Geochemistry of trace metals associated with reduced sulfur in freshwater sediments

Porewater concentration profiles were determined for Fe, trace elements (As, Cd, Co, Cu, Mn, Ni, Pb, Zn), sulfide, SO₄ and pH in two Canadian Shield lakes (Chevreuil and Clearwater). Profiles of pyrite, sedimentary trace elements associated with pyrite and AVS were also obtained at the same sites. Thermodynamic calculations are used, for the anoxic porewaters where sulfide was measured, to characterize diagenetic processes involving sulfide and trace elements and to illustrate the importance of sulfide, and possibly polysulfides and thiols, in binding trace elements. The ion activity products (IAP) of Fe sulfide agree with the solubility products (K_s) of greigite or mackinawite. For Co, Ni and Zn, IAP values are close to the K_S values of their sulfide precipitates; for Cu and Pb, IAP/K_s indicate large oversaturations, which can be explained by the presence of other ligands (not measured) such as polysulfides (Cu) and thiols (Pb). Cobalt, Cu, Ni and Zn porewater profiles generally display a decrease in concentration with increasing ΣH₂S, as expected for transition metals, whereas Cd, Pb and Zn show an increase (mobilisation). The results suggest that removal of trace elements from anoxic porewaters occurs by coprecipitation (As and Mn) with FeS(s) and/or adsorption (As and Mn) on FeS(s), and by formation of discrete solid sulfides (Cd, Cu, Ni, Pb, Zn and Co). Reactive Fe is extensively sulfidized (51–65%) in both lakes, mostly as pyrite, but also as AVS. Similarities between As, Co, Cu and Ni to Fe ratios in pyrite and their corresponding mean diffusive flux ratios suggest that pyrite is an important sink at depth for these trace elements. High molar ratios of trace elements to Fe in pyrite from Clearwater Lake correspond chronologically to the onset of smelting activities. AVS can be an important reservoir of reactive As, Cd and Ni and, to a lesser extent, of Co, Cu and Pb. Overall, the trace elements most extensively sulfidized were Ni, Cd and As (maximum of 100%, 81% and 49% of the reactive fraction, respectively), whereas Co, Cu, Mn, Pb and Zn were only moderately sulfidized (11–16%).     

Synthesis of PGE sulfide standards for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

Sulfide compositions with known Re, Os, Ir, Ru, Rh, Pt, and Pd contents are synthesized to be used as standards for noble metal analysis in solid solution in sulfides. Major elements were added as metals and elemental S. The noble metals, i.e. 35 and 60 ppm each, were added as solutions by micro syringe. Following synthesis at 1 atm the sulfides were sintered at 1.5 to 2 GPa to obtain pellets with theoretical density. Aliquots of the pellets were analysed by isotope dilution ICP-MS for bulk Re and platinum-group elements (PGE). The spatial noble metal distribution was investigated with an ArF excimer laser coupled to a single collector ICP mass spectrometer. Sample homogeneity is shown to depend on the metal/S spectrum and the major element composition of the sulfide, as well as on more subtle factors like oxygen partial pressure during synthesis, run temperature, and degree of partial melting. The most homogeneous sulfide composition is a (Fe,Ni)_{1 − x} S monosulfide with 5 wt % Ni and 1-sigma variations in ³⁴S-normalized noble metal count rates of <3.6%. Nearly as homogeneous is a pure Fe_{1 − x} S monosulfide with 1-sigma variations in ³⁴S-normalized noble metal count rates of <5.8 %. A Cu-bearing Fe_{1 − x} S monosulfide with 2 wt % Cu was found to be considerably more heterogeneous, suggesting that Cu in solid solution in monosulfides promotes noble metal heterogeneity. The sulfide composition least suitable for the synthesis of noble metal sulfide standards is NiS.     

Sulfide oxidation as a process for the formation of copper-rich magmatic sulfides

Typical magmatic sulfides are dominated by pyrrhotite and pentlandite with minor chalcopyrite, and the bulk atomic Cu/Fe ratio of these sulfides is typically less than unity. However, there are rare magmatic sulfide occurrences that are dominated by Cu-rich sulfides (e.g., bornite, digenite, and chalcopyrite, sometimes coexisting with metallic Cu) with atomic Cu/Fe as high as 5. Typically, these types of sulfide assemblages occur in the upper parts of moderately to highly fractionated layered mafic–ultramafic intrusions, a well-known example being the Pd/Au reef in the Upper Middle Zone of the Skaergaard intrusion. Processes proposed to explain why these sulfides are so unusually rich in Cu include fractional crystallization of Fe/(Ni) monosulfide and infiltration of postmagmatic Cu-rich fluids. In this contribution, we explore and experimentally evaluate a third possibility: that Cu-rich magmatic sulfides may be the result of magmatic oxidation. FeS-dominated Ni/Cu-bearing sulfides were equilibrated at variable oxygen fugacities in both open and closed system. Our results show that the Cu/Fe ratio of the sulfide melt increases as a function of oxygen fugacity due to the preferential conversion of FeS into FeO and FeO_1.5, and the resistance of Cu₂S to being converted into an oxide component even at oxygen fugacities characteristic of the sulfide/sulfate transition (above FMQ?+?1). This phenomenon will lead to an increase in the metal/S ratio of a sulfide liquid and will also depress its liquidus temperature. As such, any modeling of the sulfide liquid line of descent in magmatic sulfide complexes needs to address this issue.     

A transmission electron microscopy analysis of secondary minerals formed in tungsten-mine tailings with an emphasis on arsenopyrite oxidation

Grains of naturally oxidized arsenopyrite [FeAsS] collected from the oxidation zone in W-mine tailings were investigated, primarily using transmission electron microscopy. The grains are severely pitted and are surrounded by secondary minerals. The pitted nature of the grains is related to mechanisms governing the electrochemical oxidation of sulfide minerals, with prominent cusp-like features occurring at cathodic regions of the surface, and pits occurring at anodic regions. In general, the oxidation of arsenopyrite leads to the formation of an amorphous (or nanocrystalline) Fe–As–O-rich coating that contains small amounts of Si, Ca, Cu, Zn, Pb and Bi; nanoscale variation in the As, Pb, Bi and Zn contents of the coating was noted. Secondary Cu sulfides, thought to be chalcocite [Cu₂S] and (or) djurleite [Cu₃₁S₁₆], occur as a layer (generally <500 nm thick) along the arsenopyrite grain boundary, and also within the coating as aggregates, and as layers that parallel the grain boundary. Although the precipitation of secondary Cu minerals along the grain boundary is a nanoscale feature, the process of formation is thought to be analogous to the supergene enrichment that occurs in weathered sulfide deposits. As the oxidation of arsenopyrite proceeds, layers and clusters of secondary Cu sulfides become isolated in the Fe–As–O coating. Secondary wulfenite [PbMoO₄] and an unidentified crystalline Bi–Pb–As–O mineral occur in voids within the coating, suggesting that these minerals precipitated from the local pore-water. Small and variable amounts of W, Ca, Bi, As and Zn are associated with the wulfenite, and Zn, Fe and Ca are associated with the Bi–Pb–As–O mineral. Some of the wulfenite is in contact with inclusions of molybdenite [MoS₂], suggesting that the oxidation of molybdenite in the presence of aqueous Pb(II) led to the formation of wulfenite. Mineralogical analyses at the nanoscale have improved the understanding of geochemical sources and sinks at this location. The results of this study indicate that the mineralogical controls on aqueous elemental concentrations at this tailings site are complex and are not predicted by thermodynamic calculations.     

Mechanism of enrichment of trace metals on fine sludges collected from filtration plants

Fine sludges were collected from five filtration plants, and the partitioning of ten metals (Ag, Cd, Mn, Zn, Pb, Cu, Sn, Co, Ni, and Fe) in them was determined by selective leaching techniques. (1) The available amounts, which shows the total of each metal leached between 1 M CH₃COONH₄ and 30 percent H₂O₂, for Ag, Cd and Mn, ranged from 51 to 98 percent for five sludges. (2) The available amounts for Zn, Pb, Cu, and Sn were 47–92 percent for five sludges. (3) The most important fraction for Co, Ni, and Fe, except the Inagawa sludge, which is markedly polluted by organic matter, was the crystalline particle. Therefore, the above metals, except Co, Ni, and Fe, are thought to be enriched on ion-exchangeable sites, organic matter, hydrous Fe/Mn oxides, and sulfides in fine sludges.     

Evaluation of phosphate fertilizers for ameliorating acid mine waste

The aim of the study was to determine whether the application of bulk industrial chemicals (potassium permanganate and water-soluble phosphate fertilizer) to partly oxidized, polyminerallic mine wastes can inhibit sulfide oxidation, and metal and metalloid mobility. The acid producing waste rocks were metal (Pb, Zn, Cu) and metalloid (As, Sb) rich and consisted of major quartz, dickite, illite, and sulfide minerals (e.g., galena, chalcopyrite, tetrahedrite, sphalerite, pyrite, arsenopyrite), as well as minor to trace amounts of pre- and post-mining oxidation products (e.g., hydrated Fe, Cu, Pb, and alkali mineral salts). SEM-EDS observations of treated waste material showed that metal, metal–alkali, and alkali phosphate coatings developed on all sulfides. The abundance of phosphate phases was dependant on the fertilizer type and the availability of metal and alkali cations in solution. In turn, the release of cations was dependent on the amount of sulfide oxidation induced by KMnO₄ during the experiment and the dissolution of soluble sulfates. Mn, Ca, Fe, and Pb phosphates remained stable during H₂O₂ leaching, preventing acid generation and metal release. In contrast, the lack of complete phosphate coating on arsenopyrite allowed oxidation and leaching of As to proceed. The mobilized As did not form phosphate phases and consequently, As displayed the greatest release from the coated waste. Thus, the application of KMnO₄ and the water-soluble phosphate fertilizer Trifos (Ca(H₂PO₄)₂) to partly oxidized, polyminerallic mine wastes suppresses sulfide oxidation and is most effective in inhibiting Cu, Pb, and Zn (Sb) release. However, the technique appears ineffective in suppressing oxidation of arsenopyrite and preventing As leaching.     

Evidence of sulfide melting and melt fractionation during amphibolite facies metamorphism of the Rajpura–Dariba polymetallic sulfide ores

Partial melting of sulfide ores during prograde metamorphism could have been more prevalent than generally accepted. However, identification of such melting is difficult as sulfide melts do not form glasses and the textures generated on quenching are obliterated due to the tendency of sulfides for ready recrystallization. The polymetallic base metal sulfide deposit at Rajpura–Dariba, Rajasthan, India is a typical stratiform ore metamorphosed to the middle amphibolite facies. The peak metamorphic temperature of 600 °C should have been sufficient to initiate sulfide melting as evident from experimental studies in the ZnS–PbS–Cu₂S–FeS₂–S system. Further, syn-metamorphic melting of the original SEDEX ore was abetted by the high f_S2 condition that prevailed as a consequence of barite dissolution. A Zn–Fe–S melt containing minor Pb, Sb and Cu but no Ag fractionated from an initial melt in the above system resulting in a residual immiscible sulfosalt-bearing PbS melt. The final metallic melts, represented by formation of dyscrasite (Ag₃Sb) from the sulfosalt-bearing melt and breithauptite (NiSb) or ullmannite (NiSbS) from the sulfosalt-absent melt, were a product of independent fractional crystallization of the immiscible sulfide and PbS–sulfosalt melts.     

Transport and sediment–water partitioning of trace metals in acid mine drainage: an example from the abandoned Kwangyang Au–Ag mine area, South Korea

Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO₃–HClO₄) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K _d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K _d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.     

Chemical influences on trace metal-sulfide interactions in anoxic sediments

Interactions of trace metals with sulfide in anoxic environments are important in determining their chemical form and potential toxicity to organisms. In recent years, a considerable body of observational data has accumulated that indicates very different behavior for various trace metals in sulfidic sediments. These differences in behavior cannot be entirely attributed to thermodynamic relationships, but also reflect differences in ligand exchange reaction kinetics, and redox reaction pathways.Pb, Zn, and Cd, which are generally pyritized to only a few percent of the “reactive” fraction, have faster water exchange reaction kinetics than Fe²⁺, resulting in MeS phases precipitating prior to FeS formation and subsequent pyrite formation, whereas, Co and Ni, which have slower H₂O exchange kinetics than Fe²⁺, are incorporated into pyrite. Although Hg and Cu have faster reaction kinetics than Fe²⁺, both are incorporated into pyrite or leached from the pyrite fraction with nitric acid. Hg undergoes significant chloride complexation, which can retard reaction with sulfide, but can also replace Fe in FeS to form HgS, which can only be dissolved in the pyrite fraction. Cu²⁺ is reduced by sulfide and forms a variety of sulfides with and without Fe that can only be dissolved with nitric acid. Mn²⁺ does not form a MnS phase easily and is incorporated into pyrite at high iron degrees of pyritization (DOP).Oxyanions of Mo and As are first reduced by sulfide. These reduced forms may then react with sulfides resulting in incorporation into pyrite. However, the oxyanion of Cr is reduced to Cr³⁺, which is kinetically inert to reaction with sulfide and, therefore, not incorporated into pyrite.     

Trace metals in recharge and discharge ground waters at two sites at the Baltic coast of Sweden

The distribution and controls of trace elements (Cd, Cr, Cu, Ni, Pb, Zn and U) in shallow groundwater in discharge and recharge zones were analysed at two sites on the Baltic coast of Sweden; one granite-dominated and one with a significant addition of calcite. Although the study sites differ in overburden geochemistry and groundwater trace metal concentrations, which were well reflected in the general groundwater composition, the relative hydrochemical differences between recharge and discharge ground waters were similar at both sites, and temporally stable. The concentrations of Cd, Cu, Ni and U were higher in soil tubes in recharge areas, but Cr was higher in discharge zones. Also concentrations of HS, Fe, Mn and NH₄ were higher in discharge samples, which in combination with increased ³⁴S values provide strong evidence of a transition from oxidizing to more reducing conditions along the groundwater flow gradient. In terms of trace metals, this might mean either mobilisation due to dissolution of trace-metal carrying Fe(III) and Mn(IV) phases, or immobilisation caused by precipitation of discrete trace-metal sulfides or co-precipitation with Fe sulfides. The results from this study show that the latter is dominant in both the carbonate and granite environments for the metals Cd, Cu and Ni. Chromium concentrations were likely coupled to organic complexation and were higher in discharge groundwater, where DOC was also more abundant. As the concentration of several potentially toxic trace metals were found to differ between recharge and discharge areas, a climate driven change in hydrology might have a substantial impact on the distribution of these metals.     

Minerals in the Triassic carbonaceous silicites of Sikhote Alin

Over 60 minerals, including native elements, intermetallic compounds, haloids, sulfides, sulfates, arsenides, oxides and hydroxides, silicates, borosilicates, wolframates, phosphates and REE phosphates, were established in Triassic siliceous rocks of Sikhote Alin. Allothigenic and authigenic minerals in the carbonaceous silicites were formed over a long period through several stages. Judging from morphology, chemical composition, and structural position, K-feldspar (K-Fsp), illite, kaolinite, metahalloysite, monazite, xenotime, zircon, rutile, or its polymorphs are the disintegration products of sialic rocks of continental crust. Authigenic sulfides are dominated by diagenetic pyrite (fine-crystalline, microglobular, framboidal, as well as those developed after biogenic siliceous and carbonate fragments), which has been formed prior to precipitation of siliceous cement and lithification of siliceous rocks. Most of other sulfides (sphalerite, galena, chalcopyrite, pyrrhotite, argentite, pentlandite, antimonite, ulmanite, and bravoite), arsenides and sulfoarsenides (arsenopyrite, nickeline, skutterudite, cobaltite, glaucodot, and gersdorffite), wolframates (scheelite and wolframite), intermetallides (Cu₂Zn, Cu₃Zn₂, Cu₃Zn, Cu₄Zn, CuSn, Cu₄Sn, Cu₈Sn, Cu₄Zn₂Ni, Ni₂Cu₂Zn, Ni₄Cd), and native elements (Au, Pd, Ag, Cu, Fe, W, Ni, Se) were crystallized later (during catagenesis after the lithification and brecciation of siliceous beds) from metals involved in the easily mobile fractions of bitumens. Supergene mineral formation was mainly expressed in the sulfide oxidation and replacement of diagenetic pyrite by jarosite and iron hydroxides.     

Chemistry of some Pb-(Cu,Fe)-(Sb,Bi sulfosalts from France and Portugal. Implications for the crystal chemistry of lead sulfosalts in the Cu-poor part of the Pb2S2-Cu2S-Sb2S3-Bi2-Bi2S3 system

Electron microprobe analysis of Pb-Cu(Fe)-Sb-Bi sulfosalts from Bazoges and Les Chalanches (France), and Pedra Luz (Portugal), give new data about (Bi, Sb) solid-solution and incorporation of the minor elements Cu, Fe or Ag in jaskolskiite, and in izoklakeite-giessenite and kobellite-tintinaite series. Jaskolskiite from Pedra Luz has high Sb contents (from 17.9 to 20.7 wt.%), leading to the extended general formula: Cu _x Pb_2+x (Sb_1–y Bi _y )_2–x S₅, with 0.10 x 0.22 and 0.19 y 0.41. Fe-free, Bi-rich izoklakeite from Bazoges has high Ag contents (up to 2.2 wt. %), leading to the simplified formula Cu₂Pb₂₂Ag₂(Bi, Sb)₂₂S₅₇; in Les Chalanches it contains less Ag content (1.2 wt.%), but has an excess of Cu that gives the formula: Cu_2.00 (Cu_0.49Ag_1.18)_=1.67Pb_22.70(Bi_12.63Sb_8.99)_=21.62S_57.27.In tintinaite from Pedra Luz, the variation of the Fe/Cu ratio can be explained by the substitution: Cu + (Bi, Sb) Fe + Pb; Fe-free kobellite from Les Chalanches has a Cu-excess, corresponding to the formula Cu_2.81Ag_0.54Pb_9.88(Bi_10.37Sb_5.21)_=15.38S_35.09. Eclarite from the type locality, structurally related to kobellite, shows a Cu excess too. In natural samples of the kobellite homologous series, Fe is positively correlated with Pb, and its contents never exceed that of Cu. Ag substitutes for Pb, together with (Bi, Sb). Taking into account the possibility of Cu excess, but excluding formal Cu²⁺ and Fe³⁺, general formulae can be written:     

Joint toxic effects of heavy metals and atrazine on invasive plant species <Emphasis Type="Italic">Solidago Canadensis L</Emphasis>.

In this study, the joint effects of Cd(Ⅱ), Pb(Ⅱ) and atrazine (ATR) on Solidago Canadensis L. were investigated. The results showed that soil containing Cd, Pb and ATR could inhibit root elongation of Solidago Canadensis L., and that there was a positive linear relationship between the inhibitory rate of root elongation and the concentrations of Pb(Ⅱ). The mixture of Cd(Ⅱ) and Pb(Ⅱ)-ATR in soil showed a significant adverse effect on root and shoot biomass of Solidago Canadensis L. Acetylsalicylic acid (ASA) contents increased slightly at the lower concentrations of Cd(Ⅱ)-ATR, then decreased when Cd(Ⅱ)-ATR concentrations were higher than those of 1.0 TUmix(Cd+ATR). The toxic effect of Pb(Ⅱ)-ATR on the ASA contents of Solidago Canadensis L. was greater than that of Cd(Ⅱ)-ATR. Soluble sugar contents firstly decreased and then increased with increasing concentrations of Cd(Ⅱ)-ATR and displayed fluctuation with increasing concentrations of Pb(Ⅱ)-ATR. Total protein contents in-creased with increasing concentrations of Cd(Ⅱ) and Pb(Ⅱ)-ATR , relative to the control sample. The NP-SH con-tents showed a significant increase up to 12.2 mg/gfw of Cd(Ⅱ)-ATR, followed by a significant decline to 4.5 mg/gfw after 14 days of exposure. The effect of Pb(Ⅱ)-ATR was similar to that of Cd(Ⅱ)-ATR but the amount of NP-SH was not higher than that of Cd(Ⅱ)-ATR.     

Fate and transport of metals in H2S-rich waters at a treatment wetland

The aqueous geochemistry of Zn, Cu, Cd, Fe, Mn and As is discussed within the context of an anaerobic treatment wetland in Butte, Montana. The water being treated had a circum-neutral pH with high concentrations of trace metals and sulfate. Reducing conditions in the wetland substrate promoted bacterial sulfate reduction (BSR) and precipitation of dissolved metal as sulfide minerals. ZnS was the most common sulfide phase found, and consisted of framboidal clusters of individual spheres with diameters in the submicron range. Some of the ZnS particles passed through the subsurface flow, anaerobic cells in suspended form. The concentration of "dissolved" trace metals (passing through a 0.45 μm filter) was monitored as a function of H₂S concentration, and compared to predicted solubilities based on experimental studies of aqueous metal complexation with dissolved sulfide. Whereas the theoretical predictions produce "U-shaped" solubility curves as a function of H₂S, the field data show a flat dependence of metal concentration on H₂S. Observed metal concentrations for Zn, Cu and Cd were greater than the predicted values, particularly at low H₂S concentration, whereas Mn and As were undersaturated with their respective metal sulfides. Results from this study show that water treatment facilities employing BSR have the potential to mobilize arsenic out of mineral substrates at levels that may exceed regulatory criteria. Dissolved iron was close to equilibrium saturation with amorphous FeS at the higher range of sulfide concentrations observed (>0.1 mmol H₂S), but was more likely constrained by goethite at lower H₂S levels. Inconsistencies between our field results and theoretical predictions may be due to several problems, including: (i) a lack of understanding of the form, valence, and thermodynamic stability of poorly crystalline metal sulfide precipitates; (ii) the possible influence of metal sulfide colloids imparting an erroneously high "dissolved" metal concentration; (iii) inaccurate or incomplete thermodynamic data for aqueous metal complexes at the conditions of the treatment facility; and (iv) difficulties in accurately measuring low concentrations of dissolved sulfide in the field.     

Heavy metal contamination of soils and tea plants in the eastern Black Sea region,NE Turkey

The study area covers two geologically different regions which have intensively been carpeted by tea plants in the eastern Black Sea. The rocks exposed in the region contain considerable amount of trace metals due to Upper Cretaceous massive sulfide formations and tertiary epithermal mineralizations. Tea plants that grow in soils derived from such mineralized rocks contain different concentrations of Cu, Pb, Zn, Fe, Cd, P, Al, Na, K, and S. The content ratios of most of the analyzed elements except Al are higher in basaltic and sedimentary rocks. To describe the transfer of metals from soil to tea leaf, the Freundlich-type model (log c _plant = ac _soil + log b) is used. The metal concentrations in leaves of tea plant in the studied soils are ranked as Zn > Cu > Pb > Al > Cd > Fe. The capacity of the plant to affect the metal accumulation decreased as follows: Fe > Cd > Pb > Cu > Zn > Al. Negative correlations were found between pH and availability of Cu, Pb, Zn, Mn, and Al elements by the tea plant. Experimental applications indicated that tea plant leaves growing on soils with high metal contents show some signs of toxicity. In soils where, particularly, ammonium sulfate fertilizer is used, metal uptake by the tea plant was found to be significantly higher as a result of extremely acidic character of the soil.     

H-O-S-Cu-Pb Isotopic Constraints on the Origin of the Nage Cu-Pb Deposit, Southeast Guizhou Province, SW China

The Nage Cu-Pb deposit,a new found ore deposit in the southeast Guizhou province,southwest China,is located on the southwestern margin of the Jiangnan Orogenic Belt.Ore bodies are hosted in slate and phyllite of Neoproterozoic Jialu and Wuye Formations,and are structurally controlled by EW-trending fault.It contains Cu and Pb metals about 0.12 million tonnes with grades of 0.2 wt% to 3.4 wt% Cu and 1.1 wt% to 9.27 wt% Pb.Massive and disseminated Cu-Pb ores from the Nage deposit occur as either veinlets or disseminations in silicified rocks.The ore minerals include chalcopyrite,galena and pyrite,and gangue minerals are quartz,sericite and chlorite.The H-O isotopic compositions of quartz,S-Cu-Pb isotopic compositions of sulfide minerals,Pb isotopic compositions of whole rocks and ores have been analyzed to trace the sources of ore-forming fluids and metals for the Nage Cu-Pb deposit.The δ65CuNBS values of chalcopyrite range from-0.09% to +0.33‰,similar to basic igneous rocks and chalcopyrite from magmatic deposits.δ65CuNBS values of chalcopyrite from the early,middle and final mineralization stages show an increasing trend due to63Cu prior migrated in gas phase when fluids exsolution from magma.δ34SCDT values of sulfide minerals range from 2.7‰ to +2.8‰,similar to mantle-derived sulfur(0±3‰).The positive correlation between δ65CuNBS and δ34SCDT values of chalcopyrite indicates that a common source of copper metal and sulfur from magma.δDH2OSMOW and δ18OH2O-SMOW values of water in fluid inclusions of quartz range from 60.7‰ to 44.4‰ and +7.9‰ to +9.0‰(T=260°C),respectively and fall in the field for magmatic and metamorphic waters,implicating that mixed sources for H2O in hydrothermal fluids.Ores and sulfide minerals have a small range of Pb isotopic compositions(208Pb/204Pb=38.152 to 38.384,207Pb/204Pb=15.656 to 17.708 and 206Pb/204Pb=17.991 to 18.049) that are close to orogenic belt and upper crust Pb evolution curve,and similar to Neoproterozoic host rocks(208Pb/204Pb=38.201 to 38.6373,207Pb/204Pb=15.648 to 15.673 and 206Pb/204Pb=17.820 to 18.258),but higher than diabase(208Pb/204Pb=37.830 to 38.012,207Pb/204Pb=15.620 to 15.635 and206Pb/204Pb=17.808 to 17.902).These results imply that the Pb metal originated mainly from host rocks.The H-O-S-Cu-Pb isotopes tegather with geology,indicating that the ore genesis of the Nage Cu-Pb deposit is post-magmatic hydrothermal type.     

The biogeochemistry of heavy metals in polluted lakes and streams at Flin Flon,Canada, and a proposed method for limiting heavy-metal pollution of natural waters

The biogeochemistry of Zn, Cd, Cu, Hg, and Fe in lakes and streams polluted by mine and smelter wastes emitted at Flin Flon, Canada, was investigated. In Schist Lake, a repository for both tailings-pond drainage and sewage, green algal blooms generated by nutrients from sewage promote entrapment of metals in sediments by (1) accumulation of metals from solution by algal seston, with preferential uptake of Zn, the most abundant metal, followed by sinking of the seston; and (2) production of H₂S during decomposition of dead algae, resulting in sulfide precipitation. Metals are partially resolubilized from seston as it decomposes while sinking. Preferential retention of Cu by sinking seston and by mud promotes Cu enrichment in the mud but the Cu/Zn ratio of mud varies with the Cu/Zn ratio of surface water seston. In bottom muds, partitioning of a metal between sulfide and organic matter is strongly dependent on the stability of the metal sulfide as measured by its standard entropy, the proportion of sulfide-bound metal decreasing in the order Hg>Cd>Cu>Fe>Zn. When sulfide-rich muds were heated under helium, x-ray diffraction revealed abundant well-crystallized ZnS (sphalerite) containing Cd, Hg, and Fe; only poorly crystallized traces of the mineral were detected in unheated mud, however. Cu sulfide failed to crystallize, suggesting interference by sorbed impurities. Metals were concentrated in H₂S-rich muds and extraction of muds with various solvents and by electrodialysis showed that sulfide was much more effective than organic matter in suppressing remobilization of metals. Remobilized Cu is probably bound to organic complexing agents. Some extractable complexing agents bind Cu preferentially with respect to Zn and Cd but others preferentially bind Zn and Cd; the complexes, being stable in the presence of free sulfide, may cause some release of metals from sulfide-rich muds in nature. These results indicate that introduction of sewage together with heavy-metal effluents into settling ponds could be an effective and economic method for limiting heavy-metal pollution of natural waters.     

Aquifer geochemistry at potential aquifer storage and recovery sites in coastal plain aquifers in the New York city area,USA

The effects of injecting oxic water from the New York city (NYC) drinking-water supply and distribution system into a nearby anoxic coastal plain aquifer for later recovery during periods of water shortage (aquifer storage and recovery, or ASR) were simulated by a 3-dimensional, reactive-solute transport model. The Cretaceous aquifer system in the NYC area of New York and New Jersey, USA contains pyrite, goethite, locally occurring siderite, lignite, and locally varying amounts of dissolved Fe and salinity. Sediment from cores drilled on Staten Island and western Long Island had high extractable concentrations of Fe, Mn, and acid volatile sulfides (AVS) plus chromium-reducible sulfides (CRS) and low concentrations of As, Pb, Cd, Cr, Cu and U. Similarly, water samples from the Lloyd aquifer (Cretaceous) in western Long Island generally contained high concentrations of Fe and Mn and low concentrations of other trace elements such as As, Pb, Cd, Cr, Cu and U, all of which were below US Environmental Protection Agency (USEPA) and NY maximum contaminant levels (MCLs). In such aquifer settings, ASR operations can be complicated by the oxidative dissolution of pyrite, low pH, and high concentrations of dissolved Fe in extracted water.     

Monitoring and modelling of the solid-solution partitioning of metals and As in a river floodplain redox sequence

For a period of 2 a, pore water composition in a heavily contaminated river floodplain soil was monitored in situ. Pore water samples were collected 12 times over all seasons in a profile ranging from aerobic to sulphidic redox conditions, and As, Cd, Cr, Cu, Pb, Zn, Mn, Fe, Ca, Cl, SO₄, DOC, IOC and pH were determined. The variability of pH, IOC, DOC and Ca was found to be rather small during the year and within the profile (rsd < 0.04, 0.16, 0.24 and 0.22, respectively). The temporal variability of the metal and As concentrations was small, too, whereas changes with depth were distinct. Under sulphidic conditions, concentrations were below 1 μg L⁻¹ (Cd, Cu, Pb) or 10 μg L⁻¹ (Zn, As). The data set was compared with results from a geochemical model that was fully parameterised from literature data and included equilibrium speciation, sorption and mineral dissolution. The general pattern of the solid–solution partitioning of Cd, Cu, Zn and As in the profile was predicted well by mechanistic geochemical modelling on the basis of solid phase composition. Metals strongly bound to organic matter such as Cd and Cu were predicted better than metals mainly present within a mineral. Detailed information regarding the presence of colloidal Fe and Mn in pore water might improve the prediction of the solid–solution partitioning of a number of metals. The study also indicates that the chemical behaviour of Pb is still not understood sufficiently.     

Secondary mineral-forming processes in natural—anthropogenic hydrogeological systems at sulfide deposits. Simulation of the origin of the phase (Fe,Mg)SO4 · 7H2O in the course of sulfide oxidation at the Degtyarka copper sulfide deposit

Data on the decommissioned Degtyarka Cu sulfide deposit, Urals, confirm the hypothesis that the flooding of abandoned mine workings is associated with the synthesis of secondary sulfates. Numerical simulation of hydrogeochemical processes in the rock—water system imitating the flooding of an underground void makes it possible to evaluate the conditions under which kirovite (Fe,Mg)SO₄ · 7H₂O and melanterite are formed at the oxidation of ore sulfides. Secondary sulfates are formed when the redox potential of the system is transformed from reducing to oxidizing within the stability field of Fe(II) species. The Fe/Mg ratio of the kirovite (Fe,Mg)SO₄ · 7H₂O is controlled first of all by the percentage of sulfides in the rock—water system, the rock/water ratio, the openness of the system with respect to atmospheric gases, and the temperature.