Sharp debate erupted Wednesday over a new report that shows that developing the controversial Pebble copper and gold deposit in Southwest Alaska could be very profitable for its owners.

The economic assessment was funded by Northern Dynasty Minerals, the smaller of two mining firms studying Pebble.

Northern Dynasty said the report shows 45 years of open-pit mining at Pebble could generate an average annual return on investment, called the internal rate of return, of 14.2 percent before taxes and pay back the estimated $4.7 billion cost of building the mine in roughly six years.

That's the sort of payback that would make a mining company decide to go mining, said Phil St. George, an Alaska geologist who is credited for discovering the Pebble deposit decades ago.

For comparison, one of the richest undeveloped copper-gold projects in the world, Oyu Tolgoi in Mongolia, has an estimated internal rate of return of 17.6 percent before taxes.

"It is good news for the people who want to see a mine built out there," St. George said.

Northern Dynasty's partner, global mining giant Anglo American, wasn't happy about its partner's announcement early Wednesday afternoon.

Later that day, Anglo called the report premature. The report reflects only the views of Northern Dynasty and its experts and is too early to draw conclusions about Pebble's economics or final design, Anglo said.

Pebble critics said the report is another reason for Alaskans to ignore mining companies' requests that they wait to pass judgment on the project until the Pebble studies are finalized.

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