The identification of constituents in waste waters from gold mining using ICP-MS

Gold mining has been undertaken in the Northern Territory since the 1870's in the mining district around Pine Creek, 180 km south of Darwin. This is a tropical region experiencing a monsoonal wet season each year from November to April. During the last 10 years, the use of the carbon-in pulp (CIP)/carbon-in-leach (CIL) process coupled with larger machinery to move material has permitted the mining of relatively low grades of ore and has created larger waste rock dumps than in the past. Oxidation of any sulfidic material incorporated in waste rock occurs during the dry season. With the onset of the wet season, rainwater percolates through the waste rock, flushing out acidic solutions containing a range of trace elements which may be indicative of the origin of the waste material itself. ICP-MS (inductively coupled plasma-mass spectrometry) has proved to be a particularly useful analytical tool for generating trace element patterns of waste rock materials and associated waste water. Certain elements and their compounds such as arsenic are readily absorbed by biota and are not transported via fluvial systems. However, species present in anionic forms are not readily adsorbed by particulate matter and appear to be more readily transported. Trace elements showing an indication of origin of waste rock are rare earths, groups of transition metals, gold itself and tellurium (co-association with sulfur). The predictive value of certain trace elements is demonstrated through a comparison of mine waste waters at different sites with uncontaminated surface and groundwaters. A comparison is also made with alluvial gold mining tailings where element are primarily in particulate forms.