a variety of gold alloys are imo best used in ways that narratively suggest and lead to extinct cultures and technology, ideally with strange markings and found with cultural artifacts that send the party to a sage who can direct the party as to their significance in a manner that furthers the campaign. (Alternatively a high-level bard might just make a lore roll, or be told by the DM to smooth gameplay.) Electrum has been a part of standard D&D rules since at least 1st ed. one coin generally worth 1/2 a gp.