I can confirm that the ore veins are random.
I quicksaved at the entrance of the Depleted Mines. At the end of the corridor on the bottom-most floor, there is a malachite ore vein. I got 0 to 1 Malachite Gems for 5-6 tries, and in the next one, I got 3!
My eyes are glittering with lust for loot, and my mouth drools.
I could not find the second ore vein in the Patriarch cave, though. The one I could find is just by Patriarch. Anybody care to share?
