It's the ore that makes Swedish steel the purest in the world. Recently, we had a group touring the U.S. from Sweden. Teaching Viking games. Anyhow, they are a bunch of young college grads looking for a little fun before they settle down to big boy jobs. I asked one of them who was a geologist and he said it was because of a good balance of sulfides. I'm not a steelmaker or a chemist, but that's what he said. It tends to attract impurities and those can all be removed in one shot. Pretty interesting.
On the transport of ore, yes it happened. Sweden pretty much felt like they had a gun to their heads, though. Literally. It was like doing business with a gangster. "Do bidness wit me, for dis price, or I'll kill ya".