The London-listed company, which holds its AGM tomorrow, funnelled the cash to Dan Gertler, a controversial billionaire linked to a string of mining scandals. It did so through complex transactions involving secretive offshore firms registered in the British Virgin Islands. In all, Glencore advanced Gertler’s offshore companies more than half a billion dollars and allowed him to make at least $67 million in risk-free profit, our new research shows.

Global Witness’s revelations, detailed in its report “Glencore and the Gatekeeper”, come as Gertler’s deals attract growing scrutiny.

Shares in New York-based hedge fund company Och-Ziff Capital Management Group crashed by as much as 11 per cent on 28 April after its backing of some of Gertler’s deals in Congo was reported by the Wall Street Journal. US authorities have launched a corruption investigation into Och-Ziff’s investments in Africa. This investigation is looking into the Congo deals, according to a new class action suit against the firm.

Last year the UK’s Serious Fraud Office announced a criminal investigation into the Eurasian Natural Resources Corporation, including at least one of its deals with Gertler. Despite this, both Glencore and Gertler deny any corruption risk and insist their relationship is problem-free

“Glencore appears to have knowingly entered loss-making deals with the president’s friend, a man who is central to all its investments in Congo,” said Leigh Baldwin of Global Witness. “The corruption risks here are obvious. Glencore should now face up to them and commission an independent and detailed investigation into its Congo deals.”

Glencore said in an e-mail to Global Witness that all its transactions with Gertler’s companies have been “conducted on arm’s length terms” and that he was not given preferential treatment over other co-investors. “These transactions were entirely proper,” it added.

Gertler’s spokesman, the UK’s Lord Mancroft, said that any suggestion “that Glencore offered Mr Gertler preferential treatment is wholly misconceived”. He said “there are legitimate commercial reasons for every transaction we are involved in”.

Our latest analysis examines three transactions, each designed in a way that concealed cash flows to Gertler. In one example, Glencore sold him shares at less than half the market rate only to buy them back a few months later at full price.

Last year, Kofi Annan’s Africa Progress Panel estimated that just five of Gertler’s deals lost the Congolese state at least $1.4 billion - twice Congo’s annual spending on health and education combined. Global Witness has previously reported on “potentially corrupt” transactions involving Gertler and Glencore. Our new report heightens concerns over the Glencore-Gertler relationship.

Glencore’s copper and cobalt mines are key to Congo’s future growth but corruption is rife in the country. There are few mining assets as coveted in the country as those held by Katanga Mining, the Toronto-listed company at the centre of the transactions detailed in our new report.

Canadian regulators should examine the deals to ensure stock market rules were not abused by the way in which Glencore and Gertler took over Katanga Mining. This should include examining the loopholes that allowed Glencore to avoid takeover regulations and favour one shareholder above all others.

Global Witness has been calling on Glencore to commission an investigation into its Congo deals since mid-2012, meeting repeated refusals. At tomorrow’s annual general meeting, investors should ask the company:

 why it continues to work hand in glove with a businessman whose dealings have attracted the attention of law enforcement bodies in both the United Kingdom and United States;
 why it was prepared to enter loss-making deals with him;
 when it is going to commission an independent review into the corruption risk of its Congo deals.

Notes to editors:
 A 14 May response from Glencore to Global Witness’s most recent questions can be found here: .
 A response from Lord Mancroft, on behalf of Dan Gertler’s holding company Fleurette, can be found here: .