Thanks for the reply dj420; it is much appreciated.
I hope a mining engineer does comment.
However 'risk' and it's assessment is everything.
And of course there is the 'time rule of money' so getting the timing right is also vital.
I am also a bit daunted by the idea of the material being embedded in granite; nothing funny about that!
Thanks again; I can now leave this idea until there are a few more holes. HC42