Why Milling Matters in Gold Processing
Gold is rarely found as loose free metal. In most ores it is locked inside the surrounding rock, often as tiny grains within sulphide minerals. Before any recovery method — gravity, flotation or cyanidation — can reach that gold, the ore must be broken down to a particle size where the gold-bearing minerals are exposed. This is the job of the milling stage.
A well-designed gold milling circuit ensures the recovery stages downstream receive a consistent, correctly sized feed. Get it wrong and you leave gold in the tailings regardless of how good the rest of the plant is.
The Stages of a Gold Milling Circuit
A typical gold milling circuit has three linked stages:
- Crushing — jaw and cone crushers reduce run-of-mine ore, often from hundreds of millimetres down to a coarse mill feed.
- Grinding — rod and ball mills reduce the ore further to the target grind size (often expressed as P80). Xinhai builds ball mills up to 7 m in diameter.
- Classification — hydrocyclones or spiral classifiers separate the mill discharge, returning oversize particles for another pass and passing correct-size particles to recovery.
Each stage is sized from ore testwork. The grind size you target depends on how the gold is locked in your ore — which is exactly why metallurgical testing comes before design, not after.
Testwork First, Design Second
At our CNAS-accredited laboratory, gold ores are characterised before any equipment is committed. This includes element analysis (around 5,000 analyses are performed each month), Bond work index testing to measure how hard the ore is to grind, and recovery testwork for gravity, flotation and leaching routes.
Bond work index tells us exactly how much grinding energy your ore needs. That single number drives the mill size, motor power and circuit configuration — which is why we never guess when we design a gold milling plant.
From Milling to Recovery
Once the ore is ground to size, gold is recovered by the route that fits the ore:
- Gravity — for coarse, free gold, using centrifugal concentrators and shaking tables.
- Flotation — for gold-bearing sulphide ores, concentrating the gold before smelting or leaching.
- Leaching (CIL/CIP) — for fine gold, dissolving it with cyanide and recovering it onto activated carbon.
Many plants combine routes. A gravity circuit may pull free gold before flotation, and a flotation concentrate may then be leached. The combined flowsheet is optimised from testwork.