"Réalisations - 2007 - Xstrata Zinc - Laval Fortin
http://www.lavalfortin.com/repertoire/detail/61
Il s'agit en fait d'une immense rampe d'accès à l'entrée de la mine, recouverte d'un dôme (le couvercle en question) servant à éviter les inconvénients de la .."

"Accessing underground ore can be achieved via a decline (ramp), inclined vertical shaft or adit."
https://en.wikipedia.org/wiki/Underground_mining_(hard_rock)

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Note added at 6 mins (2016-02-01 08:54:56 GMT)
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"The decline will assist with early access to underground for the construction of the K01 and K02 production infrastructure, concurrent to the vertical shafts still being sunk and will also serve as an additional air intake and logistics management facility, reducing the requirement of the loading stations on the Service Shaft. The decline portal is sited off the surface terrace and due south of the vertical shafts. The decline will serve as a third means of egress from the underground workings whereas the Service and Production Shafts are the other two means of egress."
http://www.miningweekly.com/article/main-sinking-to-commence...

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Note added at 1 hr (2016-02-01 10:44:55 GMT)
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picture worth 1000 words

"This is the decline portal which is approximately 420m long and descends to the -300 level. Ore is also trucked to the surface using this decline"
http://wikimapia.org/27727203/Decline-Portal