Portals spawn at rune locations in replace of rune respawns. If you have a rune farming route you will get a portal on avrg every 15 mins if someone doesn't get it first. For this to happen you have to take all rune and Psijic goods for it to respawn another. DO NOT LEAVE ANYTHING because of inventory. If you do not collect it all another one will not respawn. A addon like Harvest or something to mark your rune route helps a lot. Best of luck.