Vertical crater retreat

From Queen's University Mine Design Wiki

This article is about the orebody requirements and developmental steps involved in Vertical Crater Retreat planning and mining.

Vertical crater retreat (VCR), also known as Vertical retreat mining, is an open stoping, bottom-up mining method that involves drilling large-diameter holes into the orebody vertically from the top, and then blasting horizontal slices of thethe orebody into an undercut. 

Similar to Sublevel open stoping and Blasthole stoping methods, VCR mining is used for steeply-dipping (>45º), or both vertically and horizontally large orebodies with competent ore and waste rock strength.  It differs from other open stoping methods in that it is a bottom-up method, as opposed to a left-to-right method, and it does not require the excavation of sublevel drifts before blasting and mucking can take place.

Holes are typically 165mm in diameter, allowing for a blast pattern spacing of 4.0 by 4.0m, and the thickness of one slice of ore varies between 2 and 5m .

Orebody Characteristics

VCR is a suitable mining method for orebodies that exhibit the following characteristics:

Characteristic	Requirements
Orebody Dimensions	Steeply-dipping orebodies (>45º), with widths of no less than 12-15m, or Very large both vertically and horizontally
Ore and Rock Strength	The strength of the waste rock must be competent in order to blast against it without having excessively large amounts of dilution The ore deposit is to be of medium to competent strength
Grade	VCR is not a selective mining method, therefore the ore grade should be low to medium, and it should be relatively uniform throughout the entire orebody
Depth	VCR mining can occur in mines at any depth.  Work is carried out in reinforced, small drifts; and given the nature of the mining method, no personnel has to work directly within the drift.  Therefore safe execution of VCR mining can be carried out in deep mines
Oxidizing Ores	Given the small, localized stope size in VCR mining, ore can be recovered very soon after blasting occurs.  Therefore, oxidizing and self-cementing ores such as pyrrhotite can be mined using this method

Advantages

• Safety: miners are working in a drift taht is adequately ventilated and has a fully supported roof.  Furthermore, no workers are required to work inside the stope, minimizing the risk of unexpected injuries.  As automated Machinery can be used, workers are not at risk of equipment-related injuries
• Good Recoveries: Continuous mucking from the drawpoints can take place after blasting.  In addition, VCR mining can be used with a high degree of mechanization, generating a high level of productivity.
• Cost: Once the pre-mining development is in place, VCR mining has a low operating cost, as it is a bulk mining technique and employees are not required to manually operate the mucking machinery
• Wall Support: VCR stoping shares some great features with sublevel open and shrinkage stoping.  Good wall support is offered during the VCR stoping phase, using shrinkage