Fortescue Metals Group engaged a law firm to investigate the behaviour of executive chairman Andrew Forrest after receiving an anonymous letter.
Seyfarth Shaw LLP concluded that none of the matters in the letter were substantiated and there were no adverse findings, a Fortescue Metals spokesman said in a statement on Monday.
The statement did not disclose the nature of the allegations.
The West Australian reported on Sunday that the investigation involved whether Mr Forrest had had a relationship with a Fortescue employee.
Mr Forrest, 61, and his wife Nicola Forrest announced on Thursday that they had decided to separate after 31 years of marriage.
Fortescue said it selected Seyfarth Shaw to investigate because the law firm had demonstrated expertise in investigations of this nature and were independent, having never previously represented Fortescue or Mr Forrest.
The law firm’s legal fees weren’t contingent on any particular finding or outcome, and Seyfarth Shaw was provided with full access to electronic records, documents, employees and information to conduct a forensic review, Fortescue said.
Seyfarth Shaw Australian managing partner Darren Perry led the probe.
Fortescue said it provides a number of channels for team members to report complaints either anonymously or in person, in keeping with accepted whistle-blower protocols, and remained committed to doing so.