It seems that Prospector Ironband in Loch Modan has been having problems getting supplies to continue his excavations, and he is in need of a courier to find out what happened.
In Ironforge, you find out that a shipment of blastpowder had been sent out weeks ago. As Ironband didn't mention it in his report, it seems likely that it never arrived.
Prospector Stormpike authorizes the shipment (and sends word ahead, so the shipment can be prepared). However, he wants you to personally shepherd the shipment to Ironband. To that end, he asks you to return to Jern Hornhelm and and make sure of it.
Unfortunately, when you return to Thelsamar, you find that the blastpowder shipment is already on its way, in the care of Huldar, and a couple of porters: Miran and Saean. You'll have to catch up to it.
Huldar and Miran survive the ambush (perhaps thanks to you), but the wagon is broken. The supplies still need to be delivered, but Huldar doesn't trust that the Dark Iron Dwarves won't mount another assault. He asks you to escort Miran to Prospector Ironband with the barrels of blastpowder that he can carry, while he guards the remainder of the supplies.
... just long enough to lull you into a sense of complacency. Not far from the compound, you are ambushed by more Dark Iron Dwarves. You and Mirian handily defeat them, and continue on.