Once the pumps were turned off, the mines flooded back to the level of Lake Superior. It took the pumps from several (many) mines to keep the level of the water down enough to do any ore extraction. They were working at the extreme depth for the equipment available at that time. It became economicaly unfeasible to continue mining operations.The mines were interconnected through many shafts. If you have a chance, take a look at the inside of the Quincy hoist house. The hoist machinery is very interesting to look at and it was steam operated. If you are interested in history and geology, there is a lot to see.
Allan