Editing Open-pit mining (section)

==Untopping==
A form of open-cast quarrying may be carried out as 'untopping'. This is done where a previous underground mine is becoming uneconomic or worked-out, but still leaves valuable rock in place, often as a result of [[room and pillar mining]]. Untopping removes the overburden from above this, opens up the mine from above, and then allows the previously 'trapped' minerals to be won.

Untopping was a feature of [[Welsh slate]] workings in the 1930s and 2000s, where Martyn Williams-Ellis, manager at [[Llechwedd quarry|Llechwedd]] found that earlier Victorian workings could be kept profitable with the newly mechanised techniques for bulk excavation to extract their pillars, and more recently across a number of worked-out mines.<ref>{{Cite web |title=Quarry Proprietors – The Welsh and English Entrepreneurs |url=http://www.llechicymru.info/IQPEntrepreneurs.english.htm |website=Slatesite |date=17 October 2002}}</ref>