Gina Rinehart has upped her bid for Atlas Iron despite already holding a 76.3 per cent stake in the junior iron ore miner.

Hancock Prospecting announced yesterday it would lift its bid for Atlas from 4.2¢ to 4.45¢ conditional on it securing at least 87 per cent of the target.

The sweetened offer represents an attempt to flush out the last remaining hold-outs in the stock likely to be aggrieved retail shareholders.

However, Mrs Rinehart’s biggest remaining obstacle to securing full control of Atlas is Andrew Forrest’s Fortescue Metals Group, which still holds an 11.37 per cent stake in the company after selling down its holding from 19.9 per cent last month.

The revised offer lifts the price Hancock is paying for Atlas from $390 million to about $413 million.

The offer remains open until 5pm Friday, September 21.

Fortescue revealed last month that it had sold down its 19.9 per cent stake in the loss-making miner to 11.37 per cent.

Hancock Chief Executive Garry Korte urged remaining Atlas shareholders to accept the offer prior to it closing.

“Support from the remaining Atlas shareholders will allow all Atlas shareholders who have already accepted the offer to benefit from a higher price,” he said.

“The offer has been unanimously recommended by the Atlas board, and the high level of acceptances to date reinforces that our offer represents a compelling opportunity for Atlas shareholders to realise value from their shares, which is in excess of their fair valuation as determined by the independent expert.”

Atlas became the subject of an intriguing three-way battle earlier this year when Fortescue and Hancock emerged on its share register, each with 19.9 per cent stakes. Their interest followed an all-scrip bid for the company from Chris Ellison’s Mineral Resources.

Image: Gina Rinehart, The West Australian.