There are two typos for the description of the bonus missions in game for this battle. One is for the "Lair Ergs" which are actually "Rare" Erg Crystals. Remnants do not count. The other typo was for the Exquisite Iron Ore. The game says you only need 1 Exquisite Iron Ore, but it is actually 5. Both of these bonuses count for the entire party.
Since there is no map for this battle quest on this page yet, the paths can be defined according to which door is unlocked in the first room in Area 2. If the left door is unlocked, you are in Area 1 (the gate behind you is also open, allowing you to see the Ahglan battle area) and if the right door is unlocked, you are in Area 2 (the gate behind you is shut in this Path).
There are three ore deposits in Area 1; in the room with the golem (after the first spiral staircase), in the first room after the second spiral staircase and in the storage room immediately before the entrance to Area 2.
There are three ore deposits in Area 2 Path 1; in the first trap room, in the first big room (with pillars) and in the dungeon (back left cell) at the bottom of the spiral staircase that is located in the room after the first arrow trap corridor.
There is one ore deposit in Area 2 Path 2 in the storage room opposite the exit to the first spiral staircase.
Since both Area 1 and Area 2 Path 1 also have three ore deposits, when running the battle on hard or hero modes be careful not to miss with your Mine Bombs, else you won't have enough to collect all the ore.