The generation of Blackstone and Basalt appears to override Ancient Debris, Nether Quartz Ore, and Nether Gold Ore spawns. I've used command blocks to remove all blocks besides Ancient Debris and there is a noticeable difference where Blackstone and Basalt veins are.
Linked issues
is duplicated by 4
Comments 5
Can confirm using a mapper. Ancient debris does still generate in basalt deltas, but it is so much rarer that it is virtually nonexistent.
It appears that ancient debris can only replace netherrack. It would be like coal ore spawning only in stone and not andesite, diorite or granite.
Basalt and blackstone should be included as valid spawn locations for all Nether ores.
Confirmed, though I think this issue should be closed as a "back duplicate" of MC-178298, as it describes the issue more completely and accurately. Blackstone and basalt don't replace ancient debris, it's just not in the code.
Also happens with nether quartz and nether gold ore, see MC-181467.
I'm experiencing the same issue. I didn't use commands to replace blocks, I just used beds to blow everything up below y = 20 approximately. I didn't find any ancient debris in a few dozen chunks in that biome but as soon as I got to a different biome I was getting veins almost once per chunk. So it seems like the blackstone and basalt veins override the ancient debris (unless it intentionally doesn't spawn in that biome?).