Source, distribution and economic significance of trace elements in groundwaters from Lake Tyrrell, Victoria, Australia

Abstract Anomalous radioactivity highlighted the Lake Tyrrell area as a potential mineral exploration target and prompted a 5-year study of its groundwater geochemistry. The groundwaters are very acid (median pH=4.2) and saline (median ionic strength ( I ) = 1.24). Some samples contain unusually high concentrations of Cu (up to 3.5 mg l −1 ), Pb (up to 38.5 mg l −1 ) and Al (up to 155 mg l −1 ). Concentrations of most other trace elements exceed seawater values but are not different from those in groundwaters near two other randomly selected Australian salt lakes. Waters with elevated trace-element concentrations are spread at isolated sites across the area but some clustering of Cu-Pb-enriched waters occurs in the west and southeast. R and Q mode correspondence analysis identifies factors which relate to both trace elements and samples, and are interpreted as reflecting processes whereby trace elements are taken into groundwaters. Factor 1 involves Al, Cu, Fe, Mn and Zn whose concentrations relate directly to high acidity; factor 2 involves B and Sr and probably relates to local sediment enrichments of B and Sr; factor 3 is strongly weighted by Pb and can be explained by contact between groundwaters and locations where clays, organic solids and Fe-Mn-oxides are particularly enriched by heavy metals; factor 4 involves F, Y and I, and probably relates to residual mineral dissolution. Sample locations, grouped according to the influence of each factor on each groundwater composition, identify zones where a particular process is dominant. Laboratory leaching of Blanchetown Clay and Parilla Sand confirms that many of the trace elements could have entered the groundwater from local aquifer sediments. The potential of these waters as agents of present or future ore formation is also considered by comparing amounts of trace elements carried into the salt lake basin over the last 30 kyr with what persists in present-day lake brines. Results demonstrate that large tonnages of trace elements appear to have been deposited, but that sediment dilution mitigates against ore-grade concentrations.