jantimot -
Watch the next two minutes of this video.
http://www.youtube.com/watch?v=rlBOD1OsbdY&feature=player_detailpage#t=178s
'Of 600 samples, all drilled in same area, half/half diamond /RC, results from the lab, the proportion of coarse copper metal weight is less in RC... by a factor of 20%-50%.'