Midrasch zu Bamidbar 7:86

(Bamidbar 7:86) "Golden spoons, twelve": Why is this mentioned? (Ibid. 14) "One spoon ten gold": It is of gold, and its weight is of silver (shekels). You say it is of gold and its weight is of silver. But perhaps it is of silver and its weight is of gold! It is, therefore, written (Ibid. 86) "All the gold of the spoons — one hundred and twenty." It is not the second assumption that is correct, but the first. It is of gold, and its weight is of silver. "Golden spoons": the same that were donated, no unfitness having befallen them. And it is accounted to each one as if he had offered twelve dishes, twelve bowls, and twelve spoons.