The relationship between basin-hosted ore deposits and atmospheric oxygen was further investigated with a focus on sedimentary Cu deposits and sediment-hosted Zn-Pb-Ag deposits in 2019. A major breakthrough in quantifying the sedimentary pyrite proxy, based on the Se/Co ratio in pyrite, in terms of % O₂ in the atmosphere has led to a revolutionary understanding of oxygen trends. When compared to the timing of sediment-hosted Cu and Zn-Pb-Ag through Earth history, it becomes clear that sedimentary copper deposits have formed during periods of above average atmospheric oxygen, whereas Zn-Pb-Ag deposits have formed during periods of below average atmospheric oxygen. This work was published in Mineralium Deposita during 2019.

This project is investigating the relationship between variation of oxygen in the atmosphere and the cycles of basin-hosted ore deposits. Oxygen cycles have been estimated using the chemistry of sedimentary pyrite through time. Redox sensitive trace elements in pyrite, particularly Se, Mo, Co, Sb and Tl, have proved to be the best indicators of oxygen variation. A paper is in preparation relating to sedimentary copper and zinc-lead genesis to cycles in atmosphere oxygen through time. This work was also presented at international conferences in Vancouver, New Hampshire and Sydney during 2018.

This project is investigating the relationship between variation of oxygen in the atmosphere and the cycles of basin-hosted ore deposits. Oxygen cycles have been estimated using the chemistry of sedimentary pyrite through time. Redox sensitive trace elements in pyrite, particularly Se, Mo, Co, Sb and Tl, have proved to be the best indicators of oxygen variation. In a 2017 paper published in Economic Geology, the research team discussed the controls of atmosphere oxygen on the genesis of uranium, copper, gold and lead-zinc in sedimentary basins in the Proterozoic.

Sean Johnson led a study of metalliferous black shales containing enrichments of Se, Zn and Mo, in addition to Ni, Co, Cu and Ag. The results, published in 2017 in Mineralium Deposita, demonstrate how highly metalliferous black shales coincide with periods of elevated oxygen in the atmosphere throughout the Phanerozoic.

Indrani Mukherjee’s PhD thesis, ‘Pyrite trace element geochemistry of Proterozoic organic matter-rich shales of the Boring Billion period (1800–800 Ma)’, was submitted in 2017. It investigated the importance of nutrient availability in the Proterozoic oceans in the ‘Boring Billion’ period. The thesis focussed on analysing bio-essential trace element concentrations and sulphur isotopic compositions of sedimentary pyrite in Proterozoic black shales using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) and Sensitive High Resolution Ion Microprobe-Stable Isotope (SHRIMPSI) respectively, to further our understanding of the ‘Boring Billion’.

The thesis provided insights on trace element availability and paleo-redox structure of the Proterozoic oceans and atmosphere, including its effect on biologic evolution and results were published in Precambrian Research and Nature’s Scientific Reports. In addition, the thesis also explored the possibility of using trace element concentrations in pyrite as mineralisation vectors such as in the Barney Creek Formation hosting the McArthur River deposit. Application of pyrite chemistry for exploration of SEDEX Zn-Pb deposits in the McArthur Basin was discussed in a publication in Ore Geology Reviews.

This project is investigating what ore deposits can reveal about upper crustal, ocean and atmosphere conditions. For example, why are sediment-hosted gold, banded iron formations and VHMS deposits abundant in the period 3800 to 1800 Ma, whereas SEDEX Pb-Zn- Ag, sedimentary uranium and IOCG deposits are more prevalent in the period 1800 to 800 Ma? Most previous researchers ascribe this difference to a plate tectonic process, but there is increasing evidence, based on geochemical proxies derived from sedimentary pyrite, that atmosphere and upper crustal pO2 and pCO2 were the most important parameters. A manuscript on this topic has been reviewed for Economic Geology and will be published early in 2017.

A second focus of the research is on the genesis of highly metalliferous black shales containing Zn, Mo, Se, Ni, Cu and U. Sean Johnson successfully completed his PhD on this topic, with a focus on the Talvivaara deposit in Finland. The team’s research has shown that metalliferous organic-rich shales occur at particular times through Earth history that correspond with pulses in the level of O2 in the atmosphere. A manuscript on this aspect of the research has been submitted to Mineralium Deposita.

This project is being conducted in parallel with the Trace Elements in Past Oceans project in the Discipline of Earth Sciences. The combined research projects won the prestigious 2016 Eureka Award for Interdisciplinary Research.