RRR are quoting % copper minerals not %copper. Chalcopyrite is approx. 34% Cu so if it was 50% chalcopyrite the grade will be approx. 17%Cu (note that visuals are a volume estimate not a weight estimate and assay grades are weight estimates, this calc is therefore effected by what the other 50% of the rock is...Other copper minerals have lower and high percentages of contained copper. see https://en.wikipedia.org/wiki/List_of_copper_ores
