At the same time, the timeline for developing the project has slipped.
A new estimate released Monday is larger than the 2008 estimate -- growing 12 percent for copper, 14 percent for gold and 16 percent for molybdenum, which is used to strengthen steel.
Pebble contains an estimated 80 billion pounds of copper, over 100 million ounces of gold and 5.6 billion pounds of molybdenum, said Canadian-based Northern Dynasty Minerals Ltd., which is developing the prospect with London-based Anglo American.
The updated estimate was achieved through drilling 37 new core holes since mid-2008, bringing the number to 509, the mining companies said.
Northern Dynasty CEO Ron Thiessen said Pebble has the potential to be "one of the great metal producers of the 21st century."
"Based on this estimate, the Pebble Project has further entrenched its status among the top-tier of global copper and molybdenum resources, and the most significant undeveloped gold resource in the world," Thiessen said.
Numerous Alaska Native groups and commercial fishermen in the region oppose Pebble out of concern for the risk a mine poses for some of the Bristol Bay salmon they rely on for food and money.
The mining companies have delayed their plan to start applying for permits this year. They now plan to start in 2011 the several-year process of seeking permits. Before filing for permits, they plan to take their preliminary plans to Bristol Bay communities to get feedback from residents, said Mike Heatwole, spokesman for the Pebble Partnership in Anchorage.
Pebble is actually two mines, Pebble East and Pebble West. Pebble East, where the minerals are of higher quality but deeper in the ground, probably would require an underground mine. Pebble West, if developed, would be an open pit mine.
Pebble could provide 2,000 jobs during construction and 1,000 jobs when in operation, Heatwole said.
Elizabeth Bluemink with the Anchorage Daily News/adn.com contributed to this article.
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