Alluvial Gold Deposit Types, Mining Methods and Processing

Alluvial gold is formed by vein gold under long-term weathering. Long-term alluvial action causes alluvial gold to be mixed with other minerals besides gold. Therefore, it is necessary to process it to separate gold from other minerals and improve the purity of gold in order to obtain gold concentrate. This article introduces the common types of alluvial gold, alluvial gold mining methods and process.

01Types of alluvial gold deposits

According to the different sedimentary environments, gold grain characteristics and occurrence locations, alluvial gold deposits can be divided into four types: riverbed gold deposits, river valley gold deposits, alluvial fan gold deposits and beach placer gold deposits.

Riverbed gold mine and valley gold mine: shallow burial, no need for complicated underground work, lowest mining cost, highest return on investment.

Alluvial fan gold placer: due to the wide distribution of gold, it is difficult to enrich, and requires investment in large-scale gold washing plants, which requires high investment. If the gold grade is above 0.5g/t, it has investment value.

beach placer gold deposit: It is difficult to obtain good mineral processing results by relying on traditional gravity separation, and chemical leaching is required, which is costly. If high-value minerals (such as titanium and rare earth) are present, comprehensive recovery can be considered to increase profits.

02alluvial mining methods

The mining technology of alluvial gold mines is very mature. After years of mining experience, the mining methods can be summarized into the following 8 types:

1. Gold Panning

Gold panning is a manual method. People hold shallow pans filled with water and sediment and rotate the pans. The lighter materials are washed away, leaving heavier minerals, including gold, to settle at the bottom of the pan.

2. Gold Washing

The equipment for washing ore is a washing box, which is a long, narrow channel with corrugations (raised barriers) on the bottom. Water carrying sediment is directed into the washing box, and as the water flows through, the corrugations capture the heavier minerals, while the lighter materials are washed away.

3. Dredging

Dredging is used for mining underwater or in deep riverbeds. A dredger is a floating barge equipped with a suction pump and a series of buckets or conveyor belts to remove sediment from the riverbed. The sediment is then processed on board to separate out valuable minerals.

4. Dry Cleaning

Dry cleaning is used in arid areas where water is scarce. A dry cleaning machine is used, which blows air through a plate of sand and gravel to separate the lighter materials. The heavier minerals remain in the plate, including gold.

5. Concentrating Table

A concentrating table, also known as a shanking table, uses a vibrating motion to separate minerals based on their size and density. The table has an inclined surface with corrugations, and as the material moves down the table, the heavier minerals settle in the corrugations, while the lighter material is washed away.

6. Spiral Chute

Spiral chutes use the principle of centrifugal force to separate minerals based on their density and size. The spiral-shaped device allows water to flow through, carrying sediment with it. As the water spirals downward, heavier minerals settle along the inner wall of the spiral, while lighter materials are carried away with the overflow.

7. Jig

A jig alternately dips and lifts a sediment-filled screen into the water. The up-and-down motion causes heavier minerals to settle at the bottom of the jig while lighter material is washed away.

8. Heavy medium separation

Heavy media separation separates minerals based on their density. Sediment is mixed with heavy media and denser minerals sink while less dense materials float.

These methods may be used alone or in combination, depending on the type of deposit, the size and density of the minerals, and the scale of the mining operation.

03alluvial mining process

1. Mining operations

Choose the appropriate mining method according to the characteristics and geographical location of the ore deposit. Common mining methods include:

Gold mining by dredging ship: Applicable to placer gold mines in water bodies, gold mining ships operate directly in the water through excavation and washing.

Engineering machinery mining method: Use engineering machinery such as bulldozers and loaders to dig and load in arid areas.

Hydraulic machinery mining method: Use high-pressure water flow to flush the ore sand, and complete flushing, transportation and washing through water flow.

2. Preliminary processing

The mined ore sand needs to be processed to remove large rocks and impurities. This step usually includes screening and gravity separation.

3. Washing operation

Washing is an important step in the beneficiation of placer gold ore. Through hydraulic washing and mechanical action, the sand and gravel are separated into individual particles and clay and other impurities are removed.

4. Gravity separation

Gravity separation is the main method of gold placer beneficiation, which uses the density difference between gold and sandstone to separate. Commonly used equipment includes spiral chutes, shaking tables, etc.

5. Concentration and purification

The concentrate after roughing needs to be further concentrated to improve the grade and recovery rate of gold. This step can be carried out using equipment such as shaking tables. The final concentrate can be cast into gold ingots by pyrometallurgical smelting.

6. Tailings treatment

The tailings after beneficiation need to be properly handled, usually by discharge or reuse to reduce environmental impact. Modern beneficiation plants pay more and more attention to environmental protection, and use circulating water systems and tailings dams to manage tailings.

The above introduces the types, mining methods and processing of alluvial gold placer. Xinhai can build alluvial gold ore washing plants for customers and sell alluvial gold equipment.