The Prairie Creek Mine, NWT, is a non-producing Zn-Pb-Ag mine located within the Mackenzie Mountains. The 320 km2 area is surrounded by the Nahanni National Park Reserve, and is found approximately 40 km upstream of a UNESCO World Heritage Site. Geochemical characterization of weathered material in the area is useful from both an exploration geochemistry and environmental geochemistry perspective. This investigation attempted to characterize geochemical and mineralogical controls on metal mobility in natural and manufactured environments. Surface waters and sediments were sampled, analyzed, and interpreted. Detailed mineralogical analyses were also performed, including SEM, XRD, and synchrotron-based µXRF and µXRD. Prairie Creek contains sulphide and supergene mineralization hosted in carbonate rocks, which supply the area with a high pH, as well as a wealth of alkalinity and buffering capacity. This study aims to provide some insight as to the geochemical and mineralogical controls on the weathering processes which may enhance or inhibit mobility of metals downstream of known mineralization. Results show that the metals are found in much higher concentration in the stream sediments than in the stream waters. Pb and Zn show the highest concentrations, and Zn appears to be more mobile than Pb. Based on water versus sediment chemistry, it may be possible to differentiate between mineralization types. Dissolution textures and alteration of detrital grains indicates that chemical weathering does occur within the streams and releases metals to the aqueous environment, though they are likely quickly attenuated through adsorption or co-precipitation. The mine site hosts a historic ore stockpile and waste rock pile, established in the early 1980’s. Geochemical characterization of the reactions occurring within these piles and of the mineralogical controls on metal mobility can contribute to the mitigation of risk from leachate. Metal concentrations are variable and do not support a trend, which indicates that metal mobility within these piles may be attributed to micro-environments. There appears to be a trend in increasing alkalinity and decreasing sulphate towards the bottom of the piles. Therefore, metals appear to have limited mobility in the studied environments, although small scale chemical reactions are occurring which may release and attenuate metals. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2013-07-04 20:00:21.774

This study is part of the Diavik Waste-Rock Pile Project taking place at the Diavik Diamond Mine in the Northwest Territories, Canada. The project involves the construction of three 15m-scale low sulfide test waste-rock piles and monitoring of fluid flow, geochemical reactions, heat and gas transport within the waste-rock piles and characterization of the physical properties of the waste-rock piles. The focus of this thesis is characterizing grain-size distribution of the waste-rock and quantifying gas transport in the test waste-rock piles. Grain size of waste rock ranges from millimeters to meters. Sieve analysis typically only provides information of grain size <0.1 m at a single location. A computer program was developed using digital image-processing techniques to obtain a spatial grain-size distribution from photographs of tip faces of the test waste-rock piles acquired in the field. The program characterizes grain size >0.1 m and employs a region-growing algorithm for segmentation of waste-rock grains with pre- and post-processing techniques to improve the accuracy of segmentation. The program was applied to photographs of six different tip faces of the test waste-rock piles. For grain size <0.1 m, data from sieve analyses were attached to the grain-size curves generated from image grain-size analyses to obtain a full spectrum grain-size analyses ranging from boulders to fines. The results show that fine fractions are retained at the top of the tip faces and grain size increases non-linearly from top to bottom of a waste-rock pile. Calculations show that although the greatest mass is associated with the medium and coarse fractions, the greatest surface area is associated with the fine fractions. The results are consistent with field observation that the initial solute concentrations are greatest at the top of the pile and saturated hydraulic conductivity are lower at the top of the pile than in the pile interior. Statistical moments show that the test waste-rock piles have mean grain size of granules and are very poorly sorted, coarse skewed and leptokurtic. Permeability is calculated using empirical formulae and good agreement is obtained between calculated values and field measurements. The heterogeneity of grain size obtained from this study can provide a basis for future modeling efforts. Gas transport analysis focused on 1) substantiating the relationship between wind flow external to the waste-rock pile and gas pressures within the pile, 2) determining the gas flow regime in the pile, and 3) quantifying the temporal variation in wind speed and direction and determining the relevant time scales. Differential gas pressures were measured in 2008 at 49 locations within one of the three test waste-rock piles and 14 locations on the surface of the pile at one-minute intervals. Wind speed and direction were measured at 10-min intervals. Correlations between wind vectors and pressure measurements show that the wind influences pressure fluctuations in the test pile. The strength of the correlation is roughly inversely proportional to the distance between measurement ports and the atmospheric boundary. The linear relationship between internal pressure measurements and surface pressure measurements demonstrate that gas flow is Darcian within the test waste-rock pile. Spectral analysis of wind data and a one-dimensional analytical solution to the flow equations show that the persistence of wind in a certain direction has most pronounced effects on transient gas flow within the pile. The penetration depth of wind-induced gas pressure wave is a function of the periodicity of the wind and permeability of the waste-rock pile.

No description available.

An experimental waste-rock pile (50m x 60m x 15m, 0.053 wt. % S) was constructed at the Diavik Diamond Mine, in the Northwest Territories, Canada to evaluate the generation of acid-rock drainage and the seasonal and annual release of various metals in drainage leachate. A dense internal instrumentation network enabled well resolved observations of temperature, air content, water content, fluid flow, microbiology, mineralogy and geochemistry within the waste-rock pile. Water samples were collected from soil water solution samplers (SWSSs) to measure core pore-water characteristics, from 4 m2 to 16 m2 scale basal collection lysimeters (BCLs) to measure core leachate characteristics, and from basal drains (3000 m2 basal area) to measure aggregated leachate characteristics. Monitoring of pore-water geochemistry within the core of the test pile indicated an evolving weathering front characterized by changes in predominant acid-consuming mineral-dissolution reactions. Initially, acid neutralization occurred through dissolution of carbonate minerals. A subsequent decline in pH was limited by acid neutralization through dissolution of Al- and Fe-bearing minerals. This lower pH environment was accompanied by increasing concentrations of SO4, Al, Fe, Ni, Co, Cu, Zn, Cd, Ca, Mg, K, Na and Si. Annual drainage cycles in the core of the test pile were characterized by distinct, high concentration ‘spring flushes’ followed by a steady decline of all dissolved constituents with minimums prior to freeze-up. Core trends were typical of freshets observed in polar environments and primarily explained by a combination of fluid residence time and the build-up of oxidation products over the winter. The opposite trend was observed in the aggregated pile drainage, whereby early-season low-concentration leachate was derived from snowmelt and batter flow and late-season high-concentration leachate was dominated by contributions from the core of the pile. Thermal data demonstrating the annual freeze-thaw cycle was used to delineate core and batter subsystems within the pile. Mean annual solute concentrations and geochemical speciation modelling results revealed two different environments within these subsystems. Concentrations in the core of the test pile were 2.5 to 8.5 times greater than concentrations in the batter. Dilution through snowmelt contributions and shorter flow pathways were expected to control solute concentrations in the batter subsystem. Aggregated basal leachate loading exhibited a linear annual increase for all ARD reaction products, with the maximum annual release observed in 2012. Between 2007 and 2012 core flow accounted for 13 % of the total drainage volume; whereas 35 to 51 % of major and trace metal loads were attributed to this zone. Parameter correlation analysis and core contribution estimates were used to identify common source minerals for elements and infer mechanisms controlling the mobility of dissolved metals (sorption, co-precipitation and precipitation-dissolution). By 2012, the release of pyrrhotite oxidation products from the < 5 mm reactive fraction of waste rock reached as high as 5.1 %, 9.0 %, 7.2 % and < 0.1 % for S, Ni, Co and Fe respectively. The results of this study indicate that a comprehensive understanding of thermal cycling is imperative when estimating seasonal and annual releases of weathering products from waste rock. Observations of active zone dynamics and the temporal and spatial evolution of waste rock drainage loading recognized in this study will assist in the advancement of reactive transport models describing ARD in cold climates.

This study is part of the Diavik Waste-Rock Pile Project taking place at the Diavik Diamond Mine in the Northwest Territories, Canada. The project involves the construction of three 15m-scale low sulfide test waste-rock piles and monitoring of fluid flow, geochemical reactions, heat and gas transport within the waste-rock piles and characterization of the physical properties of the waste-rock piles. The focus of this thesis is characterizing grain-size distribution of the waste-rock and quantifying gas transport in the test waste-rock piles. Grain size of waste rock ranges from millimeters to meters. Sieve analysis typically only provides information of grain size <0.1 m at a single location. A computer program was developed using digital image-processing techniques to obtain a spatial grain-size distribution from photographs of tip faces of the test waste-rock piles acquired in the field. The program characterizes grain size >0.1 m and employs a region-growing algorithm for segmentation of waste-rock grains with pre- and post-processing techniques to improve the accuracy of segmentation. The program was applied to photographs of six different tip faces of the test waste-rock piles. For grain size <0.1 m, data from sieve analyses were attached to the grain-size curves generated from image grain-size analyses to obtain a full spectrum grain-size analyses ranging from boulders to fines. The results show that fine fractions are retained at the top of the tip faces and grain size increases non-linearly from top to bottom of a waste-rock pile. Calculations show that although the greatest mass is associated with the medium and coarse fractions, the greatest surface area is associated with the fine fractions. The results are consistent with field observation that the initial solute concentrations are greatest at the top of the pile and saturated hydraulic conductivity are lower at the top of the pile than in the pile interior. Statistical moments show that the test waste-rock piles have mean grain size of granules and are very poorly sorted, coarse skewed and leptokurtic. Permeability is calculated using empirical formulae and good agreement is obtained between calculated values and field measurements. The heterogeneity of grain size obtained from this study can provide a basis for future modeling efforts. Gas transport analysis focused on 1) substantiating the relationship between wind flow external to the waste-rock pile and gas pressures within the pile, 2) determining the gas flow regime in the pile, and 3) quantifying the temporal variation in wind speed and direction and determining the relevant time scales. Differential gas pressures were measured in 2008 at 49 locations within one of the three test waste-rock piles and 14 locations on the surface of the pile at one-minute intervals. Wind speed and direction were measured at 10-min intervals. Correlations between wind vectors and pressure measurements show that the wind influences pressure fluctuations in the test pile. The strength of the correlation is roughly inversely proportional to the distance between measurement ports and the atmospheric boundary. The linear relationship between internal pressure measurements and surface pressure measurements demonstrate that gas flow is Darcian within the test waste-rock pile. Spectral analysis of wind data and a one-dimensional analytical solution to the flow equations show that the persistence of wind in a certain direction has most pronounced effects on transient gas flow within the pile. The penetration depth of wind-induced gas pressure wave is a function of the periodicity of the wind and permeability of the waste-rock pile.

The Aitik Mine is the largest copper mine in Europe and every year, 15 – 20 Mt waste rock is deposited in dumps located close to the mine. This waste rock can contain sulfides, which if exposed to oxygen can cause leeching and formation of acid rock drainage. To prevent this from happening, Boliden has designed a dry cover system to prevent leaching from occurring. The purpose of this study was to characterize existing stockpiles of till at Boliden’s Aitik Mine site in the context of requirements for the closure cover system. The till was evaluated primarily of its suitability for use in a highly compacted layer (HCL), since Boliden has a cover system design that has to provide the necessary control on oxygen diffusion rates to underlying waste rock material over the long term. The sampling took place on three of the stockpiles and a total of 31 test pits were excavated. A total of 27 samples of soil were collected and analyzed for particle size distribution (PSD) testing. Following review of PSD results, select samples were tested for hydraulic conductivity and compaction testing. The PSD results showed that all materials were fine-grained sand with some gravel, cobbles and silt. Results also show the amount of clay particles (0,004 mm) were relatively low across the three stockpiles. The result for the hydraulic conductivity were higher than Boliden’s prescriptive criteria. The results indicate that the sampled till would require addition of sodium bentonite to be able to construct a HCL with a hydraulic conductivity not exceeding Boliden’s criteria.

Mittels künstlichen neuronalen Netzen wurden die in den rekultivierten Tagebaukippen im Nordraum Lausitz (Tagebaue Schlabendorf und Seese) auftretenden Geländedeformationen infolge Bodenverflüssigung für die Jahre 2009 - 2013 als Zeitreihe modelliert. Das Modell ist in der Lage, grob die zeitliche Entwicklung und exakt die räumliche Lage des in den Kippen auftretenden Gefährdungspotenzials nachzuvollziehen und als Funktion des sich ändernden Grundwasserspiegels und der sich ändernden Oberflächenmorphologie in die Zukunft zu prognostizieren. Das Modell zeigt dynamisch das Entstehen neuer Risikoflächen in bisher scheinbar stabilen Bereichen des Untersuchungsgebietes. Die Korrektheit des Modells wurde mittels verschiedener Tests geprüft sowie anhand einer Prognoserechnung für das Jahr 2014 und des Vergleichs mit den real in 2014/2015 gegangenen Ereignissen nachgewiesen. Folgende Gefährdungsfaktoren wurden ermittelt: Destabilisierend wirken eine möglichst einförmige Lithologie folgender Zusammenset-zung: 31 % Feinsand, 34 % Mittelsand, 31 % Grobsand, 3 % Schluff, < 1 % Kies, < 1 % Kalk, < 1 % Ton, < 1 % Kohle, kf-Werte zwischen 10-4 und 10-4,5 m/s, ein Grundwasserflurabstand bei 3,45 m (Medianwert), möglichst hohe Gradienten der nicht lithologisch kontrollierten Parameter: Tagebauoberfläche, Grundwasseroberfläche, Grundwasserflurabstand und Mächtigkeit der gesättigten Kippe. Stabilisierend wirken vor allem eine möglichst große Heterogenität der Lithologie auf kleinem Raum (möglichst hohe Gradienten der lithologisch kontrollierten Parameter (z.B. Kiesgehalt, Sandgehalt, Tongehalt, Kohlegehalt)), ein möglichst geringer Sandanteil, möglichst hohe Anteile an Kies, Schluff, Ton, Kalk, bzw. Kohle, ein möglichst großer Grundwasserflurabstand sowie möglichst geringe Gradienten der nicht lithologisch kontrollierten Parameter: Tagebauoberfläche, Grundwasseroberfläche, Grundwasserflurabstand, Mächtigkeit der gesättigten Kippe sowie wechselnde kf-Werte 10-7 bzw. >10-2 m/s. Für die Bearbeitung wurden ausschließlich die bei der LMBV vorhandenen bzw. laufend flächendeckend erhobenen Daten genutzt: Lage des Grundwasserspiegels, Relief der Tagebauoberfläche, Liegendes der Kippe, geologische Daten der Vorfeldbohrungen. Das Modell kann als dynamisches Instrument zum Risikomanagement vor bzw. während der Sanierungsmaßnahmen genutzt werden. Mittels der Variation der prozesskontrollie-renden Parameter können die geotechnischen Auswirkungen verschiedener Sanierungsszenarien (z.B. Gestaltung der Tagebauoberfläche, Schüttung der Kippen, Grundwasseranstieg) auf die Stabilität der Kippen prognostiziert werden. / Geotechnical events (terrain deformation due to soil liquefaction) in lignite mining waste rock piles of the northern Lausitz area (opencast pits Schlabendorf and Seese), have been modeled as time series for the years 2009 – 2013 by using artificial neural networks. The model has clearly recognized the influences of various lithological and non-lithological controlled parameters on the occurrence of geotechnical events, and these have been quantified and weighted in terms of their importance. The model is able to predict the tem-poral evolution and the exact spatial location of the events occurring in the dumps as a function of changing groundwater levels and surface morphology. The model shows dynamically the emergence of new risk areas in hitherto seemingly stable areas. The correctness of the model was confirmed by means of various tests and its predictive success was demonstrated through forecasting of events for the years 2014 and 2015 and their comparison with the observed events of those years. The following main risk factors were identified: Important destabilizing factors are a monotonous lithology with the following composition: 31% fine sand, 34% medium sand, 31% coarse sand, 3% silt, <1% gravel, <1% lime, <1% clay, <1% coal, kf-values between 10-4 and 10-4.5 m/s, a surface to groundwater distance of 3.45 meters (median value), high gradients of non-lithological controlled parameters: waste dump surface, groundwater level, depth to groundwater and thickness of saturated dump. 2. Important stabilizing factors are a high heterogeneity of lithology (high gradients of the lithological controlled parameters: e.g. gravel content, sand content, clay content, carbon content), a low proportion of sand in the dump composition, high proportions of gravel, silt, clay, lime, or coal, a high depth to groundwater, low gradients of non-lithological controlled parameters: open pit surface, groundwater surface, depth to groundwater, thickness of saturated dump, strongly changing kf values between 10-7 and 10-2 m/s. The model can be used as a dynamic tool for risk management before and during the re-habilitation of lignite waste dumps, and for constructing stable waste dumps. By means of varying the model parameters (e.g. design of the dump surface, composition of dumped rocks, rising groundwater) the geotechnical effects of dump design and remediation scenarios can be predicted.

Ammonium-nitrate based explosives (NH4NO3) used within the operations of Kiruna iron ore mine release nitrate (NO3-) into the environment, potentially having adverse effects on local river-systems. One way of reducing NO3- impacts to the environment is through a woodchip denitrifying bioreactor (DBR). Waste rock leachate is collected and passed through the bioreactor, where denitrifying microbial communities reduce NO3- to nitrogen gas (N2) using a carbon energy source. However, the efficiency of the DBR present in Kiruna iron ore mine has declined since the start of its operation leading to lower values of NO3-removal throughout the years.  Denitrification being a temperature dependent process, a heating device was installed to warm up the water prior to the DBR treatment to counterbalance this decrease. The effect of which has been assessed within this thesis. Chemical analyses encompassing NO3-, nitrite (NO2-), ammonium (NH4+), total organic carbon (TOC), phosphorus compounds (tot-P, PO4-P), and bacterial abundance were then investigated along a flowpath in the DBR. Overall, the results have shown that with an increase in temperature prior to the treatment, TOC, tot-P, PO4-P release was improved. Moreover, NO3- removal doubled compared to the previous year. TOC, tot-P and PO4-P are the result of the hydrolysis process, transforming the woodchips in available carbon source and providing nutrients for the bacteria to perform denitrification. Similarly, the bacterial abundance presented a significant increase with temperature. This suggest that both hydrolysis and bacteria growth enhancement with temperature ultimately participated in the improvement of the denitrification reaction. Moreover, a long-lasting effect of temperature on NO3- removal was observed during a following cold period as NO3- removal stayed above 45% after two months without heating. It is suggested that the cost of heating can be reduced by inducing “heat pulse” instead of continuous heating. Adding a heating system prior to treatment represents a promising solution for the future of sustainable mining, particularly for mines located in extreme climates such as Kiruna. / NITREM

O presente estudo trata da determinação da resistência de aderência de três rochas: arenito, mármore e quartzito assentados com três diferentes argamassas (industrializada, resíduo e para porcelanato). Os ensaios de resistência de aderência à tração foram executados tanto na face lisa como na não polida (natural) dos corpos de prova e seguiram a norma NBR 14084 utilizada para material cerâmico. Os resultados obtidos foram diferentes para os conjuntos argamassas/rochas, entretanto evidenciaram o melhor desempenho da argamassa para porcelanato em todas as determinações. Alguns resultados anômalos verificados em algumas combinações foram explicados pelas características petrográficas (composição mineral, textura e estrutura), evidenciando sua relevante influência nos valores obtidos de resistência de aderência à tração. / The present study deals with the determination of bond strength of three stones: sandstone, marble and quartzite seated with three different mortars (industrialized, waste and porcelain). Tests on tension bond strength were performed in both the smooth face and the non-polished (natural) of the specimens and followed NBR 14.084 used for ceramic material. The results were different for the joint mortar/stone, but showed the best performance of the mortar for porcelain tile in all determinations. Some anomalous results observed in some combinations were explained by petrographics characteristics (mineral composition, texture and structure), indicating its important influence on the values of tension bond strength.

The percolation of water through waste rock dumps at mine sites can lead to the production of a leachate with high concentrations of dissolved metals, sulfate and nitrogen compounds. It is important to understand how water flows in waste rock dumps in order to predict the environmental impact of this leachate on recipients. The dynamics of percolation and leachate discharge are controlled by climatological conditions at the site, where relatively large flows in northern Sweden correspond to snowmelt during late Spring. Rock dumps are often tens of meters in height, resulting in an unsaturated water flow system through heterogeneous material. Hence, the simulation of leachate generation requires an accurate representation of the subsurface materials as well as the flow processes, where water flow in waste rock dumps is dominated by matrix flow with macropore flow being of secondary importance. Matrix flow is rather slow and may thus potentially yield relatively high concentrations of contaminants in the leachate, in response to precipitation and snow melt. This study uses Hydrus-1D to predict leachate generation from a small-scale waste rock dump in Kiruna in terms of discharge magnitude and timing. The 3-dimensional geometry of the waste rock dump is approximated by summing simulations from 1225 one-dimensional columns of different length, with a surface area of 1 m2 each. There are four output parameters that are compared between the model results and measured data: snow accumulation, water content, temperature, and discharge. There are some discrepancies between the model results and field measurements, most likely due to uncertainties in the input parameters (especially waste rock properties), limitations in the Hydrus-1D model (i.e. freeze-thaw dynamics), and assumptions that are used in constructing the conceptual model. For better agreement between model results and measured data, a new modelling approach is recommended, potentially using a different program than Hydrus-1D.