I've done a lot of research on gold in Michigan and you won't find any hard rock possibilites in the lower peninsula. The bedrock layer is too deep. However, placer or flour gold can be found in many streams and rivers in the lower and panning is the usual method. In the Upper Peninsula where bedrock is exposed or near the surface there are old gold mines that did produce sometimes considerable quantities and I suppose you could head up there and start whacking away with a pick on public land.