If you are involved in mere trading of gold and silver, which entails simple buyng and selling of gold and silver without any value addition bring done by you, then 2.5% Zakat will be applicable on trading inventory (maal-e-tijarat) as at the date when “Zakat on Wealth” is to be calculated. Total Zakat would be 2.5% of cash-in-hand plus cash-in-bank plus value of stock-in-hand and any other form of asssets/wealth. Value of obsolete stock can be deducted from the total value of stock-in-hand (Zakat is applicable only if total value is above the set Nisab for Zakat excluding value of items for personal use).
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Discussion 58129
However, if the busness is not of retail nature but involves some value addition being done on the raw material of gold and silver, then production zakat would be applicable on the amount of value addition only.
Please see for further details:
Discussion 50336