Svetlana Tessalina

Globally asynchronous sulphur isotope signals require re-definition of the Great Oxidation Event

The Great Oxidation Event (GOE) has been defined as the time interval when sufficient atmospheric oxygen accumulated to prevent the generation and preservation of mass-independent fractionation of sulphur isotopes (MIF-S) in sedimentary rocks. Existing correlations suggest that the GOE was rapid and globally synchronous. Here we apply sulphur isotope analysis of diagenetic sulphides combined with U-Pb and Re-Os geochronology to document the sulphur cycle evolution in Western Australia spanning the GOE. Our data indicate that, from ~2.45 Gyr to beyond 2.31 Gyr, MIF-S was preserved in sulphides punctuated by several episodes of MIF-S disappearance. These results establish the MIF-S record as asynchronous between South Africa, North America and Australia, argue for regional-scale modulation of MIF-S memory effects due to oxidative weathering after the onset of the GOE, and suggest that the current paradigm of placing the GOE at 2.33–2.32 Ga based on the last occurrence of MIF-S in South Africa should be re-evaluated.The Great Oxidation Event (GOE) is considered to have occurred at 2.33–2.32 Ga based on the last occurrence of MIF-S in South Africa. Here, based on sulphur isotope analysis of samples from Western Australia, the authors show preservation of MIF-S beyond 2.31 Ga and call for a re-evaluation of GOE timing.

Application of radiogenic isotopes in Geosciences: Overview and perspectives

Wider use of radiogenic isotopes in geosciences has been enabled by developments in massspectrometry at the beginning of the 21st century. Nowadays, radiogenic isotope geochemistry forms an integrated part of geosciences in a range of applications, starting from formation of planetary systems, genesis, and the evolution of Earths lithosphere and associated mineral and oil deposits, as well as environmental tracers. Two primary types of information are available from radiogenic isotopes studies: age determination and isotopic source tracing. In this chapter, the range of isotope systematics currently used in geosciences and their applications are reviewed, together with progress in analytical technologies. The chapter brings together internationally recognised researchers whohave been at the forefront of analytical technologies in the field of geochemistry of radiogenic isotopes.

Lead isotopic systematics of Urals massive sulphide deposits

The isotopic composition of lead from a total of 53 samples of galena from 18 VHMS deposits shows a range between 17.437 and 18.111 for 206Pb/204Pb; 15.484 and 15.630 for 207Pb/204Pb and 37.201 — 38.027 for 208/204Pb. The results show a systematic trend with the leads of the Sibay, Barsuchiy Log and Djusa deposits being most radiogenic by comparison with those of Bakr-Tau and Oktiabrskoe which are the least radiogenic deposits. The Bakr-Tau and Oktiabrskoe deposits occur within most primitive fore-arc rocks at the lower part of the Baymak-Buribay formation, which contain lavas of boninitic affinity. The Sibay, Barsuchiy Log and Djusa deposits are found in intra- and back-arc setting and are hosted by a sequence of bimodal tholeiites. The deposits in “arc” setting such as the Balta- Tau, Gai and Alexandrinka deposits occupy an intermediate position. This trend is explained in term of mixing between mantle wedge and continental blocks.

2.7 Ga plume associated VMS mineralisation in the Eastern Goldfields Superterrane: insights from the Ag-Zn-(Au) Nimbus deposit

35th International Geological Congress, Cape Town, South Africa, 27 August -04 September 2016