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Diamantiferous wire
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In order to reduce to the minimum mining width, tests have been made to cut, before the blast, the hanging wall with a diamantiferous wire. The idea is to reduce the damage in the hanging wall from blasting holes creating a weakness plan.
In the test stope, the height of the panel is 10 m (33 ft). The length of the stope depends on the length of the drive, as it is a continuous method along strike, the advance can be anything between 0.5 m and 5 m (1.6 ft to 16.4 ft).
The drilled hole diameter is 64 mm (2.5 in). The burden and spacing are from 400 mm to 500 mm (15.75 in to 20 in). The holes are drilled in a straight line on strike along the middle of the orebody.
The resulting width of the stope after blasting can be 0.4 m (1.3 ft) although this is dependant upon how accurate the access holes are drilled. The best result so far has been 0.25 m (0.82 ft).
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Underhand cut-and-fill mining method.
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Refer to the mining method 2 description.
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The mine is deep with two main shafts and internal shaft
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The maintenance costs for the shafts are very important.
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Mechanized cut-and-fill method
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The method preferred to control dilution is mechanized cut-and-fill. Where the development requirements for a cut-and-fill stope cannot economically justify this method, long-hole method is used. At this point, the mine is under a closure plan, for this reason, more long holes are drilled.
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Lean operation
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A new operating plan was initiated in 1998 in order to improve the ore grade, limit the production levels, and reduce infrastructure and production costs. Under this plan, manpower was reduced ; jobs such as chief engineer, chief geologist and mine supervisor were eliminated. For the underground department, it implies that the miners were responsible for the shift alignment and only one supervisor working during the day shift. This system worked well mostly because the workers are experienced and there was a strong sense of belonging.
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Geological mapping
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Through his geological daily follow-up, the geologist fills a face map and sample data sheet. In addition, a photography of the face is taken.
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Cemented Aggregate Fill
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In order to achieve a high percentage ore recovery in the Darlot stopes, two types of backfill are used. Once a stope has been mined out, it is generally filled with CAF (Cemented Aggregate Fill) or rough waste (blasted rock from development headings). Generally, stopes with pillars separating them are filled with rough waste, as there are no free faces that need to stand until the adjacent stope is completed.
If it is deemed that no pillar is required, a stope will be filled with CAF. CAF is generated by crushing waste rock to a size of 40 mm (1.5 in), and then mixing this with a cement mixture to achieve a consistency of 5% cement by weight. This mixture sets and allows a stope to stand unsupported while an adjacent stope is being mined. The backfill is delivered to the stopes from the top of each mining block with haul trucks.
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Sprayed gypsum
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To build walls for refuge bays or ventilation barricades, sprayed gypsum is used instead of shotcrete. This product is less expensive and strong enough for this type of work.
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Longhole mining of shallow dipping vein
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Retreating longhole mining method
Up to now, the longhole mining for this mine was relatively simple, from retreating backfilled sub-level. The mine is developed from top to bottom and sub-levels were developed every 20 m (66 ft). Forward-looking challenge is to gain the same successful results for the gently dipping areas which are less than 40 degrees to obtain the reserves in the future levels. Considering this, the technical services had prepared a mining sequence which is described in the attached document. The modified Avoca method with unconsolidated rock fill was selected. The spacing between sub-levels is 10 m (32.8 ft) vertically. Some interrogations remain about the mining method, particularly on the vein positioning during development, the stope mucking and backfilling. A scraper and water gun for the mucking cycle are expected to be used.
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Operation plan
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A detailed operation plan is prepared before mining the zone. This plan is revised annually according to the budget.
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Conveyor belt to control dilution
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A conveyor belt installed to identify the limit between the ore and the waste is used to control the dilution. This technique is described in the backfill section. Refer to mining method description for detailed sketches.
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Protection plate for boreholes
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In order to fill a stope, scooptram must travel on the upper drift. Usually, production holes are previously drilled. In order to protect hole integrity, steel plates are welded to a metal pipe and are used to cover each hole.
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Control of the ore-waste
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A conveyor belt is unrolled over the waste rocks before blasting the stope. During mucking, this indicates the limit between ore and waste.