Which metal was first used by the Vedic people?

'Ayas' term has been used for the copper metal in the Early Rig Vedic age.
Among the metals in the Rigveda, copper or bronze is first mentioned. 
He was familiar with gold and silver but iron is not mentioned in Rigveda.
The barter system existed in the transaction.
Gold was known as "Hiranya".
Iron was discovered by the Aryans.