The sites of ancient asteroid strikes dating from million of years ago could provide clues as to the locations of as yet undiscovered mineral and metal deposits.

Geologists believe that the impacts could have created some of the planet's most extensive deposits.

A huge deposit of nickel and platinum is currently being explored in Canada - in the middle of an impact area. Work is ongoing at a similar gold deposit in South Africa.

The chief scientist at Canada's Natural Resources Department, Richard Grieve, told the BBC World Service that a large proportion of impact sites are associated with deposits of some kind.

'On average I would say that one quarter of the known impact structures on the Earth have some sort of deposit associated with them', he said.

'Of that quarter, maybe about half have been actually exploited, either in the past or currently so.'

Some geologists are increasingly interested in challenging the long-held assumption that the mineral composition of the Earth's crust can only change very slowly.

The possibility that trauma associated with the massive impacts could have engendered the formation of important precious metals is gaining increasing currency.

Speaking about research carried out at University College London, Dr Adrian Jones said, "The idea from our modelling and our smaller experiments [is] that the impact crater itself may still retain a mixture of materials, both from the melted crust and from the residue of the meteorite impact that has been redistributed around the crater. 

"That would contain a lot of nickel-rich metals and platinum-group elements."