In Call of Duty: Modern Warfare 4's DMZ mode, the coin mining den key unlocks a room filled with valuable loot. This key is acquired by completing the "Operation Shopping Hacks" mission and provides access to the e-coin mining lab.
Coin Mining Den Key Location
The e-coin mining lab is situated in a small apartment building directly north of The Grid, accessible via the road north of the Netshin Tech Complex. It lies east of the gas station on the northwest road from The Grid and west of the NuriGO Mall stronghold. The building is identifiable by a sunglasses advertisement on one of its first-floor windows.
Upon entering the building, proceed to the top floor. The locked door is located at the top of the staircase. Using the coin mining den key here will grant access to the room, which contains a significant amount of loot, including eight electronic servers. This location is particularly useful for players seeking electronic sensors or comms modules.