A vote by the striking workers on whether to accept a new workplace agreement is due to close on Thursday, with the union anticipating a strong "no" vote.
Deal gives Orion mine access to mineral rights for more than 80,000 hectares of land in Northern Ireland, which includes one of the world's top ten undeveloped gold deposits by grade.
BHP will gain access to SolGold's Cascabel project, in northern Ecuador, believed to have the potential to become one of the largest copper-gold assets ever discovered.