If you got to 2nd mines, then you can kill Skolas. 2nd mines comes when Skolas has 25% health left. When it's near this, make sure every has full rockets ready (No GHorn needed, but does help obviously). Basically at around 30% health kill all adds first, then use primary / secondary only on Skolas until you hear the announcement for the 2nd mines. Once you hear it, everyone on your fireteam switch to rockets and let rip on him (still keeping an eye on your taint timer). By doing this Skolas dies around the time the 1st mine spawns, with him dead just dismantle the mines in peace. Give it a go next time. good luck!