Most likely this is site dependent or deposit dependent as trace element content, crystallinity, grain size, degree of oxidation, gangue mineralogy etc will also influence the result. In general a porous pyrite would be more reactive (more surface area, less organized solid) than a euhedral crystal and single pyrite crystals are more likely to be insulated from reaction by gangue than say pyrite concretions where pyrites are connected and on oxidation can transfer electrons thus adding to the chemical oxidation of associated sulfides.

Thanks for the reply (very informative). It is a non oxidised gold ore sourced from the Witwatersrand Basin (South Africa). If you have more information on the subject,  I'm busy running more lab test work on this ore and mineralogical characterisation showed the presence of this three generations of pyrite of which I haven't found any literature that describe their reactivity. Thank again

I think the porous pyrite should be more reactive due to the increased contact surface does get to the gold cyanidation in comparison with the other two types.

I agree. As long as there is no outside or contamination of other minerals/elements, the more anhedral or "spongy" the pyrite, the more reactive it is during cyanidation. Euhedral pyrite is typically harder to leach. Surface area also plays an important part of the cyanidation.

What is the ratio of contained gold within each of the 3 generations of pyrite? Are silver or electrum present in the metallurgy? The % recovery of gold will be significantly determined in the lab leach tests by the above and other gangue mineralogy as advised earlier. Have you completed a gold deportment study?

The porous/spongy pyrite contains more gold grains locked within it (100% locked in sulphide), compact pyrite is the second gold host (associated with poly-mineral boundary) and euhedral pyrite the least (gold occurring in boundary between it and silicates and to some extent occluded on it). Quartz contribute 70% of the mineral composition, Mica(14%), chlorite (7%) and Fe-sulphides (4%). dominant gold host is the fe-sulphide bearing minerals and matrix silicates. For this ore, gold occurs as native and there's hardly an electrum component on it.