Recommendations to the LRMP Table

Development of Small to Medium Underground Mining Operations

Overview

Underground mines call for selective mine plans. The ore body may be in a narrow vein or a large irregular shape and can extend to great depths into the earth. Tunnels must therefore be extended to access the mineral deposit. Depending on the nature and shape for the deposit, three common methods of underground mining are typically considered, including self-supported methods, supported methods, and caving methods.

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  Room and Pillar Mining, which is used in flat or gently dipping bedded ores or mantos. Supporting pillars are left in place, generally in a regular pattern, while the rooms are mined out. Room and pillar methods are well adapted to mechanization, and are used in deposits such as coal, potash, phosphate, salt, oil shale, bedded uranium, and base-metal deposits.
  
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  Square-set Stoping is slow and expensive and requires skilled workers. It is generally used only for the extraction of high-grade ore bodies where rock walls are not strong enough to support an opening.
  
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  Shrinkage Stoping is usually employed in the extraction of steeply dipping veins where the walls are sufficiently strong to support themselves during the mining. It is done by stoping the vein or ore body from beneath, allowing broken ore to support the stope walls, but leaving a space above the broken ore sufficient for the miners to stand and drill overhead for the next break.
  
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  Cut and Fill Stoping is used in vein structures where the vein is moderately dipping, and/or where one or both walls lack the strength to stand up during mining of the ore block.
  

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  Longwall Mining is used primarily in the extraction of coal, but may be used in extraction of flat-lying oil shale, salt, phosphate, or sedimentary metalliferous beds. It might be considered as a modification of room and pillar mining, but offers better opportunity for mechanization. Extraction is from long panels, with widths up to 1,000 feet where roof conditions are favourable.
  
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  Sublevel Caving is a mass mining method based upon gravity flow of blasted ore and caved waste rock. Its major advantage is safety, since all mining activities are conducted from relatively stable openings.
  
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  Block Caving is the lowest cost of all underground mining methods. It is a mass mining method where the extraction and breaking of ore depends largely on gravity. It is used when large ore bodies have good vertical dimensions, but have a barren or low-grade cap too thick to strip for open pit mining, or a cap, which extends to depths where stripping ratios make open pit mining uneconomic.
  
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  Vertical Crater Retreat mining is a variation of sublevel caving, using a spherical charge to break the ore. Blasting is carried out at the base of vertical holes, making horizontal cuts and advancing upward. The shrinkage technique can be used for wall support. This method can be used where the ore body is well defined between steeply dipping walls and broken ore will flow to draw points under the influence of gravity.
  

In Northwestern British Columbia there have been several underground producing mines over the years, as the region is very rich in metallic mineral lands. In the Morice Plan area the most noticeable past producing underground operations were the Equity Silver Mine that operated as an open pit silver-gold-copper producer from 1981 to 1992 and then converted to an underground mine until its closure in January 1994. During its underground phase the mine employed 23 workers. The other noticeable underground past producer was the Dome Mountain Mine, which operated from in the 1980s and then again from 1992 until the middle of 1993. It was a gold producing operation and employed approximately 80 workers during the production phase.