Environmental geochemistry of the derelict Webbs Consols mine,New South Wales,Australia

Small-scale mining and mineral processing at the Webbs Consols polymetallic PbZnAg deposit in northern New South Wales, Australia has caused a significant environmental impact on streams, soils and vegetation. Unconfined waste rock dumps and tailings dams are the source of the problems. The partly oxidised sulphidic mine wastes contain abundant sulphides (arsenopyrite, sphalerite, galena) and oxidation products (scorodite, anglesite, smectite, Fe-oxyhydroxides), and possess extreme As and Pb (wt% levels) and elevated Ag, Cd, Cu, Sb and Zn values. Contemporary sulphide oxidation, hardpan formation, crystallisation of mineral efflorescences and acid mine drainage generation occur within the waste repositories. Acid seepages (pH 1.9–6.0) from waste dumps, tailings dams and mine workings display extreme As, Pb and Zn and elevated Cd, Cu and Sb contents. Drainage from the area is by the strongly contaminated Webbs Consols Creek and although this stream joins and is diluted by the much larger Severn River, contamination of water and stream sediments in the latter is evident for 1–5 km, and 12 km respectively, downstream of the mine site. The pronounced contamination of local and regional soils and sediments, despite the relatively small scale of the former operation, is due to the high metal tenor of abandoned waste material and the scarcity of neutralising minerals. Any rehabilitation plan of the site should include the relocation of waste materials to higher ground and capping, with only partial neutralisation of the waste to pH 4–5 in order to limit potential dissolution of scorodite and mobilisation of As into seepages and stream waters.     

Arsenic distribution during formation and capping of an oxidised sulphidic minesoil, Macraes mine, New Zealand

A minesoil has developed over 5 years oxidative exposure on sulphide concentrate tailings (ca. 1 wt.% As) at the Macraes mesothermal gold mine, New Zealand. The minesoil has a dry crust which has formed due to evaporative drying. This dry crust is enriched in arsenic (ca. 5 wt.% As) as scorodite (FeAsO₄·2H₂O) because of upward mobility of dissolved arsenic during drying. Similar enrichment of arsenic has occurred along the walls of desiccation cracks which extend over 1 m into the minesoil. Capping of the tailings and minesoil with wet tailings (pH=8) results in dissolution of scorodite and remobilization of arsenic on the millimetre scale. Experimental capping of the minesoil with wet calcium carbonate remobilized some arsenic from scorodite on the centimetre scale, but much original arsenic enrichment was preserved after 400 days. A layer of gypsum (CaSO₄·2H₂O) and iron oxyhydroxide cementation developed at the interface between the minesoil and the experimental calcium carbonate cap, restricting water flow. This layer was ca. 1 mm thick after 400 days. Theoretical comparison between advection and diffusion in the minesoil suggests that diffusion is an important mechanism for chemical mobility on the 1–50-year time scale. However, advection can be important in secondary porosity of the dry crust of the minesoil and water penetrates this zone at a rate of 1.5 mm/day.     

贵州水银洞金矿构造蚀变体稀土元素地球化学特征

水银洞金矿构造蚀变体(SBT)为产出于茅口租(P2m)和龙潭组(P3l)之间不整合面上的一套强硅化灰岩、灰岩角砾岩、硅化粘土岩组合.呆用ICP-MS测定钻孔岩芯中构造蚀变体样品稀土元素组成,对比研究SBT围岩、区域岩浆岩及现代海底热水系统流体稀土元素组成.结果显示,SBT的轻重稀土分馏明显[LREE/HREE=4.92～17.51,(La/Yb)N=5.94～38.37],曲线右倾型;轻稀土分异明显,曲线右倾程度大;重稀土分异不明显,曲线平坦;负Eu(0.61～0.94)、Ce(0.52～1.07)异常明显;SBT及围岩均具有明显W型稀土元素四分组效应,而不同于区域岩浆岩和现代海底热水系统流体,表明热液流体来源以壳源为主.     

Chemical and petrographical characterization of feed coal, fly ash and bottom ash from the Figueira Power Plant, Paraná, Brazil

The aim of the present study is the petrographic and chemical characterization of the coal at the Figueira Power Plant, Paraná, Brazil, prior and after the beneficiation process and the chemical characterization of fly and bottom ashes generated in the combustion process.Petrographic characterization was carried out through maceral analysis and vitrinite reflectance measurements. Chemical characterization included proximate analysis, determination of calorific value and sulphur content, ultimate analysis, X-ray diffraction, X-ray fluorescence, Inductively Coupled Plasma — Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma — Atomic Emission Spectrometry (ICP-AES) analysis, and determination of Total Organic Carbon (TOC) content.Vitrinite reflectance analyses indicate a high volatile B/C bituminous coal (0.61 to 0.73% Rrandom). Maceral analyses show predominance of the vitrinite maceral group (51.6 to 70.9 vol.%, m.m.f). Except of the Run of mine (ROM) coal sample, the average calorific value of the coals is 5205 kcal/kg and ash yields range from 21.4 to 38.1 wt.%. The mineralogical composition (X-ray diffraction) of coals includes kaolinite, quartz, plagioclase and pyrite, whereas fly and bottom ashes are composed by mullite, ettringite, quartz, magnetite, and hematite. Analyses of major elements from coal, fly and bottom ashes indicate a high SiO₂, Al₂O₃, and Fe₂O₃ content. Trace elements analysis of in-situ and ROM coals by ICP-MS and ICP-AES show highest concentration in Zn and As. Most of the toxic elements such as As, Cd, Cr, Mo, Ni, Pb, and Zn are significantly reduced by coal beneficiation. Considering the spatial distribution of trace elements in the beneficiated coal samples, which were collected over a period of three months, there appears to be little variation in Cd and Zn concentrations, whereas trace elements such as As, Mo, and Pb show a larger variation.In the fly and bottom ashes, the highest concentrations of trace elements were determined for Zn and As. When compared with trace element concentrations in the feed coal, fly ashes show a significant enrichment in most trace elements (As, B, Be, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, Pb, Sb, Tl, and Zn), suggesting a predominantly volatile nature for these elements. In contrast, Sn is distributed evenly within the different ash types, whereas U shows depleted concentration in both bottom and fly ash samples.According to the International Classification of in-seam coals the Cambuí coals are of para/ortho bituminous rank of low grade (except for the ROM sample), and are characterized by the predominance of vitrinite macerals.     

阜平杂岩年龄及其地质意义：兼论前寒武高级变质地体的定年问题

本文通过对比锆石TIMS（热电离质谱法），SHRIMP（高灵敏度离子探针）及ICPMS－LP（等离子体质谱－激光探针）分析方法对阜平杂岩中主要岩石获得的年龄结果，讨论了阜平杂岩中几种主要岩石的形成时代及其地质意义。研究结果表明阜平杂岩是由不同时代、不同成因的各种高级变质岩组成，其主体是2．51Ga的TTG片麻岩并包裹了少量2．7Ga的大陆残片。同时阜平地区还发育一期2．05Ga的岩浆活动。阜平杂岩中的湾子表壳岩可能沉积发育于2．5Ga和2．1Ga之间。本文还通过比较三种锆石同位素定年方法的特点，进而讨论了几种方法在高级变质地体定年上的可行性，特别强调了锆石内部结构、化学组成等成因矿物学方面的研究对锆石年代学的主要意义。     

Arsenic attenuation in tailings at a former Cu–W–As mine,SW Finland

Nearly half a century after mine closure, release of As from the Ylöjärvi Cu–W–As mine tailings in groundwater and surface water run-off was observed. Investigations by scanning electron microscopy (SEM), electron microprobe analysis (EMPA), synchrotron-based micro-X-ray diffraction (μ-XRD), micro-X-ray absorption near edge structure (μ-XANES) and micro-extended X-ray absorption fine structure (μ-EXAFS) spectroscopy, and a sequential extraction procedure were performed to assess As attenuation mechanisms in the vadose zone of this tailings deposit. Results of SEM, EMPA, and sequential extractions indicated that the precipitation of As bearing Fe(III) (oxy)hydroxides (up to 18.4 wt.% As₂O₅) and Fe(III) arsenates were important secondary controls on As mobility. The μ-XRD, μ-XANES and μ-EXAFS analyses suggested that these phases correspond to poorly crystalline and disordered As-bearing precipitates, including arsenical ferrihydrite, scorodite, kaňkite, and hydrous ferric arsenate (HFA). The pH within 200 cm of the tailings surface averaged 5.7, conditions which favor the precipitation of ferrihydrite. Poorly crystalline Fe(III) arsenates are potentially unstable over time, and their transformation to ferrihydrite, which contributes to As uptake, has potential to increase the As adsorption capacity of the tailings. Arsenic mobility in tailings pore water at the Ylöjärvi mine will depend on continued arsenopyrite oxidation, dissolution or transformation of secondary Fe(III) arsenates, and the As adsorption capacity of Fe(III) (oxy)hydroxides within this tailings deposit.     

Arsenic in iron cements developed within tailings of a former metalliferous mine—Enguialès,Aveyron, France

Arsenopyrite-rich waste from a former metalliferous mine were spread out over the sloping side of a deep valley after processing. Over the past 30 a, they have been subjected to rainfall and acid water originating from the abandoned mine galleries. This intensive leaching has led to the formation of thin layers of As–Fe crusts on the tailings surface acting as a cement. X-ray diffraction and SEM coupled with EDS determined that jarosite was present in all mineral samples and could contain a small amount of As (∼5.7 wt.%). In addition EMPA and Raman microspectroscopy characterised the presence of amorphous As(V) Fe hydrates as well as rare arsenate minerals (e.g. scorodite). Raman microspectroscopy in particular identified a preponderance of goethite or hematite within the mineral framework of the tailings materials that is likely to sorb recalcitrant As species. The characterisation of the components of the tailings enable the identification of their evolution, shows the progressive decrease of their As-content and emphasises the consequences of the temporary trapping of As in the very acidic and oxidising conditions prevailing in such environments. Resinous amorphous material was identified as the richest in As with As ∼17.1 wt.%. This material evolved toward more crystallised phases (e.g. goethite, jarosite) which contained less As (3.2 wt.%<As <5.7 wt.%). Paragenesis showed the progressive release of As with the crystallisation evolution of the As-trapping material.     

Influence of hardpan layers on arsenic mobility in historical gold mine tailings

Hardpans, or cemented layers, form by precipitation and cementation of secondary minerals in mine tailings and may act as both physical and chemical barriers. Precipitation of secondary minerals during weathering of tailings can sequester metal(loid)s, thereby limiting their release to the environment. At Montague Gold Mines in Nova Scotia, tailings are partially cemented by the Fe arsenate mineral scorodite (FeAsO₄·2H₂O). Previous studies have shown that the formation of scorodite can effectively limit aqueous As concentrations due to its relatively low solubility (<1 mg/L at pH 3–4) and high As content (43–52 wt.% As₂O₅, this study). Co-existing waters and solids were sampled at Montague Gold Mines to identify present-day field conditions influencing scorodite precipitation and dissolution, and to better understand the mineralogical and chemical relationship between hardpan and tailings. In addition to scorodite, hardpan cements were found to include amorphous Fe arsenate and Fe oxyhydroxide. Nearly all hardpan is associated with historical arsenopyrite-bearing concentrate which provides a source of acidity, As⁵⁺ and Fe³⁺ for secondary mineral precipitation. Pore waters sampled from the hardpan have pH values ranging from 2.43 to 7.06. Waters with the lowest pH values also have the highest As concentrations (up to 35.8 mg/L) and are associated with the most extensive hardpan and greatest amount of weathered sulfide. Samples from areas with discontinuous hardpan and less sulfide have near-neutral pH and lower As concentrations. Detailed petrographic observations indicate that the identity and stability of As-bearing secondary minerals depends on the continued availability of sulfide concentrate. The results of this study are being used to develop remediation strategies for highly weathered, hardpan-bearing tailings that consider the stability of both primary and secondary minerals under various cover scenarios.     

准格尔煤田串草圪旦煤矿5号煤元素地球化学特征

为研究准格尔串草圪旦5号煤微量元素地球化学特征,采用光学显微镜、扫面电子显微镜和X射线衍射（XRD）方法观测煤中矿物组成及形态特征,应用电感耦合等离子质谱（ICP MS）方法测定煤中多种微量元素含量,运用数理统计方法研究微量元素在煤中的赋存特征。结果表明：5号煤中Li、Be、F、U、Hg 5种元素相对富集,含量高于研究区6号煤及中国煤中含量水平。5号煤中Li、F、Ga、Se无机亲和性强,Be、As、U为亲有机元素;Hg与硫含量显著正相关。各元素在煤中主要以有机结合态、无机结合态和硫化物结合态赋存。     

多接收器电感耦合等离子体质谱的新应用

无机地球化学研究的进展通常依赖于新的技术开发。电感耦合等离子体质谱（ICP—MS）技术可以进行高精度的同位素比值分析，使以前很难测定的元素的分析成为可能。牛津大学地球科学系已经越来越多地开展多接收器电感耦合等离子体质谱分析，着重于解决从宇宙至环境化学领域的诸多问题。目前主要研究Cr同位素，确定Cr对Jurassic—Triassic边界可能产生的影响事件，以及采用铀系列同位素进行海洋学研究。     

黔西北天桥铅锌矿床热液方解石C、O同位素和REE地球化学

利用连续流动质谱和电感耦合等离子体质谱(ICP-MS)对黔西北天桥铅锌矿床原生矿石中脉石矿物热液方解石C、O同位素组成和稀土元素含量进行了分析,结果表明热液方解石C、O同位素组成相对均一,不同标高方解石C、O同位素组成不具明显差别,其δ13CPDB和δ18OSMOW分别为-3.4‰～-5.3‰和14.7‰～19.5‰,在δ13CPDB-δ18OSMOW图上介于原始碳酸岩与海相碳酸盐岩之间。热液方解石总稀土元素含量较低(ΣREE=6.80×10-6～49.1×10-6),表现为轻稀土富集、Eu负异常的"M"型,其Eu/Eu*变化范围为0.30～0.55,与硫化物具有相似的稀土配分模式。根据热液方解石与蚀变围岩、远矿围岩及不同时代地层碳酸盐岩的C、O同位素组成和REE含量特征对比结果,结合前人研究成果,认为该矿床成矿流体具"多来源混合"特征,其中围岩碳酸盐岩为成矿流体提供了主要的C和REE来源,地层中膏岩海相硫酸盐岩为成矿流体提供了主要的S来源,而成矿流体中的水则主要为变质基底昆阳群等提供的变质水,并受到大气降水的影响。     

Associations of trace elements in the sulfides of black smokers from the Broken Spur,Menez Gwen,and Snake Pit hydrothermal fields

Thorough processing of a huge amount of analytical data from Electron-Probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) allowed us to define several trace-element associations in sulfides from three hydrothermal vent fields at the Mid-Atlantic Ridge (Broken Spur, Menez Gwen, and Snake Pit). The presence of such association may indicate the occurrence of certain mineral phases at the micro- and/or nano-scales.     

地下水中砷形态标准物质研制

砷元素的不同形态对人体有不同的毒性,无机砷的毒性最大,有机砷毒性较小,准确测定水体中尤其是地下水中砷形态的含量对于人体健康和环境保护有重要意义。但目前国内外尚缺乏地下水中砷形态的标准物质。文章研制了5个地下水砷形态标准物质,候选物样品采自山西和内蒙古高砷地区,在样品的采集和制备过程中使用冷冻干燥法和加保护剂两种方法保证砷形态稳定,定值参数为砷全量、As(Ⅲ)、As(Ⅴ),定值方法采用氢化物发生-原子荧光光谱法、电感耦合等离子体光谱法、电感耦合等离子体质谱法、高效液相色谱-电感耦合等离子体质谱法。经检验,制备的砷形态标准物质具有良好的均匀性和稳定性。该系列标准物质研制中首次应用冷冻干燥技术,样品保存问题得到了很好的解决,采用多家实验室协作定值,测试方法准确、可靠,标准值和不确定度合理,填补了国内外砷形态标准物质研制的空白。     

Mineralogical controls on environmental mobility of arsenic from historic mine processing residues,New Zealand

Processing of arsenopyrite ore took place at Blackwater Au mine, New Zealand, between 1908 and 1951 and no rehabilitation was undertaken after mine closure. High As concentrations in solid processing residues (up to 40 wt% As) are due to secondary As minerals. Site pH regimes vary from 4.1 to circum-neutral. Originally, all processed As was present as arsenolite (arsenic trioxide polymorph, As^III), a by-product of arsenopyrite roasting. Near the roaster, scorodite precipitated as a result of the high dissolved As concentration during arsenolite dissolution. The formation of scorodite has two major consequences. Firstly, the scorodite precipitate cements the ground in the vicinity of the roaster area, thereby creating an impermeable surface crust (up to 30 wt% As) and encapsulating weathered arsenolite grains within the cement. Secondly, formation of scorodite temporarily immobilizes some of the dissolved As that is generated during nearby arsenolite dissolution. Where all the available arsenolite has dissolved, scorodite becomes soluble, and the dissolved As concentrations are controlled by scorodite solubility, which is at least two orders of magnitudes lower than arsenolite solubility. Downstream Eh conditions fall below the As^V/As^III boundary, so that scorodite does not precipitate and dissolved As concentrations are controlled by arsenolite solubility. Dissolved As reaches up to 52 mg/L in places, and exceeds the current WHO drinking water guideline of 0.01 mg/L by 5200 times. This study shows that dissolved As concentrations in discharge waters at historic mine sites are dependent on the processing technology and associated mineralogy.     

Geological impact of some tailings dams in Sardinia,Italy

This article deals with the results of a survey carried out in Sardinia on both active and abandoned tailings dams, and we also discuss the geological impact of tailings dams of two mines: the Masua mine, a large syngenetic Pb-Zn deposit located in Cambrian limestones, and the Montevecchio mine, a Pb-Zn vein deposit near a Hercynian granite intrusion. The characteristics and metal content of material in the dams were analyzed. A high contamination of heavy metals (Pb, Zn, Cd, Cu) was found both in the soils and water of Rio Montevecchio, a stream draining the tailings dams and other mining operations in the area.The study indicates that a control plan to minimize heavy metal pollution must be drawn up for all mines of the area, whether active or abandoned.     

碱熔-电感耦合等离子体发射光谱法测定大气颗粒物样品中无机元素

大气颗粒物(TSP和PM10)中Si、Al、Ca、Mg、K、Fe、Na等元素含量较高,是颗粒物源分析的指示性元素。目前分析大气颗粒物样品中无机元素的方法有中子活化分析法、X射线荧光光谱法、微波消解(或高压釜消解)电感耦合等离子体发射光谱法和电感耦合等离子体质谱法。本文建立了碱熔-电感耦合等离子体发射光谱法测定大气颗粒物样品中Si、Al、Ca、Mg、Fe、Ti、Ba、Sr、Zr等无机元素的分析方法,样品于镍坩埚中530～550℃灰化60 min后用NaOH融熔,水提取,再用2 mL 50%的HCl酸化,钠基体匹配消除干扰,解决了大气颗粒物滤膜样品中Si易产生的溶解不完全等问题,提高了Ti、Ba、Sr、Zr等主、次量元素测定的精密度和准确度。讨论了坩埚和熔剂的选择、灰化温度、灰化时间、酸度、干扰等影响因素。在选定条件下,测定结果相对误差(RE)﹤4%,相对标准偏差(RSD,n=12)﹤5%,检出限为0.0047～1.2 ng/g。方法所需设备简单,分析成本低,快速简便,精密度好,准确度高,适宜批量样品的测定。     

Geochemistry and Modes of Occurrence of Hazardous Trace Elements in the No. 11 Coal Seam, Antaibao Surface Mine, Shanxi Province

Concentrations of seventeen hazardous trace elements including As, Pb, Hg, Se, Cd, Cr, Co, Mo, Mn, Ni, U, V, Th, Be, Sb, Br and Zn in the No.ll coal seam, Antaibao surface mine, Shanxi Province were determined using Instrumental Neutron Activation Analysis （INAA）, Inductively Coupled Plasma Atomic Emission Spectrometry （ICP-AES）, Cold-Vapor Atomic Absorption Spectrometry （CV-AAS） and Graphite Furnace Atomic Absorption Spectrometry （GF-AAS）. Comparisons with average concentrations of trace elements in Chinese coal show that the concentrations of Hg and Cd in the No. 11 coal seam, Antaibao surface mine are much higher. They may be harmful to the environment in the process of utilization. The variations of the trace elements contents and pyritic suffur in vertical section indicated that： （a） the concentrations of As, Pb, Mn, and pyritic sulfur decrease from roof to floor; （b） the concentrations of Cr, Zn and Mo are higher in roof, floor and lower in coal seam; （c） the concentration of Br, Sb, and Hg are higher in coal seam and lower in roof and floor; （d） the concentrations of Mo, V, Th and AI vary consistently with the ash yield. Cluster analysis of trace elements, pyritic sulfur, ash yield and major elements, such as AI, Fe, P, Ca shows that： （a） pyritic sulfur, Fe, As, Mn, Ni, Be are closely associated and reflect the influence of pyrite; （b） Mo, Se, Pb, Cr, Th, Co, Ca and A! are related to clay mineral, which is the main source of ash; （c） U, Zn, V, Na, P maybe controlled by phosphate or halite; （d） Hg, Br, Sb and Cd may be mainly organic-associated elements which fall outside the three main groups. The concentration distribution characteristics of trace elements in coal seam and the cluster analysis of major and trace elements showed that the contents of trace elements in the No. 11 coal seam, Antaibao surface mine, are mainly controlled by detrital input and migration from roof and floor.     

Geochemical controls on arsenic distribution in the Baccu Locci stream catchment (Sardinia,Italy) affected by past mining

The Baccu Locci stream catchment (Sardinia, Italy) is affected by serious As contamination as a consequence of past mining. The presence of both point and widespread sources of contamination (waste-rock dumps and flotation tailings, respectively) strongly affects surface water chemistry, and produces high As concentrations (hundreds of μg l⁻¹) in stream waters. Water chemistry of the Baccu Locci stream changes considerably over a distance of about 10 km as a consequence of various, locally concomitant, processes acting along the stream course: (1) mixing with metal-rich SO₄ waters; (2) dissolution/precipitation of metal-bearing phases; (3) mixing with HCO₃-dominated lake waters; (4) gypsum dissolution coupled with calcite precipitation; (5) mixing with dilute surface and/or ground waters. In contrast to metals (e.g. Pb, Cu, Zn and Cd), whose dissolved concentrations rapidly decrease downstream of the mined area through (co-)precipitation/adsorption mechanisms, As concentrations tend to gradually increase (up to 0.9 mg l⁻¹) along the stream course as far as the alluvial plain, though significant variations are locally observed. This behaviour is mainly due to the higher mobility of As than metals under the near neutral-oxidative conditions occurring in the Baccu Locci stream waters. Results of a leaching test indicate that part of the As contained in the flotation tailings occurs as As(III), which is more mobile and less strongly sorbed than As(V). The As released to the waters by various mechanisms (i.e. release/desorption from the Fe(III)-hydroxides coatings of silicate grains, oxidation of residual arsenopyrite, decomposition of scorodite) tends to remain in solution and to be transported long distances. As a consequence of the widespread presence of highly As-contaminated flotation tailings all over the medium-lower Baccu Locci stream catchment, long-term As contamination is expected.     

Geological analogue for circumneutral pH mine tailings: implications for long-term storage,Macraes Mine,Otago, New Zealand

Tailings from the Macraes Au mine cyanidation process are stored in an impoundment about 0.6 km² and 80 m deep whose pH is maintained near 8 by the neutralizing capacity of the gangue minerals. The tailings are sandy (>50 μm particles), have a hydraulic conductivity of about 10⁻² m/day, and contain 0.1–1.0 wt.% S and 0.1–1.5 wt.% graphitic C from the primary deposit. Concentrations of As in the pore water of the mixed tailings, which are a combination of various tailings types, range from 0.1 to 20 ppm, HCO₃^- is 100 to 200 ppm, and dissolved SO₄ is 100–1700 ppm. The mixed tailings will be stored in this impoundment in perpetuity after mining ceases. Confidence in the long-term pH stability of these tailings can be gained from examination of mineralogically and chemically similar geological analogues in the immediate vicinity. A sequence, typically about 5 m thick, of sands and gravels derived from the Macraes mineralized zone 12–28 ka ago contains rounded detrital sulfide mineral grains which are unoxidized despite their close proximity to the surface and the occasional incursion of oxygenated waters. These sediments have a hydraulic conductivity of about 10⁻⁴ m/day. Saturating water pH is currently 7–8. Sands with 0.2–0.8 wt.% organic C host SO₄-reducing bacteria (SRB), and local cementation by authigenic framboidal pyrite has occurred. SRB were found in water-saturated sediments with decreased hydraulic conductivity and alkaline and anoxic conditions. These bacteria are involved in the formation of authigenic framboidal pyrite, reducing the cycling of dissolved Fe in the sediments. Carbon is not a limiting factor in this process as organic matter is present in the sandstone and ground water contains up to 180 ppm HCO₃^-. Comparison of the 28 ka old sediments with the modern tailings suggests that the chemical behaviour of the two will be similar, possibly with the crystallization of authigenic pyrite in the tailings over the long term. As long as the present slightly anoxic and circumneutral pH environmental conditions are maintained in the mixed tailings impoundment, sulfide decomposition and acidification are unlikely.     

Anomalous lead isotope ratios and provenance of offshore sediments,Gulf of Carpentaria,northern Australia

Anomalous Pb isotope ratios measured by Inductively Coupled Plasma Mass Spectrometry in terrigenous marine sediments (<63 μm fraction) from the Gulf of Carpentaria originated from depositional mixing of clay/silt with average modern crustal Pb isotope ratios and detrital monazite with high ²⁰⁸Pb/²⁰⁶Pb and low ²⁰⁷Pb/²⁰⁶Pb. This interpretation is supported by strong correlations between Pb isotope ratio and Th, U and light rare‐earth element concentrations in the sediments as well as by monazite compositional data. A likely source of the detrital monazite is the western portion of the Georgetown Inlier of mainly Proterozoic S‐type granitic rocks. A clear distinction between Pb isotope ratios in sediments deposited from the Norman and Bynoe Rivers in the southeast Gulf of Carpentaria and the persistence of catchment‐specific Pb isotope ratios 45 km offshore suggest that Pb isotope data are useful in tracing the provenance of terrigenous offshore sediments when the source rocks of catchments show sufficient chemical and/or mineralogical variation.