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Author Topic: Sluice box Length  (Read 7567 times)

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Offline Montana

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Sluice box Length
« on: May 04, 2011, 08:47:05 PM »
Ok here is another question.  What length should a sluice box be?
I under stand 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 to long?

Offline Meke

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Re: Sluice box Length
« Reply #1 on: May 04, 2011, 10:01:33 PM »
It depends on so many things.  One thing you will find out that sluice boxes are easy to build but they are very finicky.  Can't over flow them can't have too much water can't have not enough water.  Can't be too steep can't be too low of a slope.  You shouldn't run straight water over them.


How many yards per hour are you trying to achieve?  What is the material?  Is it muddy?

If you are going to use a sluice,  the length is more for a longer holding period, less cleanouts but more to clean.  It also depends on if you are going to use different styles of riffles.  So the more sections you have the longer the sluice box.  The longer the sluice box the higher you have to have your system above ground level.

Keep in mind the faster the water flow over your system the more loss of small gold.  Think of a leave in the wind, the faster the wind the farther the leave will travel.

Well enough for now.  lol
good luck
Meke

Offline Geo Bill

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Re: Sluice box Length
« Reply #2 on: May 28, 2011, 11:39:21 AM »
 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

Offline garyww

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Re: Sluice box Length
« Reply #3 on: May 28, 2011, 12:54:05 PM »
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.

Offline Goldbug

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Re: Sluice box Length
« Reply #4 on: May 28, 2011, 05:14:45 PM »
I read a widely published in the 1930 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.

Offline Vagadero

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Re: Sluice box Length
« Reply #5 on: May 29, 2011, 03:09:15 PM »
off: What space were between the riffles in the hydraulic miner's long tom?

Offline Meke

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Re: Sluice box Length
« Reply #6 on: June 04, 2011, 08:46:15 AM »
There have been many studies on sluice action.  The problem with this is that every area has different composition of material.  One would have to do several test on each type of ground.  You will have to adapt to your area.  What they did 90 years ago would mostly catch the big stuff.  This is why we look for old tailing's and go through them again.  If you create a system that is focusing on the small stuff the big stuff will be easy to get.  It doesn't work the same in reverse application.  90% of the gold I have collected is 8 mesh and smaller.  I have had 1 inch nuggets near the bottom of my sluice box.  I was using studies based on other areas.  I had adapted my sluice but now I use Jigs.  The stress is gone.

 You can build jigs too.