The development of a cover for inclined acid-generating areas, such as the external face of dykes and the slope of waste rock piles, is undoubtedly one of the biggest technical reclamation challenges at several mine sites. The LaRonde mine site, owned and operated by Agnico Eagle Mines (Quebec, Canada) is currently engaged to identify an optimal reclamation scenario for the Dyke 1 of its acid-generating tailings storage facilities. One of the promising reclamation options for controlling water infiltration in the acid-generating waste rock on the Dyke 1 is the use of an inclined cover built with available mine waste materials. An instrumented inclined cell with an inclination angle of 18.3 degrees was built on a slope of this dyke to validate if low sulfide tailings and non potentially acid-generating waste rock can be used as cover material to reclaim the Dyke 1. The instrumented inclined cell was monitored for 3 years (2017 to 2019) using volumetric lysimeters, suction sensors, and volumetric water content sensors. The monitoring was done under natural climatic conditions and artificial wetting events. Under natural conditions, less than 1% (5 mm) of incident rainfall percolated in the volumetric lysimeters installed along the slope of the inclined cell. Under controlled conditions associated with artificial wetting events of 6.4 mm/h over a period of 12 h, net percolation values between 1 and 9% (4 to 60 mm) of the sum of incident precipitation were measured. The distance between the top of the cell and the Down Dip Limit (DDL) point was greater than the slope length of the cover under natural conditions and the DDL point moved from the bottom toward the top to reach values between 12 and 20 m from the top of the slope when the wetting events were applied on the cover. These results confirmed the suitability of mining materials as an inclined cover material to control water infiltration in reactive mine waste rocks.

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The hydrogeochemical behavior of highly reactive tailings with no or very low neutralizing capacity and their hydrogeochemical response when covered by a cover with capillary barrier effects (CCBE) were evaluated in laboratory columns. The hydrogeochemical response of highly reactive tailings under wetting-drying cycles and saturated conditions was also simulated using the MIN3P code, a finite volume model for coupled groundwater flow, oxygen diffusion and multi-component reactive transport. Laboratory tests were conducted for approximately 18 wetting and drying cycles, over a period of one and a half years. A numerical simulation model was validated using laboratory results of uncovered highly reactive tailings under wetting and drying cycles conditions. The acceptable agreement between the geochemical observations in the laboratory and the numerical simulations shows that MIN3P can simulate the hydrogeochemical response of highly reactive tailings (initially very acidic) under laboratory experimental conditions and can make realistic predictions. The laboratory hydrogeochemical response of highly reactive tailings covered by a CCBE and the numerical modeling results of highly reactive tailings under saturated conditions (an equivalent CCBE oxygen barrier) indicated a decrease in the concentration of sulfate and most metals in the leachate compared to uncovered highly reactive tailings, indicating that both scenarios decreased sulfide oxidation. The simplified approach for geochemical modeling of saturated reactive tailings evaluated in this paper could be used to determine the required oxygen barrier efficiency to reach the target effluent geochemistry as a preliminary stage of reclamation design.

Abstract

Blasting is considered an indispensable process in mining excavation operations. Generally, only a small percentage of the total energy of blasting is consumed in the fragmentation and displacement of the rock, and the rest of the energy is transmitted to the structures and environment surrounding the mined area. The air overpressure (AOp) induced by explosions in open-cast mines has unavoidable environmental and safety consequences, but can be minimized to an acceptable threshold to limit environmental damage and the impact on the sustainability of mining activities. The development of numerical predictive models of AOp was the main objective of this study. Thus, the methodology used to achieve this main objective was articulated around six parts: knowledge of the study area, processing and statistical analysis of the data collected, development of both numerical and empirical prediction models, and evaluation of model performance of the numerical model parameters. The results show that only numerical models are suitable for predicting AOp. Moreover, numerical models generally perform better than empirical models in predicting this phenomenon. Among these AI models, the results show that the DT model is the best suited for predicting AOp in this study, with remarkable performance results (RRSE of 0.08, RAE of 0.05, RMSE of 0.29, MAE of 0.37, MAPE of 0.07, and an R² of 0.994). This could therefore justify its application in practical engineering to predict blast-induced AOp in open-cast mines to reduce undesirable environmental effects.

Keywords

Numerical Prediction, Artificial Intelligence (AI), Air Overpressure (AOp), Blasting, Open Pit Mining

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