Kill them and destroy the crumbling gate by igniting the Oil Barrels right next to it. Further exploring the Mine will end you up at a Workshop with several Magisters.Behind that stonewall, there is a strange device that teaches you how to make a Shapeshifter Mask when you have at least 1 source point. One of them has a key that opens a door to a nearby room that has a hidden stonewall in it.You can help them against the Voidwokens and persuade the Magisters after the fight or just kill them as well. After the Shrieker you will encounter some Magisters on an excavation site.You can also just use the Purging Ward if it still has charges left.There is also a key and a letter on the track to your right.Facing the Shrieker, teleport onto the right track and sneak behind close enough to use Source Vampirism on him.Further down the mine, you will encounter a Shrieker right in front of a waypoint.