A Leader in Alimak Mining
Manroc Developments Inc. is recognized as a leading Alimak Mining Contract firm, working with major mining companies around the world. We succeed through our commitment to serving our customer’s needs for safe, innovative, low cost mining techniques, that yield high tonnage/low dilution results.
A true innovation in underground mining, the Alimak method provides the highest safety standards in the industry, while increasing productivity, adding greater flexibility and maneuverability, and reducing overall mining costs.
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The Alimak Mining Method
Raise Climber Mining Conditions
This type of mining is best suited to tabular narrow vein ore bodies with enough dip for gravity ore flow.
There is often considerably less waste development with raise mining than with regular open stoping. A narrow vein ore body has less ore to soak up waste development costs, making the raise mining method an obvious choice.
It is better if the ore body is continuous over several hundred feet vertically. Experience has shown that raises from 75 to 150 metres length are the most economical.
The method works best if the ore boundaries can be interpolated between adjacent raises. This allows the drill planning to be done before the production drill is set up in the raise. This is less important in sulphides, where the driller can tell if the bit is in ore by the colour of the cuttings.
Raise Climber Mining Method Details
The raise climber mining method will generally be comprised of the following steps:
- Bottom Sill: Access and haulage: These drifts are driven from the shaft or established mining areas to the new ore zone. The drifts are commonly sized to accommodate the large scooptrams used for production mucking and are often driven with jumbos.
- Drawpoints and Climber Nest: Drawpoints can be driven from either footwall or hangingwall, depending on how the ore zone is accessed. The climber nests are always in the hangingwall. The climbers require about 4.3 metres (14') width, 2.7 metres (9') of height and 12 metres (39') of length with extra added on for "Alicabs" and/or for low angle raises. The nest will be slashed out of the drawpoint backs if development is from the hangingwall side.
- Top Sill Access: These drifts are also driven from the shaft or existing development but, unless there is another lift, they often need only be large enough for the movement of supplies.
- Raise Development: Raises must be driven big enough that a 2.4 metre (8') drill can be rotated within them, or about 2.7 x 2.7 metres (9' x 9') horizontally.
- Raise Rehabilitation: After the raise is driven it often must be rehabilitated, subject to ground conditions, for the safety of production crews.
- Hangingwall Support: Where required, the stope hangingwall can be supported with deformed strand resin-grouted cable bolts in a regular pattern along the raise. This is very cost effective as the raise is centred in the stope, which concentrates the support where it is needed most.
- Drilling: Drill holes extend to just less than half way to the next raise and are oriented slightly down from horizontal. The down dip helps the toes break to the stope wall. Hole diameters are often fairly small to avoid hangingwall / footwall damage in narrow veins.
- Loading & Blasting: The holes are most often mechanically loaded with either ANFO or an emulsion explosive. The blasts are timed to slash down, with the footwall holes often the last to fire. It is safest to take a few rings per blast, so that miss-holes or other blasting problems are accessible for correction.
- Mucking Swell: It is often best to leave ore in the stopes while blasting because of the support it gives. The broken ore often compacts slightly, resulting an effective swell of about one third its unbroken volume.
- Final Mucking: This step is done once the stope is completely blasted.
Fill fence and piping (if required). This step will be included if the stope is in an area that requires fill and the fill method requires a fence.
Truck dump back slash (if required). This step is often required where rock fill is used.
Filling (if required). This final step should be done in such a way that concerns about adjacent stope stability and hydraulic heads are addressed satisfactorily.
Raise mining is a "longhole" method of bulk mining tabular narrow vein ore bodies. The main ore access is gained by driving a raise up dip along the centre of the stope hangingwall, rather than from over and under-cuts driven along strike, as is done with regular open stoping. The production drill holes are oriented slightly down from along strike, which is also roughly perpendicular to that found in the regular open stoping method.
The advantages of this mining method are:
The bulk of the waste development required with this method is the ore zone access and the raise climber nests. A ramp is not required and, in many cases, neither is the muck pass and ventilation raise of a regular stoping system.
The change in geometry and improvement in ground support allows stope heights in the order of 75 to 150 metres, eliminating many sub-levels and their associated development.
The sub-horizontal production drill hole direction allows the use of the undercut as a slot and because of the increased stope height, there will be significantly fewer of these than there would be slots required for regular open stoping in the same area.
Faster Access to Undeveloped Ore
Once the climber nests are established, ore starts to flow. Most of the rest of the development is in ore (see centerfold). Ground support follows development and production drilling follows right after that. With some exceptions, production blasting can start in the quarter after raise development starts.
Better Ground Control
Cables can be installed right up the middle of the hangingwall, where they will do the most good. The stopes can also be mined in a shrinkage fashion, with added support gained from the broken ore in place.
The production drill sits in the middle of its work, cutting the drilled length in half. This improves drill accuracy which, in conjunction with the better ground control, reduces dilution substantially.
The short drill holes make this method very effective in narrow veins. The geology is exposed down the entire dip length of the stope on both sides of the raise. The ore contacts can be both extrapolated from across the raise and interpolated between raises. Stopes can be as little as 3 feet thick, or even less in ideal circumstances.
Faster Overall Extraction
With better ground control, larger stopes can be taken. Fewer, larger stopes can be taken quicker because there are fewer cycles, i.e., fewer final surveys, fill fences, and backfill arrangements.
With less development, faster ore access, better ground control, and faster overall mining, it is easy to see how raise mining will cost less than regular open stoping.
Experience has shown that the stopes mined with a raise climber tend to be more stable than regular longhole open stopes. There are several explanations, which include:
- Intuitively, geometry favors raise climber mining, in that access is gained to the centre of the stope hangingwall where the ground support does the most good. This advantage is easily visualized if one imagines the hangingwall as a fractured beam or plate. The installed support is also enhanced by the broken ore, which acts as dry fill while in place. It is also quite common that the production holes in the raise mining method are smaller than in regular stoping, which will spread the explosive energy more evenly. This should also contribute to a more stable hangingwall.
- There is an empirical Stability Graph Method (Potvin (1988), Nickson (1992), Hutchinson & Diederichs (1996)) that has been used to design and/or compare stopes. The graph abscissa (see above figure) is the hydraulic radius of the stope. The hydraulic radius is defined as the cross-sectional area of the opening divided by its perimeter. The graph ordinate is an estimate of the rock stability and includes factors for block size, joint surface condition, rock strength, joint orientation and the effect of gravity. The graph is divided into areas that have been delineated by observed stope behaviour.
Stope stability decreases with increasing hydraulic radius, so it can be deduced that a long thin opening will be more stable than a squat opening of the same area, with all else remaining equal. The raise mining method takes advantage of this concept because, even though the hangingwall is only supported up its centre, the resulting two unsupported strips are long and narrow and are more likely to be self-supporting.
- In theory, and if properly cabled, the foliated hangingwall could be approximated as a laminate beam by the Voussoir approach, as described by Hutchinson and Diederichs (1996). Formation of this beam is helped by the ability to cablebolt up the centre of the hangingwall as well as on top and bottom sills.
Manroc is on the frontline developing, drilling, and blasting on some of the world’s best deposits. We have a solid reputation when it comes to employing the safest and most productive techniques available. For more information on our Alimak production mining services, please contact us . We are your preferred underground mining professionals.