Geochemical Characteristics and Genetic Significance of Datangpo‐Type Manganese Ore Deposits during the Cryogenian Period

The Datangpo‐type manganese ore deposits, which formed during the Nanhuan (Cryogenian) period and are located in northeastern Guizhou and adjacent areas, are one of the most important manganese resources in China, showing good prospecting potential. Many middle‐to‐large deposits, and even super‐large mineral deposits, have been discovered. However, the genesis of manganese ore deposits is still controversial and remains a long‐standing source of debate; there are several viewpoints including biogenesis, hydrothermal sedimentation, gravity flows, cold‐spring carbonates, etc. Geochemical data from several manganese ore deposits show that there are positive correlations between Al₂O₃ and TiO₂, SiO₂, K₂O, and Na₂O, and strong negative correlations between Al₂O₃ and CaO, MgO, and MnO in black shales and manganese ores. U, Mo, and V show distinct enrichment in black shales and inconspicuous enrichment in Mn ores. Ba and Rb show strong positive correlations with K₂O in manganese ores. Cu, Ni, and Zn show clear correlations with total iron in both manganese ores and black shales. ∑REE of manganese ores has a large range with evident positive Ce anomalies and positive Eu anomalies. The Post Archean Australian Shale (PAAS) normalized rare earth element (REE) distribution patterns of manganese ores present pronounced middle rare earth element (MREE) enrichment, producing “hat‐shaped” REE plots. ∑REE of black shales is more variable compared with PAAS, and the PAAS‐normalized REE distribution patterns appear as “flat‐shaped” REE plots, lacking evident anomaly characteristics. δ¹³C values of carbonate in both manganese ores and the black shales show observable negative excursions. The comprehensive analysis suggests that the black shales formed in a reducing and quiet water column, while the manganese ores formed in oxic muddy seawater, which resulted from periodic transgressions. There was an oxidation–reduction cycle of manganese between the top water body and the bottom water body caused by the transgressions during the early Datangpo, which resulted in the dissolution of manganese. Through the exchange of the euphotic zone water and the bottom water, and episodic inflow of oxygenated water, the manganese in the bottom water was oxidized to Mn‐oxyhydroxides and rapidly buried along with algae. In the early diagenetic stage, Mn‐oxyhydroxides were reduced and dissolved in the anoxic pore water and then transformed into Mn‐carbonates by reacting with HCO₃^? from the degradation of organic matter or from seawater. In the intervals between transgressions, continuous supplies of terrigenous clastics and the high productive rates of organic matter in the euphotic zone resulted in the deposition of the black shales enriched in organic matter.     

The interaction of cobalt with hydrous manganese dioxide

Adsorption of cobalt on synthetic hydrous manganese dioxide was studied as a function of pH and surface area in NaCl solutions and solutions containing sea water concentrations of Na, Ca and Mg. The amount of cobalt adsorbed increased sharply at pH 6, a significantly lower pH than that required for significant hydrolysis of Co(II) or precipitation of Co(OH)₂(S) in bulk solution. Sea water concentrations of Na, Ca and Mg have little effect on adsorption until the cobalt concentration is less than 10^?7 M.Micro-electrophoresis experiments from 1 × 10^?3 M to 1 × 10^?5 M to Co(II) show three charge reversals. The first is the pH of zero point charge of hydrous manganese dioxide. The second correlates well with the abrupt increase in adsorption at pH 6 and may reflect both specific adsorption of Co(II) and precipitation of Co(OH)₂ on the surface. The third agrees well with literature values for the pH of zero point of charge of Co(OH)₂.An adsorption isotherm was constructed for cobalt and these data were used to test the hypothesis that the enrichment of cobalt in the suspended matter of the Black Sea is due to adsorption of cobalt from sea water by manganese dioxide. The calculations indicate that adsorption is a feasible explanation for this example.     

Formation of iron-containing colloids by the weathering of phyllite

The formation of colloids during the weathering of phyllite was investigated by exposing ground phyllite to Milli-Q water. Secondary mineral colloids of 10¹–10² nm were detected in significant concentrations. At pH of about 8.5, the solution concentration of these colloids reached up to 10 mg/L (however, acidification to pH 4.0 prevented the formation of the colloids). The mineralogical composition of the secondary mineral colloids is assumed to be a mixture of ferrihydrite, manganese oxyhydroxides, aluminosilicates, amorphous Al(OH)₃ and gibbsite with possible additions of iron silicates and␣iron-alumino silicates. The colloids were stable over longer periods of time (at least several weeks), even in the presence of suspended ground rock. Direct formation of iron-containing secondary mineral colloids at the rock–water interface by the weathering of rock material is an alternative to the well-known mechanism of iron colloid formation in the bulk of water bodies by mixing of different waters or by aeration of anoxic waters. This direct mechanism is of relevance for colloid production during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine waste rock piles. Colloids produced by this mechanism, too, can influence the transport of contaminants such as actinides because these colloids have a large specific surface area and a high sorption affinity.     

Formation and stability of schwertmannite in acidic mining lakes

Schwertmannite (ideal formula: Fe₈O₈(OH)₆SO₄) is typically found as a secondary iron mineral in pyrite oxidizing environments. In this study, geochemical constraints upon its formation are established and its role in the geochemical cycling of iron between reducing and oxidizing conditions are discussed. The composition of surface waters was analyzed and sediments characterized by X-ray diffraction, FTIR spectroscopy and determination of the Fe:S ratio in the oxalate extractable fraction from 18 acidic mining lakes. The lakes are exposed to a permanent supply of pyritegenous ferrous iron from adjacent ground water. In 3 of the lakes the suspended matter was fractionated using ultra filtration and analyzed with respect to their mineral composition. In addition, stability experiments with synthetic schwertmannite were performed. The examined lake surface waters were O₂-saturated and have sulfate concentrations (10.3 ± 5.5 mM) and pH values (3.0 ± 0.6) that are characteristic for the stability window of schwertmannite. Geochemical modeling implied that i) the waters were saturated with respect to schwertmannite, which controlled the activity of Fe³⁺ and sulfate, and ii) a redox equilibrium exists between Fe²⁺ and schwertmannite. In the uppermost sediment layers (1 to 5 cm depth), schwertmannite was detectable in 16 lakes—in 5 of them by all three methods. FTIR spectroscopy also proved its occurrence in the colloidal fraction (1-10 kDa) in all of the 3 investigated lake surface waters. The stability of synthetic schwertmannite was examined as a function of pH (2-7) by a 1-yr experiment. The transformation rate into goethite increased with increasing pH. Our study suggests that schwertmannite is the first mineral formed after oxidation and hydrolysis of a slightly acidic (pH 5-6), Fe(II)-SO₄ solution, a process that directly affects the pH of the receiving water. Its occurrence is transient and restricted to environments, such as acidic mining lakes, where the coordination chemistry of Fe³⁺ is controlled by the competition between sulfate and hydroxy ions (i.e. mildly acidic).     

Uranium in pacific deep-sea sediments and manganese nodules

A total of 1344 manganese nodules and 187 pelagic sediments from 9 areas in the North and the South Pacific were analyzed for U by the delayed-neutron counting technique. A strong positive correlation between U and Fe in nodules and sediments suggests a co-precipitative removal from sea water into the Fe-rich ferromanganese mineral phase δ -MnO₂. Enrichment of U and Fe in nodules from the northwestern slopes of two submarine hills (U between 6 and 9 ppm) in the equatorial nodule belt is thought to be caused by directional bottom water flow creating elevated oxygenized conditions in areas opposed to the flow. Economically important nodule deposits from the nodule belt and the Peru Basin have generally low U contents, between 3 and 5 ppm. Insignificant resources of U of about 4 × 10⁵ in the Pacific manganese nodules are estimated.     

Characterization of manganese oxide precipitates from Appalachian coal mine drainage treatment systems

The removal of Mn(II) from coal mine drainage (CMD) by chemical addition/active treatment can significantly increase treatment costs. Passive treatment for Mn removal involves promotion of biological oxidative precipitation of manganese oxides (MnO_x). Manganese(II) removal was studied in three passive treatment systems in western Pennsylvania that differed based on their influent Mn(II) concentrations (20–150 mg/L), system construction (±inoculation with patented Mn(II)-oxidizing bacteria), and bed materials (limestone vs. sandstone). Manganese(II) removal occurred at pH values as low as 5.0 and temperatures as low as 2 °C, but was enhanced at circumneutral pH and warmer temperatures. Trace metals such as Zn, Ni and Co were removed effectively, in most cases preferentially, into the MnO_x precipitates. Based on synchrotron radiation X-ray diffraction and Mn K-edge extended X-ray absorption fine structure spectroscopy, the predominant Mn oxides at all sites were poorly crystalline hexagonal birnessite, triclinic birnessite and todorokite. The surface morphology of the MnO_x precipitates from all sites was coarse and “sponge-like” composed of nm-sized lathes and thin sheets. Based on scanning electron microscopy (SEM), MnO_x precipitates were found in close proximity to both prokaryotic and eukaryotic organisms. The greatest removal efficiency of Mn(II) occurred at the one site with a higher pH in the bed and a higher influent total organic C (TOC) concentration (provided by an upstream wetland). Biological oxidation of Mn(II) driven by heterotrophic activity was most likely the predominant Mn removal mechanism in these systems. Influent water chemistry and Mn(II) oxidation kinetics affected the relative distribution of MnO_x mineral assemblages in CMD treatment systems.     

Experiments on canopy/soil leaching effects of air pollutants in model ecosystems with forest trees

In 1982 an experiment was started at the University of Hohenheim to investigate the long term effects of O₃, SO₂ and simulated acid rain in realistic concentrations, single and in combination, on mineral cycling, biochemistry, physiology and anatomy of spruce-, fir- and beech seedlings in modelecosystems. During the 5 year duration of this experiment definite effects on mineral cycling were observed. Most noticeable are throughfall enrichment with sulfate through dry deposition of SO₂, connected with elevated leaching of calcium, magnesium, manganese, zink and ammonia from needles, in total leading to an enhanced acid input to the soil. The consequence of this was that after 15 months the water percolating the soils in the lysimeters of these treatments was acidified, with elevated flowrates of sulfate, manganese, calcium and magnesium. Effects on mineral cycling are discussed in connection with observations of other groups working in the modelecosystems.     

The determination of trace elements in Fe–Mn oxide coatings on pebbles using LA-ICP-MS

Iron–manganese oxide coatings form on a wide range of geologic samples where they have the ability to adsorb elements and potentially act as a mineral exploration/environmental monitoring tool. In this study, Fe–Mn oxide coatings on stream pebbles were collected from streams in four study areas located across the province of Newfoundland and Labrador, Canada. The study locations were in areas of former copper mines (Tilt Cove and Betts Cove), carbonate geology (Robinsons River), and a metropolitan area (Rennies River). Collected pebbles underwent a simple sample preparation procedure and were then analyzed for a wide range of elements by LA-ICP-MS after optimization of the operating conditions. Water samples accompanied the pebbles, and these were analyzed for pH, dissolved oxygen, conductivity, and a large selection of elements by ICP-MS. Multivariate statistics, in the form of Principal Component Factor Analysis (PCFA) was performed on both data sets. Graphs of the factor scores from the PCFA produced groupings of the samples that were related to geologic/environmental inputs. The loading of variables in each factor was related to the adsorption of the element either to the MnO₂ or Fe₂O₃ phase with most elements except Cr and Cu displaying preferential adsorption to MnO₂. Elemental Fe–Mn oxide coating concentrations were a result of the element's affinity (chalcophile, lithophile, or siderophile), pH of the environment, stream water concentration, and amount of each oxide phase present. Even with these complications, LA-ICP-MS analysis of Fe–Mn oxides was able to identify areas of heavy metal pollution and locate geologic inputs.     

The shallow ground water chemistry of arsenic,fluorine, and major elements: Eastern Owens Lake,California

Owens Lake in SE California became essentially dry by the 1920s after the Los Angeles Aqueduct was constructed and diversion of water from the Owens River began. Frequent dust storms at Owens Lake produce clouds of efflorescent salts which present human health hazards as a result of their small particle size and elevated concentrations of As and SO₄. This study was conducted to characterize the evolution of major elements in ground water in eastern Owens Lake and to examine the factors controlling the concentrations of dissolved As and F. Evapoconcentration of shallow ground waters at the lakebed surface produces high pH, high alkalinity brines with major ion compositions that are consistent with those predicted by the Hardie–Eugster Model. Evaporite minerals identified in the surface salts using XRD were halite (NaCl), thenardite (Na₂SO₄), trona (Na₃H(CO₃)₂·2H₂O), pirssonite (Na₂Ca(CO₃)₂·2H₂O), and nesquehonite (MgCO₃·3H₂O). Significant correlations between both As and F with Li in shallow ground waters indicate that As and F are not partitioned into surface salts until very high salinities are reached (>9.0 m). Leaching experiments show that As and F can be readily released from lakebed salts when exposed to natural precipitation. Conservative behavior of As and F results from the high pH values and low Ca activities of shallow ground waters that contribute to: (1) redox stability of As(V) even at moderately reducing conditions, (2) a decrease in the adsorption affinities of As and F to mineral surfaces, (3) undersaturation with respect to fluorite (CaF₂(s)).     

On the distribution of iron and manganese at the sediment/water interface: thermodynamic versus kinetic control

Iron and manganese solubility at the sediment/water interface has been studied at a water depth of 20 m in Kiel Bight, Western Baltic. By means of an in situ bell jar system enclosing 3.14 m² sediment surface and 2094 l water a complete redox turn-over in the bottom water was simulated in an experiment lasting 99 days. The concentration of dissolved Fe in the bell jar water never exceeded 0.041 μmol · dm^?3during the first 50 days of the experiment and then rose abruptly as the Eh fell from +600 to ?200 mV. The concentration of dissolved Fe under oxic and anoxic conditions seems to be limited by equilibria with solid Fe-phases (hydroxides and amorphous sulphide, respectively). In contrast to Fe, manganese was released continuously from the bottom during the first 50 days of the experiment leading to exponentially increasing manganese concentrations in the bell jar water. During this time dissolved O₂ had become ready depleted and pH had dropped from 8.3 to 7.5. Contrary to iron, manganese being solubilized in reduced sediment layers can penetrate oxic strata in metastable form due to slow oxidation kinetics; when the redoxcline moves upwards Mn²⁺ is enriched in bottom waters. The maximum concentration of dissolved Mn under anoxic conditions is controlled by a solid phase with solubility properties similar to MnCO₃ (rhodochrosite). Bottom water enrichment in dissolved Mn²⁺ could be traced to originate from excess solid manganese within the top 3 cm of the sediment.     

Geochemical modeling approach to predicting arsenic concentrations in a mine pit lake

Between 1968 and 1983, the North pit at the Getchell Mine, Humboldt County, NV, filled with water to form a lake. In 1983, water quality data were collected with the following results: As concentrations of 0.29 to 0.59 mg/L, pH of 7.1 to 7.9, SO₄ concentrations of 1490 to 1640 mg/L, and TDS of 2394 to 2500 mg/L. Using geochemical modeling techniques presented here, pit lake waters have been theoretically allowed to react for 8.5 a, the approximate time that the North pit had been completely full by 1983. Modeling results predict pH of 7.9 to 8.2, SO₄ concentrations of 1503 to 1644 mg/L, TDS of 2054 to 2366 mg/L, and As concentrations ranging from 0.57 in the hypolimnion to 96 mg/L in the epilimnion. In the epilimnion, model results do not match observed As concentrations, suggesting that mechanisms, such as precipitation of arsenate salts or adsorption to mineral surfaces, may control As levels in an actual pit lake system. Adsorption to Fe oxyhydroxide surfaces is questioned by the authors because of the low Fe content in the Getchell system, but adsorption to Al(OH)₃ (gibbsite) and clay mineral surfaces may be important in controlling natural As concentrations.     

Geochemical reactions and dynamics during titration of a contaminated groundwater with high uranium, aluminum, and calcium

This study investigated possible geochemical reactions during titration of a contaminated groundwater with a low pH but high concentrations of aluminum, calcium, magnesium, manganese, and trace contaminant metals/radionuclides such as uranium, technetium, nickel, and cobalt. Both Na-carbonate and hydroxide were used as titrants, and a geochemical equilibrium reaction path model was employed to predict aqueous species and mineral precipitation during titration. Although the model appeared to be adequate to describe the concentration profiles of some metal cations, solution pH, and mineral precipitates, it failed to describe the concentrations of U during titration and its precipitation. Most U (as uranyl, UO₂²⁺) as well as Tc (as pertechnetate, TcO₄⁻) were found to be sorbed and coprecipitated with amorphous Al and Fe oxyhydroxides at pH below ∼5.5, but slow desorption or dissolution of U and Tc occurred at higher pH values when Na₂CO₃ was used as the titrant. In general, the precipitation of major cationic species followed the order of Fe(OH)₃ and/or FeCo_0.1(OH)_3.2, Al₄(OH)₁₀SO₄, MnCO₃, CaCO₃, conversion of Al₄(OH)₁₀SO₄ to Al(OH)_3,am, Mn(OH)₂, Mg(OH)₂, MgCO₃, and Ca(OH)₂. The formation of mixed or double hydroxide phases of Ni and Co with Al and Fe oxyhydroxides was thought to be responsible for the removal of Ni and Co in solution. Results of this study indicate that, although the hydrolysis and precipitation of a single cation are known, complex reactions such as sorption/desorption, coprecipitation of mixed mineral phases, and their dissolution could occur simultaneously. These processes as well as the kinetic constraints must be considered in the design of the remediation strategies and modeling to better predict the activities of various metal species and solid precipitates during pre- and post-groundwater treatment practices.     

Modeling transport of arsenic through modified granular natural siderite filters for arsenic removal

Groundwater arsenic(As)contamination is a hot issue,which is severe health concern worldwide.Recently,many Fe-based adsorbents have been used for As removal from solutions.Modified granular natural siderite(MGNS),a special hybrid Fe(II)/Fe(III)system,had higher adsorption capacity for As(III)than As(V),but the feasibility of its application in treating high-As groundwater is still unclear.In combination with transport modeling,laboratory column studies and field pilot tests were performed to reveal both mechanisms and factors controlling As removal by MGNS-filled filters.Results show that weakly acid pH and discontinuous treatment enhanced As(Ⅲ)removal,with a throughput of 8700 bed volumes(BV)of 1.0 mg/L As(Ⅲ)water at breakthrough of 10 μg/L As at pH 6.Influent HCO_3~-inhibited As removal by the filters.Iron mineral species,SEM and XRD patterns of As-loading MGNS show that the important process contributing to high As(Ⅲ)removal was the mineral transformation from siderite to goethite in the filter.The homogeneous surface diffusion modeling(HSDM)shows that competition between As(III)and HCO_3~-with adsorption sites on MGNS was negligible.The inhibition of HCO_3~-on As(Ⅲ)removal was connected to inhibition of siderite dissolution and mineral transformation.Arsenic loadings were lower in field pilot tests than those in the laboratory experiments,showing that high concentrations of coexisting anions(especially HCO_3~-and SiO_4~(4-)),high pH,low EBCT,and low groundwater temperature decreased As removal.It was suggested that acidification and aeration of highAs groundwater and discontinuous treatment would improve the MGNS filter performance of As removal from real high-As groundwater.     

Geochemical modeling of arsenic sulfide oxidation kinetics in a mining environment

Arsenic sulfide (AsS (am), As₂S₃ (am), orpiment, and realgar) oxidation rates increase with increasing pH values. The rates of arsenic sulfide oxidation at higher pH values relative to those at pH∼2 are in the range of 26-4478, 3-17, 8-182, and 4-10 times for As₂S₃ (am), orpiment, AsS (am), and realgar, respectively.Numerical simulations of orpiment and realgar oxidation kinetics were conducted using the geochemical reaction path code EQ3/6 to evaluate the effects of variable DO concentrations and mineral reactivity factors on water chemistry evolution during orpiment and realgar oxidation. The results show that total As concentrations increase by ∼1.14 to 13 times and that pH values decrease by ∼0.6 to 4.2 U over a range of mineral reactivity factors from 1% to 50% after 2000 days (5.5 yr). The As release from orpiment and realgar oxidation exceeds the current U.S. National Drinking Water Standard (0.05 ppm) approximately in 200-300 days at the lowest initial dissolved oxygen concentration (3 ppm) and a reactivity factor of 1%. The results of simulations of orpiment oxidation in the presence of albite and calcite show that calcite can act as an effective buffer to the acid water produced from orpiment oxidation within relatively short periods (days/months), but the release of As continues to increase.Pyrite oxidation rates are faster than orpiment and realgar from pH 2.3 to 8; however, pyrite oxidation rates are slower than As₂S₃ (am) and AsS (am) at pH 8. The activation energies of arsenic sulfide oxidation range from 16 to 124 kJ/mol at pH∼8 and temperature 25 to 40°C, and pyrite activation energies are ∼52 to 88 kJ/mol, depending on pH and temperature range. The magnitude of activation energies for both pyrite and arsenic sulfide solids indicates that the oxidation of these minerals is dominated by surface reactions, except for As₂S₃ (am). Low activation energies of As₂S₃ (am) indicate that diffusion may be rate controlling.Limestone is commonly mixed with sulfide minerals in a mining environment to prevent acid water formation. However, the oxidation rates of arsenic sulfides increase as solution pH rises and result in a greater release of As. Furthermore, the lifetimes of carbonate minerals (i.e., calcite, aragonite, and dolomite) are much shorter than those of arsenic sulfide and silicate minerals. Thus, within a geologic frame time, carbonate minerals may not be present to act as a pH buffer for acid mine waters. Additionally, the presence of silicate minerals such as pyroxenes (wollastonite, jadeite, and spodumene) and Ca-feldspars (labradorite, anorthite, and nepheline) may not be important for buffering acid solutions because these minerals dissolve faster than and have shorter lifetimes than sulfide minerals. However, other silicate minerals such as Na and K-feldspars (albite, sanidine, and microcline), quartz, pyroxenes (augite, enstatite, diopsite, and MnSiO₃) that have much longer lifetimes than arsenic sulfide minerals may be present in a system. The results of our modeling of arsenic sulfide mineral oxidation show that these minerals potentially can release significant concentrations of dissolved As to natural waters, and the factors and mechanisms involved in arsenic sulfide oxidation warrant further study.     

Rare earth elements,neodymium and strontium isotopic systematics in mineral waters: evidence from the Massif Central,France

Rare Earth Elements (REEs), and Sr and Nd isotope distributions, have been studied in mineralized waters from the Massif Central (France). The CO₂-rich springs are characterized by a neutral pH (6–7) associated with total dissolved solids (TDS) from 1 to 7 g l⁻¹. The waters result from the mixing of very mineralized water pools, thought to have equilibrated at a temperature of around 200°C with superficial waters. These two mineral water pools evidenced by Sr isotopes and dissolved REEs could reflect 2 different stages of water–rock interaction and an equilibrium with different mineral assemblages.The concentrations of individual dissolved REEs and total dissolved REEs (ΣREE), in the mineral waters examined, vary over several orders of magnitude but are not dependent on the main parameters of the waters (TDS, T°C, pH, Total Organic C). The dissolved REE concentrations presented as upper continental crust normalized patterns show HREE enrichment in most of the samples. The time evolution of REE patterns does not show significant fluctuations except in 1 borehole, located in the Limagne d’Allier area, which was sampled on 16 occasions over an 18 month period. Ten samples are HREE-enriched, whereas 6 samples show flat patterns.The aqueous speciation of REEs shows that CO²⁻₃ complexes dominate (>80%) over the free metal, F⁻, SO²⁻₄ and HCO⁻₃ complexes. The detailed speciation demonstrates that the fractionation of REEs (i.e. the HREE enrichment) in CO₂-rich and pH neutral fluids is due essentially to the predominance of the CO²⁻₃ complexes.The Sr isotopic composition of the mineral waters in the Massif Central shows different mixing processes; in the Cézallier area at least 3 end-member water types exist. The most dilute end-member is likely to originate as poorly mineralized waters with minimal groundwater circulation. Two other mineralized end-members are identified, although the link between the geographical location of spring outflow and the mixing proportion between the 2 end-members is not systematic. The range in ϵ_Nd(0) for mineralized waters in the Massif Central correlates well with that of the known parent rocks except for 4 springs. One way to explain the ϵ_Nd(0) in these instances is a contribution from drainage of volcanic rocks. The isotopic systematics help to constrain the hydrogeological models for this area.     

Effects of pH on arsenic mineralogy and stability in Poldice Valley,Cornwall, United Kingdom

Many abandoned mine sites in Cornwall, UK, are characterised by elevated concentrations of arsenic (As), which can cause contamination of surrounding soil and water resources. These sites have important historical value that requires access to be maintained, despite exposure of humans to toxins that may lead to health issues including hyperpigmentation keratosis (including skin cancers) and liver fibrosis. The abandoned mine tailings at Wheal Maid has been assessed for As-bearing mineralogy and stability taking into account the public footpaths made by the local council to areas of potential contamination.To assess the potential risk associated with these mine sites, the As concentration in waters along the tailings dam and Carnon River have been measured and range up to 3.6 ppm, which is 2 orders of magnitude above the WHO guideline value of 0.01 ppm for drinking water. Samples of water, rocks and soils from the mine tailings ponds and the Carnon River were analysed using Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) to determine the concentration of individual elements in each sample followed by mineral identification using X-Ray Diffraction (XRD). Mineralogical evaluation indicated that the majority of mine tailings consist of clay-rich rocks, with few associated As-bearing minerals. Scorodite (FeAsO₄·2H₂O) is observed in the mine tailings pond and appears critical to the As distribution and storage in this surface environment. Using the analysed water chemistry, a modified version of PHREEQC is used to calculate the saturation index of scorodite as a function of pH conditions. The strong variation of the solubility of this mineral with pH and oxidation state highlights potential risks for using scorodite for As fixation and storage.     

Status of arsenic contamination in potable water of Northern areas of Mizoram State and its adjoining areas of Southern Assam, India

A reconnaissance survey was conducted to examine the physicochemical properties of the potable water of Northern parts of the State of Mizoram, India, as well as the adjoining southern parts of the State of Assam, India. Groundwater samples were taken from those sources of water which were used as potable water source in the area. All the samples were analyzed for ionic concentrations of potassium (K⁺), sodium (Na⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chlorine (Cl^?), sulfate (SO ₄ ^2? ), manganese (Mn), iron (Fe), and arsenic (As). Parameters such as pH, electrical conductivity, total dissolved solids, and total hardness were also measured in situ using digital instruments. The aim of the present work is to study the various physicochemical parameters following the recommendations of World Health Organization in order to test whether these sources are safe enough to be used as potable water resources. Furthermore, present work will throw light on the probable causes of presence of arsenic in Silchar City of southern Assam and total absence of it in neighboring state of Mizoram.     

Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range,Germany: A Laboratory and Field Study

Field and laboratory investigations were performed to identify the principal mechanisms of the hydrochemical groundwater evolution among low mineralised groundwater in the Triassic Bunter sandstone aquifer of the Odenwald low mountain range, central Germany. Hydrochemical composition comprises low pH, SO₄-rich shallow groundwaters issued by springs (Ca-Mg-SO₄-type) grading to SO₄-poor deep groundwaters with near-neutral pH (Ca-HCO₃-type). Batch experiments of the original rock were run to determine primary mineral alteration reactions and the origin of dissolved ions. Principal experimental reactions comprise the decomposition of anorthite, K-feldspar, biotite and jarosite as mineral components of the original sandstone rock and the formation of clay minerals of the smectite group (Ca-montmorillonite, beidellite), and iron hydroxides as secondary minerals. Mobilisation of fluid inclusion in quartz grains contributes to Na and Cl concentrations in the leachates. The evolution of deep groundwater circulation proceeds by mineral alteration reactions calculated by the inverse modelling of both primary and secondary minerals to produce low-T mineral phases. The dissolution of K-feldspar converts Ca-montmorillonite to illite (illitisation). The formation of Na-beidellite correlates with decreasing concentration of Na in solution. Mineral reactions further proceed to the formation of kaolinite as stable mineral phase. As indicated by modelled adsorption curves, the decrease of SO₄ concentrations during groundwater evolution relates to the adsorption of SO₄ on iron hydroxides. The leaching of calcite indicated for individual groundwaters relates to the distribution of loess in the appropriate catchment areas.     

Linking groundwater quality to residence times and regional geology in the St. Lawrence Lowlands,southern Quebec,Canada

The assessment of groundwater quality in shallow aquifers is of high societal relevance given that large populations depend directly on these water resources. The purpose of this study was to establish links between groundwater quality, groundwater residence times, and regional geology in the St. Lawrence Lowlands fractured bedrock aquifer. The study focuses on a 4500 km² watershed located in the St. Lawrence Lowlands of the province of Quebec in eastern Canada. A total of 150 wells were sampled for major, minor, and trace ions. Tritium (³H) and its daughter element, ³He, as well as radiocarbon activity (A¹⁴C) were measured in a subset of wells to estimate groundwater residence times. Results show that groundwater evolves from a Ca–HCO₃ water type in recharge zones (i.e., the Appalachian piedmont) to a Na–HCO₃ water type downgradient, toward the St. Lawrence River. Locally, barium (Ba), fluoride (F), iron (Fe), and manganese (Mn) concentrations reach 90, 2, 18, and 5.9 mg/L respectively, all exceeding their respective Canadian drinking water limits of 1, 1.5, 0.3, and 0.05 mg/L. Release of these elements into groundwater is mainly controlled by the groundwater redox state and pH conditions, as well as by the geology and the duration of rock–water interactions. This evolution is accompanied by increasing ³H/³He ages, from 4.78 ± 0.44 years upgradient to more than 60 years downgradient. Discrepancies between calculated ³H/³He and ¹⁴C water ages (the latter ranging from 280 ± 56 to 17,050 ± 3410 years) suggest mixing between modern water and paleo-groundwater infiltrated through subglacial recharge when the Laurentide Ice Sheet covered the study area, and during the following deglaciation period. A linear relationship between ³H activity and corrected ¹⁴C versus Mg/Ca and Ba support a direct link between water residence time and the chemical evolution of these waters. The Ba, F, Fe, and Mn concentrations in groundwater originate from Paleozoic rocks from both the St. Lawrence Platform and the Appalachian Mountains. These elements have been brought to the surface by rising hydrothermal fluids along regional faults, and trapped in sediment during their deposition and diagenesis due to reactions with highly sulfurous and organic matter-rich water. Large-scale flow of meltwater during subglacial recharge and during the subsequent retreat of the Laurentide Ice Sheet might have contributed to the leaching of these deposits and their enrichment in the present aquifers. This study brings a new and original understanding of the St. Lawrence Lowlands groundwater system within the context of its geological evolution.