I only have a small sample size, but I went to Woh Gates and went through a stack of 99 pickaxes and got 4 ores.
As for mining them, the mining points are very spread out and you have to cross through reives. There is also a fatigue system, which allows ~23ish mining attempts without any gear. The fatigue can be reset by zoning.
I'd recommend trying mog garden over mining at this point. Or just buy them and farm something else.
