The QCA ruled Prime could charge coal producers $A1.72 a tonne to use the port, a 9.02% return on investment. This was up from a draft QCA decision to allow $A1.53/t.
Shares in Prime jumped more than 6% following news of the deal last week and were trading at $A1.56 at close of business Friday.
The expansion will increase capacity to 68 million tonnes per annum. Work to expand the terminal's capacity from 54Mtpa to 60Mtpa is well under way but the terminal is still not coping with demand. Prime said it was well advanced with engineering and design plans for the additional expansion and expected to release tenders by May.
"We would like to issue contracts by the middle of this year. We would like to issue tenders for those contracts within the next month," Prime's managing director Chris Chapman told the ABC.
The new tenders will be for a third rail loop and additional stockyard machinery, which is expected to handle further expansions after the 68Mtpa limit is reached.
The rail unloader is to be finished by July 2007 and will cost $350 million.
The QCA said it would approve the expansion automatically, as long as it was consistent with plans agreed with the Government, had commitments from miners for 60% of the capacity, and had 60% support from other users.
