Comparison of methods of concentrating and recovering fine gold particles
The data for this article comes from the British Geological Survey Technical Report WC/97/14.
With gold selling for around $1,600 per ounce (2013), many individuals have become interested in gold, or more specifically, recovering gold from the rocks where is hides. Many quackery devices are sold by hobby stores promising claims of recovering 0.5 micron gold with a sluice with a magic carpet, or some such nonsense. This data was gathered by using scientific examination of many common types of gravity separation equipment, and the results were analyzed to determine the suitability and performance of various types of machines on gold recovery of various particle sizes.
First, the most common device used by the placer miners is a sluice box. This is hundreds of years old, and has been used by miners for a few centuries. Based on the results of testing, it was found that sluice boxes generally tend to recover coarse gold well (no news here), in the particle sizes from 2.5 mm down to 100 microns ((140 mesh). On particles between 2.5 mm and 1 mm, it was found to be 96% effective. However as the particle size of the gold decreased, the efficiency decreases dramatically, until when particles are below 100 microns, it is only 20% effective in recovering them. That means 80% are going down the drain.
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