First thing that we need to keep in mind is to decide the domain. Since, they did'nt specified what x is, we will take x as all ornaments in the universe.
Second thing, Here in the question the word and is misleading & it does'nt mean that the ornament will be Gold & Silver. It can either be Gold or Silver.
Third is correct choice of quantifier.
if we use existential quantifier, it will mean that at least one Gold or Silver ornament is precious, which is not what the statement is saying. if the ornament is Gold or Silver then it will be precious.(all Gold or Silver ornament are precious). So we have to use universal quantifier.