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.
The people I know that used to work at Bellevue were airleg miners. The grade was high and the production low. Looking at the mechanised mining method for vertical and sub horizontal orebodies may result in higher dilution and trying to push 750ktpa production profile with such narrow vein oredbodies without getting excessive dilution is going to be challenging. Backfilling subhorizontal waste oreobodies with waste rock is fraught with danger as you cannot get enough shoved in there to support the backs and the stress will build up on the remaining opening.
Grade can go up in reserves and generally does. The reason is the resource not making a positive net smelter return are left off pushing the grade up the grade tonnage curve. Generally this pushes it higher than the loss attriubted to dilution except for extreme cases such as 300mm wide high grade orebodies with consistent lodes or high grade resources that sit outside pit boundaries but in not enough quantities to justify the capital to develop to them underground and after the pit optimisation will bring the pit reserve grade lower than the overall resource grade.
BGL Price at posting:
77.5¢ Sentiment: Hold Disclosure: Not Held
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