Gold producer Caledonia Mining Corporation is well on track to increase gold production from its 64%-owned Blanket mine in Zimbabwe to 80 000 oz pa from 2021 following completion of its Central Shaft project.
The Central Shaft, currently at a depth of 1 150 m, will be sunk to a depth of 1 204 m at shaft bottom. It is anticipated that the shaft sinking portion of the project will be completed in June 2019, after which the shaft will be equipped and commissioned over the following 12 months.
Exploration at the Blanket mine has been instrumental to the success of the operation, says Curtis noting that through consistent exploration, the company was able to successively increase the resource base seven times – growing Blanket’s resource by approximately 86% (about 800 000 oz) since 2011 despite having mined over 300 000 oz over this period.
As a result, Blanket’s life of mine has been extended from an initial six years at the end of 2014, to 15 years following the latest resource upgrade in September 2018.
The total measured and indicated resources at Blanket now stands at 6.74 Mt at a grade of 3.72 g/t, while total inferred resources are 6.63 Mt at a grade of 4.52g/t, taking the total resource endowment at the mine to almost 1.8 Moz.
Caledonia Mining Corporation is not stopping there.
Curtis says exploration activity at Blanket will continue with the objective of further extending the operation’s life of mine.
Taking Blanket to new depths
Blanket mine, prior to the execution of the Central Shaft project, operated to a depth of 750 m – the depth at which the mine was when it was purchased from Kinross Gold Corporation in 2006.
The mine, although operated from a single shaft, comprises five significantly independent near vertical ore bodies.
“The vertical nature of the ore bodies makes it difficult to explore the extension until reaching lower depths” explains Curtis.
In early 2015, Caledonia Mining Corporation embarked on a life of mine extension plan aimed at taking the Blanket mine into the future, and so the Central Shaft project was born.
The 6 m diameter Central Shaft, which has winder capacity that is capable of being extended to 2 000 m below surface, will add three further production levels to the mine below the current 750 m level – on 26 (870m), 30 (990m) and 34 (1 110 m) levels.
In due course a production level on 38 level (1 230 m below surface) will be accessed via a decline.
The Central Shaft – aptly named so because of its central location among the five ore bodies – will enable more efficient mining.
“Because the current shaft is located on the extremity of the ore bodies, we only mine in one direction, but the centrality of the Central Shaft will allow us to mine more efficiently in both directions on all three levels, accessing the mining areas in approximately half the time and also reducing workers traveling time to workplaces significantly,” Curtis explains.
At the moment, Blanket processes about 1 600 tpd of ore to produce just below 60 000 oz of gold.
The life of mine plan including production from the Central Shaft, will require the processing of approximately 2000 tpd of ore initially, reducing to 1800 tpd with the expected improvement in grade over the medium-term, to produce approximately 80 000 oz of gold as targeted by 2022.
The only additional infrastructure required to meet the 80 000 oz pa gold production target is an additional crusher and an extra mill in the primary crushing circuit of the existing 3 500 tpd carbon-in-leach (CIL) plant.
Once the ore is mined, using both mechanised and conventional mining methods depending on the nature of the orebody encountered, the ore is processed using a typical CIL process.
Using Knelson concentrators and gravity separation, about 50% of the gold is easily liberated and recovered as free gold.
The balance of this (the overflows) is sent to the CIL plant where the remaining gold is recovered via a CIL process achieving a combined gold recovery of about 93%, explains Curtis.
“Since 2015, we have spent close to US$70 million in capital at the Blanket mine.
“This amount includes sustaining capex with the remainder mostly on Central shaft – all funded by Blanket’s internal cash generation.
“Central shaft is being sunk at about half the cost of a similar shaft elsewhere due to the fact that the sinking is done by the company’s own in-house team that is supervised by experienced shaft sinking professionals hired by Blanket.
“The cost of the shaft is also reduced because the ground conditions are very good, which requires no lining of the shaft below the initial collar,” he explains.
“The completion of the Central Shaft project, which is expected to increase cash flow and production, combined with the consistent increase in resource base, will set the mine up for many years into the future,” says Curtis.
Meeting production targets and growing through acquisition
Total gold production from Blanket for 2018 was 54 512 oz, which was in line with the production guidance range of 54 000 to 56 000 oz, while gold production for 2019 is expected to be between 53 000 and 56 000 oz.
Until the Central Shaft has been commissioned during the second half of 2020, production from Blanket is expected to remain at broadly the same levels.
Once it has completed its investment into the Central Shaft project, Caledonia Mining Corporation will have sufficient free cash flow to enable it to invest in other opportunities in Zimbabwe.
“We will more than likely look at acquiring a Brownfield operation as there are many assets in Zimbabwe that have been dormant for decades,” says Curtis.
Despite the fact that Zimbabwe has removed its indigenisation law within the gold industry, by removing the compulsory 51% state-ownership requirement, Caledonia Mining Corporation always intends to have a percentage of staff and community ownership of the business.
“We believe this to be the correct way to run our business in Zimbabwe,” he explains.