"Mine All Mine" is the side quest in Borderlands 2
Sidequest (Optional Mission)
How to start
Speak to Lilith
Kill bandit miners 0/10
TURN IN: Tiny Tina
4 Eridium and XP
If you've ever wanted to shoot someone who says stuff like "tarnation," this is the mission for you.
You discovered the bandit miners are selling their Eridium to Hyperion, presumably under the mistaken assumption that Hyperion won't eventually massacre the lot of them and take their money back. If anything, you just helped the miners skip the middle man.