Delbert Parr, the mine's environmental manager, said the two animals became mired in the slurry last weekend at the mine 26 miles northeast of Fairbanks.
The cow died sometime late Sunday or early Monday. Biologists from the Alaska Department of Fish and Game euthanized the calf Monday afternoon after conferring with mine officials.
Fairbanks area biologist Don Young said there was nothing biologists or mine officials could do to save the two animals.
Assistant area biologist Tom Seaton flew over the pond Monday morning and reported the cow was dead, Young said. The calf was lying down.
"It's not safe to go out there; that's the limiting factor for us," said Young, who learned of the mired moose Monday morning. "They're out in a really soft spot."
Fort Knox is the largest gold mine in Alaska. It discharges processed ore into the tailings pond, which then settles and behaves like quicksand.
"It's a little bit like a mud flat," Young said.
The moose were about 200 yards out in the pond
Mine officials brainstormed for a way to save the moose, Parr said.
"If there was any way to get those moose out we would have done it," he said. "We couldn't come up with a way that didn't put the safety of some person at stake. We couldn't justify that."
The calf, a bull with spike antlers, "was still alive but not moving much except its ears," Young said. Shooting the moose was "the humane thing to do," he said.
Parr said it was the first time in the 14 years that the mine has been in operation that a moose has got stuck in the tailings pond.
"Moose on that tailings pond is almost a daily event," he said. "This is the first time we've ever had an animal get stranded out there."
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