What happens when the main financial backer pulls out of a project? The answer is usually clear: The deal fails, which is what the foes of a gigantic gold and copper mine in Alaska are counting on. But in this case the mine has only been dealt a setback and is far from dead.

That about sums up the state of play after last month's announcement by Anglo American Plc that it would pull out of a partnership that planned to build what's known as Pebble Mine, proposed for the Bristol Bay region of southwest Alaska. If the mine were developed, it would be the biggest of its type in North America -- and located on the headwaters of rivers flowing into the world's most productive salmon fishery.

Environmentalists, the commercial salmon industry and local indigenous tribes were ecstatic, as one might expect. They had argued -- no doubt correctly -- that the mine couldn't be safely developed without damaging the salmon fishery, and they waged a savvy campaign that no doubt raised the stakes for Anglo American.

The anti-mine forces recruited personalities such as filmmaker and actor Robert Redford to inveigh against the project; companies such as Tiffany & Co. and Zale Corp. and dozens of others signed pledges to boycott the mine's products; and when the Environmental Protection Agency sought public input on an assessment of the mine's impact, more than 650,000 comments out of almost 900,000 filed were in opposition.

The more interesting story is why London-based Anglo American pulled out in light of what the company's chief executive officer, Mark Cutifani, had to say about the mineral deposit: "Pebble is a deposit of rare magnitude and quality." More specifically, the deposit might hold metals worth as much as $300 billion.

So it's worth asking why Anglo American might have walked away after sinking more than $500 million into Pebble Mine. The timing is interesting too: To maintain its share of the development partnership with Canadian mineral exploration company, Northern Dynasty Minerals Ltd., Anglo American would have had to put another $1 billion into the project.

That wasn't something that would have been easy for Anglo American, given its recent results. In the past four quarters, the company has reported net losses of $2.2 billion. The company also was handed a setback in an iron-ore mining project in Brazil that led to a $4 billion write-down. (Pulling out of Pebble Mine will result in a charge of $300 million.) To top it off, Anglo American's stock has been less than spectacular during the past year, declining about 15 percent. Anglo American had said it was reviewing all of its capital spending plans: Pebble Mine didn't make the cut.

There's also the broader context of the market for commodities. Although the deposits in the Bristol Bay area have been known about for a couple of decades, development plans only started taking off in the mid-2000s. This coincided with one of the great bull markets for commodities, including gold and copper. Now, though, this so-called super cycle for commodities has come to an end, in part because of China's economic slowdown.

That leaves Northern Dynasty, based in Vancouver, as the main developer of the mine. Building out Pebble Mine isn’t something Northern Dynasty can do solo; it's an exploration company, not a mining concern.

It does have a big backer that develops mines in London-based Rio Tinto Plc, which owns about 19 percent of Dynasty. Yet Rio Tinto has financial concerns that rival or exceed those of Anglo American, starting with last year's $7.2 billion net loss.

Rio Tinto also is likely to feel some of the same PR pressure that weighed on Anglo American, and already the demands are coming for it too to withdraw support for the mine.
The force of anti-mine campaign shouldn't be discounted. Mitsubishi Corp., which at one point held as much as 11 percent of Northern Dynasty, received petitions with more than 100,000 signatures urging it to abandon the venture. It did so two years ago.

What's the way forward for Pebble Mine? Here's something to think about: Say Northern Dynasty hooks up with a Chinese company, loaded with cash and less concerned with the reputational niceties that colored the thinking of Anglo American and Mitsubishi? The minerals under the rivers that feed Bristol Bay aren't going away and a mining project that seems unappealing today might look much more attractive when commodities prices rise again, as they inevitably will.

So that leaves the matter in the hands of the EPA, which has come under attack by conservative politicians who say the agency has acted as a surrogate for the mine's opponents. The Clean Water Act is the main tool at the EPA's disposal that might put a permanent kibosh on the mine. The law is serious stuff, but does anyone think it wouldn’t result in a legal challenge? Don't imagine that this fight is over.

(James Greiff is a Bloomberg View editorial board member. Follow him on Twitter.)