Grade Control

Aurizon Mines Ltd. - Beaufor mine (Québec)


Daily visits are made by the department of geology and mapping is done. Following these visits, a geological report is written and distributed to the production and technical service departments.

No sampling of development faces is done at this time. The evaluation technique of the trammed ore consists in taking approximately 1/2 kg (1 lb) of ore per 3-t mine car for the development ore, and also for the production ore. This sampling is taken at the ore chute by the miners. History shows that in a one-year period, there is a reconciliation of about 1% between the grades evaluated at the haulage and the grades at the mill.


The quality and reliability of sampling are difficult to control.

The ore and waste management is difficult.


Continuous awareness on the importance of sampling is done among the miners.

The daily visits of the geology technician allow the identification of the ore and waste to be properly managed.

Barrick Gold Corporation - Bousquet mine (Québec)



The heading is measured and rounds are drawn out to ore or waste depending on the in-situ sampling results (DDH, chip sampling).

For rounds, the length to excavate is customized in order to cut the drift at the hanging wall contact and at the ore/waste limit of the footwall.

The walls are sampled approximately every meter to define the zones. Previously, the whole waste from development was sampled; the waste sampling has been reduced to a maximum of 2 samplings from the footwall elevation.



Each face is panel sampled depending on the geology, and longitudinally located with a starting point and endpoint, using lateral left-right limits.



Sampling of development rocks from walls and faces is mapped. Every sample has 3-D dimensions end can be used in calculation model of reserves.

Ore sampling ratio from development has decreased from 1 sample every 5 buckets to 1 sample every 10 buckets. Lately, only ore rounds are sampled.

Samples were analyzed for gold, silver, copper and zinc (Au, Ag, Cu, Zn). Since 2001, only gold is analyzed.



Stopes are visited daily, from the beginning of blasting operation until backfilling is completed.

Selective mucking of waste inbreaks in the stopes.

Wall behaviours are reported daily to the concerned departments.



It happens that the mucking is not consistent, that is, the rock is not sent to the requested destination point.



Dilution problems in stope occur during non-conforming development (quality).

Tolerance limit: 0.3 m (1 ft), more or less, on each side of the vein.



During the mucking cycle, the workers hardly ever respect the sampling procedures, in terms of frequency and quality level.



The heading and the destination of each round are reported on a daily geological report by the technician who patrols underground. The direct communication between the technician, the foreman and the captain makes it easier for the follow-up. Excavation of rounds with customized length had increased the quality of development.



During development, the tolerance limit is 0.3 m (1 ft) on each side of the drift. In order to ensure development compliance, a follow-up is accomplished, along with a report for the foreman and the captain. If problems need to be solved, employees are met.



In order to improve the sampling quality, the concerned production workers are met to raise their awareness to its importance.

Furthermore, a monthly follow-up of the sampling compliance during mucking operations has been implemented for the foremen and captains.

Cambior Inc. - Mouska Mine (Québec)


In the development and stope operations, technicians process the vein interpretation and the chip sampling of the face daily, whenever possible. Short test holes are drilled, where necessary, inside the stope to identify secondary veins. Following the technician's visit, a geological report is written and sent to the production and technical service departments.

During mucking operations of development faces and stope pulling, the rock is sampled at random following a precise procedure:

  • 1 sample per 20 t for stope pulling
  • 1 sample per 10 t for development work.

 Since the beginning of the project in 1989, a total of 1 042 000 t of ore has been produced at an average grade of 10.52 g/t gold. There is 0.1% difference between the milling grade and the sampling. The Mouska mine has always processed its ore in collaboration with other mines.


A good geological follow-up is closely related to good communication between working shifts. Communication between working teams remains a daunting challenge.


To make available the geological information to both working shifts (day and night), a daily detailed geological report is distributed with instructions written directly on the mining or development plans.

To ensure a better vein follow-up, the round length is limited to 2.4 m (8 ft) and horizontal holes are mined in the stope.

Cambior Inc. - Doyon mine (Québec)


During ore development works, vein identification and grab sampling of the face are performed by technicians on a daily basis whenever possible. Following the visit, a geological report is written by the geological department and is distributed to the technical and production services.

When mucking development faces or stope, the rock is randomly sampled according to a specific procedure:

  • 1 sample per 20 t for stope drawings.
  • 1 sample per 10 t for development works.

The ore grades are easier to estimated when large quantities of sulphide are present in the orebody, whereas the mineralization is distributed more evenly. If the orebody contains less sulphide, more nugget effects occur.


The geological structure of the deposit is very complex.

Even if in some areas, less sampling could be taken, the same sampling procedure is requested everywhere in order to simplify the worker's tasks.


In order to overcome the complexity of the deposit, the mine has been divided in horizons where work teams are assigned.

Cambior Inc. - Sleeping Giant Mine (Québec)


In development and stope works, the vein identification and chip sampling are done by geology technicians everyday, whenever possible.


The variation of the vein requires that the vein to be opened on at least 0.9 m (3 ft) in order to follow it.


During developments, the geology department gives daily instructions to the miners.

Campbell Resources Inc. - Joe Mann Mine (Québec)


In the development work and in the stopes, the identification of the vein as well as chip samplings are performed by geology technicians every day, whenever possible.

Claude Resources Inc. - Seabee Mine (Saskatchewan)


To follow the ore development, diamond drill holes are used for a first alignment and test holes complete the information during the development.

A representative from the geology department visits the work heading every day to identify and to sample the vein. The face is sampled by chip sampling every 3.5 m to 3 m (11.4 ft to 10 ft) interval. Following the visit, instructions are given to the underground supervision with a copy of the geologist's note.

There are very few muck samples taken. It is only done to double-check the grade, or to determine if an area has to be shutdown.

The results from chip sampling are used to evaluate the grade of the broken rock. From 1992 to 1999, the average mill reconciliation has been 0.89%.

During and after completion of a development heading, mapping is done.

Falconbridge Ltd. - Fraser Mine (Ontario)


Actual grade control and design mark-up:

  • Tonnage and grade. 
  • Characteristics of the orebody. 
  • Structure. 
  • Rock type.
  1. Faces are mined too wide.
  2. Irregularity of the orebody.
  3. Vein increasingly narrow.
  4. Poor quality of mining method.
  5. Grade control problems.
  6. Floor not cleaned up.
  7. Mix of ore and waste.

1.  In order to control the face width, extra bonus are given to employees when the requirements are met.
2.  Due to irregularity of the orebody, seven-day grade control is now achieved instead of five.
3.  Smaller equipments are used.
5.  In order to solve the grade control problems, the wrecking of waste is done separately, veins sequencing and design audit are achieved.
6.  Floor sign-off sheet and back height monitoring sheet are filled out.
7.  Separate chutes were designated for each, ore and waste.

Kinross Gold Corporation - Hoyle Pond Mine (Ontario)


In development and conventional stope work, chip sampling and mapping of the face are done daily.

The vein contact is usually easy to recognize.

In development, sampling frequency is every 3 m (10 ft) of advance. Each round is sampled by the worker at the ratio of one sample for every 20 tons of ore.

The geologist reports his daily visit in a log book for the shift boss and requires an approval signing after reading.

To follow the grade, a summary sheet is produced every day to compare the cumulative grade with the month planning.


It is difficult to have the worker follow the sampling procedure.

There is only one tractor for four geologists and it gets hard sometimes to visit every face since the mine is widespread.

There are important delays before getting the sampling results.


The samples are now tagged and computerized. The results are entered directly from the lab and are available within a short delay.

McWatters Mining Inc. - Sigma Mine (Québec)


In the development and stope works, identification of the vein and chip samples are done by a geology technician every day, whenever practicable.

The samples are taken, using chisel and rock hammers, across the width of the vein and from host rocks of the altered zone.

Following a visit, a geological report is prepared and distributed to the production department and technical services.

Test holes are drilled inside the stope in order to identify the occurence in secondary lodes.

Historically, two samplers were working full time. The drift's roof was systematically sampled every 1.5 m (5 ft).

The reconciliation of grades is done every month in comparison with the tapping.


It is difficult to promote awareness among the workers on the importance of sampling.

Sampling boreholes in a longhole stope is a long and costly process.

During the gold recovery process at the mill, there is a retention period within the circuit. This implies that the poured quantity of gold at the end of the month does not necessarily corresponds to the amount processed at the mill. On a monthly basis, this delay results in reconciliation problems.


To encourage the miners to sample well, the procedures are posted in strategic places. More so, reminders are given at regular intervals by the supervisor and technical services on the importance of sampling.

For the sampling of long-holes drilling, the geologist targets the holes that need to be sampled. These holes are drilled first in order to obtain rapid results and to be ready for production blastings.

For the reconciliation of the grades, it was estimated that monthly reconciliation could be very variable. However, on a yearly basis, the difference between the estimated grade and the one processed at the mill is approximately 5%. Actually, the reconciliation is estimated every month from haulage results and finalized at year-end.

Miramar Mining Corporation - Con Mine (N.W.T.)


In ore development heading or in stopes, each face is mapped and sampled daily. Based on lithology, 30 cm to 1.2 m (1 ft to 4 ft) chip samples are taken.

Along with the sampling, the geologist identifies the vein to align the worker for the next round. A short report is then written to brief the underground supervision on the geology.

During the mucking of longhole and shrinkage stopes, the muck is sampled. This procedure does not apply to cut-and-fill where the chip sampling is used to evaluate the grade.


In the muck sampling procedure, the size fraction that best represents the grade is a fixed measurement that might not be the optimum.

Newmont Mining Corporation - Golden Giant Mine (Ontario)


In development, the dyke is easy to identify. The workers are well trained to recognize the type of rock and align themselves.

The faces are mapped and sampled every 3 rounds or less.

There is one muck sample taken per shift, it gives around 100 to 200 tonnes per sampling. This sampling is balanced with the mill at the end of the month.


With the use of diesel equipment, the back of the development gets too dirty to do back mapping.

Placer Dome North America Ltd. - Dome Mine (Ontario)


In cut-and-fill stopes, the muck sample results are compared with the chip sample results to monitor the production. For the longhole stopes, the muck samples are compared with the evaluated block model.


The gold distribution in the mineralization is highly nuggetty.

The grade distribution is not constant through stope cut.

The face sampling is done in assuming simple vein shapes.


To give a better evaluation of the gold grade, two chip samples are taken in the ore and only one is taken for the waste. (Refer to the chip sampling procedure).

Following the chip sampling in the cut-and-fill stope, if the grade is lower than the cutoff grade, the broken rock is left in the stope when it is possible.

When the vein is not continuous in a face, an average vein width is considered for grade evaluation.

Richmont Mines Inc. - Francoeur Mine (Québec)


In the development and in the stope work, the chip sampling is done by technicians daily, whenever practicable, and test holes are taken when necessary.

Daily visits in the stopes or development faces are done by the geology technician to identify the vein. Following the visit, a geological report is prepared and distributed to the production personnel and technical services.

For development follow-ups, discussions between representatives of all levels take place pursuant to the receipt of the analysis.

For the mucking, the sampling is not done systematically but only when needed, and this, especially for the longhole mining method.

Grade reconciliation is not done because the grade is relatively continuous in the stopes.


By its geological identity, the vein is sometimes difficult to follow.

The sampling method for mucking must be modified, now that the longhole mining method is mainly used in the # 7 zone.


For the grade follow-up, daily reports are used. In follow-up problems, a red stamp is used to indicate an excessive dilution.

To facilitate the follow-up of the vein in shrinkage stopes, the vein is marked at the roof of the entire stope, allowing the miners to align for the mining advances.

The mucked ore is not sampled by the trammer but only by technicians on their round. Great savings are realized this way.

River Gold Mines Ltd. - Eagle River Mine (Ontario)


The ore development is sampled and mapped every day. The mapping is drawn on a standard sheet form. Some geologists draw the mapping, others prefer to take a Polaroid shot and attach it to the mapping sheet.

In the stope, the back is sampled every 3 lifts on every 4 m (13 ft) interval. The results from back sampling are used to evaluate the grade of the stope.

The geology department has written a procedure for underground sampling (refer to attached document).

Chip samples from development faces correlate well with zones where visible gold was mapped. This implies that chip sampling is successful in measuring gold distribution within the quartz vein.

Teck-Corona Corporation - David Bell Mine (Ontario)


During ore excavation, the development is usually under geology control. The geologist follows a standard procedure.

During development, chip samples are taken to verify reserve grades. Sampling parameters are similar to those for drill core sampling. Sample strings are taken every 6 m to 10 m (20 ft to 33 ft) along the strike. A sample string is a chip sample from a face. It is usually taken at 1.2 m (4 ft) from the floor that crosses the ore of the hanging wall and footwall, and then analyzed.

The chip samples are taken every second round. The sampling is done by rock stratigraphic unit. The ore contacts are painted at the roof, and the surveyors localize the reference lines.

Following the daily visit, the geologist prepares a daily geologic report.

There is no muck sample taken. The initial evaluation of the mining block is adjusted after the survey with CMS (Cavity Monitoring System) of the open stope. The grade then obtained is used for reconciliation with the mill.

TVX Gold Inc/High River Gold Mines Inc. - New Britannia Mine (Manitoba)


There is a very tight follow-up on grade from the geology department. In order to ensure a good control, there is a geologist working on day shifts and another one on night shifts. This way, they are able to see all development faces and inspect every longhole. The development faces are chip sampled. The raise faces are chip sampled or often only grab samples are taken. In longhole stopes, oversized rocks are sent to ore or waste depending on the geologist's evaluation. The information from the geologist is reported in a log book for the shift boss, and the geologist's notes taken underground are given to the other geologist.

In longhole drilling, the hole sludge is sampled by the driller. This procedure is required to enable the operation to effectively longhole mine the ore while minimizing the dilution (refer to the following procedure).

Truck samples are also required to provide information as to the grade of material being sent to the mill and to allow an accurate estimate of the amount of dilution that is being generated (refer to attached procedure).

A reconciliation is made monthly between the estimated tonnage, estimated grade and mill output.


The worker did not understand the necessity of sampling and neglected the sampling procedure. The longhole sludge sampling used to be done on lengths of 1.2 m (4 ft) but the costs were too high.


The costs related to the truck sampling were very high. In order to explain the effect of sending waste to the mill, a meeting was organized with every crew. The data presented at the meeting surprised everyone and they were a lot more assiduous afterwards.

Following a study, the longhole sampling was extended from 1.2 m to 2.4 m (4 ft to 8 ft) in order to reduce the costs; the obtained information is not as good.

In an effort to reduce the costs, the procedure for truck sampling was modified to sample every second truck instead of every truck. The result has shown no impact on the grade evaluation.

Also for the same reason, sampling of the tram ore was eliminated. It only represented 2% of the ore and didn't give any additional information.