The fifth and final episode has been aired in a series of five weekly free-to-attend webinars hosted by geoscience collective the Overberg Geoscientists Group (OGG), in collaboration with nonprofit organisation the Geological Society of South Africa (GSSA).

In the final webinar in the series, which took place on March 31, Melbourne and Stellenbosch universities' Professor Neil Phillips delivered a presentation on ‘Applying Archean gold alteration to the Witwatersrand goldfields’ to a group of fellow geologists and other interested parties.

The weekly webinar series, which has been taking place every Thursday at 10:30 on Zoom since March 3, was aimed at capitalising on the significant advances on the Barberton gold deposits, in Mpumalanga, under the leadership of Stellenbosch University's Professor Alex Kisters – who became a Draper Memorial Medal recipient in November last year for his work and leadership in greenstone gold mineralisation research.

The Barberton area is characterised by high-grade gold-bearing reefs that have seen sustained mining for more than a century. The Barberton Greenstone Belt has produced about 11-million ounces of gold since its discovery.

The webinars have reviewed the intimate relationships between fluids and many crustal processes including partial melting, metamorphism, deformation, alteration and ore formation.

“Like so many rapid advances in science, introduction of this new view of crustal fluids heralded a period in which there were virtually two geological languages depending upon one’s background and training,” Philips explained.

He said that, traditionally, rocks were viewed as solid and dry, and they cracked under a stress to offset an orebody. The alternative viewpoint emphasised heat that generated fluid and new minerals, migration of that fluid through a network of structures, deformation driven by high fluid pressures and controlled by rheological contrasts and that all this crustal activity may include a major gold forming event.

Much of the evidence for all of this is contained with alteration mineral assemblages, he added.

Kisters said previously that it was critically important to recognise the intimate relationships between structure, fluid movement and alteration by applying modern geological technologies and interpretations in greenstone and other gold deposits, and, thereby, unlock new economic gold horizons in old deposits.

Phillips said that, over the past 50 years, there has been a “massive” shift in geological thinking with respect to alteration and its relationships to fluids, structure and metamorphism.

No longer is crustal fluid flow envisaged as being up and down open cracks, nor is structural geology simply the measuring of fault displacement, he added.

The webinar series has highlighted how alteration is an integral part of much ore formation and that metamorphism goes well beyond the estimation of pressure and temperature. Mineralogy and whole rock geochemistry become intertwined and influence how rocks deform. Linking all these fields are heat energy, fluids and deformation.

The view of the OGG and the GSSA is that improved scientific understanding of these matters, which was the rationale for the webinar series, might lead to more successful exploration and mining.

The five-part webinar series was facilitated by Phillips – all episodes were open to industry, explorationists and the general public, and have sought to highlight new research in Barberton and other well-known gold provinces. 

All the webinar episodes were recorded and made available on the GSSA YouTube channel for on-demand viewing at no cost.

On March 3, the ‘Introduction to presentation series: Fluid wall-rock alteration in greenstone gold deposits’ was presented by Phillips.

March 10 featured a presentation on ‘Structural settings and alteration of the Barberton gold deposits’ by Tect Geological Consulting geoscientist Caitlin Jones.

On March 17, Kisters presented on ‘Barberton gold deposits as examples of the interplay of structure and alteration’.

Then on March 24, economic geologist Julian Vearncombe presented ‘Optimising the use of structural geology in the gold industry’.

The final webinar in the series was Phillips presenting ‘Applying Archean gold alteration to the Witwatersrand goldfields’ on March 31.

Exploration, evaluation and mining geologist Dr John Bristow said there would be more webinars on other topics coming soon.

For additional information on the webinar series, contact Bristow at jwbdia@gmail.com or Hennie Greeff at hennie.greeff@gmail.com.