The Ore Grade and Depth Influence on Copper Energy Inputs

The study evaluated implications of different ore grades and mine-depth on the energy inputs to extract and process copper. Based on a 191 value dataset from 28 copper mining operations, seven model equations explaining operational energy costs were statistically evaluated. Energy costs for copper mines with leaching operations were not found to be significantly affected by ore grades nor mine-depth as all tested equations were rejected in the analysis. In case of mines with milling/flotation operations, a significant relation was established (p < 0.000, R2 = 0.63 for surface mines and R2 = 0.84 for underground mines) which was found to be: energy cost is log-linearly dependent on depth plus the reciprocal of ore grade. On the basis of the equation, an ore grade of 0.5, 0.4 and 0.3% at 300 m of depth results in an energy cost of 60, 127 and 447 MJ/kg to obtain a 30%+ copper concentrate from underground mines, and 52, 95 and 255 MJ/kg for surface mines, respectively. Energy costs are found to accelerate significantly below the 0.5% ore grade level, which can be interpreted as a biophysical barrier below which mining plus milling/flotation becomes increasingly challenging under current efficiency. In splitting out energy use into diesel and electricity, the study found both impacted by decreasing ore grades, but only electricity usage to be substantially influenced by mine-depth. Depth impacts were established as a 7% increase in electricity costs per 100 m and compounded by ore grades.