I dont know in which mine are you but I mine all the time in gecko and there is plenty iron ore there I always pick up around 150 iron ores + other ores and minerals, I often go in early or late hours for example if i wake up in 6:00 i take toor arond mine and all ores are intact and they give me 20 ores each, and respown is good as it is right now
people who play all day would just sit in mine and mine with one char and duallogibg crafting on other chars very fast it would unbalace game,
respawn quantity and respawn time should not change