However as reported by PI Financial's Digging the Dirt there is analysis which shows production grades in line with reserve grades. It would be interesting to dig further.
Certainly a mine by mine analysis like PI's graphs is important. At a company level the average grade can be adjusted by scaling up and down individual mines' production with the most appropriate economics for the current gold price, while this questions the longer term furtures of the higher cost and lower grade mines it does not change each mine's economics.
PI note that Barrick and Newmont's production does indicate some high grading.
We should also consider that as gold prices fall and miners take write-downs and reduce reserves of their marginal mines the reserve grade will increase into line with production grade.