Some issues of Zakaat of gold and silver
If any person has gold/silver less than the prescribed criterion, or has only gold or only silver, but has so much cash or trade goods that on including them the criterion is met, then Zakaat is Compulsory on such a person. If the criterion is not met by adding up both gold/silver and other wealth, then Zakaat isn’t Compulsory on such a person.
‘Allama Ibn A’abideen Shaami (May Allah shower His mercy on him) has written in this regard in Durre Mukhtaar, Kitab Uz Zakaat)
If any person has gold and silver, both less than the prescribed criterion in that case if gold is near the criterion, then silver will be included to complete the criterion of gold and then Zakaat will be given from the gold criterion. On the contrary, if silver is near the criterion, then gold will be included to complete the criterion of silver and the 40th part will be given from the price of silver.
As mentioned in Fath Ul Qadeer, Vol. 2, Pg. No. 220.