Rio Tinto has terminated the contract of legal chief Debra Valentine amid an inquiry into payments made to a consultant in 2011, after concluding that she "failed to maintain the standards expected" of her under the company's code of conduct.

The mining company has also terminated the contract of energy and minerals chief executive, Alan Davies, citing the same reasons.

The firings come after the company became aware of payments amounting to $10.5m (£8.5m) made to a consultant on its Simandou iron ore project in Guinea (pictured above).

Valentine, who joined Rio Tinto as global head of legal in 2008 and was promoted to legal and regulatory affairs group executive the following year, had been due to retire next May.

A Rio Tinto spokesperson stated: "The board's decision does not pre-judge the course of any external inquiries into this matter. However, the board concluded that the executives failed to maintain the standards expected of them under our global code of conduct."

The firing of Valentine and Davies means they will not be eligible for any short-term incentive plan awards for 2016, and the company will cancel all unvested incentive plans from previous years. The company said it has reported the issue to US, Australian and UK authorities.

"Rio Tinto intends to cooperate fully with any subsequent inquiries from all of the relevant authorities," the company added.

Chief financial officer Chris Lynch has temporarily taken over Valentine's role and the recruitment process for a new chief legal counsel is underway.

Valentine also previously worked for United Technologies Corporation, where she was deputy general counsel (GC) and corporate secretary. Before that, she was a partner at O'Melveny & Myers in Washington, while she also served as GC at the US Federal Trade Commission from 1997 until 2001.

Law firms Rio Tinto has used in recent years include Sullivan & Cromwell, Linklaters and the magic circle firm's Australia ally, Allens.