Applied Geochemistry (v.36, #C)
Using dual isotopes to evaluate sources and transformation of nitrogen in the Liao River, northeast China by Fu-Jun Yue; Si-Liang Li; Cong-Qiang Liu; Zhi-Qi Zhao; Jian Hu (1-9).
The Liao River Basin is one of seven primary river Basins in China. The concentration of dissolved inorganic N (DIN), dual isotopes of NO 3 - using the denitrifier method, the N isotopes of NH 4 + and the N flux in the basin were determined to identify the sources of N and their transformation. The results show that NO 3 - ranges from 0.3 μmol/L to 1316 μmol/L. In general, NO 3 - is the dominant inorganic N species during both flow seasons, but the fraction of NO 3 - /DIN is variable and high NH 4 + is present in some waters. Samples collected from the up-stream portion of the Liao River typically had N isotope values of <+8‰, while those from the middle and lower portions had values of >+8‰ during the high flow season. Most water samples had O isotope values of <+10‰ during the high flow season. During the low flow season, the ranges of N and O isotopic values were limited, with average values of +10.3‰ and +4.9‰, respectively. There is a wider isotopic range of NO 3 - during the high flow season than the low flow season. The isotopic pattern of NO 3 - suggests that wastewater and soil organic N are the sources of NO 4 + during the high flow season, while wastewater is the main source during low flow season. It appears that no intense denitrification occurs in the river according to the isotopic and chemical data. The N flux of the Liao River system entering the Liao Dong Bay annually is nearly 7.0 × 104 tons, which amounts to 5.0% of the N from chemical fertilizers used in this basin.
U–Pb, Rb–Sr, and U-series isotope geochemistry of rocks and fracture minerals from the Chalk River Laboratories site, Grenville Province, Ontario, Canada by L.A. Neymark; Z.E. Peterman; R.J. Moscati; R.H. Thivierge (10-33).
As part of the Geologic Waste Management Facility feasibility study, Atomic Energy of Canada Ltd. (AECL) is evaluating the suitability of the Chalk River Laboratories (CRL) site in Ontario, situated in crystalline rock of the southwestern Grenville Province, for the possible development of an underground repository for low- and intermediate-level nuclear waste. This paper presents petrographic and trace element analyses, U–Pb zircon dating results, and Rb–Sr, U–Pb and U-series isotopic analyses of gneissic drill core samples from the deep CRG-series characterization boreholes at the CRL site. The main rock types intersected in the boreholes include hornblende–biotite (±pyroxene) gneisses of granitic to granodioritic composition, leucocratic granitic gneisses with sparse mafic minerals, and garnet-bearing gneisses with variable amounts of biotite and/or hornblende. The trace element data for whole-rock samples plot in the fields of within-plate, syn-collision, and volcanic arc-type granites in discrimination diagrams used for the tectonic interpretation of granitic rocks.Zircons separated from biotite gneiss and metagranite samples yielded SHRIMP-RG U–Pb ages of 1472 ± 14 (2σ) and 1045 ± 6 Ma, respectively, in very good agreement with widespread Early Mesoproterozoic plutonic ages and Ottawan orogeny ages in the Central Gneiss Belt. The Rb–Sr, U–Pb, and Pb–Pb whole-rock errorchron apparent ages of most of the CRL gneiss samples are consistent with zircon U–Pb age and do not indicate substantial large-scale preferential element mobility during superimposed metamorphic and water/rock interaction processes. This may confirm the integrity of the rock mass, which is a positive attribute for a potential nuclear waste repository. Most 234U/238U activity ratios (AR) in whole rock samples are within errors of the secular equilibrium value of one, indicating that the rocks have not experienced any appreciable U loss or gain within the past 1 Ma. However, 234U/238U AR in fracture mineral samples collected down to borehole lengths of about 740 m deviate from the secular equilibrium value and 234U/238U model ages calculated for fracture mineral samples showing excess 234U range from 593 to 1415 ka, thus providing evidence of fracture flow in the associated bedrock during the past 1.5 Ma. Rare earth element patterns are variable in fracture-filling calcites and Fe oxides/hydroxides but are similar to those observed in associated whole-rock samples. The observed Ce anomalies are very small ( Ce N / Ce N ∗ ≈ 1 ), do not vary with depth, and, therefore, do not contain evidence that the studied fracture minerals precipitated from oxidizing waters at the conceptual depth of a repository.
Anthropogenic impacts on mineral weathering: A statistical perspective by Fernando A.L. Pacheco; Paulo M.B. Landim; Teodora Szocs (34-48).
Correspondence Analysis was adopted as tool for investigating the statistical structure of hydrochemical and weathering datasets of groundwater samples, with the main purpose of identifying impacts on mineral weathering caused by anthropogenic activities, namely fertilizing of farmlands. The hydrochemical dataset comprised measured concentrations of major inorganic compounds dissolved in groundwater, namely bicarbonate, silica (usually by-products of chemical weathering), chloride, sulphate and nitrate (typically atmospheric plus anthropogenic inputs). The weathering dataset consisted of calculated mass transfers of minerals being dissolved in loess sediments of a region located in SW Hungary (Szigetvár area), namely Na-plagioclase, calcite and dolomite, and of pollution-related concentrations of sodium, magnesium and calcium. A first run of Correspondence Analysis described groundwater composition in the study area as a system of triple influence, where spots of domestic effluents-dominated chemistries are surrounded by areas with agriculture-dominated chemistries, both imprinted over large regions of weathering dominated chemistries. A second run revealed that nitrification of N-fertilizers is promoting mineral weathering by the nitric acid reaction (anthropogenic pathway), in concurrence with the retreating of weathering by carbonic acid (natural pathway). It also indicated that dolomite and calcite are being players in a dedolomitization process driven by dissolution of gypsum fertilizers and nitrification of N-fertilizers.
Mobilization of arsenic from mine tailings through reductive dissolution of goethite influenced by organic cover by Dogan Paktunc (49-56).
Display OmittedMine tailings at the former Delnite gold mine in northern Ontario were characterized to assess the impact of a biosolids cover on the stability of As species and evaluate options for long-term management of the tailings. Arsenic concentrations in the tailings range from 0.15 to 0.36 wt% distributed among goethite, pyrite and arsenopyrite. Pyrite and arsenopyrite occur as small and liberated particles that are enveloped by goethite in the uncovered tailings and the deeper portions of the biosolids-covered tailings. Sulfide particles in the shallower portions of the biosolids-covered tailings are free of goethite rims. Arsenic occurs predominantly as As5+ with minor amount of As1− in the uncovered tailings. Coinciding with the disappearence of goethite rims on sulfide particles, the biosolids-covered tailings have As3+ species gradually increasing in proportion towards the cover. Leaching tests indicated that the As concentrations in the leachate gradually increase from less than 0.085 to 13 mg/L and Fe from 28 to 179 mg/L towards the biosolids cover. These are in sheer contrast to the leachate concentrations of less than 0.085 mg/L As and 24–64 mg/L Fe obtained from the uncovered tailings confirming the role of biosolids-influenced reduction and mobilization of As in the form of As3+ species. The evidence suggests that reductive dissolution of goethite influenced by the biosolids-cover caused the mobilization of As as As3+ species.
Geochemistry, water balance, and stable isotopes of a “clean” pit lake at an abandoned tungsten mine, Montana, USA by Christopher H. Gammons; Barbara L. Pape; Stephen R. Parker; Simon R. Poulson; Carrine E. Blank (57-69).
The Calvert Mine is a small tungsten-rich (scheelite) skarn deposit in a remote, mountainous region of southwest Montana, USA. The open-pit mine closed in the 1970s and subsequently flooded to form a pit lake that is roughly conical in shape, 30 m deep and 120 m in diameter, with no surface inlet or outlet. The lake is holomictic with a groundwater flow-through hydrology and an estimated residence time of 2.5–5 y. Water isotopes show that the lake is at an approximate steady state with respect to water balance and has experienced 30% evaporation. The lake has a near-neutral pH, exceptional clarity, and extremely low concentrations of nutrients, sulfate, and most metals, including tungsten. Manganese concentrations are slightly elevated and increase with depth towards the sediment–water interface. Despite seasonally anoxic conditions in the deep water, dissolved Fe concentrations are orders of magnitude lower than Mn, suggesting that insufficient organic carbon is present in the sediment of this oligotrophic lake to drive bacterial Fe reduction. Based on stable isotope fingerprinting, diffuse seepage that enters a nearby headwater stream at the base of a large waste-rock pile can be directly linked to the partially evaporated pit lake. However, this seepage has neutral pH and low metal concentrations, and poses no threats to the environment. Stable isotopes of dissolved inorganic carbon (DIC) and dissolved oxygen (DO) are used to track the relative importance of photosynthesis and respiration with depth. In summer, a zone of high productivity exists near the base of the chemocline, releasing DO that is isotopically light. Respiration exceeds photosynthesis below the Secchi depth, which causes DO concentrations to approach zero towards the bottom of the lake. In winter, thick ice and snow cover prohibits photosynthesis. However, because of the low nutrient content, most of the volume of the lake remains oxic through the winter. Overall, the Calvert Lake is a good example of a pit lake formed from metal mining that has excellent water quality, which is a result of its favorable geology (paucity of sulfide minerals) and hydrology (flow-through lake with short residence time in a temperate climate).
Reconstructing the sedimentation history of the Bengal Delta Plain by means of geochemical and stable isotopic data by Harald Neidhardt; Ashis Biswas; Dominik Freikowski; Santanu Majumder; Debashis Chatterjee; Zsolt A. Berner (70-82).
The purpose of this study is to examine the sedimentation history of the central floodplain area of the Bengal Delta Plain in West Bengal, India. Sediments from two boreholes were analyzed regarding lithology, geochemistry and the stable isotopic composition of embedded organic matter. Different lithofacies were distinguished that reflect frequent changes in the prevailing sedimentary depositional environment of the study area. The lowest facies comprises poorly sorted fluvial sediments composed of fine gravel to clay pointing at high transport energy and intense relocation processes. This facies is considered to belong to an early Holocene lowstand systems tract that followed the last glacial maximum. Fine to medium sands above it mark a gradual change towards a transgressive systems tract. Upwards increasing proportions of silt and the stable isotopic composition of embedded organic matter both indicate a gradual change from fluvial channel infill sediments towards more estuarine and marine influenced deposits. Youngest sediments are composed of clayey and silty overbank deposits of the Hooghly River that have formed a vast low-relief delta-floodplain. Close to the surface, small concretions of secondary Mn-oxides and Fe-(oxyhydr)oxides occur and mark the fluctuation range of the unsaturated zone. These concretions are accompanied by relatively high contents of trace elements such as Zn, Ni, Cu, and As. To sum up, the outcomes of this study provide new insights into the complex sedimentation history of the barely investigated central floodplain area of West Bengal.
The nature and distribution of Cu, Zn, Hg, and Pb in urban soils of a regional city: Lithgow, Australia by Marek Rouillon; Damian B. Gore; Mark P. Taylor (83-91).
This study investigates the concentration and spatial distribution of Cu, Zn, Hg and Pb in the surface (0–2 cm) soils of a regional city in Australia. Surface soils were collected from road sides and analysed for their total Cu, Zn, Hg and Pb concentrations in the <180 μm and <2 mm grain size fractions. The average metal concentration of surface soils, relative to local background soils at 40–50 cm depth, are twice as enriched in Hg, more than three times enriched in Cu and Zn, and nearly six times as enriched in Pb. Median surface soil metal concentration values were Cu – 39 mg/kg (682 mg/kg max), Zn – 120 mg/kg (4950 mg/kg max), Hg – 44 μg/kg (14,900 μg/kg max) and Pb – 46 mg/kg (3490 mg/kg max). Five sites exceeded the Australian NEPC (1999) 300 mg/kg guideline for Pb in residential soils. Strong positive correlations between Cu, Zn and Pb, coupled with the spatial distribution of elevated soil concentrations towards the city centre and main roads suggest traffic and older housing as major sources of contamination. No spatial relationships were identified between elevated metal loadings and locations of past or present industries.
Surface complexation modeling for sulfate adsorption on ferrihydrite consistent with in situ infrared spectroscopic observations by Keisuke Fukushi; Kazuki Aoyama; Chen Yang; Norio Kitadai; Satoru Nakashima (92-103).
Sulfate, a major anion in nature, can affect the mobility of coexisting dissolved toxic trace elements by influencing the adsorption properties of the species on mineral surfaces. Ferrihydrite is an important scavenger for trace elements in natural water because of its adsorption capacity and its ubiquitous formation in surface conditions. To elucidate the adsorption behavior of the trace elements in natural water, it is important to construct a predictive model of sulfate adsorption on ferrihydrite that can predict the adsorption behavior of sulfate quantitatively under widely various environmental conditions based on the spectroscopic information of sulfate adsorption. In situ infrared spectra for sulfate adsorption on ferrihydrite as a function of pH (3–7), ionic strength (I = 0.01 and 0.1) and sulfate loading ([ SO 4 2 - ] = 0.1 and 0.2 mM) were obtained to constrain the surface speciation of sulfate on ferrihydrite. The shape of the spectra was pH-dependent. The degree of ν 3 band splitting decreases with pH. Little difference of the spectra was found between different ionic strengths and sulfate loadings for the same pH. The little influence of ionic strength on the IR spectra reflects that the inner sphere and outer sphere species most likely do not exist simultaneously in the same pH conditions. Based on the IR spectra obtained from lower pH showing the splitting of ν 3 band to two peaks with activation of ν 1 band, the surface species is identified to be single inner sphere monodentate sulfate. The changes of spectra with pH are most likely attributable to the changes of the electric field strength posed to the sulfate on ferrihydrite surface, which is strongly pH-dependent.The predictive model for sulfate adsorption was constructed using an extended triple-layer model (ETLM). The pH adsorption edges and proton surface charges in the presence of sulfate as a function of ionic strength and sulfate concentration were obtained, respectively, from batch adsorption and acid–base titration experiments. The sulfate adsorption on ferrihydrite increases continuously with decreasing pH and ionic strength. These macroscopic adsorption data were analyzed using ETLM to retrieve the sulfate adsorption reaction and the equilibrium constant. Results of ETLM analyses showed that adsorption of sulfate on ferrihydrite is a single monodentate inner sphere process that is consistent with in situ infrared spectroscopic observation, as expressed by the following complexation reaction: 2 FeOH + H + + SO 4 2 - = ( FeOH) ( FeOSO 3 - ) + H 2 O, where >FeOH denotes a surface hydroxyl. Batch adsorption data from earlier studies of sulfates on ferrihydrite were reasonably reproduced using ETLM with the same adsorption reaction and equilibrium constant.Prediction of the effect of sulfate on trace dissolved anionic species adsorption on ferrihydrite was conducted using previously reported adsorption parameters for iodine and arsenic. The predictions showed that the adsorption of I− and As(V) on ferrihydrite were diminished because of the competition with sulfate, although the adsorption of IO 3 - and As(III) were enhanced in the presence of sulfate. The sulfate surface species ( ( FeOH) ( FeOSO 3 - ) ) possesses net negative charge. To compensate the negative surface charge, the formations of net positive surface species, which are dominant IO 3 - and As(III) surface species, are enhanced. The predictions demonstrated that sulfate strongly influences the adsorption behavior of trace anionic species on a ferrihydrite surface.
Sorption of U(VI) onto Opalinus Clay: Effects of pH and humic acid by C. Joseph; M. Stockmann; K. Schmeide; S. Sachs; V. Brendler; G. Bernhard (104-117).
Display OmittedThe sorption of U(VI) onto Opalinus Clay, a natural clay rock from Mont Terri, Switzerland, was investigated as a function of pH in the absence and presence of humic acid (HA) under aerobic conditions ([U(VI)] = 1 × 10−6 M, [HA] = 50 mg/L, I = 0.1 M NaClO4, S/L = 4 g/L, pH 3–10). Due to leaching of Opalinus Clay, several competing ions are present in solution, where especially Ca2+ and CO 3 2 - ions affect the speciation of U(VI) and HA in solution and consequently, their sorption properties. From pH 7.0 to 8.2, the Ca2UO2(CO3)3(aq) complex predominates U(VI) speciation and sorbs only weakly onto Opalinus Clay. In the case of HA, the CaHA(II) complex dominates HA speciation over a wide pH range. However, in the pH range 4.2–6.7, the presence of HA leads to the formation of the aquatic complex UO2(OH)HA(I), which decreases U(VI) sorption. In the pH range from pH 7.5–10, HA seems to have no significant influence on the U(VI) sorption. The sorption characteristics of U(VI) on Opalinus Clay in the absence of HA were predicted using PHREEQC. Thereby, the investigation was focused on the influence of the different mineral binding sites on U(VI) sorption onto Opalinus Clay.
Circulation of water masses in the Baltic Proper revealed through iodine isotopes by P. Yi; X.G. Chen; A. Aldahan; G. Possnert; X.L. Hou; Z.B. Yu; D.H. Xiong; B. Wang (118-124).
Tracer technology has been used to understand water circulation in marine systems where the tracer dose is commonly injected into the marine waters through controlled experiments, accidental releases or waste discharges. Anthropogenic discharges of 129I have been used to trace water circulation in the Arctic and North Atlantic Ocean. Here, 129I, together with 127I, is utilized as a tracer of water pathways and circulation in the Baltic Sea through collection of seawater depth profiles. The results indicate the presence of 129I signatures which are distinct for each water mass and provide evidence for: (1) inflow water masses through the Drogden Sill that may reach as far as the SW of the Arkona Sea, (2) a portion of North Atlantic water in the bottom of Arkona basin, (3) cyclonic upwelling which breaks through the halocline in a pattern similar to the Baltic haline conveyor belt and (4) more influx of fresher water from the Gulf of Finland and Bothnian Sea in August relative to April. These findings provide advances in labeling and understanding water pathways in the Baltic Sea.
Competitive interaction between soil-derived humic acid and phosphate on goethite by Zhiyou Fu; Fengchang Wu; Kang Song; Ying Lin; Yingchen Bai; Yuanrong Zhu; John P. Giesy (125-131).
In order to better understand the influence and mechanism of soil-derived humic acid (SHA) on adsorption of P onto particles in soils, the amounts of PO4 adsorbed by synthetic goethite (α-FeOOH) were determined at different concentrations of SHA, pH, ionic strength and order of addition of adsorbents. Addition of SHA can significantly reduce the amount of PO4 adsorption as much as 27.8%. Both generated electrostatic field and competition for adsorption sites were responsible for the mechanism by which SHA inhibited adsorption of PO4 by goethite. This conclusion was supported by measurement of total organic C (TOC), infrared spectral features and Zeta potential. Adsorption of PO4 onto goethite was inversely proportional to pH. Order of addition of PO4 and SHA can influence adsorption of PO4 as follows: prior addition of PO4 ⩾ simultaneous addition > prior addition of SHA. Iron and SHA apparently form complexes due to prior addition of SHA. Observations made during this study emphasized that PO4 forms different types of complexes on the surface of goethite at different pH, which dominated the interaction of SHA and PO4 adsorption on goethite. Based on these observations, the possible modes of SHA inhibition of PO4 adsorption on goethite were proposed.
The luminescent humic substances in speleothems by Steven M. Smailer; William B. White (132-139).
Calcite speleothems deposited in caves by seepage waters derived from the overlying soils of the epikarst are typically coarsely crystalline, colored various shades of brown through orange and white, and strongly luminescent. For most speleothems, the color and luminescence is due to humic substances incorporated in the calcite crystals. For a quantitative assessment of the luminescent properties of these materials, the organic content of the dissolved speleothems was separated by gel chromatography and spectra measured as a function of molecular weight. The most intense luminescence was obtained from molecular weight fractions in the range of 4000–6000 daltons, a range characteristic of fulvic acids. In addition, there was considerable variation in detail from sample to sample that would merit further investigation.
Groundwater acidification near the water table of the Superficial aquifer, Gnangara Mound, Swan Coastal Plain, Western Australia by S. Clohessy; S. Appleyard; R. Vogwill (140-152).
This study improves the spatial understanding of the magnitude of the groundwater acidification issue in a poorly buffered sandy aquifer in Western Australia. The study provides more information to assess the risk the acidification poses to groundwater dependent ecosystems of the Gnangara Mound. Groundwater acidification (pH < 5) was identified on a regional scale, mainly due to pyrite oxidation, with the lowest pH of 3.13. Groundwater was fresh (TDS < 500 mg/L) with low concentrations of base cations, negligible alkalinity (<10 mg/L as CaCO3), high SO 4 2 - / Cl - ratios (>0.5 mg/L units), low Ca to Al molar ratios and elevated concentrations of Al and Fe.Acidic groundwater in the capture zones of wetlands may pose a long term risk to ecological values. Acidic groundwater in poorly buffered systems also poses a risk for users of untreated groundwater. Land and water use management should consider poorly buffered aquifers to be highly sensitive, particularly where rainfall and recharge trends have declined over a period of time. A comprehensive and consistent groundwater sampling program should be developed to fully delineate the groundwater acidification issue near the water table of the Gnangara Mound to assist the formulation of groundwater allocation plans.
Isotopic indicators of source and fate of particulate organic carbon in a karstic watershed on the Yunnan-Guizhou Plateau by Yongbin Jiang; Hongbing Ji (153-167).
The studied watershed is a Karst-dominated area on the Yunnan-Guizhou Plateau. The local karstic environment might cause the biogeochemical processes involving POC to be different from those in non-karstic regions. Isotopic composition of particulate organic C (POC) and total N (TN) (δ13CPOC, δ15NTN) and C/N ratios (atomic) were used to identify sources and fates of POC in suspended particulate matter (SPM) and sediments over space and time in the karstic watershed. Distributions of POC in SPM and sediments show great seasonal and spatial variations. The δ13CPOC in SPM ranges from −27.4 to −19.0‰ and −33.4 to −22.3‰ in summer and winter, respectively. The C/N ratios in SPM in both seasons are lower than 12 and most are around 7. The surface and core sediments have lower δ13CPOC but higher C/N ratios than those of SPM. According to source analysis using C/N ratios, δ13CPOC and δ15NTN, the major source for POC in SPM is phytoplankton, while POC in surface sediments are attributed to land-derived and aquatic sources. Core sediments in the region affected by less anthropogenic impact have a similar POC source to surface sediment. However, in regions with intense deforestation and farming, land-derived sources may be major contributors to POC in core sediments. Calculated contributions from these sources to POC in the riverine-lacustrine system confirm the above observation. The flux and export rate of POC in SPM are 7.85 × 108 g a−1 and 492 mg m−2 a−1, respectively. In contrast to some world rivers, POC output from the karstic watershed is mainly from in-stream photosynthesis. Land-derived POC is merely redistributed in river and lake beds and sediments in the karstic riverine-lacustrine system act as an organic C pool. The observed features are likely due to intense anthropogenic impact and particular geomorphology of the karstic environment.
Geochemical modelling of CO2–water–rock interactions in a potential storage formation of the North German sedimentary basin by Addisalem B. Mitiku; D. Li; S. Bauer; C. Beyer (168-186).
The lower Triassic/Bunter sandstone and lower Jurassic/Rhät formations of the Northern Germany sedimentary basin constitute feasible reservoirs for the storage of CO2 from combustion of fossil fuels or industrial production processes. This study presents analyses of geochemical interactions between CO2, formation fluid and rock of these potential reservoirs using geochemical modelling in order to assess the short and long term impact of CO2 sequestration. Batch equilibrium modelling was performed first for assessing the consistency of fluid and mineralogy field data and for identifying potential secondary minerals under the influence of injected CO2. Inclusion of reaction kinetics in the batch models allowed an observation of reaction paths and to estimate the time frame of geochemical reactions. Finally, one-dimensional equilibrium reactive transport modelling was used in order to investigate the direction of reactions under conditions of fluid flow and mass transport and to quantify feedbacks of reactions on transport processes.Results of the simulations performed show that dawsonite may act as the main CO2 storage mineral in both formations, while the carbonates calcite and dolomite dissolve over time. Also, changes in porosity and permeability are significant in the equilibrium reactive transport simulations. The time scale of kinetically controlled reactions observed in the kinetic batch modeling, however, suggests that CO2 mineral trapping in both formations requires very long time frames, and hence other mechanisms such as structural or solubility trapping seem to be more relevant within the injection or early post-injection phase for the studied formations.
The Diavik Waste Rock Project: Design, construction, and instrumentation of field-scale experimental waste-rock piles by Lianna J.D. Smith; Michael C. Moncur; Matthew Neuner; Michael Gupton; David W. Blowes; Leslie Smith; David C. Sego (187-199).
► Three experimental waste rock piles are constructed at the Diavik diamond mine. ► The test piles are granitic and sulfide-bearing metasedimentary waste rock. ► Geochemistry, microbiology, matrix flow and temperature, are monitored. ► Gas concentrations, air permeability, and thermal conductivity are monitored. ► Characterize physicochemical processes at various scales.The physicochemical processes that affect acid mine drainage (AMD) in unsaturated waste rock piles and the capabilities of small-scale laboratory experiments to predict AMD from waste rock are not well understood. An integrated laboratory and field study to measure and compare low sulfide waste rock and drainage characteristics at various scales has been initiated. This paper describes the design, construction and instrumentation of three field-scale experimental waste rock piles (test piles), and six active zone lysimeters at the Diavik diamond mine in the Northwest Territories, Canada. The test piles are comprised of granitic and sulfide-bearing metasedimentary waste rock excavated during open pit mining operations. One test pile contains waste rock with a target S content of <0.04 wt.% S; the second test pile contains waste rock with a target S content of >0.08 wt.% S; and the third test pile contains the higher sulfide waste rock (>0.08 wt.% S) and was re-sloped and capped with a low permeability till layer and a low sulfide waste rock cover. The first two test piles are approximately 15 m high with bases of 50 m by 60 m, and the re-sloped test pile has a larger base of 80 m by 125 m. Instrumentation was selected to measure matrix flow, geochemistry of pore water and drainage, gas-phase O2 concentration, temperature evolution, microbiological populations, waste rock permeability to air, and thermal conductivity, as well as to resolve mass and flow balances. Instrument locations were selected to characterize coupled physicochemical processes at multiple scales and the evolution of those processes over time. Instruments were installed at a density such that the number of instruments that survived construction (40% to >80% by instrument type) was sufficient to allow adequate characterization of the physicochemical processes occurring at various scales in the test piles.
The Diavik Waste Rock Project: Particle size distribution and sulfur characteristics of low-sulfide waste rock by Lianna J.D Smith; David W. Blowes; John L. Jambor; Leslie Smith; David C. Sego; Matthew Neuner (200-209).
Three large-scale instrumented waste rock piles were constructed at the Diavik Diamond Mine in the Northwest Territories, Canada. These experimental waste rock piles (test piles) are 15 m high and are part of an integrated field and laboratory research program to characterize and compare low-sulfide waste rock and drainage at various scales. During test pile construction, samples of the <50 mm fraction of waste rock were collected from two types of waste rock that are segregated during mining operations based on S content. The samples were analyzed for S content and particle size distribution. One test pile contained waste rock with an average of 0.035 wt.% S in the <50 mm fraction, within the operational S target of <0.04 wt.% S for the lower S waste rock type. The second test pile contained waste rock with an average of 0.053 wt.% S in the <50 mm fraction, lower than the operational S target of >0.08 wt.% S for the higher S waste rock type. The third test pile has a low permeability till layer and a low sulfide waste rock thermal layer covering a core of waste rock with average 0.082 wt.% S in the <50 mm fraction, which is within the operational S target of >0.08 wt.% S for the higher S waste rock. Particle size distributions for the lower and higher S waste rock are similar, but the higher S waste rock has a higher proportion of fine-grained particles. Sulfur determinations for discrete particle sizes of the <50 mm fraction illustrate higher S concentrations in smaller particles for both the lower S waste rock and the higher S waste rock. Similarly, S concentrations calculated for the >10 m scale, from composite blast hole cuttings, are lower than those calculated for the <50 mm scale. Acid–base accounting using standard methods and site-specific mineralogical information was used to calculate the ratio of neutralization potential to acid generating potential. A comparison of calculation approaches to pH and alkalinity data from humidity cell and test pile effluent suggest that ratios are very sensitive to the calculation method. The preferred calculation method was selected by comparing calculation results to pH and alkalinity data from humidity cell effluent collected over 95 weeks and test pile effluent collected over five field seasons. The preferred acid–base accounting values were obtained by calculating the average neutralization potential divided by the average acid potential of a sample set. This approach indicates that waste rock with >0.05 wt.% S is of uncertain acid-generating potential and effluent data indicate this waste rock generates acidic effluent; whereas lower S waste rock does not produce acidic effluent, consistent with the acid–base accounting predictions.
The Diavik waste rock project: Initial geochemical response from a low sulfide waste rock pile by Lianna J.D. Smith; Brenda L. Bailey; David W. Blowes; John L. Jambor; Leslie Smith; David C. Sego (210-221).
► Geochemistry from a test-scale waste rock pile with 0.053 wt.% S is characterized. ► Blasting residues and oxidation products derived from waste rock are characterized. ► Changes in SO4, pH, and metal concentrations indicate sulfide oxidation. ► Dissolution of Al and Fe (oxy)hydroxide phases buffers the pH. ► Effluent concentrations are influenced by temperatures and flow path lengths.Three large-scale experimental waste rock piles (test piles) were constructed and instrumented at the Diavik Diamond Mine in the Northwest Territories, Canada, as part of an integrated field and laboratory study to measure and compare physical and geochemical characteristics of experimental, low sulfide waste rock piles at various scales. This paper describes the geochemical response during the first season from a test pile containing 0.053 wt.% S. Bulk drainage chemistry was measured at two sampling points for pH, Eh, alkalinity, dissolved cations and anions, and nutrients. The geochemical equilibrium model MINTEQA2 was used to interpret potential mineral solubility controls on water chemistry. The geochemical response characterizes the initial flushing response of blasting residues and oxidation products derived from sulfides in waste rock exposed to the atmosphere for less than 1 year. Sulfate concentrations reached 2000 mg L−1 when ambient temperatures were >10 °C, and decreased as ambient temperatures declined to <0 °C. The pH decreased to <5, concomitant with an alkalinity minimum of <1 mg L−1 (as total CaCO3), suggesting all available alkalinity is consumed by acid-neutralizing reactions. Concentrations of Al and Fe were <0.36 and <0.11 mg L−1, respectively. Trends of pH and alkalinity and the calculated saturation indices for Al and Fe (oxy)hydroxides suggest that dissolution of Al and Fe (oxy)hydroxide phases buffers the pH. The effluent water showed increased concentrations of dissolved Mn (<13 mg L−1), Ni (<7.0 mg L−1), Co (<1.5 mg L−1), Zn (<0.5 mg L−1), Cd (<0.008 mg L−1) and Cu (<0.05 mg L−1) as ambient temperatures increased. Manganese is released by aluminosilicate weathering, Ni and Co by pyrrhotite [Fe1− x S] oxidation, Zn and Cd by sphalerite oxidation, and Cu by chalcopyrite [CuFeS2] oxidation. No dissolved metals appear to have discrete secondary mineral controls. Changes in SO4, pH and metal concentrations indicate sulfide oxidation is occurring and effluent concentrations are influenced by ambient temperatures and, possibly, increasing flow path lengths that transport reaction products from previously unflushed waste rock.
The Diavik waste rock project: Water flow through mine waste rock in a permafrost terrain by Matthew Neuner; Leslie Smith; David W. Blowes; David C. Sego; Lianna J.D. Smith; Nathan Fretz; Michael Gupton (222-233).
► Unsaturated flow in waste rock in a continuous permafrost region is investigated. ► Porosity, water retention, and hydraulic conductivity functions are estimated. ► Net infiltration in 2007 is estimated to be 37% of the rainfall. ► Early-season infiltration freezes and is remobilized as the waste rock thaws. ► Sulfate mass loading is dictated primarily by the flow behavior.A field experiment is being carried out at the Diavik diamond mine in northern Canada to investigate the influence of unsaturated flow behavior on the quality of drainage from mine waste rock piles in a region of continuous permafrost. This paper is part of a series describing processes affecting the weathering of waste rock and transport of reaction products at this site; here the focus is on unsaturated water flow and its role in mass loading. Two 15 m-high instrumented test piles have been built on 60 m by 50 m collection systems, each consisting of lysimeters and a large impermeable high-density polyethylene (HDPE) liner. Collection lysimeters are installed nearby to investigate infiltration in the upper 2 m of the waste rock. Porosity, water retention curves, and hydraulic conductivity functions are estimated from field measurements and for samples ranging in size from 200 cm3 to 16 m3. Net infiltration in 2007 is estimated to have been 37% of the rainfall for mean annual rainfall conditions. Early-season infiltration freezes and is remobilized as the waste rock thaws. Wetting fronts migrate at rates of 0.2–0.4 m d−1 in response to common rainfall events and up to 5 m d−1 in response to intense rainfall. Pore water and non-reactive solutes travel at rates of <10−2 to 3 × 10−2 m d−1 in response to common rainfall events and up to 0.7 m d−1 in response to intense rainfall. Time-varying SO4 mass loading from the base of the test piles is dictated primarily by the flow behavior, rather than by changes in solute concentrations.
The Diavik Waste Rock Project: Measurement of the thermal regime of a waste-rock test pile in a permafrost environment by Nam H. Pham; David C. Sego; Lukas U. Arenson; David W. Blowes; Richard T. Amos; Leslie Smith (234-245).
The interior thermal regime of a field-scale experimental waste rock pile in the Northwest Territories, Canada, was studied. Test pile construction was completed in the summer 2006, and temperature data was collected continuously since that time to February 2009. The temperature data indicates the test pile cooled over the study period, with an average heat energy release of −2.5 × 104 and −2.6 × 104 MJ in 2007 and 2008, respectively. The mean annual air temperature (MAAT) at the site was −8.9 °C during the period between 2006 and 2009, with a permafrost table at a depth of 4 m in bedrock away from the pile. Because of this cold environment, the upward movement rate of the 0 °C isotherm into the test pile at its base was approximately 1.5 m a−1 during 2007 and 2008. Thermistor strings installed immediately below the base of the test pile showed the test-pile basal temperatures remained near and below 0 °C during the study period. Furthermore, due to low rates of sulfide mineral oxidation, elevated temperatures in the interior of the test pile were not observed. The average air velocity in the pore space in July 2007 and 2008 was about one third of that during January of each year based on temperature distributions. Therefore, due to higher air velocity during the winter, it is expected that heat transfer is greater during winter.
The Diavik Waste Rock Project: Implications of wind-induced gas transport by Xiaotong Chi; Richard T. Amos; Marek Stastna; David W. Blowes; David C. Sego; Leslie Smith (246-255).
► Wind-induced gas transport was investigated in a test-scale waste rock pile. ► Correlations indicate that the wind influences pressure fluctuations in the pile. ► Correlations between internal and surface pressure measurements are linear. ► Transient gas flow is a function of wind periodicity and permeability.Wind-induced gas transport in a test-scale unsaturated waste rock pile was investigated at the Diavik diamond mine, Northwest Territories, Canada. Differential gas pressures were measured in 2008 at 49 locations within a field-scale experimental waste rock pile (test pile) and at 14 locations on the surface of the test pile at 1-min intervals. Wind speed and direction were measured at 10-min intervals and decomposed into north, south, east, and west vectors. Correlations between wind vectors and pressure measurements indicate that the wind influences pressure fluctuations in the test pile. The strength of the correlation is roughly inversely proportional to the distance between the measurement ports and the atmospheric boundary. The relationship between the magnitude of the wind vector and pressure fluctuations on the surface of the test pile is non-linear. However, the relationship between internal and surface pressure measurements is linear, suggesting that gas flow within the test pile follows Darcy’s Law. Spectral analysis demonstrates that the dominant periods of the wind range from 1 to 14 d. A 1-D analytical solution to the flow equation is used to demonstrate that long periods have the most pronounced effect on transient gas flow within the test pile and that the penetration depth of the wind-induced gas pressure wave is a function of wind period and permeability of the test pile.
The Diavik Waste Rock Project: Persistence of contaminants from blasting agents in waste rock effluent by Brenda L. Bailey; Lianna J.D. Smith; David W. Blowes; Carol J. Ptacek; Leslie Smith; David C. Sego (256-270).
► Blasting residuals and undetonated explosives in waste rock were studied. ► High concentrations of residuals were recorded in the first flush of water. ► Sulfate was released from the oxidation of sulfur during blasting. ► Sulfate from blasting is correlated to the sulfide content of the waste rock. ► The mass of sulfur released due to blasting was estimated.During mining operations, explosives are used to fragment rock into workable size fractions. Mine-water chemistry can be affected by blasting agent residuals, including NH3, NO 2 - , NO 3 - , Cl−, and ClO 4 - . At the Diavik diamond mine, Northwest Territories, Canada, waste rock generated from open-pit and underground mining is stockpiled on site. Three large-scale test piles measuring 60 by 50 m at the base and 15 m in height, along with four 2 × 2 m lysimeters each 2 m in height, were constructed at Diavik as part of a comprehensive research program to evaluate the quality of water emanating from waste rock stockpiles. Ongoing monitoring of the water chemistry since 2007 shows that blasting residuals comprise a large proportion of the dissolved constituents in the initial pore water and effluent. Leach tests conducted on freshly blasted rock from Diavik indicate the mass of N released corresponds to a 5.4% N loss from the blasting explosives; this mass is in the range for N loss reported for blasting operations at Diavik during the period when the test piles were constructed. The total mass of N released from the lysimeters was also within this range. The three large-scale test piles have only released a small fraction of the N estimated to be contained within them. Blasting of waste rock contributes SO 4 2 - to effluent through the oxidation of sulfide minerals in the rock during the blast. During the initial flush of water, the test pile that contained waste rock with the higher S content was observed to release higher concentrations of SO 4 2 - than the test pile with lower S content waste rock. Mass-balance calculations based on the ratios of SO 4 2 - to total N can be used to estimate the relative contributions of sulfide oxidation within the test piles and SO 4 2 - released when S in the host rock is oxidized during blasting. These calculations provide an estimate of S mass released during the first flush of the test piles.