well i\'ve read most of the posts in this topic and i think that the best way to handle mining is a sort of mini-game where you will have to make you\'re own mine: you could start with a cave or just some flat ground or a little hill,.... and you\'ll need to start digging with equipment you buy from a player or NPC, these may be pickaxes, shuvels (don\'t know if you spell it this way),...  and you\'ll need wood to prevent cavins.
for the sort of ores: it depends on the location where you dig, and how deep you dig. also if you start digging deeper the risk of gasses, monsters that live in the ground will rise. but the higher you\'re mining lvl is the better you can notice these things and react on them.

this will make everything less boring, more realistic and hard to bot