How to separate placer gold?

After primary gold deposits are exposed at the surface, mechanical and chemical weathering causes the gold-bearing veins or parent rocks to gradually break down into rock fragments and gold particles. Then, under the influence of external forces for transport and sorting, heavier minerals (such as gold particles) are deposited on hillsides, riverbeds, and lakeshores, forming concentrations. Those deposits with industrial mining value are called placer gold deposits.

Placer gold deposits are typically mined using dredges, hydraulic mining, excavator mining, and underground (shaft) mining. In my country, placer gold mining is mainly done using dredges, but hydraulic and excavator mining are also used.

Placer gold beneficiation processes mainly include preparatory work before beneficiation and the beneficiation process itself. Preparatory work mainly consists of two processes: crushing and screening. Crushing mainly separates the mineral particles and clayey slime from the mined ore. Screening removes coarse particles that do not contain gold. Commonly used equipment includes flat screens, cylindrical screens, and cylindrical scrubbing machines. The primary beneficiation method for placer gold is gravity separation. This is because placer gold has a high specific gravity (average 17.50-18.0 mm) and a relatively coarse particle size (generally 0.074-2 mm). Furthermore, gravity separation is relatively economical and simple. Gravity separation equipment typically includes various types of sluices, jigs, and shaking tables (often used for fine finishing).

The specific recovery process for coarse gold particles in placer gold ore is: screening-jigging-mercuration or screening-jigging-shaking table. For the recovery of coarse gold particles in vein gold ore, gravity separation is also generally used. A rod mill is used to grind the gold ore to the point where coarse gold particles are separated from the gangue, and then the ore is fed into a jig to recover the coarse gold particles as early as possible. Multi-stage grinding and multi-stage separation processes are also used, with the aim of recovering coarse gold particles as early as possible and avoiding gold loss after over-grinding.