I found three malachite after killing the High Dragon in Hinterlands, Fereldan Frostback. I found them NorthEast of the dragon's nest by the shore on a dwarfen boat. You will need a mage to repair the little bridge so you can get across. The loot is on the boat. The fourth one I found while sealing the 3rd cave during the Keeping the Darkspawn Down mission. By the Driftwood Margin Camp. First walk north from the camp down the hill, turn right along the shoreloine. You will see a boat on its side followed by white petrofied wood. Turn right when you see the last peice of to petrofied wood. The cave is just up the hill. I killed the darkspawn in front of the cave.One of the darkspawn dropped one malachite.
