Mars is my best farming spot. Right where you spawn on patrol, to the left is a cave, to the right, and straight ahead. Then go to the left to the section where vex are fighting cabal and there a LOT of chest spawns in that area. Learn them all and you can get 100+ iron relic an hour. On the moon, I use the spawn poiint as well in the Archers Line. Chests spawn all along the top railway way up high. They also spawn in the far building, and by the far rocks nearest the cliff. There are 3 caves here i believe, and a lot of helium filaments lying on the ground. 60+ an hour once perfected.