"The Serious Fraud Office has opened an investigation into suspected corruption in the conduct of business in the Republic of Guinea by the Rio Tinto group, its employees and others associated with it," the SFO said in a statement on Monday.

In November last year Melbourne-based Rio fired two executives involved in the project after an internal investigation uncovered a $10.5m payment in 2011 to a French national acting as a go-between with the West African nation’s government.

Simandou hasn't only dented Rio Tinto’s reputation
Rio, the world’s second largest mining company, announced in October it was fully exiting the project by selling its stake to former partner Chinalco for up to $1.3 billion. Rio has spent more than $3 billion advancing the project (including a $700m payment to the Guinea government to resolve "outstanding issues" in April 2011) having first acquired the property in the late nineties.

Shares in Rio Tinto lost nearly 2% of its value in London on Monday amid a generally positive day for the mining sector, reducing its market valuation to $79 billion. Rio stock is up just over 5% year to date in line with a better trading environment for miners.

Israeli billionaire Beny Steinmetz is fighting allegations of bribery when it acquired the rights to one half of Simandou (stripped from Rio over development delays) in 2008 when Guinea was under military rule.

BSGR, the mining arm of the diamond magnate, signed a multi-billion dollar deal with Brazil's Vale in 2010 to jointly develop the project, but Guinea stripped BSGR’s rights in 2014. BSGR is seeking international arbitration over the loss of its rights and has also sued George Soros for $10 billion, accusing the hedge fund billionaire of running a defamation campaign against the company.

Rio last year had its lawsuit for damages against BSGR and Vale dismissed in a New York court.

In June, ex-Wall Street banker Mahmoud Thiam who served as Guinea’s mining minister during 2009–2010 was convicted of laundering $8.5 million he was alleged to have taken to help a Chinese company gain mining concessions. Guinea is one of the world's largest producers of bauxite, the primary ore used in the production of aluminum.

With complete control of Simandou, Beijing-based Chinalco may revive the stalled project for the southern block of the 2 billion-tonne deposit of high-grade iron ore.

The original $20 billion agreement signed in 2014 with the backing of the World Bank (which has since withdrawn support) called for a new 650km railway to Conakry, Guinea's capital in the north, plus a new deep water port at a conservatively estimated cost of $7 billion, and infrastructure investments that would double the economy of the impoverished country.

Coal-fired power demand rose last month during a prolonged heatwave in the north ahead of the peak consumption period.

Since mid-February the two nations have helped fill a supply gap left by China's ban on coal from North Korea. In the first half of the year, imports from Mongolia were up 79.5 percent from last year's 10.4 million tonnes, customs data showed on Monday.