That is always a problem when you have mineralized ground, especially something that will cause the detector to go NUTS, in a big way.
You did not say where you are located, so we are looking at a continent. If in the Minnesota/Michigan area you are in luck. The state Geological Survey can provide you with old and current reports that might include maps, of the area you are wanting to search. The U. S. Geological Survey also has printed hundreds of papers, available on the internet book seller sites, of very local mining areas. Some have photographs of the actual sites from the 19th and early 20th century sites. They are inexpensive and can provide names of previous owners, when it was in operation and when it closed down. The defunct Bureau of Mines printed material since the early 1900's with the same coverage of detailed MAPS.
When I am hunting with metal detector along... I will not put much time into hunting an area unless it is early 1900's at the latest away from a town in the hills. I do not coin shoot, but am looking for old campsites that can produce some interesting items, other than rusty tin and nails. Some sites are mid to late 1800's that I like the most, so ANYTHING that triggers the slightest hit... I check it out. So good luck and do some research. Knowing WHERE to search is better than trying to attack the entire State!
