Kaolinite Deposits Research Articles

High-cellulose content of in-situ Miocene fossil tree stumps and trunks from Lusatia lignite mining district, Federal Republic of Germany

Second Miocene Seam Complex (2nd MFK; germ.: 2. Miozäner Flözkomplex) holds many in-situ, not permineralised fossil tree stumps and trunks with high-cellulose contents. The state of preservation of a set of in-situ fossil trees (Taxodioxylon cryptomerioides, Sciadopityoxylon wettsteinii, and Quasisequoioxylon piskowitzense) collected from three open-cast mines (Welzow-Süd, Meuro, and Piskowitz) in Lusatia lignite mining district, Federal Republic of Germany was investigated using a multi-method research schema.Examination of preservation state of thermally immature fossil woods revealed: (1) well-preserved (non-deformed, non-degraded, and non-flattened) textinite, (2) a retained structural integrity represented by multilayered (multi-zoned) cells with primary, secondary cell wall, and middle lamella, (3) microfracturing restricted to secondary walls only, (4) preservation of polyphenolic parenchyma cells (PP cells), (5) excellent preservation of pits in ray tracheids, (6) presence of amorphous silica (opal-A) coating, and (7) crystalline silica (opal-CT) fillings of small-bladed crystals.Thermogravimetric analysis results showed dissimilar gelification status of fossil samples, supporting chlorite holocellulose assay results. The latter indicated anomalously high-cellulose values (15.6–37.6% holocellulose). The micro-FTIR data obtained revealed an excellent preservation of both hemicellulose (bands at 1740 and 1245 cm−1) and cellulose (bands at 1110 and 1040 cm−1). Micro-FTIR spectrometry indicated lack of preferential hydrolytic removal of polysaccharides in examined samples.Biomarker patterns in lignite revealed forested and prevailing reed-mire vegetation. The results indicated lower contribution of Cupressaceae and emergent macrophyta to precursor organic matter of Welzow-Süd in comparison to Piskowitz lignite. Piskowitz lignite formed in permanent mire with stable water table under reducing, mesotrophic conditions. In contrast, more pronounced water level fluctuations (reducing to slightly oxic settings) and/or post-depositional events are postulated for Welzow-Süd samples.Biomarker assemblages obtained from fossil wood show a distinct dominance of diterpenoids and δ13C values (−24.6 ‰ to −20.3 ‰) that clearly confirm gymnosperm sources. Distributions of diteprenoids and sesquiterpenoids, as well as fatty acids indicate the higher amount of saturated diterpenoids (pimarane, abietane) in fossil than in modern wood. This indicates reducing conditions promoting hydrogenation reactions. In addition to low Eh, preservation of cellulose in fossil wood was also favored by acidic conditions, very low degrees of aerobic fungal degradation, and protection of wood by Cupressaceae-derived resins.While δ13C values of fossil wood are generally consistent with stratigraphic trends and chemotaxonomical classification, slightly elevated δ13C values recorded in T. cryptomerioides and S. wettsteinii in Welzow-Süd and Meuro open-cast mines, respectively, compared to published δ13C data of fossil gymnosperm wood are also indicative for good cellulose preservation.Both preservation of in-situ Miocene fossil stumps and trunks and retention of high-cellulose contents are suggested to be related to high-amplitude temporal fluctuations associated with repeated eustatically-controlled wet-dry cycling inducing: (1) weathering of tuff- and rhyolite-dominated acidic volcanics and Lausitz granodiorite, (2) associated erosion of saprolites, and (3) peat-sourced circulation of humic acid- and fulvic acid-rich waters. The latter led to the formation of Middle Miocene kaolinite deposits, as well as to the release of silicic acid and its subsequent precipitation in form of opal-A. The latter influenced preservation of high-cellulose contents in fossil wood.

Geology and exploration indications of the lithocap in Qianpu area, Luzong Basin, Anhui

The lithocap is a large-scale alteration including silicification, advanced argillic and argillic that developed near the surface by hydrothermal activities. It is helpful for exploring high-sulfidation epithermal deposits and porphyry deposits in its root and deep parts, respectively, and is used as a new prospecting indicator. There are many minerals in the lithocap and it is difficult to identify them; alunite is the most representative mineral and one of the new minerals used to guide exploration; it plays an important role in assessing the metallogenic potential and guiding ore prospecting. The Luzong basin is dominated by iron oxide apatite deposits (IOAs). In recent years, many researchers have been searching for porphyry copper–gold deposits and epithermal deposits as studies on alunite and lithocaps in the basin have gradually been undertaken. In field explorations and investigations of the Luzong basin, the author found that in Qianpu area of the central basin, where kaolinite deposits were mainly explored in the past, Well-occurring alunite minerals and advanced argillic alterations have developed. A typical lithocap developed in Qianpu area after a series work of geology and mineralogy, such as alteration mineral species, alteration types, and alteration zoning, which were formed by the hydrothermal alteration of the volcanic rocks of the Zhuanqiao Formation. The minerals in this lithocap are mainly quartz, alunite (including aluminum-phosphate-sulfate, APS), pyrite, zunyite, dickite, pyrophyllite, kaolinite, and a small amount of illite, which are present sequentially from the center to the peripheral quartz-alunite-pyrite alteration, alunite-dickite alteration, dickite-pyrophyllite alteration, alunite-kaolinite-illite alteration, and alunite veins superimposed on quartz-alunite-pyrite alteration and alunite-dickite alteration. Three types of alunite were produced in large quantities and were formed in three kinds of environments. The I-type alunite, which was formed by hydrothermal metasomatism alteration in the early stage and is densely disseminated distribution, coexisting with quartz and pyrite, is a magmatic hydrothermal alunite. Relatively pure alunite veins (II-alunite) of varying thicknesses formed in the open space in the mid-hydrothermal period in a magmatic steam environment. The fine-grained III-alunite that coexists with kaolinite formed in the late hydrothermal period and in a steam-heated environment. The alunite produced by various origins represents multiphase hydrothermal activity in the Yanshanian period in the Qianpu area; the Na content decreased, the K and Pb content increased, and the K/Na molar ratios ranged from 2.82 to 6.58 (EPMA) and 1.59 to 3.93 (LA-ICP MS) from the early to middle and late hydrothermal stages, indicating that the formation temperatures were more than 200 °C and gradually decreased with hydrothermal evolution. There is a high-sulfidation epithermal system in Qianpu area. In combination with the specific environmental significance of zunyite indicating a high temperature and closeness to the fluid channel, as well as the characteristics and genesis of the Huangzhuyuan silver polymetallic deposit near Qianpu, it is inferred that the Qianpu-Huangzhuyuan area has prospecting potential for porphyry-epithermal deposits.

Kaolinite Deposition Dynamics and Streambed Clogging During Bedform Migration Under Losing and Gaining Flow Conditions

AbstractClogging of streambeds due to clay deposition influences the stream‐subsurface exchange flux and thus directly modulates hyporheic ecological and biogeochemical processes. Clogging of sandy streambeds has previously been studied under losing and gaining flows and during streambed movement, but not when these two flow conditions coincided. We conducted flume experiments to quantify the combined effect of moving bedforms and losing or gaining flows on kaolinite deposition and streambed clogging. The experiments were conducted by adding pulses of kaolinite in a flume packed with sand under a stream water velocity of 25 cm/s. We measured the deposition rates, dynamics of hyporheic exchange flux (HEF) and vertical hydraulic conductivity (Kv), and the vertical distribution of kaolinite at the end of the experiments under two losing and two gaining flows (Darcy velocity of 10 and 20 cm/day). Kaolinite deposition led to clogging and reduction in Kv and HEF under all flow conditions. Deposition occurred faster under losing flow conditions than under gaining flow conditions. However, the changes in Kv and HEF were similar under losing and gaining flow conditions for similar kaolinite concentrations in the bed. Our results indicate that the deposition patterns of kaolinite were more influenced by bedform movement than by losing or gaining flow conditions, which is markedly different from the behavior observed under losing and gaining conditions for stationary bedforms. This implies that bedform morphodynamics control local‐scale clogging of sandy streambeds and should be accounted for when studying the hydrology of catchments at larger scales.

Kaolinite deposition from moving suspensions: The roles of flocculation, salinity, suspended sediment concentration and flow velocity/bed shear

ABSTRACTUnderstanding how mud moves and deposits is essential for conceptualizing the dynamic nature of surface environments and their ancient counterparts. Experimental study has largely been pursued by civil engineers, using kaolinite as an active ingredient. Yet, applying their data to the physical comprehension of mudstone sedimentology is hampered by multiple flume configurations between labs, and data sets tailored to specific engineering needs. The need for a better grasp of underlying processes is acute, given recent flume studies that show that moving suspensions form large bedload floccules, migrating floccule ripples and bed accretion under currents capable of moving sand grains. To advance mudstone sedimentology, integrated study of suspended sediment concentration, salinity and bed shear stress on the deposition of floccules is crucial. Described here is a set of tightly controlled experiments that explored suspended sediment concentrations from 70 to 900 mg/l, freshwater, brackish and marine salinities, flow velocities in the 5 to 50 cm/s range (equivalent to 0.01 to 0.58 Pa bed shear), measured the size of in‐flow and bedload floccules, and the critical velocity of sedimentation that marks the onset of sustained bedload accumulation. The critical velocity of sedimentation of kaolinite clays is in the 26 to 28 cm/s flow velocity range (0.22 to 0.25 Pa), appears insensitive to a wide range of suspended sediment concentrations and salinities, and coincides with the formation of sand‐size bedload floccules. Further decrease of flow velocity/bed shear stress is accompanied by a steady increase in the size of bedload floccules. Large bedload floccules appear to form in the high‐shear basal part of the flow, a phenomenon requiring further investigation. Better understanding of the mechanisms that facilitate mud deposition from moving suspensions is critical for more realistic assessments of the depositional conditions of mud and mudstones, as well as for refining predictive models for the flux of fine‐grained sediments across the Earth's surface.

Kaolinite clays as a source of raw materials for the aluminum industry of the Republic of Kazakhstan

Kaolinite clays can serve as an additional source of alumina in the Republic of Kazakhstan. The most promising is the Alekseevsky kaolinite deposit. To obtain high-quality kaolinite and quartzite products, it is necessary to develop special enrichment techniques, since no satisfactory results were achieved when using standard methods of gravitational enrichment of kaolinites. The paper presents the results of studies of the effect of preliminary chemical activation during the processing of kaolinite clays of the Alekseevsky deposit. Previously, the method of preliminary chemical activation of raw materials in a solution of sodium bicarbonate has proven itself well in the processing of various mineral raw materials. It was determined that during the preliminary chemical activation in a solution of sodium bicarbonate, changes occurred in the phase composition of the kaolinite fraction: the content of muscovite decreased almost twice; the phase of sodium aluminosilicate was formed. The dependence of the yield of Al2O3 in the kaolinite fraction on the temperature of chemical activation, duration, and the ratio of L:S and the concentration of the sodium bicarbonate solution during chemical activation. The optimal mode of preliminary chemical activation of kaolinite clay of the Alekseevsky deposit has been established: the temperature is 150 oC, the duration is 120 minutes and the concentration of sodium bicarbonate solution is 120 g/dm3. A basic technological scheme is proposed for the processing of kaolinite clays.

Genesis of Kaolinite Deposits in the Jungar Coalfield, North China: Petrological, Mineralogical and Geochemical Evidence

AbstractPetrological, mineralogical and geochemical studies carried out on kaolinite deposits in Haerwusu surface mine, Jungar Coalfield, northern Ordos Basin, North China, define their characteristics, ore genesis and economic interest. Based on the crystalline size, two different types of kaolinite rocks, cryptocrystalline and grainy, were identified under the microscope. XRD data show that kaolinite is the predominant mineral, associated with boehmite, magnesite, anatase, pyrite, diaspore and calcite. However, high boehmite content (mean 70%) shows up in the middle layers. Kaolinite minerals present homogeneous shape and a good crystallinity (HI = 0.96–1.26). Geochemical studies show that the SiO2/Al2O3 molar ratio of kaolinite is close to the theoretical value, and the contents of Na2O, K2O, CaO, MgO are less, suggesting a strong chemical weathering environment. The REE and Eu anomalies show a close relationship between kaolinite and the Yinshan Oldland granite. A Ce anomaly reflects a continental sedimentary environment with shallow water. A temperature range of 26.7–34°C was calculated on the basis of the isotopic signatures (δ18O, δD) of the kaolinite rocks. All these data indicate that the formation of the kaolinite is caused mainly by the dissolution, coagulation, precipitation and recrystallization of aluminosilicate clastics in acidic conditions. The formation of boehmite in the middle layers indicates that the source rocks have changed. Boehmite is mainly formed by dehydration and compaction of an aluminum‐rich colloid which transported into peat swamp during diagenesis. In addition, it formed by desiliconization of kaolinite under acidic conditions. Due to its high kaolinite content (up to 90%) and low iron mineral content (less than 1%), and good crystallinity, kaolinite deposits occurred at Haerwusu surface mine probably have great economical value in the future.

Dynamics of Hyporheic Exchange Flux and Fine Particle Deposition Under Moving Bedforms

AbstractDeposition of fine suspended particles can reduce hyporheic exchange flux (HEF), which may result in impairment of various ecological processes. However, the dynamics of fine particle deposition and streambed clogging are still not well understood, especially when the bed is in motion. We conducted flume experiments to study the effects of coupled sand‐clay dynamics on HEF with episodic (pulse) inputs of suspended kaolinite. Three experiments with a mobile sand bed and constant discharge were conducted with repeated injection of suspended kaolinite pulses at fixed concentration increments of 0.16, 0.41, and 0.66 g/L, respectively. HEF and participating porewater volume were assessed using tracer tests. Kaolinite deposition rates were inferred from turbidity measurements while deposition patterns were measured using core samples. We found that fine sediment primarily accumulated within a layer below the bedform scour zone, and that this layer was thicker when kaolinite was added in larger pulses. HEF declined linearly over time as kaolinite accumulated in the bed sediment; an increase of 0.1% kaolinite in the bed led to a decrease in HEF of 26.6 cm/day, regardless of the pulse concentration. However, the same kaolinite increase led to a reduction of 50% in participating pore volume for larger kaolinite pulses, versus only 30% for the smallest pulse. These results indicate that clogging occurs not just during and after high‐flow events, but also under constant flow conditions in which episodic deposition of suspended clay by HEF leads to the formation of a low‐conductivity layer in the bed.

Fine Sediment Deposition and Filtration Under Losing and Gaining Flow Conditions: A Particle Tracking Model Approach

AbstractFine particle deposition within riverbeds plays a major role in riverine ecology and biogeochemistry by altering hyporheic exchange flux. Moreover, it is ubiquitous within streams and rivers across all flow stages. However, the dynamics of fine particle deposition are still not completely understood in rivers, and continuum models like the advection dispersion equation require modifications to represent the processes accurately. To enhance understanding of fine particle dynamics, we developed a novel numerical particle tracking model that simulates fine particle deposition as a stochastic process under losing, neutral, and gaining streamflow conditions. These flow conditions generate three different velocity profiles by combining the free surface and groundwater flows. In addition, a novel aspect of our model is the storage of filtered particles to estimate concentration fields within the bed. Our simulated results are qualitatively compared with previous laboratory flume experimental results of kaolinite deposition under similar conditions. The model indicates that fine particle deposition patterns and residence time functions depend heavily on the exchange flux between stream and groundwater, as well as bed filtration properties as the deposition of particles occurs at greater depths in the losing stream condition than in the neutral and gaining cases. Therefore, the spatial pattern of particle deposition is a direct result of pore water velocity profiles, while the concentration depends on filtration dynamics within the bed.

Influence of the weathering rate on the response of granite to nanosecond UV laser irradiation

Laser ablation is an accepted cleaning technology for cultural heritage stonework. Optimized laser ablation may, however, have different side effects depending on the mineralogical composition of the stone. In the case of granitic rocks, observed side effects – colour changes, fracturing or/and mineral melting – have been attributed to laser parameter interactions with the patina to be cleaned from this complex rock with a grained texture and polymineral composition. We describe the influence of the weathering degree of a granite on its response to laser irradiation, confirming that the existence of secondary minerals in the rock influences the intensity and typology of side effects. Knowledge of this influence is of special relevance to the conservation of heritage built with Western European Variscan granites, which are already slightly weathered in quarry.Two specimens of the same Variscan granite taken from the same quarry but with different colours (suggesting different weathering rates) were subjected to nanosecond (ns) Nd:YVO4 laser irradiation, working at 355 nm (UV irradiation) under different fluences. The specimens responded very differently to laser irradiation in terms of colour changes and resistance of the main minerals to laser radiation. The existence on one of the specimens of kaolinite deposits covering feldspar grains and Fe oxyhydroxides filling fissures seemed to be the reason for the different response to laser radiation. Our findings would suggest the need, during laser interventions, to take into account – in addition to texture and porosity – the degree of weathering of this particular kind of granite, widely used in the architectural and archaeological heritage of Western Europe.

Impact of Solution Chemistry on Deposition and Breakthrough Behaviors of Kaolinite in Silica Sand

AbstractUnderstanding the transport and deposition behavior of particles within porous media is of importance because clogging can degrade the long-term performance of hydraulic infrastructure (e.g...

Interactions Between Suspended Kaolinite Deposition and Hyporheic Exchange Flux Under Losing and Gaining Flow Conditions

AbstractFine particle deposition and streambed clogging affect many ecological and biogeochemical processes, but little is known about the effects of groundwater flow into and out of rivers on clogging. We evaluated the effects of losing and gaining flow on the deposition of suspended kaolinite clay particles in a sand streambed and the resulting changes in rates and patterns of hyporheic exchange flux (HEF). Observations of clay deposition from the water column, clay accumulation in the streambed sediments, and water exchange with the bed demonstrated that clay deposition in the bed substantially reduced both HEF and the size of the hyporheic zone. Clay deposition and HEF were strongly coupled, leading to rapid clogging in areas of water and clay influx into the bed. Local clogging diverted exchanged water laterally, producing clay deposit layers that reduced vertical hyporheic flow and favored horizontal flow. Under gaining conditions, HEF was spatially constrained by upwelling water, which focused clay deposition in a small region on the upstream side of each bed form. Because the area of inflow into the bed was smallest under gaining conditions, local clogging required less clay mass under gaining conditions than neutral or losing conditions. These results indicate that losing and gaining flow conditions need to be considered in assessments of hyporheic exchange, fine particle dynamics in streams, and streambed clogging and restoration.

Nature, genesis and industrial properties of the kaolin from Masirah Island, Oman

AbstractKaolin deposits >10 m thick overlie unconformably a Mesozoic ophiolite sequence at Jabal Humr, Masirah Island, Oman. The clay's mineralogical and chemical composition, plasticity and moisture content were measured to determine its genesis and suitability for commercial usage. The clay-rich raw material contains 76–94% kaolinite and varying amounts of quartz (micro sheets coating kaolinite) and calcite as well as secondary sulfates. The mode of occurrence, an associated shallow-marine iron oolite/pisolite unit, various secondary minerals which can only form in a gossan environment (oxidation zone of a much older sulfide deposit), and minerals such as gypsum that are highly unstable within a laterite, have led to the conclusion that the Jabal Humr kaolinite deposit cannot have the lateritic origin that has been suggested previously. Rather, it must have formed in a coastal marine environment with a subsequent strong geochemical overprint from the underlying gossan environment, after being enveloped by Tertiary carbonates. A high plasticity and its light colour after firing indicate that this material is suitable for industrial use, especially in pottery. Occasional high contents of up to ∼25% extremely fine-grained quartz (sheet-like, <50 nm thick) reduce the need for quartz addition during the processing for ceramic materials; such natural kaolinite-quartz mixtures already produce a suitable blend of materials. The possible occurrence of spalling during or after firing, caused by the sporadic presence of accessory calcite, can be avoided by by further addition of quartz which leads to the formation of calcium silicate.

Influence of secondary compression on undrained strength of soft kaolinites

ABSTRACTSoft kaolinite deposits of marine origin are encountered as foundation soils in many parts of the world. The well-developed flocculated structure of kaolinite-bearing marine deposits is amenable to alterations from leaching of pore solution salts, loss of overburden, and secondary compression. Secondary compression causes densification of microstructure that may impact the viscous resistance, soil stiffness, and undrained shear strength of kaolinite-bearing marine deposits. This study examines the influence of secondary compression on viscous resistance and constrained stress–strain modulus of soft kaolinites prepared in synthetic seawater and sodium chloride solutions. The impact of secondary compression on undrained shear strength is interpreted from changes in microstructure, percent monovalent cation concentration, viscous resistance, and constrained stress–strain modulus. Kaolinite specimens experience reduction in void space during secondary compression. Breakdown of edge–face (E–F) and edge–edge (E–E) contacts of kaolinite particles during secondary compression and creation of interlocking zones is observed from scanning electron micrograph studies. Breakdown of E–F and E–E contacts is considered responsible for reduction in constrained stress–strain modulus during secondary compression. Concomitant, creation of interlocking zones at particle contacts increases the viscous resistance of microstructure that enhances the undrained shear strength of soft kaolinites.

Mineralogical and Geochemical Characteristics and Genesis of the Gülzelyurt Alunite-Bearing Kaolinite Deposit Within the Late Miocene Gödeles Ignimbrite, Central Anatolia, Turkey

AbstractThe Güzelyurt kaolinite deposit is an important source of raw material for the ceramics industry in Turkey. No detailed mineralogical or geochemical characterizations of this deposit have been undertaken previously and these were the goals of the present study. The Güzelyurt alunite-bearing kaolinite occurs along a fault zone in the Late Miocene Gödeles ignimbrite, which consists of dacitic and andesitic tuffs. Horizontal and vertical mineralogical zonations with gradual transitions were observed within the alteration zone. The inner kaolinite, alunite, and 7 Å halloysite zones progress horizontally outward to a smectite zone; and native sulfur- and cinnabar-bearing alunite with 7 Å halloysite and porous silica zones increase as one progresses up through the profile. Fe-(oxyhydr)oxide phases associated with native sulfur and cinnabar demonstrate that multiple hydrothermal-alteration processes resulted in kaolinization and alunitization of the deposit. The kaolinization of feldspar, Fe-(oxyhydr)oxidation of hornblende and mica, the presence of kaolinite as stacked and, locally, book-like forms, and of 7 Å halloysite tubes, and smectite flakes as a blanket on altered volcanic relicts indicate an authigenic origin for this deposit. The leaching of Si + Mg + K and Ba + Rb, the retention of Sr, the enrichment of light rare earth elements relative to the heavy rare earth elements, and the negative Eu anomalies suggest that fractionation of plagioclase and hornblende occurred within the volcanics. The oxygen- and hydrogen-isotopic values of the kaolinite, 7 Å halloysite, smectite, and smectite + kaolinite fractions reflect a steam-heated environment at temperatures in excess of 100°C. An increase in the δD and δ18O values of 7 Å halloysite relative to kaolinite suggests its formation under steam-heated magmatic water, the mixing of steam and meteoric water near the surface, and evaporation. The oxygen- and sulfur-isotopic compositions of alunite suggest the direct influence of steam-derived sulfur. The Güzelyurt alunite-bearing kaolinite deposit is inferred to have formed after an increase in the (Al±Fe)/Si ratio and the leaching of alkali elements, which are driven by the sulfur-bearing low-temperature hydrothermal alteration of feldspar, hornblende, and volcanic glass under acidic conditions within the Neogene dacitic and andesitic tuffs.

Formation of a hydrothermal kaolinite deposit from rhyolitic tuff in Jiangxi, China

The Longmen kaolinite deposit is one of the largest hydrothermal clay deposits of Ganxi volcanic basin (northern Wuyi Mountain area, China). The pristine host rocks are rhyolitic crystal-vitric tuff and minor lapilli tuff from the Late Jurassic Ehuling Formation. The ore consists of kaolin-group minerals (kaolinite, dickite), pyrophyllite with minor quartz, sericite, pyrite, etc.. From the host rocks to the transition zones (altered rocks) then to the vein ores, contents of SiO2 and TFe2O3 decrease, whereas Al2O3 and LOI increase, consistent with the contents increase of kaolin minerals and pyrophyllite in the samples. The total REE abundances of the ores are much lower than that of the host and altered rocks, Rb, Nb, Nd, Zr, Ti and Y are significantly depleted. Apparent zoning features of bulk geochemistry and mineral component reflect that the kaolinite deposit occurred at the expense of the host rock by ascending hydrothermal fluids with distinct removal of SiO2, TFe2O3, Na2O, K2O. According to the mineral assemblage, the formation temperature of this deposit falls within the range of 270–350 °C. With regard to the industrial applications, the kaolinized ores are suitable for use in ceramics and gemologic materials crafted for seal stones. Moreover, in mineralogical terms, this deposit is also proved to be an excellent example for studying channeled hydrothermal alterations of rhyolitic tuff.

Genesis of the hydrothermal Karaçayır kaolinite deposit in Miocene volcanics and Palaeozoic metamorphic rocks of the Uşak-Güre Basin, western Turkey

The Karaçayır kaolinite deposit, situated in the Uşak-Güre basin of western Turkey, is hosted by rhyolite and andesite of the Miocene Dikendere volcanics, and by muscovite schist, glaucophane schist, talc schist and chlorite schist of the Palaeozoic Eşme Formation. The association of kaolinization with silicification and Fe-oxidation, and the presence of pyrite, chalcopyrite and gypsum, suggest that hydrothermal alteration processes in the volcanics and schists were controlled by faults. Thus, prevalent kaolinite is associated with quartz, smectite, illite and opal-CT in the centre of the deposit, with relative increases in smectite, illite, chlorite and Fe (oxyhydr)oxide phases outwards and upwards. Texturally, sanidine and plagioclase crystals are sericitized and kaolinized in rhyolite and andesite respectively, whereas muscovite, chlorite and feldspar in schists exhibit partial kaolinization and illitization. Micromorphologically, authigenic kaolinite, having hexagonal book-like and vermiform textures, occurs as rims on feldspar, muscovite and chlorite suggesting a dissolution-precipitation mechanism. Pyrite, locally transformed to hematite, is euhedral to subhedral, with grain sizes of ±400 µm. Iron occurs as Fe^{2+} and Fe^{3+} within the structures of the Karaçayır kaolinites and smectites, as determined by Mössbauer spectroscopy. Enrichment of Mg, Ca and Fe in the kaolinite deposit is related to the presence of smectite, calcite, dolomite, pyrite ± chalcopyrite, goethite and hematite. Kaolinized volcanic and schist samples from the Karaçayır area are characterized by 35.77-87.58% SiO_2, 3.27-22.83% Al_2O_3, 0.91-9.16% Fe_2O_3, 0.01-5.94% K_2O and 0.26-12.41% MgO, revealing moderate degrees of kaolinization ± illitization ± smectitization coexistent with high degrees of silicification and Fe (oxyhydr)oxidation. Increases of Fe_2O_3, MgO, CaO and Zr and decreases of Rb, Sr, and Ba (except for decreases in partially altered volcanics) in kaolinite samples adjacent to schists and volcanic rocks suggest that kaolinite developed by alteration of both schists and volcanics. The Karaçayır kaolinite and smectite have \delta^{18}O and deltaD values ranging from 11.6 to 20.4%o, and -79%o to -112%o, respectively. Using the isotopic fractionation factor (\alpha), the temperatures of formation for the Karaçayır kaolinite and smectite were determined to be 61.6-131.7 °C and 61.2-148.9 °C, respectively, and negative \delta^{34}S values for pyrite, chalcopyrite and gypsum reflect formation under the influence of hydrothermal activity; this assumption is supported by isotope equilibrium temperatures of 80-125 °C calculated from pyrite-chalcopyrite pairs. Thus, the Karaçayır kaolinite deposit formed by an increase in Al±Fe/Si under acidic environmental conditions, which facilitated epithermal alteration of feldspar and volcanic glass in volcanic rocks, and muscovite, chlorite and feldspar in

Alum Production from some Nigerian Kaolinite Deposits

The Development of Sustainable Processing Technologies for the Vast Mineral Resources Available in Nigeria and their Varied Applications Is a Major Pursuit by the Federal Ministry of Science and Technology. in this Work, Alum Was Produced from Three Different Kaolin Deposits in Nigeria Namely Kankara Brown, Bauchi and Kankara White by Acid Dealumination of the Metakaolin Obtained by Calcination of the Beneficiated Kaolinites and the Yields Were Measured to Ascertain the Process Repeatability. the Reproducibility Studies Carried Out on Samples from each Deposit Showed a Mean Yield of 80 %, 92 % and 87 % and Standard Deviation of 2.50 %, 1.063 % and 1.296 %, for Kankara Brown, Bauchi and Kankara White Respectively. the Values from the Three Deposits Fall within 3 Standard Deviations of the Mean in Accordance with the 68-95-99.7/three-Sigma Rule. the Alum Quality Also Compares Well with Available Commercial Alums in the Market. BET Analysis, of the Alumina Obtained by Calcination of the Alum (Kankara White), Gave a Surface Area of 192.2441m2/g Comparable to Commercial Alumina. these Results Suggest/establishes the Huge Possibility of Commercial Alum Production, Including Alumina, Using Kaolinite Clay from these Deposits as Starting Materials.

전남일원 점토광상의 광물 및 지화학적 특성과 효과적 탐사를 위한 건층의 선정

전남지역의 점토광상은 그 구성광물이 단사정계형 엽납석(pyrophyllite), 1T형 고령석(kaolinite)을 주로 하고 부구성 광물로서 견운모, 석영 및 장석류를 포함한다. 이들 점토광상은 유사한 시기에 유사한 성분을 가진 화산암류로부터 생성되었으며, 각 광상은 광물학적으로 엽납석과 고령석 중의 하나를 우세하게 포함하는 경향이다. 고령토 광상은 주로 다이아스포나 강옥을 포함하지 않지만, 광체 상부에 명반석을 흔히 포함한다. 반면에 강옥이나 다이아스포는 납석 광상에서 흔히 수반된다. 점토광체 상부의 규화응회암류와 응회암류 등 지질시대가 젊어짐에 따라 엽납석 및 고령석의 양은 감소하는 경향이며, 마침내는 나타나지 않게 된다. 반면에 견운모, 석영 및 사장석류는 미약한 상부층에서 흔히 나타난다. 대부분의 점토광체는 상단부에 저색 응회암층이 오고, 그 상부로는 규화대층, 응회암층, 그리고 최상부에 각력 응회암층이 온다. 화학성분 분석에 의하면, <TEX>$Al_2O_3$</TEX>는 중-저급의 점토광체뿐 아니라 응회암류에서도 다소 높게 나타내며, 그 이유는 응회암류의 주요 구성광물인 사장석 때문이다. 광체와 모암에서 <TEX>$Na_2O$</TEX>와 CaO는 비교적 낮은 함량을 나타내나, <TEX>$K_2O$</TEX>는 광체에서 좀더 낮게 나타난다. 점토의 작열 감량은 명반석이나 다이아스포를 포함하는 부분에서는 특히 높게 나타나는 것은 이들이 포함하는 <TEX>$Al_2O_3$</TEX> 및 <TEX>$SO_4$</TEX> 성분에 의한다. 희토류함량분석에 의하면, 경희토류가 중희토류보다 많이 포함되는 경향이며, 다소 미약하지만 부의 유러피움(Eu)이상대를 나타낸다. 대부분의 점토광체는 주로 유백-담회색의 미립이며 층리가 양호하여 야외에서 구분이 어렵지 않은 경우가 많지만, 괴상광체 등이 나타나는 곳에서의 효과적인 탐사를 위해서는 광체 상부 지층 중에서 확인되는 특징적 지층을 선정하는 것이 바람직하다. 전남지역에서 광체를 배태하는 층의 상단부에 연속성이 양호한 저색점토/응회암과 함께 그 상부로 층리와 연장성이 지극히 좋은 규화대가 확인되며, 광물조성 상으로도 광체 및 인근 지층과의 구분이 확실하므로 효과적인 점토광체 탐사를 위한 건층(key bed나 mark horizon)으로서의 역할이 가능하다. Clayey ores of the Jeonnam province mainly consist of pyrophyllite (monoclinic), kaolinite (1T), and minor amounts of quartz, muscovite, and feldspars. Mineralogical studies revealed that two kinds of clay minerals were mainly produced from the volcanic sediments with similar ages and compositions. Kaolinite deposits sometimes contain neither diaspore nor corundum, but alunites are often found in the upper portions of the kaolin ore bodies. On the other hand, corundum and diaspore are commoner in the pyrophyllite deposits than the kaolin deposits. As ages of rock formations are becoming younger, amounts of pyrophyllite and kaolinite are rather radically decreased, and finally disappeared. But muscovite, quartz, and plagioclase feldspars are inclined to be preserved because of weak alteration. Most of clay ore bodies contain purple tuff beds on the uppermost portion, and silicified beds, tuff, and lapillistone are found in an ascending order in the most of clay quarries. Chemical analyses show that higher contents of <TEX>$Al_2O_3$</TEX> might not necessarily be due to the argillization, since some tuffs contain higher <TEX>$Al_2O_3$</TEX> contents originated from feldspars. <TEX>$SiO_2$</TEX> contents are fairly higher in the silicified beds than in those of adjacent formations, which might have been introduced from the ore bodies. And <TEX>$K_2O$</TEX> contents are obviously lower than those of <TEX>$Na_2O$</TEX> and CaO in the ores and their vicinities. Ignition losses of some of clays represent much higher contents than those of the ordinary ones because of the sporadic presence of alunite, diaspore and corundum which are accompanied with lots of <TEX>$SO_4$</TEX> and <TEX>$Al_2O_3$</TEX> contents. REE (rare earth element) abundances of most of volcanics and clay ores show rather higher LREE (light rare earth elements) contents, and represent small to moderately negative Eu anomalies. Though most of ores ususally show milky white color, fine-grained and well bedded formations which could be easily discernible in the most of outcrop. But more distinct characteristics are desirable where rather massive ore bodies exist. Purple tuffs and silicified beds above the ore bodies would be useful as marker horizons/key beds since they have rather obvious lithology, extension and mineralogy than those of other adjacent formations.

Mineralogy, micromorphology, geochemistry and genesis of a hydrothermal kaolinite deposit and altered Miocene host volcanites in the Hallaçlar area, Uşak, western Turkey

AbstractThe Hallaçlar kaolinite deposit of the Uşak Province (western Turkey) is hosted by dacite, andesite and siliceous materials of the Miocene Karaboldere volcanites. Mineralogical zonation, such as the prevalence of kaolinite at the centre of the deposit, coexisting with silica polymorphs such as quartz and cristobalite along with feldspar and hornblende, and a relative increase of smectite, illite, chlorite, and Fe-oxide/-hydroxide phases outward and upward, demonstrate that hydrothermal-alteration processes resulted in kaolinization. Micromorphologically, kaolinite occurs as pseudohexagonal blocky kaolinite with coarse-grained quartz in microfractures, and the presence of relatively fine-grained vermiform kaolinite that edges volcanic materials indicates that kaolinite developed in several phases coexisting with goethite, lepidocrocite, hematite, pyrite, jarosite, alunite, and gypsum/anhydrite with smectite in fractures. The highly crystallized Hallaçlar kaolinite is identified by: (1) sharp reflections at 7.23 and 3.57 Å, with triplet and doublet non-basal reflections; (2) sharp infrared spectral bands at 3687, 3651 and 3620 cm-1; (3) well defined, pseudohexagonal and hexagonal kaolinite crystal growth; (4) a chemical index of weathering of 98.6-100; and (5) SiO2/Al2O3ratios between 1.04 and 1.45. Enrichment of Sr and depletion of Rb+Ba, Ti, andHREErelative toLREE, with a distinct negative Eu anomaly, are responses to the fractionation of feldspar and hornblende by the hydrothermal fluid; these results are also supported by the O- and H-isotopic character and formation temperatures of the Hallaçlar kaolinite and smectite; namely, 134.1-183.4°C and 65.6°C, respectively. The negative δ34S (-20.7‰) value of gypsum/anhydrite reflects its formation from geothermal-water-derived sulphur. Under the influence of a tectonically controlled hydrothermal process, feldspar, hornblende and volcanic glass were altered, resulting in the conservation of Al and depletion of Si, Na, Ca, K, Mg and Fe in an open hydrological system such that formation of kaolinite in the central part of the deposit under acidic conditions and development of smectite and illite upward and outward under basic conditions were favoured.

Mineralogical and Geochemical Characteristics and Genesis of Hydrothermal Kaolinite Deposits within Neogene Volcanites, Kütahya (Western Anatolia), Turkey

AbstractThe Kütahya kaolinite deposits are the most important source of raw materials for the ceramics industry in Turkey. To date, no detailed mineralogical or geochemical characterizations of these materials have been carried out; the present study aims to fill that gap. The Kütahya kaolinite deposits formed by alteration of dacite and andesite tuffs related to Neogene volcanism whichwas associated withe xtensional tectonics. The kaolinite deposits contain silica and Fe- and Ti-bearing phases (pyrite, goethite, and rutile) in vertical and subvertical veins that diminish and then disappear upward. Mineralogical zonation outward from the main kaolinite deposit is as follows: kaolinite ± smectite + illite + opal-CT + feldspar; feldspar + kaolinite + quartz + smectite + illite; quartz + feldspar + volcanic glass. The veins and mineral distributions demonstrate that hydrothermal alteration was the main process in the development of the kaolinite deposits of the area. The very sharp, intense, diagnostic basal reflections at 7.2 and 3.57 Å, as well as non-basal reflections, well defined pseudohexagonal to hexagonal crystallinity with regular outlines, ideal differential thermal analysis-thermal gravimetric curves, and ideal, sharp, infrared spectral bands indicate well crystallized kaolinite. Micromorphologically, the development of kaolinite plates at the edges of altered feldspar and devitrified volcanic glass indicates an authigenic origin. Lateral increase in (SiO2+Fe2O3+MgO+Na2O+CaO+K2O)/(Al2O3+TiO2) from the center of the kaolinite deposit outward also indicates hydrothermal zonation. Enrichment of Sr in altered and partially altered rocks relative to freshvolca nic-rock samples demonstrates retention of Sr and depletion of Rb, Ba, Ca, and K during hydrothermal alteration of sanidine and plagioclase within the volcanic units. In addition, depletion of heavy rare earth elements (HREE) relative to light rare earth elements (LREE) in the kaolinized materials may be attributed to the alteration of hornblende. The negative Eu anomaly suggests the alteration of feldspar by hydrothermal fluids. The isotopic data from kaolinite and smectite indicate that hydrothermalalteration processes developed at 119.1–186.9°C and 61.8–84.5°C, respectively. Thus, the kaolinite deposits formed by hydrothermal alteration of volcanic glass, feldspar, and hornblende by a dissolutionprecipitation mechanism which operated under acidic conditions within Neogene dacite, andesite, and tuffs.