HELENA, Mont. (AP) -- An Australian mining company has offered to purchase a controlling share of Tintina Resources Inc., the company that proposes a copper mine in central Montana.

Sandfire Resources NL of Perth, Australia, has agreed to buy 80 million shares of Tintina at 20 cents per share for a total of $16 million, Tintina officials announced. Two other large shareholders — Quantum Partners and Electrum Strategic Metals — have agreed to the sale, which would give Sandfire a 36 percent stake in Tintina, the company said.

With the investment, the Vancouver, British Columbia-based Tintina would have about $18.5 million in cash on hand to help pay for a feasibility study of the Black Butte Copper Project about 15 miles north of White Sulphur Springs.

"Part of it will go toward" a feasibility study, spokeswoman Nancy Schlepp said. "Some work needs to be done on the mine operating permit, and they might do a little more exploring. A plan hasn't been made yet."

As part of the sale, Sandfire will appoint its chief business development officer, Bruce Hooper, as the new president and CEO of Tintina. Tintina's interim CEO and director had already planned to retire, Schlepp said.

The sale will not affect the management team in Montana, she said.

"This should not change anything — we'll still have the same core team and philosophies," Schlepp said. "They like the approach and the team that's been built."

The proposed mine is about a mile from Sheep Creek, a tributary of the scenic and popular Smith River. The state holds a lottery each year for permits to float along a 59-mile stretch of the river.

"With Sandfire's financial and technical support, we can realize our vision of a 21st century mining operation that fits well with our ranching community and protects the landscape and waterways we all value," said Jerry Zieg, vice president of exploration for Tintina.

Environmental groups aren't so sure.

"The biggest point to take home is now we seem to be dealing with a multinational corporation," said Derf Johnson, associate program director with the Montana Environmental Information Center. "It's concerning about who's calling the shots with a board of directors thousands of miles away, and the locals they've hired in the community not having any real power. This is a turn for the worse for this project."

Montana Trout Unlimited spokesman Mark Aagenes said the move "reinforces our argument that this is not a local company, despite what the local representatives say."

The agreement includes the option for Sandfire to buy up to a 53 percent stake in Tintina over the next five years.