What is under you depends on where you are. Dig down and the rock changes with a real geological map of 1.2 million mapped areas. Ore follows real enrichment data too, so some ground really is richer in a given metal than other ground.
Sea level here is y120, not y63. Every depth instinct you have is 57 blocks out.
Prospecting
Prospecting is a pickaxe enchantment with four levels, and you can only get it by trade. It reads the ore data and tells you how rich the surrounding region is.
It gives you a reading for a region. It is not x-ray and it will never tell you where a block is. It answers one question: is this part of the world worth mining for iron.
Two things a miner notices straight away
- Nether portals in the overworld no longer produce gold. The Nether's own gold farm still works.
- The Deep Dark has no ancient city. The Warden carries what the city held. See The deep.