Long toms are small sluice boxes used for clean-up or with rocker boxes which were hand-fed by shovel. They used the same technology as larger sluice boxes. Wooden or metal riffles across the bottom create undercurrents as the slurry of water and 'pay' gravels travel down the box.
This action encourages the heavier materials - gold, black sand, iron pyrite or fool's gold, and other minerals and heavy sands - to move to the bottom of the box where coco-matting was placed to trap these concentrates. Today punch-plate (sheets of steel with drilled tapered holes) and expanded metal screen are also used to create undercurrents. Artifical turf with no backing is often used instead of coco-matting. Riffles are made of angle-iron 'Hungarian riffles' or sometimes square tubing.
"Gravels are shovelled directly into the water, which can be flowing through the long tom or be bailed. It is a rough trough, as much as 24 feet long, from 15-20 inches wide, with the lower end 30 inches wide. The whole thing is about 8 inches deep. It is usually built in three sections, the first two sections being about six feet long, and the lower, wider section, which has the gold saving riffles, as much as 12 feet long. The top section, into which the gravel is shoveled, is lined with metal. The middle section, the lower end of which has half-inch holes in it, is also lined with metal. This section known as a grizzle, is on a level plane while the rest of the long tom is on a grade of eight to 12 inches per 12 feet of length. The water, gold and fines go through this grizzle and on to the riffles. The coarse material stops here and has to be shoveled off.
- "Frozen Gold: A Treatise on Early Klondike Mining Technology, Methods and History”, John A. Gould
Dawson City Museum, Dawson City