Innovation: A drop that helps miners strike gold

A MACHINE that can analyse minute amounts of liquid that have been trapped in rocks for up to 2,000 million years is leading mining companies to valuable mineral deposits.

These microscopic droplets, called fluid inclusions, are nature's own time capsules. They show traces of minerals left behind by changing geological processes. But until recently, it has not been possibleto work out their composition. Now the British Geological Survey in Nottingham has developed a mass spectrometer that is capable of analysing less than one billionth of a gram of fluid.

The technology is applied by analysing the composition of fluid inclusions from places where there are known to be mineral deposits, for example old tin mines in Cornwall. Once the droplets associated with different metals have been characterised they can be compared with those in samples of rock from survey areas.

Prospecting companies use a variety of geological indicators to decide where to explore. Dr Tom Shepherd, at the British Geological Survey, said fluid inclusion analysis was not a tool for telling companies which areas to survey, but added: 'It could narrow down the survey area from 1,000 square miles to two square miles.' he said. This would cut exploration costs.

The technique has been tested in prospecting for new gold resources in Spain and Portugal in a project funded by the European Union. The researchers analysed fluid inclusions from Roman gold mines. It was used commercially in a similar study in the north of Spain for a consortium of mining companies. The Britsh Geological Survey has also analysed rocks from County Mayo, Ireland, where several companies have been granted licences to prospect for gold. The gold occurs in some veins of quartz: the problem is that there are millions of veins to choose from. 'There are a number of techniques for finding and analysing deposits at the surface, but if the deposit is below the surface there is no signature in the soil,' said Dr Shepherd. Quartz samples drilled from below the surface can be analysed to pinpoint gold-bearing veins.

The technology can also be applied to oil and gas exploration. Dr Shepherd said it would be important because it would point the way to less accessible finds. It would also be important in studies of the formation of oil and gas reservoirs.

The British Geological Survey has also carried out work for the nuclear power company Nirex, to analyse what, if any, fluids have moved through rocks in the Sellafield area where Nirex is considering underground containment of nuclear waste, to assess the probability of fluids from the waste getting into the rocks.

The BGS is building up a reference database by characterising droplets associated with other minerals.