When GoldMiner turned the slime into gold, he turned the core of the slime into gold as well. So he had met the conditions of destroying the core of the slime which caused the slime to die.
Any attacks on the slime's body wouldn't cause any damage to it. It was immune to any attacks aside from damages inflicted on its core.
Furthermore, the blue slimes had the ability to devour almost anything as long as it was within its limits.
'The blue slime couldn't devour my turn to gold ability since it's more of a rule-type attack than a physical or elemental one. The blue slime's devour ability isn't a rule-type ability unlike Illya's Gluttony Authority or Ayame's Gourmet Authority so they aren't that much of a threat to me.'
Having that thought in mind, GoldMiner still didn't underestimate the blue slimes since this was the real world and wasn't the game world.
