SELECTIVE MINING

Amrit Prakash Jonko08MN23

A method of mining whereby high value ore is mined in such a manner as to make the low-grade ore left in the mine incapable of future profitable extraction. In other words, the best ore is selected in order to make good mill returns, leaving the low-grade ore in the mine. Frequently called robbing a mine.

Selective mining ensures the most complete extraction of a useful mineral with minimal depletion, but it increases the costs of extraction and complicates the organization of mining operations.

In most mining operations, the high grade blocks are mined while the others are either left in place or are dumped as waste.

Deposits with complex structures are selectively worked by blasting blocks without disturbing the geological structure, by blasting the various useful minerals and gangue separately, by blasting along the contact areas of ore bodies , by blasting and separating layers of rocks , and by loosening layers of rocks by means of rippers.

Blasted rocks are removed from the face by means of controlled caving, selective vertical or horizontal excavation, sorting within the face, and combined removal. Selective mining is especially efficient when valuable ores are mined because it permits a significant improvement in the quality of the rock mass to be concentrated.

Operation

The objective of selective mining is to obtain a relatively high-grade mine product; this usually entails the use of a much more expensive stoping system and high exploration and development costs in searching for and developing the separate bunches and bands of ore.

In general, selective methods are applicable where the valuable sections of the deposit are rather large, comparatively few in number, and separated by relatively large volumes of waste.

OBJECTIVE

Cut and Fill mining is a method of short hole mining used in steeply dipping or

irregular ore zones, in particular where the hanging wall limits the use of long hole methods. The ore is mined in horizontal or slightly inclined slices, and then filled with waste rock, sand or tailings. Either fill option may be consolidated with concrete, or left unconsolidated. Cut and fill mining is an expensive but selective method, with low ore loss and dilution.

This system can be adapted to many different ore body shapes and ground conditions. It is the most flexible of underground methods. In cut-and-fill mining, the ore is removed in a series of horizontal drifting slices.In overhand cut-and-fill mining, the most common variation, mining starts at the lower level and works upward. In underhand cut-and-fill mining, work progresses from the top downward.

Methods

is similar to cut and fill, except it is used in ore zones which are wider than the method of drifting will allow to be mined. In this case the first drift is developed in the ore, and is backfilled using consolidated fill. The second drift is driven adjacent to the first drift. This carries on until the ore zone is mined out to its full width, at which time the second cut is started atop of the first cut.

Drift and Fill

is a short hole mining method which is suitable for steeply dipping ore bodies. The method is similar to cut and fill mining with the exception that after being blasted, broken ore is left in the stope where it is used to support the surrounding rock and as a platform from which to work. Only enough ore is removed from the stope to allow for drilling and blasting the next slice.

The stope is emptied when all of the ore has been blasted. Although it is very selective and allows for low dilution, since the most of the ore stays in the stope until mining is completed there is a delayed return on capital investments.

Shrinkage Stoping

Room and pillar mining is commonly done in flat or gently dipping bedded ore bodies. Pillars are left in place in a regular pattern while the rooms are mined out. In many room and pillar mines, the pillars are taken out starting at the farthest point from the stope access, allowing the roof to collapse and fill in the stope. This allows for greater recovery as less ore is left behind in pillars.

Room and Pillar mining

Improve ore grades through accurate selective mining Improve safety through Fixed Hazard and Proximity Warnings Improve efficiency and reduce errors by putting the digital

design directly on the machine Achieve results faster, with fewer passes Reduce rework caused by over or under cutting of filling Significantly reduce dependence on survey and grade checking Machine based production reporting removes errors and

improves timeliness and accuracy of management information

Increase the metal content of the ore material (grade up to

20%)

Reduce waste to be processed (30%+ reduction of waste to

mill)

Benefits

➤ First priority degree parameters—ease of rockexcavation, high selective ability of the machinery➤ Second priority degree parameters—rate of production,capacity and productivity of machinery, capital andoperating cost of machinery➤ Third priority degree parameters—geological/miningfeatures (faulting, bench width, seam dip, waste rock features, floor condition, material size after fragmentation),flexibility, maintainability (labour’s skill and technical knowledge required, maintenance support, spare parts availability, back-up service).

Optimum method selection for high Selective Mining

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