The 8 g/t is the Reserve grade. This is different to the Resource grade which isn't subject to the same set of parameters and economic criteria when it gets reported.
A Reserve shape by itself is just a constrained volume which overlaps an area where the Geologists have predicted the highest and most continuous gold grades are (the Resource model grade). However, the Reserve also needs to meet minimum mining dimensions (i.e. width, height, strike length) for it be classified as a Reserve, and of course generate a realised profit once it is mined (primarily driven by the Resource grade, but other factors such as mining cost to get there, trucking distance etc. play a part).
Geologists enjoy modeling orebodies in squiggly lines and also like producing contorted shapes to give to Engineers. The Engineers job is to produce something approaching a mineable shape from this, and this often involves accepting some dilution (or waste material) into the Reserve shape so it can be mined with the equipment you have available. For example, to mine bonanza Resource model blocks of 100g/t that might be sitting within a 30cm-wide quartz vein, the Reserve grade of the 2,000t (for example) shape around that material might only be 10g/t, because a good portion of that 2,000 is mining dilution that is unavoidable if we want to mine and extract that gold-bearing vein.
So commonly, it would be expected that Reserve grades are lower than Resource grades by necessity. To preserve the Resource grade in these kinds of high-grade narrow orebodies, you need to use progressively smaller equipment or use airleg mining, but this is seen as a somewhat boutique and inefficient mining method these days.
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