Indian company Adani needs to come clean about how it is going to fully fund its controversial $16.5 billion Carmichael mine project in Central Queensland.

While Adani chairman Gautam Adani's announcement on Tuesday of a final investment decision on the mine, rail and port project should be taken at face value, the fact there is still a $3.3 billion funding hole for the first stage of the project should cast serious doubt on whether the project will ever get off the ground.