Editing Placer mining (section)

==Environmental effects==
Although this procedure is not required, the process water may be continuously recycled and the ore from which the sought-after minerals have been extracted ("the tailings") can be reclaimed.  While these recycling and reclamation processes are more common in modern placer mining operations they are still not universally done.

[[File:Panorámica de Las Médulas.jpg|thumb|View of [[Las Médulas]]]]
In earlier times the process water was not generally recycled and the spent ore was not reclaimed. The remains of a [[Ancient Rome|Roman]] alluvial gold mine at [[Las Médulas]], [[Spain]] are so spectacular as to justify the site being designated [[UNESCO World Heritage]] status.  The methods used by the Roman miners are described by [[Pliny the Elder]] in his work [[Naturalis Historia]] published in about 77 AD. The author was a [[Procurator (Roman)|Procurator]] in the region and so probably witnessed large-scale hydraulic mining of the placer deposits there. He also added that the local lake Carucedo had been heavily silted by the mining methods.

Environmental activists describe the [[hydraulic mining]] form of placer mining as environmentally destructive because of the large amounts of silt that it adds to previously clear running streams (also known as the "Dahlonega Method").<ref>{{cite book |title=Dahlonega, Georgia: a brief history |first=Anne |last=Amerson |year=2006 |page=70 |publisher=History Press |isbn=9781596291300 |url=https://books.google.com/books?id=xfoF6DtQWfMC&q=Dahlonega+Method&pg=PA70}}</ref> Most modern placer mines use [[settling pond]]s, if only to ensure that they have sufficient water to run their sluicing operations.

In California, from 1853 to 1884, "hydraulicking" of placers removed an enormous amount of material from the gold fields, material that was carried downstream and raised the level of portions of the [[Central Valley, California|Central Valley]] by some seven feet in affected areas and settled in long bars up to 20 feet thick in parts of [[San Francisco Bay]]. The process raised an opposition calling themselves the "Anti-Debris Association". In January 1884, the [[North Bloomfield Mining and Gravel Company]] case banned the flushing of debris into streams, and the hydraulic mining mania in California's gold country came to an end.<ref>{{cite web|url=http://www.150.parks.ca.gov/?page_id=27596|title=California's First Environmental Law |publisher= California Parks and Recreation Department|access-date= 21 April 2019}}</ref>

Despite environmental concerns, placer mining is still important in areas such as the Yukon, and it has considerable support, with local businesses often displaying signs to that effect.<ref>Kiley, Brendan. 125 years after gold was discovered in the Yukon, we ventured up to Dawson City. Here's what it looks like now. Seattle Times, 10 September 2021. https://www.seattletimes.com/life/travel/125-years-after-gold-was-discovered-in-the-yukon-we-ventured-up-to-dawson-city-heres-what-it-looks-like-now/ Retrieved 2 October 2024.</ref>
[[File:SupportPlacerMining-DawsonCity 1165-c.jpg|thumb|Sign supporting Placer Mining displayed in Dawson City, Yukon, July 2022]]