The announcement comes as the joint bidders criticised Macarthur’s track record in developing projects and delivering earnings growth to shareholders.

“Macarthur Coal has a strong growth pipeline of metallurgical coal deposits that it is committed to exploring and developing, as evidenced by this further increase in our inferred coal resources at Yeerun,” Macarthur chief executive Nicole Hollows said.

“Macarthur has the assets, operational capability, strong balance sheet and access to sufficient port and rail infrastructure to meet the increasing demand for metallurgical coal as the company embarks on its next phase of growth.”

The Yeerun deposit, located approximately 20km southeast of Macarthur’s Moorvale mine and adjacent to its Codrilla mine, has potential as an open cut mine development producing a product similar to the company’s benchmark “Coppabella PCI” brand of low volatile pulverised coal injection coal.

Macarthur Coal has an 85% interest in the Yeerun deposit (EPC 676), providing an attributable net coal resource of 56.1Mt. The remaining 15% interest is held by CITIC Resources Australia.

Peabody and ArcelorMittal formed a new company, PEAMCoal, which is offering $A15.50 per Macarthur Coal share plus a final 16c dividend.

In its bidder’s statement PEAMCoal accused Macarthur of ''persistently falling short of earnings and growth targets''.

In a letter accompanying the bidder’s statement Peabody chief executive officer Gregory Boyce and ArcelorMittal chief financial officer Aditya Mittal urged shareholders to accept the offer, which they said represented “outstanding value”.

“Quite simply, we believe it offers you greater value than Macarthur has to date been able to deliver,” they said.

The bidder’s statement lists in detail what the bidders see as Macarthur management’s shortcomings.

''Macarthur has fallen short of its original production guidance for four of the past five years; ongoing delays reaching first large-scale production from Middlemount, which Macarthur originally planned for late 2009 but is now expected in 2012; downgrades to core earnings and production forecasts during financial year 2011; selection of the fourth mine [Codrilla] announced five months behind schedule in May 2011 and failure to complete the acquisition of mining lease MDL162 [in Queensland’s Bowen Basin] as planned.''