A gas essential to modern medicine and scientific research has been discovered in exceptional concentrations beneath South Africa’s gold fields. It is about helium, an extremely rare element, “held captive” of billions of years in the ancient rocks of the Witwatersrand basin, at levels considered unique on a global scale.
The field is exploited in the Virginia Gas Project, where helium-rich natural gas is already reaching consumers, according to earth.com. Estimates show that the reserve could exceed 11.32 trillion cubic meters of helium, turning the region into a veritable natural laboratory for researchers interested in how this gas forms, migrates through rocks and survives underground over geologic time scales.
The study is being led by Fin Stuart, from the University of Glasgow’s Isotope Science Center (SUERC). His team uses helium measurements to trace the movement of gases through some of the oldest structures in the Earth’s crust.
By mapping helium’s path from deep-seated radioactive minerals to modern extraction wells, scientists hope to gain clues that could change the way the world searches for this irreplaceable resource.
Ancient helium beneath the Witwatersrand Basin
In the southern part of the Witwatersrand basin, the Virginia project exploits natural gas with up to 12% helium content, according to detailed analyses. Based on the regional geological structure, the researchers believe that this reservoir has held helium since the Karoo sediments sealed it around 270 million years ago.
The main sources of helium would be the uranium-rich auriferous reefs beneath the basin, supplemented by a fractured granite bedrock at even greater depths.
A vital gas for hospitals and industry
Helium plays a crucial role in cooling the superconducting magnets in NMR machines, which can transport electricity without resistance. Because helium forms extremely slowly through the radioactive decay of uranium and thorium, it is virtually non-renewable on a human lifetime scale.
The stark difference between the slow pace of production and accelerated consumption has already led to supply crunches for hospitals, research labs and the semiconductor industry. In this context, a deposit capable of sustaining helium production for decades is of significant global importance.
Radioactive rocks, the key to the formation of helium
The helium in the Virginia field is mostly radiogenic, that is, the result of radioactive decay of rocks over millions of years. The Witwatersrand Basin contains 2.8–3 billion year old gold reefs rich in uranium and thorium minerals.
Beneath these sediments is a granitic plinth made of very old crystalline rocks, which generate helium that seeps into deep fractures. By estimating the contribution of each rock layer, researchers can assess the lifetime of the deposit and identify similar regions in other parts of the world.
Ancient clues hidden in modern gases
The project involves the use of petrography, the microscopic study of thin sections of rock, to identify minerals containing uranium, thorium and helium. The researchers are also applying thermochronology methods to determine which minerals retain helium and which release it quickly.
In the SUERC laboratories, rock grains are heated to release isotopes, providing clues as to when the helium left the mineral structure. The data is then correlated with helium and methane analyzes from the wells to build a complete model of helium generation, storage and migration.
Microorganisms, methane and groundwater
Research shows that the methane in the Virginia area is biogenic, produced by microorganisms. Waters harboring chemical-feeding microbes have been identified in nearby mines at depths of about three kilometers.
Groundwater flowing through the basin’s network of faults carries methane, helium and salts. As these gas-rich waters rise, bubbles of methane trap the helium and concentrate it in geological traps like the Virginia deposit.
Renergen has managed to overcome technological challenges related to cooling, reaching temperatures of -269°C, necessary for the production of liquid helium. Phase 1 of the project is designed to deliver liquefied natural gas and approximately 350 kilograms of liquid helium daily.
As production increases, correlating geological data with actual extraction will become essential for planning future stages of this globally strategic project.
