Ok, just got back to my tent from a education session by the drill foreman. First off, pulling all the rod is old tech, today, in diamond drilling, the core sits in a core barrel, that rides in the drill rod just behind the bit. Every 10ft, the driller lifts the rod and a core spring just in front of the core barrel (inside the bit) will grab the core and break it off. Then, the driller will send down a device that clicks onto the top of the barrel and then the core (within the barrel) is brought to surface. After the core is removed, the barrel is sent back own the hole to repeat. The drills here are going down 3000ft, so pulling all those rods is out of the question except if they have to change the bit. The last job I was on, in Labrador, the drillers came in with 100meters of core in a 12 hour shift.