The NRGI looked at miners' payments to Ghana in 2017 and found the country was getting little revenue from the 10% free carry it requires each operator to hand over.

Of the US$79.2 million paid in revenue in 2017 by Canadian companies (who are required to disclose company payments), 72% came from royalties and 22% came from taxes.

This is far less than the total take, with Gold Fields and Newmont each reporting around $100 million in payments to the Ghana government, but the Canadian system provides the most detailed reporting data to analyse.

The two major US-listed miners publish their payment information voluntarily.

The NRGI report said the ineffectiveness of a free carry holding had been highlighted already this year by the Ghanaian vice president Mahamudu Bawumia.

"From 2012 [our dividend chart] is largely populated by a matrix of zeros, so it means to a large extent, the carried interest in mining is virtually useless as far as Ghana is concerned because we are earning zero for it," he said.

"The zero earnings is because many of the mining companies say they are not making profits to pay dividends but they keep mining notwithstanding the fact that they are unprofitable."

The NRGI was more restrained in its critique, underlining the long road to profitability for a mine, but agreed the system was not working for Ghana. 

"Companies are able to limit their requirement to pay dividends on their operations by reinvesting the free cash into Ghana by expanding their operations, which may generate future benefit for the country, or by shifting profits in the form of payments to related party creditors as part of the international mining company's global operations," the Ghana revenue report said.

"The payments-to-governments disclosures made by international mining companies operating in the country suggest that if revenue generation is the primary purpose of this state equity participation, then the government may want to reconsider this approach."