Tonne
The lab said "grams per tonne". They have no way of knowing whether the original sample was 19 tonnes, or 6 tonnes or 500,000 tonnes. It is their JOB to NEVER take the miner's word for ANYTHING. Once they do that, their results are useless, or worse than useless. So when they say "tonne", I have to assume they mean a straight extrapolation from the sample they received. They said 70 grams, so I have to assume they actually had 1/200 that much in their 5 kg sample.
Another thing.... how do you go from 6 tonnes to 5 kg, down 99.9%? They say the 5 kg were "selected". How?