What Gold Ore Milling Does
Gold ore milling is the grinding step between crushing and recovery. Its job is to reduce ore to a particle size where gold-bearing minerals are exposed, so the recovery stage that follows — gravity, flotation or cyanidation — can actually reach the gold.
Most gold in hard-rock deposits is locked inside the ore as fine grains, often within sulphide minerals. Until that ore is milled fine enough, no recovery method works well. Milling is where a plant earns or loses its recovery.
Oxide vs Sulphide Gold Ores
Gold ores split broadly into two types, and they mill differently:
- Oxide ores — weathered, near-surface ores where gold is often free or only lightly locked. They usually mill easily and respond to gravity or direct cyanidation.
- Sulphide ores — deeper ores where gold sits inside pyrite, arsenopyrite or other sulphide minerals. They often need finer grinding and a flotation stage to concentrate the gold before leaching.
The ore type drives the grind target. Sulphide ores frequently need a finer grind to liberate gold from the sulphide host, which is why testwork fixes the target grind size before equipment is committed.
The Milling Circuit
A gold ore milling circuit has three linked stages:
- Crushing — jaw and cone crushers reduce run-of-mine ore to a coarse feed.
- Grinding — rod mills followed by ball mills take the ore to the target size. Xinhai builds ball mills up to 7 m in diameter.
- Classification — hydrocyclones separate the discharge, returning oversize for another pass and sending correctly sized material to recovery.
The grind size is set from a Bond work index test, which measures how much energy your ore needs to grind. That single number sizes the mill, the motor and the whole circuit.
Testwork Before Design
At our CNAS-accredited laboratory, gold ores are characterised before design. Element analysis, Bond work index testing and recovery testwork fix both the grind target and the recovery route. A milling circuit sized on test data, not guesswork, protects both recovery and capital cost.