The Swiss-based mining company, which explores iron-ore in Ukraine, said it donated $9.5m (£7.3m) to charity Blooming Land during the first half of last year, but has not made further donations since.
Blooming Land was established to co-ordinate the Ferrexpo’s corporate social responsibility programme and to provide medical and social services across Ukraine.
The FTSE 250 company said on Monday that Deloitte found discrepancies in the charity’s bank statements, which has prompted an independent investigation.
The statement warned Deloitte could qualify or modify its audit opinion relating to its 2018 accounts following the review.
The news follows the abrupt departure of Ferrexpo’s senior independent director Simon Lockett, who resigned from the board with immediate effect. He joined in 2017 from Premier Oil, where he was the CEO for nine years.
Ferrexpo said it plans to publish its full-year results next month, despite not being able to guarantee the review will be complete by then. However, it expects its EBITDA to be $500m (£384.5m), compared to $551m (£423.7m) in 2017.
Shares at the mining company fell by 8% following the news.
Deloitte has declined to comment.