Weathering Of Biotite Research Articles

Assessment of groundwater quality for drinking and irrigation in Dindigul district, southern India: Hydrochemical characterization and spatial analysis

There are many renewable resources, but groundwater is one of the most important. The use of groundwater for various purposes is inevitable in the modern world. This study aimed to investigate the groundwater resources in the Dindigul and Vedasandur taluks of Dindigul district, southern India, for these various uses. About 36 groundwater samples were collected from dug wells and borewells. The samples were analyzed for total dissolved solids, total hardness, and both major and minor ions to determine the water type, ion concentration and suitability for drinking purposes. Analysis reveal that, based on TH and TDS, most wells exhibited hard to very hard with fresh to brackish characteristics. TDS, TH, Mg, Na, and K levels in drinking water exceeded permissible limits in 8 %, 14 %, 14 %, 39 %, and 25 % of samples, respectively. For irrigation purposes, parameters such as sodium adsorption ratio, residual sodium carbonate, electrical conductivity, Kelley’s ratio, magnesium hazard, and permeability index were found to be unsuitable in 36 %, 3 %, 14 %, 69 %, 97 %, and 3 % of the samples, respectively. The Study area shows that 89 % of the samples are fit for drinking purposes. Sodium, bicarbonate and chloride ions were identified as the dominant hydrochemical components in the region. The hydrochemistry varied spatially, with higher concentrations observed primarily in the northwestern parts of the area. Most wells were found suitable for drinking, with the exception of a few in the northwest. The quality of water for agricultural use was generally acceptable. The drinking water quality index indicated that most areas were good for drinking, except those in the northwest. The hydrochemistry of the region appears to be influenced by processes such as evaporation, silicate weathering, and irrigation return flow. Evaporation, along with the weathering of hornblende, biotite, and charnockite rocks played a significant role in the groundwater.

Impact of the Iron-Response Regulator Genes on the Release of Iron and Aluminum from Biotite by Rhizobium pusense S41

In this study, the biotite weathering activities of strain S41 and mutants with deletion of the iron response regulator genes fur, rirA, and irr were compared. S41ΔrirA had a 35%–60% increase in Fe and Al concentrations, a 95%–112% increase in siderophore production, and a 18%–22% increase in EPS concentration, while S41Δirr had a 29%–48% decrease in Fe and Al concentrations and a 32%–42% decrease in siderophore production, compared with strain S41. Under iron-sufficient conditions, S41ΔrirA had a 1.5-fold–2.7-fold increase in siderophore production, while there was similar siderophore production between strain S41 and S41Δirr. Under iron-limited conditions, S41Δirr had a 34%–40% decrease in siderophore production compared with strain S41. The expression of genes related to the synthesis of siderophores, iron uptake and transporters, and EPS production in strain S41 significantly increased in iron-limited conditions compared with that in iron-sufficient conditions. The expression of genes associated with the synthesis of siderophores and iron uptake and transporters significantly increased in S41ΔrirA in iron-sufficient and iron-limited conditions but decreased in S41Δirr in iron-limited conditions. Our results suggested that rirA- and irr-modulated multiple genes may be related to the mineral weathering activities of strain S41.

Physicochemical Variation of Clay Minerals and Enrichment of Rare Earth Elements in Regolith-hosted Deposits: Exemplification from The Bankeng Deposit in South China

AbstractThe wide application of rare earth elements (REEs) in the development of a carbon–neutral society has urged resource exploration worldwide in recent years. Regolith-hosted REE deposits are a major source of global REE supply and are hosted mostly in clay minerals. Nonetheless, the ways in which changes in the physicochemical properties of clay minerals during weathering affect the concentrations of REEs in the regolith are not well known. In the current study, a world-class regolith-hosted REE deposit (Bankeng, South China) has been studied to illustrate further the effect of clay minerals on sorption and fractionation of REEs during weathering to form economic deposits. In the weathering profile, halloysite and illite are abundant in the saprolite due to weathering of feldspars and biotite from the bedrock. During weathering, halloysite and illite transform gradually to kaolinite and vermiculite. The large specific surface area, pore volume, and cation exchange capacity of the clay mineral assemblages are favorable to the sorption of REEs, probably because of the formation of vermiculite. The abundance of vermiculite could explain the enrichment of REEs in the upper part of the lower pedolith. For the saprolite-pedolith interface, halloysite is probably the main sorbent for the REEs, as indicated by the distinctive appearance of pore sizes of 2.4–2.8 nm characteristic of halloysite. The progressive transformation of halloysite to kaolinite reduces the pores and desorbs the REEs, causing REE depletion in the shallower soils. As a result, REEs were mobilized downward and re-sorbed in the lower pedolith-upper saprolite causing gradual enrichment and formation of these regolith-hosted deposits.

Mineral weathering of iron ore tailings primed by Acidithiobacillus ferrooxidans and elemental sulfur under contrasting pH conditions

The acidophilic sulfur oxidizing bacterium (SOB), Acidithiobacillus ferrooxidans, has been found to stimulate elemental sulfur (S0) oxidation and mineral weathering in alkaline Fe ore tailings. However, A. ferrooxidans growth and activities depend on the pH conditions surrounding their interfaces with minerals. The present study aimed to investigate how pH influences bacterial growth and functions in Fe ore tailings. A simulated aquatic ‘homogeneous’ incubation system was initially adjusted into acidic (pH 4), neutral (pH 7) and alkaline (pH 9) conditions, which mimicked the microenvironmental conditions of the water-cell-mineral interfaces in the tailings. It was found that A. ferrooxidans grew well and oxidised S0 under the prevailing and initially acidic conditions (pH < 6). These stimulated the weathering of biotite and amphibole-like minerals and the formation of nanosized jarosite and ferrihydrite-like minerals mediated by extracellular polymer substrate (EPS). In contrast, the initially neutral/alkaline pH conditions (i.e., pH > 7) with the presence of the alkaline tailings restricted SOB growth and functions in S0-oxidation and mineral weathering. These findings suggest that it is essential to prime acidic conditions in microenvironments to support SOB growth, activities, and functions toward mineral weathering in tailings, providing critical basis for involving SOB in eco-engineered pedogenesis in tailings.

Anisotropy and Microcrack Propagation Induced by Weathering, Regional Stresses and Topographic Stresses

AbstractThis paper presents a new model for anisotropic damage in bedrock under the combined influences of biotite weathering, regional stresses, and topographic stresses. We used the homogenization theory to calculate the mechanical properties of a rock representative elementary volume made of a homogeneous matrix, biotite inclusions that expand as they weather, and ellipsoidal cracks of various orientations. With this model, we conducted a series of finite element simulations in bedrock under gently rolling topography with two contrasting spatial patterns in biotite weathering rate and a range of biotite orientations. In all simulations, damage is far more sensitive to biotite weathering than to topographic or regional stresses. The spatial gradient of damage follows that of the imposed biotite weathering rate at all times. The direction of micro‐cracks tends to align with that of the biotite minerals. Relative to the topographic and regional stresses imparted by the boundary conditions of the model, the stress field after 1,000 years of biotite weathering exhibits higher magnitudes, wider shear stress zones at the feet of hills, more tensile vertical stress below the hilltops, and more compressive horizontal stress concentrated in the valleys. These behaviors are similar in simulations of slowing eroding topography and static topography. Over longer periods of time (500 kyr), the combined effects or weathering and erosion result in horizontal tensile stress under the hills and vertical tensile stress under and in the hills. These simulations illustrate how this model can help elucidate the influence of mineral weathering on Critical Zone evolution.

New insight into biotite weathering in the subtropic Tongcheng granite regolith, Hubei Province, South China

Alteration of biotite during igneous rock weathering plays an important role in global geochemical cycle and formation of ion-adsorption type rare earth element ores. In order to better understanding the transformation and geochemical processes of biotite weathering, investigation of alteration of biotite was undertaken in the granite regolith in subtropical Tongcheng, Hubei Province, South China. Our results show that weathering of biotite synchronously produced randomly interstratified biotite/vermiculite (B/V) and halloysite, and the B/V clay partially decomposed into discrete vermiculite in the topsoil due to increasing weathering. Vermiculitization of biotite involved leaching of K+ and accumulation of hydrated Mg2+ and Fe3+ in the interlayer space of biotite precursor and thus occurred in a solid-solid state transformation. The vermiculite components in B/V phase are hydroxyl-interlayered species, and the neoformed halloysite could not be expanded by formamide treatment, indicative of dehydrated halloysite. Halloysite occurs in tubular morphology at the edge of biotite or in well-oriented lath-like clusters on the basal surface of biotite crystals. The former crystallized from solutions, whereas the latter formed from local leaching of SiO sheets of biotite and subsequently in situ recrystallization. The parallel lath-like halloysite clusters occur in certain extending directions with angles of ~30° and ~ 60° respectively, resulting from the size misfit between the tetrahedron and octahedron of the crystal structure of biotite precursor. Thus, the formation of halloysite can be considered as a dissolution–precipitation process.

A Combination of Genomics, Transcriptomics, and Genetics Provides Insights into the Mineral Weathering Phenotype of Pseudomonas azotoformans F77.

Silicate mineral weathering (dissolution) plays important roles in soil formation and global biogeochemical cycling. In this study, a combination of genomics, transcriptomics, and genetics was used to identify the molecular basis of mineral weathering activity and acid tolerance in Pseudomonas azotoformans F77. Biotite was chosen as a silicate mineral to investigate mineral weathering. The genome of strain F77 was sequenced, and the genes significantly upregulated when grown in the presence of biotite included mineral weathering-related genes associated with gluconic acid metabolism, flagellar assembly, and pilus biosynthesis and acid tolerance-related genes associated with neutralizing component production, reducing power, and proton efflux. The biotite-weathering behaviors of strain F77 and its mutants that were created by deleting the tkt, tal, and gntP genes, which are involved in gluconic acid metabolism, and the potF, nuoF, and gdtO genes, which are involved in acid tolerance, were determined. The Fe and Al concentrations in the strain F77-inoculated medium increased 2.2- to 13.7-fold compared to the controls. The cell numbers of strain F77 increased over time, while the pH values in the medium ranged from 3.75 to 3.90 between 20 and 36 h of incubation. The release of Al and Fe was significantly reduced in the F77 Δtal, F77 ΔgntP, F77 ΔpotF, and F77 ΔnuoF mutants. Bacterial growth was significantly reduced in the presence of biotite in the F77 ΔpotF and F77 ΔnuoF mutants. Our results demonstrated the acid tolerance of strain F77 and suggested that multiple genes and metabolic pathways in strain F77 are involved in biotite weathering and acid tolerance during the mineral weathering process. IMPORTANCE Acid production and tolerance play important roles in effective and persistent mineral weathering in bacteria, although the molecular mechanisms governing acid production and acid tolerance in bacteria have not been fully elucidated. In this study, the molecular mechanisms underlying biotite (as a silicate mineral) weathering (dissolution) and acid tolerance of P. azotoformans F77 were characterized using genomics, transcriptomics, and genetics analyses. Our results showed that the genes and metabolic pathways for gluconic acid metabolism, flagellar assembly, and pilus biosynthesis may play important roles in mineral weathering by strain F77. Notably, the genes associated with neutralizing component production, reducing power, and proton efflux may be related to acid tolerance in strain F77. The expression of these acid production- and acid tolerance-related genes was observed to be increased by biotite in strain F77. Our findings may help to elucidate the molecular mechanisms governing mineral weathering and, especially, acid tolerance in mineral-weathering bacteria.

Stratigraphic and Geochemical Evidence for the Alteration of Calcareous Glauconitic Marine Sediments to Calcium Bentonite

ABSTRACT Calcium bentonite mined in Smith County, Mississippi, has been reported in numerous publications to be derived from the weathering of volcanic ash. These interpretations were based on the bentonite having similar properties to bentonites actually formed from volcanic precursors. No recent detailed stratigraphic mapping in combination with modern laboratory analyses had been conducted for this area. Calcium bentonite, found at Olmstead, Illinois, in contrast, formed in situ from the weathering of biotite, glauconite, quartz, and other materials found in shallow calcareous marine deposits. Detailed stratigraphic mapping in Smith County in 2011 was carried out by Mississippi State University as part of a proposed surface reservoir study. The mapping, utilizing GPS and continuous sonic core samples, indicated that calcium bentonite was present and similarly formed by the in situ weathering of calcareous, glauconitic, marine marl in several formations in the Oligocene Vicksburg Group. The bentonite was not restricted to one stratigraphic interval as would be the case for a true ashfall deposit. Additional research conducted at Mississippi State University and more recently by others confirmed that the bentonite was formed by weathering and contemporaneous microbial action of the calcareous glauconitic marls. No volcanic ash was detected in any of the samples tested. The preponderance of other material present in the Smith County bentonite renders the presence of minute amounts of volcanic detritus volumetrically insignificant in the formation of the clay mass. A conceptual model is presented showing how the bentonite was formed and why it is restricted to this small area of the Oligocene outcrop.

Groundwater quality index assessment at Raebareli district: A part of Indo‐Gangetic Alluvium, India

The present study highlights the water quality of groundwater and associated health risks with the consumption in various parts of district Raebareli. The water quality at 16% of the total sampling sites was found to be under the ‘highly polluted’ category with high values of Total Hazard Index (THI). The values of fluoride exceeded the permissible limits at44% of the sites. A good correlation of fluoride with WPI and magnesium was seen in the study, with the impact of mild weathering of biotite as a potential cause. The severe health risks found in the study area raise an urgent need for remedial actions and authoritarian interventions.

Complete Genome Sequence of Pseudomonas taiwanensis WRS8, a Plant Growth-Promoting and Biotite-Weathering Strain.

Pseudomonas taiwanensis WRS8 is a biotite-weathering organism isolated from wheat root. Here, we report its complete genome sequence, which may shed light on its role in plant growth promotion and biotite weathering.

Identification of a novel type of glucose dehydrogenase involved in the mineral weathering ability of Collimonas pratensis strain PMB3(1).

The exact molecular mechanisms as well as the genes involved in the mineral weathering (MW) process by bacteria remain poorly characterized. To date, a single type of glucose dehydrogenase (GDH) depending on a particular co-factor named pyrroloquinoline quinone (PQQ) is known. These enzymes allow the production of gluconic acid through the oxidation of glucose. However, it remains to be determined how bacteria missing PQQ-dependent GDH and/or the related pqq biogenesis genes weather minerals. In this study, we considered the very effective mineral weathering bacterial strain PMB3(1) of Collimonas pratensis. Genome analysis revealed that it does not possess the PQQ-based system. The use of random mutagenesis, gene complementation and functional assays allowed us to identify mutants impacted in their ability to weather mineral. Among them, three mutants were strongly altered on their acidification and biotite weathering abilities (58% to 75% of reduction compared to WT) and did not produce gluconic acid. The characterization of the genomic regions allowed noticeably to the identification of a Glucose/Methanol/Choline oxidoreductase. This region appeared very conserved among collimonads and related genera. This study represents the first demonstration of the implication of a PQQ-independent GDH in the mineral weathering process and explains how Collimonas weather minerals.

Field biotite weathering rate determination using U-series disequilibria

The chemical weathering rate of silicates is a key parameter of several geochemical processes; however, the long-term field measurement of these rates remains challenging. Currently, there are several methods for quantifying field weathering rates, but each presents it's own unique set of difficulties. In this study uranium-series nuclides were used to investigate long-term biotite weathering in a soil profile. For this purpose, pseudomorph grains of biotites (including weathering products) were hand-picked from four horizons of a soil profile and from underlying granitic saprolite from the experimental Breuil-Chenue site (France).Unexpected behaviors of U and Th nuclides were recorded from these samples. An unambiguous leaching of 232Th occurs during the weathering of biotite, while reduced U release relative to Th was observed, implying an efficient redistribution of U between the primary mineral and weathering products within the pseudomorphs. The measured U-series activity ratios reflect a regular and self-consistent pattern evolution. However, the “U-series-derived-weathered-stage” is not always coherent with the weathering features of major elements and/or with the location of the samples within the soil profile. For instance, biotite from the saprolite displays U-series activity ratios typical of significantly weathered samples, while major elements present rather limited signs of weathering. These results suggest an incongruent leaching of U and Th isotopes and suggest that U- and Th-series nuclides probe some water-mineral interactions that occur before macroscopic mineral tansformation.Using an open-system leaching model, coupled (234U/238U), (234U/230Th), and (226Ra/230Th) disequilibria measured from the samples allow us to calculate a weathering duration range of 6–52 ky for most weathered samples of this soil profile. The biotite weathering rate deduced from these data ranges from 7.8 × 10−17 mol·m−2·s−1 to 6.5 × 10−16 mol·m−2·s−1, which is consistent with the range of field rates previously reported. This rate was compared to the weathering rate of biotites induced by the substitution of vegetation occuring 35 years ago in a nearby soil profile, which was about 2–3 orders of magnitude higher than the long-term rate reported above. This feature is perfectly consistent with the decrease in the weathering rate with time that was previously widely documented but that still remains debated. Our results allude to a valuable use of U-series isotopes for mineral-weathering field rate determination and report a decrease in silicate weathering rates over long- (10,000s of years) and short-term (10s of years) weathering events recorded from the same site. The results show that short term laboratory experiments can be representative of field processes, and suggest that some forms of mineral weathering reactivation, similar to that observed during laboratory experiments, may naturally occur in soils in response to high frequency perturbation processes such as land cover change.

Impact of the fliF Gene on Biotite Weathering of Rhizobium pusense S41

Rhizobia have been reported to weather silicate mineral, however, molecular mechanisms underlying mineral weathering of Rhizobium strain is unclear. In this study, biotite weathering behaviors were compared among the mineral-weathering Rhizobium pusense S41, its mutants created by deleting the fliF gene involved in flagellar protein synthesis, and its complemented strain. Flagellum was observed in strain S41 but not in its mutant S41ΔfliF. Mobilized Fe and Al concentrations decreased in the presence of S41ΔfliF during mineral weathering process compared to strain S41. No significant differences in the gluconic acid concentration and pH values were found between strains S41 and S41ΔfliF during the mineral weathering process except for day 2. A similar bacterial growth in the culture medium was observed between strains S41 and S41ΔfliF, however, significantly lower cell numbers on the mineral surface were observed for S41ΔfliF compared to strain S41. Furthermore, biofilm production was depressed for S41ΔfliF compared to strain S41. The results showed the important role of a flagellum of strain S41 in biotite weathering and that the fliF gene of strain S41 exhibited important impacts on mineral weathering activity and biofilm production.

Incipient Weathering of the ~74ka Young Toba Tuff (YTT) Biotite Grains, Sagileru Valley, Andhra Pradesh

ABSTRACT The Young Toba Tuff (YTT) ash containing biotite flakes was once spread over the Indian peninsula, and is now exposed at several sites in the Sagileru river basin in Andhra Pradesh. The ash beds form a distinct marker horizon in the landscape and have been recognized in a variety of sedimentary sequences associated with middle Paleolithic archaeological tools. In the present study, biotite grains from the volcanic ash beds were separated that were collected from Vankamarri (VKM), Porumamilla (PRM) and Jammulamadugu (JMD), sites in the Sagileru river valley, Cuddapah, Andhra Pradesh. The biotite grains were separated to understand the state and stage of weathering since the ash deposition ~74ka. Electron microprobe data of the biotite grains exhibit low FeO/MgO values. The chemical discrimination diagrams characterizing the physicochemical properties of the biotite flakes from VKM, PRM and JMD sites indicate calc-alkaline composition and in the A–CN–K diagram, most of the samples fall above the plagioclase feldspar zone signifying low degree of alteration. Both the CIA and A-CN-K values depict the low weathering state of biotite, and this probably is owing to long periods of dry, semi-arid to arid climatic conditions since ~74ka. Scanning Electron microscope (SEM) of the biotite grains reveal micro and nanopores on the surface and many a times these coalesce to form curls along the edges of the biotite grains further supporting incipient but very early stage of biotite weathering since its deposition ~74ka.

Hydrochemical and isotopic characterization of groundwater in the southeastern part of the Plateaux Region, Togo

ABSTRACTHydrochemical, inverse geochemical modelling and isotopic approaches are used to assess the hydrogeochemical evolution of groundwater from the basement aquifers in the southeastern part of the Plateaux Region, Togo. Groundwater originates from present-day rainwater infiltration and is mostly fresh and slightly acidic to neutral. Hydrochemical facies are predominantly mixed cations-HCO3 associated with Ca/Mg-Cl, Na-HCO3 and Na-Cl water types in equilibrium with kaolinite and Ca/Mg-smectites. They are related to silicates hydrolysis, anthropogenic contamination, nitrification/denitrification, mixing along flowpaths and dissolution/precipitation of secondary minerals. The pattern of flow paths is in accordance with an increasing trend in total dissolved solids (TDS) toward the potentiometric depression located in the central and southern parts of the aquifer system. Inverse geochemical modelling using the NETPATH-WIN model showed the relative importance of biotite, plagioclase and amphibole weathering and dissolution of secondary carbonate minerals along the flowpath, suggesting that an abundance of minerals is not necessarily the main factor controlling the groundwater chemistry evolution.

Geochemical controls on the distribution of radio-trace elements in groundwater resources of Shir-Kuh granitoid aquifer, central Iran

Abstract Granitic groundwaters are important resources in arid regions. However, they are not always pure due to having appreciable amounts of trace elements. The present study was conducted to investigate chemical compositions for finding controls on distribution of heavy metals and natural radioelements (U and Th) in groundwater resources of Shir-Kuh granitoid aquifer (SGA), central Iran. Thirty water samples were collected and analyzed for major and trace elements. The average values of electrical conductivity (EC) and pH are 624 μs/cm and 7.5, respectively. The dominant groundwater type is Ca-HCO3, as a result of the calcite dissolution and biotite weathering. Principal component analysis in support of mass balance studies recognizes dissolution of fracture-filling sediments and rock mineral weathering as the main factors enhancing major ions in SGA. These processes also release trace elements in decreasing order of Sr &amp;gt; Ba &amp;gt; Sn &amp;gt; W &amp;gt; Cu &amp;gt; U &amp;gt; Zn &amp;gt; Th. Weathering of biotite enclosing accessory minerals of monazite and zircon is introduced as the main source of radio-trace elements in SGA. Health concerns are currently related to U in drinking groundwater, as the maximum concentration (13.6 μg/L) approaches the Iranian drinking standard of 15 μg/L, in response to the oxidizing nature of the groundwater, calcite dissolution-related mobilization, and the degree of the water–rock interactions.

Geochemical and Mineralogical Characteristics of the Middle Jurassic Coals from the Tongjialiang Mine in the Northern Datong Coalfield, Shanxi Province, China

There is limited information available on the minerals and elements present in the Jurassic coals from Datong Coalfield. This paper investigates the geochemical and mineralogical characteristics of the Middle Jurassic coals from the Tongjialiang Mine using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy in combination with energy-dispersive X-ray spectrometry (SEM-EDS). No.12 coal is a low-medium volatile bituminous coal and is characterized by low ash yield content, low moisture content, and ultra-low sulfur content. Compared with Chinese coals, the Tongjialiang coals have slightly higher average percentages of MgO and P2O5, and lower average percentages of the other major oxides, including SiO2, TiO2, Al2O3, Fe2O3, CaO, MnO, Na2O, and K2O. Compared with the World hard coals, Be, Cr, Co, Ni, Ge, Sn, Ta, and W are slightly enriched in the Tongjialiang coals. The concentrations of Li, F, Sc, V, Cu, Ga, Se, Sr, Zr, Nb, Hf, Pb, Th, and U are close to the average values of the world’s hard coals. The minerals in No.12 coal mainly include quartz, kaolinite, siderite, and ankerite, along with smaller amounts of pyrite, illite, calcite, and rutile. The formation of syngenetic siderite in No.12 coal is related to the weathering of biotite in the gneiss of the Yinshan Upland. The modes of occurrence of ankerite indicate that the coals may be affected by the injection of low temperature hydrothermal fluids. It is noteworthy that a portion of epigenetic ankerite may be a product of metasomatism between syngenetic siderite and the epigenetic Fe-Mg-Ca rich hydrothermal fluids. The ratios of Al2O3/TiO2, REY (rare earth elements and yittrium) enrichment patterns, the modes of occurrence of siderite and ankerite, as well as the enriched lithophile and siderophile elements indicate that the No.12 coal may have originated from the Yinshan Upland and may also have been influenced by low temperature hydrothermal fluids that might have circulated in the coal basin.

Chemical weathering in a moraine at the ice sheet margin at Kangerlussuaq, western Greenland

ABSTRACTWeathering caused by interaction between glacial sediments and water in exposed moraines needs to be studied to evaluate their possible effects on the global carbon cycle. In this study, moraine ponds, moraine porewaters, and till samples were collected at a moraine adjacent to the Greenland Ice Sheet at Kangerlussuaq. Scanning electron microscopy (SEM) studies of the till show limited evidence of silicate chemical weathering, but the moraine waters have substantial solute concentrations. δ34SSO4 and δ18OSO4 data indicate that the origin of dissolved sulfate is the oxidation of sulfides, in agreement with the SEM observations. The dissolved HCO3−/SO42− molar ratios indicate an uneven balance between sulfuric and carbonic acid weathering; C-isotope data indicate that some of the CO2 originates from organic carbon mineralization. Ion–ion plots provide evidence of carbonate weathering and of the formation of secondary gypsum and calcite through evaporation and (or) cryoconcentration. The 87Sr/86Sr ratios in the waters correlate with the corresponding till samples, supporting the local origin of the dissolved strontium, which is higher in the waters than in the till due to the selective weathering of biotite. The data evidence a large degree of chemical weathering in moraines promoted by large rock–water ratios and by the hydraulic isolation created by the frozen till. The high PCO2 in the studied moraine waters indicates that they may represent a previously underestimated CO2 source.

Petrology of saprolite developed on gneisses in the Matomb region, south Cameroon

The petrological study of saprolite developed on gneisses in the Matomb region (South Cameroon) was carried out by petrographic, mineralogical and geochemical analyses. The gneisses have a granoblastic heterogranular texture and are made up of quartz, biotite, feldspars, kyanite, garnet, rutile and enstatite. Chemically, they show high contents in SiO2 (64.93%), Ba (723 ppm), Sr (347 ppm), V (135 ppm), Zr (126 ppm) and moderate contents in Al2O3 (15.24%). The REE content is low (99.12%) with a slight positive Eu anomaly and no Ce anomaly. From bottom to top, the soil is composed of a coarse saprolite and fine saprolite. The coarse saprolite is mainly sandy, showing gray, pink, red phases as well as white loamy sand and yellow sandy loam phases. The main minerals are quartz, kaolinite, gibbsite, goethite, hematite, biotite, muscovite, kyanite and rutile. In addition, the coarse saprolite also contains chlorite, smectite, vermiculite and chlorite-vermiculite. The fine saprolite is composed of white, pink and red brown phases. They have a similar mineral assemblage, with the exception of the concomitant disappearance of biotite and 2/1 clay minerals which certainly represent the first fugacity steps of biotite weathering. The SiO2 content decreases from the coarse saprolite to the fine saprolite compared to the parent rock, but the white sample of the fine saprolite shows high SiO2 (70.31%) content. The Al2O3 content increases up the profile while the Fe2O3 content is variable. The white samples show low Fe2O3 values (4.07–0.19%). The red material is particularly rich in Fe2O3 (15.32%). Ba, Zr, Zn and V show high contents in the profile. Cr (967.00 ppm) shows the highest value in the profile and U (1982 ppm) content is very high in one of the pink materials of the fine saprolite. SiO2 has negative correlation with Al2O3, Fe2O3, TiO2, Zr, Ni and V. The correlations of Fe2O3 with Cr and V are positive. The correlations between Zr and Th, Nb, Hf are positive. The REE contents increase up the profile and fluctuate in the saprolite phases. The white samples are very poor in REE. The Matomb soil samples show positive Ce anomalies and negative Eu anomalies probably due to the depletion of Eu, the relative enrichment of other REE or to the absence of carrier minerals. Contrary to what has always been observed in the South Cameroon plateau, the white samples of the fine saprolite show positive Eu anomalies. This could be indicative of the probable presence of other carrier minerals apart from feldspars which always occur in this milieu or the leaching of some elements. The (La/Yb)N < 1 ratio in some weathered phases indicates a high mobility of LREE in these materials. Mass balance shows that the transition from the rock to the weathered materials is accompanied by a strong depletion of several elements particularly HREE and a moderate LREE enrichment. Thus, the relative mobility of elements determines the colour differenciation of phases in the saprolite.

Fluoride contamination of groundwater and its seasonal variability in parts of Purulia district, West Bengal, India

The contamination of aquifers by fluoride and arsenic is a major cause of concern in several parts of India. A study has thus been conducted to evaluate the extent and severity of fluoride contamination and also its seasonal variability. Two blocks (Purulia-1 and Purulia-2) were considered for this purpose. Twenty groundwater samples (in each season) were collected from tube wells during the pre-monsoon and post-monsoon seasons. In addition to fluoride, groundwater samples were also analyzed for major cations, anions, and other trace elements. The concentration of fluoride shows significant seasonal variation and ranges between 0.94–2.52 and 0.25–1.43 mg/l during the pre-monsoon and post-monsoon seasons, respectively. In pre-monsoon season, more than 40% of the water samples show fluoride concentrations higher than the WHO limit. However, during the post-monsoon season, none of the groundwater sample shows fluoride concentrations higher than the WHO limit. Lesser concentration during the post-monsoon season is attributed to the dilution effect by the percolating rainwater, which has also been reflected in the form of a decrease in concentrations of other elements. The petrographic studies of the rock samples collected from the study area show that the rocks are mainly composed of plagioclase, orthoclase, and quartz with abundant biotite. The weathering and dissolution of biotite plays an important role in controlling the fluoride concentrations in the groundwater of the study area. © 2018, Saudi Society for Geosciences.