This may be stating the obvious if you know the area but have you tried the Country Historical Society in Hurley? They are open sporadically and staffed by volunteers but the place is crammed with all kinds of artifacts and records from the mining days. I remember reading about the discovery of records from the only synagogue in the area where the Torah had been left for safekeeping and ended up in a shed at someones farm (didn't know what was in the box) but its been returned to the people it should be. They have an odd collection of things including record books if I recall. Might be worth a phone call.http://ironcountymuseum.org/index.html
If the people you are looking for were in the mining industry there is a good resource in Wakefield, MI by the name of Bruce Cox who helped find some relatives of mine in Ironwood that I'd hit a brick wall with. You can ask at the library in Ironwood about him.