Varrock armour 4

The Varrock armour 4 is a reward from gaining and spending 150 achievement points. Equipping the armour grants you 10% chance of obtaining an extra ore when mining, or smelting an extra bar. You do not however gain extra items when smithing on an anvil, or any other form of a boost.

The best way to utilize this item is to smelt ore into bars, by starting with 20-25 ores in your inventory. This way, you benefit the most from the armor's ability.