A 230 million tonne increase takes Cook’s resource to 406Mt while 50Mt was added to Minyango, giving it a total of 342Mt.

Neither upgrade was the result of recent drilling.

For Cook, Caledon said a review of geological data previously held, plus the recent receipt of additional historical data, led to the upgrade.

Cook now has a resource of 86.1Mt measured, 90Mt indicated and 230Mt inferred.

Caledon said a total of 303Mt was at a depth of less than 300m, with this amount comprising 99% of the measured resource, 86% of the indicated and 61% of the inferred.

“The balance of the resource estimate occurs at depths less than 500m,” the company said.

At Minyango, Caledon said the boost resulted from including the areas of EPC997 and MDL375 into the resource estimate.

The previous estimate was based solely on EPC699 and excluded EPC997.

The London-based company said a total of 308Mt at Minyango was above 300m in depth, including 99% of the measured and indicated resources, and 83% of the inferred.

Drilling will start this month, targeting the southern portion of Minyango.

Caledon, which also has a London listing, lost 5c on the Australian Securities Exchange, closing at 65c yesterday.