The bottom line is that gold in the ground, and not producing, is currently valued at about $85/oz, which is roughly 1/10th the value of gold bullion in the hand.

Cannacord produces a chart weekly that tracks POG vs Market cap per oz of gold in situ for a survey of about 40 explorers (non-producers).

Currently the market cap per ounce is about $40 on average. It was $100 back in Nov 07 bit steadilty declined through 2008 and has since recovered to $40.