"We look forward to becoming a major iron ore producer on an international scale," Rinehart, chairman of Roy Hill and Asia's richest woman, said in a statement.
The $10 billion project is already 30 percent built, the company said, including dredging for two deep water port berths, an airport with a runway big enough for a Boeing 737 plane and villages to house 3,600 construction workers and 2,000 operational staff onsite and at Port Hedland.
The debt financing, the biggest ever provided for a mining project, is made up of loans and guarantees from five Export Credit Agencies from Japan, South Korea and the United States and 19 commercial banks from Australia, Japan, Europe, China, Korea and Singapore.
(Read more: Rio Tinto turns up mine output in iron ore, other minerals)
Rinehart's Hancock Prospecting Pty Ltd owns 70 percent of the project, with Japanese trading house Marubeni Corp holding 15 percent, South Korean steel giant POSCO 12.5 percent and Taiwan's China Steel Corp 2.5 percent.
The impending oversupply is unlikely to deter Rinehart and her partners from going ahead with the project, despite major banks forecasting iron ore prices will fall to around $80-$90 a ton, about 23 percent below current prices.