In the northwestern corner on the ground floor of Tartarus - the bar in the Kadara Slums - you’ll find a Salarian named Derc accompanied by two Asari babes. Chat with him and he’ll make a suspicious-sounding and vague business proposal, before getting into the details. He’s convinced that Baryte is going to increase in value soon, and needs you to check in on his surveyor, who went missing collecting Baryte samples in Draullir.
Fortunately you don’t have to go too far into Draullir to reach the navpoint Derc gave you. Simply fast-travel to the Sulfur Springs Forward Station and follow the road uphill to the south until you reach a fork, at which point dismount the Nomad and continue on foot to the southeast towards a comm tower on the slope of a mountain. The comm tower is merely a landmark, your real destination is a cave in the rocks just east of the comm tower.
Enter the bowels of Kadara and follow the linear cavern until you reach a larger chamber with a pillar in the middle, at which turn west and continue down another passage. Plunder a Lithium node (there are numerous mineral nodes throughout these caves) read a Datapad “Whoever turned off the lights…”, and chatter with SAM about the presence of a rather significant bit of material. Took more than one person to haul all this here.
Continue down the tunnel and you’ll reach a fork. To the southwest you’ll find some ledges behind a shallow - but still dangerous - pool of toxic water. On these ledges you’ll likely encounter a Rylkor, which is all too happy to sit back and spit acid at you. Kill it, leap over the toxic water and search a dead-end cavern behind it to find some Uranium and a container. Backtrack down the slopes and over the water, then continue down another tunnel to the east, southeast, where you’ll have to put down a pack of Wild Adhi. Kill them and carry on, looting a Lithium deposit shortly along the way.
Shortly thereafter you’ll pick up a search area, which is rather redundant, as… well, the caves aren’t exactly linear, but aside from a few short-run dead-ends they’re not terribly labyrinthine, either. Speaking of which, continue east until you reach a fork, at which turn southeast and kill another Rylkor. Plunder a container down a short dead-end to the northeast, then continue southeast down the passage past where you fought the Rylkor until you find… another fork!
Ignore the path to the south, southwest, as it leads to another quest, which you’ll get to shortly. Instead continue east and follow that branch of the cavern under you find the body of a Salarian, which you need merely scan to get the information Derc wants. Loot some Uranium nodes on the ground, jump up onto a ledge and read an… ironic Datapad “Personal Log: Nebar”. You can also score a Titanium node up here, too. Now that you’ve found out what happened to Derc’s surveyor, you need merely return to him in Tartarus and report what you found. You’ll be rewarded with the conventional fare of 29 AVP, +2% Kadara viability and 270 XP.