One of the features introduced in late 4.85 was depleting mining fields. This feature defined a maximum capacity and a regenration rate for each field's yield, and it meant frequently-mined fields would get lower drops until they run dry, and then would need a few hours to regenerate. This was mainly done to spread the mining activity throughout the server, as back then, majority of miners were focused only on 3 main fields.

Since mining system as a whole has undergone major reworks a couple of times since then, and furthermore, current server activity does not require to be regulated with such measures, field depletion is disabled until such time it's deemed necessary again. This in simple means, regardless of the quantity of ore mined from a field, or number of miners occupying that field per day, drop rates would remain the same and will not be reduced.

P.S: Not so unrelated to this announcement - We'll also be restarting Jammi's ore events in a week or two.