Never tried mines before to take down the pirate base, but it should actually work quite well. The only catch is that you'd have to distract the pirates, as even one flak frigate near the minefield deployment site would clear them out completely.
I tried to abuse the ruiner to clear terran/desert plants early in the game by tanking the enemy with my cap while the ruiner makes a minefield some distance away. The results were very good, but it takes too much valuable time to get the ruiner going for this to be a viable strategy (labs, research et al), plus it's a bit too pricey.
It is not hard to set up a sizeable minefield before pirate flaks even get close. With every ruiner you can easily throw two clouds of mines before they come to wipe them. Then you just run the pirates through the minefield, voila.
You just have to
- make sure the enemy frigs are facing the opposite direction to where the ruiner is laying mines (lure them with your cap/fleet)
- the distance needs to be a little greater than the radius of a typical gravwell
