Solwezi, Zambia — Zambia’s Northwestern province has a reputation as a rural backwater, away from the more industrialized and urbanized Copperbelt. Remote and generally ignored through the colonial period, so it remained after independence.
Thus it is a big deal for the Northwest when there is a major mining project under development, one that matches many of the producers on the relatively prosperous Copperbelt. And at the Kansanshi project, about 15 km north of the region’s main city, Solwezi,
A startup at Kansanshi wouldn’t really be a novelty: mining of native copper started here in the fourth century A.D. European prospectors, fanning out over northern Rhodesia near the end of the 19th century, discovered the old workings and underground copper mines in the Kansanshi area, and operated off and on between 1903 and 1957.
After independence and Zambia’s subsequent nationalization of the copper industry, Zambia Consolidated Copper Mines operated a small open pit at Kansanshi through the late 1970s, shutting down finally in 1998. With the government’s privatization program, Cyprus Amax Minerals bid successfully on the Kansanshi properties in 1997, and looked for ways to bring a large operation into production.
Cyprus, though, wound up in a merger battle between
Thus it was that a small company with a Vancouver listing and a Central African pedigree was able to buy the large copper producer out of its share of the project; and as metal markets and the economic atmosphere in Zambia have turned around, First Quantum has grown into a significant player in the Central African copper industry, with a large metallurgical plant at Bwana Mkubwa, near Ndola, and mining interests in both Zambia and the Congo. At Kansanshi, First Quantum holds an 80% interest, and Zambia Consolidated retains 20%.
And it’s at Kansanshi where the company is concentrating its new-project efforts, now that Bwana Mkubwa is running smoothly and has a reliable source of ore from the Lonshi mine in the southeastern Congo.
Like many of the copper mines of Central Africa, Kansanshi is big, low-grade, and near the surface. But First Quantum management points out that the gross value of Kansanshi ore is $26.28 per tonne, with copper at US$2,100 per tonne and gold at US$325 per oz. That rivals the rich Salobo and Sossego deposits of northeastern Brazil — a significant comparison for quite another reason.
Kansanshi shows some unusual affinities to the iron-oxide family of copper-gold deposits (apart from an irritating lack of iron oxides). Part of the mineralization occurs in very high-grade veins and sulphide-breccia bodies, some of which are nearly pure chalcopyrite containing xenoliths of the host rocks; the only other primary copper mineral of any significance is bornite. One trace mineral is the uranium titanate, brannerite.
The veins dip steeply and strike mainly northward, across the axis of a doubly-plunging anticline that trends northwest and southeast.
Extending outward from the central breccia-vein complex are replacement zones in beds of marble and metamorphosed clastic rocks, mainly described as phyllites and knotted schists in mine usage. In the marbles, the replacement zones hug the central complex tightly, but in the phyllites they extend as much as 800 metres along strike. “Stratabound,” they certainly are; but their close association with the breccia marks them out as epigenetic.
Surrounding the veins, and extending out into the permeable sediments, is an envelope of albite and carbonate alteration, which carries disseminated copper sulphides as well.
Typically for the Copperbelt, the primary sulphides are oxidized and supergene-enriched near surface. The most strongly fractured parts of the deposit can have oxide mineralization as deep as 200 metres below surface. Oxide mineralization — chiefly chrysocolla and malachite — and mixed oxide-sulphide mineralization, which may include chalcocite, tenorite and native copper, make up roughly a third of the tonnage in Kansanshi’s reserves.
Feasibility work by Perth-based consulting firm GRD Minproc used a measured and indicated resource of 302 million tonnes with average grades of 1.17% copper and 0.17 gram gold per tonne, with an additional inferred resource of 111 million tonnes at 1.11% copper and 0.12 gram gold, all based on a cutoff grade of 0.5% copper. From that, Minproc blocked out minable reserves of leachable and primary ore.
The first phase of mining is built around these reserves, starting with a leachable reserve of 46.9 million tonnes grading 2.25% copper and 0.29 gram gold per tonne. This oxide and mixed oxide-sulphide material has an acid-soluble copper grade of 1.75% (or, put another way, about 78% of the total copper is leachable).
Two pits
This reserve is to be exploited by two pits; about 70% of it is in the Main pit, with the rest in the slightly lower-grade Northwest pit.
In the sulphide zones, Minproc has outlined a reserve of 95.6 million tonnes running 1.03% copper and 0.19 gram gold per tonne; in that reserve, the Northwest zone contains about a quarter of the tonnage and is slightly higher-grade than the Main zone. Between them, the two pits have an expected stripping ratio of 1.4-to-1, and should produce 723,000 tonnes of cathode copper and 913,000 tonnes of copper in concentrate over a 16-year mine life.
The feasibility study proposes mining the open pits with 200-tonne-class backhoes and 95-tonne trucks. The backhoes, with 12-cubic-metre buckets, offer the ability to excavate selectively, which First Quantum expects to have to do in a vein-type mining scenario; geological staff have identified four ore types and three waste types. Grade control will be based on drill holes in 3-by-6-metre blocks.
First Quantum found that building a plant and treating tailings at its Bwana Mkubwa operation near Ndola were a challenge for the company; material-handling problems, especially, were costly and took technical savvy to solve properly. But there was value in the experience: “all the ‘school fees’ that have been paid [at Bwana Mkubwa] have been incorporated into Kansanshi,” says Matt Pascall, First Quantum’s group operations executive.
Fortunately, the lessons of Bwana Mkubwa are eminently portable to Kansanshi. The sulphide ores are amenable to conventional flotation treatment, and comminute well in a semi-autogenous grinding mill. Oxide ores can undergo simple leaching and recovery using solvent extraction and electrowinning.
It’s the mixed ores that present the principal metallurgical challenge. Testing has shown the best results will come from a combined float-and-leach process, with a pre-flotation stage followed by acid leaching of the flotation tailings, solvent extraction, and electrowinning. With mixed ores dominating the leachable reserve, First Quantum has decided to design the leach plant around the mixed-ore process, and mill the oxides purely on a campaign basis, leaving out the flotation stage.
Gold credits are a significant part of the project economics, and will be recovered as part of the flotation concentrate from sulphide and mixed ores, a process that will recover 80% of the gold in mixed ore and 90% of the gold in sulphides. In the oxide ores, the only economic recovery process is gravity concentration, which recovers about 30% of the gold.
Tailings
Waste rock dumps are being placed on areas that are already disturbed, and a tailings impoundment is to be built in a shallow valley south of the pit, with a pipeline from the plant to feed tailings to it. The weathered mineralization is unlikely to be acid-generating, but some of the sulphides may be.
The project will need a better power supply, though the national grid does run to Kansanshi. First Quantum is considering a range of options, including a contract with Zambia Electricity Supply Corp., the para-statal power utility. A road, running from Solwezi north to the Congo border, will be re-routed around the project area, and the local airport will have to be upgraded.
The feasibility study estimated a capital cost of US$163 million, with US$119 million of that going into the process plant. The mine would require almost US$36 million. Part of that was financed in a 5.5-million-share equity issue, with proceeds of $29.4 million (Canadian); the rest will be provided by a US$60-million commercial credit line and a US$60-million export credit facility, through Standard Bank and West LB, plus some smaller debt facilities, including a US$26-million loan for the equipment fleet.
The feasibility study estimated cash operating costs at US38 per lb. (US$840 per tonne), after gold credits, assuming First Quantum would do its own mining. Contract-mining would cut the capital costs by US$20 million and increase the operating cost to US43 per lb. (US$950 per tonne).
A proposed second phase of mining at Kansanshi, with feasibility work at the conceptual stage, would see a further 188 million tonnes mined, at a grade of 0.88% copper and 0.12 gram gold per tonne. The expanded pits would have a 12-year life.
Be the first to comment on "First Quantum takes fresh look at Kansanshi"