A Complete Guide to Alluvial Placer Gold Processing Equipment and Methods

Alluvial placer gold primarily refers to gold formed when rock gold in a mountain is separated from quartz veins by river erosion. Because this type of gold ore is often as fine as sand, it is called placer gold. Since gold is free in placer gold ore and the specific gravity difference between gold and sand and gravel is significant, gravity separation is an ideal method for extracting gold from placer gold.

The principle of placer gold beneficiation is to first use gravity separation to recover as much gold and associated heavy minerals from the ore as possible. The minimum particle size limit for gold recoverable by gravity separation is generally 0.01mm. In practical production, the placer gold beneficiation process generally includes crushing and screening, followed by gravity separation.

I. Crushing and Screening Operations in Alluvial Placer Gold Ore: Many placer gold ores contain cemented mud, some with particle sizes exceeding 100mm, sometimes even cemented to gravel or pebbles. If not broken up promptly, these clumps will be discharged along with the waste rock during screening, resulting in gold loss. Screening can remove 20-40% of the waste rock (gravel and pebbles) and is an essential step in the placer gold beneficiation process. Screening parameters must be determined based on the gold particle size composition of the raw ore. Depending on the washability of the ore, screening equipment such as flat vibrating screens, drum screens, belt scrubbers, and hydraulic washers are generally used for screening.

II. Impact Placer Gold Gravity Separation: Due to the varying gold particle size composition of placer gold ores, the effective particle size limits of various gravity separation equipment vary. Typically, placer gold beneficiation equipment uses jigs as roughing equipment and shaking tables as concentrators to refine the jig concentrate. However, some low-grade placer gold ores use chutes as roughing equipment, jigs as scavenging equipment, and shaking tables as concentrators.

Therefore, a reasonable gold placer beneficiation process often involves the combined operation of several gravity separation equipment.

1. Jigging Gold Separation: The primary equipment for gold jigging is a jig. This machine mixes mineral particles of varying specific gravities and separates them into separate layers within a vertically moving, variable-speed medium flow. Minerals with lower specific gravities settle in the upper layer, while those with higher specific gravities settle in the lower layer. The separated materials are then discharged using mechanical and water flow. Jigs are suitable for separating coarse mineral particles (minerals of any size except fines). The particle size range for metallic minerals is 0.074-50mm. For gold placer beneficiation, the lower particle size can reach 0.04mm, provided the specific gravity difference is ≥1.25 and the ore is dissociated. The simple process and high processing capacity make them highly effective in roughing gold ore.

2. Shaking Table Gold Separation: The main equipment for gold separation is a shaking table, which performs separation in an inclined medium flow. A transmission mechanism drives the bed in longitudinal reciprocating motion, creating differential motion between the flow and the bed surface. During this reciprocating motion, the mineral particles undergo stratification perpendicular to the bed surface and separation parallel to the bed surface, allowing materials of different particle sizes to be discharged from different sections of the bed surface, achieving separation. Shaking table gold separation is suitable for sorting finer minerals and can be divided into three types: coarse sand bed, fine sand bed, and ore slime bed, depending on the particle size of the ore. The coarse sand bed is suitable for sorting mineral particles with a particle size between 0.5-2.0 mm, the fine sand bed is suitable for processing mineral particles with a particle size range of 0.074-0.5 mm, and the ore slime bed is suitable for processing mineral particles with a particle size of 0.037-0.074 mm. The feed particle size range for shaking table gold separation is generally between 0.019 and 3mm. Gold separation is stable and reliable, with clear ore distribution and a higher proportion of rich ore compared to other beneficiation methods. It is easy to manage and can select the desired ore in a single pass.

3. Chute Gold Separation: A gold chute utilizes an inclined water flow for separation. The combined forces of water flow, mineral gravity, and friction between the ore particles and the chute bottom cause the ore particles to settle in different zones within the chute according to their specific gravity. The lighter particles are carried away by the water flow, leaving the heavier particles behind, completing the separation.

In actual production, the placer gold beneficiation method and equipment configuration must be determined based on the specific ore properties and characteristics. Not all placer gold beneficiation plants can achieve ideal separation results using the same beneficiation method and equipment. It is recommended to conduct beneficiation trials first to develop a reasonable placer gold beneficiation method and tailor-make the appropriate placer gold beneficiation equipment.