The hoard, which includes silver pennies dating back to the 10th and 11th centuries, was discovered by Walter Hanks in Llandwrog in March.
National Museum Wales said some of the coins were made under the ruler Sihtric Anlafsson and were a type rarely found on the British mainland.
It said they were likely to have been hidden or lost between 1020 and 1030.
Dr Mark Redknap, of the department of history and archaeology at National Museum Wales, said the mixed nature of the collection showed bullion played an active role in the 11th Century economy and gave an idea of the wealth of Gwynedd at the time.
The museum now hopes to buy the coins and put them on display.
Viking coins and ingots found by a metal detectorist in Gwynedd have been declared treasure by a coroner.