Structural and vibrational behaviour of fluorapatite with pressure. Part II: in situ micro-Raman spectroscopic investigation

 High-pressure Raman investigations were carried out on a synthetic fluorapatite up to about 7 GPa to analyse the behaviour of the phosphate group's internal modes and of its lattice modes. The Raman frequencies of all modes increased with pressure and a trend toward reduced splitting was observed for the PO₄-stretching modes [(ν_3a(A_g) and ν_3b(A_g); ν_3a(E_2g) and ν_3b(E_2g)] and the PO₄ out-of-plane bending modes [ν_4a(A_g) and ν_4b(A_g)]. The pressure coefficients of phosphate modes ranged from 0.0047 to 0.0052 GPa⁻¹ for ν₃, from 0.0025 to 0.0044 GPa⁻¹ for ν₄, from 0.0056 to 0.0086 GPa⁻¹ for ν₂ and 0.0046 for ν₁ GPa⁻¹, while the pressure coefficients of lattice modes ranged from 0.0106 to 0.0278 GPa⁻¹. The corresponding Grüneisen parameters varied from 0.437 to 0.474, 0.428, 0.232 to 0.409 and 0.521 to 0.800 for phosphate modes ν₃, ν₁, ν₄, ν₂, respectively, and from 0.99 to 2.59 for lattice modes. The vibrational behaviour was interpreted in view of the high-pressure structural refinement performed on the same crystal under the same experimental conditions. The reduced splitting may thus be linked to the reduced distortion of the environment around the phosphate tetrahedron rather than to the decrease of the tetrahedral distortion itself. Moreover, the amount of calcium polyhedral compression, which is about three times the compression of phosphate tetrahedra, may explain the different Grüneisen parameters. Received: 25 April 2000 / Accepted: 20 December 2000     

Phase relations in the MgO–P2O5–H2O system and the stability of phosphoellenbergerite: petrological implications

The polymorphic relations for Mg₃(PO₄)₂ and Mg₂PO₄OH have been determined by reversed experiments in the temperature-pressure (T-P) range 500–1100 °C, 2–30 kbar. The phase transition between the low-pressure phase farringtonite and Mg₃(PO₄)₂-II, the Mg analogue of sarcopside, is very pressure dependent and was tightly bracketed between 625 °C, 7 kbar and 850 °C, 9 kbar. The high-temperature, high-pressure polymorph, Mg₃(PO₄)₂-III, is stable above 1050 °C at 10 kbar and above 900 °C at 30 kbar. The low-pressure stability of farringtonite is in keeping with its occurrence in meteorites. The presence of iron stabilizes the sarcopside-type phase towards lower P. From the five Mg₂PO₄OH polymorphs only althausite, holtedahlite, β-Mg₂PO₄OH (the hydroxyl analogue of wagnerite) and ɛ-Mg₂PO₄OH were encountered. Relatively speaking, holtedahlite is the low-temperature phase (<600 °C), ɛ-Mg₂PO₄OH the high-temperature, low-pressure phase and β-Mg₂PO₄OH the high-temperature, high-pressure phase, with an intervening stability field for althausite which extends from about 3 kbar at 500 °C to about 12 kbar at 800 °C. Althausite and holtedahlite are to be expected in F-free natural systems under most geological conditions; however, wagnerite is the most common Mg-phosphate mineral, implying that fluorine has a major effect in stabilizing the wagnerite structure. Coexisting althausite and holtedahlite from Modum, S. Norway, show that minor fluorine is strongly partitioned into althausite (K_D ^F/OH≈ 4) and that holtedahlite may incorporate up to 4 wt% SiO₂. Synthetic phosphoellenbergerite has a composition close to (Mg_0.9□_0.1)₂Mg₁₂P₈O₃₈H_8.4. It is a high-pressure phase, which breaks down to Mg₂PO₄OH + Mg₃(PO₄)₂ + H₂O below 8.5 kbar at 650 °C, 22.5 kbar at 900 °C and 30 kbar at 975 °C. The stability field of the phosphate end-member of the ellenbergerite series extends therefore to much lower P and higher T than that of the silicate end-members (stable above 27 kbar and below ca. 725 °C). Thus the Si/P ratio of intermediate members of the series has a great barometric potential, especially in the Si-buffering assemblage with clinochlore + talc + kyanite + rutile + H₂O. Application to zoned ellenbergerite crystals included in the Dora-Maira pyrope megablasts, western Alps, reveals that growth zoning is preserved at T as high as 700–725 °C. However, the record of attainment of the highest T and/or of decreasing P through P-rich rims (1 to 2 Si pfu) is only possible in the presence of an additional phosphate phase (OH-bearing or even OH-dominant wagnerite in these rocks), otherwise the trace amounts of P in the system remain sequestered in the core of Si-rich crystals (5 to 8 Si pfu) and can no longer react. Received: 7 April 1995 / Accepted: 12 November 1997     

The effects of fertilizer applications on runoff loss of phosphorus

The phosphorus index (PI) can be used to effectively identify areas with high risks of phosphorus losses. Manures and fertilizers are important source factors for the establishment of the PI system. An artificial precipitation experiment was performed to evaluate phosphorus losses with the applications of different types of fertilizers and manures. The results showed that the total phosphorus (TP) losses in runoff followed the order of ammonium phosphate monobasic (NH₄H₂PO₄), ammonium hydrogen phosphate ((NH₄)₂HPO₄), monobasic potassium phosphate (KH₂PO₄), chicken manure, and cattle manure with surface application of these fertilizers and manures. The order was slightly changed to NH₄H₂PO₄, KH₂PO₄, (NH₄)₂HPO₄, chicken manure, and cattle manure with incorporation application under the same rainfall condition. Both the methods and the rate of manure application can affect the amounts of phosphorus in water and particles of runoff. More than 90 % of TP in runoff were lost through suspended particles. Manure application had a significant contribution to the P load in runoff.     

P-T stability of the lazulite-scorzalite solid-solution series

Summary The stability of members of the lazulite-scorzalite solid-solution series, (Mg,Fe)Al₂ (OH)₂(PO₄)₂, was investigated as a function of T (505 to 675 °C), P (0.1 to 0.3 GPa) and Fe/Mg ratio in hydrothermal synthesis experiments. The oxygen fugacity was controlled by means of the Ni/NiO buffer. It was found that starting from end-member lazulite the stability of the solid-solution members strongly decreases with increasing content of scorzalite component. At 0.2 GPa pure lazulite decomposes at about 660 °C whereas at the same pressure a solid-solution with 80% of lazulite component is only stable up to 590 °C under the oxygen fugacity of the Ni/NiO buffer. The members of the lazulite-scorzalite solid-solution series with limiting composition coexist with an Fe-richer member of the (Mg,Fe)Al(PO₄)O series and berlinite. The mixing behaviour of both the lazulite-scorzalite and the (Mg,Fe)Al(PO₄)O solid-solution series disregarding small amounts of Fe³⁺ is interpreted in terms of a model on the basis of a simple mixture for the lazulite-scorzalite system and of an ideal mixture for the (Mg,Fe)Al(PO₄)O series. With this model the interaction parameter which expresses the non-ideality of the lazulite-scorzalite solid-solution series amounts to . Zusammenfassung P-T Stabilit?t von Lazulith-Scorzalith Mischkristallen Die Stabilit?t der Glieder der Lazulith-Scorzalith Mischkristallreihe, (Mg, Fe)Al₂(OH)₂(PO₄)₂ wurde als Funktion der Temperatur (505 bis 675 °C), des Druckes (0.1 bis 0.3 GPa) und des Fe/Mg-Verh?ltnisses in hydrothermalen Syntheseversuchen untersucht. Die Sauerstoffugazit?t wurde mittels eines Ni/NiO-Puffer kontrolliert. Es konnte festgestellt werden, da? ausgehend vom Lazulith-Endglied die Stabilit?t der Mischkristalle mit zunehmendem Scorzalith-Gehalt stark abnimmt. Reiner Lazulith, MgAl₂(OH)₂(PO₄)₂ zerf?llt unter 0.2 GPa bei 660 °C, w?hrend ein Mischkristall mit 80 mol% Gehalt an Lazulith-Komponente nur bis 590 °C unter der Sauerstoffugazit?t des Ni/NiO-Puffers stabil ist. Hierbei koexistieren die Lazulith-Scorzalith Mischkristalle mit Grenzzusammensetzung mit eisenreicheren Mischphasen des Systems (Mg,Fe)Al(PO₄)₂O und Berlinit. Das Mischungsverhalten sowohl der Lazulith-Scorzalith- als auch der (Mg,Fe)Al(PO₄)₂O-Reihe wurde mit Hilfe eines quantitativen Modelles auf der Basis einer symmetrischen Mischung für Lazulith-Scorzalith und einer idealen Mischung für das System (Mg,Fe)Al(PO₄)₂O interpretiert. Mit Hilfe dieses Modelles wurde der Wechelwirkungsparameter , der die Nichtidealit?t der Lazulith-Scorzalith Mischreihe ausdrückt zu bestimmt. Received August 26, 1998; revised version accepted July 30, 1999     

Phosphorus solubility mechanisms in haplogranitic aluminosilicate glass and melt: effect of temperature and aluminum content

The solubility behavior of phosphorus in glasses and melts in the system Na₂O-Al₂O₃-SiO₂-P₂O₅ has been examined as a function of temperature and Al₂O₃ content with microRaman spectroscopy. The Al₂O₃ was added (2, 4, 5, 6, and 8 mol% Al₂O₃) to melts with 80 mol% SiO₂ and ∼2 mol% P₂O₅. The compositions range from peralkaline, via meta-aluminous to peraluminous. Raman spectra were obtained of both the phosphorus-free and phosphorous-bearing glasses and melts between 25 and 1218 °C. The Raman spectrum of Al-free, P-bearing glass exhibits a characteristic strong band near 940 cm⁻¹ assigned to P=O stretching in orthophosphate complexes together with a weaker band near 1000 cm⁻¹ assigned P₂O₇ complexes. With increasing Al content, the proportion of P₂O₇ initially increases relative to PO₄ and is joined by AlPO₄ complexes which exhibit a characteristic P-O stretch mode slightly above 1100 cm⁻¹. The latter complex appears to dominate in meta-aluminosilicate glass and is the only phosphate complex in peraluminous glasses. When P-bearing peralkaline silicate and aluminosilicate glasses are transformed to supercooled melts, there is a rapid decrease in PO₄/P₂O₇ so that in the molten state, PO₄ units are barely discernible. The P₂O₇/AlPO₄ abundance ratio in peralkaline compositions increases with increasing temperature. This decrease in PO₄/P₂O₇ with increasing temperature results in depolymerization of the silicate melts. Dissolved P₂O₅ in peraluminous glass and melts forms AlPO₄ complexes only. This solution mechanism has no discernible influence on the aluminosilicate melt structure. There is no effect of temperature on this solution mechanism. Received: 7 October 1997 / Accepted: 11 May 1998     

The crystal structure of arsentsumebite, Pb2Cu[(As, S)O4]2(OH)

Summary The crystal structure of arsentsumebite, ideally, Pb₂Cu[(As, S)O₄]₂(OH), monoclinic, space group P2₁/m, a = 7.804(8), b = 5.890(6), c = 8.964(8) ?, β = 112.29(6)°, V = 381.2 ?³, Z = 2, d_calc. = 6.481 has been refined to R = 0.053 for 898 unique reflections with I> 2σ(I). Arsentsumebite belongs to the brackebuschite group of lead minerals with the general formula Pb₂ Me(XO₄)₂(Z) where Me = Cu²⁺, Mn²⁺, Zn²⁺, Fe²⁺, Fe³⁺; X = S, Cr, V, As, P; Z = OH, H₂O. Members of this group include tsumebite, Pb₂Cu(SO₄)(PO₄)(OH), vauquelinite, Pb₂Cu(CrO₄)(PO₄)(OH), brackebuschite, Pb₂ (Mn, Fe)(VO₄)₂(OH), arsenbracke buschite, Pb₂(Fe, Zn)(AsO₄)₂(OH, H₂O), fornacite, Pb₂Cu(AsO₄)(CrO₄)(OH), and feinglosite, Pb₂(Zn, Fe)[(As, S)O₄]₂(H₂O). Arsentsumebite and all other group members contain M = M–T chains where M = M means edge-sharing between MO₆ octahedra and M–T represents corner sharing between octahedra and XO₄ tetrahedra. A structural relationship exists to tsumcorite, Pb(Zn, Fe)₂(AsO₄)₂ (OH, H₂O)₂ and tsumcorite-group minerals Me(1)Me(2)₂(XO₄)₂(OH, H₂O)₂. Received June 24, 2000; revised version accepted February 8, 2001     

Geochemical modeling of coal mine drainage, Summit County, Ohio

 Geochemical modeling was used to investigate downstream changes in coal mine drainage at Silver Creek Metro-park, Summit County, Ohio. A simple mixing model identified the components that are undergoing conservative transport (Cl^–, PO₄ ^3–, Ca²⁺, K⁺, Mg²⁺ and Na⁺) and those undergoing reactive transport (DO, HCO₃ ^–, SO₄ ^2–, Fe²⁺, Mn²⁺ and Si). Fe²⁺ is removed by precipitation of amorphous iron-hydroxide. Mn²⁺ are removed along with Fe²⁺ by adsorption onto surfaces of iron-hydroxides. DO increases downstream due to absorption from the atmosphere. The HCO₃ ^– concentration increases downstream as a result of oxidation of organic material. The rate of Fe²⁺ removal from the mine drainage was estimated from the linear relationship between Fe⁺² concentration and downstream distance to be 0.126 mg/s. Results of this study can be used to improve the design of aerobic wetlands used to treat acid mine drainage. Received: 4 June 1996 · Accepted: 17 September 1996     

Fluid chemistry and processes at the Porgera gold deposit, Papua New Guinea

The Porgera gold deposit in Papua New Guinea is a world-class example of an alkalic-type epithermal gold system (stage II), which overprints a precursor stage of magmatic-hydrothermal gold mineralization (stage I). Gas and ion chromatographic analyses of fluid inclusions contained in vein minerals from both mineralization stages have been carried out in order to constrain the compositions of the fluids involved in, and the processes attending, ore deposition. These data indicate the presence of three end-member liquids, the most dilute of which was present throughout the mineralization history and is interpreted to represent evolved groundwater of meteoric origin. Its composition is estimated to have been approximately 500 mM Na⁺, 10 mM K⁺, 5 mM Li⁺, 250 mM Cl⁻, 0.15 mM Br⁻, and 0.01 mM I⁻, plus significant concentrations of dissolved gases. More saline liquids were also present during the two main stages of ore formation, and although their compositions differ, both are interpreted to have been derived at least in part from magmatic fluids, and to have been the media by which gold was introduced into the system. Stage I minerals contain fluid inclusions which decrease in salinity towards this dilute end-member composition through the vein paragenesis, reflecting progressive dilution at depth of the magmatic fluid source by groundwaters. Ore deposition is thought to have been caused largely by simple cooling and/or wallrock reactions, although limited in situ fluid mixing may also have occurred. The most saline fluids, present in early quartz and pyrite, contain at least 810 mM Na⁺, 530 mM Ca²⁺, 130 mM K⁺, 12 mM Li⁺, 87 mM SO₄ ²⁻, 960 mM Cl⁻, 1.1 mM Br⁻, and 0.05 mM I⁻, plus significant but variable concentrations of dissolved gases. Fluid inclusions from stage II hydraulic breccia veins reveal the presence of two distinct liquids with contrasting salinities, which were present at different times during vein formation. A higher salinity liquid appears to have predominated during mineralization, whereas lower salinity groundwaters filled the structures during intervening periods. The ore-forming fluid may have been forcibly injected into the veins from depth during fracturing and depressurization events, displacing the resident groundwaters in the process. The original composition of this fluid is estimated to have been at least 1770 mM Na⁺, 59 mM K⁺, 180 mM Li⁺, 210 mM SO₄ ²⁻, 680 mM Cl⁻, 1.4 mM Br⁻, and 0.09 mM I⁻, plus 1.5 mol% CO₂, 0.19 mol% CH₄, and 0.04 mol% N₂. Gas chromatographic analyses of fluid inclusions from stage II samples show a decrease in total gas content between early unmineralized veins and post-mineralization vuggy quartz (suitable samples could not be obtained from the ore stage itself). Post-mineralization samples plot along an experimental gas-saturation curve in the CO₂-CH₄-H₂O-NaCl system, obtained at conditions similar to those attending stage II ore deposition at Porgera (200–300 bar, ˜165 °C). These results are interpreted to indicate a period of depressurization-induced phase separation during hydraulic fracturing, which resulted in rich ore deposition. Volatile gases such as CH₄ and N₂, in addition to CO₂ in solution, are shown to have a significant negative effect on total gas solubility. This effect may be of critical importance in lowering the temperature and increasing the depth (pressure) at which phase separation can occur in epithermal systems. Received: 28 November 1995 / Accepted: 17 July 1996     

A modern, guano-related occurrence of foggite, CaAl(PO4)(OH)2 · H2O and churchite-(Y), YPO4 · 2H2O in Cioclovina Cave, Romania

Summary This study reports foggite and churchite-(Y) from two spatially separate locations in the guano-related phosphate deposit from the Cioclovina Cave, Romania. Optical microscope observations, powder X-ray diffraction, electron microprobe analyses, and FTIR were used in the analysis of the two minerals. The chemical composition of foggite was determined to be Ca_0.925(Al_0.91Fe²⁺_0.016)_Σ0.926(P_0.991Si_0.043)_Σ1.034O_3.74(OH)_2.26 · H₂O and churchite-(Y) [(Y_0.830Dy_0.043Er_0.033Gd_0.029Yb_0.022)_Σ0.957Ca_0.009]P_1.023O_4.00 · 2H₂O. Chemical analyses of Cioclovina churchite-(Y) clearly revealed enrichment in lanthanides of even atomic number. The refined unit-cell parameters are for foggite (orthorhombic) a = 9.264(1) ?, b = 21.334(8) ?, c = 5.197(7) ?, and V = 1027.13(8) ?³ (Z = 8); for churchite-(Y) (monoclinic): a = 5.578(8) ?, b = 15.013(6) ?, c = 6.277(8) ?, β = 117.94(4)°, and V = 464.38(5) ?³ (Z = 4). FTIR spectrum of churchite-(Y) exhibits all the bands assigned to the vibrations of PO₄, OH, and water groups. Unlike other documented occurrences of foggite and churchite-(Y), in Cioclovina Cave, the occurrence of these minerals are related to a process that phosphatized subjacent limestone and various cave sediments (sand, clay, and limy mud) to form a complex phosphate assemblage. The minerals are presumably derived from phosphate-rich solutions that reacted with clay earth while moving downward through the sediments. Foggite was formed at the expense of the originally precipitated crandallite. Locally concentrated yttrium, REE, and dissolved phosphate are probably responsible for the precipitation of churchite-(Y). Present address: Department of Geology, University of South Florida, Tampa, FL, USA     

Geochemistry characterization of groundwater in an agricultural area of Razan,Hamadan, Iran

This study was conducted to evaluate factors regulating groundwater quality in an area with agriculture as main use. Thirty groundwater samples have been collected from Razan area (Hamadan, Iran) for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater. The chemical compositions of the groundwater are dominated by Na⁺, Ca²⁺, HCO₃ ⁻, Cl⁻ and SO₄ ²⁻, which have been derived largely from natural chemical weathering of carbonate, gypsum and anthropogenic activities of fertilizer’s source. The production of SO₄ ²⁻ has multiple origins, mainly from dissolution of sulphate minerals, oxidation of sulphide minerals and anthropogenic sources. The major anthropogenic components in the groundwater include Na⁺, Cl⁻, SO₄ ²⁻ and NO₃ ⁻, with Cl⁻ and NO₃ ⁻ being the main contributors to groundwater pollution in Razan area.     

Chromitites of komatiitic affinity from the Archaean Nuggihalli greenstone belt in South India

Summary Mineral chemistry and petrological data of chromites from chromitite bands in the N–S trending schist belt of Nuggihalli (southern Karnataka, India), belonging to the Dharwar craton of South India, are presented in this paper. Crystal chemical data indicate a komatiitic affinity of the chromitite. P–T calculations of the chromite-hosting peridotites yielded a pressure range of 13 to 28 kbar and temperatures ranging from 775 to 1080 °C; the oxygen fugacity (log fO₂) varies from +0.5 to +1.6 above the QFM buffer. The P, T and fO₂ data indicate that Nuggihalli chromitites crystallized in an environment akin to the upper mantle. The studied samples also show partial resetting; the lower temperatures ranging from 515 to 680 °C are ascribed to subsequent metamorphism of the area.     

Metamorphism and phase relations in carbonate rocks from the Nevado-Filábride Complex (Cordilleras Béticas, Spain): application of the Ttn + Rt + Cal + Qtz + Gr buffer

Phase relations and metamorphic conditions have been studied in metacarbonate rocks from the Nevado-Filábride Complex (Cordilleras Béticas) through forward modeling. In many rock samples, the assemblage titanite + rutile + calcite + quartz + graphite buffered the composition of the C-O-H fluid present during metamorphism. Over a wide range of P-T conditions, fluid compositions computed for this buffer are essentially binary H₂O-CO₂ mixtures. This buffer also constrains the chemical potentials of TiO₂, CaO and SiO₂. Consequently it is possible to make a thermodynamic projection through these components to predict the stable phase relations consistent with the buffer. Using this method, phase relations have been analyzed in a rock containing the buffer assemblage and paragonite, albite, phengite, epidote, and chlorite. The equilibrium P-T conditions for this assemblage are constrained, by minimization of the differences between predicted and observed mineral compositions, to be 560 ± 15 °C and 9.5 ± 1 kbar. Conditions obtained compare well with those estimated from other studies in different lithologic units. The inferred metamorphic fluid composition is H₂O-rich (). Received: 11 October 1995 / Accepted 5 August 1996     

Effects of quarry mining and of other environmental impacts in the mountainous Chicam-Toctina drainage basin (Córdoba, Argentina)

 The environmental conditions prevailing in the Chicam-Toctina drainage system (approx. 138 km² in Córdoba, Argentina) are considered representative of a number of catchments in Argentina's Sierras Pampeanas Range. Two groups of ions reflect the sources of dissolved species in the catchment: a) a group (Cl^–, SO^2– ₄, and Na⁺) which recognizes natural and anthropogenic sources, and which exhibits significant correlations with N^– ₃ and NO^– ₂, and b) another group of components (Ca²⁺, Mg²⁺, and HCO^– ₃) which is clearly controlled by carbonate rocks and their waste rock products. In the headwaters, stockpiled marble quarry mining wastes provide a more open system to CO₂ gaseous exchange than the outcropping rocks, thus promoting the increase of carbonate dissolution (up to 4.88 g km^–2 s^–1 during the rainy season). This specific yield was 20% higher than the amount estimated for an area with fewer extended mining activities. The dissolved load delivered by the upper reaches is subjected in the lower drainage area to various processes, mainly controlled by the presence of the city of Alta Gracia (approx. 40,000 inhabitants). In the dry season, due to nutrient inputs supplied by the city, photosynthetic activity plays a major role controlling stream pH. Hence, the high values of calcite saturation indexes and the increase of CaCO₃ concentration in bed sediments can be explained by calcite precipitation. Such a process could be accompanied by the coprecipitation on calcium carbonate of low solubility heavy metal carbonates. Received : 17 January 1997 · Accepted : 31 March 1997     

Groundwater chemistry and occurrence of arsenic in the Meghna floodplain aquifer,southeastern Bangladesh

Dissolved major ions and important heavy metals including total arsenic and iron were measured in groundwater from shallow (25–33 m) and deep (191–318 m) tube-wells in southeastern Bangladesh. These analyses are intended to help describe geochemical processes active in the aquifers and the source and release mechanism of arsenic in sediments for the Meghna Floodplain aquifer. The elevated Cl⁻ and higher proportions of Na⁺ relative to Ca²⁺, Mg²⁺, and K⁺ in groundwater suggest the influence by a source of Na⁺ and Cl⁻. Use of chemical fertilizers may cause higher concentrations of NH₄⁺ and PO₄³⁻ in shallow well samples. In general, most ions are positively correlated with Cl⁻, with Na⁺ showing an especially strong correlation with Cl⁻, indicating that these ions are derived from the same source of saline waters. The relationship between Cl⁻/HCO₃⁻ ratios and Cl⁻ also shows mixing of fresh groundwater and seawater. Concentrations of dissolved HCO₃⁻ reflect the degree of water–rock interaction in groundwater systems and integrated microbial degradation of organic matter. Mn and Fe-oxyhydroxides are prominent in the clayey subsurface sediment and well known to be strong adsorbents of heavy metals including arsenic. All five shallow well samples had high arsenic concentration that exceeded WHO recommended limit for drinking water. Very low concentrations of SO₄²⁻ and NO₃⁻ and high concentrations of dissolved Fe and PO₄³⁻ and NH₄⁺ ions support the reducing condition of subsurface aquifer. Arsenic concentrations demonstrate negative co-relation with the concentrations of SO₄²⁻ and NO₃⁻ but correlate weakly with Mo, Fe concentrations and positively with those of P, PO₄³⁻ and NH₄⁺ ions.     

Effect of chemical fertilizers on the fractionation of Cu,Cr and Ni in contaminated soil

Effect of chemical fertilizers (urea, NH₄Cl, Ca(NO₃)₂, KCl and KH₂PO₄) on the fractionation of Cu, Cr and Ni was studied by a 4-month incubation experiment. Using sequential extraction procedure, it was found that the application of fertilizers could change the distribution of Cu, Cr and Ni in the fractions of soil. Applying urea (CO(NH₂)₂) significantly decreased the concentrations of Cu, Cr and Ni in water soluble plus exchangeable (WE) fraction, but increased those in Fe–Mn oxides bound (FM) fraction (p < 0.01). However, application of NH₄Cl caused an increase in the WE fraction by 27.7% for Cu, 111.5% for Cr and 20.4% for Ni. The CO(NH₂)₂ raised the soil pH from 4.51 to 4.96, whereas NH₄Cl lowered the pH of soil by 0.44 units. The WE fraction of the three heavy metals was significantly increased, while the FM fraction was significantly decreased by adding KCl (p < 0.01). Moreover, the supply of KH₂PO₄ reduced the WE and carbonate bound (CB) fractions of Cu, Cr and Ni in the soil, however, it raised Cu and Ni in the residual (RS) fraction and Cr in the FM fraction. In addition, the mobility index indicated that KCl and NH₄Cl increased the mobility of Cu, Cr and Ni in the soil, whereas urea and KH₂PO₄ decreased the mobility of the three metals in the soil. These results suggest that applying chemical fertilizers does not only provide plant nutrients, but may also change the speciation and mobility of heavy metals in the soil.     

Mineralogy and origin of stichtite in chromite-bearing serpentinites

Stichtite, a rare (14 known localities worldwide) hydrated carbonate-hydroxide of Mg and Cr with ideal formula Mg₆Cr₂ (OH)₁₆ CO₃ · 4H₂O, occurs exclusively in Cr-rich serpentinites of ophiolites or greenstone belts. Physical properties (hardness = 1.5–2, specific gravity = 2.16–2.2, perfect basal [0001] cleavage, grain size commonly < 100 μm) resemble talc, but the mineral has an attractive purple to lilac color; chemical analyses demonstrate it to be a non-silicate. Stichtite generally occurs as irregular to rounded masses (< 1 cm – 30 cm across) and as veinlets (< 1 mm – > 2 cm wide) within serpentinite. Macroscopic and microscopic textures, such as crosscutting veinlets and stringers, demonstrate that stichtite formation invariably post-dated serpentinization. In some specimens stichtite surrounds relict grains of Cr-rich spinel; in others stichtite has completely replaced euhedral or subhedral chromites. Chemical analyses of stichtites reveal substantial substitution of Al and Fe³⁺ for Cr in specimens from many localities, reflecting a possible compositional continuum between stichtite and rhombohedral polymorphs hydrotalcite (Mg₆Al₂ (OH)₁₆ CO₃ · 4H₂O) and pyroaurite (Mg₆Fe₂ (OH)₁₆ CO₃ · 4H₂O). We report the first electron microprobe analyses of stichtites from seven localities, and summarize all available published chemical data. Stichtites very likely inherited part of their trivalent cation chemistry from precursor Cr-rich spinels, but stichtite growth apparently post-dated characteristic “ferritchromit” alteration, as demonstrated by the depletion of Al and enrichment in Fe³⁺ in stichtite relative to primary chromite core compositions. Stichtite appears to form by reaction between serpentine and altered chromite, during addition of substantial fluid, either as separate H₂O and CO₂ phases, or as a mixed volatile phase. Such reactions must involve removal of substantial SiO₂, possibly by transport and remote deposition of silica by throughgoing aqueous and carbonic fluid. Received: 4 April 1996 / Accepted: 16 September 1996     

Tracing the sources of nitrate in karstic groundwater in Zunyi,Southwest China: a combined nitrogen isotope and water chemistry approach

Nitrate (NO₃ ⁻) is major pollutant in groundwater worldwide. Karst aquifers are particularly vulnerable to nitrate contamination from anthropogenic sources due to the rapid movement of water in their conduit networks. In this study, the isotopic compositions (δ¹⁵N–NO₃ ⁻, δ¹⁵N–NH₄ ⁺) and chemical compositions(e.g., NO₃ ⁻, NH₄ ⁺, NO₂ ⁻, K⁺) were measured in groundwater in the Zunyi area of Southwest China during summer and winter to identify the primary sources of contamination and characterize the processes affecting nitrate in the groundwater. It was found that nitrate was the dominant species of nitrogen in most of the water samples. In addition, the δ¹⁵N–NO₃ ⁻ values of water samples collected in summer were lower than those collected in winter, suggesting that the groundwater received a significant contribution of NO₃ ⁻ from agricultural fertilizer during the summer. Furthermore, the spatial variation in the concentration of nitrate and the δ¹⁵N–NO₃ ⁻ value indicated that some of the urban groundwater was contaminated with pollution from point sources. In addition, the distribution of δ¹⁵N–NO₃ ⁻ values and the relationship between ions in the groundwater indicated that synthetic and organic fertilizers (cattle manure) were the two primary sources of nitrate in the study area, except in a few cases where the water had been contaminated by urban anthropogenic inputs. Finally, the temporal and spatial variation of the water chemistry and isotopic data indicated that denitrification has no significant effect on the nitrogen isotopic values in Zunyi groundwater.     

CO2-rich thermomineral groundwater in the Betic Cordilleras, southeastern Spain: Genesis and tectonic implications

The CO₂-rich thermal groundwater in the Betic Cordilleras in Spain has been studied with regard to the geological and hydrogeological setting, physical and chemical characteristics, and ¹³C-isotope content. The study area is about 60 km northeast of Almería city, in southeastern Spain. The thermomineral waters are plentiful and are related to regional geothermal anomalies. Temperatures of 20 −41°C, high bicarbonate concentrations (183–1824 mg/L), and high amounts of PCO₂ (<1.1 bar) characterize the groundwater. CO₂ spatial variations are related to proximity to the Carboneras, Palomares, and Guadalentín fault systems, which may be the surface representation of the zone of crustal thinning and magmatism. δ ¹³C values probably indicate a deep source for the CO₂, either the mantle or perhaps carbonate rocks in the metamorphic substratum. The high amount of CO₂ in the groundwater causes problems in wells and severely restricts water usage. The hydrothermal features of this area are probably related to neotectonic activity. Received, September 1998/Revised, June 1999, September 1999/Accepted, December 1999     

Groundwater problems resulting from CO2 pollution and overexploitation in Alto Guadalentín aquifer (Murcia,Spain)

 The Alto Guadalentín detrital aquifer is both overexploited and polluted. Water conductivity ranges between 1200 and 4900 μS cm^–1, HCO₃ ^– between 1000 and 1990 mg l^–1, and PCO₂ between 0.041 and 1.497 bars. The temperature and chemical composition of the water show a positive thermal anomaly directly attributable to the neotectonic activity in the area. The high CO₂ content has caused the abandonment of numerous wells due to water corrosiveness which attacks pumping equipment. Received: 10 October 1995 · Accepted: 14 November 1995     

Tourmaline in Proterozoic Massive Sulfide Deposits from Rajasthan, India

We have analyzed the chemical composition and boron isotope composition of tourmaline from tourmalinites, granite and a quartz-tourmaline vein from the Deri ore zone and from a pegmatitic band in the Rampura-Agucha ore body. These two Proterozoic massive sulfide deposits occur in the Aravalli-Delhi orogenic belt, Rajasthan, northwest India. Tourmaline from stratiform tourmalinites closely associated with the massive sulfides in the Deri deposit have preserved their original chemical compositions despite regional and thermal metamorphism in the area. These tourmalines have low Fe/(Fe + Mg) ratios (0.19–0.30; mean 0.26) that suggest formation close to the sediment-sea water interface. The δ¹¹B values (−15.5 and −16.4‰) are compatible with boron derived from leaching of argillaceous sediments and/or felsic volcanics underlying the original massive sulfide deposit during its formation. Boron isotope compositions measured in tourmaline from a post-ore granite and quartz-tourmaline vein in the Deri deposit indicate that boron in these tourmalines was derived from the tourmalinites produced during ore formation. The boron isotope systematics of a coarse brown tourmaline crystal from a pegmatitic band on the hanging wall contact of the Rampura-Agucha deposit indicate that 45 ± 25% of the boron within the original tourmaline was lost during upper amphibolite facies regional metamorphism. Received: 3 April 1996 / Accepted: 11 April 1996