It is a waste od time making gold and turning it into coins.
It costs 1.4k marble, 1.4k hardwood and 1.5k tools to build a gold mine which yields 300 gold ore. It then costs 1.2k coal to turn that into gold and this yields 75 gold.
I can sell those resources on the open market for 350-400 gold.
I suggest that you rethink this.