Anglo American, the London-based company that owned a 50 percent share in the Pebble Mine project slated for Alaska’s Bristol Bay watershed, announced Monday that it is pulling out of the venture.

The mine’s original backer, Northern Dynasty Minerals, plans to proceed anyway, but the decision could hamper development of the controversial proposed copper and gold mine.

“Despite our belief that Pebble is a deposit of rare magnitude and quality, we have taken the decision to withdraw following a thorough assessment of Anglo American’s extensive pipeline of long-dated project options,” Mark Cutifani, Anglo American’s chief executive, said in a statement.

Battles over the proposed mining operation — which aims to extract 80 billion pounds of copper, 107 million ounces of gold and 5.6 billion pounds of molybdenum — have dragged on for years, though Northern Dynasty has not yet filed for permits to operate it.

The mine’s proponents say it will generate new jobs and millions of dollars in state and federal revenue. Opponents are lobbying the Environmental Protection Agency to block it under the Clean Water Act on the grounds that it could contaminate Bristol Bay and imperil a thriving wild salmon fishery.

As of June 30, Anglo American had funded $541 million of the Pebble project’s expenses. Northern Dynasty CEO Ron Thiessen said his company would push ahead with the project and aims to begin filing for a permit by the end of the year.