Basalt

June Editorial      

 

Finding Helium

 

Even though helium is the second most common element in the universe, on the Earth it is relatively rare. This is because helium is a gas, and when released it disperses irrecoverably into the atmosphere. As a result the global stock of helium has been running dangerously low. At a rough estimate there are some 35 billion cubic meters in known reserves, while the world gets through 227 million cubic meters every year. Half of that is used in the USA, where it is used for welding, in some computer screens and in specialized medical equipment. It is also used for lifting balloons, be these commercial blimps or kids party balloons.

The thing about helium is that unlike the other 'lifting gas' hydrogen helium is non-flammable, and can be chilled to nearer absolute zero than other gasses. It is so important that one Nobel Prize winning scientist (Robert Richardson of Cornell University) has suggested that party helium balloons should cost $100 each to discourage such frivolous usage.

Helium is created through nuclear fusion in the sun, which has a huge abundance of the stuff. On Earth, helium is released through the decay of radioactive particles in thorium, uranium or other heavy metals in the granitoid rocks of Earth's continental crust. The problem is that, once produced, most helium escapes into the atmosphere. A special set of circumstances is needed for helium to be available for use. Firstly the granitoid rocks have to be rich in thorium, uranium or both. The basement rocks need fractures and faults to allow the escaped gas to accumulate and escape. Then a layer of porous sedimentary rocks must be present above the basement fault which is in turn capped by substances such as halite (rock salt) or anhydrite (calcium sulphate , CaSO4 ).

Under those circumstances the helium is trapped in the sedimentary rock, whence it can be extracted by the usual techniques used by drilling for natural gas. Indeed, most helium is found as a by-product of drilling for natural gas, but so rare are the circumstances that result in helium being trapped that most of America's natural resources come from a single field just north of the Texas Panhandle. Because the decay of rock produces helium so slowly, the gas is considered a non-renewable resource, and until recently it was believed that the world would run out of helium at some time around 2030.

Yet the most remarkable thing about helium is that no-one has been looking for it. There was always enough discovered serendipitously through drilling for natural gas to meet the demands of the market. This changed with worries about the increasing shortage of the gas and prices starting to creep upwards. As a result a start-up company called Helium One combined with researchers from British Universities Durham and Oxford to look specifically for helium. They chose as their target parts of Africa with good conditions for producing and trapping helium which had been previously unexplored because it was highly unlikely that natural gas or oil was also present.

The team explored areas of Tanzania, focusing on the Rift Valley because the tectonic activity produced by the ongoing rift creates intense underground heat which aids radioactive decay. The same effect is found near active volcanoes, but Durham researcher Diveena Danabalan has observed that gas traps too close to the volcano would be polluted by other gasses, while insufficient decay would occur further away. The question of whether there is a 'Goldilocks zone' just far enough out to produce relatively pure helium is still being explored.

The team announced its results at the Goldschmidt Geochemistry conference in Yokohama, Japan in June. According to their evidence, just the Tanzanian reserve of helium contains around 1.5 billion cubic meters at a concentration of 10.6 percent. As Peter Barry, an Oxford researcher remarked, 'We can apply this same strategy to other parts of the world with a similar geological history to find new helium resources'.

In other words, the world's supply of helium is still finite, but that supply is now much greater than was thought just two years ago.

 

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