Lonshi Production Marks Watershed in the Copperbelt

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Lonshi production marks watershed in the Copperbelt

An excavator loads a haul truck at First Quantum Minerals' Lonshi open pit mine in southeastern Katanga. Waste and ore at Lonshi are easily rippable.

BY: JAMES WHYT E OCTOBER 13, 2003

Ndola, Zambia — The border between Zambia and the Democratic Republic of the Congo is, physically, the height of land between the Congo River and Zambezi River watersheds.

On the ground, it’s scarcely visible; but in the development of the Copperbelt mining camps of the two countries, it has always been a stark division. In the colonial period, British and South African-based companies such as Selection Trust and Anglo American owned the Zamibian mines and shipped out copper through South Africa; across the line, Union Minire du Haut-Katanga shipped its copper out by way of the Congo River ports or through Portuguese West Africa. After independence, Zambia and the Congo (later Zaire) nationalized the mines, and the state-owned companies that took over had little or no dealings with one another.

So seeing Congolese ore being trucked across the border to a modern leaching- electrowinning plant in Zambia is a century-making novelty. A hundred years since ore started coming out of the ground at the Bwana Mkubwa copper mine in Zambia, First Quantum Minerals (FM-T) is now straddling the border with its Lonshi-Bwana Mkubwa copper operation.

First Quantum took on Bwana Mkubwa in the late-1990s privatization of Zambia Consolidated Copper Mines assets, starting up its original solvent-extraction and electrowinning (SX-EW) plant in 1998. Zambia Consolidated had left about 7 million tonnes of tailings, which contained about 0.7% soluble copper, at Bwana Mkubwa, and the ﬁrst plant — with an annual capacity of 10,000 tonnes of cathode copper — was built merely to exploit the old tailings dumps.

The question was, Where could Bwana Mkubwa go after the tailings resource runs out? The answer was found about 35 km to the southeast: new ore from the Lonshi deposit, across the Congolese border in Katanga province.

Lonshi sits in a forgotten corner of Katanga, in the narrow strip the Belgians named “la botte” — the boot. The ﬁrst showings at Lonshi were discovered by Union Minire around 1930; some colonial-era prospect pits can still be found on the property. At the time, road connections into the “boot” were poor and Union Minire had little need for such remote projects when the vast deposits of the central Katanga arc were ready to hand. Lonshi remained a few grades on tracing paper for almost seven decades.

It was a sleuthing job by First Quantum geologist Michael Parker — and persistence in the face of management’s skepticism — that led the company to the area as the feed requirement loomed at Bwana Mkubwa. Drilled in 2000, Lonshi shortly saw a resource of 5.1 million tonnes grading 5.75% copper proved up, and contract-mining started in 2001.

The Lonshi discovery changed the picture at Bwana Mkubwa radically; instead of a low-grade tailings reprocessing operation, Lonshi oxide ore justiﬁed a larger SX-EW plant. In late 2001, the company began plans for an expansion to a nominal 30,000- tonne-per-year capacity; that work started in early 2002, and the plant started its commissioning by September of that year.

“The emphasis here has always been on building the thing, on getting it going,” says Sean Whittome, Bwana Mkubwa’s general manager.

Having justiﬁed the plant expansion at Bwana Mkubwa, Lonshi got a lucky break of its own; contract operations were being wrapped up at the Chibuluma open pit owned by South African mining group Metorex, and the mine contractor there was looking for something to do. By September 2001, stripping had begun and Bwana Mkubwa began taking Lonshi ore late in the year.

“We had to get deep quick,” says Parker, noting the deep, narrow pit that Lonshi is now. The plant’s needs drove the early stages of the mining plan. Following an eastward pushback over the coming months, a more normal top-down pit sequence should be resumed. Contract mining currently costs First Quantum about US$1.50 per tonne; moving to owner-mining is expected to cut that cost in half.

First Quantum’s lenders, feeling the need for assurance about the political risks in the Congo, made it a requirement of ﬁnancing that some Lonshi ore be stockpiled inside the Zambian border. The required size of the stockpile decreases as the loan is paid oﬀ. Trucks from the mine are waved past a small border post on their way to the plant; the Congolese government was receptive to a direct-trucking operation in an area where there is so little infrastructure available, and has more pressing concerns in any event.

Lonshi represented a departure for the Congo, which had traditionally enforced a majority role for the state enterprise Gnrale des carrires et des mines (Gecamines) in new projects. First Quantum’s wholly owned Congolese unit, Minire de Sakania, was permitted to own the property outright and to ship ore across the border, before the Congo’s new Mining Code came into force earlier this year.

Now, the Mining Code, developed at the instance of the World Bank, takes Gecamines (currently in desperate ﬁnancial shape) out of its former automatic ownership role, substituting a tax-and-royalty system that allows companies to own full title to mineral properties. That title was irrevocably conﬁrmed for Minire de Sakania in August.

As Lonshi settles into a 5,000-tonne-per-day pace, and as the company takes over mining, First Quantum’s priority has become expanding the resource there. An estimate at the beginning of 2003 put the measured and indicated resource at 7.3 million tonnes grading 4.91% copper; about 86% of the total copper is recoverable by direct acid leaching.

Lonshi’s host rocks are dolomites, and the deposit forms a neat lens-like bed, gently dipping to the east. Its contact with the footwall is sharp, and most of the grade control in the pit can be done by eye. The hangingwall dolomites are strongly leached, with two results: the waste rocks are easily rippable using conventional tracked excavators, and they are light, with a density down around 1.7 tonnes per cubic metre.

The other side of the weathering coin is that the Copperbelt’s wet season (broadly, November through March) cuts production almost in half. That’s when the border stockpile is expected to prove its usefulness.

Drilling was under way north of the Lonshi pit at the time of The Northern Miner’s visit. First Quantum has drilled exploration holes along a strike length of close to 2 km; the drilling follows a favourable contact of the lower Kundelungu group, a sequence of ﬁne-grained sedimentary rocks and carbonates lying stratigraphically above the shales and carbonates of the Upper Roan Group, which host most of the Copperbelt mines.

There are targets along strike both north and south of the pit, and downdip from the known ore zone. The potential along strike will likely mean more to the Bwana Mkubwa operation in the near term, as tonnage built up along strike is likely to be all oxidized (and therefore leachable) material. Downdip, the ore ultimately would convert to primary sulphide mineralization, which would presumably require a mill.

Once it gets to the Bwana Mkubwa plant, the Lonshi ore is crushed and ground before moving in slurry to a set of four leach tanks. From there, the process is a typical SX- EW operation; weak acid leaching produces a leachate with about 6-8 mg copper per litre, which is ﬁltered and mixed with diesel oil dosed with organic solvent that collects the copper from the weak acid solution.

Allowed to separate, the organic solution goes to a second tank for stripping with stronger sulphuric acid; the aqueous solution from the ﬁrst tank is recycled in the leach circuit.

The strong acid, routed to the tankhouse, contains about 30 mg copper per litre, and gets an 8-day turn in the electrolytic tank; electroplated copper meeting London Metal Exchange standards is stripped and bundled for delivery. First Quantum sells directly to dealers, who take delivery at the plant gate, leaving the company without distribution and dealing headaches.

The combined Lonshi and Bwana Mkubwa operation produced copper at just under US$1,000 per tonne (US44 per lb.) in the first half of the year, well above its 2002 average near US$600 (US27 per lb.). Rainy-season material handling problems slowed production in the first quarter, which brought costs up. Front-end modifications to the crusher and mill are expected to fix that problem in the next rainy season.

Historically, there had been a shortage of sulphuric acid on the Copperbelt, so Bwana Mkubwa was built with extra capacity. The operation gets elemental sulphur (produced in petroleum reﬁning) from South Africa, the Middle East, or Western Canada, and the acid plant converts the sulphur to sulphur dioxide in a burner unit; then a vanadium-pentoxide catalytic bed oxidizes the gas to sulphur trioxide. Both reactions are exothermic — exothermic enough to be felt on a Copperbelt afternoon, in fact. Bwana Mkubwa produced just over 60,000 tonnes of sulphuric acid in the ﬁrst half of the year, selling just over 60% of it. (The acid counts against production cost as a byproduct credit.)

With the first half’s production problems providing a school of hard knocks for the plant staff, process improvements are working their way through Bwana Mkubwa — the principal bottleneck was found to be slurry handling. In July, production was 2,500 tonnes, a pace that would put annual production near design capacity, and with modifications to the system, First Quantum is now expecting production to run at 40,000 tonnes of copper annually.