Minelab metal detectors can distinguish between different targets using discrimination. They analyze two properties:

ferrous (how much iron a target contains)
and conductive (how well it conducts electricity).

Ferrous items are often trash and can be filtered out.
Conductive readings help differentiate junk like nails or foil from valuable items such as coins or rings.

The specific settings and the way detectors indicate “trash vs. treasure” vary across Minelab models.