Experimental study of the stability of metals associated with iron oxyhydroxides precipitated in acid mine drainage

Iron oxyhydroxide precipitates associated with acid mine drainage (AMD) from the Stearns Coal Zone in southeastern Kentucky were analyzed for their metal (Al, Cu, Pb, Mn, Ni, and Zn) content. The most concentrated metals within these sediments are nickel (27–32×10³μmol/kg), manganese (16–29×10³μmol/kg), and aluminum (13–22×10³μmol/kg) as determined by HCl-HNO₃ digestion. Metal concentrations associated with the organic fraction as determined by H₂O₂ digestion were generally far lower, with the exception of aluminum. "Batch" experiments (at initial pH=2.0) were used to analyze the stability of these metals associated with a contaminated soil. Aluminum was the most mobile of the metals, presumably the result of the formation of aluminum-sulfate aqueous complexes. The solubilization rates for nickel and iron were very similar, suggesting that nickel, unlike the other metals, coprecipitated with iron in these sulfatic oxyhydroxides. Received: 9 October 1997 · Accepted: 15 December 1997     

Specification and prediction of nickel mobilization using artificial intelligence methods

Groundwater and soil pollution from pyrite oxidation, acid mine drainage generation, and release and transport of toxic metals are common environmental problems associated with the mining industry. Nickel is one toxic metal considered to be a key pollutant in some mining setting; to date, its formation mechanism has not yet been fully evaluated. The goals of this study are 1) to describe the process of nickel mobilization in waste dumps by introducing a novel conceptual model, and 2) to predict nickel concentration using two algorithms, namely the support vector machine (SVM) and the general regression neural network (GRNN). The results obtained from this study have shown that considerable amount of nickel concentration can be arrived into the water flow system during the oxidation of pyrite and subsequent Acid Drainage (AMD) generation. It was concluded that pyrite, water, and oxygen are the most important factors for nickel pollution generation while pH condition, SO₄, HCO₃, TDS, EC, Mg, Fe, Zn, and Cu are measured quantities playing significant role in nickel mobilization. SVM and GRNN have predicted nickel concentration with a high degree of accuracy. Hence, SVM and GRNN can be considered as appropriate tools for environmental risk assessment.     

Hydrogeochemical evaluation of groundwater in the lower Offin basin,Ghana

Alumino-silicate mineral dissolution, cation exchange, reductive dissolution of hematite and goethite, oxidation of pyrite and arsenopyrite are processes that influence groundwater quality in the Offin Basin. The main aim of this study was to characterise groundwater and delineate relevant water–rock interactions that control the evolution of water quality in Offin Basin, a major gold mining area in Ghana. Boreholes, dug wells, springs and mine drainage samples were analysed for major ions, minor and trace elements. Major ion study results show that the groundwater is, principally, Ca–Mg–HCO₃ or Na–Mg–Ca–HCO₃ in character, mildly acidic and low in conductivity. Groundwater acidification is principally due to natural biogeochemical processes. Though acidic, the groundwater has positive acid neutralising potential provided by the dissolution of alumino-silicates and mafic rocks. Trace elements’ loading (except arsenic and iron) of groundwater is generally low. Reductive dissolution of iron minerals in the presence of organic matter is responsible for high-iron concentration in areas underlain by granitoids. Elsewhere pyrite and arsenopyrite oxidation is the plausible process for iron and arsenic mobilisation. Approximately 19 and 46% of the boreholes have arsenic and iron concentrations exceeding the WHO’s (Guidelines for drinking water quality. Final task group meeting. WHO Press, World Health Organization, Geneva, 2004) maximum acceptable limits of 10 μg l⁻¹ and 0.3 mg l⁻¹, for drinking water.     

Supergene alteration of the Mt Windarra nickel sulphide ore deposit,Western Australia

Three main zones of progressive oxidation, termed the transition, violaritepyrite and oxide zones, can be delineated in the supergene profile of the Mt Windarra massive/matrix ore deposit. In the broad transition zone from pure primary ore, pentlandite is progressively oxidised to an iron rich violarite of composition Co_0.02Fe_1.38Ni_1.60 S₄, releasing Fe²⁺ and Ni²⁺ ions into solution. Up to 43% of this Ni²⁺ moves to nearby pyrrhotite margins which are replaced firstly by nickeliferous smythite and then by a second lamellar-textured violarite with an even higher iron content but lacking in cobalt (approximately Fe_1.6Ni_1.4S₄). On completion of violaritisation of the pentlandite, violaritisation of the pyrrhotite also ceases and the remainder of the pyrrhotite is rapidly replaced by secondary pyrite/marcasite, siderite and void space, this reaction defining the top of transition zone. Both sulphur and nickel are extracted from solution and further Fe²⁺ ions are released into solution. The violarite-pyrite zone is characterised by the absence of pentlandite and pyrrhotite and continued stability of violarite and secondary iron disulphides. Most, if not all, of the iron generated by these oxidation reactions precipitates as magnesian siderite at the expense of magnesite, giving rise to solutions containing mainly Mg²⁺ and Ni²⁺ ions. At and just above the water table atmospheric oxygen is reduced while the sulphides are oxidised to sulphate and hydroxides. Much of the iron remains in situ as characteristic goethite relicts while nickel and copper are leached, producing the enrichment below the water table. The overall genetic model proposed is electrochemical and is analogous to the corrosion of a piece of metallic iron partially immersed in differentially aerated water.     

Pyrite geochemistry in the Toarcian Posidonia Shale of south‐west Germany: Evidence for contrasting trace‐element patterns of diagenetic and syngenetic pyrites

Authigenic pyrite grains from a section of the Lower Toarcian Posidonia Shale were analysed for their trace‐element contents and sulphur‐isotope compositions. The resulting data are used to evaluate the relationship between depositional conditions and pyrite trace‐element composition. By using factor analysis, trace‐elements in pyrite may be assigned to four groups: (i) heavy metals (including Cu, Ni, Co, Pb, Bi and Tl); (ii) oxyanionic elements (As, Mo and Sb); (iii) elements partitioned in sub‐microscopic sphalerite inclusions (Zn and Cd); and (iv) elements related to organic or silicate impurities (Ga and V). Results indicate that trace‐element contents in pyrite depend on the site and mechanism of pyrite formation, with characteristic features being observed for diagenetic and syngenetic pyrites. Diagenetic pyrite formed within anoxic sediments generally has a high heavy metals content, and the degree of pyritization of these elements increases with increasing oxygen deficiency, similar to the degree of pyritization of reactive Fe. The highest gradient in the increase of the degree of trace element pyritization with bottom‐water oxygenation was found for the elements Ni < Cu < Mo = As < Tl. In contrast, syngenetic pyrite formed within a euxinic water column typically is enriched in As, Mo and Sb, but is low in heavy metals, and the geochemical variation reflects changes in sea water composition.     

Mineralogy and geochemistry of gold-bearing arsenian pyrite from the Shuiyindong Carlin-type gold deposit, Guizhou, China: implications for gold depositional processes

Arsenian pyrite in the Shuiyindong Carlin-type gold deposit in Guizhou, China, is the major host for gold with 300 to 4,000 ppm Au and 0.65 to 14.1 wt.% As. Electron miroprobe data show a negative correlation of As and S in arsenian pyrite, which is consistent with the substitution of As for S in the pyrite structure. The relatively homogeneous distribution of gold in arsenian pyrite and a positive correlation of As and Au, with Au/As ratios below the solubility limit of gold in arsenian pyrite, suggest that invisible gold is likely present as Au¹⁺ in a structurally bound Au complex in arsenian pyrite. Geochemical modeling using the laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of fluid inclusions for the major ore forming stage shows that the dominant Au species were Au(HS)₂⁻ (77%) and AuHS_(aq)⁰ (23%). Gold-hydroxyl and Gold-chloride complexes were negligible. The ore fluid was undersaturated with respect to native Au, with a saturation index of −3.8. The predominant As species was H₃AsO₃⁰ _(aq). Pyrite in the Shuiyindong deposit shows chemical zonation with rims richer in As and Au than cores, reflecting the chemical evolution of the ore-bearing fluids. The early ore fluids had relatively high activities of As and Au, to deposit unzoned and zoned arsenian pyrite that host most gold in the deposit. The ore fluids then became depleted in Au and As and formed As-poor pyrite overgrowth rims on gold-bearing arsenian pyrite. Arsenopyrite overgrowth aggregates on arsenian pyrite indicate a late fluid with relatively high activity of As. The lack of evidence of boiling and the low iron content of fluid inclusions in quartz, suggest that iron in arsenian pyrite was most likely derived from dissolution of ferroan minerals in the host rocks, with sulfidation of the dissolved iron by H₂S-rich ore fluids being the most important mechanism of gold deposition in the Shuiyindong Carlin-type deposit.     

The diagenetic geochemistry and contamination assessment of iron,cadmium, and lead in the sediments from the Shuangtaizi estuary,China

Sediment and pore water samples have been collected from the coastal tidal flat in the Shuangtaizi estuary, China, in order to investigate the geochemical behavior of iron, cadmium, and lead during diagenesis and to assess the degree of contamination. The calculated enrichment factors and geoaccumulation indices for separate elements show that anthropogenic activities have had no significant influence on the distribution of Fe and Pb in the study area, whereas the distribution of Cd has been closely influenced in this way. The high percentage of exchangeable Cd (average of 56.34%) suggests that Cd represents a potential hazard to benthic organisms in the estuary. The calculated diffusive fluxes of metals show that the most mobilized metal is Fe (9.22 mg m^?2 a^?1), followed by Cd (0.54 mg m^?2 a^?1) and Pb (0.42 mg m^?2 a^?1). Low Fe²⁺ contents in surface pore water, alongside high chromium-reducible sulfur contents, and low acid-volatile sulfur, and elemental sulfur contents at 0–25 cm depth in sediments show that Fe²⁺ is formed by the reduction of Fe oxides and is transformed first to a solid phase of iron monosulfides (FeS) and eventually to pyrite (FeS₂). The release of adsorbed Pb due to reductive dissolution of Fe/Mn oxides during early diagenesis could be a source of Pb²⁺ in pore water. From the relatively low total organic carbon contents measured in sediments (0.46–1.28%, with an average of 0.94%) and the vertical variation of Cd²⁺ in pore water, sulfide or Fe/Mn oxides (instead of organic matter) are presumed to exert a significant influence on carrying or releasing Cd by the sediments.     

骨炭钝化含黄铁矿多重金属尾矿的研究

钝化处理被广泛应用于含重金属尾矿的处理,可以从源头上防止酸矿废水(AMD)的产生,寻找一种价廉易得且对环境危害小的钝化剂十分必要。本文主要研究在骨炭作用下,用pH值为4的双氧水对黄铁矿进行氧化,探讨骨炭对黄铁矿氧化释放重金属的钝化作用。实验结果表明,添加不同含量的骨炭(分别为0.5、2.5和5 g)能将溶液的pH值分别提高到8.93、10.01和10.42,表明骨炭具有较强的中和能力,同时黄铁矿氧化释放的Pb、Zn和Cd等重金属离子浓度明显地降低。但当骨炭含量超过2.5 g时,对As有促进释放的趋势。红外光谱分析显示钝化后黄铁矿样品位于420、563、603、1 044、1 091 cm~(-1)处的特征峰主要来自PO_4~(3-)的振动,XRD进一步揭示了黄铁矿表面主要含磷次生矿物是磷铁矿和羟磷铁铅石,这些次生矿物对重金属钝化起着重要作用。因此,骨炭有望作为钝化含多重金属尾矿的钝化剂。     

Contamination of superficial sediments by heavy metals and iron in the Bizerte lagoon,northern Tunisia

According to the norms adopted by the National Network of observation of the marine life quality (RNO 1997) and US National Oceanic and Atmospheric Administration (US NOAA 1999), the superficial sediments of the Bizerte lagoon (northern Tunisia) show a contamination by nickel, which is the probable consequence of the closeness to the industrial zone, and by lead, the result of detrital material rich in lead of the geological lands of Jbel Kchabta and Jbel Messeftine. In the lagoon southern and eastern sectors, the contamination of superficial sediments is essentially by copper, zinc, nickel and iron. This pollution is related, on one hand, to the rejections of the steelworks El Fouledh and the military arsenal, and on the other hand, to Menzel Bourguiba waste disposal. The rest of the lagoon is exempted from any metallic contamination of the surface sediments. The enriched zones in manganese and zinc correspond to the higher contents in kaolinite and in smectite. Positive correlations were recorded between the percentage in fine fraction on the one hand, and the sedimentary contents in TOC, total nitrogen and heavy metals on the other hand. The majority of the analysed elements are “argilophilous” except zinc and manganese, which are clayey organophile. These results show that this lagoon receives concentrations in anthropogenic metals that risk provoking more or less important disruptions, which are harmful and irreversible on the fauna and flora of this lagoon and on the whole ecobiological equilibrium.     

Effect of acid mine drainage on a karst basin: a case study on the high-As coal mining area in Guizhou province,China

Acid mine drainage (AMD) is a common pollution in mining areas due to the oxidation of pyrite and associated sulfide minerals at mines, tailings and mine dumps. Elevated metals (Fe, Mn, Al) and metalloids (As, Hg) in AMD would deteriorate the local aquatic environment and influence the water supply. A carbonate basin with deposits of high-arsenic coal in Xingren County, southwestern China, was chosen to study the behavior of As and other chemical constituents along a river receiving AMD. Heavy metals (Fe, Mn) and major ions such as (Ca²⁺, Mg²⁺, Cl⁻, SO₄ ²⁻) in surface water, and As in sediment and surface water were analyzed. It was found that high concentrations of SO₄ ²⁻ (1,324–7,560 mg/L) and Fe (369–1,472 mg/L) in surface water were mainly controlled by the interactions between water and rocks such as the oxidation of pyrite in the local coal seams, precipitation and adsorption of iron minerals. Although ubiquitous carbonate minerals in the bedrock and the riverbeds, low pH (<3) water was maintained until 2 km downstream from the AMD source due to the Fe(hydro)oxide minerals coating on the surface of carbonate minerals to restrain the neutralization of acidic water. Moreover, the formation of Fe(hydro)oxide precipitations absorbed As was dominated the attenuation of As from water to sediment. Whereas, the dilution also played an important role in decrease of As in river water.     

Pyritization processes and greigite formation in the advancing sulfidization front in the upper Pleistocene sediments of the Black Sea

Pyritization in late Pleistocene sediments of the Black Sea is driven by sulfide formed during anaerobic methane oxidation. A sulfidization front is formed by the opposing gradients of sulfide and dissolved iron. The sulfidization processes are controlled by the diffusion flux of sulfide from above and by the solid reactive iron content. Two processes of diffusion-limited pyrite formation were identified. The first process includes pyrite precipitation with the accumulation of iron sulfide precursors with the average chemical composition of FeS_n (n = 1.10-1.29), including greigite. Elemental sulfur and polysulfides, formed from H₂S by a reductive dissolution of Fe(III)-containing minerals, serve as intermediates to convert iron sulfides into pyrite. In the second process, a “direct” pyrite precipitation occurs through prolonged exposure of iron-containing minerals to dissolved sulfide. Methane-driven sulfate reduction at depth causes a progressive formation of pyrite with a δ³⁴S of up to +15.0‰. The S-isotopic composition of FeS₂ evolves due to contributions of different sulfur pools formed at different times. Steady-state model calculations for the advancement of the sulfidization front showed that the process started at the Pleistocene/Holocene transition between 6360 and 11 600 yr BP. Our study highlights the importance of anaerobic methane oxidation in generating and maintaining S-enriched layers in marine sediments and has paleoenvironmental implications.     

Particulate sulfur species in the water column of the Cariaco Basin

The biogeochemistry of iron sulfide minerals in the water column of the Cariaco Basin was investigated in November 2007 (non-upwelling season) and May 2008 (upwelling season) as part of the on-going CARIACO (CArbon Retention In A Colored Ocean) time series project. The concentrations of particulate sulfur species, specifically acid volatile sulfur (AVS), greigite, pyrite, and particulate elemental sulfur, were determined at high resolution near the O₂/H₂S interface. In November 2007, AVS was low throughout the water column, with the highest concentration at the depth where sulfide was first detected (260 m) and with a second peak at 500 m. Greigite, pyrite, and particulate elemental sulfur showed distinct concentration maxima near the interface. In May 2008, AVS was not detected in the water column. Maxima for greigite, pyrite, and particulate elemental sulfur were again observed near the interface. We also studied the iron sulfide flux using sediment trap materials collected at the Cariaco station. Pyrite comprised 0.2-0.4% of the total particulate flux in the anoxic water column, with a flux of 0.5-1.6 mg S m⁻² d⁻¹.Consistent with the water column concentration profiles for iron sulfide minerals, the sulfur isotope composition of particulate sulfur found in deep anoxic traps was similar to that of dissolved sulfide near the O₂/H₂S interface. We conclude that pyrite is formed mainly within the redoxcline where sulfur cycling imparts a distinct isotopic signature compared to dissolved sulfide in the deep anoxic water. This conclusion is consistent with our previous study of sulfur species and chemoautotrophic production, which suggests that reaction of sulfide with reactive iron is an important pathway for sulfide oxidation and sulfur intermediate formation near the interface. Pyrite and elemental sulfur distributions favor a pathway of pyrite formation via the reaction of FeS with polysulfides or particulate elemental sulfur near the interface. A comparison of thermodynamic predictions with actual concentration profiles for iron sulfides leads us to argue that microbes may mediate this precipitation.     

Biogeochemistry of sulfur and iron in Thioploca-colonized surface sediments in the upwelling area off central chile

The biogeochemistry of sedimentary sulfur was investigated on the continental shelf off central Chile at water depths between 24 and 88 m under partial influence of an oxygen minimum zone. Dissolved and solid iron and sulfur species, including the sulfur intermediates sulfite, thiosulfate, and elemental sulfur, were analyzed at high resolution in the top 20 cm. All stations were characterized by high rates of sulfate reduction, but only the sediments within the Bay of Concepción contained dissolved sulfide. Due to advection and/or in-situ reoxidation of sulfide, dissolved sulfate was close to bottom water values. Whereas the concentrations of sulfite and thiosulfate were mostly in the submicromolar range, elemental sulfur was by far the dominant sulfur intermediate. Although the large nitrate- and sulfur-storing bacteria Thioploca were abundant, the major part of S⁰ was located extracellularly. The distribution of sulfur species and dissolved iron suggests the reaction of sulfide with FeOOH as an important pathway for sulfide oxidation and sulfur intermediate formation. This is in agreement with the sulfur isotope composition of co-existing elemental sulfur and iron monosulfides. In the Bay of Concepción, sulfur isotope data suggest that pyrite formation proceeds via the reaction of FeS with polysulfides or H₂S. At the shelf stations, on the other hand, pyrite was significantly depleted in ³⁴S relative to its potential precursors FeS and S⁰. Isotope mass balance considerations suggest further that pyritization at depth includes light sulfide, potentially originating from bacterial sulfur disproportionation. The δ³⁴S-values of pyrite down to −38‰ vs. V-CDT are among the lightest found in organic-rich marine sediments. Seasonal variations in the sulfur isotope composition of dissolved sulfate indicated a dynamic non-steady-state sulfur cycle in the surface sediments. The ¹⁸O content of porewater sulfate increased with depth at all sites compared to the bottom water composition due to intracellular isotope exchange reactions during microbial sulfur transformations.     

Denitrification coupled to pyrite oxidation and changes in groundwater quality in a shallow sandy aquifer

This study focuses on denitrification in a sandy aquifer using geochemical analyses of both sediment and groundwater, combined with groundwater age dating (³H/³He). The study sites are located underneath cultivated fields and an adjacent forested area at Oostrum, The Netherlands. Shallow groundwater in the region has high nitrate concentrations (up to 8 mM) due to intense fertilizer application. Nitrate removal from the groundwater below cultivated fields correlates with sulfate production, and the release of dissolved Fe²⁺ and pyrite-associated trace metals (e.g. As, Ni, Co and Zn). These results, and the presence of pyrite in the sediment matrix within the nitrate removal zone, indicate that denitrification coupled to pyrite oxidation is a major process in the aquifer. Significant nitrate loss coupled to sulfate production is further confirmed by comparing historical estimates of regional sulfate and nitrate loadings to age-dated groundwater sulfate and nitrate concentrations, for the period 1950-2000. However, the observed increases in sulfate concentration are about 50% lower than would be expected from complete oxidation of pyrite to sulfate, possibly due to the accumulation of intermediate oxidation state sulfur compounds, such as elemental sulfur. Pollutant concentrations (NO₃, Cl, As, Co and Ni) measured in the groundwater beneath the agricultural areas in 1996 and 2006 show systematic decreases most likely due to declining fertilizer use.     

Seasonal and spatial changes of metal concentrations in groundwater outflows from porous sediments in the Gryżyna-Grabin Tunnel Valley in western Poland

Groundwater outflows (springs and seeps) from porous sediments on European lowlands play a significant role in the surface water balance. It is therefore important to document these outflows’ water quality and spatial and temporal changes. The present study focused on changes in iron, manganese, and heavy metals in waters of groundwater outflows in an area of low anthropogenic impact—the Gryżyna-Grabin Tunnel Valley in western Poland. Eleven outflows were studied for a period of 2 years. Most of the samples analyzed revealed low element contents and little variation in time and space. Only values of iron and lead were above World Health Organization limits for drinking water. The concentrations of these elements were also variable in time and space. The seasonal changes in iron content are probably due to natural, temperature- and pH-controlled reactions of shallow groundwater with aquifer sediments. On the other hand, the elevated lead content points to regional water contamination.     

富铁橄榄石的水溶性实验研究SCIEI北大核心CSCD

地幔的力学性质主要受橄榄石流变性的控制,含水对橄榄石流变性质的影响很大,而橄榄石的水溶性受到温度和铁含量的影响,因此,本文进行了不同铁含量橄榄石在不同温度下的水溶性实验研究。实验使用的样品为天然橄榄石单晶Fa_(17)和Fa_(24.7)(Fe_(No.)=100×molar Fe/(Mg+Fe))以及人工合成的橄榄石单晶Fa_(22);橄榄石单晶的水溶性实验在300MPa围压和1273~1473K的温度条件下进行,每隔50K进行一组实验,氧逸度被控制在Ni NiO水平上。实验结束后,对橄榄石单晶沿b面进行双面研磨抛光,用电子探针分析确定橄榄石单晶成分,采用EBSD精确测量橄榄石的单晶方向,使用红外光谱仪(FTIR)的非偏振光路测试橄榄石单晶在b轴上的吸收光谱。对FTIR吸收光谱进行积分得到富铁橄榄石的水溶性实验结果:当温度由1273K升至1473K时,橄榄石单晶Fa_(17)的水溶性变化为600~1200H/10^(6) Si,橄榄石单晶Fa_(24.7)的水溶性变化为1000~1300H/10^(6) Si,人工合成的橄榄石单晶Fa_(22)的水溶性变化为500~900 H/10^(6) Si。因此,相同铁含量橄榄石单晶的水溶性随温度的增加而增加,相同温度条件下,天然形成的橄榄石的水溶性随着铁含量的增加而增加,百分之一的铁含量的增加,可以导致约百分之十的水溶性的增加。本文所研究的不同铁含量的橄榄石可以为更好地估算上地幔水溶性提供依据。     

Mineralogical criteria in the origin of marine iron-manganese nodules

In iron-manganese nodules from the floor of Pacific ocean, Baltic, White Sea and Kara Sea, iron bydroxide '-FeOOH was analysed in the laboratory. In buried ooze, reduction processes generate Fe(HCO₃)₂ which migrates into the upper part of the bottom ooze and into near bottom sea water where Fe(OH)₂ is formed. The oxidation process of Fe²⁺ to Fe³⁺, without participation of iron bacteria, leads to the topotactic transformation of Fe(OH)₂ to '-FeOOH. Marine water does not contain Fe²⁺ and cannot be a direct source of iron deposited in the nodules. Discovery of '-FeOOH in marine nodules permits the consideration that both iron and manganese were derived from the buried bottom mud, which during diagenetic processes led to the transfer of these metals in solutions and their upward migration.     

新疆南天山阿沙哇义金矿床的成因与找矿启示:来自流体和硫化物成分的限定

阿沙哇义金矿位于中国新疆南天山造山带,属于著名的中亚南天山锑-汞-金成矿带的东延部分。该矿床严格受断裂所控制,以浸染状黄铁矿化、毒砂化为特征。矿化可分为三个阶段:早期无矿或贫矿石英阶段,中期石英多金属硫化物阶段,晚期石英-碳酸盐阶段。其中,中期是主要成矿阶段。成矿流体气相成分以H_2O为主,摩尔含量为75%～93%,其次为CO_2,摩尔含量为6%～25%,其余为CH_4、C_2H_6、H_2S、N_2和Ar;液相成分阳离子以Na~+为主,含少量K~+、Ca~(2+)离子,阴离子以Cl~-为主,SO~(2-)次之;矿石的Au含量与其流体的CO_2含量呈反相关,与K~+含量呈正相关。硫化物成分分析结果表明:(1)围岩地层和矿石中的黄铁矿和毒砂是重要的载金矿物,黄铁矿Au含量为0～0. 09%,平均值0. 03%;毒砂Au含量为0～0. 28%,平均值0. 07%;(2)黄铁矿和毒砂Au含量与其自形程度没有明显的相关性;(3)环带状黄铁矿较均质结构黄铁矿具有更高的Au含量;(4)岩体中的黄铁矿几乎不含Au。在成矿构造环境、成矿流体特征及演化、金矿富集机制、成矿温压条件等方面,该矿床与世界上大多数造山型金矿显示出一致性,成矿类型应属于剥蚀程度较浅的造山型金矿。断层阀作用控制的断层愈合-破裂导致的流体不混溶作用是本区金富集、沉淀的最重要机制,但流体混合机制对金的富集沉淀也发挥了作用。黄铁矿、毒砂发育及较多的含炭物质三者共存是本区寻找富矿的关键标志。     

胶东地区招贤深部金矿床金和载金矿物化学成分及其地质意义

胶东地区-1000 m以下深部找矿的重大突破,使得探明储量已达5000多t,成为探讨深部金的赋存状态及成矿作用的天然实验室。招贤金矿为焦家成矿带近年深部找矿重大突破之一,矿体主要产于-1260 m以深的晚侏罗世二长花岗岩中,受控于焦家断裂。金属矿物主要为黄铁矿、黄铜矿和银金矿等,脉石矿物包括石英、绢云母、方解石、钾长石等。围岩蚀变以钾长石化、硅化、黄铁绢英岩化、碳酸盐化为主。金矿物以自然金和银金矿为主,呈裂隙金或包体金分布于黄铁矿中,少数不可见金呈晶隙金分布于黄铁矿等矿物中。其中,黄铁矿w(S)=52.227%～54.915%、w(Fe)=44.749%～47.134%,原子个数比S/Fe=1.99～2.11,化学式FeS_1.99～FeS_2.11;黄铜矿w(S)=34.282%～35.140%、w(Fe)=29.263%～30.268%,w(Cu)=33.130%～34.114%,化学式Cu_0.96FeS_2.01～Cu_1.01FeS_2.10,平均化学式为C...     

A mechanism for the production of hydroxyl radical at surface defect sites on pyrite

A previous contribution from our laboratory reported the formation of hydrogen peroxide (H₂O₂) upon addition of pyrite (FeS₂) to O₂-free water. It was hypothesized that a reaction between adsorbed H₂O and Fe(III), at a sulfur-deficient defect site, on the pyrite surface generates an adsorbed hydroxyl radical (OH^•).