This achievement is straight forward, just escape the mine. There is one caveat that I would add as I missed it the first playthrough, in the experimentation chamber are two levers and a pit of poisonous gas, alternate between the levers to disperse the gas and head down for the chest. Once you leave the mine you will NOT be able to re-enter and get the chest later.
The achievement pops at the end of the obligatory cut-scene.