The 66-year-old businessman was convicted in January 2021 of setting up a complex financial web to pay bribes to ensure his company could obtain permits in Guinea's southeastern Simandou region, which is estimated to contain the world's biggest untapped deposits of iron ore.
He was sentenced by a Geneva court to five years in prison and also ordered to pay 50 million Swiss francs ($52 million) in compensation.
He has been issued another free-passage for the appeal, which is expected to last until September 7, with the verdict set to fall later.
Steinmetz maintained his innocence throughout the original trial and immediately appealed against the ruling, decrying it as a "big injustice."
"I am confident the appeals court can be convinced," he told AFP in an email before the hearings, adding a deeper look at the case revealed "a totally different picture than the one painted by the first verdict".
"We expect that the tribunal recognizes that Beny Steinmetz did not bribe anyone."
During the first trial, Swiss prosecutors convinced the court that Steinmetz and two partners had bribed a wife of the then Guinean president Lansana Conte and others in order to win lucrative mining rights in Simandou.
The prosecutors said Steinmetz obtained the rights shortly before Conte died in 2008 after about $10 million was paid in bribes over a number of years.
Conte's military dictatorship ordered global mining giant Rio Tinto to relinquish two concessions which were subsequently granted to Beny Steinmetz Group Resources (BSGR) for around $170 million in 2008.
Just 18 months later, BSGR sold 51 percent of its stake in the concession to Brazilian mining giant Vale for $2.5 billion.
But in 2013, Guinea's first democratically-elected president Alpha Conde launched a review of permits allotted under Conte and later stripped the VBG consortium formed by BSGR and Vale of its permit.
To secure the initial deal, prosecutors claimed Steinmetz and representatives in Guinea entered a "pact of corruption" with Conte and his fourth wife Mamadie Toure.
Toure, who has admitted to having received payments, has protected status in the United States as a state witness.
Steinmetz's team also rejects the narrative that corruption was behind the transfer of mining rights from Rio Tinto to BSGR, insisting that Rio Tinto had lost half of its concessions for failing to develop them, in line with Guinea's mining laws.
"The mining rights were withdrawn from a competitor because it was hoarding them and then awarded to BSGR on the basis of a solid and convincing business case, with no need to bribe a public official," Kinzer told AFP.