Experimental studies have indicated that an increase in ore hardness is associated with an increase in point load index and Bond work index and a decrease in impact breakage parameter (A 脳 b). Moreover, an increase in ore hardness corresponds to an increase in feed size. Hard ore grinding in the SAG mill resulted in finer products compared to the soft ore milling. In addition, it was found that the products of the soft ore milling were more elongated, angular and less rounded than those of the hard ore milling. This was attributed to changes in breakage mechanisms as ore strength changes. The weaker ore is ground mainly by the impact breakage while the stronger ore is subjected to abrasion and attrition events where the media impact could not sufficiently break the stronger particles. It was also found that the particle angularity and elongation distributions were fitted to the 3-parameter lognormal distribution, providing a convenient way to quantify changes in particle shape properties as a function of the ore characteristics. It was concluded that the main reason underlying the decrease of circuit throughput from 939 to 498 t/h was due to changes in breakage mechanisms.