Predicting C aromaticity of biochars based on their elemental composition

Three models were examined to predict C aromaticity (f_a) of biochars based on either their elemental composition (C, H, N and O) or fixed C (FC) content. Values of f_a from solid state ¹³C nuclear magnetic resonance (NMR) analysis with Bloch-decay (BD) or direct polarisation (DP) techniques, concentrations of total C, H, N, and organic O, and contents of FC of 60 biochars were either compiled from the literature (dataset 1, n = 52) or generated in this study (dataset 2, n = 8). Models were first calibrated with dataset 1 and then validated with dataset 2. All models were able to fit dataset 1 when atomic H to C ratio (H/C) < 1 (except two ash rich biochars) and to estimate f_a of HF treated biochars (H/C < 1). Model 1, which was based on values of H/C only and calibrated with a root mean square of error (RMSE) of 0.04 f_a-unit (n = 41), could predict the experimental data with a RMSE = 0.02 f_a-unit (n = 6). Model 2, which was based on biochar elemental composition data, showed the most accurate prediction, with a RMSE of 0.03 f_a-unit (n = 41) for the calibration data, and of 0.02 f_a-unit (n = 6, H/C < 1) for the validation data. Model 3, which was based on contents of FC and C, and modified with a correction factor of 0.96, displayed the highest RMSE (0.06 f_a-unit, n = 19) among the three models. Models 1 and 2 did not work properly for samples having either an H/C ratio > 1, high concentrations of carbonate or high inorganic H. These models need to be further tested with a wider range of biochars before they can be recommended for classification of biochar stability.     

Arsenic mobility in mildly alkaline drainage from an orogenic lode gold deposit,Bralorne mine,British Columbia

The historical (1932–1971) Bralorne mine produced over 87 million grams of Au from an archetypal orogenic lode gold deposit in southwest British Columbia. High concentrations of As in mine drainage, however, represent an on-going environmental concern prompting a detailed study of effluent chemistry. The discharge rate at the mine portal was monitored continuously over a fourteen-month period during which effluent samples were collected on a quasi-weekly basis. Water samples were also collected on synoptic surveys of the adit between the portal and the main source of flow in the flooded workings. Total concentrations of As in the mildly alkaline (pH = 8.7) portal drainage average 3034 μg/L whereas at the source they average 5898 μg/L. As emergent waters from the flooded workings flow toward the portal, their dissolved oxygen content and pH increase from 0 to 10 mg/L and from 7.7 to 9, respectively. Near the emergence point, dissolved Fe precipitates rapidly, sorbing both As(III) and As(V). With increasing distance from the emergence point, dissolved As(III) concentrations drop to detection limits through sorption on hydrous ferric oxide and through oxidation to As(V). Concentrations of dissolved As(V), on the other hand, increase and stabilize, reflecting lower sorption at higher pH and the lack of available sorbent. Nonetheless, based on synoptic surveys, approximately 35% of the source As load is sequestered in the adit resulting in As sediment concentrations averaging 8.5 wt%. The remaining average As load of 1.34 kg/d is discharged from the portal. Partitioning of As(V) between dissolved and particulate phases in portal effluent is characterized by a sorption density of 0.37 mol As (mol Fe)⁻¹ and by a distribution coefficient (K_d) of 130 L/g HFO. The relatively high sorption density may reflect co-precipitation of As with Fe oxyhydroxides rather than a purely adsorption-controlled process. Results of this study show that the As self-mitigating capacity of drainage from orogenic lode gold deposits may be poor in high-pH and Fe-limited settings.     

Uptake of dissolved lead by anhydrite surfaces

The fate of harmful metals in the Earth crust is importantly affected by sorption processes on mineral surfaces. Here, a study of the ability of anhydrite surfaces to uptake dissolved Pb is presented. Experiments were conducted at room temperature using initial Pb concentration ([Pb_aq]₀) ranging between 10 and 1000 mg/L and a batch type set-up. Inductively coupled plasma optical emission spectrometry analyses showed that [Pb_aq] progressively decreased as the time of interaction increased, to reach a final steady state value of ∼3.0 mg/L, irrespectively of [Pb_aq]₀. However, the time elapsed before the steady state value was reached strongly depended on [Pb_aq]₀, with the drop to this final value occurring in less than 1 day interaction when [Pb_aq]₀ ⩾ 50 mg/L and after 20 days when [Pb_aq]₀ < 50 mg/L. Scanning Electron Microscopy and X-ray diffraction analyses confirmed the epitactic growth of anglesite (PbSO₄) crystals on anhydrite surfaces when [Pb_aq]₀ ⩾ 50 mg/L. X-ray Absorption Near Edge Structure spectroscopy points to a different sorption mechanisms when [Pb_aq]₀ < 50 mg/L. The results show that the epitactic growth of anglesite on anhydrite has no significant impact on the ability of anhydrite surfaces to remove Pb_aq, which show equal effectiveness as that of gypsum surfaces. The high reactivity of anhydrite surfaces renders this phase potentially important in the control of the fate of dissolved metals in nature.     

Ore minerals down to the nanoscale: Cu-(Fe)-sulphides from the iron oxide copper gold deposit at Olympic Dam,South Australia

Cu-Fe-sulphide mineral assemblages from the Olympic Dam (OD) Fe-oxide Cu-U-Au-Ag deposit, South Australia, are studied down to the nanoscale to explore the potential these minerals have for understanding genetic processes such as primary deposit zonation. Cu-Fe-sulphide pairs: ‘brown’ bornite associated with chalcopyrite (bornite-chalcopyrite zone); and symplectites of ‘purple’ bornite with species from the chalcocite group, Cu_2 − xS (bornite-chalcocite zone), co-define an upwards and inwards deposit-scale zonation at OD. In the bornite-chalcocite zone, there is also an increase in the proportion of chalcocite relative to bornite within the symplectites towards upper levels. In this case, two-phase Cu_2 − xS assemblages are also present, as anisotropic, hexagonal chalcocite (CcH) with lamellar exsolutions of digenite, distinguishable at the μm-scale. Using compositional data (electron microprobe) combined with Transmission Electron Microscopy (TEM) study of foils prepared in–situ via Focused Ion Beam (FIB)-SEM, we show that Cu-Fe-sulphides from different ore zones feature nanoscale intergrowths, lattice defects, superstructure domains (na) and antiphase boundary domains (APBs) that can be interpreted as due to exsolution, coarsening and phase transformation during cooling from high-T solid solutions in the system Cu-Fe-S and sub-systems according to published phase diagrams. ‘Brown’ bornite [(Cu + Fe)/S > 5] contains pervasive lamellae of chalcopyrite which extend down to the nanoscale; such specimens appear homogeneous at the μm-scale. ‘Purple bornite’ [(Cu + Fe)/S < 5] in high-bornite symplectites is associated with chalcocite that shows APBs with 6a digenite and low-T chalcocite. Comparable APBs are also found in the ‘chalcocite’ zone with apparent homogeneity at the μm-scale. Both bornites contain exsolutions of djurleite. Systematic variation of Me/S and Cu/Fe in the two types of bornite points, however, to distinct origins from different bornite solid-solutions in the system Cu-Fe-S. Both show 2a and 4a intermediate superstructures. High-order superstructures (6a and incommensurate na) are restricted to the ‘purple’ bornite whereas the 2a4a low-T superstructure is found in both cases. Me/S ratios in the chalcocite group are variable; lower ratios (down to 1.8; digenite) are more common in chalcocite from symplectites with ‘purple’ bornite. Me/S can be as low as 1.4 where associated with ‘blue’ varieties (‘blaubleibender covellin’) of replacement origin. The two-phase Cu_2 − xS associations contain hexagonal chalcocite (Me/S = 1.95), lamellae of Cu-rich digenite (Me/S = 1.92), and anilite (Cu₇S₄) as nm-scale lamellae. Digenite shows 3a and 6a superstructures and CcH shows transition to pseudo-orthorhombic chalcocite. The presence of superstructures, high-T species and APBs is evidence for Cu-(Fe)-sulphide formation from high-T solid solutions at T > 300 °C (high-T phases, Cu-poor digenite), followed by cooling along distinct paths down to < 120 °C (APBs). The scenario of ‘exsolution from primary solid-solution’, corroborated by the consistency in phase relations within each zone across different scales of observation from deposit scale to nanoscale, backs up a model of primary hypogene ore precipitation rather than replacement, and accounts for the observed vertical zoning at OD. The FIB-TEM approach here is readily applicable to other deposits and shows that nanoscale observations are a valuable, although often overlooked, source of information to constrain ore genesis.     

Interaction of U(VI) with Äspö diorite: A batch and in situ ATR FT-IR sorption study

Pristine diorite drill cores, obtained from the Äspö Hard Rock Laboratory (HRL, Sweden), were used to study the retention properties of fresh, anoxic crystalline rock material towards the redox-sensitive uranium. Batch sorption experiments and spectroscopic methods were applied for this study. The impact of various parameters, such as solid-to-liquid ratio (2–200 g/L), grain size (0.063–0.2 mm, 0.5–1 mm, 1–2 mm), temperature (room temperature and 10 °C), contact time (5–108 days), initial U(VI) concentration (3 × 10⁻⁹ to 6 × 10⁻⁵ M), and background electrolyte (synthetic Äspö groundwater and 0.1 M NaClO₄) on the U(VI) sorption onto anoxic diorite was studied under anoxic conditions (N₂). Comparatively, U(VI) sorption onto oxidized diorite material was studied under ambient atmosphere (pCO₂ = 10^−3.5 atm). Conventional distribution coefficients, K_d, and surface area normalized distribution coefficients, K_a, were determined. The K_d value for the U(VI) sorption onto anoxic diorite in synthetic Äspö groundwater under anoxic conditions by investigating the sorption isotherm amounts to 3.8 ± 0.6 L/kg which corresponds to K_a = 0.0030 ± 0.0005 cm (grain size 1–2 mm). This indicates a weak U sorption onto diorite which can be attributed to the occurrence of the neutral complex Ca₂UO₂(CO₃)₃(aq) in solution. This complex was verified as predominating U species in synthetic Äspö groundwater by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Compared to U sorption at room temperature under anoxic conditions, U sorption is further reduced at decreased temperature (10 °C) and under ambient atmosphere. The U species in aqueous solution as well as sorbed on diorite were studied by in situ time-resolved attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. A predominant sorbing species containing a UO₂(CO₃)₃⁴⁻ moiety was identified. The extent of U sorption onto diorite was found to depend more on the low sorption affinity of the Ca₂UO₂(CO₃)₃(aq) complex than on reduction processes of uranium.     

Kinetics of selenium release in mine waste from the Meade Peak Phosphatic Shale,Phosphoria Formation,Wooley Valley,Idaho, USA

Phosphorite from the Meade Peak Phosphatic Shale member of the Permian Phosphoria Formation has been mined in southeastern Idaho since 1906. Dumps of waste rock from mining operations contain high concentrations of Se which readily leach into nearby streams and wetlands. While the most common mineralogical residence of Se in the phosphatic shale is elemental Se, Se(0), Se is also an integral component of sulfide phases (pyrite, sphalerite and vaesite–pyrite_ss) in the waste rock. It may also be present as adsorbed selenate and/or selenite, and FeSe₂ and organo-selenides.Se release from the waste rock has been observed in field and laboratory experiments. Release rates calculated from waste rock dump and column leachate solutions describe the net, overall Se release from all of the possible sources of Se listed above. In field studies, Se concentration in seepage water (pH 7.4–7.8) from the Wooley Valley Unit 4 dump ranges from 3600 µg/L in May to 10 µg/L by Sept. Surface water flow, Q, from the seep also declines over the summer, from 2 L/s in May to 0.03 L/s in Sept. Se flux ([Se] ? Q) reaches a steady-state of < 150 mg/day in 1–4 months, depending upon the volume of Q. Se release (mg/L) follows a first order reaction with a rate constant, k, = 1.35 – 6.35e?3 h^? 1 (11.8–55.6 yr^? 1).Laboratory experiments were performed with the waste shale in packed bed reactors; residence time varied from 0.09 to 400 h and outlet pH ～ 7.5. Here, Se concentration increased with increasing residence time and release was modeled with a first order reaction with k = 2.19e?3 h^? 1 (19.2 yr^? 1).Rate constants reported here fall within an order of magnitude of reported rate constants for oxidation of Se(0) formed by bacterial precipitation. This similarity among rate constants from both field and laboratory studies combined with the direct observation of Se(0) in waste shales of the Phosphoria Formation suggests that oxidation of Se(0) may control steady-state Se concentration in water draining the Wooley Valley waste dump.     

Kinetic studies of the homogeneous abiotic reactions of several chlorinated aliphatic compounds in aqueous solution

The base mediated and neutral abiotic reactions of 4 chlorinated aliphatic compounds have been studied as a function of temperature and pH. Arrhenius parameters obtained for base mediated reactions were as follows: 1,1,2-trichloroethane, log₁₀A=14.36±0.55, E_a=95.6±3.6 kJ/mol; 1,1,1,2-tetrachloroethane, log₁₀A=14.56±0.33, E_a=101.4±2.1 kJ/mol; 1,2,3-trichloropropane, log₁₀A=13.31±0.53, E_a=95.9±3.5 kJ/mol. For the neutral reaction of 2,3-dichloro-1-propene the Arrhenius parameters were log₁₀A=10.2±1.3, E_a=98±9 kJ/mol. For 1,1,2-trichloroethane the product of the base mediated reaction was identified as 1,1-dichloroethene, in contrast to previous studies. 2,3-dichloro-1-propene was found as an intermediate in the base mediated reaction of 1,2,3-trichloropropane, with 2-chloro-2-propen-1-ol as the major final product. Results from the present study are compared to those found in previous work.     

Geochemical and isotopic variations in shallow groundwater in areas of the Fayetteville Shale development,north-central Arkansas

Exploration of unconventional natural gas reservoirs such as impermeable shale basins through the use of horizontal drilling and hydraulic fracturing has changed the energy landscape in the USA providing a vast new energy source. The accelerated production of natural gas has triggered a debate concerning the safety and possible environmental impacts of these operations. This study investigates one of the critical aspects of the environmental effects; the possible degradation of water quality in shallow aquifers overlying producing shale formations. The geochemistry of domestic groundwater wells was investigated in aquifers overlying the Fayetteville Shale in north-central Arkansas, where approximately 4000 wells have been drilled since 2004 to extract unconventional natural gas. Monitoring was performed on 127 drinking water wells and the geochemistry of major ions, trace metals, CH₄ gas content and its C isotopes (δ¹³C_CH4), and select isotope tracers (δ¹¹B, ⁸⁷Sr/⁸⁶Sr, δ²H, δ¹⁸O, δ¹³C_DIC) compared to the composition of flowback-water samples directly from Fayetteville Shale gas wells. Dissolved CH₄ was detected in 63% of the drinking-water wells (32 of 51 samples), but only six wells exceeded concentrations of 0.5 mg CH₄/L. The δ¹³C_CH4 of dissolved CH₄ ranged from −42.3‰ to −74.7‰, with the most negative values characteristic of a biogenic source also associated with the highest observed CH₄ concentrations, with a possible minor contribution of trace amounts of thermogenic CH₄. The majority of these values are distinct from the reported thermogenic composition of the Fayetteville Shale gas (δ¹³C_CH4 = −35.4‰ to −41.9‰). Based on major element chemistry, four shallow groundwater types were identified: (1) low (<100 mg/L) total dissolved solids (TDS), (2) TDS > 100 mg/L and Ca–HCO₃ dominated, (3) TDS > 100 mg/L and Na–HCO₃ dominated, and (4) slightly saline groundwater with TDS > 100 mg/L and Cl > 20 mg/L with elevated Br/Cl ratios (>0.001). The Sr (⁸⁷Sr/⁸⁶Sr = 0.7097–0.7166), C (δ¹³C_DIC = −21.3‰ to −4.7‰), and B (δ¹¹B = 3.9–32.9‰) isotopes clearly reflect water–rock interactions within the aquifer rocks, while the stable O and H isotopic composition mimics the local meteoric water composition. Overall, there was a geochemical gradient from low-mineralized recharge water to more evolved Ca–HCO₃, and higher-mineralized Na–HCO₃ composition generated by a combination of carbonate dissolution, silicate weathering, and reverse base-exchange reactions. The chemical and isotopic compositions of the bulk shallow groundwater samples were distinct from the Na–Cl type Fayetteville flowback/produced waters (TDS ∼10,000–20,000 mg/L). Yet, the high Br/Cl variations in a small subset of saline shallow groundwater suggest that they were derived from dilution of saline water similar to the brine in the Fayetteville Shale. Nonetheless, no spatial relationship was found between CH₄ and salinity occurrences in shallow drinking water wells with proximity to shale-gas drilling sites. The integration of multiple geochemical and isotopic proxies shows no direct evidence of contamination in shallow drinking-water aquifers associated with natural gas extraction from the Fayetteville Shale.     

Inorganic,isotopic, and organic composition of high-chloride water from wells in a coastal southern California aquifer

Chloride concentrations were as high as 230 mg/L in water from the surface discharge of long-screened production wells in Pleasant Valley, Calif., about 100 km NW of Los Angeles. Wells with the higher Cl⁻ concentrations were near faults that bound the valley. Depending on well construction, high-Cl⁻water from different sources may enter a well at different depths. For example, Cl⁻ concentration in the upper part of some wells completed in overlying aquifers influenced by irrigation return were as high as 220 mg/L, and Cl⁻ concentrations in water sampled within wells at depths greater than 450 m were as high as 500 mg/L. These high-Cl⁻ waters mix within the well during pumping and produce the water sampled at the surface discharge. Changes in the major ion, minor ion, trace element, and δ³⁴S and δ¹³C isotopic composition of water in wells with depth were consistent with changes resulting from SO₄ reduction, precipitation of calcite, and cation exchange. The chemical and isotopic composition of high-Cl⁻ water from deep wells trends towards the composition of oil-field production water from the study area. Chloride concentrations in oil-field production water present at depths 150 m beneath freshwater aquifers were 2200 mg/L, and Cl⁻ concentrations in underlying marine rock were as high as 4400 mg/L. High-Cl⁻ concentrations in water from deeper parts of wells were associated with dissolved organic C composed primarily of hydrophobic neutral compounds believed to be similar to those associated with petroleum in underlying deposits. These compounds would not be apparent using traditional sampling techniques and would not be detected using analytical methods intended to measure contamination.     

Effects of acid-sulfate weathering and cyanide-containing gold tailings on the transport and fate of mercury and other metals in Gossan Creek: Murray Brook mine,New Brunswick,Canada

Gossan Creek, a headwater stream in the SE Upsalquitch River watershed in New Brunswick, Canada, contains elevated concentrations of total Hg (Hg_T up to 60 μg/L). Aqueous geochemical investigations of the shallow groundwater at the headwaters of the creek confirm that the source of Hg is a contaminated groundwater plume (neutral pH with Hg and Cl concentrations up to 150 μg/L and 20 mg/L, respectively), originating from the Murray Brook mine tailings, that discharges at the headwaters of the creek. The discharge area of the contaminant plume was partially delineated based on elevated pH and Cl concentrations in the groundwater. The local groundwater outside of the plume contains much lower concentrations of Hg and Cl (<0.1 μg/L and 3.8 mg/L, respectively) and displays the chemical characteristics of an acid-sulfate weathering system, with low pH (4.1–5.5) and elevated concentrations of Cu, Zn, Pb and SO₄ (up to 5400 μg Cu/L, 8700 μg Zn/L, 70 μg Pb/L and 330 mg SO₄/L), derived from oxidation of sulfide minerals in the Murray Brook volcanogenic massive sulfide deposit and surrounding bedrock. The Hg_T mass loads measured at various hydrologic control points along the stream system indicate that 95–99% of the dissolved Hg_T is attenuated in the first 3–4 km from the source. Analyses of creek bed sediments for Au, Ag, Cu, Zn, Pb and Hg indicate that these metals have partitioned strongly to the sediments. Mineralogical investigations of the contaminated sediments using analytical scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), reveal discrete particles (<1–2 μm) of metacinnabar (HgS), mixed Au–Ag–Hg amalgam, Cu sulfide and Ag sulfide.     

Mineralogy and genetic features of the Cu-As-Ni-Sb-Pb mineralization from the Mlakva polymetallic deposit (Serbia) — New occurrence of (Ni-Sb)-bearing Cu-arsenides

(Ni-Sb)-bearing Cu-arsenides are rare minerals within the Mlakva and Kram mining sectors (Boranja ore field) one of the less-known Serbian Cu deposits. (Ni-Sb)-bearing Cu-arsenides were collected from the Mlakva skarn-replacement Cu(Ag,Bi)-FeS polymetallic deposit. The identified phases include β-domeykite, Ni-bearing koutekite and (Ni-Sb)-bearing α-domeykite. (Ni-Sb)-bearing Cu-arsenides are associated with nickeline, arsenical breithauptite, chalcocite, native Ag, native Pb and litharge. Pyrrhotite, pyrite, chalcopyrite, cubanite, bismuthinite, molybdenite, sphalerite, galena, Pb(Cu)-Bi sulfosalts and native Bi, as well as minor magnetite, scheelite and powellite are associated with the sulfide paragenesis. The electron microprobe analyses of the (Ni-Sb)-bearing Cu-arsenides yielded the following average formulae: (Cu_2.73,Ni_0.17,Fe_0.03,Ag_0.01)_∑ 2.94(As_0.98,Sb_0.05,S_0.02)_∑ 1.06–β-domeykite (simplified formula (Cu_2.7,Ni_0.2)_∑ 2.9As_1.1); (Cu_3.40,Ni_1.40,Fe_0.11)_∑ 4.91(As_1.94,Sb_0.13,S_0.02)_∑ 2.08–Ni-bearing koutekite (simplified formula (Cu_3.4Ni_1.5)_∑ 4.9As_2.1); and Cu_1.97(Ni_0.98,Fe_0.03)_∑ 1.01(As_0.81,Sb_0.22)_∑ 1.03–(Ni–Sb)-bearing α-domeykite (simplified formula Cu₂NiAs). The Rietveld refinement yielded the following unit-cell parameters for β-domeykite and Ni–bearing koutekite: a = 7.1331(4); c = 7.3042(5) Å; V = 321.86(2) ų, and a = 5.922(4); b = 11.447(9); c = 5.480(4) Å; V = 371.48(5) ų, respectively. Ore geology, paragenetic assemblages and genesis of the Mlakva deposit are discussed in detail and the Cu-As-Ni-Sb-Pb mineralization has been compared with similar well-known global deposits.     

Geochronological and geochemical study of mafic dykes from the northwest Chinese Altai: Implications for petrogenesis and tectonic evolution

Fifteen zircons separated from a mafic dyke in the Chinese Altai give a concordant age population with a weighted mean ²⁰⁶Pb/²³⁸U age of 375.5 ± 4.8 Ma, suggesting a Devonian emplacement. On the basis of their mineralogical compositions and textures, the coeval dykes can be divided into gabbroic and doleritic types. They are both sub-alkaline, tholeiitic, characterized by similarly low SiO₂ contents (45.2–52.7 wt.%) and total alkaline (K₂O + Na₂O = 0.99–4.93 wt.%). Rare earth element patterns of the gabbroic dykes are similar to N-MORB (La/Yb_N = 0.86–1.1), together with their high ε_Nd(t) values (+ 7.6 to + 8.1), indicating that their precursor magma was mainly derived from a N-MORB-type depleted asthenospheric mantle. While the REE patterns of the doleritic dykes resemble that of E-MORB (La/Yb_N = 1.12–2.28), enriched in LILEs and strongly depleted in HFSEs, with relative low ε_Nd(t) values (+ 3.4 to + 5.4) and high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7057–0.7060). The zircon Hf isotopic analysis of the doleritic dykes give ε_Hf(t) values from + 10.7 to + 13.8. These signatures suggest that a depleted mantle wedge metasomatized by slab-derived fluids and/or melts was possibly involved in the generation of the doleritic magma. The refractory peridotite may have been melted with variable degrees caused by upwelling of the hot asthenosphere. The petrogenesis of the mafic dykes suggest a high heat flux as a result of upwelling of the hot asthenosphere and the contrast geochemical signatures can be interpreted by a ridge subduction, which could be an important tectonic control in the accretionary process of the Chinese Altai.     

Metasomatic silicate chemistry at the Bayan Obo Fe–REE–Nb deposit,Inner Mongolia,China: Contrasting chemistry and evolution of fenitising and mineralising fluids

Fenite aureoles around carbonatite dykes, and alteration associated with Fe–REE–Nb ore bodies at Bayan Obo, Inner Mongolia, China, show alkali silicate assemblages containing aegirine–augite, (magnesio-)riebeckite, (magnesio-)arfvedsonite, and phlogopite, accompanied by varying amounts of apatite, albite and quartz. In both fenites and orebodies simple thermodynamic constraints indicate mineral parageneses are consistent with rock buffered cooling accompanied by the infiltration of a range of externally buffered hydrothermal fluids. Statistical analysis of amphibole chemistry indicates that even in apparently texturally well constrained paragenetic stages wide variations in chemistry occur in both the ore bodies and fenites. Much of this variation is attributable to the Mg and F content of amphibole, and is therefore interpreted as a result of variation in externally controlled variables (P, T, initial fluid composition) rather than internally controlled variables such as protolith composition. Similarities in chemistry exist between fenite and some ore body amphiboles. Thermodynamic analysis of the composition of biotite and apatite allows constraints to be placed on the F-content of hydrothermal fluids, and indicates relatively consistent compositions in fenites and orebodies (log a_HF/a_H2O = − 3.8 to − 3.6 at 300 °C and 1 kbar). Amphibole and biotite associated with niobate mineralization are both enriched in fluorine relative to the rest of the paragenesis, and biotite compositions indicate significantly higher HF activities in the hydrothermal fluid (log a_HF/a_H2O = − 2.6 at 300 °C and 1 kbar). The data presented here reinforce previous interpretations of the complex, multistage nature of mineralisation at Bayan Obo, but are still consistent with a direct involvement of carbonatite derived fluids during ore genesis.     

Kinetics of Au (III) extraction by DBC from hydrochloric solution using Lewis cell

The kinetics of forward extraction [AuCl₄]^? from aqua regia medium by diethylene glycol dibutyl ether (DBC) have been investigated by the Lewis cell (LC) technique. At first gold extraction has been carried out under different experimental conditions for achieving the stoichiometry coefficients and the value of the extraction equilibrium constant (K = 0.1). For kinetic data treatment, flux ‘F’ method has been applied. Reaction order with respect to DBC, pH and [AuCl₄]^? was determined and then the rate constant was calculated. The rate of gold extraction from 2 M chloride medium can be expressed as F = 10^0.88[AuCl₄^?]^1.25 [DBC]^0.4 [H⁺]^?0.22. Kinetics data were treated by EVIEWS software and coefficients were obtained. The comparison of manual and software results indicated that the results had good conformity. Influence of temperature was studied and then activation energy, E_a, (11.17 kJ/mol), activation enthalpy (11.66 kJ/mol) and entropy (?187 J/mol K) were calculated by using Arrhenius and activation complex theory respectively. E_a value (< 20.9 kJ/mol) indicates that, the extraction of gold (III) in the investigated system is controlled by diffusion process.     

Pressure-induced dehydration of dioptase: A single-crystal X-ray diffraction and Raman spectroscopy study

We present a synchrotron-based, single-crystal X-ray diffraction and Raman spectroscopy study of natural green dioptase (Cu₆Si₆O₁₈·6H₂O) up to ∼30 GPa at room temperature. The lattice parameters of dioptase exhibit continuous compression behavior up to ∼14.5 GPa, whereupon a structural transition is observed. Pressure–volume data below 14.5 GPa were fitted to a second-order Birch–Murnaghan equation of state with V₀ = 1440(2) ų and K₀ = 107(2) GPa, with K₀′ = 4(fixed). The low-pressure form of dioptase exhibits anisotropic compression with axial compressibility β_a > β_c in a ratio of 1.14:1.00. Based on the diffraction data and Raman spectroscopy, the new high-pressure phase could be regarded as a dehydrated form of dioptase in the same symmetry group. Pressure-induced dehydration of dioptase contributes broadly to our understanding of the high-pressure crystal chemistry of hydrous silicates containing molecular water groups.     

Metamorphic evolution of the Maud Belt: P–T–t path for high-grade gneisses in Gjelsvikfjella,Dronning Maud Land,East Antarctica

A metamorphic petrological study, in conjunction with recent precise geochronometric data, revealed a complex P–T–t path for high-grade gneisses in a hitherto poorly understood sector of the Mesoproterozoic Maud Belt in East Antarctica. The Maud Belt is an extensive high-grade, polydeformed, metamorphic belt, which records two significant tectono-thermal episodes, once towards the end of the Mesoproterozoic and again towards the late Neoproterozoic/Cambrian. In contrast to previous models, most of the metamorphic mineral assemblages are related to a Pan-African tectono-thermal overprint, with only very few relics of late Mesoproterozoic granulite-facies mineral assemblages (M₁) left in strain-protected domains. Petrological and mineral chemical evidence indicates a clockwise P–T–t path for the Pan-African orogeny. Peak metamorphic (M_2b) conditions recorded by most rocks in the area (T = 709–785 °C and P = 7.0–9.5 kbar) during the Pan-African orogeny were attained subsequent to decompression from probably eclogite-facies metamorphic conditions (M_2a).The new data acquired in this study, together with recent geochronological and geochemical data, permit the development of a geodynamic model for the Maud Belt that involves volcanic arc formation during the late Mesoproterozoic followed by extension at 1100 Ma and subsequent high-grade tectono-thermal reworking once during continent–continent collision at the end of the Mesoproterozoic (M₁; 1090–1030 Ma) and again during the Pan-African orogeny (M_2a, M_2b) between 565 and 530 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions (M_2c) followed and is ascribed to post-orogenic bimodal magmatism between 500 and 480 Ma.     

Laboratory chalcopyrite oxidation by Acidithiobacillus ferrooxidans: Oxygen and sulfur isotope fractionation

Laboratory experiments were conducted to simulate chalcopyrite oxidation under anaerobic and aerobic conditions in the absence or presence of the bacterium Acidithiobacillus ferrooxidans. Experiments were carried out with 3 different oxygen isotope values of water (δ¹⁸O_H2O) so that approach to equilibrium or steady-state isotope fractionation for different starting conditions could be evaluated. The contribution of dissolved O₂ and water-derived oxygen to dissolved sulfate formed by chalcopyrite oxidation was unambiguously resolved during the aerobic experiments. Aerobic oxidation of chalcopyrite showed 93 ± 1% incorporation of water oxygen into the resulting sulfate during the biological experiments. Anaerobic experiments showed similar percentages of water oxygen incorporation into sulfate, but were more variable. The experiments also allowed determination of sulfate–water oxygen isotope fractionation, ε¹⁸O_SO4–H2O, of ~ 3.8‰ for the anaerobic experiments. Aerobic oxidation produced apparent ε_SO4–H2O values (6.4‰) higher than the anaerobic experiments, possibly due to additional incorporation of dissolved O₂ into sulfate. δ³⁴S_SO4 values are ~ 4‰ lower than the parent sulfide mineral during anaerobic oxidation of chalcopyrite, with no significant difference between abiotic and biological processes. For the aerobic experiments, a small depletion in δ³⁴S_SO4 of ~? 1.5 ± 0.2‰ was observed for the biological experiments. Fewer solids precipitated during oxidation under aerobic conditions than under anaerobic conditions, which may account for the observed differences in sulfur isotope fractionation under these contrasting conditions.     

Magma mixing origin for the Aolunhua porphyry related to Mo–Cu mineralization,eastern Central Asian Orogenic Belt

Many Cu–Mo–Au deposits are considered to be related to adakitic porphyries formed in non-arc settings, e.g., in collisional orogenic zones and intra-plate environments, but their genesis is still under discussion. The Aolunhua porphyry complex and its related Mo–Cu deposit from the eastern Central Asian Orogenic Belt (CAOB) provide important insights into this issue. The porphyries are characterized by high Sr (496–705 ppm) and Sr/Y and La/Yb ratios similar to those of typical adakitic rocks, and low I_Sr ratios (0.7049–0.7052) and positive ε_Nd(t) (+ 0.5 to + 1.4) and ε_Hf(t) (+ 3.5 to + 9.8) values. These features, along with the occurrence of mafic microgranular enclaves (MMEs), compositional and textural disequilibrium of plagioclase phenocrysts and relatively high Mg# values (45–52), indicate that they were derived from mixing of felsic magma from partial melting of a juvenile arc-type lower crust and mafic magma from a lithospheric mantle previously metasomatized by subduction zone fluids/melts. High Sr/Y and La/Yb ratios are indicative of contribution from enriched mantle-derived materials (with high LILEs; e.g., Sr, La), which were strengthened by subsequent fractionation of ferromagnesian phases such as pyroxene and hornblende. MMEs hosted by the ore-bearing porphyry have zircon U–Pb ages of ca. 132 Ma, similar to those of the host rocks. The enclaves have elevated Mg^# (56–63), LILEs (e.g., Sr = 660–891 ppm), LREE (La_N = 68–150, (La/Sm)_N = 3.0–4.0, (La/Yb)_N = 12.0–19.6) and ratios of radiogenic isotopes of Nd- and Hf (ε_Nd = + 0.7 to + 1.6; ε_Hf = + 3.3 to + 10.9), suggesting that their parental magmas were derived from the metasomatized mantle source. The Mo–Cu mineralization was probably related to the high water content, high oxygen and sulfur fugacity of hybrid magma. Formation of the adakitic porphyries and related Mo–Cu deposits of the eastern CAOB could be related to the Early Cretaceous lithospheric extension, caused by the subduction of the Paleo-Pacific plate and its induced reactivation of juvenile arc-type lower crust.     

Sicilian bottled natural waters: Major and trace inorganic components

Sixteen bottled waters of various Sicilian brands, 11 natural mineral waters and five normal drinking waters, were analyzed for major and trace inorganic components by ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. The bottled waters represent a variety of water types with significantly different compositions in terms of salinity, major components and trace elements. Chemically, they range from Ca–HCO₃ and Ca–SO₄ to Na–HCO₃ types. Total dissolved solids ranges from 54 to 433 mg/L, total hardness from 25 to 238 mg/L CaCO₃, and measured Na content from 5.7 to 57 mg/L. According to total dissolved ions, all the bottled waters were classified as oligomineral (50 < TDS < 500 mg/L). All the bottled waters analyzed here had elemental concentrations which did not exceed the guideline and directive values, although a high concentration of Al was noted for one bottled water (O7, central Sicily) and high Rb and V in a bottled water (O1) from the Etna volcanic area. With regard to trace elements, the chemical quality of bottled waters was assessed by a metal index (MI). Chemical characteristics were compared with 10 tap water samples from private houses or public places, representative of the public water supply in Palermo, the largest and most densely populated city in Sicily. The municipal waters analyzed, belonging to HCO₃-alkaline earth and Cl–SO₄-alkaline earth waters, showed concentrations of chemical inorganic components well within drinking water limits. The data also indicated that the water supplied by the municipal authority is of fair quality, although fairly hard and high in Na concentration. Several considerations indicate that there is no sufficient reason to prefer bottled waters to tap waters.     

Synthesis and characterization of polycrystalline KAlSi3O8 hollandite [liebermannite]: Sound velocities vs. pressure to 13 GPa at room temperature

A polycrystalline specimen of liebermannite [KAlSi₃O₈ hollandite] was synthesized at 14.5 GPa and 1473 K using glass starting material in a uniaxial split-sphere apparatus. The recovered specimen is pure tetragonal hollandite [SG: I4/m] with bulk density of within 98% of the measured X-ray value. The specimen was also characterized by Raman spectroscopy and nuclear magnetic resonance spectroscopy. Sound velocities in this specimen were measured by ultrasonic interferometry to 13 GPa at room T in a uniaxial split-cylinder apparatus using Al₂O₃ as a pressure marker. Finite strain analysis of the ultrasonic data yielded K_S0 = 145(1) GPa, K₀′ = 4.9(2), G₀ = 92.3(3) GPa, G₀′ = 1.6(1) for the bulk and shear moduli and their pressure derivatives, corresponding to V_P0 = 8.4(1) km/s, V_S0 = 4.9(1) km/s for the sound wave velocities at room temperature. These elasticity data are compared to literature values obtained from static compression experiments and theoretical density functional calculations.