research program 2
mineral exploration in areas of cover
Gold and metal geochemistry and mobility in the regolith
Project Leader : D.C. “Bear” McPhail, Australian National University
Start date and duration: July 2003-June 2008
Participants : Australian National University, CSIRO Exploration & Mining, University of Adelaide
Brief project description :
This is the continuation and extension of Project 2.37 Gold Geochemistry and mobility, which started in July 2003 and was originally intended to last for three years. The original project has been extended to the end of LEME in June 2008. Shown below are the original objectives, a brief background and summaries of work to date and a list of specific studies and outputs for final financial year of LEME.
The objectives are to understand:
- the geochemistry and mobility of gold in waters and brines;
- the impact of microbiota (bacteria and fungi) on the mobility of gold in regolith;
- sorption of metals, e.g., Cu and Zn, to iron oxyhydroxide minerals, in particular as a function of salinity;
- the solubilities of zinc alteration minerals and the dispersion and mobility of zinc in the regolith;
- the aqueous transport of base and precious metals through the regolith; and
- the leaching from and uptake of metals in ferruginous and carbonate regolith materials.
Much of the work has been accomplished by three PhD students, whose theses were submitted in 2006-2007.
• field, experimental and molecular microbiology studies to identify correlations between microbiota and gold distribution in the regolith (Frank Reith's Ph.D. study, now complete and published); and
• experimental studies (UV-Vis spectrophotometry, mineral solubility) to identify aqueous gold complexes (chloride, iodide, thiosulphate) and measure their thermodynamic properties (Alistair Usher's Ph.D. study; thesis submitted in September 2006 and positive examiners' reports received in April 2007);
• experimental studies of copper and zinc sorption onto goethite as a function of pH and NaCl, Na2SO4 and NaNO3 concentrations (Chris Gunton's study, thesis submitted in February 2007, awaiting examiners' reports).
In addition, there have been ongoing studies that are complete or will be by the end of the 2006/07 financial year:
• column experiments to study the mobility of copper, zinc and possibly gold and other metals through synthetic and natural regolith under different salinity, pH and redox conditions (Jennifer de Livera Honours work completed in 2005 plus additional experiments by David Little in 2006/07);
• solubility experiments for hemimorphite (experiments completed in 2006/2007, interpretation and writing continuing); and
• experimental study of the effect of salts on the measurement of pH (started in 2006/2007, necessary to publish Chris Gunton's Ph.D. work).
Deliverables:
In the final year of LEME, the focus of this project is to write and submit a LEME Open File Report and as many journal publications as possible. The following is a list of proposed publications.
- Report: McPhail , D.C. Experimental studies of metal speciation, sorption, solubility and mobility in regolith materials. To be submitted as a LEME Open File Report.
- Journal publications:
- Usher, McPhail and Brugger. UV-Visible spectrophotometric studies of ligand competition and complex formation at Au(III) metal centres: Part I – gold chloride-bromide complexes. To be submitted to Geochimica et Cosmochimica Acta.
- Usher, McPhail and Brugger. UV-Visible spectrophotometric studies of ligand competition and complex formation at Au(III) metal centres: Part II – pH dependence of Au(III) halide complex formation. To be submitted to Geochimica et Cosmochimica Acta.
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Gunton, Christy and McPhail. The effect of NaCl on the adsorption of CuII on synthetic goethite. To be resubmitted to Geochimica et Cosmochimica Acta.
- Gunton, Christy and McPhail. The effect of NaCl on the adsorption of ZnII on synthetic goethite. To be submitted to Geochimica et Cosmochimica Acta.
- Usher and McPhail. Analytical methods for measuring gold concentrations in groundwater. To be submitted to Geochemistry: Exploration, Environment and Analysis or Journal of Geochemical Exploration.
- McPhail, Lenahan and Jayaratne. The effect of salts on the measurement of pH. To be submitted to Chemical Geology or Geochemistry: Exploration, Environment and Analysis.
- McPhail, Jayaratne, Brugger and Summerhayes. The solubility of hemimorphite and phase relations of low-temperature zinc alteration minerals. To be submitted to Chemical Geology or Geochimica et Cosmochimica Acta.
- Gunton, McPhail and Christy. The effect of sulfate on the adsorption of CuII and ZnII on synthetic goethite. To be submitted to Geochimica et Cosmochimica or Chemical Geology.
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