The Long Tom
The long tom and its cousins the riffle board, and the rocker are used to mine alluvial gold. They are mining instruments that came out of the gold rush. The early mines in California were all alluvial, and could be worked by the masses unlike a hardrock mine that required a lot of capital before it produced a nickel’s worth of gold. This is a mining method that is still used today. The long tom comes into action once the miner has discovered a deposit of alluvial gold rich enough to warrant its cost. It also needs some other features to be constructed.
Once the decision to use a long tom has been made the first thing you have to do is secure a ready supply of water. This is accomplished usually by building a dam upstream from your diggings. The water from this dam is channeled in such a way as to run into the head end of the long tom.
A long tom is a method used for small scale mining that is far more efficient then either the gold pan or the rocker as it is less work then these other methods. The long tom was originally used by the forty-niners in late 1848 just when the California gold rush was just getting underway. By 1850 it was in common use in the goldfields, and coupled with a hydraulic nozzle created such environmental damage it was shortly outlawed. This was probably one of the earliest environmental laws in America.
In practice the long tom was constructed of several different components. It consists of a short receiving box to receive the unworked gravel. The gravel was then washed into a laundering box set below so that the gravel and water would have to drop into it thereby breaking up any clods of clay. The laundering box is where the gravel was actually washed to allow the gold to be separated by gravity from the gravel. Gold is about 19 times as dense as water. The washing box was from 6 to 12 feet long with the lower end covered by a perforated plate or screen set at an angle. This caught any stones that were over inches in size. These stones were forked out of the long tom by one of the workers. The pay gravel then dropped into a shorter box that was equipped with riffles to catch the gold. The different components are setup so that they have a drop of 1 to 1-1.2 inches per foot.
A good supply of running water is necessary to effectively operate a long tom. This running water is introduced into the receiving box along with the gravel that is being worked. After the water and gravel are introduced the force of the water washes it out of the receiving box into the laundering (washing) box where the action of the water causes the gold to sink to the bottom of the gravel layer. At the end of the wash box is a plate or screen that allows anything smaller then inch to pass through to the riffle box. At this point one of the workers forks the larger stones out of the long tom.
A twelve tined pitchfork or manure fork has been found to be the most efficient way to remove gravel.
The gold is caught by the riffles in the riffle box. This only concentrates the gold which is finally removed from the concentrated ore by using a gold pan. Another method if there are lots of fines is to amalgamate the gold using mercury. Great care should be taken using this method as mercury is very dangerous to the environment.
The amount of gravel that can be treated per hour depends on the nature of the gravel, and the amount of water available. The number of men who are available to shovel the gravel into the receiving box, and who those available to fork the large stones out of the end of the long tom as well as a man to shovel the fines away from the lower end of the long tom. A good team of four men should be able to process should process 6 yards of ordinary gravel or 3 4 yards of clay cemented gravel in a ten hour day.
A long tom may be operated by four men; two who are shoveling into the receiving box, one forking stones out of the long tom, and one shoveling away the smalls from the lower end of the long tom.
A sluice box is a later invention that combines the different components of the long tom into a single long box. It is simpler to operate, and easier to build.
A mining company I saw in the northern part of Canada used a large sluice box in their operation. This was quite a sophisticated operation with two pay loaders to load the upper end of the sluice box, a backhoe to remove the large stones, and a skid steer loader to remove the fines from the lower end of the sluice box. For riffles they actually used catch basin grills. I’d imagine these probably came from the streets of Toronto.
Instead of cleaning up every day, and recovering their gold they waited until the end of the mining season. They worked for several months 24/7 to mine their gold. It was quite a sight when they turned off the water, and started to remove the grills from the bottom of the sluice. You can vet the tax man was right there to get the government’s cut first. Under the upper grills there were deposited large nuggets of gold. And for several feet down the sluice there was hardly anything but gold. Even the fines from the lower end contained gold that had to be recovered by panning. This single sluice box contained several million dollars worth of gold. Not bad for one season of mining!