The complaint said Thiam used that money to, among other things, reimburse an associate who helped him buy a 30-acre, $3.75 million estate in New York state, enroll his children in private schools and pay $46,375 to a piano company.
Thiam, 50, was arrested at his apartment in Manhattan, prosecutors said. U.S. Magistrate Judge James Francis later denied Thiam bail, after a prosecutor called him a flight risk.
"The defendant cannot be trusted to appear in court," Assistant U.S. Attorney Elisha Kobre said in court.
Andrew Solomon, Thiam's lawyer, declined to comment. But in court, he called the conduct at issue "quite ancient," and questioned why Thiam would have disclosed those bank accounts to the court when there was no evidence he had money in them.
"There's nothing here other than a lot of smoke," Solomon said.
The Chinese conglomerate was not named in court papers, but a key deal in the case matched the description of an agreement reached in 2009 involving a joint venture majority owned by China International Fund and China Sonangol.
China International did not respond to an email seeking comment. China Sonangol could not be immediately reached. Both companies during the period in question had the same address in Hong Kong.
The complaint said that Thiam had helped the unnamed Chinese conglomerate receive valuable rights in a wide range of sectors in Guinea's economy, including near control of the country's mining business.
He received $8.5 million from its senior executives and officers, the complaint said, money that was deposited into a Hong Kong bank account that Thiam established by concealing his nationality and position as a public official.
In court, Kobre contended Thiam was not being candid about his assets when detailing them to court officials, claiming to only have $30,000 in assets despite a $1.2 million annual income and holding multiple accounts and companies worldwide.
Solomon denied that Thiam was trying to conceal anything, however, saying he had long had problems with the U.S. Internal Revenue Service, which property records show has taken out millions of dollars in liens on his apartment.
The case is U.S. v. Thiam, U.S. District Court, Southern District of New York, No. 16-mj-7960.
(Reporting by Nate Raymond in New York; editing by Bill Trott, G Crosse)