Bauxite Deposits Research Articles

Change in seismic activity and rockburst hazard in stoping at SUBR’s Kalia deposit

Seismic activity at the rockburst-hazardous deposits of SUBR causes sudden failures in underground excavations in the course of room-and-pillar mining. The regional forecast used seismological observations with determination of coordinates and energy of seismic events. This made it possible to find out that the most of seismic events was connected with natural concentrators: abrupt changes in the thickness of ore bodies down to sterile ground and faulting. Using the kriging method, the contour map was constructed for the sheetlike bauxite deposit thickness in Kalia Mine, in block 5u, Level -1220 m, being mined using the room-and-pillar system. The thickness map of the ore deposit is superimposed on the mining plan. For locating source sites of seismic events relative to the deposit, the vertical sections of the latter were constructed in different directions. The results obtained indicate the susceptibility of the ore body thickness to the effects of seismic events. Using the spatial model section, the seismic circumstances of a rock burst were determined. The numerous studies prove the dependence of energy of a seismic event on the distance between its source and a failure point. The rock mass envelope around an extraction panel where rock falls and failures take place in underground excavations after a seismic event is determined. It is revealed that the total released energy of rocks directly depends on the volume and span of the mined-out stope. With decreasing size of the test block along the strike, the specific energy density increases. The forecast calculation of the total energy of seismic events for the next excavation panel is performed. The procedure to detect the increased energy activity areas is developed. It makes it possible to locate high energy sources in advance.

Composition, environment, and economic value of the Permian to Cretaceous coated grains from Zagros and the Persian Gulf

Ooid grainstone/packstone carbonate facies of the Dalan, Kangan, and Arab formations are the main hydrocarbon reservoirs in the Persian Gulf. Based on detailed petrographic and petrophysical analyses, sedimentological and mineralogical features of the Permian to Late Cretaceous carbonate and iron-rich coated grains from Zagros and the Persian Gulf were investigated. Frequent ooids in these formations indicate a high-energy environment and a wave-dominated shallow carbonate platform. Because of wide-spread Permian–Triassic epiric seas and long-lasting periods of arid and hot climate, Permian–Triassic carbonate ooids have more vertical and lateral distribution in comparison with Late Jurassic carbonate ooids. Dolomite, calcite, and anhydrite are the major minerals of carbonate ooid grains. Early Cretaceous iron-rich ooids have been deposited above a major Late Aptian disconformity during the highstand systems tract. Ooid ironstone bulk sample X-ray diffraction (XRD) analysis shows that goethite, siderite, fluorapatite, calcite, quartz, and pyrite are the major phases of ooid ironstone deposits. This layer of iron bearing ooids could have economic importance in its outcrops in the Zagros area. Late Cretaceous iron-rich coated grains (pisoid–oncoids) were deposited above the Sarvak exposure surface during the Late Cretaceous, long-lasting sea-level fall on the Arabian Plate. Boehmite, diaspore, hematite, and goethite are the main minerals of these kind of iron-rich deposits. Late Cretaceous karst-type bauxite deposits have also been reported from different sections of the Zagros area and have economic value for mining.

Metallogenic process of Permian Taiping karstic bauxite deposit in Youjiang Basin, China

More than 1 billion tons of bauxite was formed on the karstic surface of the Permian Maokou Formation limestone in the western Guangxi area of Youjiang Basin (YB). However, its formation mechanism is still a matter of debate. In this study, the Taiping bauxite deposit, a representative large deposit in this area, was selected to carry out detailed mineral microanalysis and pyrite sulfur isotope analysis to further understand the metallogenic process of bauxite in this region. Taiping bauxite contains two layers: the lower bauxite layer and the upper claystone layer. Bauxite ore was mainly composed of diaspore, pyrite, anatase, kaolinite, minor pyrophyllite, parisite, and bastnäsite. Small amounts of detrital moissanite, native boron, and zircon were also found in the ore. The claystone was dominated by kaolinite, diaspore, pyrite, and chlorite. The occurrence of detrital zircon, moissanite, and native boron suggests that they were most likely derived from volcanic ash or lava, further confirming the contribution of volcanoes. The mineral assemblages of diaspore, pyrite, anatase, parisite, and bastnäsite in the bauxite ore indicate alkaline and reducing depositional environments. The extensive development of ovoid microorganisms and the significant negative δ34S values of pyrite (−42.80 ‰ to −12.54 ‰) indicate that microorganisms were involved in the formation of bauxite. This view was further confirmed by the wide development of fine pyrite (∼1 μm) cemented by cryptocrystalline diaspore in the ore. Extensive volcanism promotes the weathering of parent rocks, releasing Al3+, Fe3+, Ti4+, and REE3+ ions into the weathering system. Under strongly acidic and oxidizing conditions in the upper part of the weathering profile, these ions can migrate downward until they reach an alkaline and reducing environment on the carbonate surface. A large amount of diaspore, pyrite, anatase, parisite, and bastnäsite was formed near the karstic surface with the participation of microorganisms. Epigenetic modifications were also evident in the widespread development of kaolinite and pyrophyllite formed by the silicification of diaspore.

Comprehensive Utilization and Sustainable Development of Bauxite in Northern Guizhou on a Background of Carbon Neutralization

As a developing country, China is also a major producer and consumer of mineral resources. At present, China is still in a critical period of rapid development of industrialization and urbanization, which will inevitably lead to huge resource consumption. It is only 30 years between the peak carbon consumption and the timepoint planned to achieve the goal of carbon neutrality. Coming from a background of dual pressure in terms of the total amount and intensity of “carbon neutrality”, the development and utilization of mineral resources has become one of the important factors in affecting and realizing carbon neutrality in China, and comprehensive utilization has become increasingly important. There are abundant bauxite resources in northern Guizhou, more than 700 million tons, and an industrial resource chain could be built around bauxite. The ore-forming process of bauxite is very complex, and there are enrichment phenomena of other useful elements in the ore-bearing rock series, among which the enrichment of associated Ga, Li and rare earth elements is very obvious. It is of great economic and scientific significance to study the migration law of associated Ga, Li and rare earth elements and to find out whether these elements in bauxite have development value. On the basis of systematically collecting and sorting previous research results, this study carried out supplementary tests on some areas with insufficient data; summarized and studied the migration law of associated Ga, Li and rare earth elements in the Wuzhengdao bauxite deposit in northern Guizhou; and conducted a feasibility analysis on the development and utilization prospects of associated Ga, Li and rare earth elements.

Investigation of Radiological and Chemical Contents of Bauxite Ore Extracted in Turkey.

In this study, which consists of two parts, the radiological and chemical content of bauxite ore was investigated. Gamma-ray spectrometry was used in the first part of the study to determine the activity concentrations of natural radionuclides in samples taken from bauxite deposits in Turkey. The measured activity concentrations of 226Ra, 232Th, and 40K varied from 12.1 ± 2.5 to 132.6 ± 11.4 Bq kg-1 with a mean of 78.4 ± 8.3 Bq kg-1, 6.5 ± 0.5 to 97.3 ± 9.9 Bq kg-1 with a mean of 64.5 ± 5.9 Bq kg-1, and 5.1 ± 0.0 to 356.4 ± 40.1 Bq kg-1 with a mean of 52.6 ± 5 Bq kg-1, respectively. The calculated mean radium equivalent activity value is 177.4 Bq kg-1, the mean gamma dose rate absorbed in the air is 78.8 nGy h-1, the mean corresponding annual effective dose value is 96.6 μSv y-1, and the mean lifetime risk of cancer is 3.85 × 10-4. The chemical content of the bauxite samples was determined in the second part of the study using X-ray fluorescence spectrometry (XRF). For which sectors in the industry the existing bauxite deposits in Turkey can be used was investigated based on this information.

Mechanisms of Ni[sbnd]Co enrichment in paleo-karstic bauxite deposits: An example from the Maochang deposit, Guizhou Province, SW China

Many paleo-karstic bauxite deposits contain elevated concentrations of Ni and Co. It has been known that Co and Ni are dominantly hosted in sulfides, but it remains unclear how Ni and Co were incorporated into sulfides and what kind of physiochemical conditions were involved. The Maochang bauxite deposit, as one of the large Ni- and Co-bearing paleo-karstic bauxite deposits in Guizhou Province, southwest China, was selected to tackle these questions. Detailed mineralogical and sulfur isotopic analyses using integrated EBSD, EPMA, LA-ICPMS, and LA-MC-ICPMS methods revealed three stages of sulfide mineralization: stage I with pyrite (PyI), stage II with pyrite (PyII), millerite, sphalerite, chalcopyrite and violarite, and stage III with pyrite (PyIII), chalcopyrite and galena. The fine-grained, euhedral PyI has up to 0.79 wt% Ni and up to 0.53 wt% Co. In contrast, PyII, which replaced or overgrew PyI, exhibits high but variable Ni, Co and As contents, and is further divided into three sub-types: Ni-rich PyII-a (up to 16.54 wt% Ni, 0.94 wt% Co, and 0.38 wt% As) and PyII-b (up to 3.30 wt% Ni, 1.41 wt% Co, and 0.36 wt% As), and Co-rich PyII-c (up to 0.99 wt% Ni, 7.57 wt% Co, and 1.81 wt% As). PyIII is Ni- and Co-poor. Ni increases from PyI to PyIIa and PyIIb, and then decreases to PyIIc and PyIII, whereas Co remains at similar levels for PyI, PyIIa and PyIIb, significantly increases to PyIIc, and then drops abruptly to PyIII. δ34SV-CDT values vary dramatically from negative values for PyI (−6.9 to −16.6‰) to positive values for PyII-b (+19.4 to +22.8‰), sphalerite (+17.2 to +19.7‰), and PyIII (+25.3 to +32.3‰). Based on these results, and considering that the protoliths of the bauxites were likely Ni- and Co-rich black shales according to previous studies, a four-step model is proposed to explain the enrichment of Ni and Co in the bauxites: 1) during weathering and bauxite formation on the surface, Ni and Co were leached from the black shale together with sulfate; the metals were dissolved in the solution and partly adsorbed by Fe-oxides/hydroxides under moderate to high fO2; 2) during early diagenesis, the sulfate was partially reduced to sulfide via the bacterial sulfate reduction (BSR) process and formed PyI; much of the Ni and Co, together with sulfate, remained in the solution; 3) with increasing burial, temperature increased and fO2 decreased, and the remaining sulfate (with elevated δ34SV-CDT) was reduced to sulfide via the same BSR process and formed PyII; Ni was largely consumed and incorporated into PyIIa and PyIIb, whereas Co remained in the solution until precipitation of PyIIc; 4) by the time of PyIII precipitation, both Ni and Co had been taken by PyII, leaving a Ni- and Co-poor solution and PyIII. Step 1 occurred in a relatively open system, whereas steps 2–4 likely occurred in a closed system.

Application of Volume Uncertainty for Resource Classification: A Case Study on the Rondon Do Pará Bauxite Deposit, Brazil

This study illustrates the application of conditional simulations to calculate the uncertainty associated with the thickness of bauxite ores. The bauxite deposit of Rondon do Pará in northern Pará State, Brazil, is characterized by a well-defined lateritic profile, with the ore being composed of two sequential horizons: massive bauxite and ferruginous bauxite. This study used ore thickness data from 1.005 drillholes with different grid spacing. Drillhole intervals of both types of bauxite ore were accumulated, converting the database from 3D to 2D. Sequential Gaussian simulation produced probability maps calculated from certain confidence intervals, which permits obtaining the uncertainty associated with estimates in thickness. Results show that in portions with the same regular drillhole spacing there are different ranges of uncertainty and variability, which could be useful to support resource classification, associating different confidence intervals to resource classes. This analysis could also guide the drilling program for resource conversion in order to optimize costs, indicating areas where there is greater uncertainty and would need to be densified. The incorporation of this information into the resource model could be very helpful for supporting subsequent studies of economic evaluation and risk analyses with respect to this type of deposit or similarly in mineral exploration.

Spatial Simulation Model of Bauxite Grades Using R Data Analysis: Its Implication for Exploration Activity

DOI:10.17014/ijog.9.3.In exploration, the investigation of prospective area encounters several barriers of land ownership, budget limitation and exhausting permit procedures. To speed up the exploration activities of bauxite deposits, bauxite characteristics and grades of the gap areas should be simulated based on the available set of test pit data. This study aimed to address the limitations and optimize the exploration boundaries using R. R data analysis weaves the framework of kriging geostatistics that required information from the adjacent data. This study utilizes the geochemical data of Al2O3, Fe2O3, SiO2 and TiO2 from 296 test pit sampling sites to extrapolate the blank data. The geochemical data used for R analysis were taken from bauxite horizon, while the other mineralogical properties were taken entirely from the exposed bedrock and test pit data. To verify the result of R analysis, recent data of the simulated area were used as a comparison. The R result shows the prediction value is slightly below the actual value of Al2O3. The kriging simulation of Al2O3 was correlated with test pit and mineralogical characters of samples and reveals that the predicted value of simulation closely represents the true value of Al2O3 grades. Extrapolation results of Fe2O3 and RSiO2 with regards to Al2O3 grades are suggesting that higher grade of bauxite underwent desilication and deferruginization as evidenced by a high value of Index of Lateritization. It can be inferred that this attempt points out the advantages of a quick and reliable projection of bauxite laterite deposits from the limited parameters.

The World’s Largest Fouta Djallon–Mandingo Bauxite Province (West Africa): Part III. The Influence of Geomorphic Factors and the Age of Relief on the Spatial Distribution, Size, and Quality of Bauxite Deposits

The World’s Largest Fouta Djallon–Mandingo Bauxite Province (West Africa): Part III. The Influence of Geomorphic Factors and the Age of Relief on the Spatial Distribution, Size, and Quality of Bauxite Deposits

Processing of Multispectral ASTER Data to Delineate Bauxite Abundant Zones and its Geochemical Characterisation Deposited over Deccan Traps of Central India in Mainpat Plateau, Surguja District, Chhattisgarh

Abstract The current study deals with the application of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) multispectral data to delineate bauxite deposits over Mainpat plateau, Surguja district, Chhattisgarh, India. Application of specific band combinations help to delineate bauxite in the (SWIR) region (2.16-2.33 μm) and visible near infrared (VNIR) band (0.4–1.0 μm) of multispectral ASTER data. Various image processing techniques like atmospheric correction, minimum noise fraction, pixel purity index, n-dimensional visualiser, and spectral angle mapper were applied to ASTER image to delineate bauxite rich zones. The pure pixels were differentiated from the mixed pixels using pixel purity index which were further subjected to n-dimensional visualiser to identify the target end-members. The presence of bauxite was confirmed by comparing the spectral signatures of end-members with in-built spectral plots of United States Geological Survey spectral libraries and categorized as bauxite and ferruginous bauxite. Finally, the end-members were categorised as bauxite and ferruginous bauxite and mapped using spectral angle mapper. The result obtained was further compared with the lithological map provided by Geological Survey of India for accuracy. Then XRF analysis was carried out for the collected samples to confirm the presence of bauxite and ferruginous bauxite. Geochemical analysis also categorized the samples as bauxite and ferruginous bauxite that added accuracy to the results obtained from remote sensing technique. This study might be considered as a time saving eco-friendly exploitation of natural resources and finally the potential of multispectral ASTER data for mapping mineral resources.

Geochemistry and genesis of rare earth minerals in the Tange Pirzal karstic bauxite deposit, Zagros Folded Belt, SW (Iran)

Geochemistry and genesis of rare earth minerals in the Tange Pirzal karstic bauxite deposit, Zagros Folded Belt, SW (Iran)

Effects of Regional Metamorphism on Karst Bauxite Deposits in Northwestern Iran

Effects of Regional Metamorphism on Karst Bauxite Deposits in Northwestern Iran

MENDERES MASİFİ’NİN GÜNEYBATI KANADINDAKİ (AYDIN-MUĞLA) DİASPOR OLUŞUMLARININ JEOLOJİK, JEOKİMYASAL VE GEMOLOJİK ÖZELLİKLERİNİN ARAŞTIRILMASI

With the increasing interest in gemstones, which have started to offer an important underground wealth for countries. Menderes Massive is one of the most widespread and most important areas of bauxite deposites in the Turkey. Gemstone quality diaspore crystals are formed only within these deposits. In this study, diaspore formations in the southwest wing of the Menderes Massive (Aydın - Muğla) were examined and their geological, geochemical and gemological properties/characteristics were investigated. Bauxite deposits in the study area are observed along the discordance between white crystallized limestone (lower) and gray-dun colored crystallized limestone (upper) contact. The deposits generally extend in NW - SE direction and the samples show massive, pisolotic, oolitic and leopard texture. Diaspore crystals of different lengths and colors are unique to our country, which starting from Bafa Lake and advancing towards Yatağan in the form of dashed arc. It has been extracted as a by-product as a result of diasporitic bauxite production in a single mine for many years and it is not thought to have an economic value.
 Diaspore formations in the study area are generally observed as lenticular, brecciated, cracked and pockets in crystallized limestones, bauxite and altered zones with calcite, muscovite and chloritoid minerals. Diaspores are generally observed in the form of sheet around Milas. Increased interest in diaspore crystal, especially in the last 30 years and this study will be important in terms of gaining the deserved value of diaspore crystal which is unique to our country. Since it is likely that new diaspore deposits will be found in the region, further studies are planned on this subject. The data to be obtained will be important in the determination of new diaspore deposits.

Geochemistry of the early Jurassic Soleiman Kandi karst bauxite deposit, Irano–Himalayan belt, NW Iran: Constraints on bauxite genesis and the distribution of critical raw materials

In the Irano–Himalayan karst bauxite belt, in northwestern Iran, karst bauxite orebodies are widespread. Although several of these orebodies have been characterized, no comprehensive data are available for the early Jurassic karst bauxite ores. The early Jurassic Soleiman Kandi karst bauxite deposit consists of a mineral assemblage of diaspore, hematite, kaolinite, and rutile, with lesser amounts of illite, pyrophyllite, chlorite, siderite, amesite, and quartz. The ores are characterized by similar Eu/Eu*, Sm/Nd, and Nb/Ta ratios, suggesting that they share the provenance from a mafic protolith. R-mode factor analysis indicates that most of the variance of the dataset is explained by a factor accounting for an inverse relationship between the between clay minerals–diaspore–rutile–resistant minerals (e.g., zircon and monazite) pool and hematite, driven by redox fluctuations related to an upward decrease in Eh under dry climate. The other two factors are related to the capability of clay minerals in controlling the distribution of bivalent large ion lithophile elements Ba and Sr, and also to the control exerted by authigenic fluorocarbonates on rare earth elements (REE: La-Lu) + Y distribution. The Soleiman Kandi karst bauxite ores are enriched in critical raw materials, including V, Co, Ga, and Ta, with respect to the average Upper Continental Crust. Among these elements, Ta is particularly abundant, probably as a consequence of the occurrence of a Ta-rich variety of rutile, representing a peculiar feature of the Soleiman Kandi bauxite deposit.

Genesis of the Danping bauxite deposit in northern Guizhou, Southwest China: Constraints from in-situ elemental and sulfur isotope analyses in pyrite

The super large bauxite deposit known as the Danping deposit is hosted in the Dazhuyuan formation, Lower Permian, and is located in northern Guizhou (Southwest China). The geochemical signatures of five generations of pyrite from Danping have been identified, and their genesis has been constrained by analyzing their geochemical signatures. Oolitic pyrite (Py-O), which has two sub-generations, occurs in the upper part of the oolitic bauxite. Typically, Py-O2 has a core and rim structure, where the core may contain altered primary Py-O1. While Py-M appears as occurs in the form of interstitial material in the lower part of the oolitic bauxite, Py-C is cubic in shape and is reported in the earthy bauxite. Moreover, Py-Q is found in the Qixia formation. Py-M has a Co/Ni ratio of ∼ 1 and a δ34SV-CDT value of ∼ 0 ‰, thus suggesting a magmatic hydrothermal origin. The primary Py-O1 has a uniform geochemical composition. The reformed Py-O1 and the core of Py-O2 have considerably lower δ34S values of −19.15 ‰ to −4.72 ‰, indicating that a brief pulse of seawater injection can result in the replacement of Py-O1 and the formation of Py-O2. Py-M, Py-O and Py-Q all have positive Ce anomalies, while Py-C has negative Ce anomalies. These contrasting characteristics demonstrate that the original aluminous rock series was largely deposited in an oxidic environment, while the earthy bauxite was formed in a reducing environment. Lithium, Sc and Ga are positively correlated with one another, reflecting their similar geochemical behavior during sedimentary–weathering processes. Py-M has higher contents of Li, Sc and Ga, implying that magmatic fluids contributed to the presence of critical metals even in the weathering conditions.

Obituary: R.H.Sawkar (1935 –2022)

An eminent Geologist, Shri R.H.Sawkar breathed his last peacefully on the morning of June 1,2022 at the age of 87 in his home at Bengaluru. Shri R.H. Sawkar is survived by his Wife, Son, Daughter and Grand-Children and their families are settled in Bengaluru. Born on March 29, 1935 to Hem Reddy Sawkar and Lingamma Hiregoudar, he is from Magala Village, Huvinhadagalli taluk, Vijayanagar dist, Karnataka. He had four brothers and two sisters. He graduated with B.Sc. (Hons) in Geology in 1959 and M.Sc. in Geology in 1961 from Mysore University followed by Diploma in Aerial Photo Interpretation and training in I.T.C (Australia)-Mineral Exploration and Mine Development Programme under Colombo Plan. He was sportsman, swimmer and wrestler. Started his career in Dept of Mines and Geology, Govt of Karnataka as Assistant Geologist in1959. During 1959 -1964, he was associated for the exploration of Iron ore of West Coast, Clay & Feldspar deposits in Goribidanur taluk, mineral resources of South Canara, Limestone deposits in Bijapur and Belgaum, Gold deposits of Gadag Gold Fields, Karnataka. From 1964-1966 as Geologist (Jr.) he was deputed to National Mineral Development Corporation Ltd (NMDC), here he was associated with the exploration of Iron ore deposits of Kudremukh area, for the preparation of the detailed project report for Visvesvaraya Iron and Steel Ltd for mining iron ore. During 1966 -1970, he was associated the Dharwad division inspection of mining leases, exploration of Iron, Manganese ores of North Canara,Bauxite deposits of coastal area, site selection of Vijayanagar steel Plant, Karnataka. From 1970 - 1976, on deputation, he was associated with the Mysore Minerals Ltd (Karnataka State Minerals Corporation Ltd) as Project Manager and Agent for ore production, sales, shipment, transportation, mine planning, exploration of various minerals, etc. During 1976-1985, on deputation, he worked as Project Manager of Karnataka Copper Consortium Ltd. for the exploration and mine development of Kalyadi Copper Project, Ingaldhal Copper Mine, assisted the Karnataka State Govt in the merger proposal of these copper companies with the Hutti Gold Mines Co Ltd (HGML), merger took place with HGML on 12.07.1985. From1985 -1995, he worked in different capacities in HGML for the Chitrdurga Copper Unit, Gadag Gold Project and Corporate Planning etc. After Retiring from HGML on 31.3.1995 as Executive Director, he worked in HGML as Technical Advisor up to 1.6.1997. He was associated with all the leading earth science associations in India and abroad. Currently, he was Secretary General of the Geological Society of India and actively associated with the MEAI, Rashtriya Jal Biradari, Water Development Rural and Urban societies, Dam Safety etc. He was a member of various State and Central Govt committees. He has presented and published several papers in the national and international seminars and also chaired the technical sessions. He was actively involved as advisor/consultant to the exploration, mining and metallurgy industries. He travelled widely, a simple man with tons of curiosity to discover new things. He guided and inspired the many. Shri R.H. Sawkar will remain in the hearts of the many. He will be missed deeply by his family and colleagues.

Synthesis of geopolymer with KOH by two kaolinitic clays from the Amazon: Influence of different synthesis parameters on the compressive strength

The term geopolymer refers to “inorganic polymers” formed by a chemical reaction between solid aluminosilicate compounds and a highly concentrated alkaline hydroxide solution. The properties of geopolymers mostly result from the chemical and mineralogical composition of the material used as a source of aluminosilicates. Considering the influence of the raw material for the synthesis of geopolymers, the present study evaluates the use of two different types of kaolin in the synthesis of geopolymers using KOH as an alkaline activator. For the present study, a sample of Belterra clay (KLN-1) from the bauxite deposits of Rondon do Pará, a sample of processed kaolin (KLN-2), and microsilica (MCR-1) (Ecopodium) and PA reagent from Sigma (KOH) were selected. The samples were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. For the synthesis of the geopolymers, the KLN-1 and KLN-2 samples were calcined at 750 °C for 2 h. The syntheses of the geopolymers were performed at different KOH molar concentrations (12, 13, 14, 15 and 16), at different curing temperatures (60, 70, 80, 90 and 100 °C) and for different curing times (24, 48, 72, 96, and 120 h). The geopolymers were characterized by mechanical strength testing and FTIR. The samples had different mineralogical compositions, which contributed to different compressive strength results. The samples showed greater resistance at concentrations of 12 and 16 M. The curing temperature of 80 °C exhibited better mechanical compressive strength. At 120 h, the best compressive strength value was obtained, indicating that a longer time favored the geopolymerization reaction. The greater mineral diversity affects negatively the geopolymer reaction contributing to lower mechanical resistance.

Application of Induced Polarization and Resistivity Methods to Identify Subsurface Layers in Bauxite Deposits Area of Kendawangan, West Kalimantan

Kendawangan Sub-district, Ketapang Regency is one of the areas in West Kalimantan Province containing minerals of economic value, namely bauxite deposits. This study has applied both induced polarization and resistivity methods. It aims to identify subsurface layers in the Kendawangan bauxite deposit area based on resistivity and chargeability distribution. Measurements in the field apply a north-south line using the dipole-dipole configuration, have a length of 144 m, and electrode distance of 3 m. The results showed that the subsurface layer in the study area identified the presence of bauxite deposits. In addition, it showed that the subsurface layers were topsoil, bauxite deposits, saprolite, and bedrock. Topsoil has a thickness of about 1 m, and it is a product of the weathering process. The bauxite deposit has a thickness of about 9 m, and it contains the minerals aluminum oxide, quartz, hematite, and titanium oxide. Saprolite has a thickness of about 2 - 4 m, and it contains aluminum silica (kaolinite) and minerals quartz, titanium oxide, zircon, and it is a weathering product of bedrock. The bedrock is at a depth of more than 10 m, which is interpreted as volcanic tuff, sandstone, and claystone.

Geology, geochemistry, and genesis of REY minerals of the late Cretaceous karst bauxite deposits, Zagros Simply Folded Belt, SW Iran: Constraints on the ore-forming process

The present study focuses on the geochemistry and occurrence of REY (rare earth elements and yttrium)-bearing minerals in the Late Cretaceous karst bauxite deposits in the central part of the Zagros Simply Fold Belt (ZSFB), SW Iran. The ore bodies comprise a series of individual pods and/or contiguous lenses that occur as infills of deep karst cavities, depressions, and fractures within the upper neritic carbonates of the Cenomanian–Turonian Sarvak Formation. Karst bauxites from the ZSFB show, overall, the same mineral components, which consists of boehmite, hematite (commonly occurring as Al-rich), anatase, and kaolinite, with lesser amounts of diaspore, goethite, chamosite, rutile, and zircon. Among minor constituents, single crystals rich in rare earth elements (REEs) occur mainly in the form of authigenic REY fluorocarbonate, phosphate, and oxide minerals (bastnasite, parisite, rhabdophane, churchite and cerianite). Some textural features, such as spheroidal concretions, pisoids with cortexes lacking radial and circular fractures, growth of simple cortex around earlier pisoids, and pelitomorphic matrix suggest the ores are mostly autochthonous in origin. R-mode factor analysis revealed several significant interelemental relationships including: (i) significant and positive weightings for TiO2, Al2O3, Cr2O3, Ni, Zr, Nb, Hf, Ta, W, and Th, and a significant, negative weighting for SiO2 represent a later bauxitization stage involving silica depletion under drier conditions, promoting formation and stability of a range of minerals including detrital minerals and Al and Ti oxyhydroxides which also control, through scavenging, cations of first-row transition metals such as Ni2+ and Cr6+; (ii) Supergene conditions, mainly acidic pH, probably played an efficient role in the formation of secondary REE-rich phosphates and Ga-hydroxide; (iii) similar and meaningful weightings for U and V suggest that the redox environment would be most important in controlling the U and V mineral phases; and (iv) the scandium co-variance with Fe2O3 represents the control exerted by iron oxy-hydroxides on the critical metal Sc. In the ZSFB bauxites, the most frequent authigenic REE-bearing minerals are light REE (LREE) fluorocarbonates of the bastnaesite group that forms a solid solution series between end members parisite [CaCe2(CO3)3F2] and bastnäsite (CeCO3F). The mode of occurrence of bastnäsite-Ce and parisite-Ce suggests that cerium as fluoride and/or carbonate–fluoride complexes were readily leached by acidic downward solutions and finally precipitated on the geochemical barrier of the carbonate bedrock under alkaline and reducing conditions. Rhabdophane [(Ce, La) PO4·H2O] as an LREE phosphate mineral appears in two generations with different chemical compositions, an early one as irregular and/or acicular particles within the cavities and a later one along the margin of a goethite microvein that cuts the pelitomorphic matrix. Cerianite (CeO2) occurs mainly as sub-micrometer to micrometer grains in the porous aggregates of the aphanitic matrix and as microdomains or microveins that coexist with Al-oxyhydroxide and goethite. Cerianite precipitation may occur due to the predominance of acidic/oxidizing conditions and the dissolution of Ce-rich fluorocarbonates in the bauxitic profile, respectively. The only heavy REE (HREE) phosphate mineral within the ZFSB bauxite deposits is churchite[Y(PO4)·2(H2O)] that forms as single euhedral crystals at the core of the sub-spheroidal structures under an acidic condition.

Mineralogy and geochemistry of major, trace and REE elements, Pirashkaft Bauxite Deposits, Mamasani, Fars Province

Mineralogy and geochemistry of major, trace and REE elements, Pirashkaft Bauxite Deposits, Mamasani, Fars Province