In a memorandum, the two companies agreed to establish a major international metallurgic company that could become a global producer within five years. Joint investment in the project is expected to be around $50-$60 billion.
Gallagher said it had agreed to buy a 10% share in metal giant Norilsk Nickel, co-owned by Potanin, while Interros is "considering the possibility" of a 25% + 1 stake in Metalloinvest, a leading Russian iron-ore producer.
The companies said in a joint press release that they had agreed to invite Russian industrial holding Basic Element (BasEl) owned by Russia's richest man, Oleg Deripaska, to become a partner in the project.
The companies also said they could take part in developing Russia's largest Udokansk copper field in Chita, East Siberia.
Earlier on Wednesday, metal giant Norilsk Nickel and Metalloinvest said they had suspended merger negotiations, which were launched in late February.