Electrum

A very pale yellow, natural alloy of gold with between twenty and fifty per cent silver, found in the rivers of Asia Minor and used by the Egyptians as early as 5000 BC for gold artefacts and by 3100 BC as standardised gold bars for exchange. Early coins were also made of electrum. Around 2000 BC the Egyptians mastered the technique of separating out the gold and silver.
In modern terminology, electrum may describe any gold alloy where the proportion of silver is sufficient to affect the colour.