• Contrast in mechanical properties of sulphides vs. gangue influence liberation.
• During crushing, early liberation in the scale of singular grains is unlikely.
• Clustering of sulphides grains creates conditions required for early liberation.
• Blasting could prepare ore for early liberation of sulphides during crushing.
Assuming the random distribution of sulphide mineral grains and random rock breakage, a relatively small percentage of sulphide grains will be exposed on the rock surface. Early liberation of sulphide grains needs to be considered in terms of the mechanical properties of such grains relative to the properties of the host rock matrix.
Clustering of sulphide mineral grains, will make early liberation possible. Depending on the nature of mineral associations, crushing of such rocks will result in different outcomes. Where clustering is manly of very soft copper minerals, with the host rock being moderately strong feldspars or quartzite’s, the copper rich parts of rock are likely to fragment first, resulting in relatively small size being rich in copper minerals. However, in the case of moderately strong chalcopyrite, the difference in elastic properties between chalcopyrite and feldspar or quartz, will not be significant enough to cause a propensity for early liberation.
Where clustering of copper minerals occurs with grains of pyrite (or magnetite), the stronger part of the rock fragment will be one rich in valuable minerals. During crushing of such rock, the sulphides rich zones will fragment in a different way than gangue. Stress concentration within pyrite (or magnetite) will result in failure of the relatively soft surrounding matrix, thus promoting liberation of chalcopyrite or chalcocite grains. Therefore, textural information about the associations of sulphide minerals (copper sulphides vs. pyrite/magnetite/garnet) will be of critical significance in the evaluation of the propensity for coarse liberation of copper sulphide minerals. An absence of close spatial associations will significantly reduce the possibility of early liberation of copper sulphides.
During blasting ore is exposed to sufficiently intense, high-strain rate loading to be able to induce micro-fracturing originating from individual sulphides mineral grains as well as their clusters. Due to the high rate of loading, a substantial amount of energy can be dissipated with embryonic rock fragment, before macro-failure of rock, which will relieve rock of blast induced stress. Created micro-cracks will play a significant role in subsequent comminution, where rock fragments with enhanced density of micro-cracks will be crushed more easily. Extensive micro-cracking is also likely to play a significant role during heap or dump leaching, stimulating infiltration/diffusion of leaching fluids into the interiors of rock fragments.