The behavior of arsenic and antimony at Pezinok mining site,southwestern part of the Slovak Republic

Arsenic and antimony contamination is found at the Pezinok mining site in the southwest of the Slovak Republic. Investigation of this site included sampling and analysis of water, mineralogical analyses, sequential extraction, in addition to flow and geochemical modeling. The highest dissolved arsenic concentrations correspond to mine tailings (up to 90,000 μg/L) and the arsenic is present predominately as As(V). The primary source of the arsenic is the dissolution of arsenopyrite. Concentration of antimony reaches 7,500 μg/L and its primary source is the dissolution of stibnite. Pore water in mine tailings is well-buffered by the dissolution of carbonates (pH values between 6.6 and 7.0) and arsenopyrite grains are surrounded by reaction rims composed of ferric iron minerals. Based on sequential extraction results, most solid phase arsenic is in the reducible fraction (i.e. ferric oxyhydroxides), sulfidic fraction, and residual fraction. Distribution of antimony in the solid phase is similar, but contents are lower. The principal attenuation mechanism for As(V) is adsorption to ferric oxide and hydroxides, but the adsorption seems to be limited by the competition with Sb(V) produced by the oxidation of stibnite for adsorption sites. Water in mine tailings is at equilibrium with gypsum and calcite, but far from equilibrium with any arsenic and antimony minerals. The concentrations of arsenic and antimony in the surrounding aquifer are much lower, with maximum values of 215 and 426 μg/L, respectively. Arsenic and antimony are transported by ground water flow towards the Blatina Creek, but their loading from ground water to the creek is much lower compared with the input from the mine adits. In the Blatina Creek, arsenic and antimony are attenuated by dilution and by adsorption on ferric iron minerals in stream sediments with resulting respective concentrations of 93 and 45 μg/L at the site boundary south of mine tailing ponds.     

Mineral/water interactions in tailings from a tungsten mine, Mount Pleasant, New Brunswick

The pore-water geochemistry and mineralogy of tailings derived from a granitic tungsten deposit were characterized by collecting pore-water samples at discrete depth intervals throughout the tailings for the analysis of major and minor element concentrations. Mineralogical samples from the oxidation zone were analyzed by X-ray diffraction, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDS), electron microprobe (EMP) combined with wavelength dispersive X-ray spectroscopy (WDS), and transmission electron microscopy (TEM). The oxidation of sulfide minerals in the near-surface tailings leads to a decrease in pore-water pH and elevated SO₄, As, and metal concentrations. The unusual mineralogy of this deposit, compared with that of commonly studied base-metal and gold deposits, results in several unique geochemical characteristics. The dissolution of fluorite releases F into the pore water; the F forms strong complexes with Al and enhances the dissolution of aluminosilicate minerals within the oxidation zone. As a result, high Al concentrations (up to 151.7 mg/L) are detected in the near-neutral pore water in the oxidation zone. The combined dissolution of aluminosilicates and carbonate minerals maintains the pH near 10 in the pore water at depth. Elevated concentrations of W (up to 7.1 mg/L) are detected in the pore water throughout the tailings, likely as a result of the dissolution of wolframite. Consistent with geochemical model calculations, results from SEM/EDS, EMP/WDS and TEM/EDS analyses indicate that secondary minerals, which occur as orange-brown coatings on grains of primary-minerals, are Fe oxyhydroxides. Examples of these secondary minerals display a fibrous habit at high resolution in the TEM. One of these minerals, which contains substantial amounts of Al, As, and Si as impurities, was identified by selected-area electron diffraction (SAED) analyses to be goethite. Another mineral contains relatively high amounts of Si, Pb, Bi, and As, and SAED analyses suggest that the mineral is two-line ferrihydrite.     

Characterisation of the Sarcheshmeh copper mine tailings,Kerman province,southeast of Iran

Mineral processing operation at the Sarcheshmeh porphyry copper mine has produced huge quantities of tailings materials containing sulphide minerals in particular pyrite. These tailings materials were geochemically and mineralogically characterised to assess pyrite and chalcopyrite oxidation, acid mine drainage generation, and trace element mobility to lead development of a proper remediation plan. Five vertical trenches up to 4.2 m deep were excavated from the tailings surface, and 70 solid samples were taken in 0.3 m intervals. The samples were first mineralogically analysed. Pyrite was the main sulphide mineral found in the tailings. The gangue minerals include quartz ± muscovite–illite ± chlorite ± albite ± orthoclase ± halite. The samples were geochemically analysed for total concentrations of 62 elements, paste pH, SO₄ ^2?, CO₃ ^2?, and HCO₃ ^?. The maximum concentrations of SO₄ ^2? (1,300, 1,170, 1,852, 1,960 and 837 mg/L) were observed at a depth of 0.9 m in profiles A, B, C, D and E, respectively. The tailings have a high acid-producing potential and low acid-neutralising potential (pyrite 4–6 wt %, calcite 1 wt %). Fe₂(SO₄)₃, CuSO₄, MgSO₄ and MnSO₄ were the dominant secondary sulphate minerals in the tailings. The lowest pH values (2.9, 3 and 3) were measured at a depth of 0.3 m in the profiles A, B and C, 3.9 at a depth of 0.6 m in the profile D and 3 at a depth of 0.9 m in the profile E. The upper portions of the profiles C (1.8 m) and D (2.1 m) were moderately oxidised, while oxidation in the profiles A, B and E did not extend more than 1.2, 1.2 and 1.5 m beneath the tailings surface. Zn, Pb, Rb, U, Hf, Nd, Zr and Ga show almost a constant trend with depth. Cd, Sr, Th, La and Ce increased with increasing depth of the tailings materials while, Co, V, Ti, Cr, Cu, As, Mn, Ag, Mo and Ni exhibit initially a decreasing trend from tailings surface to the depths that vary between 0.9 and 1.2. They then remained constant with the depth. The results show pyrite and chalcopyrite oxidation at surface layers of the tailings and subsequent leaching of the oxidation products and trace elements by infiltrated atmospheric precipitation.     

Geochemical,mineralogical and microbiological characterization of a sulphide-bearing carbonate-rich gold-mine tailings impoundment,Joutel, Québec

The results of an integrated geochemical and mineralogical study conducted at the Agnico-Eagle gold-mine tailings impoundment, Joutel, Québec, are correlated with bacterial populations determined from an enumeration of 3 groups of Thiobacilli. The tailings were determined to contain approximately 5 wt.% sulphide–S, predominantly as pyrite, and up to 30 wt.% carbonate minerals, chiefly as dolomite–ankerite and siderite. The objective of the study was to evaluate the potential for the development of acidic drainage and dissolved-metal migration in carbonate-rich tailings impoundments, and to compare the results of the geochemical and microbiological characterization of the tailings. Sulphide-oxidation reactions have proceeded to a depth of 20–100 cm below the tailings surface. Pyrrhotite consistently shows more alteration than pyrite and arsenopyrite. Pyrrhotite is altered mainly through the replacement by goethite. The most abundant Thiobacilli are neutrophilic bacteria of the Thiobacillus thioparus type. The maximum most probable number values for these bacteria occur 20–40 cm below the tailings surface, a depth that coincides with the disappearance of oxide coatings. This observation, coupled with the sharp decline in gas-phase O₂ concentration, suggests that rapid bacterially-mediated S–oxidation is occurring at this depth. The pore-water pH throughout the tailings varies between 6.5 and 8.5; no low-pH waters were observed in the impoundment. These neutral pH conditions are attributed to the effect of acid-consuming carbonate-mineral dissolution reactions, which are also indicated by increased concentrations of Mg and Ca and alkalinity in the shallow zone of the tailings. As a result of these acid-neutralization reactions, dissolved metal concentrations are low.     

Mineralogical and geochemical characterization of the Old Tailings Dam,Australia: Evaluating the effectiveness of a water cover for long-term AMD control

Establishing a shallow water cover over tailings deposited in a designated storage facility is one option to limit oxygen diffusion and retard oxidation of sulfides which have the potential to form acid mine drainage (AMD). The Old Tailings Dam (OTD) located at the Savage River mine, western Tasmania contains 38 million tonnes of pyritic tailings deposited from 1967 to 1982, and is actively generating AMD. The OTD was constructed on a natural gradient, resulting in sub-aerial exposure of the southern area, with the northern area under a natural water cover. This physical contrast allowed for the examination of tailings mineralogy and geochemistry as a function of water cover depth across the OTD. Tailings samples (n = 144, depth: ≤ 1.5 m) were collected and subjected to a range of geochemical and mineralogical evaluations. Tailings from the southern and northern extents of the OTD showed similar AMD potential based on geochemical (NAG pH range: 2.1 to 4.2) and bulk mineralogical parameters, particularly at depth. However, sulfide alteration index (SAI) assessments highlighted the microscale contrast in oxidation. In the sub-aerial zone pyrite grains are moderately oxidized to a depth of 0.3 m (maximum SAI of 6/10), under both gravel fill and oxidized covers, with secondary minerals (e.g., ferrihydrite and goethite) developed along rims and fractures. Beneath this, mildly oxidized pyrite is seen in fresh tailings (SAI = 2.9/10 to 5.8/10). In the sub-aqueous zone, the degree of pyrite oxidation demonstrates a direct relationship with cover depth, with unoxidized, potentially reactive tailings identified from 2.5 m, directly beneath an organic-rich sediment layer (SAI = 0 to 1/10). These findings are broadly similar to other tailings storage facilities e.g., Fox Lake, Sherritt-Gordon ZnCu mine, Canada and Stekenjokk mine, Sweden where water covers up to 2 m have successfully reduced AMD. Whilst geotechnical properties of the OTD restrict the extension of the water cover, pyrite is enriched in cobalt (up to 2.6 wt%) indicating reprocessing of tailings as an alternative management option. Through adoption of an integrated mineralogical and geochemical characterization approach for tailings assessment robust management strategies after mine closure can be developed.     

Environmental geochemistry of the Guanajuato Mining District, Mexico

The Guanajuato Mining District, once one of the major silver producers in the world, has been exploited for silver and gold from low-sulfidation quartz- and calcite-rich epithermal veins since 1548. Currently, there are some 150 million tonnes of low-grade ore piles and mine-waste material (mostly tailings) piles, covering a surface area of 15 to 20 km² scattered in a 100-km² region around the city of Guanajuato. Most of the historic tailings piles were not deposited as formal tailings impoundments. They were deposited as simple valley-filling piles without concern for environmental issues. Most of those historical tailings piles are without any vegetation cover and undergo strong eolian and hydrologic erosion, besides the natural leaching during the rainy season (which can bring strong thunderstorms and flash flows). There is public concern about possible contamination of the local aquifer with heavy metals (Fe, Mn, Zn, As and Se) derived from the mining activities.Experimental and field data from this research provide strong geochemical evidence that most of the mine-waste materials derived from the exploitation of the epithermal veins of the region have very low potential for generation of acid mine drainage due to the high carbonate/sulfide ratio (12:1), and very low potential for leaching of heavy metals into the groundwater system. Furthermore, geochemical evidence (experimental and modeled) indicates that natural processes, like metal adsorption onto Fe-oxy-hydroxides surfaces, control the mobility of dissolved metals. Stable isotope data from surface water, groundwater wells (150-m depth) and mine-water (300- to 500-m depth) define an evaporation line (δD=5.93 δ¹⁸O=13.04), indicating some deep infiltration through a highly anisotropic aquifer with both evaporated water (from the surface reservoirs) and meteoric water (not evaporated). Zinc concentrations in groundwater (0.03 to 0.5 ppm) of the alluvial aquifer, some 15 km from the mineralized zone, are generally higher than Zn concentrations in experimental tailings leachates that average less than 0.1 ppm. Groundwater travel time from the mineralized area to the alluvial valley is calculated to range from 50 to several hundred years. Thus, although there has been enough time for Zn sourced from the tailings to reach the valley, Zn concentrations in valley groundwater could be due to natural dissolution processes in the deep portions of the epithermal veins.     

Geochemistry of arsenic in uranium mine mill tailings,Saskatchewan, Canada

The Rabbit Lake U mine in-pit tailings management facility (TMF) (425 m long×300 m wide×91 m deep) is located in northern Saskatchewan, Canada. The objectives of this study were to quantify the distribution of As phases in the tailings and evaluate the present-day geochemical controls on dissolved As. These objectives were met by analyzing pore fluid samples collected from the tailings body for dissolved constituents, measuring Eh, pH, and temperature of tailings core and pore fluid samples, conducting sequential extractions on solid samples, conducting geochemical modeling of pore fluid chemistry using available thermodynamic data, and by reviewing historical chemical mill process records. Dissolved As concentrations in 5 monitoring wells installed within the tailings body ranged from 9.6 to 71 mg/l. Pore fluid in the wells had a pH between 9.3 and 10.3 and Eh between +58 and +213 mV. Sequential extraction analyses of tailings samples showed that the composition of the solid phase As changed at a depth of 34 m. The As above 34 m was primarily associated with amorphous Fe and metal hydroxides while the As below 34 m was associated with Ca, likely as amorphous poorly ordered calcium arsenate precipitates. The change in the dominant As solid phases at this depth was attributed to the differences in the molar ratio of Fe to As in the mill tailings. Below 34 m it was <2 whereas above 34 m it was >4. The high Ca/As ratio during tailings neutralization would likely precipitate Ca₄(OH)₂(AsO₄)₂:4H₂O type Ca arsenate minerals. Geochemical modeling suggested that if the pore fluids were brought to equilibrium with this Ca-arsenate, the long-term dissolved As concentrations would range between 13 and 126 mg/l.     

Pyrite Oxidation in Leaching Process of Radionuclides and Heavy Metals from Uranium Mill Tailings

Pyrite is a sensitive mineral in the geological environment,and its oxidation produces an important geochemical and environmental effect on the control of the redox and pH conditions.Column experiment results were used for modeling the geochemical processes in uranium mill tailings under leac-hing conditions.Oxidation of pyrite dominates the control of the tailings leaching process.The experi-mental and modeling results show that the leachate chemistry changes substantially with the decrease in pyrite consumption.In the initial stage of the leaching experiment,the pyrite is consumed several hun-dred times grater than that in the later stages,for much more oxygen is present in the tailings in the ini-tial stage.As the experiment continues,the tailings is gradually saturated with water and the oxygen concentration greatly decreases and so does pyrite consumption.The experimental and modeling results are useful for the design of mill tailing decommissioning:oxidation process and transport of radioactive nuclides and heavy metals can be constrained by controlling the oxygen concentration of tailings and the infiltration of meteoric water.     

Acid neutralization mechanisms and metal release in mine tailings: a laboratory column experiment

Mining and milling of base metal ore deposits can result in the release of metals to the environment. When sulfide minerals contained in mine tailings are exposed to oxygen and water, they oxidize and dissolve. Two principal antagonistic geochemical processes affect the migration of dissolved metals in tailings impoundments: sulfide oxidation and acid neutralization. This study focuses on acid neutralization reactions occurring in the saturated zone of tailings impoundments. To simulate conditions prevailing in many tailings impoundments, 0.1 mol/L sulfuric acid was passed continuously through columns containing fresh, unoxidized tailings, collected at Kidd Creek metallurgical site. The results of this column experiment represent a detailed temporal observation of pH, Eh, and metal concentrations. The results are consistent with previous field observations, which suggest that a series of mineral dissolution-precipitation reactions control pH and metal mobility. Typically, the series consists of carbonate minerals, Al and Fe(III) hydroxides, and aluminosilicates. In the case of Kidd Creek tailings, the dissolution series consists of ankerite-dolomite, siderite, gibbsite, and aluminosilicates. In the column experiment, three distinct pH plateaus were observed: 5.7, 4.0, and 1.3. The releases of trace elements such as Cd, Co, Cr, Cu, Li, Ni, Pb, V, and Zn were observed to be related to the pH buffering zones. High concentrations of Zn, Ni, and Co were observed at the first pH plateau (pH 5.7), whereas Cd, Cr, Pb, As, V, and Al were released as the pH of the pore water decreased to 4.0 or less.     

Oxygen penetration and subsequent reactions in flooded sulphidic mine tailings: a study at Stekenjokk,northern Sweden

A study of O₂ penetration and pore water geochemistry of the flooded tailings at Stekenjokk has been performed. The results show that there is a diffusion of elements from the tailings pore water to the overlying water. The presence of elements such as Ca, Mg, S, Si, Ba and Sr are likely the result of diffusion of older process water trapped in the tailings. Oxygen concentrations in the tailings measured with microelectrodes show that there is O₂ available down to 16 to 17 mm depth in the tailings. Pore water analyses show that there are subsurface maxima for the elements Cu, Zn, Ni, Co and Cd at depths of 0.25 to 2.75 cm. The highest concentrations of almost all elements were found where previously oxidised material was deposited before the flooding. Lower pH is measured in the uppermost part of the tailings compared with the pond water and the tailings pore water at depth. Oxidation of sulphides in the uppermost part of the tailings is probably occurring. A decrease in oxidation rate can be expected in the future due to deposition of organic material at the tailings surface. Flooding seems to be an efficient remediation method at Stekenjokk.     

Mine drainage from the weathering of sulfide minerals and magnetite

Pyrite and pyrrhotite are the principal minerals that generate acid drainage in mine wastes. Low-pH conditions derived from Fe-sulfide oxidation result in the mobilization of contaminant metals (such as Zn, Cd, Ni and Cr) and metalloids (such as As) which are of environmental concern. This paper uses data from detailed mineralogical and geochemical studies conducted at two Canadian tailings impoundments to examine the mineralogical changes that pyrite, pyrrhotite, sphalerite and magnetite undergo during and after sulfide oxidation, and the subsequent release and attenuation of associated trace elements. The stability of sphalerite in tailings impoundments generally is greater than that of pyrrhotite, but less than pyrite. Dissolved Ni and Co derived from Fe sulfides, and to a lesser extent, dissolved Zn and Cd from sphalerite, are commonly attenuated by early-formed Fe oxyhydroxides. As oxidation progresses, a recycling occurs due to continued leaching from low-pH pore waters and because the crystallinity of Fe oxyhydroxides gradually increases which decreases their sorptive capacity. Unlike many other elements, such as Cu, Pb and Cr, which form secondary minerals or remain incorporated into mature Fe oxyhydroxides, Zn and Ni become mobile. Magnetite, which is a potential source of Cr, is relatively stable except under extremely low-pH conditions. A conceptual model for the sequence of events that typically occurs in an oxidizing tailings impoundment is developed outlining the progressive oxidation of a unit of mine waste containing a mixed assemblage of pyrrhotite and pyrite.     

几个矿床技术经济评价问题探讨

矿床技术经济评价在地质勘查工作中占有重要地位。目前编写地质勘查报告都必须包括技术经济评价章节。但我国矿床技术经济评价的理论和方法还存在一些问题，某些评价方法和基本概念还不够统一。通过对投资回收期、净现值、总现值、销售成本、经营成本等参数的研究认为，矿床技术经济评价要进一步规范化。     

基于Hyperion数据的江西德兴矿区粘土矿物信息提取及其找矿意义

江西德兴矿区为我国重要的矿产资源基地, 目前面临资源枯竭的困境, 寻找替代的新矿产迫在眉睫.根据研究区野外土壤实测样品分析, 利用连续统去除的方法提取土壤实测光谱的特征吸收位置, 从而建立粘土矿物含量为因变量的预测方程.检验得知, 高岭石相关系数R为0.811, 拟合系数R2达到0.658, F值为5.275, Sig值为0.047 7, 其小于0.05;绿泥石相关系数R为0.893, 拟合系数R2达到0.797, F值为1.602, Sig值为0.016 6, 其小于0.05;伊利石相关系数R为0.783, 拟合系数R2达到0.619, F值为5.57, 对应的Sig值是0.075 4, 其大于0.05, 说明自变量与因变量之间具有高度相关性, 反演精度较好.从反演结果可知, 研究区的高岭石整体含量较高, 整体上粘土矿物高岭石、绿泥石和伊利石在1号坝、2号坝、4号坝和铜矿区含量较低.由于粘土矿物不断地经过地球化学变化、累积, 产生黄铁矿、黄铜矿及赤铁矿, 所以挑选粘土矿物富集并且地质构造活跃的区域为铁矿石及铜矿石预测区.结合研究区地质解译图与粘土矿物反演结果, 在采矿场与IV号尾矿坝向NE方向沿线上圈定两个遥感找矿有利区.      

Prediction of the long-term performance of abandoned lead zinc mine tailings in a Welsh catchment

In this study we investigated the sulphidic mine tailings from Frongoch and Grogwynion, two abandoned lead zinc mines in mid-Wales, UK. Despite falling within the same ore field the mine waste characterisation has identified differences in the tailings from the two sites. Bulk concentrations range from 10 to 52 g kg^− 1 for Pb, 1.1 to 2.9 g kg^− 1 for Zn in Grogwynion and from 1.0 to 130 g kg^− 1 for Pb, 11 to 110 g kg^− 1 for Zn in Frongoch. An experimental (European standard leaching tests TS 14429 and TS 14405) and geochemical modelling approach was used to study the leaching composition as a function of pH and liquid/solid ratio. There was little correlation between the tailings bulk metal concentrations and the leachate composition, but variations in Pb and Zn concentrations were found to be consistent with control of dissolved Pb and Zn by secondary minerals and the mechanisms of dissolution/precipitation/sorption involving them. Specifically, the Grogwynion mine tailings with near-neutral pH have predominantly lead and zinc carbonates controlling Pb and Zn solubility in the leachates, whereas the Pb and Zn concentrations in Frongoch leachates are best modelled with a surface complexation model for metal sorption to oxyhydroxides. The different speciation results in a greater sensitivity of Grogwynion tailings to acidification with a potential release of Pb in solution up to 10 times higher than in Frongoch, despite similar bulk Pb concentrations. At acid pH, Zn is similarly dissolved to a greater extent in Grogwynion than in Frongoch tailings. There was no evidence of sulphide oxidation during the batch and column leaching tests and the suitability of using these European leaching standards for the characterisation of sulphidic mine waste materials for waste management purposes has been considered.     

黄铁矿风化过程中元素的活性及对环境的影响

在对安徽铜陵鸡冠山硫铁矿尾矿中黄铁矿风化产物组构特征研究的基础上,划分出代表不同风化程度的4种矿石组构型,并进而对不同组构型中硫和金属元素的含量、宫集系数、流失系数变化进行了研究。研究表明在风化过程中,As、Sb、Cu、Zn明显富集,其中As、Cu、Zn对环境的潜在危害较Sb大;Co、Ni、Bi明显流失或严重流失,对环境已经形成污染,其中Bi的污染程度较高。     

广西贵港六梅金矿地球化学研究

广西贵港六梅金矿床位于贵港市龙山矿田福六岭金矿区,为微细浸染型金矿床。矿床中主要矿石矿物为毒砂和黄铁矿。通过载金矿物毒砂和黄铁矿含金性、金浸出提取、晶体结构测定等方法,查明矿床的金存在形式。浸出率试验中平衡计算表明,载金矿物毒砂中的晶格金形式约占25%,超显微包体形式金约为75%。矿床流体包裹体测温和稀土元素地球化学研究表明,六梅金矿床为中-低温热液型矿床,成矿物质来源与地层有关。     

A comparative mineralogical and geochemical study of sulfide mine tailings at two sites in New Mexico, USA

A comparative study of sulfide mine tailings from two sites near Silver City in southwest New Mexico has shown the need for environmental monitoring in a geological context. The Cyprus-Piños Altos and Cleveland deposits consist of Cu and Zn skarn mineralization in the Piños Altos Mountains of New Mexico. Primary ore minerals in both deposits include chalcopyrite, sphalerite, and galena. The Cyprus-Piños Altos Mine ceased operation in 1995 and the Cleveland Mill closed in 1950. The deposits have similar mineralogical characteristics; however, the tailings are different in terms of age, degree of oxidation and method of disposal. The Cyprus-Piños Altos tailings (CPAT) are stored in a lined, bermed impoundment. They are dominantly water-saturated and exhibit no secondary-phase formation. The grains are not cemented and show no evidence of primary-mineral dissolution. The geochemical data show a predominantly primary signature. The tailings pond water is neutral to slightly alkaline (pH?from 7 to 8.3), partly as a result of processing methods. The Cleveland mill tailings (CMT) were deposited in a valley at the headwaters of an ephemeral stream. They are highly oxidized and differentially cemented. They have undergone numerous wet/dry cycles resulting in extensive oxidation. Secondary minerals predominate, and consist mainly of jarosite, goethite, hematite, and Fe-oxyhydroxides and -oxyhydroxysulfates. The pH of the stream draining the CMT is as high as 2.15. Maximum metal contents in the stream immediately downstream from the tailings are 5305?ppm Zn, 454?ppm Cu, 1.16?ppm Pb, 17.5?ppm Cd, 1.4?ppm As, and 0.01?ppm Hg.     

Geological and anthropogenic influences on sediment metal composition in the upper Paracatu River Basin, Brazil

This work reports a geochemical study of sediments from the upper Paracatu River Basin. The objective is to define the influences of Au, Zn, and Pb mineral deposits and mining activities on the sediment metal sources, distribution, and accretion. The samples were analyzed using ICP/OES, AAS, and XRD techniques and were treated with principal components analysis and the geo-accumulation index. The main geochemical processes that control the sediment composition are pyrite oxidation, muscovite weathering, carbonate dissolution, and the erosion of oxisols enriched with Zn and Pb. The upper Rico Stream has high Al, Fe, Cu, Cr, Co, and Mn concentrations due erosion of oxisols and pyrite oxidation and muscovite alteration present in the parental rock. The artisanal alluvial gold mining increased the primary rock-minerals?? weathering and Hg sediment concentration. The lower Escuro River and Santa Catarina Stream are enriched with Zn and Pb due the erosion of metal-rich soils formed over galena, sphalerite, calamine, and willemite mineral deposits located upstream. Elements such as Ca, Mg, and Ba have low concentrations throughout the sampled area due the high solubility of these metals-bearing minerals. The dispersion of metals is limited by the basin geomorphology and their affinity to silt-clayey minerals and Fe and Mn oxides and hydroxides in circumneutral pH waters.     

Characterization of Kolar gold field mine tailings for cyanide and acid drainage

The gold mining process at Kolar gold field (KGF) mines has generated about 32 million tons of tailings. Gold was extracted from the mined ores using cyanidation technique that involved dissolution of gold in the ore by water soluble alkali metal cyanides (example, sodium cyanide or potassium cyanide). Of the several dumps that received the mine tailings only the Kennedy’s Line dump was active prior to closure of the KGF mines in the year 2000. The Kennedy’s Line dump received sulfide bearing tailings in slurry form that comprised of spent ore and process water bearing soluble alkali metal cyanide. Depending on the pH of the tailing slurry, the free cyanides may exist as aqueous hydrogen cyanide that can escape to the atmosphere as hydrogen cyanide gas or occur as soluble cyanide (CN⁻) ions that can be leached by infiltrating water to the sub-surface environment. Additionally, the presence of pyrite minerals in the Kennedy’s Line dump makes them susceptible to acid drainage. This study examines the potential of gold tailings of Kennedy’s Line dump to release cyanide ions (CN⁻) and acid drainage to the sub-surface environment by performing physico-chemical and leaching tests with tailing samples collected from various depths of the dump, sub-surface soil samples beneath the dump and groundwater samples from vicinity of Kennedy’s Line dump. The chemical mechanisms responsible for the ambient cyanide and pH levels of the tailing dump, sub-surface soil samples and groundwater are also inferred from the laboratory results.     

Mineralogical controls on element dispersion in regolith over two mineralised shear zones near the Peak, Cobar, New South Wales

Effective exploration for polymetallic ore deposits in the Cobar region is hampered by incomplete knowledge of the mineralogical controls on element dispersion in the different regolith-landform settings throughout the area. A detailed mineralogical and geochemical study of regolith profiles over two major mineralised shear zones in a strongly weathered but dominantly erosional setting has delineated the important host minerals for a range of base metal cations. Iron oxides/oxyhydroxides, particularly goethite and to a much lesser extent hematite, are major hosts for Pb, Cu, and Zn as substituted/adsorbed cations and as constituents of associated or intergrown minerals, probably including members of the jarosite–alunite group. Correlations between elements and major regolith minerals suggest that goethite is also a host phase for As, Bi and Sb. Minor manganese minerals, including lithiophorite and cryptomelane group minerals, also host base metals in appreciable amounts. No clear association was found between gold and any particular secondary mineral. It is likely that gold is present largely as elemental gold particles associated with a range of minerals.Sampling strategies for geochemical exploration in variably leached and stripped regolith in the Cobar area should take into account the relative abundance of goethite and manganese oxides/oxyhydroxides within the profiles and overlying lag. Goethite would appear to be the preferred sampling medium for base metals. Highly ferruginous lag has a high proportion of hematite with variable maghemite and very low manganese oxide contents. Most of the base metal content in this surface material is strongly bound to the crystalline oxides/oxyhydroxides. More work is required to understand the effects of surface transformation of goethite to hematite and maghemite on the mobility and distribution of base metal cations in soil and ferruginous lags.