EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

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The EarthWord: Placer

Definition:

• If you’re panning for gold, you’ve come to the right place-r, that is! Placers are a type of mineral deposit in which grains of a valuable mineral like gold or the rare earths are mixed with sand deposited by a river or glacier.

• Placer is also a mining method term. Placer mining uses water and gravity to separate gold from surrounding material.

Etymology:

• Placer is an Americanization of the Catalan word placel, which itself came from the Spanish word plaza, meaning “open space.”

Use/Significance in the Earth Science Community:

• Placer deposits containing gold are areas that have highly concentrated accumulations due to stream/river erosional processes taking place around/over geologic terranes that contain gold, over a very long period of time.

• Placer deposits are an important source of many valuable minerals, particularly gold and rare earth elements. They occur throughout the world.

USGS Use:

• USGS studies placer deposits as part of its Mineral Resources Program. From the 1890s Alaska Gold Rush (where 72% of the gold found came from placers) to modern-day rare earth deposits (of which quite a few are in placer deposits), USGS has placed an emphasis on studying these rich formations.

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