective flocculation processes practiced today that have increased process recoveries from those technologies practiced beginning in the 1960s.

Mineralogy of Kaolin Minerals and Its Relation to the Genesis of Sedimentary Kaolin Deposits around Nagoya

Mineralogy of Kaolin Minerals and Its Relation to the Genesis of Sedimentary Kaolin Deposits around Nagoya

The geology and mineralogy of a range of kaolins from the Santa Cruz and Chubut Provinces, Patagonia (Argentina)

In the Santa Cruz and Chubut provinces, Patagonia, Argentina, kaolin deposits were formed by “in situ” alteration of volcaniclastic rocks, such as the Bajo Grande, Chon Aike or Marifil Formations, or by erosion, transportation, and deposition of residual clays in small basins. This paper describes the genesis; geology; mineralogy; major, minor, and trace element geochemistry; grain size distribution; and specific surface area of natural and washed kaolins in an attempt to understand their behavior in the ceramic process. The sedimentary clays of the Baqueró Fm Lower Member, related to the Bajo Grande basement, are kaolinitic–smectitic, very fine-grained, and with a very high specific surface area. The clays related to the Chon Aike or Marifil Fms are kaolinitic, showing intermediate values of specific surface area and a coarser particle size distribution, associated with quite a fine-grained texture. The Baqueró Fm Upper Member received a considerable pyroclastic supply, fostering the development of a fine-grained clay in which kaolinite (± halloysite) with higher values of kaolinite crystal order prevailed. Primary kaolins – derived from weathering of pyroclastic sequences of Chon Aike and Marifil Fms – are coarse-grained, composed of kaolinite + quartz ± halloysite and exhibit a very low specific surface area. Alteration of mostly crystalline pyroclastics yielded ordered kaolinite and illite (+ halloysite) with a fine particle size distribution and intermediate values of specific surface area. Alteration of mainly vitreous pyroclastics produced halloysite (+ kaolinite) with a fine-grained texture and moderately high values of specific surface area. A supergene origin of primary kaolins is inferred on the basis of palaeoclimatic and geochemical evidence that corroborates stable isotopic data. The mineralogy, grain size, and textural characteristics of clays are controlled by parent rock composition (primary kaolins) or by provenance and proximity to source areas (sedimentary kaolins).

Inheritance vs. neoformation of kaolinite during lateritic soil formation: A case study in the middle Amazon basin

AbstractThe tropical weathering of sedimentary kaolin deposits from the plateaux surrounding Manaus (Alter do Chao formation, Amazon basin, Brazil) leads to the in situ formation of thick kaolinitic soils. The structural changes of kaolinite have been investigated quantitatively by infrared spectroscopy and electron paramagnetic resonance. Both techniques consistently show that each sample contains two types of kaolinite in various proportions. The progressive decrease in kaolinite order from the bottom to the top of the profile results from the gradual replacement of an old population of well-ordered kaolinite, typical of the underlying sedimentary kaolin, by a more recent generation of poorly ordered soil kaolinite. The vertical pattern of kaolinite replacement differs from that of the transformation of Fe oxides and oxyhydroxides previously observed in the same profile. The inherited fraction of well-ordered kaolinite ranges from 60% at a depth of 9 m to 30% in the upper levels of the soil. The persistence of sedimentary kaolinite in the upper horizons suggests that the rate of kaolinite transformation is relatively slow at the time scale of lateritic soil formation. Kaolinite inheritance unlocks the lateritic record of past weathering conditions.

Geobacter pickeringii sp. nov., Geobacter argillaceus sp. nov. and Pelosinus fermentans gen. nov., sp. nov., isolated from subsurface kaolin lenses

The goal of this project was to isolate representative Fe(III)-reducing bacteria from kaolin clays that may influence iron mineralogy in kaolin. Two novel dissimilatory Fe(III)-reducing bacteria, strains G12(T) and G13(T), were isolated from sedimentary kaolin strata in Georgia (USA). Cells of strains G12(T) and G13(T) were motile, non-spore-forming regular rods, 1-2 mum long and 0.6 mum in diameter. Cells had one lateral flagellum. Phylogenetic analyses using the 16S rRNA gene sequence of the novel strains demonstrated their affiliation to the genus Geobacter. Strain G12(T) was most closely related to Geobacter pelophilus (94.7 %) and Geobacter chapellei (94.1 %). Strain G13(T) was most closely related to Geobacter grbiciae (95.3 %) and Geobacter metallireducens (95.1 %). Based on phylogenetic analyses and phenotypic differences between the novel isolates and other closely related species of the genus Geobacter, the isolates are proposed as representing two novel species, Geobacter argillaceus sp. nov. (type strain G12(T)=ATCC BAA-1139(T)=JCM 12999(T)) and Geobacter pickeringii sp. nov. (type strain G13(T)=ATCC BAA-1140(T)=DSM 17153(T)=JCM 13000(T)). Another isolate, strain R7(T), was derived from a primary kaolin deposit in Russia. The cells of strain R7(T) were motile, spore-forming, slightly curved rods, 0.6 x 2.0-6.0 microm in size and with up to six peritrichous flagella. Strain R7(T) was capable of reducing Fe(III) only in the presence of a fermentable substrate. 16S rRNA gene sequence analysis demonstrated that this isolate is unique, showing less than 92 % similarity to bacteria of the Sporomusa-Pectinatus-Selenomomas phyletic group, including 'Anaerospora hongkongensis' (90.2 %), Acetonema longum (90.6 %), Dendrosporobacter quercicolus (90.9 %) and Anaerosinus glycerini (91.5 %). On the basis of phylogenetic analysis and physiological tests, strain R7(T) is proposed to represent a novel genus and species, Pelosinus fermentans gen. nov., sp. nov. (type strain R7(T)=DSM 17108(T)=ATCC BAA-1133(T)), in the Sporomusa-Pectinatus-Selenomonas group.

Kaolin deposits at Melthonnakkal and Pallipuram within Trivandrum block, southern India

The kaolin deposits at Melthonnakkal and Pallipuram mines form part of the Warkalli Formation belonging to the Tertiary sequence in southern Kerala and occur at the boundary between the Tertiary sequence and Precambrian granulite facies metapelites (khondalites). The sedimentary clays are composed mainly of kaolinite, quartz and gibbsite. XRD and SEM studies have revealed that kaolinite is well-crystallized variety and the platy crystals are scarcely broken in the sedimentary clays. These sedimentary kaolins are considered to have been formed by intense tropical weathering of the khondalites, and subsequently transported and deposited with high organic input into lakes near the weathering crust over the basement rock. Besides, the surficial parts of the sedimentary deposits are extensively lateritized with the formation of goethite and hematite by Quaternary tropical weathering processes.