*Information in this current blog is based on information obtained up to mid 2018 and should be considered legacy at this time and should no longer be relied upon.*
The decisions that are made now with respect to the open pit mine could have dramatic impact of an underground mining scenario.
The biggest question for the open right now is the location of the mill.
Do you put the mill closest to CH-6 where you can start getting even higher margin material based on milling cost. Then you would need to haul the material from ch-7 to the distant mill about 10 km's away.
Do you put the mill closest to CH-7 where you have several other kimberlite pipes that could be mined over the next 2 decades. Then you would need to haul the material from ch-6 to the distant mill about 10 km's away.
Haulage trucking does have a cost...but it isn't outrageous. You just add a few $$'s per tonne to haul that material.
On the face of it, it looks like you would go with mill closest to CH-7.
Now, you bring in the underground scenario. Are you going to use pastefill? or cemented rockfill? A pastefill plant does not like transporting paste horizontally over a frozen tundra. You usually put the pastefill plant somewhat close to the mill...but not necessarily. If you are going to use pastefill in both pipes...maybe it is a dead heat....so that hasn't really helped with the location of the mill.
That brings us back to the underground scenario. What do underground mines like?
Sure, you can haul the material up the ramp with underground trucks over and over again and the deeper you go, the deeper the cost. Underground mines like Shafts to haul material. Are you going to put in multiple shafts and the material coming up the shaft will need to be shipped to the mill (either closest by or 10 km's away). Shafts are very capital intensive as well. It doesn't sound like shafts at Chidliak make any sense.
Underground mines like conveyors to haul material. Yes, conveyors are great and can be cost effective over straight truck haulage. Conveyors are also powered, so can easily be connected into a hydro feed (if it exists) or a wind farm or any power generation that comes to be at Chidliak. Trucks, yes you can go electric/battery...but the end winners are usually diesel. It is much more efficient to burn diesel at the source than have it converted on the surface and then into battery power, etc.
So, conveyors at Chidliak would be an option. What do conveyors like? They like to be straight. The straighter the better, no curves and you can put in a switchback/transfer point if you must...but that can get a bit complicated....so straight is the best.
Conveyors also can designed at the traditional -15% gradient and you can pop them up on the back (ceiling) of the decline, so that the same decline can be used by personnel and equipment. Very efficient.
So, that clearly brings the option back to putting the mill almost directly in between CH-6 and CH-7.
The conveyor decline goes for 5 km's and that gets you down to the -750 metre level. Perfect for underground mining. Better yet, the conveyor from both ch6 and ch7 go up the conveyor and arrive directly at the mouth of the mill. Even better. The conveyor to ch7 can also be used as a materials transfer point for other kimberlites in the vicinity.
You can still do a portal off the bottom of the pits for more accesses into the development.
You could drive a raise up to surface from the conveyors and you could actually drop material (slightly crushed) from the open pit's down into that raise to feed onto the conveyor belt and then you would not even have to truck haulage the material to the mill on surface.
Serious thought has to be put into a concept like this before you just put a mill close to ch-6 or ch-7.
These straight declines could actually be completed with a tunnel boring machine.
Tunnel boring machines haul a conveyor with them and that can be left up and the belt can be replaced with a permanent belt afterwards.
Tunnel boring machines are expensive...but very fast. Anything less than 5 to 7 km's, usually the cost doesn't make sense. Anything 7 to 10 km's or more and the economics actually start making it more sense than traditional drill and blast. This concept above has 10 km's of straight development (5 km x 2).
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