In Sonora during Story mode, during the beginning you will have one gold, one silver, and one iron patch. You can build two mines on both of those. For half a patch each, it equals six mines. After a short while, you will get a request for 75 Pickaxes. Fulfill the request to get access to a second gold patch. The best way to complete this is to start out with a gold mine, an open trade route to sell gold, an iron mine and a smelter. Afterwards, purchase a Blacksmith as soon as possible to get 75 Pickaxes ready to deliver. You will only have a short amount of time to deliver them.