In a natural stream, dense particles moving along the bed will collect downstream of obstructions like rocks or ridges. Long ago, prospectors panning for gold learnt to take advantage of this property by building artificial stream beds of their own, called sluice boxes. Sluices have multiple obstructions, called riffles, concentrated within a short distance. Simply toss a shovel load of sand and gravel scooped from the stream bed into the top of a sluice, and running water washes the material over the riffles. Just as in a real stream, gold particles preferentially remain just below the riffles.
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Things you need
- 1-by-2 inch board, 8 feet long
- Table saw
- 1-by-10 inch board, 6 feet long
- 2 boards, 1-by-6 inches, 6 feet long
- 1 1/4-inch deck screws or galvanised nails
- 1 1/2-inch deck screws or galvanised nails
- Power drill and bits
- 2-by-4 inch board, 10 3/4 inches in length
Cut an 8-foot, 1-by-2 inch board into two pieces that are 6 and 8 feet long. Cut two pieces that are 10 3/4 inches shorter than the 6-foot board.
Rip a 6-foot piece of 1-by-2 in half with a table saw. Cut 12 strips 9 1/4 inches long from the resulting 3/4-by-3/4 inch strips.
Attach one of the 9 1/4-inch strips crosswise 1 foot from the end of a 6-foot, 1-by-10 board with 1 1/4-inch nails or screws. Prevent splitting by drilling holes in the strip. Align the ends of the strip to the edges of the board.
Attach the other 9 1/4-inch strips at 6-inch intervals. Leave about 1 foot of space at the other end.
Attach a 1-by-6 board, 6 feet long, to each side of the 1-by-10 with galvanised nails or 1 1/2-inch deck screws. The result should be an open trough, with wood strips crosswise on the bottom; these are riffles or obstructions intended to trap heavy grains such as gold.
Attach a 10 3/4-inch, 2-by-4 to the bottom of the box about 1 foot from the top end. Attach the box floor to the narrow edge of the 2-by-4 with galvanised nails or deck screws.
Fasten a 10 3/4-inch length of 1-by-2 crosswise on the top of the trough about 1 foot from each end with 1 1/2-inch nails or screws. These function as handles when carrying the sluice and help support the open trough under rough treatment.
Place the sluice in a stream with the top end pointing upstream. Empty a shovel of sand, gravel and dirt into the large space in the top end. Let the water wash the soil over the riffles. Carefully inspect the sediment trapped under the overhang of the riffles for flakes and even small nuggets of gold.
Tips and warnings
- Prospecting hobbyists often fabricate their sluices from sheet metal, which is lighter, more durable and doesn't become waterlogged like wood.
- Many do-it-yourself prospectors attach industrial carpet, AstroTurf or other rough fabric to the floor of the sluice to trap the finest particles of gold.
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