Here is a Google Search on the....Gold Nugget Effect .

There are numerous links and reports on this.

http://www.google.ca/search?source=ig&hl=en&rlz=&=&q=core+gold+nugget+effect&aq=f&aqi=&aql=&oq=&gs_rfai=

On this one there is a Power Point Link just at the end of the Introduction...

http://www.geochemist.com/estimation-bias-mineral-deposits-caused-grade-based-staging-multiple-analyses-samples-exhibiting-nu-0

Enjoy your findings and weekend.

........RL