Ok do not have leviation spell tp get pass the acid bit on the sec floor of mine. Found serect door that leads nowhere. Have mine key but does not open up door sec floor.

Enjoying backtracking to town, grinding for hours to level up your Magic of Miracles skill, buying the Levitation spell, and then walking all the way back to the Iron Mines.

That, or use the heretical magic spell Uninstall.exe. It's far more effective.

is that the secret door with an old miner?

If you have a melee paladin build you can just walk across the acid.
But there's not really anything on the other side, except bunch of enemies, some crappy loot and bunch of traps.

Like the poster above me said, there's a trapdoor next to the pool that lets you continue the dungeon.