Settlers can be buil1t yes, although 250

is a bit more than other civs, and jotnar cities don't tend to do so well on production
with the new cost, expanding is incredibly slow. The entire game seems to be just about saving up for the next settler. It's kind of a drudge.
why so high?
Also, on the subject of mountain yields. If anyone's going to be working them, it should be the Khazad. I'd love to see them able to build a "Deep Mine" in a mountain, which gives +5

but no food or commerce.
Jotnar woing them would be nice too, I suppose. Although I find it a bit silly in general, that the jotnar can even build mines. How do they fit in those cramped tunnels? You can't just build mines to giant scale. The earth wouldn't take it, and would just collapse in on itself
Mostly as a flavour thing, I think it would be apt for the Jotnar to be unable to build mines, but get a special version of a quarry instead, that harnessews the same resources, and gives the same output. Essentially just an open-cast mine