KEGS Seminar - Regional assessment of diamond prospectivity: Example from Southern Africa

   

Dr. Alan Jones,
Senior Professor and Head of Geophysics (retired),
School of Cosmic Physics,
Dublin Institute for Advanced Studies


Tuesday, June 21st
4:30 p.m.  

Harrison Hall
Room 177
Geological Survey of Canada
601 Booth Street

 

Abstract 

Almost all geophysical exploration is for targetting resources at recoverable depths, essentially down to a maximum depth of the order of 10 km. Regional assessment of diamond prospectivity is radically different, as industry wants to locate regions where the lithosphere is sufficiently thick that diamonds exist in its roots - this is a depths greater than the graphite-diamond stability field which is typically 150 km in cratons. Tele-seismological methods have been the tool of choice for regional diamond prospectivity, but over the last decade MT has been adopted, pioneered by work undertaken on the Slave Craton in Canada by Jones. Following on from that Slave Craton work, in the early 2000s De Beers encouraged Jones and colleagues to conduct a regional survey of the Kaapvaal Craton, South Africa - a superb natural laboratory given the vast wealth of geochemical knowledge based on mantle xenoliths from the many hundreds of kimberlites across the craton. Consequently in 2004 the Southern African MT Experiment (SAMTEX) was launched. SAMTEX was originally conceived to be over two field seasons, but additional funding and logistical partners resulted in four field seasons and significant expansion of the project to cover Terra Incognita of the lithosphere beneath Botswana and Namibia for a total of 750+ MT sites over one million square kilometres. The SAMTEX data are still to be completely modelled and interpreted, but results to date in over 10 publications show not only the depth to the lithosphere-asthenosphere boundary but also some intriguing spatial correlations between diamond occurrence in kimberlites and electrical anisotropy.
As a more general justification for regional assessment of lithospheric structures, deep-probing geophysical methods are becoming more established as it is now appreciated that all of the world-class mineral deposits lie above mantle chemical and physical parameter anomalies.   

 

Biography 

 Alan Jones studied Physics for his first degree (Nottingham), then Applied Geophysics for his MSc (Birmingham) and Geophysics for his PhD (Edinburgh). He undertook Post-Docs in Germany, Sweden and University of Toronto, before joining the Geological Survey of Canada (Earth Physics Branch) in 1984. He moved to Ireland in 2003 as the Senior Professor and Head of Geophysics at the Dublin Institute for Advanced Studies. He has focussed on the magnetotelluric method (MT) all of his career, from the dark ages of the early-1970s when the MT time series "data" were recorded on paper charts by coloured pens. He has been involved in advancing almost all aspects of MT, from data acquisition methodologies, instrumentation, time series processing, response analysis, modelling to inversion. His most significant contributions, in terms of impact, have been related to studies on the Tibetan Plateau and in Southern Africa. Most recently, he has been working on formal joint inversion of MT data with other geophysical and geochemical data, and consideration of electrical conductivity of olivine in terms of diffusion processes. Since "retiring" in January 2015 he continues his academic collaborations with colleagues worldwide, is a Specially-Appointed Professor at the China University of Geosciences Beijing, holds Adjunct Professor positions in Sydney (Macquarie) and Perth (UWA), and has formed an MT contracting company (Complete MT Solutions) with colleagues and former students.

 

There are no further KEGS Ottawa meetings
scheduled over the summer.

 
See you next Fall!