As soon as my quarry mines a block the game crashes and the world isn't recoverable unless the quarry is deleted with MCEdit. Note that my quarry made it around 20 blocks down before starting to crash, and that it's trying to mine a Lead Ore.

Crash report:- https://pastebin.com/GJ8KN04Q
Forge: 9.11.1.965
Buildcraft: 4.2.2
COFH Core: 2.0.0.5
Thermal Expansion: 3.0.0.6

But what is the quarry connected to?

the quarry is connected to a Nuclear Reactor. Also in messing with it I lost the world, and I didn't have a backup, so the whole point is moot, but if I messed something up I'd love to know so I don't do it again.