The Malachite veins are random..... I did the save/reload trick, from the lift near the 3 pedestals in Depleted Ore Mine, and managed to get 5 gems from the 2 veins. They were the first veins I came across...... lots more to come
That good 5 gem from 2 veins. But there actually not much malachite vein in the game actually. Just a few only. Usually you will keep them for your final equipment for rank 10 enchantments
It seems that each vein can give up to 4 gems ( can be lots of reloading though ) The two veins in the first mine are too close together for reloading too much though, so getting 5 was probably quite good.............. until I got six later