Under the agreement, which closed yesterday, Big Ridge can earn an 80% interest through a five-year, two-stage earn-in by spending C$20 million and issuing 25 million shares.
It had issued 11.5 million shares to First Mining, which is focused on its advanced Springpole project in Ontario, and paid $500,000 on closing.
First Mining's COO Ken Engquist was nominated to Big Ridge's board.
Big Ridge also announced a $5 million placement yesterday, at 20.5c per flow-through unit, to fund exploration at Hope Brook.
The project has an indicated 5.5 million tonnes at 4.77g/t gold for 844,000 ounces and an inferred 836,000t at 4.11g/t for 110,000oz.
It had produced more than 750,000oz between 1987-1997.
Big Ridge had $3.1 million in cash at March 31 and was planning to start drilling in the third quarter.
"We are excited to close the Hope Brook transaction and to commence our Phase 1 exploration programme this summer," president and CEO Mike Bandrowski said.
Big Ridge (TSXV: BRAU) shares closed up 51% to a one-year high of 28c, valuing it at $13 million (US$10.7 million).
First Mining (TSX: FF) lost 1.3% to 37c, capitalising it at $258 million (US$213 million).