Mods installed
-Buildcraft 4.2.1
-CraftGuide 1.6.7.4
-EnchantingPlus 1.16.5 (installed after world generation)
-Forestry 2.3.1.0
-Railcraft 1.6.4-8.3.2.0
-ZansMinimap1.6.4

After installing a quarry on the edge of a DOF, I started getting worried after 15 layers and NO iron at all! (Tin and Copper are present)

Using Minecraft xray (old version, displays all the BC pieces as purple cubes but I don't care), I noticed that NO iron and NO diamond was present in the whole biome! 2 chunks away, in an Extreme Hills, ores are present.

As a side note, somewhat related but maybe not at the place, is the total lack of saltpeter in DOF, even if the biome is "hot".