Benchmarking: Yanacocha Single-stage SAG Mill

Benchmarking: SAG Mill Power Draw - Yanacocha

• Burger, B., Vargas, L., Arevalo, H., Vicuna, S., Sidel, J., Valery, W., Jankovic, A., Valle, R. and Nozawa, E., Yanacocha Gold Single Stage SAG Mill Design, Operation, and Optimization, Proceedings of the International Conference on Autogenous Grinding, Semiautogenous Grinding and High Pressure Grinding Roll Technology (SAG 2011) held September 25 – 28, 2011 in Vancouver, B.C., Canada.

Mill geometry given as:

• mill nominal diameter (inside shell): 32 ft
• mill effective grinding length: 32 ft
• liner effective thickness: 175 mm (7 inches), eyeballed from new liner diagram

Ore density is 2.52 t/m³

Not stated in the paper is that the 16.5 MW motor is gearless with DCS indication assumed to be motor output power.

	Shell Power, kW	Mill Speed, RPM (%crit)	Ball charge, %v/v	Filling, %v/v	Feed %solids	Simplified Morrell model, kW	Loveday/Barratt, kW	Austin model, kW cylinder+cone	Austin model, kW cylinder only
First Survey	12,286	8.9 (64.5†)	16.5	17.9	73	11,587 (-5.7% difference)	15,005 (22.1% difference)	13,533 (10.1% difference)	12,515 (1.9% difference)
Second Survey	13,992	8.7 (63.1†)	19.1	22.9	80	13,067 (-6.6% difference)	15,858 (13.3% difference)	14,793 (5.7% difference)	13,806 (-1.3% difference)

^† The %critical speed values given in the text do not appear to account for the liner. The RPM values are assumed to be correct and the %critical speed values have been back-calculated.

Simplified Morrell SAG mill model was run, default k=1.26 (motor input basis) used. Austin model also used default fitting factors K=10.6 and A=1.03.

Further conclusions

The reported throughputs and specific energy consumption (E_SAG)

• Survey 1: 620 tonnes/hour; 19.8 kWh/t
• Survey 2: 779 tonnes/hour; 18.0 kWh/t

Bond ball mill work index is reported as 17.53 kWh/t (106 µm closing). The reported DWI and A×b values suggest a rod mill work index of approximately 12.5 (metric) and an impact crushing work index of approximately 8.0 (metric). Running these ore hardness values through the Bond/Barratt single-stage SAG model results in the following:

• Survey 1: F₈₀=79.1 mm; P₈₀=152 µm; E_asag=16.4 kWh/t (20% low)
• Survey 2: F₈₀=72.4 mm; P₈₀=154 µm; E_asag=16.3 kWh/t (10% low)

The Burger et al, 2011 paper reports that the mill was not operating efficiently during the first survey — Grate pegging was significantly more severe during the first survey, and is considered to be a major contributing factor to the difference in performance for the two surveys. Slurry pooling was also noted.