Some interesting ideas there, but let me add a few of my own.
We all remember the days of the gold mine at the magic shop don't we? Aaah, happy days, walk a hundred paces, mine gold, walk back, sell gold, repeat as often as possible!
Now of course it's only coal, but the gold mine that close was silly really, it owuld have been cleaned out of ore long ago, now here's my suggestion.
The further away from civilisation the mine is the more dangerous it should be, and that's in addition to the factors suggested in the first post. Of course the further away it is the more ore should be there due to the fact that it is little visited, in fact I believe that mines at the very edge of the explored territory should be so dangerous that only a heavily armed and defended party could go there. There should be no, "hey I've just started mining, where do I go to mine a lot of gold", it should be be "hey I've just started, where do I join the next mining expedition". They would then have to give a percentage of their earnings to the organsiers of the expedition. It should be so dangerous that new players going out on their to mine gold and heading to the furthest gold mine would be killed every time. Of course there would be a few close in gold mines for beginners but the gold would be scarce.
There are some details that need to be worked out, leaving and entering the game at the minesite would be dangerous. if you had to leave for a few hours and came back and your expedition had left you would be all alone and doomed, doooooommmeed I tell you! So a sotckade would be needed, where players could run for safety if they needed to leave, then there could pay the next expedition that comes out to get back to civilisation. Oh yes, and no /die to get back to Hydlaa with your gold, that would need to be though on seriously.
You could also have resident miners who lived there and sold gold to travelling traders who took it back to Hydlaa to sell on, it would be like a mini town. Hard to get to, hard to get back from, but well worth the trip out.
However I do see this as a future possibility, there are to many factors affecting the idea to impement it any time soon, the spawn points for one, to easy to get there with a group then /die to spawn in Hydlaa, in this scenario it is likely the death penalty would be prefferable to waiting for another mining expedition to walk back with.