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5 Necessary Processing Flow for Alluvial Gold Beneficiation

Alluvial gold deposits are diverse and widely distributed. As gold mainly exists in states of free in alluvial gold ore and has a very significant specific gravity difference with gravel, the gravity separation process is an ideal and efficient method to extract gold from alluvial ores.

01 Washing

Primary separation may be accomplished by a trommel appropriately sized to separate the gold-bearing dimensions from the oversize and trash with oversize, and trash being delivered to the stackers or tailings delivery system. 

The main purpose of the washing operation is to separate the gravels from the gold and to wash away the fine mud adhering to the gravels. In general, alluvial gold ores often contain a high level of weathered clay, in which the gold ore is encapsulated and forms a cemented mass or mud body with it. If they are not broken up in advance, the agglomerates or mud will be discharged with the waste rock in the screening process, thus losing gold and reducing the recovery rate of gold ore.

02 Screening

In general, the main purpose of the screening operation is to screen the alluvial gold ore after washing to remove large non-gold bearing gravels in order to improve the efficiency of gold separation. In general, the screening operation can screen out 20-40% of the waste rock.

Following the selection of screening equipment, screen hole size needs to be determined according to the size of the gold in the original ore composition parameters. The current common screen hole is generally 10-20mm. When using a fixed chute for roughing operations, the screen hole can be larger, but the upper limit can not exceed 60mm. Fixed plants often use vibrating screens or grizzly screens as alluvial gold screening equipment, and gold mining dredge often uses trommel.

03 Gravity Separation

Following prime separation, the gold-bearing material should be passed on to gravity separation equipment as is deemed appropriate. The gravity separation is the key operation in the alluvial gold ore beneficiation stage, often using the jig, shaker, chute, and other gravity separation equipment to discharge most of the waste rock, so as to obtain coarse gold concentrate.

Shaking Table

The shaking table is suitable for processing finer-sized minerals and the gold separation is stable and reliable. The distribution of the ore zones is clearly visible and the required ore can be sorted at once. The enrichment ratio is high compared to other beneficiation methods. According to the size of the ore, the shaking table can be divided into three types:

◆Coarse sand shaking table is suitable for processing ore particles with a material size between 0.5-2mm.

◆Fine sand shaking table is suitable for processing ore particles with a particle size range of 0.074-0.5mm.

◆Mud shaking table is suitable for processing ore particles with a particle size range of 0.037-0.074mm.

Chute

According to the particle size of the sorted ore grains, chutes can be grouped into coarse-grained chutes and fine-grained chutes.

◆Coarse grain chute：The upper limit of feed size can reach 100-200mm, and the lower limit of effective recovery size is about 0.074mm.

◆Fine-grain chutes are commonly used for separation coastal alluvial gold ores with a particle size of -2mm.

04 Concentration 

Beyond this, if tailings still exist some gold, it may be necessary to adopt other concentrate methods for recovering useful minerals. According to the different types of alluvial gold ore, the concentration can use the magnetic separation process, flotation process, or combined process to separate the gold and various heavy minerals from each other, in order to further enhance the gold grade.

The concentration operation is also one of the essential processes in the alluvial beneficiation process. The concentration operation attaches importance to the selection of technology and equipment to avoid the loss of gold during the concentration operation and to fully improve the recovery efficiency of gold and other heavy sand minerals.

05 Dewatering

The need for dewatering operation is usually determined by the process used in the concentration. The magnetic separation and flotation processes can be carried out under wet conditions.

In addition, a fully completed gold beneficiation test allows optimum selection of processing equipment. It can also guide extraction rates to maintain a continually profitable operation. The integration of the whole gold processing plant with professional mine management and operation will maximize the recovery rate throughout the life of the project.

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