We can trigger the Borderlands 2 Minecart Mischief mission by picking up the old ECHO recorder thats on a post marked by the yellow exclamation mark on the map.
By listening to this old recording we find out that a character named Amelia Harchek, said that all minerals need to be pulverized by the mineral crusher from this area; but first we need to acquire some minerals to crush.
You found an ECHO explaining that all minerals must be pulverized by the rock crusher at the end of the mining track. If you can get the mineral chunk to the rock crusher, youll be able to get at whatever goodies it holds
Experience: 3859 XP
Our first task in Borderlands 2 Minecart Mischief is to go to the indicated location and find the minecart. The minecart is at the end of the tracks, and it is guarded by a volatile crystalisk.
After the area is cleared of enemies we just have to go behind the minecart and start pushing it down the tracks.
At some point we will reach a closed door and more volatile crystalisks will attack us. When the enemies are eliminated, we push the minecart until we can go no further, and then we open the door using the rotating wheel thats now enabled.
Near the second door we get attacked by threshers, and after the door is opened in the same manner as the last one, varkids will spawn behind it.
In this tunnel, before the third and final door, we have to fight with multiple varkids, paying attention to the adults that can fly.
In the next room, we have to push the minecart on the conveyor belt at the end of the tracks, and then activate the crusher using the lever at our left side. More varkids will spawn, including a badass one, the moment we activate the crusher.
The crusher gives us five raw Eridium pieces, and we need to get them right away. Next, we turn in the Borderlands 2 Minecart Mischief mission in the exact same spot where the Eridium is discarded.