Within this update its Grants where things are interesting but still unclear.
The structure of Grants has been known since 2018. Grants was advised as a 2.89Mt @ 1.5% deposit in the 22 Oct 2018 Resource update. The June 2018 pre-feasibility study planned to mine grants purely via open pit shifting 8.92M bcm of waste for 0.644M bcm of ore (1.778Mt of ore). There was over 1Mt of the deposit that was too deep/offset making open pit mining too expensive. The 2019 first DFS appears to have preserved this mining plan but added an open pit BP33 operation meaning the totals presented are no longer Grants specific.
Fast forward a few years and Core had its 2nd DFS of July 2021. The open pit plan was scaled up with waste rock removal increased to 13.103M bcm for 0.790M bcm of ore (2.143Mt of ore). High strip ratio material was added to the plan. A small underground mining operation was also planned to recover 0.3Mt of ore. Some of the ore at the bottom of Grants that is not economic to recover via open pit was considered economic via UG.
The July 2022 Ore resource update lowered the grade cut-off to 0.5% enabling the Grants resource to be restated as 2.95Mt @ 1.45%. Mining ore started late 2022. By the April 2024 resource update Grants was 2.32Mt @ 1.45%. All the mining depletion occurred from Measured with no change to Indicated or inferred. As is usually the case, Core was mining material that had been defined to a JORC Measured level of confidence. ~0.63Mt (2.95 - 2.32) had been mined.
If Core was able to continue its July 2021 DFS plan then there should have been ~1.5Mt to mine from Grants via Open pit. If Core were able to revert to its 2019 DFS plan then there should have been around 1.1 to 1.2Mt of ore to open pit mine from Grants. This isn't what Core have presented.
The update yesterday has lowered the remaining Grants open pit ore to 0.57Mt but at a very good price point. If mining a 1.4% grade to deliver a 5.0% concentrate with 83.2% recoveries you need 4.293t of 1.40% material to create 1 ton of SC5.0 [4.293 * (1.40% / 5.00%) * 83.2% = 1.000]. Page 9 notes the costs below. It would appear this version of the Grants restart plan has a mine gate cost of ~A$623/t [4.293 * (A$64.21 + A$69.45 + A$11.48)] although on this version of the plan, Grants restart isn't until after the construction of a back-end flotation plant because an 83.2% recovery was applied to all deposits.
Speculation time
One of the plans from this update will be for analysts and others to do the calculations above and realise Grants has not reached a point of economic depletion and there remains some A$623/t ore to mine in Grants. Core may well have further open pit revisions that increase from this A$623/t price and bring in more ore but Core had to settle on something and also wanted to reset the narrative around the mining cost at Grants.
The two CE changes across 2024 from GM to a temporary CEO (Doug Warden) to Mr Brown are likely to mean Core lost a lot of momentum across 2024. I suspect the original plan was to complete the Carlton and BP33 scoping work and present both when the 2024 AR required an ore reserve update. If both these deposits were included it would take Core to a life of mine in the mid-high teen's. Core however ran out of time to complete more than the work on BP33 hence Carlton hasn't been included as an ore reserve - in this update.
I suspect Core also ran out of time to complete a revised Grants UG mine plan with the new smaller open pit envelope. The new mine plan makes no attempt to dive down the middle of Grants and capture any of the middle portion of the Measured resource. Any open pit only mine plan would have done that. The most sensible reason for not doing this is that this middle but deeper ore will be mined a different way. I suspect Core is part way through defining a new larger Grants UG mining plan that is in the region of 1.0Mt to 1.5Mt (1.0 to 1.5 years operation at 1Mtpa) but its not yet final for retail release.
The two UG mine plans below relate to Develop taking the Cade/Davy deposits of Essential that were planned to be large open pits and redefining them as smaller open pit mines with a larger portion being UG mined. They provide a guide to what Core may be thinking, particularly re the large flat bottom open pit slice for Grants.
Speculation continued
Core ran out of time to explore and present to a retail audience mixed mining permutations. For example, starting the mining of Grants earlier and stockpiling the fines and middlings so that they could be put through the flotation plant when constructed. The plan presented may also be a simplified but not optimised version of BP33. For example while the plan is bottom up mining, Core may create a BP33 divide at perhaps the 215 level where the overlap between higher and lower levels is limited. BP33 may mine levels 215 to 70 first. Profits from this fund some of the capex to push the decline down to level 785 before bottom up mining occurs from this lower level. While the capex figure is high, it may be that not all the capex needs to be funded before restart.
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