Malmberget has one of the largest underground mines for ore in the world and the second-largest in Sweden. The deepest point is 1390 meters below ground. Annual production is over 5 million tonnes of iron ore.

There is a big variety of crystals and minerals found in the mines:
https://www.mindat.org/loc-10629.html

Sometimes the miners hit pockets with crystals, but seldom they are collected as it would slow the work. Luckily there are workers who are trying to save/collect the most interesting stuff.

My father had friends in the mining companies in Sweden and traded minerals directly from them. Most of the stuff he got was back about 15-25 years ago. Much of this material is now long gone, and seldom seen on the market.