Gold Jigs

In a jig, the optimum condition of having the flow velocity reduced to nil, while maintaining the fluid condition of material trapped by riffles is achieved. The pulsating action of the jig lifts the entire bed of particles off the screen surface. As the stroke reverses, the bed tends to fall bottom layer first, next layer next, and so on. This dilation of the bed effectively fluidizes it so that the high specific gravity particles can sink through it and be concentrated.

The jig is a continuously cleaning device as small particles pass through the screen and are collected in the hutch. Nuggets are caught on top of the screen. Particles larger than 2 cm (.75 inches) have a high enough settling rate that they are not discarded to tailings, so they clog and reduce the capacity of the machine. Classification of the feed is necessary to keep a jig operating at optimal efficiency.

Although the jig, shown in Figure 4.3, is a better recovery mechanism than the sluice box, it is not perfect. Fine gold is lost due to the low residence time in the jig and the back flow of water from the hutch upward through the bed

Fig. 4.3 Cross-sectional diagram of a jig, showing the paths of particles of various densities. Fig. 4.4 Dual Cells Jig operating.