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Wednesday, December 19, 2012

A Discussion on Sluice Box Lengths

These are pictures of KY Goldenrod in Nome Harbor, Summer 2012.  There are two separate sluice boxes that are 20 feet in length.  We run 2200-2300 rpm (35 hp) Kubota engines for each sluice box.  We have had to adjust our sluices numerous times this past season in regards to the sluices quickly clogging with black sand.  We are working out the kinks in hopes of catching more than 75% of the 1-2mm and above and 50% or more of the finer gold in the coming season 2013.  Any suggestions?

Miner #1 asks: What length should a sluice box be?
I understand the width vs. flow issues but not about the length.
Is there a ratio of width to length?
If a 4 foot is good then an 8 foot is better?  At what point is a sluice box too long?

Miner #2 comments:  Keep in mind the faster the water flows over your system the more loss of small gold.  Think of a leaf in the wind, the faster the wind the further the leaf will travel.

Miner #3 comments:  I am a big supporter of long boxes but in the real world a long box doesn't mean a whole lot with respect to recovery ratios and in fact many 3-foot long boxes recover just as well as 8-foot long boxes. I still like long boxes but from a 'scientific' standpoint they aren't neccesary. Modern studies of settling rates of fine gold tend to indicate that a lot of the old studies were flawed and that particles near the bed seldom 'jump' more than a few particle diameters in a typical sluice unless they get picked up by the upper layers of the laminar flow as happens when a large pebble sweeps by. With appropriate classification this isn't a problem so I guess the new 'rule of thumb' would be classify-classify-classify and don't worry about the box length. two-feet is probably long enoug if you classify your materials.  I still prefer to use long boxes but seldom if ever find anything beyond the first 18-inches no matter what type of riffles or mesh is being used. I do think however that power sluices and dredges do need to be at least 48-inches long as they can develop some pretty significant water velocity so a lot of material gets kicked up into the higher water levels.

Miner #4 comments:  I read a widely published in the 1930s account of working placer gold and shoveling in to a sluice box by a mine engineer.  The box was one ft wide and one foot deep running nearly full of water.  He claimed 98% of all his gold was within two feet of where he shoveled in, his box was 8 ft long and he claimed that longer would likely have saved more of the flower size particles but only if a screen classier was incorporated further down the box, the point is that for the most part it comes down to the fineness of the gold  that you are after.  He was shoveling in bank run material with no preclassification and yet 98% of his gold was saved in the first two feet of box.
Obviously the question comes down to one of gold particle size.  The finer the gold the more preclassifying is necessary along with wider box and carpet or burlap to replace riffles.
Only riffles being needed for the course gold along with more water and greater water velocity to keep the gravel from clogging up the box, the course gold quickly finds the bottom and is trapped in the riffles.

Miner #5 comments:  A longer sluice will keep the gold longer, the hydralic miners of old had 100 yard sluices called long toms which they cleaned out weekly, they still blew most of the fines through because it wasn't classified material. Maybe the first sluice runs 1 inch minus material which dumps into a second sluice covered with 1/4 inch or 1/8 inch perforated sheet suspended 1/2 inch over the rifles, Rocks just slide right over perforated sheet (punch plate). You might want to check out Keene engineering, they've got this new black rubber rifled matting to catch the fine stuff ( $8 per 1x30inch strip). I bought a 10 inch wide strip to do the exact same thing (as above), I hav'nt put it together yet but I'm hoping it works on lake Superior black sand.Anyway running the finer material through a second sluice ( or train of sluices) would be the only reason to go longer than 4 feet on a 10 to 12inch wide sluice. Good luck, Bill

The Canadian Prospectors Forum


2 comments:

  1. The picture you sent is a view from about midway down sluice back. Remember this was the original Keene sluice system. The forward section did not have expanded metal over the riffles. Our later sluice was much simpler. Some riffles, and then expanded metal with a 2" gap over miners moss. We need to get some photos of the new sluice system for you when we return.

    One other thing. Everybody that is a seasoned miner told us that 80 - 90% of the gold is found in the first 4 feet of the box. Most do not clean the back part but a few times a year. The further you go back from the first 4 feet the amount of gold falls off dramatically. They do NOT want to find gold in the last section of the box as it indicates they are loosing gold off the end of their box.

    Also, per what one featured miner said " As the Clarkson study states expanded metal over un-backed nomad works best for the fines and flour gold. "...

    That is what we are doing now BUT we are using #5 expanded metal GRATING which is a little different than expanded metal.
    the grating gives more edges to catch gold.

    I believe our biggest problem is delivering the gold to the front of the boat. I think our sluice while not perfect is what the Gold Nomites say works well.

    Thanks for forwarding this. It is interesting.
    Thomas O. Palmer

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  2. It looks like a good deal of thought has been put into the construction. Very clean & tidy with great craftsmanship and execution, well done!

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