This room is populated by seven ghostly dwarves. The dwarves must be killed to pass on to The Entrance to Molten Core and The Black Forge and The Lyceum.
Before the attack, any miners should speak to Gloom'rel and do his quest to gain the ability to smelt Dark Iron Ore.
When ready speak to Doom'rel to begin the fight.
The seven dwarves will challenge you one after another, so this fight is not too difficult:
Once the dwarves are defeated, the Chest of the Seven will spawn next to the door.