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Determining the source of exceptionally high Helium concentrations in the Witswatersarand Basin, South Africa


   School of Geosciences

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  Prof F Stuart, Dr Stuart Gilfillan, Mr Stefano Marani  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

Edinburgh United Kingdom Applied Chemistry Applied Geology Environmental Physics Geochemistry Geoscience Geotechnology Hydrogeology Industrial Chemistry Petroleum Engineering

About the Project

Summary

Natural gases found in the Witswatersrand Basin, South Africa, contain up to 15% helium, making them potentially one of the richest helium deposits yet discovered. This project aims to determine the source of the He and refine the reserve estimates.

For further information and application procedures please visit the listing on the E4DTP site here: https://www.ed.ac.uk/e4-dtp/how-to-apply/supervisor-led-projects/project?item=1435

Project background

A global shortage of helium (He) has led to an unprecedented increase in exploration of the rare element in the last decade. Unlike hydrocarbon gases, helium is produced in the Earth's crust by the radioactive decay of uranium (U) and thorium (Th), so the helium concentration in any rock is dependent on the radioelement concentration, the age and the presence of a suitable trap. 

Since the late 19th century the Witswatersrand Basin, South Africa, has been the focus of gold exploration. Helium-rich methane gases have been known for several decades. Exploration by Renergen Ltd. in the Virginia licence area in the Free State has led to the discovery of gases with up to 12% He emanating along faults in the basin. Based on our understanding of the regional geology we have estimated that over 400 billion cubic feet of helium has been retained in the Renergen Production Right area since at least the deposition of the capping Karoo sediments 270 million years ago. While this represents decades of global He use, it likely underestimates the reserve given the old age (> 3 billion years) of the likely He source rocks. 

Despite the immense economic potential of the helium (and the methane!) for the region’s economy, the ultimate origin of the helium , the nature of the trap, and how the helium migrated to the trap are all unclear. The link to the world-class gold “reefs” of the 2.8 billion year old Witswatersrand Supergroup sediments is intriguing. As well as being the largest gold anomaly on Earth, the main reef strata in the Witswatersrand Basin contain extraordinarily high concentrations of U and Th, hosted by detrital minerals in the palaeo-placer deposits. While the reef rocks are a prime candidate for the source rock, the huge volume of Proterozoic granite basement beneath the Witswatersrand Supergroup sediments cannot be ignored as the main faults penetrate the basement. 

This PhD will use petrography, (U-Th)/He dating techniques and natural gas analysis to address questions regarding the source rock and the mechanism of helium loss from minerals to the gas phase, and ultimately to develop a model for the accumulation of He in the main rock types of the Witswatersrand Basin. Samples will be collected from the field and from existing collections within South Africa and UK. 

Research questions

The project will address three main questions:

1. What contribution do the main rock types make to the underground gas phase He?

2. How is the He lost from the minerals and how did it migrate to the trap?

3. What is the role of methane and groundwater in focussing He to the surface?

Methodology

The project will require optical and micro-petrography (SEM), and electron microprobe analysis of U- and Th-bearing phases in the main lithologies. The retention of radiogenic He will be determined using standard (U+Th)/He dating techniques; laser extraction-quadrupole mass spectrometry and ICPMS. The He content and isotope composition of free gases will be determined by magnetic sector mass spectrometry.

Year 1. Collection of main lithologies and petrographic study

Year 2. Determination of U and Th inventory for the main lithologies, He retention characteristics and quantification of contribution to gas phase.

Year 3. Establish model for He production, and test with analysis of free gases.

Training

A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. The student will be based in the analytical laboratories at SUERC. Full training will be provided in all the analytical techniques. The student will join an active natural gas research group. Training at Renergen will include He exploration techniques and drilling.


References

https://www.renergen.co.za/wp-content/uploads/2020/07/2020-Helium-Prospective-Resources-Final-signed-v21.pdf
Martel, D.J., O'Nions, R.K., Hilton, D. and Oxburgh, E. (1990) The role of element distribution in production and release of radiogenic helium: the Carnmenellis Granite, southwest England. Chemical Geology 88, 207-221.
Rantzsch, U., Gauert, C., Van der Westhuizen, W., Duhamel, I., Cuney, M. and Beukes, G.J. (2011) Mineral chemical study of U-bearing minerals from the Dominion Reefs, South Africa. Mineralium Deposita 46, 187-196.
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