.....from The Financial Post

" growing difficulties in finding gold suggest that high-grade deposits will command a stronger premium over time.

the cost of discovery has increased from US$10 per ounce in the 1980s to more than US$47 an ounce in 2009

there has been a decline in the average gold mining grade from 10 grams per tonne (in 1965-1975) to less than one gram in 2008, according to the data.

deposits with a potential of more than one million ounces and/or grades higher than three grams per tonne will be more and more valuable. "

http://business.financialpost.com/2011/07/07/high-quality-gold-discoveries-becoming-more-precious/