"A little place called Hardrock"; or the story of how Hardrock came to be
This is the mine previously owned by the three unnamed business men in Silvertown. After the PCs assassinated the owners and their escorts, they stole the three deeds to the mine (and also killed one’s wife and orphaned his children. Also, The Kobold Constable.
Now there is an abundance of carts (the mine produces one cartload per day). There are currently 3 additional carts at the mine right now. If the PCs cleared a path through the Thunderpeaks, the cart could get to Tilverton slightly quicker.
It consists of a small mine that connects to the underdark (close to the drow town of Elvenblood), and a little office building that houses the drivers and administrators (who pay the miners and organise who will buy the silver).