Placer Mining in BC

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Sluice Boxes

I am not an expert on mining law - I am just trying to help. Use the information in this website at your own risk. See the Notice at the bottom of this page.
A sluice box is used to separate gold from gold-bearing material - clay, sand, gravel, etc.

Water flows through a sluice box and gold-bearing sand, gravel, etc. is fed into the upstream end. Gold is captured because if is very dense. It settles into material on the bottom of the sluice box (ex. carpet or "Miners Moss") and/or it settles out behind "riffles" across the bottom where the water speed is slower.

The sluice box in the photo (and the photo, itself) are from SMI Electronics of Langley, BC. They have a wide range of metal detectors, sluice boxes, gold pans and other prospecting equipment and supplies.

A Key Stage of Processing

For mining a placer gold deposit, sluice boxes are the most common equipment used to capture gold (either fed by hand or as part of more elaborate wash plants, such as trommels and screening plants). A person feeding even a small sluice box can process far more material per hour than a person using a gold pan.

Processing gold-bearing material (clay, sand, gravel, etc.) has three basic steps...

  1. Removing anything over a certain size
  2. Separating out the gold and heavy "black sand"
  3. Separating the gold from the black sand

There are a variety of methods for steps 1 and 3. A sluice box is the usual way of doing Step 2 - it is the heart of processing and the heart of most "wash plants".

The material retained in a sluice box, black sand, regular sand and hopefully some gold, is called "concentrates".

Note: Most of the sections on this page - in fact, many of the paragraphs - could say:

See Processing for more information.
Rather than repeating this over and over, I will just make a big point of it here.

Basic Design

A sluice box has a bottom and sides but is open on top and at each end. Water flows through the sluice and gold-bearing material is fed into the upstream end. It can be made of wood, steel or aluminum.

Small sluice boxes used for prospecting and hand-digging operations are generally 10 to 18 inches across and 3 to 4 feet long. A sluice used to separate gold from the output of a large wash plant are generally a fair bit larger.

In some crude sluice boxes in the 1800s, the bottom was covered with sticks, cross-wise or lengthwise. The heavy gold would tend to move to the bottom and settle between the sticks.

A better way of capturing gold is with "riffles" across the bottom of the sluice box. The crudest type were wood with a square cross-section about 3/4s of an inch high, going across the bottom of the sluice every 6 to 12 inches. Behind each riffle was an area where the water moved slower and gold would settle out, just as it settles out behind a boulder in a stream.

Modern sluice boxes usually have some material on the bottom to help capture fine gold and use riffles that are strips of metal. Usually, these strips are part of a framework that can be lifted out in one piece to clean out the gold and black sand.

The strips are usually angled downstream about 30 to 45 degrees up from the horizontal. There are other designs - strips that angle upwards and then go horizontal for a bit, or strips that go vertically upward and then horizontal for a bit.

In each of these designs, a horizontal eddy (rolling water) is formed behind each riffle. The eddy will capture gold and heavy black sand, which is less dense than gold but denser than almost anything else.

Using a Sluice Box

The angle of the sluice box and the rate of water flow can determine what is captured and what is lost. The coarser the gold you are trying to recover, and the larger the size of pebbles/gravel also moving down the sluice, the steeper the sluice and/or the higher the water flow has to be.

If the angle of the sluice box and the flow of water are just right, gold will be retained behind the riffle and much of the black sand will be flushed out - in any case, most of the regular sand will normally be flushed out.

Miners in the olden days often ignored the very fine gold. It can be a mistake for you to do the same thing. Often the bulk of the gold that you can recover from a claim is fine gold.

Breaking up any clay is very important. If little balls of clay can roll down the sluice box, they can pickup and "steal" gold that has already been caught by the sluice box.

About the Water

Water for a sluice box may be pumped from a stream or from a man-made pond or tank (so the water flows back and is recirculated).

Warning:I am not an expert - this information is provided to help but use it at your own risk. If you want more definite information, contact the appropriate Regional Mining Offices.
In late 2011, I contacted four of the regional mining offices and I was told that a person can use a pump with proper Intake screening without a permit or water license if the pump has an intake no larger than 1.5 inches, but note the Warning, above.

In BC, using a sluice box in a stream channel or allowing water from a sluice to flow back into a stream is against the law, although many small scale prospectors and miners ignore this.

The biggest concern about placer mining in BC, no matter what the scale, is allowing dirty water to flow into a stream. Clay and silt, suspended in water from a sluice box, are bad for fish. There may not be any fish in the stream you are working, but the stream may flow into a stream that contains fish.

Using a Grizzly

A grizzly is a grate at a fairly steep angle that prevents oversize pieces from getting into the sluice box. It may have spray bars to help wash fine material off oversize pieces and to help pieces slide down the grizzly. Some grizzlies vibrate.


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Copyright 2011, 2012, 2013, 2014 by Brian Marshall     bmarshal@agt.net

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