Stanmore Coal has increased the mineral resource estimate for its Isaac Downs project to 36 million tonnes as a result of exploration work over the past 18 months.

The announcement comes after the $90 million mining project near Moranbah was declared a prescribed project earlier this month, with construction tipped to begin in early 2021.

Stanmore said work undertaken for its bankable feasibility study had produced a recoverable open-cut mining reserve of 25.9 million tonnes, of which 22.3Mt was classified as proved and 3.6Mt as probable.

The company said the bankable feasibility study undertaken by Palaris Australia was in draft form and the results would be published when completed.

The recoverable coal reserves across the Isaac Plains complex stand at more than 50 million tonnes.

This gives the site a mine life of more than 15 years using existing infrastructure , with open-cut and underground operations producing predominantly steel-making coal.

Stanmore said the coal resources across all of its tenements totalled more than 1.7 billion tonnes.