Thats exactly what I was saying before, as under...
There is a spec of gold visible from a 10kg sample. Even if that spec is:
0.5 gms then 0.5 x 100 = 50 gt
0.25 gms then 0.25 x 100 = 25 gt
Pretty awesome. Also the method they have used here would not really isolate the Fine particles, which would add to gt.