Should different types of extracted minerals be combined to meet the Nisab threshold?
Chapter on Zakat on Gold and Silver
Al-Mughni
Book of Zakat
Primary text
If a mine contains both gold and silver, there are two views regarding combining them to complete the Nisab, dependent upon differing narrations concerning combining different currencies outside of minerals. If the mineral contains types other than gold and silver (e.g., base metals), they must be combined because the Zakah obligation is based on their value, and the value is singular, thus resembling trade goods (Urood al-Tijarah). If one of the two precious metals (gold or silver) is present along with another commodity, they should be combined, just as trade goods are combined with currency for Zakah purposes.
Supporting text
The position stated by Al-Qadi is that gold and silver cannot be combined to complete the Nisab of one another, and the Nisab must be met by each substance individually, as they are distinct categories, similar to how non-mineral items are treated.