The solubility and speciation of molybdenum in water vapour at elevated temperatures and pressures: Implications for ore genesis

The solubility of molybdenum trioxide in liquid-undersaturated water vapour has been investigated experimentally at 300, 320, and 360 °C and 39-154 bars. Results of these experiments show that the solubility of MoO₃ in water vapour is between 1 and 29 ppm, which is 19-20 orders of magnitude higher than the vapour pressure of MoO₃(g). Molybdenum solubility increases exponentially with f_H2O, suggesting the formation of a gaseous hydrated complex of the type MoO₃·nH₂O by the reaction:

(A.1)     

Timing of the last deglaciation in Lithuania

Boulders from the Grūda Moraine, which is associated with the maximum extent of the Scandinavian Ice Sheet (SIS) during the last glaciation, and the Baltija (also referred to as the South Lithuanian), the Middle and North Lithuanian moraines, which are associated with recessional stages of the SIS, were sampled for surface exposure dating using ¹⁰Be. By combining these data with existing radiocarbon ages, we developed a chronology for the retreat of the SIS margin in Lithuania. Our new ¹⁰Be ages suggest that the SIS margin began to retreat from its maximum extent at 18.3 ± 0.8 ¹⁰Be kyr. Based on a probable correlation of the Baltija Moraine with the Pomeranian Moraine in Poland, we infer that the Baltija Moraine was formed following a re-advance of the SIS margin. The ice margin retreated from the Baltija position at 14.0 ± 0.4 ¹⁰Be kyr. The SIS-margin retreat paused at least two more times to form the Middle Lithuanian Moraine at 13.5 ± 0.6 ¹⁰Be kyr and the North Lithuanian Moraine (tentatively correlated to the Pajūris Moraine) at 13.3 ± 0.7 ¹⁰Be kyr. Subsequent ice-margin retreat from the North Lithuanian Moraine represented the final deglaciation of Lithuania. Direct dating of these moraines better constrains the relation of ice-margin positions in Lithuania to those in adjacent countries as well as the SIS response to climate change.     

Chemical characteristics of PM<Subscript>10</Subscript> aerosols and airmass trajectories over Bay of Bengal and Arabian Sea during ICARB

For the first time, chemical characterization of PM₁₀ aerosols was attempted over the Bay of Bengal (BoB) and Arabian Sea (AS) during the ICARB campaign. Dominance of SO ₄ ^2? , NH ₄ ⁺ and NO ₃ ^? was noticed over both the regions which indicated the presence of ammonium sulphate and ammonium nitrate as major water soluble particles playing a very important role in the radiation budget. It was observed that all the chemical constituents had higher concentrations over Bay of Bengal as compared to Arabian Sea. Higher concentrations were observed near the Indian coast showing influence of landmass indicating that gaseous pollutants like SO₂, NH₃ and NO _x are transported over to the sea regions which consequently contribute to higher SO ₄ ^2? , NH ₄ ⁺ and NO ₃ ^? aerosols respectively. The most polluted region over BoB was 13°?19°N and 70°?90°E while it was near 11°N and 75°E over AS. Although the concentrations were higher over Bay of Bengal for all the chemical constituents of PM₁₀ aerosols, per cent non-sea salt (nss) fraction (with respect to Na) was higher over Arabian Sea. Very low Ca2+ concentration was observed at Arabian Sea which led to higher atmospheric acidity as compared to BoB. Nss SO ₄ ^2? alone contributed 48% of total water soluble fraction over BoB as well as AS. Ratios SO ₄ ^2? /NO _? ³ over both the regions (7.8 and 9 over BoB and AS respectively) were very high as compared to reported values at land sites like Allahabad (0.63) and Kanpur (0.66) which may be due to very low NO.3 over sea regions as compared to land sites. Air trajectory analysis showed four classes: (i) airmass passing through Indian land, (ii) from oceanic region, (iii) northern Arabian Sea and Middle East and (iv) African continent. The highest nss SO ₄ ^2? was observed during airmasses coming from the Indian land side while lowest concentrations were observed when the air was coming from oceanic regions. Moderate concentrations of nss SO2. 4 were observed when air was seen moving from the Middle East and African continent. The pH of rainwater was observed to be in the range of 5.9–6.5 which is lower than the values reported over land sites. Similar feature was reported over the Indian Ocean during INDOEX indicating that marine atmosphere had more free acidity than land atmosphere.     

Simulation of rain-bearing summer monsoon systems along the west coast of India by use of ARMEX re-analysis

Re-analysis, using surface, upper-air, and satellite observations specially collected during the Arabian Sea Monsoon Experiment-I (ARMEX-I), has been performed with a global data assimilation system at T-80/L18 resolution. Re-analysis was performed for the entire ARMEX-I period (15th June–16th August 2002). In this paper we discuss the results based on re-analysis and subsequent forecasts for two successive intensive observation periods associated with heavy rainfall along the west coast of India during 2–12 August, 2002. Results indicate that the re-analysed fields can bring out better synoptic features, for example troughs along the west coast and mid tropospheric circulation over the Arabian Sea. Simulated rainfall distribution using re-analysis as initial condition also matches observed rainfall better than data from the initial analysis.     

Anomalous behaviour of uranium isotopes in coastal marine environment of the west coast of India

During the last few years, a remarkable anomaly between ²³⁸U and ²³⁴U activities has been observed in the top layers of the coastal sediments along the western region of the Indian sub-continent. Sediment samples from Bombay (19°N, 73°E) to Kottilppad (8°N, 77°E) were leached with saturated ammonium carbonate solution to extract uranium isotopes from the surface layers of the sediment particles without attacking the mineral cores. The ²³⁴U/²³⁸U activity ratios in these leachates are in the range of 1.12–1.14 while ²³⁵U/²³⁸U activity ratio is 0.046 which is the same as for other natural uranium.

The surface organic matter from the sediment particles was removed by treatment with hydrogen peroxide in presence of 0.05 M hydrochloric acid. ²³⁴U/²³⁸U and ²³⁵u/²³⁸U activity ratios in the extract and the residues were determined.

It is observed that disequilibrium between ²³⁸U and ²³⁴U exists only on the surface of sediment particles. ²³⁴U/²³⁸U on the surface of the sediment particles is the same as in the ambient water and as the surface organic matter is removed from the particle surface, the cores show equilibrium activities.     

Hydrogeochemical and isotopic characterizations of an aquifer in the semi-arid region of the Mexican Highlands

This work addresses hydrogeochemical processes in shallow aquifers, represented by the Quaternary alluvial deposits, from a part of the semi-arid Mexican Highlands through the evaluations of physicochemical parameters as well as the δ¹⁸O and δ²H compositions of groundwater. Mifflin diagram separates the Na-bicarbonate, sulphate and mixed groundwater into one group showing interactions with volcanic lithology in the recharge zones and another group interacting with the evaporite rich sedimentary formation. In the Gibbs diagram, the samples with Cl^?/(Cl^? + HCO₃^?) < 0.4 showed higher influence of ion exchange and the samples with Cl^?/(Cl^? + HCO₃^?) > 0.4 showed higher effects of evaporation. All of them were oversaturated with carbonate minerals (i.e., calcite and dolomite) and unsaturated with evaporites (i.e., gypsum and halite). Evaporation (earlier stage) occurred before the water-rock interactions (later stage). Evolution occurs through three different routes such as up to 7.5‰ enrichment in δ¹⁸O caused by the infiltration with a certain delay and subsequently, the water-rock interaction became dominant. Ternary mixing models revealed dominant influence of local recharge (C₁) on the water system, contributing 70.4%. Water-rock interaction (C₃) with 18% and evaporation (C₂) with 11.6% had comparatively less influences. The presence of nitrate (2–60 mg/L) in the groundwater indicated variable degrees of anthropogenic pollution.     

Proterozoic basic magmatism of the Siberian Craton: Main stages and their geodynamic interpretation

Geological data on the Precambrian basic complexes of the Siberian Craton and their isotopic age are considered. The three main episodes of Precambrian basic magmatism of Siberia correspond to certain stages of the geodynamic evolution of the craton and the Earth as a whole. In the Late Paleoproterozoic, largely in the south and the north of the craton, the basic rocks were emplaced against the background of post-collision extension, which followed the preceding collision-accretion stage responsible for the formation of the craton. In the Mesoproterozoic, primarily in the north of the craton, basic magmatism was controlled by dispersed within-plate extension apparently caused by the impact of a mantle plume. Neoproterozoic basic magmatism widespread in the southern and southeastern parts of the craton was caused by rifting, which accompanied breakdown of the Rodinia supercontinent and opening of the Paleoasian ocean along the southern margin of the Siberian Craton.     

The Triassic of the Thakkhola (Nepal). II: Paleolatitudes and comparison with other Eastern Tethyan Margins of Gondwana

During the Triassic, the Thakkhola region of the Nepal Himalaya was part of the broad continental shelf of Gondwana facing a wide Eastern Tethys ocean. This margin was continuous from Arabia to Northwest Australia and spanned tropical and temperate latitudes.A compilation of Permian, Triassic and early Jurassic paleomagnetic data from the reconstructed Gondwana blocks indicates that the margin was progressively shifting northward into more tropical latitudes. The Thakkhola region was approximately 55° S during Late Permian, 40° S during Early Triassic, 30° S during Middle Triassic and 25° S during Late Triassic. This paleolatitude change produced a general increase in the relative importance of carbonate deposition through the Triassic on the Himalaya and Australian margins. Regional tectonics were important in governing local subsidence rates and influx of terrigenous clastics to these Gondwana margins; but eustatic sea-level changes provide a regional and global correlation of major marine transgressions, prograding margin deposits and shallowing-upward successions. A general mega-cycle characterizes the Triassic beginning with a major transgression at the base of the Triassic, followed by a general shallowing-upward of facies during Middle and Late Triassic, and climaxing with a regression in the latest Triassic.     

Arsenic contamination of ground and pond water and water purification system using pond water in Bangladesh

This paper, firstly, shows the distribution of arsenic-contaminated groundwater in Samta village. This village, which is in Jessore district in Bangladesh, was chosen as a model village for investigating the mechanism of groundwater contamination. 90% of the tube wells in this village had arsenic concentrations above the Bangladesh standard of 0.05 mg/l. Tube wells with arsenic concentrations of over 0.50 mg/l were distributed in the southern part of the village with a belt-like shape from east to west. Secondly, groundwater distribution is discussed with respect to its flow and the high arsenic zone (As≥0.50 mg/l) agrees well with the drifting zone of the groundwater. Furthermore, arsenic-free water supply systems suitable for a small area in the village have been developed. A pond sand filter (PSF) system which purifies pond water is discussed in this paper. Prior to the construction of the PSF, the water quality in ponds was examined for arsenic levels. The inflow of drainage from the tube wells was found to be the major cause of arsenic contamination of pond water. The PSF installed in Samta is working very well and produces a good quality of treated water.