An industrial ball mill operating in closed-circuit with hydrocyclones was studied by five sampling surveys. The aim of the present study was to optimise operating parameters (i.e. charge volume, make-up ball size regime, slurry mean residence time, number of hydrocyclones in operation and hydrocyclone's feed solids content (S-f)) with respect to increasing throughout from 225 to 300 tons per hour (tph). The obtained results showed that increasing charge volume from 32 to 39% led to producing approximately 9% finer product size (P-80). Binary ball size regime rather than using mono-sized balls resulted in reduction of the P-80 relatively 5%. The S-f was identified as the most effective parameter on grinding efficiency. The cut-size plunged dramatically from 130 to 90m by reduction of S-f from 54 to 48%. Finally, it was concluded that the capacity of grinding circuit could be practically increased to 300 tph if all relevant parameters fell into the optimised ranges.