Particle Size distribution is the first factor in acid digestion of mineral ores. Solubilization/oxidation of mineral ores in digestion increases exponentially with increase in the surface area of the Ore.

Concurrently, the efficiency of the Ore mineral to be distributed increases as the particle size is reduced.

Best way to find out is to examine the impact of increasing the size.

Run some tests at different P80 and see how the copper assays vary. 

If you are also dissolving the silica with HF as a final step then the particle size is less important as any quartz occluded minerals will be exposed to a subsequent the acid leach.  I generally filter the solids out, treat them with HF and then leach them again in acid.

In general, better too fine than too coarse when it comes to assays involving digestion.

Regards

Got to say why wouldn't you pulverise to 100 % passing 75 microns.  Fairly standard procedure for this method.  Sure you could optimise.  But why waste the time.

Yes, you could spend a day and run in-house tests at 75, 100, 150, 200, 100 microns to see where the assays starts to deviate and maybe you can save 1 or 2 minutes on the pulverising time.

To update this question, I guess what the real inquiry was, what is the correlation  between a sample crushed to a particle size of <75 microns and the actually ore itself? Clearly, the more surface area there is, more acid can come into contact with the particles, but what is the limit of this? If we just keep crushing and creating more surface area, we can create more contact with acid, but at what point does the data become nonsense (because obviously in a heap, the P80 would not be <75 microns)? We can keep creating surface area and create more contact but at what point does the data no longer correlate to the ore? Is there a standard size to pulverize for total digestions (using aqua regia)?