(1) Whether we should consider the consider total weight * current price or (2) Get the selling price of the ornament and accordingly pay the zakah [as the jeweler will deduct some percentage in gold as impurity].
بسم الله الرحمن الرحيم
The adulteration in gold or silver ornaments is counted with the original gold and silver as it is generally very less; therefore while weighing and fixing its price both the original and adulteration shall be calculated together. It is better to consider the price on which the jeweler sells and calculate the fortieth part of the all ornaments as zakah.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.