Geochemical effects of oxidation products and framboidal pyrite oxidation in acid mine drainage prediction techniques

Acid mine drainage predictive testwork associated with the Australian Mineral Industries Research Association (AMIRA) P387A Project: Prediction and Kinetic Control of Acid Mine Drainage (AMD) has critically examined static acid assessment and kinetic information from acid–base accounting techniques, including net acid production potential (NAPP), net acid generation (NAG) and column leach tests. This paper compares results on two waste rock samples that were obtained from the Kaltim Prima Coal mine (KPC) containing significant quantities of fine-grained framboidal pyrite. In agreement with other research, the authors' results indicated that framboidal pyrite is more reactive than euhedral forms due to the greater specific surface area of framboidal pyrite. This is evidenced by optical microscopy of reacted samples. Importantly, the results showed that NAPP testing is biased by the rapid acid generating oxidation of framboidal pyrite prior to, and during the acid neutralisation capacity (ANC) test. This can result in negative ANC values for samples containing significant framboidal pyrite (often “corrected” to zero kg H₂SO₄/t) when significant ANC is actually present in the sample. NAG testing using H₂O₂ indicated that samples containing a significant quantity of framboidal pyrite can result in the catalytic decomposition of the H₂O₂ prior to complete oxidation of the sulfide minerals present, requiring sequential addition of H₂O₂ for completion. A benefit of the NAG test, however, is that it assesses the net acid generation capacity of the sample without bias towards acid generation as is observed using NAPP methods. The kinetic NAG test also gives information on the reaction sequence of framboidal and euhedral pyrite. Periodic (kinetic) analysis of sub-samples from column leach tests indicated rapid oxidation of the framboidal pyrite compared to the euhedral pyrite, which was correlated with the greater framboidal pyrite surface area.Calculations to determine the sulfide/sulfate acidity derived from the oxidation of framboidal pyrite prior to; and during the ANC test have been developed to provide a better indication of the actual ANC (ANC_Actual) of the sample. Paste pH values of <pH 4–5 may be one suitable trigger mechanism for the implementation of this new method. This has led to an improved NAPP estimation of total acid production. Together with NAG and column leach testing this improved methodology has resulted in accurate AMD characterisation of samples containing acidic oxidation products and framboidal pyrite.     

Investigation of pyrite oxidation and acid mine drainage characterization associated with Razi active coal mine and coal washing waste dumps in the Azad shahr–Ramian region,northeast Iran

Acid mine drainage (AMD) pollution is considered to be the most serious water pollution problem in mining areas. AMD containing iron sulfates and other components can affect the receiving water bodies. Pyrite oxidation and AMD generation can be considered as important processes that may take place in the wastes produced by coal mining and coal washing operations in the Golestan province (northeast Iran). The study area is characterized by appropriate atmospheric conditions that favor pyrite oxidation and the presence of a large amount of water bodies. This study attempts to consider pyrite oxidation and AMD generation in the Azad shahr–Ramian region. The impact of AMD on the quality of the surface water bodies was investigated by taking samples and analyzing them for hydro-geochemical parameters. Stiff and Piper diagrams were used to represent chemical analyses of water samples. The coal samples taken from different depths at four points on two different coal waste dumps were analyzed to find the fraction of pyrite that remained in the waste particles to investigate the pyrite oxidation process. A computational fluid dynamic package called PHOENICS was used to model pyrite oxidation process numerically. The results obtained from the geochemical analyses of water and coal samples and numerical simulation show pyrite oxidation and acid generation in the region. However, the presence of carbonate rocks raised the pH of the water samples. The drainages of the Razi mine may be recognized as natural alkaline mine drainages.     

山西王家岭矿区奥陶系碳酸盐岩溶蚀规律研究

为研究王家岭矿区奥陶系碳酸盐岩的溶蚀规律,模拟造成差异性溶蚀的主要因素进行了实验。在常温常压、溶蚀液碳酸水的pH值为6.5～6.9、每次溶蚀时间控制在24h左右的条件下,对矿区不同层段的碳酸盐岩进行溶蚀实验。实验发现,碳酸盐岩的成分和结构是影响溶蚀指标的重要因素,比溶蚀度和比溶解度总体趋势是白云岩灰岩膏岩;不溶物含量的增大使比溶蚀度和比溶解度下降,机械破坏量呈非线性增加;相同情况下方解石溶解速度快于白云石2～3倍。该实验结果为矿区进行水文地质研究提供了基础数据。     

Mineralogical and geochemical investigations of silicate-rich mine waste from a kyanite mine in central Virginia: implications for mine waste recycling

A kyanite mine in central Virginia produces a silicate-rich waste stream which accumulates at a rate of 450,000–600,000 tons per year. An estimated 27 million tons of this waste stream has accumulated over the past 60 years. Grain size distribution varies between 1.000 and 0.053 mm, and is commonly bimodal with modes typically being 0.425 and 0.250 mm and uniformity coefficients vary from 2.000 to 2.333. Hydraulic conductivity values vary from 0.017 to 0.047 cm/s. Mineralogy of the waste stream consists of quartz, muscovite, kyanite and hematite. Muscovite grains have distinct chemical compositions with significant Na₂O content (1.12–2.66 wt%), TiO₂ content (0.63–1.68 wt% TiO₂) and Fe content, expressed as Fe₂O₃ (up to 1.37 wt%). Major element compositions of samples were dominated by SiO₂ (87.894–90.997 wt%), Al₂O₃ (6.759–7.741 wt%), Fe₂O₃ (1.136–1.283 wt%), and K₂O (0.369–0.606 wt%) with other components being <1.000 wt%. Elements of environmental concern (V, Cr, Ni, Cu, Zn, As, Ag, Sn, Sb, Ba, Hg, Tl, and Pb) were detected; however, the concentrations of all elements except Ni were below that of the kyanite quartzites in the region from which the waste is derived. Both major and trace element compositions indicate minimal variation in composition. The waste stream has potential for recycling. Muscovite is suitable for recycling as a paint pigment or other industrial applications. Muscovite and hematite are commonly intergrown and are interpreted to be material where much of the elements of environmental concern are concentrated. Reprocessing of the waste stream to separate muscovite from other components may enable the waste stream to be used as constructed wetland media for Virginia and nearby states. Recycling of this mine waste may have a positive impact on the local economy of Buckingham County and aid in mitigation of wetland loss.     

Phosphate amendment of metalliferous waste rocks, Century Pb-Zn mine, Australia: Laboratory and field trials

The aim of the study was to determine whether the application of phosphate compounds (phosphorite rock, phosphate fertilizer) to polyminerallic waste rocks can inhibit sulfide oxidation and metal mobility (Cu, Pb, Zn, Cd, Ni, Mn, Mg). Waste rocks comprised sulfidic carbonaceous shales and were sourced from the Century Pb-Zn mine, NW Queensland, Australia. The acid producing, Pb-Zn rich rocks consisted of major quartz, muscovite/illite, dolomite, siderite and kaolinite as well as smaller amounts of sulfide minerals (e.g. galena, sphalerite, pyrite). Laboratory leach experiments were conducted on finely granulated phosphate-treated waste rocks (>2 to <30 mm) over 13 weeks, whereas phosphate amendment of coarsely granulated waste rocks (sand to boulder size) was investigated using heap leach piles at the mine site over an 11 months period. Results of the laboratory experiments demonstrate that the treatment of finely granulated waste rocks with phosphorite rock produced leachates with near-neutral pH values due to calcite dissolution. This in turn did not allow the leaching of apatite, formation of secondary phosphate phases and phosphate stabilization to occur. Metal mobility in these amended wastes was restricted by the dissolution of calcite and the resultant near-neutral pH conditions. By contrast, the application of the water-soluble phosphate fertilizer MKP (KH₂PO₄) to polyminerallic sulfidic waste rocks during the short-term laboratory experiments led to the formation of phosphate coatings and precipitates and inhibited acid and metal release (Cd, Mn, Ni, Pb, Zn). At least in the short term, the application of phosphate fertilizers proved to be an effective method. However, results of the long-term field trials demonstrate that coarsely granulated waste rocks were not coated by secondary phosphate phases and that amendment by phosphorite rock or superphosphate fertilizer did not improve leachate quality compared to the unamended waste. Thus, phosphate stabilization appears ineffective in suppressing oxidation of sulfides in coarsely granulated mine wastes.     

Isotopic evidence of enhanced carbonate dissolution at a coal mine drainage site in Allegheny County,Pennsylvania, USA

Stable isotopes were used to determine the sources and fate of dissolved inorganic C (DIC) in the circumneutral pH drainage from an abandoned bituminous coal mine in western Pennsylvania. The C isotope signatures of DIC (δ¹³C_DIC) were intermediate between local carbonate and organic C sources, but were higher than those of contemporaneous Pennsylvanian age groundwaters in the region. This suggests a significant contribution of C enriched in ¹³C due to enhanced carbonate dissolution associated with the release of H₂SO₄ from pyrite oxidation. The Sr isotopic signature of the drainage was similar to other regional mine waters associated with the same coal seam and reflected contributions from limestone dissolution and cation exchange with clay minerals. The relatively high δ³⁴S_SO4 and δ¹⁸O_SO4 isotopic signatures of the mine drainage and the presence of presumptive SO₄-reducing bacteria suggest that SO₄ reduction activity also contributes C depleted in ¹³C isotope to the total DIC pool. With distance downstream from the mine portal, C isotope signatures in the drainage increased_, accompanied by decreased total DIC concentrations and increased pH. These data are consistent with H₂SO₄ dissolution of carbonate rocks, enhanced by cation exchange, and C release to the atmosphere via CO₂ outgassing.     

Experimental studies on three potassium-rich ultramafic rocks from Damodar Valley, East India

Summary An experimental study on the phase relationships of three potassium-rich ultramafic rocks from the Damodar Valley, Gondawana basins, has been performed under upper mantle P–T conditions (1.0–2.5 GPa, 700–1200 °C). The Mohanpur lamproite and Satyanarayanpur minette, both from the Raniganj basins, have been investigated with the addition of 15 wt% H₂O. No water was added in the experiments done on an olivine minette from the Jarangdih coal mine, Bokaro Basin, which originally contains 15 wt% CO₂ and 2.86 wt% H₂O. In all cases, olivine is the liquidus phase followed by phlogopite. The subsolidus assemblage for the three rocks is a phlogopite-bearing harzburgite, associated with apatite, Mg-ilmenite and carbonates for the Jarangdih rock; apatite, chromian spinel and carbonates and priderite (only between 1.0 and 1.2 GPa) in the case of the Mohanpur lamproite, and finally apatite, chromian spinel, rutile, and carbonate in the Satyanarayanpur sample. Although orthopyroxene is absent in the natural potassium-rich ultramafic rocks, its presence in the run products of the Jarangdih rock is possibly related to a reaction between olivine and a CO₂-bearing fluid phase. The presence of orthopyroxene in the run products of Mohanpur and Satyanarayanpur rocks may be due to a reaction between K-feldspar, olivine and a vapour phase to produce phlogopite and orthopyroxene. On the basis of present experimental investigation and isotopic studies made by previous investigators, it has been suggested that these K-rich rocks have crystallized from melts derived by vein-plus-wall-rock melting of a phlogopite-bearing harzburgite source rock. Received December 15, 1999; revised version accepted June 17, 2001     

Analysis of Cracking in Rock Salt

Summary ?The use of underground mines in salt-rock formations for waste repositories makes the precise analysis of isolation properties of rock salt very important. One of the main mechanisms responsible for a degradation of isolation ability of the rock salt is the generation and development of cracks under influence of mining processes. Various aspects of cracking in salt rocks are studied – both in situ and in laboratory tests – for rocks of the world's largest Verkhnekamskoe potash-ore deposit (Russia). It is shown that not all the discontinuities (fractures) are closed in the course of the creep deformation of rocks. Parameters of cracking are determined for various conditions: age of pillars, mining technology, etc. Different methods – filtration, electrometric, nuclear magnetic resonance, mechanical tests – are used for crack observation and characterisation, both in specimens and in situ. Traditional investigations (partly with specially designed equipment) are accomplished by the testing methods of fracture mechanics for determination of critical values of stress intensity factors K _Ic and K _IIc. The problems and ways of the use of the obtained results in analysis of isolation properties for areas in vicinity of underground mines and/or waste repositories are discussed.     

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.     

Chemistry of acid production in black coal mine washery wastes

Column leaching tests on black coal mine washery wastes were performed, to determine the chemistry of acid generation. Coal mine coarse rejects and tailings were subjected to wet and dry cycle dissolution and subsequently column leached. The rates of iron sulphide oxidation and carbonate mineral dissolution were determined based on the drainage chemistry. The kinetic data from column leach experiments are used to predict the time required to deplete the acid producing and acid consuming minerals in the mine wastes. The acid production in the mine rejects was found to depend upon iron chemistry, carbonate chemistry, diffusion of oxygen, and permeability. The chemistry of the drainage from two different coal mines is compared.     

An experimental study of dissolution kinetics of Calcite, Dolomite, Leucogranite and Gneiss in buffered solutions at temperature 25 and 5°C

Laboratory experiments were carried out continuously for 30–35 days at 25 and 5°C in three different buffer solutions of pH 4.0, 2.2 and 8.4 to calculate dissolution rates of two minerals, calcite (CC) and dolomite (DM) and two rocks, leucogranite (LG) and gneiss (GN) from the Himalayan range. Calculated rates in terms of release of targeted elements versus time (Ca for CC; Mg for DM; Si for LG and GN) demonstrate direct correlation with temperature. Dissolution rates are higher at 25°C compared to 5°C. CC and DM were experimented only at pH 8.4 and results show that both undergo congruent dissolution with CC dissolving ∼5 times faster than DM. Ca and Mg exhibit average apparent activation energies (E _a) of 13.98 and 9.98 kcal mol⁻¹ respectively at pH 8.4 which reflects greater sensitivity of CC dissolution than DM dissolution towards an increase in temperature. Scanning Electron Microscope attached with Energy Dispersive X-Ray Analyser (SEM-EDX) data indicates that dissolution is controlled primarily by surface-reaction processes, with dislocation sites contributing maximum to the dissolution. As compared to CC and DM dissolution, LG and GN undergo relatively slower incongruent dissolution with precipitation of some secondary minerals as revealed from X-ray diffractometer (XRD) results. Rates of dissolution of LG is maximum at pH 2.2, moderate at pH 8.4 and least at pH 4.0, whereas GN shows maximum dissolution at pH 2.2, moderate at pH 4.0 and least at pH 8.4. A comparison in dissolution behavior of LG and GN at experimental conditions reveals that increase in Si-release rate in the temperature range between 5 and 25°C is maximum at pH 8.4 (∼3.4–4.5 times), moderate at pH 4.0 (∼3–1.8 times) and least at pH 2.2 (∼1.0–1.5 times). Within the experimental temperature range, calculated values of E _a for Si release during LG and GN dissolution advocates positive correlation with pH. A substantial decrease in initial values of Brunauer–Emmett–Teller (BET) surface area of DM, LG, and GN has been encountered at the end of the experiment, except for CC for which an increase is observed. The study clearly demonstrates the dissolution behavior of pure minerals and rocks under controlled conditions. The dissolution rates assume enormous significance for the release of trace elements from rocks/minerals to the reacting water.     

Stable isotope and fluid inclusion evidence for the origin of the Brandberg West area Sn–W vein deposits, NW Namibia

The Brandberg West region of NW Namibia is dominated by poly-deformed turbidites and carbonate rocks of the Neoproterozoic Damara Supergoup, which have been regionally metamorphosed to greenschist facies and thermally metamorphosed up to mid-amphibolite facies by Neoproterozoic granite plutons. The meta-sedimentary rocks host Damaran-age hydrothermal quartz vein-hosted Sn–W mineralization at Brandberg West and numerous nearby smaller deposits. Fluid inclusion microthermometric studies of the vein quartz suggests that the ore-forming fluids at the Brandberg West mine were CO₂-bearing aqueous fluids represented by the NaCl–CaCl₂–H₂O–CO₂ system with moderate salinity (mean=8.6 wt% NaCl_equivalent).Temperatures determined using oxygen isotope thermometry are 415–521°C (quartz–muscovite), 392–447°C (quartz–cassiterite), and 444–490°C (quartz–hematite). At Brandberg West, the oxygen isotope ratios of quartz veins and siliciclastic host rocks in the mineralized area are lower than those in the rocks and veins of the surrounding areas suggesting that pervasive fluid–rock interaction occurred during mineralization. The O- and H-isotope data of quartz–muscovite veins and fluid inclusions indicate that the ore fluids were dominantly of magmatic origin, implying that mineralization occurred above a shallow granite pluton. Simple mass balance calculations suggest water/rock ratios of 1.88 (closed system) and 1.01 (open system). The CO₂ component of the fluid inclusions had similar δ ¹³C to the carbonate rocks intercalated with the turbidites. It is most likely that mineralization at Brandberg West was caused by a combination of an impermeable marble barrier and interaction of the fluids with the marble. The minor deposits in the area have quartz veins with higher δ ¹⁸O values, which is consistent with these deposits being similar geological environments exposed at higher erosion levels.     

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.     

The source of fluoride toxicity in Muteh area,Isfahan, Iran

Endemic dental fluorosis has been observed in most inhabitants of three villages of Muteh area, located in northwest of Isfahan province, with mottled enamel related to high levels of fluoride in drinking water (1.8–2.2 ppm). Forty-seven groundwater samples from six villages were collected and fluoride concentrations along with physico-chemical parameters were analyzed. Fluoride concentration in this area varies from 0.2 to 9.2 mg/l with highest fluoride level at Muteh gold mine (Chahkhatun mine). Fluoride concentration positively correlates with pH and HCO₃ ⁻ indicating that alkaline pH provides a suitable condition for leaching of fluoride from surrounding rocks. The district is mainly covered by three lithological units, namely, metamorphic and granite rocks, alluvial sediments, and carbonate rocks. Factor analysis shows that parameters can be classified into four components: electrical conductivity (EC), total dissolved solids (TDS), Cl⁻, Na⁺ and K⁺, pH and F⁻, SO₄ ²⁻and Mg²⁺, HCO₃ ⁻ and Ca₂ ⁺. The groundwaters from the three geological units were compared using Mann–Whitney U test. The order of median fluoride concentration is: metamorphic and granite rocks > alluvial sediments > carbonate rocks. Hence, the fluoride content is most probably related to fluoride-bearing minerals such as amphibole and mica group minerals in metamorphic and granitic rocks. The concentration of fluoride in drinking water wells located near the metamorphic complex in Muteh area is above 2 ppm.     

Mineralogical and geochemical investigations of pyrite-rich mine waste from a kyanite mine in Central Virginia with comments on recycling

A pyrite-rich waste stream is one of three types generated from a kyanite mine in central Virginia near the town of Dillwyn, Buckingham County. Currently, ore consists of approximately 3% pyrite waste and an estimated 382,000 tons of this waste stream has been generated over the past 60 years. The mineralogy of the waste stream consists of variable amounts of pyrite (70–>99%), talc (1–20%), quartz (1–10%), kyanite (0.5–5%) with minor or trace amounts of magnetite, hematite, galena, anorthite and rare earth phosphate. Energy dispersive spectroscopy analysis indicates that talc has minor amounts of Al up to 1.57 wt% and Fe up to 4.29 wt% and pyrite grains have no impurities above detection limit of approximately 0.1 wt%. Bulk chemical analysis of selected elements using inductively coupled plasma-mass spectrometry analysis indicate that Zn (28.82–367.71 ppm), As (8.94–18.26 ppm), Se (44.62–64.50 ppm), Cd (0.19–1.03 ppm), Hg (0.87–35.91 ppm), and Pb (65.10–189.66 ppm) occur at levels of some environmental concern. Au and Ag concentrations are negligible. Currently the waste stream is well managed and sold, but for a low price. Talc is of sufficient quality to be of interest for recycling but the estimated 540 tons generated per year is not a suitable quantity to be economically viable. Currently, the waste stream is not viable for recycling for higher monetary value; however, the characteristics of the pyrite may enable such recycling in the future for solar energy technologies. This and other associated waste streams show long term promise for integrated recycling and may play important economic roles in an economically disadvantaged region.     

Effects of quarry mining and of other environmental impacts in the mountainous Chicam-Toctina drainage basin (Córdoba, Argentina)

 The environmental conditions prevailing in the Chicam-Toctina drainage system (approx. 138 km² in Córdoba, Argentina) are considered representative of a number of catchments in Argentina's Sierras Pampeanas Range. Two groups of ions reflect the sources of dissolved species in the catchment: a) a group (Cl^–, SO^2– ₄, and Na⁺) which recognizes natural and anthropogenic sources, and which exhibits significant correlations with N^– ₃ and NO^– ₂, and b) another group of components (Ca²⁺, Mg²⁺, and HCO^– ₃) which is clearly controlled by carbonate rocks and their waste rock products. In the headwaters, stockpiled marble quarry mining wastes provide a more open system to CO₂ gaseous exchange than the outcropping rocks, thus promoting the increase of carbonate dissolution (up to 4.88 g km^–2 s^–1 during the rainy season). This specific yield was 20% higher than the amount estimated for an area with fewer extended mining activities. The dissolved load delivered by the upper reaches is subjected in the lower drainage area to various processes, mainly controlled by the presence of the city of Alta Gracia (approx. 40,000 inhabitants). In the dry season, due to nutrient inputs supplied by the city, photosynthetic activity plays a major role controlling stream pH. Hence, the high values of calcite saturation indexes and the increase of CaCO₃ concentration in bed sediments can be explained by calcite precipitation. Such a process could be accompanied by the coprecipitation on calcium carbonate of low solubility heavy metal carbonates. Received : 17 January 1997 · Accepted : 31 March 1997     

Hydrogeochemistry of mine, surface and groundwaters from the Sanggok mine creek in the upper Chungju Lake, Republic of Korea

 The Sanggok mine used to be one of the largest lead-zinc mines in the Hwanggangri mining district, Republic of Korea. The present study characterizes the heavy metal contamination in the abandoned Sanggok mine creek on the basis of physico-chemical properties of various kinds of water samples (mine, surface and groundwater). Hydrochemistry of the water samples is characterized by the relatively significant enrichment of Ca²⁺, HCO₃ ^–, NO₃ ^– and Cl^– in the surface and groundwaters, whereas the mine water is relatively enriched in Ca²⁺, Mg²⁺, heavy metals, and HCO₃ ^– and SO₄ ^2–. The more polluted mine water has a lower pH and higher Eh, conductivity and TDS values. The concentrations of some toxic elements (Al, As, Cd, Cu, Fe, Mn, Pb, Se, Sr, Pb and Zn) are tens to hundreds of times higher in the mine water than in the unpolluted surface and groundwaters. However, most immobile toxic pollutants from the mine drainage were quickly removed from the surface water by the precipitation of Al and Fe oxyhydroxides. Geochemical modeling showed that potentially toxic heavy metals might exist largely in the forms of MSO₄ ^2– and M²⁺ in the mine water. These metals in the surface and groundwaters could form M²⁺, CO₃ ^2– and OH^– complex ions. Computer simulation indicates that the saturation indices of albite, alunite, anhydrite, chlorite, fluorite, gypsum, halloysite and strontianite in the water samples are undersaturated and have progressively evolved toward the saturation condition. However, barite, calcite, chalcedony, dolomite, gibbsite, illite and quartz were in equilibrium, and only clay minerals were supersaturated. Ground and mine waters seemed to be in equilibrium with kaolinite field, but some surface water were in equilibrium with gibbsite and seceded from the stability field of quartz. This indicates that surface water samples in reaction with carbonate rocks would first equilibrate with carbonate minerals, then gibbsite to kaolinite. Investigations on water quality and environmental improvement of the severely polluted Sanggok creek, as well as remediation methods on the possible future pollution of the groundwater by the acid mine drainage from the abandoned metal mines, are urgently required. Received: 4 February 2000 · Accepted: 9 May 2000     

Pressure-oxidation autoclave as an analogue for acid–sulphate alteration in epithermal systems

Gold extraction at the Macraes gold mine in New Zealand involves concentration of pyrite and arsenopyrite, oxidation of those sulphides, then cyanidation. The ore concentrate is predominantly Otago Schist host rock (andesitic composition) with up to 15% sulphides. The oxidation step is conducted on ore concentrate slurry in an autoclave at 225°C and 3,800 kPa oxygen gas pressure with continuous feed. The slurry takes ca. 1 h to pass through the autoclave, during which time the sulphides are almost completely oxidised. Sulphide oxidation causes strong acidification of the slurry, which is maintained at pH of 1–2 by addition of CaCO₃. Scales form on walls in the autoclave, with minerals reflecting progressive oxidation and alteration of the ore through the system. The schist in the ore feed has mineralogy similar to propylitically altered andesite: quartz, albite, muscovite, chlorite, and pyrite. Muscovite undergoes almost complete dissolution, with associated precipitation of quartz and alunite (KAl₃(SO₄)₂(OH)₆). Other principal minerals deposited and discharged include anhydrite (and/or gypsum), jarosite (KFe₃(SO₄)₂(OH)₆), hematite (and/or amorphous iron oxyhydroxide), and amorphous arsenates. Dissolved ferrous iron passes right through the autoclave, and variably hydrated Fe²⁺and Fe³⁺sulphate minerals, including rozenite and szomolnokite (both FeSO₄.hydrate) and ferricopiapite (Fe₅(SO₄)₆O(OH).hydrate), are formed along the way. The autoclave chemical system resembles acid–sulphate hydrothermal activity in geothermal systems and high-sulphidation epithermal mineral deposits formed in arc environments. These natural acid–sulphate systems are pervaded by volcanic vapours in the near-surface environment, where widespread dissolution of host rocks occurs and deposition of quartz, alunite, and anhydrite is common. Some of the volume loss associated with these natural systems may be due to dissolution of soluble sulphate minerals by later-stage groundwater incursion.     

Measured and computed neutralization potentials from static tests of diverse rock types

Static tests typically are used in the initial stage of environmental assessments to predict the potential for acid mine drainage, and also are used to monitor waste disposal at active mining operations. The neutralization potential (NP) of 19 sedimentary, metamorphic, and igneous extrusive rocks was measured by the Sobek method to compare the results with those computed by using the quantitative mineralogy of the rocks and the NP values that were deemed to be appropriate for the individual minerals. Most of the computed NP values of the rocks are lower than the measured values, but a close relationship is evident. If the contents of carbonate minerals are low, the NP in non-ultramafic igneous rocks typically is controlled by the amount of Ca substitution in plagioclase, whereas in ultramafic rocks the NP contribution is dominated by the amount of olivine and serpentine. Compositional and NP analyses of plagioclase concentrates indicate that the NP systematically varies from <1 for the Na end-member to about 14 for compositions near that of the Ca end-member. Among several variables that can affect the Sobek NP values, the volume and normality of the acid added to the sample are well-known to influence the results; however, the temperature and duration of the acidification stage can also have a pronounced effect on the measured NP of some rocks, depending on their mineralogy. Fizz tests to estimate the carbonate content and the consequent acid addition are highly subjective, and the ‘no fizz’ rating is not to be taken literally. The NP results themselves provide a clear indication of whether a sample has been over-acidified or under-acidified in the test procedure.     

Stability Assessment of a Pit Slope Under Blast Loading: A Case Study of Pasir Coal Mine

In Pasir mine, coal seams and host rocks of varying thickness have been uniquely deposited with an average dip angle of 85°. The host rocks are weak and mainly composed of mudstone and sandstone comprising of 90–95% of the total pit volume. The thickness of coal seams and host rocks ranges from sub-metric to few tenths of meter. The overall safe pit slope angle was evaluated to be 27° for mining depth of 50–150 m. Several slopes failure incidents have occurred in the mine causing considerable disruption in production and monetary loss. It is envisaged that slope failures may be triggered due to blasting conducted in steeply dipping stratified deposit. In order to investigate the causes of slope failures, peak particle velocity (PPV) and accelerations at various locations from the blast site have been measured. In addition, finite element models of pit slope have been analyzed by applying static or gravity loading as well as blasting or dynamic loading. This paper elaborates the results of in situ measurements of ground vibration and numerical investigation and suggests possible causes of slope failures in Pasir mine.