An integrated hydrogeological and water chemistry study at the Navachab Gold Mine, Namibia

摘要

On the eastern side of the elongate, NNE-oriented main open-pit of the Navachab Gold Mine, in the steeply westward-dipping Precambrian schist and calc-silicate rocks of the Spes Bona Formation (Footwall Schist), the water table is at -55 m below surface (May 2000), the field pH is 6.5-7.1, electrocon-ductivity (EC) is 1.02-4.10 mS/cm and the groundwater is of NaCl type. West of and within the main pit, groundwater equilibrating with dolomitic and calcareous marbles (Okawayo and Karibib Formations) and biotite schists (Oberwasser Formation), is more alkaline (field pH of 6.8-8.1), has an EC of 0.21-1.09 mS/cm, has a CaCO_3/SO_4 chemistry and the water table is at -29 m (May 2000). Groundwaters show a wide range of stable isotope values (δ~(18)O: -10.2 to +1.6per thousand; δD: -69.3 to -6.0per thousand). Gold contents of groundwater within 100 metres of the orebody are up to 31 ppb. Mining and oxidation of sulphides have neither affected water acidity, nor salinity.