My Best GuessThe metallurgical report suggests 3 modalities of ore:
1.) Free milling halides;
2.) A portion in associatation with oxides of manganese;
3.) A further portion in silicates.
Manganese oxide issues are addressed with H2SO4 of SO2. SO2 is preferable, because it is often used in flowsheets anyways, for cyanide destruction. Probably a cheaper solution as well. Silicates are addressed by finer grinding sizes.
Systematic scientific investigation requires isolation of the variable under study, holding all other inputs constant. In the recent PR, we are given a comparison of H2SO4 and SO2, for an unknown grind size. Curves will need to be generated for both H2SO4 and SO2 across the entire range of grind sizes, at least down to the lowest conventional size of 74 micron. Maybe even smaller, in Ultra Fine Grinding ("UFG") is considered.
If the data we just got is some sort of first pass baseline study, coarse-crushed for heap leaching, or even just ground to a first rougher stage, typically at about 600 micron, then the metallurgical studies still have a low way to go. A logical flow sheet might be:
1.) First stage rough grind to P80 600;
2.) Pretreat with either H2SO4 or SO2;
3.) Secondary grinding to whatever size needed for silicate ore issues
Alternatively, they might grind to the final size and then do pretreatment and cyanidation.
But if the data we just got is already optimized for gri\ne-size and power consumption (unlikely), then Vindaloo is correct and Boleras really is DOA. But this still does not mean that Sandra is DOA, overall.