2) Viking hoards rarely had gold coins. While the Vikings used silver coins and silver objects as money, they used gold coins and gold objects as jewelry. Only the very rich and powerful Viking kings and chieftains had gold; the usual Viking warrior and trader only had silver at most. And the kinds of gold coins found in Viking sites are gold dinars from the Middle East, Byzantine gold solidi and Frankish gold coins. Vikings did not have any platinum on them whatsoever. During those days, platinum was not desired, not wanted and not used. In fact, platinum was not seen as a useful metal until the 18th century. By the 19th century, platinum was seen as a precious metal.

3) As far as we can tell, Vikings were not numismatists: They treated coins like scrap metal. Vikings did not care in what form their metal came in… they could simply melt it down and re-make it into whatever they wanted. If they wanted to use their metal (chiefly silver) as money, they just took their silver coins, silver jewelry or silver anything to the shopkeeper and used it as payment.

I hope this answers your questions.