gradesyou know in my life i have never heard of grades of gold going down the lower you go....just gravity man....they have said they don`t really know the grades of gold.....they can be microscopic....i was invested in a mine 35 ish years ago in BC and the grades were 2 oz a ton gold but you could not see it , just little glimers... i still have a small core from that mine were i was taken to visit. it was just a black core my brother inlaw was a director of the mine and told me the grade. that it was microscopic ...the mine was so rich that this rock that was 2 oz was all over the top and they used to let the BC goverment take lots of it to do road work....until some one thought hey we should maybe assay some of this black chit.....eh....and the rest was history.