Regional fluid flow model developed for a section of the Barberton Greenstone Belt

14th March 2022 By: Darren Parker

A comprehensive and holistic model has been developed for the regional fluid flow patterns within the Sheba-Fairview complex, in the Barberton Greenstone Belt, in Mpumalanga, which also shows how these fluids are tapped and channelled into the localised ore bodies, geological consulting firm Tect Geological Consulting geoscientist Caitlin Jones said in a webinar on March 11.

She said the mineralisation within the Sheba-Fairview complex could be explained by the temporal and spatial coincidence of the well-bedded metasedimentary sequence, which underwent, firstly, folding and subsequent refolding during late-stage northwest-southeast shortening.

She said these refolding processes were associated with flexural slip along the bedding plains and they have been accommodated by bedding-parallel, regionally pervasive fluid infiltration, which was subsequently focused into either soft-cutting brittle fracture networks or jog geometries during the fold tightening.

“While we try to constrain the relative late time of the gold mineralisation to during the refolding, there are still uncertainties regarding, firstly, the exact timing of the gold mineralisation and, secondly, also the tectonic regimes in which it forms,” Jones said.

She said there were also some remaining uncertainties regarding the fluid sources responsible for the mineralisation.

The webinar, presented by Jones, was titled ‘Structural setting and alteration of the Barberton gold deposits’ and forms part of a series of webinars being hosted by geologist group Overberg Geoscientists Group (OGG) in conjunction with nonprofit organisation the Geological Society of South Africa on the alteration and interplay with fluids, structure and Archean gold mineralisation.

“The last half-century has seen 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,” the OGG said.

Rather, the OGG believes alteration was an integral part of much ore formation and that metamorphism goes well beyond the estimation of pressure or temperature.

“Mineralogy and whole rock geochemistry become intertwined and influence how rocks deform. Linking all these fields are heat energy, fluids and deformation. Successful exploration and mining are the goals of the improved scientific understanding,” the OGG concluded.

The next webinar in the series will be on March 17 at 10:30, where Stellenbosch University's Professor Alex Kisters will present 'Barberton gold deposits as examples of the interplay of structure and alteration'.

All the free-to-attend webinars can be accessed at this link:

https://us02web.zoom.us/j/82093178839?pwd=dWs1c2k2RkFuTS9CM2VtZ0lsUHdndz09

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