The building that the dogs sometimes reside in and take refuge in during the serum run has been known as a 'mill' But infact whale watching a ship wreck documintary I figured out that it is indeed not a mill...or a building.
It is a gold dredger.
Mining dredges were used in Yukon and Alaska from the turn of the century on into the 1950s to extract gold from the land.
The machines allowed miners to work large amounts of ground, extracting as much gold as possible from the dwindling supply in a relatively short amount of time.The mining dredges were land-locked floating machines, digging the ponds that allowed them to float—and thus move—across the area to be mined. The floating dredge most commonly operated in the North was the California-type, also known as bucket-line dredge. This type of dredge used a continuous line of buckets (called the digging ladder') to scrape the bottom and edge of the pond. The buckets carried the mud and rock to a screening area, where the heavier metal particles were separated from the rest of the material. After the metal was captured, the waste rock, or tailings, would be deposited out the back.

Looks fimiler doesn't it! In fact there seem to be a few of these floating about Nome.  So the 'old mill' Is actualy the 'old dredger'
here is another pic