TY - THES

T1 - Situation environnementale et hydrogéologique de la fosse minière de Goro en Nouvelle-Calédonie

AU - Hubert, Stephanie

N1 - embargoed until 20-06-2018

PY - 2013

Y1 - 2013

N2 - As part of the setting up of an environmental impact study of the exploitation of the future mining pit within 25 years, the company Vale Nouvelle-Calédonie has put the company Golder NC in charge of the hydrogeological follow-up of Goro’s mine, located in the south of New Caledonia. The ground-waters are regularly and strictly controlled, via the help of a concentrated network of piezometer, permitting to follow the physico-chemical behaviour of the ground-waters and to highlight the different geochemical facies that we can find within the multiple coating aquifer system in the mining pit area. This report presents the results of this follow-up between September 2011 and January 2012. It can be noticed that water levels react directly to precipitation. When these are less frequent and less intense, water-levels get down. To the contrary, they get up during rainy episodes. Maps of the isopiezes of water table have been drawn to follow up the evolution of ground-water level during the hydrological cycle. With the qualitative follow up of waters, two geochemical profiles have been distinguished depending on the captured aquifer: laterites and saprolites/peridotites. The laterites layer has acid waters, with a very low mineralization, mostly with sodium and chlorine, and slightly with magnesium and bicarbonate. To the contrary, the saprolites/peridotites layer has slightly alkaline waters, not very mineralized, silica-rich and from the carbonate-magnesium type, with a slight tendancy to chlorine at saprolites level. Responsible for the geological profile of the ultrabasic mining massif, the weathering process of peridotites explains these geochemical differentiations. Weathering can be caracterised by the dissolution of leachate, mostly silica and magnesium (they constitute the migratory phase), and also by the concentration of indissoluble elements, mostly iron, manganese and nickel, in the residual phase constituted by saprolites and laterites. New Caledonia’s environmental laws are very strict and set accurate norms about water quality and drinkability. The limite thresholds of water quality have been exceeded for five elements (ammonium, chromium, manganese, aluminium, fluoride) and in many piezometers. However, we should keep in mind that the geological and climatic environment of this area is favourable to a high weathering of soils, so to a high dissolution of elements in groundwaters. Besides, the repartition of these high contents on the study area is homogeneous and the majority of the concerned piezometers are located upstream from the mine. For these reasons we couldn’t say that they are related to the current mining activity. This study has allowed to established an initial state of the physico-chemical behavior of the underground water of the mining pit (comprising dissolved elements, conductivity, pH, temperature, groundwater level), aiming to follow the future impact of the mining activity on the environment.

AB - As part of the setting up of an environmental impact study of the exploitation of the future mining pit within 25 years, the company Vale Nouvelle-Calédonie has put the company Golder NC in charge of the hydrogeological follow-up of Goro’s mine, located in the south of New Caledonia. The ground-waters are regularly and strictly controlled, via the help of a concentrated network of piezometer, permitting to follow the physico-chemical behaviour of the ground-waters and to highlight the different geochemical facies that we can find within the multiple coating aquifer system in the mining pit area. This report presents the results of this follow-up between September 2011 and January 2012. It can be noticed that water levels react directly to precipitation. When these are less frequent and less intense, water-levels get down. To the contrary, they get up during rainy episodes. Maps of the isopiezes of water table have been drawn to follow up the evolution of ground-water level during the hydrological cycle. With the qualitative follow up of waters, two geochemical profiles have been distinguished depending on the captured aquifer: laterites and saprolites/peridotites. The laterites layer has acid waters, with a very low mineralization, mostly with sodium and chlorine, and slightly with magnesium and bicarbonate. To the contrary, the saprolites/peridotites layer has slightly alkaline waters, not very mineralized, silica-rich and from the carbonate-magnesium type, with a slight tendancy to chlorine at saprolites level. Responsible for the geological profile of the ultrabasic mining massif, the weathering process of peridotites explains these geochemical differentiations. Weathering can be caracterised by the dissolution of leachate, mostly silica and magnesium (they constitute the migratory phase), and also by the concentration of indissoluble elements, mostly iron, manganese and nickel, in the residual phase constituted by saprolites and laterites. New Caledonia’s environmental laws are very strict and set accurate norms about water quality and drinkability. The limite thresholds of water quality have been exceeded for five elements (ammonium, chromium, manganese, aluminium, fluoride) and in many piezometers. However, we should keep in mind that the geological and climatic environment of this area is favourable to a high weathering of soils, so to a high dissolution of elements in groundwaters. Besides, the repartition of these high contents on the study area is homogeneous and the majority of the concerned piezometers are located upstream from the mine. For these reasons we couldn’t say that they are related to the current mining activity. This study has allowed to established an initial state of the physico-chemical behavior of the underground water of the mining pit (comprising dissolved elements, conductivity, pH, temperature, groundwater level), aiming to follow the future impact of the mining activity on the environment.

KW - Neukaledonien

KW - Hydrogeologie

KW - Geologie

KW - Verwitterung

KW - Niederschlag

KW - Aquifer

KW - Laterit

KW - Peridotit

KW - Wasserentnahme

KW - Tagebau

KW - Verschmutzung

KW - Nickel

KW - Chrom

KW - Piper-Diagramm

KW - Grundwasserniveau

KW - Piezometer

KW - New Caledonia

KW - hydrogeology

KW - geology

KW - rain

KW - acquiferous

KW - laterite

KW - peridotite

KW - weathering

KW - geochemistry

KW - water sampling

KW - open-pit mine

KW - pollution

KW - chromium

KW - nickel

KW - piper's diagram

KW - piezometer

KW - water level

M3 - Master's Thesis

ER -