As I said in the General Map for farming Relics, Dark Sector and Orokin Derelict missions are special because rewards are given in an unusual way, and also we’ll get some special rewards in addition to Relics, that is what we are looking for, don’t we?
Dark Sectors are special missions that you’ll find in every planet (but Lua, Void, Kuva Fortress or Orokin Derelict). During these missions you’ll face infested enemies always, and there are four different kind of missions: Survival, Defense Defection and Excavation Missions. Relics are given as rewards on any case, but you’ll also be rewarded with extra credits, experience and resource increased drop rates. Looks great, isn’t it?
Here you have al the information in detail of each different mission so you can find easier what you need:
Defense and Survival are the missions where you’ll receive Relics as possible rewards between others in a different way from the same missions outside the Orokin Derelict environment. It is true that Capture missions on Derelict give us Relics as rewards, but in this case it follows exactly the same patern that other Capture missions on Warframe universe.
Hope you find this info useful, one glance, my signature.