"This has not been an easy process. We are very aware that these decisions will have a significant effect on staff and their families," O'Leary said in the newsletter.
He encouraged staff to support those affected, who would be visited by Work and Income this week.
The company was contacting other local employers and arranging workshops on CV writing and to discuss other support options.
The company was also expected to make a final decision this month on a revised structure for its exploration and geology team. Once that was made the company would know the impact on job numbers.
An OceanaGold staff member said almost half the 40 Waihī people working in exploration and geology faced uncertainty following an announcement at a meeting on January 15.
"We have mums and dads working with us, people with families who are tied to this area. We're really angry.
"We don't find out until March 1 who has got jobs and who doesn't ... so we're still fighting for our jobs."
Meanwhile, the Coromandel Watchdog group has applied for a judicial review of an October decision by Minister of Finance Grant Robertson and Associate Minister of Finance David Parker to allow OceanaGold to buy farmland for tailings storage under the Overseas Investment Act.
Their decision overturned a May decision by Land Information Minister Eugenie Sage to decline the proposed purchase.
A spokesman for both Parker and Robertson said neither minister would comment on the judicial review as the matter was before the courts.
O'Leary said the company was aware of the judicial review.
The judicial review will be heard in the High Court and no resource consents have yet been issued for the land in question at Waihī.
