afaik, units won't gather on gold mines unless the Town Hall is of a certain distance to it. i tried once to place a Town Hall and gold mine without any space in it (in WE, if you try to look at the pathing, the blue area of the Town Hall and gold mine has no space between it) the units don't mine. but when you place a Town Hall in the normal distance (in WE, if you place a Start Location near a gold mine, the normal distance is when you see an invisible Town Hall in place of the Start Location) and the units mine normally.