Sorry for the long delay in posting – I had a very bad case of kennel cough. 95% better now…
So, the Minto mine is looking to resume open pit mining now that the price of copper has gone up a bit.
At present Minto is mining about 2,000 tonnes per day from underground, at a grade of about 2% Cu. The underground ore is about 10m thick, with top and bottom cuts taken out, then longhole for the rest. A fairly efficient operation it seems. There are four stockpiles on surface, with grades ranging from about 1% Cu to 4% Cu. The mill runs at 4,000 tonnes per day, and the material is blended to an optimum grade around 2% Cu.
There is quite a lot of underground resources remaining at around 2%Cu or a bit less, but a lot of this material hasn’t been adequately drilled off to bring it into mineable reserves. I think most of it would be less than 10m thick, probably more like 4m thick and suitable for room and pillar mining. So slightly less efficient than the current u/g mining. A couple million tonnes reported from Minto East, Area 2/118 and Copper Keel zones. And development of access is required to mine the new areas.
For open pit mining, there is a lot of tonnage remaining, but at much lower grades than mined to date. There are M & I resources totalling 45 million tonnes at 1.07% Cu and Inferred resources of 25 million tonnes at 0.83% Cu.
The corporate website claims there is 7 years remaining mine life, however in this latest news release they are talking about mining only until the end of 2017 if all goes well. So the price of copper over the next year will be critical to continuing mining into 2018 and beyond. The great Otto Rock has already explained how Capstone has shot themselves in the foot by using the so-called “costless collar” to lock in prices below $2.54. I suppose the company will need something more like $3+ per pound to be able to continue mining the low grade pit material for the remaining resources. And they need to invest in developing more of the high grade underground stuff – if they can continue to produce 2% material at 2,000 tpd from underground it will make the 1% pit stuff more palatable.
Anyways, Minto has been a real success story for the Yukon. It started operations in 2007 at 1800 tpd milling rate and only a 4 year initial mine life. The mine has paid millions of dollars year in royalties to the Selkirk First Nation. I am sure that they spent it wisely…
Oh yeah, at 4,000 tonnes per day they mill about 1.46 million tonnes per year. The 70 million tonnes of resources noted above COULD therefore last for 47 years, assuming high enough copper prices! So when the mine shuts down in the next year or so, please, please ignore the calls for a permanent shutdown and reclamation of the site! There will be more mining to come later.