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Science, Maths & Technology

Automated panning system

Updated Tuesday, 27th February 2007

How can you make a machine to pan for gold? The Rough Scientists had to do just that...

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extracting gold Copyrighted  image Icon Copyright: Production team

The challenge
To make an automated panning system in order to obtain alluvial gold from a river.

Alluvial Gold
Alluvial gold (‘alluvial’ means containing 'alluvium' - alluvium’ is deposits of sand, earth etc. left by water flowing over land that is not permanently submerged, especially those left in river valleys and deltas) is made up of small flakes of gold washed down from high in the mountains by flood water. It is difficult to see because the particles are extremely small and because the gold is mixed in with lots of sand, mud and pebbles. However, it can be separated from the bits we don’t want because gold is much more dense than sand (gold is about seventeen times heavier than most rocks or sand).

A Simple Sluice
To separate the gold from the other stuff, we used a simple sluice, a wooden channel along which gold bearing gravel, sand and water runs over slats called riffles (riffles obstruct a rapid to form a piece of broken water. In gold prospecting a slat, bar or cleat is placed across the bottom of a sluice or channel of water to break the current and detain the gold). The water passes over the riffles. Light material like sand flows over the riffles with the water but the heavy material like gold is trapped between the riffles. In addition to the riffles, gold may be caught in hessian sacking, or between / within some punga wood (the wood of a tree fern which has a surface much like shredded wheat) or in gold pans but in order to increase our yield we want to automate the system mainly because it’s such damn hard work.

pan wheel

Automated panning
There are several steps in gold panning which can be automated:

Digging the gold bearing sand - this is difficult because much of the gold is hidden behind and underneath huge boulders

Taking water to the sluice - this is easier to do, and as water is often used in large volumes is an important step to automate

Agitating the sand and stones on the sluice in order to allow the heavy gold particles to fall out of the sand to the bottom of the sluice - this should also be easy to do and will save our fingers from the cold.

To operate a water pump or an automated sluice we need to harvest energy from the environment. We had several choices:

Wind power - it isn’t that windy here on New Zealand’s west coast

Solar power - although the sun ultimately supplies all the energy needed to sustain life on earth, man has found it very difficult to harvest without the help of plants. It is totally inappropriate to try here in rural New Zealand

Water power - this is the obvious option because alluvial gold is usually found close to running water.

We chose to make a water wheel because we were working next to a fast flowing river. As water runs down from the mountain it converts potential energy (energy stored in the water because it is at some height) to kinetic energy (movement). This can be harnessed by a water wheel, which uses the energy in the river to make it turn.

How to make an automated sluice
We used a rocking motion to agitate the sand and pebbles as they moved down the channel. We first built a compact sluice, rather than a long thin one, and then put rockers on it, like a baby’s cot.

We called the device our 'cradle'. As water, sand and pebbles ran down the various wooden boards, gold flakes were caught in either a ribbed rubber mat, between wooden riffles or between / within punga wood before the water flowed out back into the river.

making an automatic sluice diagram 1 making an automatic sluice diagram 2 making an automatic sluice diagram 3 making an automatic sluice diagram 4

Using simple technology available how do we pump water up to the sluice?

We needed to take water from the river and move it vertically for about one metre. There were plenty of pieces of drainpipe about, but could we defy gravity and lift water up the pipe?

We took a lesson from nature and made a type of petal valve (this valve is similar to those found in the heart). We made a wooden disc that fitted exactly into the inside of the drainpipe and secured it to the bottom of a rod (we used a broom stick). The disc fitted tightly enough within the drainpipe to prevent water leaking past it too quickly. When the rod is pulled up the pipe, water is brought with it.

Then we drilled holes through the disc. Now water will leak out of the holes, so they needed to be sealed with a circular piece of rubber. If the rubber is placed on top of the holes, but only secured in the middle by the broomstick rod, water can pass through the disc from below when the rod is forced down into the water because the flexible seal moves freely out of the way, but when the rod is drawn back up the tube and water tries flowing back through the holes it forces the flexible seal down onto the fixed wooden disc, closing the holes. Therefore, water that passed the seals to get to the top chamber of the pump on the down-stroke is caught and pours out of the top of the tube on the up-stroke.

A water wheel harvests energy in the river and provides a turning or ‘rotational’ motion, which can power machines. We needed to change this ‘rotational’ motion into a ‘rocking’ motion for the ‘cradle sluice’ and a ‘reciprocating’, back and forth or up and down motion for the water pump.

How do we do this?

Much like a pushbike or a car engine, the circular motion of a crankshaft is converted to a reciprocating linear action, or vice versa, by using connecting rods. They are very visible on the wheels of an old steam railway engine, for example. Here they convert a reciprocating ‘in and out’ movement of the steam engine into a circular motion at the wheels. We use the same technology in the form of more broomsticks.

So, now that we can rock the cradle and pump water what do we do next? In an ideal world we would have found a fast running current next to gold deposits. What problem was there with this solution? Well, gold tends to be deposited on the inside of bends in the river, so it is more likely to be found rear relatively slow moving water.

So, if the water is moving slowly near the gold what could we do?

Move gold bearing sand to the cradle - fine but it’s hard work

Use a long rod or rope to connect the water wheel to the cradle and water pump - not really suitable

Try to make the water current faster near to the gold - probably the best idea. We can make the water flow through a channel making it speed up, and turn the water wheel faster.

So will all this paraphernalia get us more gold? Well, it should save a lot of back-breaking work during the search!






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