I know that hovering over the field in the map view gives misleading numbers - it adds up the % yield of all the ore entities in the field, which is kind of silly. So if there are 43 entities in the field, each with 100% yield, the "total" it would show would be 4300% yield. 500/s for a miner is not normal though.
Do you have any other mods installed? Did you change any of the ore map generation settings?