Gold mines

I was wondering since the beginning of my play, why don't we have gold mines so we can have production same as food and ore? That will be great construction and can be also used for a new research tree. For example you can build one when you reach town hall lvl25 and you can build 2 more of each th you ug you
Research tree for example:
0/10 gold production 20% per lvl
0/20 gold production protected cap -
1.5mil per lvl
0/15 gold production cap- 2mil per lvl
and if you research the whole tree you'll be able to have like 10mil per 24h and lets say 100mil protected cap. And when you want to use gold it should show you if you want to use from your production or the one you got from volleying, stealing and mobs.

(Sorry for my english beforehand)