The $59/t figure was below the original target of A$63/t set 12 months earlier.

The company is forecasting operating costs of between $60 and $62/t for 2021. 

Yancoal CEO David Moult said 2020 unit costs benefited from lower diesel prices and deferred costs associated with the company's COVID-19 response.

He said 2021 would include the Ashton underground mine.

"During 2021 Yancoal will continue to focus on the controllable elements of our business; particularly optimising production and keeping our operating cash costs low, while pursuing additional saleable tonnes and optimising our product mix and customer base," Moult said.

"Yancoal achieved its guidance for both production and operating costs in 2020. The $5/tonne decline in unit operating costs to $59/tonne was an outstanding outcome, especially in the context of our lower overall average realised coal price.

"Critically, our low-cost production supported operating cash flow of $605 million, which covered capital expenditure commitments and the purchase of an additional 10% stake in Moolarben."