LANCASTER SOUND, Nunavut — From a distance, the northern shores of Baffin Island in the Arctic appear barren — a craggy world of snow-capped peaks and glaciers surrounded by a sea of floating ice even in the midst of summer. Yet beneath the forbidding surface of the world’s fifth largest island lies an exceptionally pure strain of iron ore, and the Baffinland mine is believed to hold enough of it to feed smelters for decades. As climate change pushes the ice a little farther north each year, it is spurring talk of a gold rush in the remote Arctic for abundant natural resources, prized shipping routes and business opportunities in tourism and fishing.