An acid rock drainage (ARD) stream emanating from the Zn-Pb XY-deposit in the Yukon Territory was examined in order to evaluate the physico-chemical and geochemical processes governing the distribution of dissolved elements from the creek. The creek showed very high concentrations of metals (300 mg/L Fe, 500 mg/L Zn, 15 000 µg/L Ni, 1300 µg/L Cu and 4500 µg/L Cd), low water temperatures (1 – 12°C) and was acidic to moderately acidic (pH 3.1 – 5.0). It was found that this stream experienced a strong seasonal evolution, with increased sulphate and metal concentrations and decreased pH over the course of the summer. The mineral precipitates that formed under low pH conditions were a mixture of schwertmannite, goethite, jarosite and barite, while those that formed under moderately acidic conditions were a mixture of jurbanite, hydrobasaluminite, gibbsite and an X-ray amorphous Al-sulphate phase. Most of the mineral precipitates were of inorganic origin, although microbes may have played a role in mineral formation and trace metal sequestration in some of the precipitates. All of the mineral precipitates contained anomalous concentrations of trace elements (up to 1.5 % wt Zn) and showed a seasonal evolution in their mineralogy, both of which were determined to be a function of the pH and prevailing geochemical conditions. The geochemistry of the ARD creek draining the XY-deposit was compared to another ARD creek in the area that was likely draining shales. The two creeks were compared in order to determine if ARD geochemical characteristics can be used as a tool for the mineral exploration industry.

Between 2004 and early 2006 a large-scale, instrumented, potentially contaminating trial waste rock dump was constructed and monitored at Cadia Hill Mine, in NSW, Australia. The trial waste rock dump was instrumented with lysimeters to measure rainfall infiltration and seepage through its base, and temperature sensors and gas sampling tubes to evaluate oxidation of the waste rock, together with three instrumented trial store and release covers on the surface. This thesis describes the construction and instrumentation of the trial waste rock dump and the monitoring results obtained to date, and applies unsaturated soil mechanics principles to understanding the early performance and predicting the future performance of the trial waste rock dump and trial store and release covers. For a given rainfall regime, the rate and quantity of rainfall infiltration into a waste rock dump of a given height, the wetting up of the dump over time, and the occurrence of base seepage will largely be dictated by the particle size distribution of the waste rock delivered to the dump, and the stratigraphy of the dump. The particle size distribution of the waste rock delivered to the dump will depend on the fragmentation of the rock due to blasting and the degree of weathering and hence breakdown on handling of the rock. A waste rock dump constructed by conventional loose end-dumping from haul trucks from a tip-head, as was the case for the trial waste rock dump, consists of a trafficked surface layer extending to a depth of approximately 1 m, underlain by discontinuous alternating coarse and fine-grained layers raveling at the angle of repose of the waste rock, with a base rubble zone of boulders which ravel to the toe of the dump on end-dumping. Trafficking of the surface of the dump by dozers and haul trucks leads to the breaking down, burial and side-casting of the rock to form a well-graded material typically finer than 100 mm in particle size, with a moderate to high water storage capacity. The underlying coarse-grained angle of repose layers serve as air pathways during dry conditions and preferred seepage pathways during and following periods of heavy rainfall resulting in base seepage. The fine-grained angle of repose layers have a moderate to high water storage capacity and largely retain water in storage rather than generating base seepage. The base rubble zone may contain boulders up to 1 m in size, depending on the fragmentation of the rock due to blasting and the degree of weathering and hence breakdown on handling of the rock. It serves largely as a pathway for air during dry conditions, while passing base seepage during and following periods of heavy rainfall. As the dump wets up, partially saturated “fingers” develop and extend into the dump. Partially saturated fine-grained layers, having a medium to high water storage capacity, largely retain their partial saturation, while coarse-grained layers drain resulting, in base seepage. Plugs of water temporarily stored within the dump drain down through the dump, so that the base seepage that emerges is “old” water, not the rainfall infiltration (“new” water) that generated it. The size of the rainfall event required to generate base seepage will decrease as the dump wets up and the partially saturated fingers extend closer to the base of the dump. The residence time of water within the dump that passes along preferred seepage pathways will be relatively short and will become shorter as the dump wets up, while the residence time of water stored within the fine-grained layers will be very long, and possibly indefinite in a dry climate. The ingress of air through the base rubble zone, up the coarse-grained angle of repose layers, through the sides of the dump, and to a lesser extent through the trafficked layer, by the processes of convection, advection and diffusion, respectively, results in the exposure of reactive waste rock to oxidation. The fine-grained reactive waste rock, presenting a far greater surface area per unit volume than the coarse-grained waste rock, and typically having a greater proportion of fresh surfaces, is by far the most reactive. The ingress of air into the fine-grained layers is largely by diffusion from the adjacent coarse-grained layers. The transport of oxidation products from the dump largely occurs during and following periods of heavy rainfall, when preferred pathway flow is mobilised and base seepage occurs. The main exposure to preferred pathway flow is along these pathways, where the surface area per unit volume and hence the proportion of oxidation products are low, with much of the oxidation products formed on the fine-grained particles retained within the dump along with stored water. Due to the discontinuous stratigraphy of a waste rock dump, the preferential pathways for flow are randomly located within the dump. In addition, preferential pathways evolve over time as the waste rock weathers, settles, and as fines are transported with the flow. The trafficked surface of the dump also evolves over time, becoming more heterogeneous as the surface settles differentially, generating internal rainfall runoff and the transport of fines, and the development of “sinkholes” for the preferred entry of ponded rainfall. The principle purpose of cover systems over waste rock dumps is to restrict net percolation into the dump, so that percolation through the reactive waste rock is minimal in the longer term. The approach used to design any cover system is dominated by climate. Semi-arid environments are conducive to store and release cover systems which take advantage of well-graded oxide materials to provide high storage capacities, low percolation and stability. Three trial store and release covers, each comprising a sealing layer overlain by a thick mounded rocky soil mulch layer, were installed at Cadia Hill Mine in 2005-2006 to assess their feasibility to limit net percolation under the climatic conditions encountered at Cadia. This research described in this thesis has demonstrated a number of key issues that should be considered in the management and closure of waste rock dumps: • the initial moisture condition of the end-dumped waste rock will effect its early ability to store incidental rainfall; • the available water storage capacity of the waste rock will affect the size of the triggering rainfall event and the base seepage response time, with the storage capacity being taken up as the dump wets up, reducing both the size of the triggering rainfall event and the response time; • iterative modelling and calculations using HYDRUS-2D suggest that the trial waste rock dump will take between 3 years and 6 years to become sufficiently saturated that it will pass any rainfall infiltration, depending on the extent to which the waste rock weathers over time; and • all three trial store and release covers have demonstrated good performance over the monitoring period, and this has been verified using HYDRUS-2D, , with any net percolation being the result of an initial high placement moisture content of the cover materials.

An acid rock drainage (ARD) stream emanating from the Zn-Pb XY-deposit in the Yukon Territory was examined in order to evaluate the physico-chemical and geochemical processes governing the distribution of dissolved elements from the creek. The creek showed very high concentrations of metals (300 mg/L Fe, 500 mg/L Zn, 15 000 µg/L Ni, 1300 µg/L Cu and 4500 µg/L Cd), low water temperatures (1 – 12°C) and was acidic to moderately acidic (pH 3.1 – 5.0). It was found that this stream experienced a strong seasonal evolution, with increased sulphate and metal concentrations and decreased pH over the course of the summer. The mineral precipitates that formed under low pH conditions were a mixture of schwertmannite, goethite, jarosite and barite, while those that formed under moderately acidic conditions were a mixture of jurbanite, hydrobasaluminite, gibbsite and an X-ray amorphous Al-sulphate phase. Most of the mineral precipitates were of inorganic origin, although microbes may have played a role in mineral formation and trace metal sequestration in some of the precipitates. All of the mineral precipitates contained anomalous concentrations of trace elements (up to 1.5 % wt Zn) and showed a seasonal evolution in their mineralogy, both of which were determined to be a function of the pH and prevailing geochemical conditions. The geochemistry of the ARD creek draining the XY-deposit was compared to another ARD creek in the area that was likely draining shales. The two creeks were compared in order to determine if ARD geochemical characteristics can be used as a tool for the mineral exploration industry.

京都大学 / 0048 / 新制・課程博士 / 博士(地球環境学) / 甲第18435号 / 地環博第117号 / 新制||地環||23(附属図書館) / 31293 / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)教授 勝見 武, 教授 高岡 昌輝, 准教授 乾 徹 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DFAM

Sulfide-bearing rock that is excavated in conjunction with construction projects can cause environmental and construction engineering problems. Sulfidic minerals oxidize when they are exposed to an oxidant and water, which can make them generate acid rock drainage (ARD) with high concentrations of metals and sulphate. Predicting the overall oxidation process and drainage properties is, however, difficult since these depend on various factors. In this master thesis the current state of a 20-year-old ARD case is studied and compared to early site conditions to improve the knowledge of how different sulfide-bearing rocks may behave over time. The study investigates the drainage water and its impact on a local watercourse, but also chemical and mineralogical properties of oxidized rock from the site. The concentrations of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, S, and Zn in the drainage and watercourse has been studied and compared to data from when the sulfide-bearing rock was excavated and deposited.  The chemical composition and occurrence of sulfides in different rock types from the area has been examined through chemical analysis, SEM-EDS techniques, and sequential extractions. XRD data has been collected but was not interpreted within this project. The results from the water chemistry investigations showed that the concentrations of Cd, Co, Cr, Cu, Ni, and Zn had decreased since 2004, while the concentrations of Al, Fe, and Mn had increased. These elements mainly originated from a drainage pipe below ground level and later precipitated in the watercourse; only nickel and sulphate concentrations remained elevated 800 meters downstream from the studied rock storage. It was also shown that other sources in the area contaminated the watercourse. Masses of the previously deposited sulfide-bearing rock were moved approximately 10 years ago, which increase the uncertainty of conclusions drawn from the drainage. However, the elevated electrical conductivity and metal content of the drainage are signs of sulfide oxidation. The high concentration of aluminium likely indicates that the pH is buffered by silicates in the rock storage, and the concentrations of iron and manganese could also originate from silicates, or from sulfide oxidation. Pyrite was found abundantly in clusters in metasedimentary rock. Mainly pyrite, but also sphalerite and pyrrhotite was found in less oxidized, mica rich metafelsic rock. Both pyrite and sphalerite appeared in conjunction with mica, whereof pyrite as crack fillings. In more oxidized samples of mica rich rock, close to no sulfides were observed. The substantial difference in this rock is likely because the sulfides in conjunction with mica are particularly exposed to oxidation since fractures tend to appear along mica, and the sulfides located there have large specific surface areas. The presence of sulfides in the mica poor rock grouping of this study proved to be very heterogenous. In future studies there is therefore a need to further divide this group and study the sulfide-bearing metasedimentary rock from this site separately. In addition, the mineralogical source of the manganese in the water should be investigated in further studies.

<p> In this study a combined field and laboratory approach was used to identify the bio-geochemical processes that control trace metal (Ni, Co, Cr) reactive transport within natural acid rock drainage (ARD) biofilms, over both diel and seasonal timescales. Results indicated that metal (Mn, Ni, Co and Cr) scavenging by these biological solids is stable on a seasonal time frame. Metal scavenging occurs within two key solids, the organic constituents of the biofilm (Ni, Co) and associated biogenic hydrous Mn oxyhydroxides (HMO; Ni, Co and Cr), and not in association with Fe-oxyhydroxysulphates which dominate the mineralogy of the biofilm samples by mass. On a diel basis, cycling of HMO and associated trace metal dynamics appear to be contingent on the vertical migration of the biofilm oxic-anoxic boundary, a microbially controlled process. </p> <p> The reactivity and sorptive capacities of synthetic HMO analogs for Ni were further examined under well-characterized laboratory conditions. Analysis of the local chemical environment of Ni sorbed to HMO by synchrotron-based X-ray absorption spectroscopy was integrated with a bulk geochemical model of the acid-base characteristics of HMO and a theoretical model of the HMO structure. The synergistic use of these techniques allowed unique insight into the structural reactivity of HMO for Ni and is the first study to mechanistically demonstrate why bulk surface complexation models (SCM) are not accurate for HMO metal uptake. </p> <p> Overall, the results of this thesis highlight the utility of combined field and laboratory investigation to characterize relevant processes for reactive metal transport and underscore the need to: (1) consider microscale microbial-geochemical linkages in geochemical behaviour; (2) use caution when applying results derived from synthetic analogs to interpret natural system behaviour; and (3) examine processes at the appropriate scale e.g. microscale, to evaluate the mechanisms involved in metal reactions with solids. </p> / Thesis / Doctor of Philosophy (PhD)

Waste rock piles from coal mining of tertiary bituminous coal in Longyearbyen, Svalbard, show sulfide oxidation and subsequent acid mine drainage (AMD) production. The aim was to establish deeper understanding of AMD prediction based on Mineralogy and Geochemistry of coal and AMD samples. Mineralogical investigation of both coal and rock samples was performed with Automated SEM (ZEISS-Sigma VP300-Mineralogic System) as well as RAMAN. ICP-MS analysis was performed on solid and water samples. The pH from in situ measurements of AMD between 2,5-7,0. Eh varied from 222-569 mV (corresponding pe value of 3,7-9,6). This study showed that time of AMD in an oxidative environment was a key factor in iron concentration and iron speciation the AMD. This could not however be concluded in terms of age of mine site but rather the site-specific setting. The main minerals found in coal samples were pyrite (FeS2), siderite (FeCO3), calcite (CaCO3) and apatite (Ca5(PO4)3). Pyrites were identified with framboidal and euhedral textures and were found inside the maceral matter and in over- and underlying rocks respectively. SEM analysis of coal samples indicated that the modes of mineral formation was changing over the course of the Longyear seam. This study found that framboidal or euhedral textures of pyrite had different impacts in the AMD production. Framboidal pyrite was found to generate a greater amount of acidity than euhedral pyrites due to larger specific surface area and could therefore pose larger problems in AMD management.

Ekobacken, Värmdö kommun, har problem med surt yt- och grundvatten med höga metallhalter. Uppmärksamheten har riktats mot berggrunden som krossats och lagrats i deponihögar. Bildningen av sur lak styrs av flertalet geokemiska egenskaper, bland annat vilka sulfidmineral som förekommer och deras kristallstruktur. Prover från Ekobacken har undersökts utifrån sulfidhalt, kristallarea för opaka mineral och surgörande potential för att kunna utröna om ett samband finns mellan kristallareafördelning och lakningsegenskaper. Proverna har mikroskopiskt undersökts i reflekterande ljus för att skilja ur vilka opaka faser som förekommer samt har tunnslip fotograferats för att bildanalysera de opaka faserna utifrån area och form. Ett statiskt laktest utfördes på proverna för att kvantifiera dess lakningsegenskaper. Resultatet visar att bergarterna bestod i stor del av kvarts, fältspat och biotit i olika fördelningar. Opaka faser som förekom var pyrit, grafit, kopparkis och magnetit. Bergarterna visade sig generellt ha hög sulfidhalt från ABA resultatet, där ett prov hade en halt på 0,61 vikt%, medan andra prov hade relativt hög bufferförmåga och därför ingen surgörande potential. Proverna som undersöktes visade sig vara likartade varandra i förhållande till kristallareafördelning av opaka faser och form. I den här studien gick ingen direkt korrelation mellan provens kristallareafördelning för opaka faser och lakningspotential att utröna / Ekobacken, Värmdö municipality, have a problem with acidic surface- and groundwater with high metal content. The attention has been directed towards the bedrock which have been crushed and stored in landfills. The production of acid drainage is controlled by multiple geochemical properties inter alia which sulphide minerals are present and the structure of crystals. Samples from Ekobacken has been collected and analysed for sulphide content, crystal-area of sulphide minerals and acidic potential to investigate if there is a correlation between crystal-area distribution and leachability. The samples were examined under reflective light microscopy to determine the different opaque phases present and the thin sections were photographed for a photo analysis regarding crystal area and shape. A static leachability test was performed to be able to quantify the samples potential to produce acidic drainage. The results show that the samples contained mostly quartz, feldspars and biotite. Opaque phases present were pyrite, graphite, chalcopyrite and magnetite. ABA results showed high sulphide content, where one sample reached 0,61 wt. % sulphide content. Other samples contained relative high ability to buffer acidic reaction and thus showed no potential to produce acidic drainage. The samples were homogenous to each other with regard of crystal-area distribution of opaque phases and aspect-ratio of individual crystals and in this study no direct correlation between the sample’s crystal-area distribution of opaque phases and potential to produce acidic drainage was apparent.

Abstract The removal of overlying waste rock in open pit mines to dumps is conventionally undertaken by draglines or by trucks and shovels, or by a combination of these. Waste rock dumps are the largest remnant structures of open cut mining operations and can absorb a large proportion of the mine operating costs. If the dumps are not properly developed they can be excessively expensive and can become a major safety risk and environmental hazard. There are many examples worldwide where poor design and construction of waste rock dumps have resulted in failures causing considerable loss of life and widespread damage, or have resulted in erosion and seepage that have led to severe environmental pollution. The proper design and scheduling of waste rock dumps and haul routes can significantly reduce costs, minimise the possibility of failures, and avoid harming the environment. This Thesis is limited to the consideration of trucks and shovels for waste rock haulage in open cut mining operations. It describes the development and application of a waste rock dump scheduling model using the Operations Research technique of Mixed-Integer Linear Programming, implemented in the mathematical modelling language AMPL. The model focuses on minimising the haulage cost for each block of waste rock taken from the open pit and placed in the dump. Allowance is made for the selective placement of benign and reactive waste rock, based on an open pit block model that delineates benign and reactive waste rock. The formulation requires input data including the xyz-coordinates of the block model for the open pit, information on whether the waste rock blocks are benign or reactive, the proposed time scheduling of waste rock haulage from the open pit, unit haulage costs, and the geometry of the waste rock dump, including the delineation of the zones that are benign and those that are reactive. The model was successfully tested by using both simple test data and actual mine site data. The application of the model to a simple case confirmed that it produces results that meet the Objective Function in producing an optimal haulage time and cost, and meets the various Constraints imposed. This model for scheduling the removal of waste rock from open cut mining operations with trucks and shovels will require further research and testing and, because the results are generated in a numerical format, there will also be a need to convert them to a graphical format to facilitate their interpretation. Ultimately, it will have the potential to provide a relatively low-cost scheduling tool that meets operators’ economic, safety and environmental goals.

Sulfidförande berg förekommer på många platser i Sveriges berggrund. När sulfidförande berg losshålls frigörs nya ytor som utsätts för kontakt med syre och vatten, vilket oxiderar sulfidmineralen och berget vittrar. Vittringsprodukten kallas surt lakvatten. Syftet med arbetet har varit att undersöka hur det sura lakvattnet påverkar den omgivande miljön, och hur spridning av det kan förhindras, samt vilka teoretiska möjligheter och risker det finns för användning av sulfidförande berg i infrastrukturprojekt. När lakvattnet kommer i kontakt med omkringliggande vattendrag orsakar det försurning och förhöjda metallhalter. Det kan också orsaka geotekniska skador. För att på ett säkert sätt kunna återanvända bergmaterialet bör provtagning och provanalys utföras enligt representativa metoder och bedömning av omgivningens förutsättningar ske. De metoder som idag används är i stor grad utvecklade för gruvnäringen och behöver därför anpassas. Om materialet bedöms lämpligt för återanvändning eller om sulfidbärande bergmaterial oavsiktligt använts finns en mängd metoder för att minska negativ påverkan på omgivningen. Mest effektivt är förhindrande av bildning av lakvatten genom övertäckning eller mikroinkapsling. Det finns även metoder för att förhindra spridning av surt lakvatten, såsom kalkning eller olika typer av barriärer eller dräneringsbäddar. För att det losshållna berget ska kunna återanvändas behöver hänsyn tas till en mängd olika lagar och regler.  Inom ramen på projektet utfördes en fallstudie av ett område där sulfidförande berg losshållits och oavsiktligt använts som fyllnadsmaterial i lokala vägar. Detta har lett till att vattendraget som rinner genom området kraftigt förorenats med metaller och på vissa platser har mycket låga pH-värden. Sex metaller (Cd, Co, Cu, Ni, Pb and Zn) och sex andra parametrar (pH, Fe, fosfat, nitrat, sulfat och DOC) valdes ut för korrelationsanalys mellan metallerna och parametrarna med Kendall's Tau i fyra olika provpunkter. Statistiskt säkerställda korrelationer förekom mellan samtliga metaller och parametrar, men inte i alla punkter. Korrelationerna med pH och DOC var starkast, men även korrelationer med järn, fosfat och sulfat förekom enligt förväntan. Korrelationer med nitrat förekom med samtliga metaller men med oregelbundenhet och utan mönster. Biotillgänglighetsmodellering med verktyget bio-met utfördes för Cu, Ni, Pb och Zn. Biotillgängligheten var starkast relaterad till DOC-halten, men även samband med pH kunde statistiskt säkerställas. Ni och Zn var de metaller med högst biotillgänglighet. I vissa fall översteg den biotillgängliga koncentrationen HC5, gränsvärdet för skydd av 95 % av organismerna i vattendraget. I flera av punkterna över- eller underskred pH och kalciumhalten modellens godkända intervall. En utveckling av modellen för inkludering av fler förutsättningar och metaller är därför något att eftersträva. / Sulfide-bering rock is found in multiple places in Swedish bedrock. When blasted, new surfaces is exposed and weathering occurs. This has the consequence that Acid Rock Drainage (ARD), water with low pH and high concentrations of heavy metals is spread to local watercourses, the environment becomes toxic. The aim of this project was to investigate theoretical possibilities and risks with recycling of sulfide-bering rock in infrastructure projects, as well as to examine how ARD affects the surrounding environment and how spreading of ARD can be prevented. To safely recycle the rock, it needs to be sampled and analysed by proper methods and the conditions of the sorrounding environment evaluated. Methods for applying this in infrastructure projects is currently being developed. If used, there is multiple methods to prevent or mitigate the spreading of ARD. The most effective way is to prevent its forming by covering or microencapsling, but prevention of spreading can also be dealt with by liming or drainage beds. A case study was made of an area affected by ARD. Correlation analysis with Kendall's tau was conducted between six metals (Cd, Co, Cu, Ni, Pb and Zn) and six other parameters (pH, Fe, phosphate, nitrate, sulphate and DOC). The correlations between the metals and pH as well as DOC was the stongest. It was difficult to find a pattern in the correlations with nitrate. Bioavailability modelling with the Biotic Ligand model bio-met was also made. Ni and Zn hade the highest bioavailable concentrations and exceeded the limit for protection of 95 % of species in one (Zn) or two (Ni) measuring stations. Expanded models for bioavailability is needed, since they have narrow boundaries for water chemistry conditions and only exist for few metals.