I say get rid of mining all together and come up with a new, more imaginative way to build characters and a functional world. Mining is such an unimaginative way of doing things in a made up world in my opinion. I always have to take a step back because people, including me, try to compare how things work in real life and how they should work in the game, but lets face it, that is unrealistic in itself. When you have magic, talking creatures from all sorts of worlds, portals, Death Realms and enchanted swords and potions and such, why do we care so much about digging for something as basic as ore, which we use to get things as trivial as trias, armor and weapons. The world should have a much more imaginative way of doing things. If we can conjure magic arrows, fire, rocks, lightning, cold, then why would we even need something as basic as a pick to dig for something as trivial as ore. Why can't we just conjure it up, or use magic to create things like weapons and armor or why do we need those things at all.
I think the whole economy, items, armor, swords, can be centralized around something more mystical, the core energy source from Yliakum that breaths the essance of life and magic to the world. Where does magic come from anyway? Maybe each person can explore and develop this energy source and use it to create an economy and they don't have to physically go anywhere to achieve it. As you develop it, you can create and conjure better sources of materials which you can use or even sell to less magically inclined characters. Maybe your aura that you develop is what determines your armor, weapon, skills. If you don't have a strong magical background, then you work with your hands and make items that are created throughout the world, or you steal what you can, or serve some other purpose.
I'm talking out of my you know what, but this type of debate and tweak will never go away unless it is completely revamped. It is always dig, kill, collect, sell, buy and repeat. Trying to solve a "problem" in an imaginary world using a realistic world as a basis will never have a realistic answer. The game has endless possibilities, stop being so restrictive to the foundations of real life. Make some stuff up. The mines replenish themselves by magic, the chances of finding a platinum ore is based on luck/skill . That is the reason why there isn't a 400 mile deep hole from the 40 million ores that we've been mining since the beginning, it is all because of magic. That is why creatures reappear when you kill and loot them and why no one really dies, you just go to some place that has a portal which brings you back to Hydlaa... See that wasn't so hard. There isn't a problem with platinum, everyone has the same shot at making the same trias from mining platinum, therefore it is fair. If platinum in general is the issue, then get rid of it along with trias and start over from a fresh angle or continue to have the same debates til the end of time.