This post will probably be one of the best gold prospecting tips I can give. Mainly because of the importance of recovering fine gold. Most of the gold on the earth is in this form. Here are a few tips I jotted down from the Clarkson study on fine gold recovery. If you are not familar with the Clarkson Study, it is pretty much the gold mining industry standard to keeping your fine gold in your equipment and not washing it out. A lot of effort went into this study with good results!
-screen your dirt/gravel before sluicing
-highest percentage of gold recoveries occurred at mines which screened their feed to minus one inch
-used both expanded metal and angle iron riffles on top of Nomad matting
-expanded metal riffles are efficient at recovering placer gold particles finer than 1mm
-angle iron riffles are more efficient at recovering those greater than 1mm
-slick plates allow gold to segregate to the bottom of pay gravel
Optimum Recovery Levels Specifications
-Pre-screen to ATLEAST minus 1 inch, washed thoroughly prior to sluicing, feed slowly
-Every sluice run should have a 16ft. long section of course expanded metal riffles (4-6lbs/ft^2) which is wide enough to process 8 loose cubic yds/hr/ft with at least 160 Igpm of process water per ft. of sluice width. The riffles must be tight against the Nomad matting to prevent scouring between the riffles and the matting.
These notes are based on gold mining on an industrial scale but can be applied to small-scale gold prospecting. Things from these notes I have applied to my homemade sluice box are as follows:
-sluice box length- 10"W X 48"L X 4"H
-I purchased a Keene A52 riffle tray for my riffle section
-also purchased a Keene A52 flare
-sluice box material includes the following:
-first 6" of sluice is slick-plate
-next 12" of sluice is ribbed rubber matting
-then outdoor carpet sits under the first 2 riffle sections
-3M Nomad Miners Moss sits under the remaining riffle sections
-the flare on the front acts as a slick plate as well so the material have plenty of time to wash out and let the gold fall out of suspension and get processed.
These sluice specifications are EXCELLENT at catching fine gold! I have recovered gold well into the micron range and not visible with the naked eye! Feel free to use my tips and advice and create your own!