I am no expert but here are some notes I got from somewhere sometime ago.
10,000 ppm = 1.00 %
Very high = 20%
High grade ore = 2%
low grade ore = 0.1%
Granite = 4 to 200 ppm
Earths continental crust = 2.8 ppm
Seawater = 0.003 ppm
Please correct this if someone knows better.
Cheers