Cokal chairman Domenic Martino told the company's annual general meeting that even that figure was a conservative estimate.

"This is based on the net present value of future cashflows using life of mine average coal prices, which are materially below current coal spot prices," he said.

"The valuation is highly sensitive to coal price assumptions, and the NPV increases materially with coal prices closer to the current spot."

Martino said BBM had highly attractive margins on spot coal prices and long-term price assumptions.

Using today's spot coal prices BBM would have a US$177 per tonne margin for coking coal and $176/t for pulverised coal injection.

Martino said BBM's path to production had been expedited to capture the market for high coking coal prices.

Its development capex of $26.9 million is fully financed and mine development and operations are fully permitted.

"BBM will generate lucrative earnings for Cokal," Martino said.

"Cokal will receive 100% of BBM's initial cash flows to repay a $67.2 million debt that BBM owes to Cokal."