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Quantitative forecasts of acid mine drainage (AMD) production are important for remediation planning. Reactive transport simulations corresponding to a detailed sampling location at a covered legacy tailings impoundment in northern Ontario, Canada, were conducted to quantitatively assess the predominant hydrogeochemical reactions. The simulations span the period from the end of tailings deposition (circa 1970) to early 2020, 12 years after remediation by a five-layer composite cover. The conceptual model of uncovered tailings weathering and subsequent geochemistry of the covered tailings system was implemented in 1D using the multi-component reactive transport code MIN3P. Transient monthly infiltration, post-cover boundary condition changes, and a dynamic temperature regime were incorporated. The shrinking core model, including parallel O 2(aq) and Fe 3+ oxidation reactions for the waste rock in the cover and the underlying tailings, was implemented to simulate the oxidation of As-bearing pyrite, chalcopyrite, and sphalerite. Primary carbonate and aluminosilicate host minerals promoted acid-neutralization reactions. Precipitation of secondary phases and sorption/desorption of Cu, Zn, and arsenite were incorporated into the model. The overall agreement between key simulated and field-measured post-cover aqueous geochemical parameters suggests that the conceptual model captured the primary hydrogeochemical processes in the covered tailings. A lack of reliable data on initial tailings mineralogy and pre-cover hydrogeochemistry increased simulation uncertainty. Simulated reaction rates indicate that where intact, the cover decreased sulfide oxidation rates by both O 2(aq) and Fe 3+ and improved pore-water quality over time. Simulation results indicate that elevated concentrations of Zn and As are likely to persist in the tailings regardless of cover performance, whereas concentrations of Cu and Al are the parameters most sensitive to cover effectiveness., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

This paper examines the applicability of a recently developed testing protocol to evaluate the potential of sulfide-bearing aggregate—mainly from Ontario—to oxidize and cause damage when used in concrete. The protocol consists of three sequential tests: total sulfur (St), the oxygen consumption test (OCT), and the oxidation mortar bar test (OMBT). The paper suggests modifications to the OCT, and the expansion criteria of OMBT based on testing aggregates with different total sulfur contents. For OCT, using crushing equipment with cast-iron working surface was found to contaminate the samples and give high values of oxygen consumption. The OMBT showed lower expansion values for carbonate aggregates compared to aggregates with silicate. Exposing siliceous aggregate—whether alkali-silica reactive or not—to the high pH and temperature encountered in the OMBT produces high expansion regardless of the oxidizable sulfide content. As such, new expansion criteria are suggested, which take into consideration the silicate nature of some aggregates. [ABSTRACT FROM AUTHOR]

Dr. Cabri has a number of criticisms of Djon and Barnes (2012). Some of the criticisms are valid and are the result of what we consider to be minor errors and omissions that can occur when an M.Sc. is converted to a paper. However, none of these change our conclusions, and we stand by our interpretations. [ABSTRACT FROM AUTHOR]

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Groundwater with total dissolved sulphide concentrations in excess of 1.0 × 10 − 4 mol L − 1 3 mg L − 1 is relatively common at intermediate depths in sedimentary basins. However, the mechanisms responsible for the formation and spatial distribution of these sulphidic waters in sedimentary basins, which have been affected by periods of glaciation and deglaciation, are not fully understood. Sulphate reduction rates depend on many factors including redox conditions, salinity, temperature, and the presence and abundance of sulphate, organic matter, and sulphate-reducing bacteria. Two-dimensional reactive transport modelling was undertaken to provide potential explanations for the presence and distribution of sulphidic waters in sedimentary basins, partially constrained by field data from the Michigan Basin underlying Southern Ontario, Canada. Simulations were able to generally reproduce the observed depth-dependent distribution of sulphide. Sulphate reduction was most significant at intermediate depths due to anoxic conditions and elevated sulphate concentrations in the presence of organic matter in waters with relatively low salinity. The simulations indicate that glaciation-deglaciation periods increase mixing of waters at this interfacial zone, thereby enhancing rates of sulphate reduction and the formation of sulphide. In addition, the simulations indicate that glaciation-deglaciation cycles do not significantly affect sulphide concentrations in low permeability units, even at shallow depths (e.g., 25 m), while concentrations in permeable units remain stable below depths of 500 m. [ABSTRACT FROM AUTHOR]

Environmentally safe disposal of sulfide-rich reactive mine tailings is one of the major challenges facing the mining industry in Canada, Scandinavia, USA, and many other parts of the world. Placing tailings under a water cover is one of the effective methods to reduce the influx of oxygen to the tailings. Wind-induced turbulence and subsequent resuspension of the tailings, however, are major concerns with this approach. In this paper, a study of wind-induced resuspension at the Shebandowan tailings storage facility, northwestern Ontario, Canada, is discussed. The study compares computer modeling of required water cover depths and resuspended tailings concentrations to observed field data. The calculated minimum water cover depths required to eliminate resuspension were found to be higher than the existing implemented water cover depths in each cell. The predicted resuspended tailings concentrations for the west cell were 6-22 mg/l with an average value of 15 mg/l and, for the east cell, 1-10 mg/l, with an average of 6.0 mg/l. In comparison, optical backscatter sensors, deployed in situ, recorded average resuspended tailings concentration up to 25 mg/l, indicating that the model results were similar to the field-measured values. Results from sediment trap measurements did not show any correlation between the amount of resuspended tailings and water cover depth. Sediment traps collect not only sediments eroded and suspended at the location of deployment but also those that have been transported from elsewhere and redeposited at the trap location. The amount of resuspension occurring at Shebandowan does not raise a major concern because discharge from the tailings area is collected and managed before it reports to the final effluent. [ABSTRACT FROM AUTHOR]

Abstract: The formation of Sudbury''s economically important magmatic Ni–Cu–PGE sulphide deposits is attributed to superheating of crustal rocks, following meteorite impact at 1.85Ga. Crustal contamination of magmatic sulphide deposits is thought to be important in the mineralization process and this paper documents the first occurrence of sedimentary carbon in the Sudbury Ni–Cu–PGE sulphides near the base of the Sudbury Igneous Complex (SIC). Spherules of graphitic and more disordered carbon inclusions were found in chalcopyrite crystals, suggesting that carbon has behaved as a chalcophilic element in the impact melt. Samples from the impact structure have been subjected to carbon isotopic analysis and Raman microspectroscopy in order to investigate the relationship between carbonaceous strata of the Huronian basement, the crater-fill impact breccias, and the mineral deposits associated with the Sudbury impact. Carbonaceous material occurs in the impact breccias of the Onaping Formation and this study presents stratigraphically constrained carbon isotopic analysis of the impact breccias. Sulphides from the hydrothermal Zn–Pb–Cu Vermilion–Errington deposits 1.5km above the SIC were found to contain both carbon spherules and larger irregular carbonaceous flakes, suggesting a genetic link between the Ni–Cu–PGE deposits and the hydrothermal Zn–Pb–Cu mineralization. A shared source of carbon for the Vermilion–Errington mineralization and the cross-cutting anthraxolite veins 100m above the deposits in post-impact carbonaceous shales of the Onwatin Formation is indicated by the similarity in their Raman spectra. This is considered to be carbon remobilized by metamorphic hydrothermal fluids preferentially scavenging disordered carbon from within the Onaping Formation breccias. The occurrence of carbon in the Sudbury Ni–Cu–PGE massive sulphide deposits indicates that carbon from the target rocks played a role in the mineralization process, hitherto unrecognized. [Copyright &y& Elsevier]