But Ashton’s chief executive Doug Bailey said shareholders should continue to take no action in relation to their Ashton shares.

Rio is a joint venture partner with Ashton in its major asset, Argyle Diamond Mine in Western Australia. Rio controls 60% and Ashton 40%.

Elsewhere, Ashton announced yesterday that it has intersected diamondiferous kimberlite at its Maqteir licence in northern Mauritania. Processing of selected drill samples has recovered 78 diamonds and diamond fragments weighing 2.86 carats.

This is believed to be the first fully-documented diamondiferous kimberlite disovered in Mauritania. Although only early results, they form a strong basis on which to proceed to the next stage of the exploration and drilling program, the company said.

The Maqteir licence is held by Ashton in joint venture with Dia Met Minerals of Canada.