i have the ability to place down a gold mine on my island i am using just for mining..ahve enough population for it but will not let me place the mine down on the side of the mountian! Whats up with that?

do you have gold on that mountain?
don't try to place it on a mountain near the one with the gold icon on it.
make sure you have enough ressources (like tools, stone and wood) and enough money to place it