What physical property and what technique make the separation of gold by panning or by the sluice-box possible

Question

Gold can be separated from sand by panning or by a sluice box. In panning, water is mixed with the sand and the resulting slurry is swirled in a shallow, saucer-shaped metal pan. In the sluice box technique, running water is passed over an agitated sand gold mixture. What physical technique make this separation possible.

Answer 1

Density is the primary method of separation. The density of gold is so different from the minerals it is associated with (quartz) for example [2.4 vs~19.3) that separation for "large" particles is easy. When the gold gets down to fine particles in contact with other minerals, pure density separation does not work. Other separation methods must be used that eliminate surface tension between small particles. The so called frothing chemicals differentiate densities and help to separate densities of minerals.

Answer 2

Gold has a high density compared to other minerals. It will sink to the bottom of the pan while the water washes out the lighter minerals.