In Minecraft, larger blobs of copper ore generates in the Dripstone Caves, which was mentioned as a specific feature of the biome. However, the deep dark also generates larger blobs of copper. This was never mentioned for the deep dark which makes me believe it might have been an oversight; perhaps when copying code; so I thought it was worth reporting.
This can be verified in the game's code and in the vanilla worldgen example files.
Note: I am not referring to the huge copper veins mixed with granite, I'm referring to the "minecraft:ore_copper_large" feature