I have way too many gold mines and I want to get rid of some. Is there a way to delete them?
You can't do this anymore. You can only delete decorations and traps. Supercell used to have the option, but too many people were accidentally deleting their things so they got rid of it.
On October 18th, 2012 Rauta (A supercell staff) posted this:
We are removing the Sell button in the next major version. Frankly, it's much more trouble than what it's worth. We get a lot of feedback from players who accidentally sold something or that their kids sold their buildings. While we acknowledge that it has been used in some tactics and strategies, we believe that removing it will result in a better overall experience for our players in the long run.