Sandfire announced it would invest $C16 million ($A15.7 million) in Toronto-listed Tintina for a 36% stake, with options to invest further to get to 53%.
The acquisition gives the company access to the Black Butte copper project in Montana, which holds more than 600,000 tonnes of contained copper at grades of about 3%.
Sandfire managing director Karl Simich today described the acquisition as "perfect" for the company and "totally and utterly in line" with its business plan.
Tintina is tightly held and Sandfire undertook months of talks and several site visits, which Simich described as a "considered and deep-penetrating effort".
"There was no opportunity for anyone to get in the front door unless you developed a strong relationship," he said on a teleconference today.
Tintina has completed a preliminary economic assessment on Black Butte on an underground mine to produce about 30,000 tonnes per annum copper over an 11-year mine life for capital expenditure of about $218 million.
"There is potential for a long-life operation there at 30,000 tonnes per annum or even more," Simich said.
"It will potentially make us a 100,000 tonne per annum producer."
Average cash costs are expected to be $US1.80 ($A1.92) per pound.
"That's essentially an all-in cost," Simich said.
Despite some community opposition, the company is confident the project will receive approvals.
"There's no reason why the permit wouldn't be forthcoming," Simich said.
Sandfire also made a $A5.9 million investment in Brisbane-based, Toronto-listed WCB in April to gain exposure to the Misima copper-gold project in Papua New Guinea.
WCB will begin drilling at Misima within days.
"We're excited about the opportunity with Misima," Simich said.
WCB is earning 70% of Misima through a joint venture with Pan Pacific Copper, a mining and smelting company that is jointly owned by JX Nippon Mining & Metals Corporation (66%) and Mitsui Mining & Smelting Company (34%).
Simich recognised that while the rewards of a discovery "would be big", developing a mine would be expensive and logistically challenging.
"We would not be deterred by that in any way, shape or form," he said.
Simich said Sandfire would continue to look for the next great opportunity.
"We're not concerned necessarily about scale," he said.
"We're interested in making money for our shareholders."
Sandfire's criteria are a mine life of at least five years, copper production of 40,000-60,000tpa or slightly lower and an internal rate of return of 15-20%.
"It's looking for business opportunities where we can add value," Simich said.
Shares in Sandfire dropped 0.5% to $6.32.