Mill feed refers to the ore or mineral material that is delivered to the entrance of a processing plant (or mill) to be processed through size reduction and subsequent beneficiation steps. In the context of gold and iron ore mining, mill feed is the run-of-mine (ROM) ore or pre-crushed ore directed into the primary grinding circuit — typically a SAG (semi-autogenous grinding) mill, ball mill, or rod mill — where it is reduced to a fine particle size to liberate the target mineral from the gangue matrix. The quality and variability of mill feed are critical operational parameters, as fluctuations in feed grade, hardness, moisture content, and particle size distribution directly affect grinding circuit performance, reagent consumption, and ultimately metallurgical recovery. In bauxite operations, mill feed quality is characterized by its available alumina content, reactive silica ratio (A/S ratio), moisture, and clay mineralogy, which together determine Bayer process performance. For iron ore operations, mill feed grade (Fe%), silica content, alumina content, and grindability determine concentrate quality and yield. In diamond mining, the term mill feed describes the ore entering the dense media separation plant, where particle size and competency are carefully managed to minimize diamond breakage. Consistent and well-characterized mill feed, achieved through blending strategies and careful mine scheduling, is a prerequisite for stable and efficient plant operation.
