Diamond drilling is achieved in two steps:
From the exploration and development drift, the structures are drilled at intervals of 15 m (49 ft) on sections spaced 20 m (66 ft) apart. This type of drilling is generally less than 100 m (328 ft) in length and is achieved with Diamoc electric drills with a BQ calibre. This first step in drilling allows calculation of the reserves and later planning of the development.
The second step, definition drilling, is achieved once development of the sub-levels is completed; the goal being to delineate with precision the ore envelope on sections spaced 10 m (33 ft) apart. This drilling is generally less than 25 m (82 ft) long, and a brief collar surveying is done. Usually, the calibre of the core is AQ.
The exploration drilling is generally performed from an exploration drift located 100 m to 300 m (330 ft to 1000 ft) north of valuable horizons. The definition drilling is performed from longitudinal development drifts and from transversal access (drawpoint) to mineralized zones.
A B20 electric drill with BQ and occasionally NQ size drill bits is used for exploration drillings. A pneumatic drill with either AQ or ATW size drill bits is used for definition drilling.
The first step of exploration drilling is done according to a dice five pattern of 120 m x 240 m (400 ft x 790 ft). If the results are encouraging, additional drilling steps can be done according to grids of 60 m x 120 m and 40 m x 80 m (200 ft x 400 ft and 130 ft x 262 ft).
The definition drilling is done according to a drilling grid of 15 m x 30 m (50 ft x 100 ft) with, occasionally, intermediate holes. In zone 3-1, the definition drilling is done according to a drilling grid of 10 m x 30 m (33 ft x 100 ft) with intermediate holes in about 50% of the stopes in order to provide a better interpretation of the economic zones.
Sometimes, definition drilling is done in active development zones; the development must be stopped for the whole drilling cycle time. To reduce the downtime when the development deadline is tight, the drilling is performed during the weekend.
The drilling is usually performed from the haulage drift. The drilling remains a priority for interpretation and work planning. Consequently, development of the undercut might be interrupted when additional drilling is required.
The exploration drillings are mainly done with an electric drill using BQ size drill holes. The definition drilling is done using ATW size drill holes.
Exploration: 50 m (164 ft) x 50 m (164 ft).
Definition: 10 m (33 ft) x 15 m (49 ft).
Undercut interruptions for additional drilling may cause delays in the production schedule. Sometimes in high development areas, the planned definition drilling is not always completed.
When production deadlines are too tight, some drill holes are cancelled. However, in these cases, the geologist ensures that the limits of the mining blocks are well identified.
Drifts, specially designed for drilling, are excavated. The drilling is generally performed with a JKS300 electric drill with a BQ core diameter, or a pneumatic drill with a AQ core diameter.
Exploration drilling is usually done with a JK5300 air operated electric drill of type BQ or AQ.
Exploration: 40 m x 40 m (131 ft x 131 ft) with drilling access every 400 m (1312 ft).
Development of resources: 20 m x 30 m (65 ft x 98 ft) with drilling access every 120 m (393 ft).
Definition: 10 m x 15 m (33 ft x 49 ft) with drilling access every 30 m (98 ft).
The boreholes are drilled using the following diameters:
- Exploration: BQ.
- Definition: AQ.
The drilling grids are:
- Exploration: 30 m x 30 m (100 ft x 100 ft).
- Definition: 20 m x 20 m (66 ft x 66 ft).
A cement plug of 5 m (16.4 ft) is systematically poured to block the boreholes. The drilling data processing is done using the softwares Prolog, Tralog, Autocad and Promine.
Given the dimension of the definition drill holes, the Tropari cannot be used to estimate the deviation.
Tropari Web site: http://www.pajari.com/tropary.html">http://www.pajari.com/tropari.html
Since the drilling grid size is too small to use the Tropari, acid tests are conducted.
Furthermore, if the drilling length is exceeding 150 m (492 ft), the BQ size is used.
The drilling is done from existing stopes.
Definition drilling is done with compressed air drills with EXT diameter.
Exploration: 45 m x 45 m (150 ft x 150 ft).
Definition: 15 m x 15 m (50 ft x 50 ft).
The accumulation of drilling mud in the ditch is problematic.
A dump car is used into which the mud is pumped and decanted. Once the mine car is filled, it is brought to surface. This procedure avoids, or at least postpones, the cleaning of the ditches. For exploration projects, a small sump is excavated in order to collect the drilling mud.
The surface drilling is done with a Longyear 38 diesel equipment or 262 Diamec electric drill. These equipment have access to the site only by winter roads.
The hole diameters are BQ and AQTK.
For the underground diamond drilling, the remuck bays are used.
The holes are usually 150 m (492 ft) long and this is enough to cover a level up and a level down. Sometimes holes can be longer in order to cover two levels but the information is not as good due to the angle of the intersection with the mineralized zone.
The drilling is achieved by their own workers, 2 workers per team. They drill 27000 m (88582 ft) annually and the drilling cost averages $13/m ($4/ft).
According to the operator, the secrets to these good results are:
- The maintenance of the drill is done by the driller. There is a maintenance bonus and the maintenance has to be pre-approved by the supervisor.
- There is one worker per drill and no helper.
- The drilling stations are well organized and have a sufficient dimension, 5 m x 5 m x 4.9 m high (16.4 ft x 16.4 ft x 16 ft).
- A complete wood floor is built and the station is well equipt.
The drill hole spacing is:
- Exploration (surface): 100 m (328 ft).
- Definition (underground): 25 m (82 ft).
The softwares used to compile the data are: Boresurv, Excel and Autocad.
Range from 12.5 m to 40 m (40 ft to 130 ft).
8 minerals: Nickel, Copper, Cobalt, Sulfur, Gold, Platinum, Lead, Silver.
Shape and orientation of the orebody dictated by dip, strike and plunge of the mine.
- Quality of set up (azimuth and dip).
- No dip testing.
- Continuity of the ore.
- Quality of set up (azimuth and dip).is checked by geologists and first line supervision.
- Surveying instrument, REFLEX, is used to measure the dip.
- Geological spot training is given to employees.
Diamond drilling is done surface and underground from existing drifts.
Sometimes, for the longhole stopes, additional definition drilling is achieved from the bypass drift.
Exploration holes are drilled with an electric drill using a BQ size drill core.
Air drills are used for definition drilling using AQT size drill core.
All diamond drilling work is contracted.
Exploration: 40 m to 100 m (131 ft to 328 ft).
Definition: 15 m to 20 m (49 ft to 65 ft).
The core log information is all processed with the GEMCOM software.
The drilling is done from existing drifts.
In some areas, exploration drifts are developed. If needed, drilling bays are excavated for electric drills.
The exploration drilling is done with electric drills on an NQ diameter.
The definition drilling is done using pneumatic drills on an LTK 48 diameter. Historically, the drilling was done on ATQ or EXK diameters.
Drilling core: Whole core samples are sent for analysis (the core is not split). Except for exploration drill holes where the core is split, half is sent for assay; the other half is kept.
Exploration: 27 m x 27 m (90 ft x 90 ft).
Definition: 14 m x 14 m (45 ft x 45 ft).
It is difficult to evaluate the folding and the dip change of the vein.
It is difficult to determine the geometry of the reserve blocks.
The grade estimate is problematic due to the nugget effect.
The error tolerance level on the evaluation of a block is low since it is close to the mining economic grade.
In order to reduce the surprises caused by changes in the geometry of the vein, the definition drilling grid is respected.
To increase the confidence level of some blocks, drill holes are added.
A reduction factor of approximately 10% is applied to the estimated grade in anticipation of the reconciliation with processed portions.
Diamond drilling of the shear zone is done from exploration drifts. These drifts are driven parallel to the shear zone to a distance of 22.8 m (75 ft). They are located either on the footwall or the hanging wall, alternating from one level to the other. They are initially used for drilling and later for production haulages and accesses.
The underground diamond drill holes are done on AQ diameter and the surface ones with an NQ or BQ diameter. When the stope development is complete, a small bazooka drill can be brought in to complete the information or to define short projects.
Exploration: An initial phase is done on a 60-m x 60-m (200-ft x 200-ft) grid. If the results are interesting, it is reduced to a 30-m x 30-m (100-ft x 100-ft) grid.
Definition: 15 m x 15 m (50 ft x 50 ft).
Due to factors such as nugget effect, variability in the geometry of the vein and deviation of the diamond drill, it is very hard to have a good image of the ore blocks.
In order to evaluate the deviation of diamond drill holes, multiple shot measurements using a Sperry Sun are done for holes longer than 30 m (100 ft). Also, the conventional mining method provides the flexibility required to follow the orebody.
The drilling is done from existing drifts.
The definition drilling is done with pneumatic drill of VAG type with a core diameter of AQ or BQ.
The exploration drilling is done with an electric drill with a core diameter of BQ.
Exploration: 50 m to 75 m (164 to 246 ft) hole spacing.
Definition: 25 m (82 ft) hole spacing. The software used to compile the data is Gemcom.
The diamond drilling is done from existing track drifts and occasionally from sub-drifts.
The exploration drilling is done with electric drill of type B10.
The definition drilling is done with pneumatic drill of type VAG or VBG with a core diameter of AQTK.
Exploration: 18-m (60 ft) sections with 24-m (80 ft) intercept.
Definition: 9-m (30 ft) sections with 12-m (40 ft) intercept.
The software Vulcan is used to compile the data. This software is used throughout Placer Dome's mines.
The rock may be magnetic in certain areas and may affect the Tropari reading results.
The survey instrument (Tropari) is too big to pass through the drilling bit. Therefore, the rod must be taken out of the hole in order to take the measurement.
The survey instrument (Tropari) is very delicate.
Diamond drill assays do not accurately represent the grade of narrow veins. An empirical review of drill results and assay results (chips and mucks) from development show high variability in drill assays.
To bypass the problem related to the presence of magnetism in the rock, the tests are taken outside the dykes.
The survey instrument (Tropari) is attached to the end of drill string in order to take a reading.
Because the instruments are so delicate, much care is taken while doing the survey.
The diamond drill hole assays do not always well represent the vein so the geologist does a preliminary evaluation and a drift is excavated to define the vein interpretation.
The drilling is done from the drifts. Cross-cuts are driven occasionally when there is an emergency.
The 40 HP electric drills are used for AQTK drilling and pneumatic drills for BQ drilling.
There is no deviation problem since the drilling is limited to 45 m (150 ft). Usually, the precision is excellent for holes less than 76 m (250 ft) long. For longer holes, such as 122 m (400 ft), deviation could reach up to 1.5 m (5 ft).
Exploration: 122 m x 45 m (400 ft x 150 ft).
Definition: 23 m (75 ft) with sections every 15 m (50 ft).
The information with reference to the description of the drilling core is processed with the Prolog and Tralog software.
The Tropari tests results may be altered by the presence of magnetism in some areas.
In order to save time for the geology department, some diamond drillers are trained to take the Tropari tests themselves.
The drilling is done from the ramp.
The drilling is done with electric or hydraulic drill on ATW hole diameter.
Exploration: First phase on 100 m (328 ft) spacing, if it gives good results, the spacing is reduced to 25 m (82 ft).
Definition: 12.5 m (41 ft) spacing.
On long diamond drill, hole deviation can be a problem.
The use of a hexagonal core barrel can control the deviation as low as 1 degree to 2 degrees per 100 m (328 ft) of drilling.
To measure the deviation during the drilling, a Sperry-Sun is used to replace the use of an acid test.
Sperry-Sun: A measurement-while-drilling technology, it enables the measurement of a number of parameters, allowing more precise and more productive drilling.
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The exploration drilling is done with an electric drill of type BQ.
The definition drilling is done with a pneumatic drill with a core diameter of AQTK.
Exploration is done on a 100 m x 100 m (328 ft x 328 ft) grid, a second phase is done on 50 m x 50 m (164 ft x 164 ft) grid.
Definition is done on a 25 m x 25 m (82 ft x 82 ft) grid.
Most of the drilling is achieved from a drift, typically 15 m (49 ft) from the ore.
If the hole is planned within 8 m (26 ft) of an existing working area, a Breakthrough Advisory report must be issued.
Diamond drill core is sampled where gold mineralization is suspected. No sample including waste material should exceed 0.5 m (1.6 ft) in length. This procedure cuts down on the "nugget effect". Any holes drilled for exploration, or holes that are used in boundary agreements (Quarter-Claim, C-Zone drilling ) must be split in half. Half the core goes to assay and half is retained in case it is required for future consultation.
Exploration drifts are located on three different levels:
- Level 1780, in the hanging wall.
- Level 2300, in the hanging wall.
- Level 3000, in the hanging wall and footwall.
The hole diameter used are BQ and AQTQ for exploration and EW for the definition hole drilled with a bazooka drill.
THE DRILLING GRID PATTERNS ARE:
Exploration: 30 m x 30 m (100 ft x 100 ft).
Definition: 15 m x 15 m (50 ft x 50 ft).
After the sill is developed, a Bazooka drill is used to drill flat hole every 7.6 m (25 ft). Also, the core log information is all entered in Gemcom. Plan sections are generated with the software at every 7.6 m (25 ft). The geological interpretation is achieved by hand using these sections. The reason is to give the geologist a better understanding of the geology. When the interpretation is completed, a block modelling evaluation is compared with the hand made.