Locked-cycle grinding tests using multicomponent feeds provide valuable insight into the dynamics of industrial closed-grinding circuits processing heterogeneous ores. These tests, however, are very laborious and time consuming. We present one general and two simplified mathematical algorithms for cycle-wise simulation of locked-cycle tests grinding mixture feeds. The algorithms have been tested against experimental data on locked-cycle grinding of calcite- quartz feed. Whereas single-component feeds require 3 to 6 cycles to attain steady state, mixture feeds need anywhere up to 35 cycles. The higher the hard mineral content of the feed, the greater is the change in the circulating load from one cycle to the next. The steady-state recycle values vary steeply and almost linearly with the composition. These results imply that the closed-circuit grinding of heterogeneous ores is inherently less stable than when processing nominally pure minerals. The predominance of a soft matrix in the ores should enhance the stability of the circuit somewhat. Random and unintended variations in ore characteristics and feed rates, even relatively minor ones, make it virtually impossible to assure a stable performance for any length of time.