UQ webinar- Metal isotopes applied to exploration.

On Thursday 11 June 2020, the University of Queensland (UQ) supported a webinar on “Metal isotopes in ore deposits and applications for exploration”. Helen Degeling acted as moderator for this webinar coming from Brisbane, held in English and attended by about 50 people. Helen emphasized that much of this isotope work is to help find ore deposits under thick cover.

Ryan Mathur [ [email protected] ], Juniata College (and many others) spoke on “metal isotopes applied to ore deposit exploration”. Strategies for exploration vectoring for ore deposits (hidden under baren cover or deep soils) may include sampling ground water, plants, transported iron oxides, rocks and soil or gravels. In Queensland the principal element sought are Cu, Zn, Ag, Sn and Sb, wherein testing for other pathfinder minerals will help (Ti, V, Cr, Mo, Fe, Ni, Cd and Te). The laboratory instruments need to detect extremely small amounts, ppb or pp-trillion, with considerable accuracy. Positive and negative isotope ratios were used in the ground water samples (glacial till over mineralized basement) from the pebble deposit in Alaska. Other Cu element isotope ratios around the Mt Isa district in Queensland show marked difference close to the known ore bodies, and far from them. Sb isotopes were examined from drill core in Xikuangshan, China. Further research is looking at using isotopes to identify the source of alluvial gold nuggets etc.

Dr. Brandon Mahan, James Cook University spoke on “Stable metal isotopes in ore Exploration – retooling lab capabilities to meet industry needs”. Isotope vectoring general rules include; A) Oxidized phases enriched in heavy isotopes. B) Fluids / organics enriched in heavy metal isotopes relative to source. C) Downstream distillation leads to isotopically heavy residues, D) Typical precipitation sequence is light to heavy, however recharge / multi-phase can mess things up. The determination of many isotope ratios may need large samples to extract extremely small amounts of isotope material, that can be very time and labour consuming, with great care for laboratory procedure. Brandon is looking into ways to speed up and reduce the price of such work.

Bruce F. Schaefer, department of earth and environmental science, Macquarie University, with contributions from others, spoke on “Os isotopes in ore forming systems and advances in analysis”. The decay rate of Os is extremely slow, wherein it is suitable for measuring the age of meteorites older than the earth etc. Exceedingly low concentrations are found in target rocks, that need to be extracted with great care and patience. The Re-Os ratio work includes research projects that look at mantle derived fluids / minerals compared to crustal sources. In the Witwatersrand this work indicates the gold mineralization may have been original sedimentary source that was remobilized after deposition. Further research work looks at ancient sources for ore deposits stretching from South Australia to Queensland.

David L. Huston [ [email protected] ]from Geoscience Australia spoke on “Lead isotopes in ore deposits”, with acknowledgements to D. Champion, G. Carr and S-S Sun. The Uranium, Thorium to Lead decay system leads to 4 lead isotopes. 2D Modelling the lead isotopes can yield clues to the age, and genesis of mineral emplacement. Examples of the lead in the Renison tin deposits (Tasmania) were related to the eastern Australia mineral regions to highlight similarities in province characterization. This leads to a postulation about ancient plate subduction and resultant remelting of the eastern proto pacific plate under the western proto Australia continental crust. This also leads to postulations about other sectors of this conceived eastern Australia mineralization belt. This ongoing work suggests vectors at the continental, province and district scales.