Your messing up the units:
0.1 gram gold per 5 kg of rock, equals:
0.00022 lbs gold per 11 lbs of rock,
Or:
1 metric ton = 1000 kg
So 0.1 gram gold per 5 kg of rock equals:
0.1 * (1000/5) = 20 gr/ton
Sounds a bit more realistic. Please correct me if I am wrong.
Martijn