Editing Placer mining (section)

==Deposits==
{{main|Placer deposit}}
An area well protected from the flow of water is a great location to find gold. Gold is very dense and is often found in a stream bed.  Many different gold deposits are dealt with in different ways.  Placer deposits attract many prospectors because their costs are very low.  There are many different places gold could be placed, such as a residual, alluvial, and a bench deposit.

===Residual===
Residual deposits are more common where there has been weathering on rocks and where there hasn't been water.  They are deposits which have not been washed away yet or been moved.  The residual usually lies at the site of the lode.  This type of deposit undergoes rock weathering.

===Alluvial===
Alluvial or eluvial deposits are the most common type of placer gold, and are often the richest. They contain pieces of gold that have been washed away from the lode by the force of water, and have been deposited in sediment in or near watercourses or former watercourses. Therefore, they are mostly found in valleys or flood plains.

===Bench===
Bench deposits are created when gold reaches a stream bed.  Gold accumulations in an old stream bed that are high are called bench deposits.  They can be found on higher slopes that drain into valleys.  Dry stream beds (benches) can be situated far from other water sources and can sometimes be found on mountaintops.  Today, many miners focus their activities on bench deposits.

=== Deep leads ===
Deep leads are created when a former stream bed is covered over by later sediments or by igneous rock from a volcanic eruption. Examples existed in the goldfields of [[Gulgong]] and [[Creswick, Victoria|Creswick]] in Australia. The gold bearing gravel is accessed by [[Shaft sinking#Mine shafts|shafts]] and drives similar to underground mining techniques but is typically processed as if alluvial gold.<ref>{{Cite web |title=Gulgong – Gold Rush Heritage |url=http://www.geomaps.com.au/scripts/gulgong.php |access-date=2023-09-05 |website=www.geomaps.com.au}}</ref><ref>{{Cite web|last=Design|first=UBC Web|title=Buried Rivers of Gold Heritage Trail {{!}} Business & Tourism Creswick Inc.|url=https://www.creswick.net/things-to-do/buried-rivers-of-gold-heritage-trail/|access-date=2021-01-22|website=www.creswick.net|language=en}}</ref><ref>{{Cite web |title=Buried Rivers of Gold {{!}} Creswick |url=https://www.buriedriversofgold.org/ |access-date=2023-11-01 |website=Buried Rivers Gold |language=en}}</ref> The heat associated with an igneous lava flow, in some cases, altered the gold bearing gravel so that it needed to be crushed first to extract the gold; an example of this kind of deep lead was found at [[Forest Reefs, New South Wales|Forest Reefs]], also in Australia.<ref>{{Cite news |date=1900-04-21 |title=The Forest Reefs Gold Field. II. |pages=41 |work=Australian Town and Country Journal |url=http://nla.gov.au/nla.news-article71379404 |access-date=2023-05-15}}</ref> If vegetation was buried along with the old stream, by a volcanic eruption, the effect of heat and decay upon that buried vegetation can result in the presence of harmful amounts of [[carbonic acid|carbonic acid gas]] ({{chem2|H2CO3|auto=on}}), as occurred in the deep lead deposit at Creswick.<ref>{{Cite web |title=The Dark Labyrinth |url=https://www.buriedriversofgold.org/the-dark-labyrinth |access-date=2023-11-01 |website=Buried Rivers Gold |language=en}}</ref>