The results are more than double the 600 million tonne target proposed in April 2007, when the prospecting licences were granted.

Aviva CEO Lindsay Reed said the estimate highlighted the potential of the project, where Aviva has been investigating the merit of a 1500MW power station.

"The resource estimate affirms the Mmamantswe Project as a very low strip ratio open pit thermal coal deposit, with the potential to supply the six million tonnes per annum required to support the 1500MW power project," Reed said.

Aviva said coal quality was in line with expectations, and test work confirmed that around half the ash was removed at high relative densities of 1.8-1.9.

The average overburden cover in the resource area suggests a stripping ratio of around 1bcm/tonne of in-situ coal.

A new drilling program to upgrade the deposit to reserve is being planned to commence in late March.