Zaritsky is to remain on as an adviser to the board of directors of the gold explorer and developer and continue in his primary role as CFO of Osisko Mining.
Zaritsky has stepped down from the O3 board.
"Mr Tyshynski brings considerable experience in international capital markets and project financing, and will be an asset in helping advance the Corporation's goals," O3 president, director, and CEO Jose Vizquerra said.
Tyshynski has two decades of experience in international capital markets, having formerly served as director of strategic development for Osisko. He also currently serves as the lead director for NewOrigin Gold, O3 said.
Prior to Osisko, he served as a portfolio manager for the Ontario Teachers' Pension Plan, and director, head of trading, for the Standard Bank of South Africa.
He was also formerly a vice president at Morgan Stanley and The Royal Bank of Canada in London, UK.
National Bank of Canada Financial Markets said it is encouraged by Tyshnski's depth of expertise in international capital markets and that it aligns with O3's increasing focus on project funding.
O3's share price was down 3% day on day at C$1.41 (US$1.41) on September 1. The company has a market capitalisation of C$96.57 million.
NBF has a price target of C$3.25 for O3.