Development of a high modulus paste fill using fine gold mill tailings

Summary In the mining industry today there is some caution about using fine tailings as a backfill material. Traditionally, hydraulic backfill has only used the coarse fraction of tailings, excluding the fines by a classification process. With the development of paste fill, the percentage of fine tailings being sent underground has increased, but still remains low due to the high percentages of sand and gravel which usually make up these fills. Sand and gravel have been added to paste fills to aid pumpability and to increase fill strength and stiffness. This leaves the remainder of fine tailings destined for surface disposal. The main focus of this paper is to evaluate what effect the addition of fine gold mill tailings in the form of agglomerated tailings pellets has on the strength and stiffness characteristics of a total tailings paste fill. The purpose is to create a high modulus fill which is made up entirely of fine tailings. A constant slump design of 20 cm (8 in) was used for each mix. Various binder dosages, curing periods and combinations of pellet to tailings ratio were studied. Raw fill slump and density, and cured fill compressive strength and modulus of elasticity were also examined. Results from the above study indicate that agglomerated tailings paste fill (ATPF) has superior strength and stiffness characteristics. Compressive strengths were enhanced while the modulus of elasticity values was tripled when compared to total tailings paste fills of the same binder content and consistency. ATPF minimizes the surface disposal of tailings and maximizes the utilization of fine tailings underground as a useful backfill material.     

Coupled Modeling of Temperature Distribution and Evolution in Cemented Tailings Backfill Structures that Contain Mineral Admixtures

Cemented paste backfill (CPB, a mixture of tailings, water and binder) is widely utilized to fill underground mine voids. To achieve a good, economical performance, one approach is to proportionally use mineral admixtures such as fly ash and slag as partial substitutes for Portland cement. Binder hydration is one of the most significant factors that can generate heat within hydrating CPB structures, which in turn, influences the mechanical and hydraulic properties of CPB, as well as the pore structure within CPB. However, the temperature evolution due to the hydration of Portland cement that contains fly ash or slag is different from that of hydration with solely Portland cement. Hence, in consideration of the heat generated by both binder hydration and transferred between CPB and its surrounding media, a numerical model is developed to predict and determine the temperature development within CPB that contains mineral admixtures. After that, data from field and laboratory studies are employed to validate the developed model. The validation results demonstrate a good consistency between the model and the field and laboratory studies. Consequently, the proposed model is applied to simulate and determine the temperature evolution with time via mineral admixtures, binder content, initial rock and CPB temperatures, stope geometry, backfilling rate, curing time and backfilling strategy. The obtained results will contribute to better designs and preparation of CPB mixtures, as well as predict the temperature distribution within CPB structures.     

Long-term coupled behaviour of cemented paste backfill in load cell experiments

A pressure cell apparatus has been developed in this research work to study the long-term hydro-mechanical behaviour of cemented paste backfill (CPB) cured under applied stress. The samples are cured for 7, 28, 90 and 150 days and the evolution of their mechanical, hydraulic, physical and microstructural properties is studied. Also, the suction, temperature and electrical conductivity are monitored for a period of 150 days of curing. The testing and monitoring programmes are conducted in undrained conditions, with and without pressure application. The obtained results show that the curing stress affects the hydro-mechanical behaviour of CPB for up to 28 days. Within this curing period, the CPB exhibits enhanced hydro-mechanical performance. However, application of sustained excessive curing stress onto the CPB samples induces the propagation of microcracks in the backfill structure, thus causing lower mechanical strength and higher fluid permeability at the more advanced ages. Furthermore, the mineralogical and chemical compositions of the tailings (e.g., sulfidic tailings) can significantly alter the mechanical strength properties (uniaxial compressive strength and elastic modulus) and the permeability of the CPB. The evolution of coupled factors and characteristics of the CPB at an early age control and influence its long-term behaviour and performance.     

Modeling the heat development in hydrating CPB structures

Cemented paste backfill (CPB) is a mixture of dewatered tailings, hydraulic binders and water. In addition to contributing to the stability of mine workplaces, CPB greatly benefits the environment by minimizing surface tailings disposal. Hence, it has become one of the most commonly used ways in mine backfilling around the world. Temperature can significantly affect the mechanical properties of cemented backfill. A source of heat in CPB is produced by binder hydration. Hence, a FLAC based numerical model is developed to predict and analyse the heat developed by hydrating CPB structures. To validate the model, results of the developed model are compared with three case studies (mathematical, laboratory, and field investigations). The validation results show a good agreement between the developed model and these cases. The effects of stope geometry, thermal properties of both rock and CPB, filling rate, binder content and initial boundary conditions are also investigated.     

Compression Behavior of Mine Tailings Amended with Cementitious Binders

The objective of this study was to evaluate the effect of fly ash amendment on the compression behavior of mine tailings. Natural and synthetic (i.e., laboratory prepared) mine tailings were used to assess the effects of tailings composition and tailings solids content on compressibility. Three types of off-specification fly ashes and Type I–II Portland cement were used as cementitious binders. Tailings-fly ash mixtures were prepared at solids content of 60–75% (water content = 33–67%), water-to-binder ratios of 2.5 and 5, and were cured for 0.1 days (2 h), 7, and 28 days. Bi-linear compression curves on semi-log plots were observed in most of the binder-amended tailings specimens. The break in slope on the compression curve was identified as the breaking stress, whereupon cementitious bonds were broken. The breaking stress increased with an increase in fly ash content, which was attributed to a lower water-to-binder ratio and void volume-to-binder volume ratio that produced more effective particle bonding. Breaking stress also increased with an increase in CaO content and CaO-to-SiO₂ ratio of fly ash, which resulted in more effective bonding between particles. The effect of curing time on the breaking stress of fly ash amended specimens was characterized by (1) an increase in breaking stress via increase in curing time and cementitious bond formation or (2) a constant breaking stress with curing time due to competing mechanisms during loading. Specimens cured under a vertical stress showed an increase in breakings stress with applied load water removal prior to cementitious bond formation that reduced the water-to-binder ratio and led to more effective cementation.     

Design and Application of Underground Mine Paste Backfill Technology

This paper reviews the design and application of paste backfill in underground hard rock mines used as ground support for pillars and walls, to help prevent caving and roof falls, and to enhance pillar recovery for improved productivity. Arching after stope filling reduces vertical stress and increases horizontal stress distribution within the fill mass. It is therefore important to determine horizontal stress on stope sidewalls using various predictive models in the design of paste backfill. Required uniaxial compressive strength (UCS) for paste backfill depends on the intended function, such as vertical roof support, development opening within the backfill, pillar recovery, ground or pillar support, and working platform. UCS design models for these functions are given. Laboratory and backfill plant scale designs for paste backfill mix design and optimization are presented, with emphasis on initial tailings density control to prevent under-proportioning of binder content. Once prepared, paste backfill is transported (or pumped) and placed underground by pipeline reticulation. The governing elements of paste backfill transport are rheological factors such as shear yield stress, viscosity, and slump height (consistency). Different models (analytical, semi-empirical, and empirical) are given to predict the rheological factors of paste backfill (shear yield stress and viscosity). Following backfill placement underground, self-weight consolidation settlement, internal pressure build-up, the arching effect, shrinkage, stope volume, and wall convergence against backfill affect mechanical integrity. An erratum to this article can be found at     

Flow behaviour of tailings paste for surface disposal

Surface disposition of mine tailings in paste form is a new disposal technique, and to achieve a desired depositional geometry, it is necessary to characterize the paste's flow properties. This study investigates how water content affects the flow behaviour and depositional geometry of tailings and kaolinite pastes, which are shear-thinning, high solids content, mineral pastes. A stress-controlled rheometer and a strain-controlled viscometer with vane fixtures were used to characterize the yield behaviour of the pastes, and three types of yield stress were determined. A flume apparatus was used to simulate paste deposition under laboratory conditions. The depositional angle, determined from the flume tests, and the yield stresses, determined from the rheometers, decreased as the water content increased. For each type of yield stress, a linear relationship was found between the depositional angle and the Sofra–Boger dimensionless group (τ_y′Fr/Re), with the linear coefficient depending on paste type.     

Relevance of SEM to Long-Term Mechanical Properties of Cemented Paste Backfill

This paper is an attempt to relate the microstructure to long-term mechanical properties of the cemented paste backfill produced from a hard rock mine tailing from North Queensland in Australia bound with flyash-based geopolymer (geopolymer), flyash-blended cement (FBC), and general purpose cement (GPC). A relatively high slump (260 mm) paste backfill mix with 74 wt% solids has been used to prepare cylindrical paste backfill samples with a diameter of 50 mm and a height of 100 mm. The uniaxial compressive strength tests were conducted on all samples after curing for 112 days to obtain their strength, failure strain and Young’s modulus. Fractured samples were examined under scanning electron microscope to understand the failure mechanisms at the microstructural scale. The results show that binders significantly affected the mechanical properties of paste backfills (ANOVA, p < 0.05). The paste backfill bound with geopolymer gave the lowest strength and Young’s modulus, while the paste backfills bounded with FBC and GPC showed comparable higher strength and modulus values. This was attributed to the relatively well-packed paste backfills with less cracks and smaller pore sizes in these paste backfills bound with FBC and GPC binders. In particular, needle-shaped particles, which were originally identified in GPC, highly influenced the mechanical property of paste backfills. These results indicate that fly ash can be used to partially replace the cement as a binder for paste backfills to achieve economic and environmental benefits.     

Temperature dependence of the reactivity of cemented paste backfill

The environmental performance of cemented paste backfill (CPB; a mixture of tailings, water and binder), which contains sulphide mineral-bearing tailings, is strongly influenced by its reactivity. However, our understanding of the reactivity of CPB under various thermal loading conditions as well as its evolution with time is limited. Hence, a laboratory investigation is conducted to study the effects of curing and ambient (atmospheric) temperatures on the reactivity of CPB. Oxygen consumption (OC) tests are conducted on CPB specimens cured at different temperatures to study their reactivity. Furthermore, microstructural analyses (e.g., x-ray diffraction (XRD), mercury intrusion porosimetry, and thermogravimetry/derivative thermogravimetry) are performed to assess the microstructural characteristics of the tested CPBs. The results show that the reactivity of CPB is temperature-dependent. As the curing temperature increases, the reactivity generally decreases. The reactivity is also affected by the ambient temperature. The reactivity increases as the atmospheric temperature increases. However, the extent of the effect of the temperature depends on the curing time and is generally more pronounced at the early ages. Furthermore, the presence of sulphate in the pore water of CPB can significantly affect the reactivity of CPB cured at high temperatures (50 °C). The findings of this study will therefore help to better assess and predict the environmental behavior of CPB under various field thermal conditions.     

超细水泥对固化软土早期抗压强度影响的试验研究

为研究超细水泥含量对水泥固化软土的早期力学性能的影响,本文通过在普通水泥中加入不同掺量的超细水泥组成复合水泥固化剂用以固化软土。具体研究不同超细水泥掺量、不同初始含水率、及不同养护围压条件下,复合水泥固化剂对固化软土早期抗压强度及刚度的影响。采用自制K₀围压养护装置(施加不同轴向压力的方式)、无侧限抗压强度仪(UCS)、X射线衍射仪(XRD)、电镜扫描仪(SEM)和低场核磁共振孔隙测试仪(NMR)等试验手段获取复合水泥固化软土不同龄期的抗压强度、刚度及微观结构的变化规律,并揭示其固化机理。研究结果表明:(1)相同轴向压力作用下,随着超细水泥掺量的增加,固化软土的抗压强度和弹性模量均有提高,其中复合固化剂中的活性颗粒发生水化反应生成大量胶凝产物用以黏聚土颗粒和填充孔隙,惰性颗粒用于填充土颗粒间的孔隙;(2)随着含水率的提高,固化软土中孔相对发育,从而使固化软土结构致密性减弱,抗压强度降低;(3)在K₀围压养护7d时,固化软土的抗压强度和弹性模量随着轴向压力的提高而增加,表明养护围压对软土颗粒的压缩作用能提高固化软土的密实性,同时围压对固化软土产生有效应力,与水化产物共同促进固化软土形成密实的土骨架,进而使其在7d内具有较高的抗压强度。基于试验结果,建立轴向压力、含水率和超细水泥掺量等多因素的固化软土强度预测公式,并提出复合水泥固化软土结构模型,为工程实践提供理论基础。     

Compressibility of cement-stabilized zinc-contaminated high plasticity clay

The presence of heavy metals at high concentrations (percent levels) in soils has been a growing concern to human health and the environment, and the cement stabilization is considered to be an effective and practical approach to remediate such soils. The compressibility of such stabilized soils is an important consideration for redevelopment of the remediated sites for building and/or roadway construction. This paper investigates the effects of high levels of zinc concentration on the compressibility of natural clay stabilized by cement additive. Several series of laboratory compression (oedometer) tests were conducted on the soil specimens prepared with the zinc concentrations of 0, 0.1, 0.2, 0.5, 1, and 2 %, cement contents of 12 and 15 %, and curing time of 28 days. The results show that the yield stress and compression index at the post-yield state decrease with an increase in the zinc concentration regardless of the cement content. The observed results are attributed to the decrease in the cement hydration of the soil. Overall, this study demonstrates that the cementation structure of the soils is weakened, and the compressibility increases with the elevated zinc concentration, particularly at relatively high levels of zinc concentration.     

Effects of alkaline-activated fly ash and Portland cement on soft soil stabilisation

This paper studies the effects of sodium-based alkaline activators and class F fly ash on soil stabilisation. Using the unconfined compressive strength test (UCS), the effectiveness of this binder is compared with that of a common cement-based binder. Influence of the activator/ash ratio, sodium oxide/ash ratio and sodium hydroxide concentration was also analysed. Sodium hydroxide concentrations of 10, 12.5 and 15 molal were used for the alkaline-activated specimens (AA), with activator/ash ratios between 1 and 2.5 and ash percentages of 20, 30 and 40 %, relatively to the total solids (soil + ash). UCS was determined at curing periods of 7, 28, 90 and 365 days, and the most effective mixtures were analysed for mineralogy with XRD. The results showed a clear increase in strength with decreasing activator/ash ratio (up to a maximum of 43.4 MPa), which is a positive result since the activator is the most expensive component in the mixture. Finally, UCS results of the cement and AA samples, at 28 days curing, were very similar. However, AA results proved to be just between 20 and 40 % of the maximum UCS obtained at 1 year curing, while cement results at 28 days are expected to be between 80 and 90 % of its maximum.     

Depositional characteristics of uranium tailings from Saskatchewan,Canada

The management of uranium tailings, generated as a by-product of ore processing, is particularly important to minimize the environmental footprint of the industry. A clear understanding of tailings slurry behavior is required at the time of deposition to help evaluate the storage capacity and life span of the containment facilities. The main purpose of this study was to investigate the segregation and self-weight settling properties of uranium tailings. Detailed laboratory investigations were conducted on tailings from 4, 5, and 6 % nominal mill feeds (high-grade McArthur River ores blended with special wastes on site) from the Cameco Key Lake operation. The results indicate that the three uranium tailings can be characterized as a sandy silt material with a negligible amount of clay. Their depositional behavior is governed by the initial solids content of the slurry. The investigated tailings showed insignificant segregation between 25 and 40 % initial solids content. The initial hydraulic conductivity during settling was about 10^?4 m/s at a void ratio of 4 and was increased by half an order of magnitude for the 4 % mill feed, and by almost two orders of magnitude for the 5 and 6 % mill feeds at a void ratio of 8. Over the same range of initial void ratio, the settling potential increased threefold: from 8 to 24 % for the 4 % mill feed and from 12 to 36 % for the 5 and 6 % mill feeds. The better rate and amount of dewatering of future high mill feed tailings as compared to the current low mill feed tailings means that the onsite containment facility can store more tailings thereby supporting a longer life span of the mill.     

Rheological characteristics of mixed kaolin–sand slurry,impacts of pH,temperature, solid concentration and kaolin–sand mixing ratio

Significant amount of slurry waste is produced from mineral processing plants globally constituting high levels of both kaolin and sand in aqueous suspension. Large quantities of slurry and mine tailings require efficient handling, transportation and storage system. The transportation and treatment of kaolin–sand slurry is dependent on its rheological behaviour which is a function of temperature, total solid concentration and pH. In this study, the effects of total solid concentration, pH and temperature on rheological behaviour of kaolin–sand mixture were investigated. These parameters were varied to analyse the viscosity, yield stress, flow index and shear force requirements of the mixed kaolin–sand suspension as a function of these varying parameters. Experimental rheological investigation conducted on rotational stress-controlled rheometer equipped with Peltier concentric cylinder system showed that the kaolin–sand mixture suspension is shear thickening in nature. The shear stress-rate rheograms for the kaolin–sand suspension can be modelled by the Herschel–Bulkley model with high levels of accuracy for pH range of 4–11, temperature range of 20–50 °C and solid concentration of 5–50 %. Solid concentration of the suspension was found to significantly affect the rheological behaviour of the mixture where higher kaolin–sand slurry concentration resulted in greater viscosity and the trend becoming less predictable for solid concentration greater than 50 % by weight. pH was another factor affecting the rheological behaviour of kaolin–sand slurry. pH of 3 or less resulted in the dramatic increase of viscosity of the suspension possibly due to the isoelectric point of the mixture system found between pH of 3 and 4.     

Undrained Strength of Deposited Mine Tailings Beds: Effect of Water Content, Effective Stress and Time of Consolidation

An understanding of the geotechnical behaviour of mine tailings is imperative when evaluating the stability and erosional resistance of sedimented tailings beds; as well as for the design and long-term management of tailings disposal facilities. Laboratory testing was conducted on mine tailings beds of various ages and thicknesses, deposited from concentrated slurries. Measured index properties allowed classifying the tailings as a coarse grained and non-cohesive material. The results obtained from the performed sedimentation experiments showed that the primary consolidation of the tailings beds was complete in approximately 1 h and negligible volume changes occurred in the beds during secondary compression. The undrained shear strength of the tailings beds was measured using an automated fall cone device at a depth interval of 1 cm and a profile of the shear strength variation with depth was obtained. At each tested surface, moisture content specimens were taken to determine the moisture content profile of the tested tailings beds. The undrained shear strength of the beds varied between 0.008 and 0.975 kPa for effective stresses below 1.19 kPa and increased with depth. Correspondingly, the moisture content decreased with depth and varied between 17 and 27%. The factor controlling the undrained shear strength of the tested beds was the vertical effective stress, with the water content also having some secondary effect. The correlation between the undrained shear strength and the vertical effective stress was expressed with a second order polynomial function. Consolidation time did not appear to influence the observed shear strength.     

Arsenic mobility in weathered gold mine tailings under a low-organic soil cover

Historical gold mining operations in Nova Scotia, Canada, resulted in numerous deposits of publicly accessible, arsenic (As)-rich mine waste that has weathered in situ for 75–150 years, resulting in a wide range of As-bearing secondary minerals. The geochemical heterogeneity of this mine waste creates a challenge for identifying a single remediation approach that will limit As mobility. A 30-cm-thick, low-organic content soil cover was evaluated in a laboratory leaching experiment where, to simulate natural conditions, the equivalent of 2 years of synthetic rainwater was leached through each column and two dry seasons were incorporated into the leaching protocol. Each column was a stratigraphic representation of the four major tailings types found at the historical Montague and Goldenville gold mine districts: hardpan tailings, oxic tailings, wetland tailings, and high Ca tailings. Hardpan tailings released acidic, As-rich waters (max 12 mg/L) under the soil cover but this acidity was buffered by surrounding oxic tailings. Leachate from the oxic tailings was circumneutral, with average As concentrations between 4.4 and 9.7 mg/L throughout the experiment. The presence of carbonates in the high Ca tailings resulted in near-neutral to weakly alkaline leachate pH values and average As concentrations between 2.1 and 6.1 mg/L. Oxidation of sulfides in the wetland tailings led to acidic leachate over time and a decrease in As concentrations to values that were generally less than 1 mg/L. This study shows that the use of a low-organic content soil cover does not create reducing conditions that would destabilize oxidized, As-bearing secondary phases in these tailings. However, oxygen penetration through the cover during dry seasons would continue to release As to tailings pore waters via sulfide oxidation reactions.     

不同黏结剂配比条件下型煤力学及渗透特性试验研究

利用含瓦斯煤热-流-固耦合三轴伺服渗流装置,为使得型煤力学及渗透特性更接近原煤,选取水泥作为黏结剂,进行了不同黏结剂配比条件下的型煤和原煤三轴压缩试验对比研究。基于欧式距离的相似性度量方法对能反映型煤的力学及渗透特性的特征值指标进行定量评价。结果表明：随黏结剂含量的增加,型煤的峰值主应力差、弹性模量近乎呈正指数函数递增趋势,泊松比呈负指数函数递减趋势;随着黏结剂含量的增加,型煤的初始渗透率、最小渗透率基本呈负指数函数递减趋势,且其渗透率变化率随黏结剂含量的增加越来越小,表现为渗透率-轴向应变曲线越来越平缓;基于欧式距离的相似性度量方法得出水泥黏结剂配比为IV型的型煤在力学及渗透特性方面与原煤最为接近,可以作为模拟原煤的相似材料。     

生石灰对理化复合法处理淤泥浆效率的影响研究

改性淤泥固化土应用于填方工程既能弥补砂石填料供应短缺的困境,还能解决大宗疏浚淤泥的弃置难题。但当淤泥含水率超高（＞300%）时,纯水泥固化法处理效果极差,而采用絮凝调理联合化学固化的理化复合法可有效解决此类问题。鉴于生石灰具有絮凝和固化双重功效,采用生石灰替代部分水泥可能会进一步提高淤泥浆的理化复合法处理效率。通过十字板剪切试验研究了生石灰替代比对高含水率淤泥浆理化复合法处理效率的影响规律,并通过X射线衍射（XRD）和场发射扫描电镜（FESEM）试验从微观层面揭示了其固化机制。结果表明：生石灰对淤泥浆理化复合法处理效率会产生较大影响,且存在一个最优生石灰替代比,在最优替代比条件下生石灰能显著发挥絮凝和固化双重功效,并有效提高处理后淤泥的早期和晚期强度;从微观试验分析,最优替代比下处理后的淤泥样生成的CSH/CAH/CASH凝胶和钙矾石等水化产物数量最多,孔隙间隙也最小。因此,实际工程中运用理化复合法处理高含水率淤泥浆时,可采用生石灰替代部分水泥以提高处理效率。     

Surface and rheological properties of as-received colloidal goethite (α-FeOOH) suspensions: pH and polyethylenimine effects

The yield stress and zeta potential (ζ) of slurries prepared from as-received goethite were evaluated as a function of pH, solids concentration, cationic polyethylenimine (PEI) concentration and molecular weight (Mw). The goethite slurries displayed a maximum yield stress at the isoelectric point (pI). These slurries do not have a low pH dispersed region. The yield stress obeyed the yield stress–DLVO force model. The maximum yield stress displayed a dependence on the solids volume fraction to a power of 3.8.PEI adsorbed and changed both the surface chemistry and rheological yield stress of the slurries. At most additive concentration ranging from 0.1 to 0.4dwb% for PEI of Mw 600, 1800 and 70,000, the maximum yield stress of the slurries is larger than that with no adsorbed additives. At low PEI concentration of 0.1dwb%, the same maximum yield stress of 30 Pa was obtained for three Mws; 600, 1800 and 70,000 representing a 1.5-fold increase. The increased attraction between particles was attributed to charge patch attraction at low surface coverages and hydrogen bonding at high coverages. Adsorbed PEI decreased the yield stress at low pH. However complete dispersion was observed only for 0.4dwb% PEI with Mw 70,000, at pH below 7. Complete dispersion was not observed at high pH for the same polymer at all concentrations.     

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.