Editing Placer mining (section)

===Sluice box===
{{redirect|Sluice box|the general topic|sluice|the Montana park|Sluice Boxes State Park}}
[[File:Blei-und-Gold.jpg|thumb|[[Riffle]]s in a sluice box. The small specks are gold, the larger ones are merely pebbles]]
[[File:Goldwaschrinne.jpg|thumb|left|A modern sluice box made of metal; in its base are the riffles used to catch gold settling to the bottom]]

The same principle may be employed on a larger scale by constructing a short [[sluice|sluice box]], with barriers along the bottom called riffles to trap the heavier gold particles as water washes them and the other material along the box.  This method better suits excavation with [[shovel]]s or similar implements to feed  ore into the device.  Sluice boxes can be as short as a few feet, or more than ten feet (a common term for one that is over six feet +/- is a "Long Tom"). While they are capable of handling a larger volume of material than simpler methods such as the rocker box or gold panning, this can come at the cost of efficiency, since conventional sluice boxes have been found to recover only about 40% of the gold that they process.<ref>{{Cite journal|last=Subasinghe|first=G. K. N. S.|date=1993|title=Optimal Design of Sluice-Boxes for Fine Gold Recovery|journal=Minerals Engineering|volume=6 |issue=11|pages=1155–1165|doi=10.1016/0892-6875(93)90093-3|bibcode=1993MiEng...6.1155S }}</ref>
[[File:Placer Mines, William G. Chamberlain photo showing mining operations - DPLA - 1beeeabe4036b0295ed517fbf7614f62.jpg|thumb|Placer mines in Park County, Colorado, 1870s. A long sluice box runs along the mine.<ref>[https://pclha.cvlcollections.org/items/show/75 Park County Local History Digital Archive]</ref>]]
The sluice box was used extensively during the [[California Gold Rush|California gold rush]] for larger scale operations. When streams became increasingly depleted, the grizzly and undercurrent variants of the sluice box were developed. The grizzly is a set of parallel bars placed at a 45-degree angle over the main sluice box, which filter out larger material. The undercurrent variety includes additional, auxiliary sluice boxes where material is initially filtered. It then travels through a trough into the primary sluice box where it is filtered again. Both the grizzly and undercurrent are designed to increase efficiency, and were often used in combination.<ref name=":0" />