Metal concentrations in surficial sediments from hypersaline lakes, Australia

Abstract

We have conducted a preliminary survey of analyzed surface sediment samples from approximately twenty lakes in Australia for their Fe, Cu, Pb and Zn concentrations. In addition lake sediments from the gold mining areas of Western Australia (WA) were analyzed for Ag, and samples from NW Victoria were analyzed for Mn, Ni, Co, Cr and V. These lakes are discharge zones for regional and/or local saline groundwaters. The groundwaters entering many of these lakes have very low pH's (pH 3–4) and contain extremely high dissolved Fe concentrations. These low pH waters may also contain high concentrations of trace metals and radionuclides from the ²³⁸U decay series.

The WA data yield the following information: (1) with the possible exceptions of Ag, these sediments show no trace metal enrichments above average shale/sandstone values; (2) some lakes draining Archean gold mining terrain have high Ag concentrations; (3) the highest Pb concentrations are in a lake where acid groundwater input occurs; and (4) the acid mineral alunite does not appear to be a metal ‘sink’ in the acid groundwater lakes.

In the two NW Victorian lakes, the sulfidic zone below the cyanobacterial mat is enriched above by about 100 × for Cu, 30 × for Zn and 78 × for Pb compared to the sediments outside the discharge zone. The Victorian data set indicates a correlation between Cu and Zn and also between Cr and Ni concentrations. Three generations of ‘ironstone-like’ sediments were also analyzed. These iron-oxide rich sediments gained Cu but lost Co with age and maturation. The Mn concentration appears to be important in controlling the Zn and Cu in these ‘ironstones’. It appears from our data that neither the oxide-rich nor the acid-rich authigenic sediment phases are major sinks for groundwater metal in these systems.