D Gregory

Comparison of metal enrichment in pyrite framboids from a metal-enriched and metal-poor estuary

Abstract The accumulation of metals and metalloids in diagenetic pyrite framboids is of interest because framboids can be a sink for heavy metal contaminants, a source of metals in ore deposits, and a tool to interpret paleo-ocean chemistry. In this study, we have used laser ablation-inductively coupled plasmamass spectrometry (LA-ICPMS) to analyze pyrite framboids from both the contaminated Derwent Estuary and the uncontaminated Huon Estuary in Tasmania, Australia. While the enrichment of many trace metals in the Huon Estuary followed expected trends, the trends in the Derwent were quite different. In addition to the expected high contents of Pb, Zn, and Cu in the contaminated interval it was found that several elements are not as strongly incorporated into pyrite within the contaminated zone. It is suggested that this is due to over-competition for adsorption sites on the growing iron sulfides in the contaminated zone resulting in diffusion of several elements to deeper levels in the sediments. This results in an increase of these elements in pyrite below the zone of major contamination. The LAICPMS technique also provided the opportunity to obtain accurate data on gold, silver, and tellurium in pyrite, something rarely achieved in sequential leach extractions due to the low concentrations of these metals observed in nature.

Mineralogy of metal contaminated estuarine sediments, Derwent estuary, Hobart, Australia: implications for metal mobility

The mobility, bioaccessibility and transfer pathways of metals and metalloids in estuarine sediments have been the focus of much detailed research. However, to date, few studies have examined the mineralogical siting of metals and metalloids in such sediments. This is despite the fact the mineralogy of sediments is an important factor that controls which and how much of a particular metal is released to pore waters and overlying water columns. This study reports on the mineralogical siting of metals in contaminated estuarine sediments, Hobart, Australia, and aims to evaluate the mobility of metals in the contaminated substrates. Mineralogical, mineral chemical and bulk chemical analyses demonstrate that the sediments contain very high levels of several metals and metalloids. The contaminated sediments have concentrations of zinc (Zn), lead (Pb), copper (Cu) and cadmium (Cd) ranging from 0.55 to 4.23 wt%, 0.16 to 0.70 wt%, 415 to 951 mg/kg and 23 to 300 mg/kg, respectively. Franklinite and lesser sphalerite are the main repositories of Zn, whereas much of the Pb and Cu is hosted by sulfides, organic matter and undetermined iron (Fe) oxides. While the release of contaminant loads from franklinite through dissolution is likely to be insignificant, even small releases of metals from the highly contaminated sediments can still cause the deterioration of local water quality. The contaminated sediments represent long-term sources of metal pollutants, particularly Zn, to local waters. This study demonstrates that mineralogical analyses are a vital tool to recognise the potential mobility of trace metals in estuarine environments.