About Placer Mining
Fine Gold - Fine Opportunity
Nuggets are great, but often, the majority of the gold that can be
recovered in an area is fine gold. Fine gold has been ignored in many
places, particularly during gold rushes when coarse gold was being found.
Rocks and Clay
It is important to wash all gravel and larger rocks so that fine gold
isn't discarded before it gets into the sluice box.
Pieces of solid clay may be able to be washed and discarded.
Any clay that goes into the sluice must be completely broken up and
suspended in the water so no balls of clay
steal gold as they move down the sluice.
Regular Sluice Boxes for Fine Gold
The old standard sluice box - with
riffles, expanded-metal-screen and matting -
can do a pretty good job of recovering fine gold.
No material over a certain size goes into the sluice box.
Larger pieces need more water to carry them and they jar things
when they bounce. Whether you use a fridge-shelf or a trommel,
everything over, maybe, half an inch, is washed and rejected.
The matting is important and is a small expense.
It needs to make a layer of the calmest water in the sluice box.
Whatever came with your sluice box may be okay.
Miner's Moss is good - there are other products.
You can also improvise. Most carpet doesn't work well, fills
with black sand quickly and is difficult to clean out.
Engineered Bottom Sluice Boxes
There are new kinds of sluice boxes that don't use mesh or matting,
and the shape of the bottom of the the sluice makes the riffles.
They can be good at capturing fine gold,
but they don't catch all of it.
Adding another sluice box will catch more.
Up to a point, the longer the sluice box,
the more fine gold you will catch.
In the image to the right, a long sluice is being used to recover
fine gold from an abandoned channel of the Fraser River.
A Sluice-Screen-Sluice Setup
A good approach to recovering fine gold is...
The Coarse Gold Sluice Box can be a fairly short, regular
type of sluice box - you may already have something that
can be used.
- a Coarse-Gold Sluice Box for sand-size gold
- a Screen passes sand and smaller material
- which flows through a Fine Gold Sluice Box
It is best if there is no physical/rigid connection between the
Fine Gold Sluice Box and the rest of the wash plant.
The Fine Gold Sluice Box
Most of this sluice box has smooth sides and bottom. We want the
water to flow as smoothly as possible, so gold can settle to the
bottom of the flow. The new fashionable word for this is
This sluice box has sections - some may be separate pieces or
they may all be parts of one piece.
You adjust the water flow and angle of the last section.
You want to see light colored sand being washed away
and black sand moving only part-way down the sluice.
- The water/sand/gold flow into
a straight, smooth section of sluice,
where the water will start to flow more smoothly and gold will
start to settle.
- The sides of the sluice angle out - the sluice
becomes fan-shaped, until it is two or more times as wide as the
first section. The sides then angle back, so that the sluice is
straight but wider. The water/sand/gold flow moves slower and the
fine gold has a better chance to settle.
- The fine gold sluice box - where you want to
capture gold - has no riffles or screen or matting. The bottom is
covered in something like black rubber floor mats
with 1 to 2 mm ribs on the mats going across the sluice box.
Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020
by Brian Marshall
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