Major coin finds like these are nearly always from late Roman Empire - 3rd Century and beyond.
currency had been so debased by massive money printing, inflation, and devaluation, coins were not worth much. Also, they fact they were buried in the ground, and not used, indicates their low value and also the social chaos of the period.
It would probably the equivalent of 1500 years from now, someone finding a huge pile of Weimer Republic Marks.
True the coins were no long bronze, silver or gold. They were like our coins, bronze, silver or gold plated.
1500 years from now archeologists will be unearthing 5 gallon plastic jugs full of copper coins with the picture of a nineteenth century president on them.