Information

LONGHOLE METHOD

• Dip: 45 degrees. 
• Power: 2.5 m to 15 m (8 ft to 49 ft).
• Vein regularity.

In spite of the low dip, this method is employed due to the width of the vein. The approach is to mine a mineralized envelope rather than to mine selectively.

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ROOM AND PILLAR METHOD

• Dip: 0 to 35 degrees.
• Selectivity: 2.2 m to 3.5 m (7 ft to 11 ft).
• Dilution control.

This method is used in zones with a low dip. It is presently limited to a few places.

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SHRINKAGE STOPE METHOD

• Dip: 45 to 90 degrees.
• Power: 1.5 m to 3.6 m (5 ft to 12 ft).
• Good ground conditions.

This method is only used to mine the lower part (about 5 m [16 ft]) of the longhole stopes in order to control the ground support surrounding the drawpoints. For this reason, the method is not described.

Information

OPEN STOPE

•  Mining method used in wide zones.
• Backfilled primary and secondary stopes.
• Reduction of development cost.

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EUREKA

• Mining method used in narrow zones to minimize dilution.
• Vertical long-hole mining method.
• Reduction of production costs.
• Faster stope production start.
• Elimination of raises.

Advantages:

• Mining cost reduction;
• Hanging wall and footwall stability is increased by the stope length, which is reduced according to the rock mass quality;
• Pre-production development is decreased and a faster stope production start; and
• Mining of ore slice can be more selective, uneconomic areas are left in place by restarting a new primary stope.

Disadvantages:

• Use of cemented backfill considerably increases production costs;
• Production is decreased due to stope dimensions of 5000 t approximately and longitudinal mucking on long distances; and
• Mining cycle is interrupted by the backfill cycle, decreasing productivity if several working areas are not available.

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UPPER STOPE

• Mining method used to complete a zone when there is no access or inaccessible to the upper level.
• Vertical long-hole mining method.

Advantage:

• Greater ore recovery.

Disadvantages:

•  Stope cannot be completely backfilled since the access is only from the bottom. On long term, spalling may occur due to the part of the stope that stays open.

Information

The shrinkage stoping has been selected for the following reasons:

• Lower cost per ounce, taking dilution into account;
• Attainable excavation width of 1.5 m to 1.8 m (5 ft to 6 ft) for the mineralized vein of 10 cm to 30 cm (4 in to 12 in) wide;
• Dip of the mineralized vein varies from 65 to 90 degrees, allowing ore flow by gravity;
• Rock quality of the mineralized zone and the walls is excellent;
• Good selectivity around the stopes.

The long-hole stoping was carried out in 1998 on Level 5 in Zone 50. The results were satisfying with very low dilution observed. The trial has proven that the long-hole stoping with a drilling diameter of 5 cm (2 in) is achieveable for this type of deposit. The rock is competent (diorite) and the mineralized zone is sub-vertical. The ideal drilling length of approximately 15 m (49 ft) is restrained due to the narrowness of the vein and the hole deviation.

Problem

Between Levels 7 and 8, the spacing is 85 m (279 ft), which:

• extends the required time to mine a stope and to fully recover the ore stockpile; and
• makes it difficult to anticipate the location of the cones while mucking in the drawpoint when the excavated height of the stope reaches 50 m (164 ft) vertical.

Solution

To accelerate the completion of the stopes and the ore recovery, the long-hole stoping is used for the last 20 m (66 ft) of the stope.

Information

For Fx6 and Fx9 zones, long-hole method with 64 mm (2.5 in) diameter boreholes has been selected. Drilling is performed upward or downward on lengths varying between 15 m and 18 m (49 ft and 59 ft).

Criteria for method selection are based on:

• location of the vein,
• drift dimensions,
• dip of the vein,
• available equipment, and
• quality of walls.

Information

SHRINKAGE STOPING

The Sleeping Giant mine mainly uses the shrinkage stope method since a good selectivity can be obtained.

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SEMI-SHRINKAGE STOPING

This method is generally used when the dip varies between 40 and 50 degrees. The mining is done like the shrinkage stoping. Given the gently dipping, the gravity sliding of the ore is difficult. In order to ensure a good recovery during the final mucking, a scraper is used. The workers remain in the stope throughout the final mucking cycle. Pillars are built as the ore lessen in order to secure the workers. In addition, wire meshed retaining fences are built.

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LONGHOLE STOPING

This method is actually being tested to increase the ore production and to reduce the physical efforts caused by the shrinkage stoping. However, this method generally creates more dilution and its effectiveness compared to the shrinkage stoping remains to be proven.

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ROOM-AND-PILLAR STOPING

The room-and-pillar method is presently in development. This method is used in areas where the dip of the vein is less than 40 degrees. Currently, the width of the stopes is 12 m (39 ft) and 3 m (10 ft) for the pillars.

Problem

Manpower, having a good expertise in conventional mining such as in the shrinkage stoping, is becoming rare. Furthermore, the risks exposure are higher with this method.

Solution

In order to solve the problems related to the availability of skilled manpower and to reduce the risks exposure to the workers using the conventional mining, the longhole stoping is being tested.

Information

BEFORE THE YEAR 2000

SHRINKAGE STOPE METHOD

This method, used and kept since the beginning of the operations, allows a good geological follow-up. To a depth of 716 m (2350 ft), this method is adapted to the ground conditions.

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LONG HOLE METHOD

This method is mainly used for the recovery of the upper part of the shrinkage stopes. Tests were conducted in order to replace the shrinkage stope method.

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CUT-AND-FILL METHOD

This method was recently introduced to replace the shrinkage stope method. Up to now, the method has not given the expected results, as much for productivity as for the grade and reduction of the average width of the stopes.

Problem

SHRINKAGE STOPE METHOD

Between the levels 21 and 23 (610 m and 716 m [2000 ft and 2350 ft] below the surface), the shrinkage stope method was no longer adapted to the ground conditions. During the final mucking, walls were collapsing, which caused dilution and therefore restraining the recovery of all the broken ore. In addition, ore pillars remained between drawpoints causing substantial lost of ore (approximately 5%).

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LONG HOLE METHOD

Due to the cost of transportation of the ore to the mill (60 km [37 miles]), the dilution generated by the longhole mining is unacceptable. Because the dilution could not be controlled with this method, it was not considered in the long-term plan elaborated in 1999.

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CUT-AND-FILL METHOD

No operational mill exists close to the mine in order to supply the backfill. The free gold recovered at the mill is estimated to have gone from 40% to less than 30% after the introduction of the cut-and-fill method. For this reason, the production grade was significantly lower than the 2000 forecasts.

Solution

SHRINKAGE STOPE METHOD

Due to the deteriorating conditions of the ground in the lower part of the mine, the shrinkage stope method was replaced by the cut-and-fill method.

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CUT-AND-FILL METHOD

Without an operational mill directly onsite, trucks bring the ore towards the processing plant and return to the mine with backfilling made of sand and fill. In order to improve the recovery of free gold, the following procedures were introduced:

• Improvement of cemented floor quality.
• Implementation of a strict cleaning process before backfilling.

Information

Where veining has been exposed on the 2-B Zone, evidence indicates that the vein and its immediate hanging wall and footwall require little artificial support. Diamond drilling and vein exposure interpretations indicated steeply dipping ore structures varying from 70 degrees to vertical. The vein width averages 2.45 m (8 ft).

Assuming that good ground conditions, as observed in the existing opening, would prevail throughout the planned veining area, mine design has been based on the use of shrinkage stoping.

Information

RMR - rock properties:

• Ore: 60 to 65 considered fair to good.
• Waste: 80 considered good to very good.

The mechanized cut-and-fill method was chosen because of these criteria:

• Ramp already existed for the Ni zone.
• Ground not suitable for Long Hole application.
• Important financial saving in Ni zone.
• Mine dilution.
• CAMP software (computer aid mine planning) developed by Falconbridge.
• Monitoring system.
• Surveying done by only one technician.

Information

Conventional cut-and-fill, shrinkage and panel mining are typically employed by Kinross to excavate the narrower gold bearing vein structures. Each of the preceding mining methods are used to extract vein structures in vertical and or near horizontal attitudes. Veins mined by these methods typically range from 0.20 m to 2 m (0.65 to 6.5 ft) and are usually higher grade material. Mucking is accomplished by the use of appropriate sized slusher.

Shrinkage mining is practised in ore zones that are steeply dipping and are continuous along strike. When there is not enough continuity, the cut-and-fill mining method is selected.

Panel stoping is necessary in areas of the mine where the ore has a shallow dip and tends to roll vertically.

Longhole method with paste backfilling is used in wider stoping areas. Longhole levels are advanced at 60 m (196 ft) vertical intervals with sub-levels at 20 m (65 ft) intervals. Haulage drifts are driven in the footwall about 12 m (39 ft) offset from the ore zone.

When selecting a method, a stope cost simulation is achieved .

Information

LONG-HOLE STOPING METHOD:

• Dip: 45 to 90 degrees.
• Power: 1.8 m to 7.6 m (6 ft to 25 ft).
• Regularity of the vein.

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CUT-AND-FILL STOPING METHOD:

• Dip: 45 to 90 degrees.
• Power: 2.7 m to 6 m (9 ft to 20 ft).
• Ground conditions: average to bad.
• Good selectivity.
• Dilution control.

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ROOM-AND-PILLAR STOPING METHOD:

• Dip: 0 to 30 degrees.
• Selectivity.
• Dilution control.
• Good grade.

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SHRINKAGE STOPING METHOD:

• Dip: 45 to 90 degrees.
• Power: 1.5 m to 3.6 m (5 ft to 12 ft).
• Good ground conditions.
• Good selectivity.
• Possibility to recover the sub-horizontal veins within the stope.

The shrinkage method is not a common practice anymore because the majority of the new mining blocks at the #3 shaft, between 960 m and 1818 m (3150 ft and 5965 ft), have ground pressures that do not allow this type of mining.

Problem

Long-hole mining at the Sigma mine is relatively recent, so very few historic details are available. Dilution was a major problem with this type of mining due to the conception parameters initially used: stope dimension (hydraulic radius), drilling length, over-excavation of sub-levels, follow-up of the vein. The geology is very variable at the Sigma mine. Each mineralized block must be treated with a personalized approach.

Solution

To reduce dilution, several changes were brought to the long-hole method. The dimension of the stopes, drilling patterns and the follow-up on drilling precision were modified. Now, the dilution is better controlled but the ground pressures remain an important cause of dilution. Planning of the stopes is done case by case and often varies from the standard method.

Information

At the Con mine, four types of method are commonly used: shrinkage, conventional cut-and-fill, mechanized cut-and-fill and longhole.

The mining method evaluation and selection are made individually for each geological block. For the evaluation, the following criteria are considered:

• ore geometry,
• ore continuity,
• mechanized access already close by,
• waste management,
• cost.

Problem

Like most of the narrow vein operations, a precise geological evaluation is very hard to achieve with diamond drill holes. The geological model is often defined only after development is completed. With the new information, the mining method originally selected is sometimes not suitable anymore. A change in the mining method can lead to additional development.

Solution

The planning is done by keeping in mind that the method selection can change following the development in ore. In order to minimize the costs related to additional development due to a change in the mining method, a first stage is done with minimum development. This approach leaves some flexibility to change the mining method if required.

Information

The long-hole retreat mining method was selected for the narrow orebody extraction. The reasons being related to economic, ground conditions and the manpower in place, experienced with the long-hole mining method.

Additional factors also lead to the selection of the mining method:

• safety,
• continuity of the orebody,
• ore recovery, and
• availability of paste fill.

Information

The mining method is selected according to the following parameters:

• economic (in order to maximise the NPV - Value added)
• ore location
• ore grade 
• ore width
• dip and plunge of the vein
• volume
• stability analysis (RMR) according to dilution
• access to the block
• recovery
• extraction rate
• scheduling.

The mining methods used at the Dome Mine are longhole, room-and-pillar and cut-and-fill. It is significant to note that, actually, all narrow veins are mined out using the cut-and-fill method. The economics and feasability are evaluated according to the listed parameters.

In the past, panel stopes, postpillar stopes, conventional and modified shrink stopes have been mined. Attempts have been made with longhole stopes. The trials were not successful because of the dilution problems.

Problem

In the past, the trial of longhole stoping has been tried unsuccessfully due to excessive dilution in ore recovery and slow extraction rate. Also, a modified shrink mining method has been tried but was abandoned due to the recovery problems. The muck was kept too long in the stopes and hardened in place. Dilution and low productivity problems were also encountered with this method.

Solution

In order to reduce the problems encountered, the modified shrink method is not used anymore. However, workers are considering the possibility of mining with shrinkage stoping, if the geological block is appropriate.

Information

The shrinkage stoping is used when the block limits are not precise (ground quality good to average, thickness 1.7 m [5.5 ft] minimum).

The longhole stoping is used when the block limits are known. Longhole stoping was realized successfully at 43 degrees.

Information

The shrinkage method was selected in order to maximise the grade. A bulk sample has been taken from Noranda to take the vein contact to contact.

The grade then obtained was 5.1 g/t. It did not give good results since the ore is located in the first 1.5 m (5 ft) from the hanging wall contact. Mining with the longhole method was introduced in the stope sill pillar for safety reasons. The ground conditions were bad. The sill pillar left is usually 13 m (42 ft). To recover that pillar, the long holes are drilled from the muck floor of the shrinkage stope.

In order to evaluate if it would be beneficial to convert to a longhole mining method according to the geology of the mine, a study was initiated in 1996. The purpose of the study was to compare the profile section of a shrinkage stope completely mined out with the profile of the interpretation that could have been made for longhole method with the geological information available. The steps were:

• Cross sections of the stope every 1.2 m (4 ft) were produced with the known survey information of the stope.
• Sublevels were positioned assuming longhole mining.
• The profile that had been planned to mine in longhole according to the geological information available from the sub-level position was put into the sections.
• By comparing the survey of the stope with the longhole planning, the dilution and the ore lost can be evaluated.

The study was not completed at the time of our visit in 2000. The process from that study is simple and could give very valuable information to evaluate the effect of converting to longhole mining.

Problem

In longhole method, an area was tested but energy has been put into it, so the development was long and a lot of deviation occurs in the drilling.

Information

During the visit, the mine was putting more emphasis on the narrow-vein mining method. The method used at David Bell mine is the Alimak mining method. However, for narrower veins, the longitudinal retreat mining is used.

The selection criteria for the Alimak mining method are numerous. The main one is based on economic and the other ones are:

• Width of the ore;
• Lower grade where the longitudinal method can't be used to economically extract;
• Good continuity of the ore; and
• Time constraints.

The mining method mostly used is a transverse primary and secondary longhole method. Usually, the development is done two years in advance of the production schedule. Therefore, when narrower areas are encountered in these sectors, the mining method generally used to recover these stopes is the longhole retreat method.

Information

TYPE OF METHOD : Longhole retreat open stoping.

SELECTION CRITERIA

• Dip of the orebody at an average of 35 to 49 degrees, not conducive to conventional longhole mining from bottom up.
• Development and budget constraints. Orebody was developed below 1780 level and the shaft had to be deepened. Production commenced prior to shaft and 3000 level completion.
• Relative competency of the rock, thus minimizing ground control requirements. (Refer to Optimization of longhole stoping document).
• In comparison to other gold operations, a very low grade orebody, thus most economic method was necessary.