Evaluation du comportement geochimique en conditions normale et froides de differents steriles presents sur le site de la mine Raglan

The objective of this project is to characterize the geochemical behaviour of different waste rock types, with no mineralogical influence of the deposit, in normal (laboratory) and cold conditions. We aim at improving our knowledge concerning the phenomena involved in the generation or attenuation of an eventual water contamination, and to evaluate the influence of temperature on these phenomena. To do so, seven samples of representative waste rock were selected, each of them representing a different geology. Kinetic and oxygen consumption column tests were performed on the samples (70 kg) at normal temperature to determine the contamination potential of the waste rocks. Other tests at smaller scale, in weathering cells (67 g), were performed to assess the effect of temperature on their geochemical behaviour. This test is more aggressive than the column test and therefore allows better observing geochemical changes.;Alteration cells showed that the oxidation rates of sulphides and silicate dissolution decrease with a temperature reduction, and can be properly predicted by the Arrhenius law. A low sulphate leaching is observed for 5 of the 7 rock types at -6°C, suggesting low sulphide oxidation at this temperature. Calcium is leached in larger quantity at lower temperatures (10°C and -6°C) than at normal temperature because of an increase in calcite reactivity (present in traces); this dissolution increase would be in response to the acidity produced by the dissolving atmospheric CO2, that is higher at lower temperatures. Calcium leaching increases at cold temperatures as reflected by the ratio of the chemical elements related to the neutralizing minerals (especially Ca+Mg) and the sulphate production related to sulphide oxidation. Freeze/thaw cycles yielded higher sulphide oxidation rates and iron leaching. When comparing the different leaching rates obtained in the study, we note that there are scale-up effects between the columns and the weathering cells, and that there is also a temperature effect. However, it is impossible to use a single relationship to extrapolate the leaching rates for all the chemical elements from one scale or temperature to another scale or temperature.;Based on the results of this study, we therefore recommend to Raglan mine to manage the waste rocks with a short term CND potential with the potentially acid generating waste rocks, and to prioritize them as underground rockfill, or filling the bottom of open pits to facilitate their integration to the permafrost and reduce their reactivity. The materials with no acid generating potential and only a long term CND potential could be stored at the surface for a longer period and even be used for rehabilitation (for example as cover materials for the waste rock in open pits or tailings stack). Thus, the production of contamination on site and the costs related to water treatment and rehabilitation could be reduced during the mine operations. (Abstract shortened by UMI.);Column tests showed that six of the seven waste rock types are not potentially acid generating (PAG). The acid generating potential of the olivine-pyroxenite from mine 3 is uncertain. In the waste rocks, the acidity can be produced by sulphide oxidation; the main sulphide minerals present in the waste rocks are pyrrhotite, pentlandite, pyrite, and chalcopyrite. The neutralization potential of the waste rocks is mainly provided by silicates and by calcite that is present in traces in the olivine-pyroxenite from mine 3. Only one waste rock type generates nickel in its drainage water: the peridotite from the Kikialik mine (with an average of 0,280 mg/kg waste rock/year, and with corresponding concentrations below the Directive 019). This contamination could be produced by the dissolution of an alteration crust present on the surfaces of this rock type (not present in significant quantity for the other rock types) and by the oxidation of nickel sulphides (pentlandite) and of pyrrhotite that can contain nickel as impurity. Nickel is not leached from the other waste rock types on a short term, even if the peridotite from mine 3 and the olivinepyroxenite from mines 2 and 3 have sulphur and nickel contents in the initial solid equivalent or higher than those of the peridotite from the Kikialik mine. The absence of nickel in the drainage water of these rock types can be due to its precipitation on hydroxide formed at pH above 8, or to its sorption on the surfaces of the waste rocks. Due to these two phenomena that could occur (but can eventually disappear), we cannot conclude on the long term CND generation potential of the waste rocks. However, probabilities that the gabbro from mine 2, the argillite from mine 3 and the volcanic generate CND are very low considering their low nickel content.