Its recently-released 2014 update also separately lifted its total Hunter Valley resources by 16% to 2718Mt.

Rio Tinto Coal Australia managing director Chris Salisbury said the assets managed by Coal & Allied (Rio 75.71%) in the Hunter Valley were truly world class.

“An extensive drilling program over many decades means we have high confidence in our increased understanding of our coal assets and their quality, which is characterised by shallow, thick seams with little geological faulting,” he said.

“This discovery of greater coal reserves and resources is the result of more than a year’s work and forms part of our wider efforts to deliver greater value to our shareholders. We continue to examine our asset base for further opportunities.

“Our extensive reserve and resource base, further amplified by this latest announcement, provides many options to sustain and grow our business in the Hunter Valley for many decades to come.”

The 2014 resources and reserves update was based on analysing data from about 1300 drill holes.

Rio said it was also transforming the strategic mine planning processes and tools used to estimate reserves plus adopted more efficient resource estimation methods.