When you say most of the mines outside the central cluster are already gone, is that just a guess based on the fact lots of people will have looked for them so many will be taken, purely from a statistical point of view. Or actually based on some sort of world-dump-y knowledge from someone in the know, like an admin?
There is no public known world dump that could ascertain what Naxza says. I have limited experience with travelling in the outer supergrids myself, so what he says
may be true for all I know, but it would amaze me if all the mines are claimed and I do personally not believe so (judging "statistically" from my rather limited knowledge of number of players, activity, tendency to cluster and observed mine density.
Will not having a mine be massively detrimental to development, or are there ample opportunities for trade? Blaze's last post about trading for copper has my hopes up. To be honest I kinda like not having a purely self-sufficient camp, because it encourages socialising with others to barter for goods I simply can't produce. If I can do everything (as I could on Wurm, for example) I tend to become a bit more reclusive, rarely straying outside my camp and rarely talking to anyone who isn't in the same camp as me, which is a shame!
As I myself have access to a mine, I may not be the one who should answer this, but I would still say that not having a mine is not detrimental to development - there are a number of resource trees/activities you can walk down, and while you'll certainly need some metal whatever you do, this can be easily traded for - I will give you good trade conditions myself - or even mined at one of Brodgars public mines (see threads in the HH forum).