UG Concept 2

UG Concept #2

The original UG concept talked about using a conveyor to both the CH6 and CH7 pipes.
The focus in that concept was to reduce the operating cost for the underground mine by utilizing a conveyor drift. The reality is that a conveyor drift is needed where it relieves a bottle neck. A high tonnage rate deposit is a clear example of this. Chidliak's PEA focuses on a 2,000 tpd production rate. There is probably a significant chance that this number will go higher before a mine gets constructed. However, the mine rate at 3,000 or 4,000 tpd is not anywhere near the top tier of production rates for underground mining. The key difference with Chidliak is the flexibility of where you need to get the kimberlite from to feed the mill. When there are a lot of places to get that tonnage from, there is not an urgent rush to get it all from one place (other then economics). From a technical point of view, a bottleneck can be relieved just by shifting some of the production to another pipe.

What does this mean for Chidliak? Focusing away from operating cost or de-bottlenecking, the main focus should be on minimizing capital costs. If you can delay the development of an underground as late as possible and still access as much high value tonnage as quickly as have reached good value for both IRR and NPV.

CH6 underground is prime target for value and also a prime target for not leaving tonnage stuck in a crown pillar until the end of the mine life.

CH6 underground:

Mine the open pit as deep as economically possible (give or take). Eg. 350 metres deep. That leaves a lot of tonnage in a pipe that has steeply narrow walls and is open at depth. Does it make sense to develop a portal from surface to meet up at depth and below? For the first 350 metres...the kimberlite has been depleted in the main pipe.

Develop the portal off of the bottom of the pit. Initially head north toward the string of pearls. Divide the ramp into a decline that will access ore at depth (below the pit) and an incline that spiral up toward the surface. At the same time develop a portal at surface to meet up with the incline ramp from below.  The general problem with a ramp is that you start off with one heading and one heading alone. The rate of that one heading creates your timeline for the rest of the ramp. In this scenario, there are now 3 active headings.

String of pearls -- The incline up to surface and the surface portal will eventually meet together at half the time that a single ramp down would take. During this development, level's can be developed to all the string of pearls to extract kimberlite material for the mill. Using a bottom up approach, the lowest levels can start be mined fairly quickly. The CH6 open pit is completed and this string of pearl of material can be combined with CH7 open pit to help boost the valuation going through the mill.

The decline going below the pit, can have the levels developed as you go. A deepened level has to be decided as a bottom up level (500 metre level?, then the 750 metre level...and a 1km level?). The use of paste fill or cemented rockfill can be used to extract the pillar material below that level at a future date.  CH6 UG from this level can start to be mined and this can be used to blend with CH7 material to add rock value premium to the mill feed.  As the mining approaches the bottom of the pit...the portal off the pit floor is in jeopardy. Once the ramp's meet up through the string of pearls, the portal off the CH6 pit can be temporarily inaccessible and the CH6 mining level can move up blast all the material up into the pit floor. It can then be replaced with waste and the portal access can be re-established.

The benefit with the portal at the bottom of the pit is that the underground equipment (small) can move kimberlite material onto the pit floor. At this point, the open pit equipment can be move and haul this from the bottom of the pit floor to the ground level and haul it away to the mill.  The haulage distance from underground is cut by the depth of the pit.


Ventilation is a key concern with development and a raise of fresh air or exhaust air needs to be brought with the development.  A single ramp heading can usually use ducting only up to ~1km in length. Beyond that, an upgrade to ducting is needing and it starts becoming a problem.  The incline to surface at 350 metres below meeting up with the portal decline from surface means that these 2 headings each only need to be about 1150 metres in length and once they meet, a circuit is established. Drop raises from each level can be developed as the ramps are created, but there is no technical rush to get them done. Once you have the drop raises completed, it can be quickly tied in with the drop raises that have been developed at depth with the lower decline.

This is all about speed. The quicker you can get the waste develop completed, the quicker mill feed is created and the quicker the payback on that mill feed is done. 

Alternative? (for comparison)

Let's assume a bottom up approach for CH6 is contemplated and the bottom level to start to work from is 1 km's deep. About 7 km's of ramp is needed to get to that level. At a rate of 100 metres per month, it would take 6 years to get any production from the underground mine.  This is not really a good alternative. The benefits are the lack of pillars needed, easy mining. Capitalizing waste development for 6 years before you see production is an absolutely horrible outcome.

The 3 quick heading scenario above really compresses the time that one needs to wait between start of underground development and mine production. The string of pearls work beautifully in this scenario and that synergy that is met should not be discounted, but should give a premium to the project.

CH1,CH7, CH31, CH44,45,46 can all be looked at for sharing similar underground development and portals can be developed from the bottom of these pits and the crown pillar at each pipe can be extracted as multiple portal accesses are all integrated.  There may not be a need for a portal at surface level in any of these area's Multiple portals from bottom of the pits should give some great flexibility in the underground development. Again, this utilizes existing open pit equipment to haul material up to the mill at a reasonable cost.

Waste dumps?

A lot of mines out in the world have multiple pits. In a lot of those mines, the waste and overburden from one pit is disposed of in another depleted pit and that nullifies portal access from the bottom of the pit. Trade offs in this area can happen. Chidliak has a lot going for it in avoiding this scenario.

1 - There is literally not much overburden in any of the pits (15 metres to outcropping). That is not going to create a lot of waste material.
2 - Pit walls - This will create the bulk of the waste material. When they do geotechnical drilling, it should confirm the more appropriate pit wall angles and reduce the amount of waste material that needs to be extracted.
3 - These are high value, small tonnage open pits, so there is not a lot of waste to be create when compared to much bigger mining projects in the world.
4 - Topography is such that multiple waste dumps can be designed and maintained for long periods of time.

Creating and accessing portals from the bottom of many of the pipes seems to be a reasonable and logical scenario for accessing underground kimberlite while minimizing the time it takes to do underground development.

There is no doubt that the underground kimberlite material at CH6, with rock value's up to $1000 per tonne, can greatly enhance value by deferring or blending in with other low value kimberlite material. The string of pearls is a bonus that is not included in any economics at this time (same as the CH6 underground material).

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