TORONTO (miningweekly.com) – Africa-focused project developer Ivanhoe Mines on Monday reported that the first batch of assay results from the company's underground diamond-drilling programme at the Kipushi copper/zinc/germanium/lead and precious-metals mine, in the Democratic Republic of Congo, had confirmed initial visual estimates of high-grade zinc and copper mineralisation in both the Big Zinc and copper-rich Serie Recurrente zones.

Among the first significant results were three holes drilled to validate historical models of the down-plunge continuity of Big Zinc mineralisation, which returned zinc grades of 40.9% over 348.5 m, 44.8% over 339.4 m and 33.3% over 305.8 m.

The Canadian firm said the down-plunge geometry of the holes did not allow it to estimate the true widths of the deposits.

The exploration programme found that internal zones of exceptionally rich mineralisation in the first two holes, KPU001 and KPU002, returned zinc grades of 60.4% over 35.1 m, 56.3% over 18 m and 56.6% over 71 m. These internal zones also returned germanium grades of 87.2 g/t, 120.4 g/t and 111.9 g/t respectively. 

An internal copper/silver/germanium-rich zone in the third hole, KPU003, graded 6.1% copper, 44.5% zinc, 144 g/t silver and 66.9 g/t germanium over 31 m from 197 m. Historical resource estimates at Kipushi excluded silver and germanium.

KPU003 also discovered a zone grading 58.6% zinc and 293.8 g/t germanium over 22.3 m, about 180 m below the historical measured and indicated resources. This exceptional grade intersection might represent an extension to the Big Zinc or the start of a new zinc- and germanium-rich zone, and would be followed up by ongoing drilling.

Further, Ivanhoe reported that two holes targeting the Serie Recurrente zone at the north end of the Kipushi deposit returned high copper and silver grades. Hole KPU008 intersected 11.4 m (estimated true width of 11.2 m) grading 17% copper and 89.6 g/t silver.

"Zinc grades of between 56% and 60% typically are found in high-quality zinc concentrates, rather than primary mineralisation. These initial assay results highlight the remarkable metal endowment of the mineralisation extending below the Kipushi deposit as previously mined by Gecamines,” Ivanhoe executive chairperson Robert Friedland said.

"At current spot prices of about $2 000/kg for germanium and $21/oz for silver, we expect the germanium and silver grades could add to the overall metal value at Kipushi. Sulphur content, particularly in the Big Zinc, also represents a potentially significant value addition given the scarcity of primary sulphur supply in the Copperbelt region and the demand for acid in conventional in-country oxide recovery circuits,” CEO Lars-Eric Johansson added.

Meanwhile, Ivanhoe reported that Kipushi staff were continuing to upgrade underground and surface infrastructure to support the drilling programme and prepare the mine for potential future redevelopment and operations, subject to engineering and other studies. The mine had been dewatered to the 1 305 m level on the Cascade side (Shafts No 1 to 4), where drilling operations were taking place.

The scope of drilling had been expanded to evaluate the high-grade, copper-rich Serie Recurrente zone. The 1 272-m-level hanging-wall drill drift had been dewatered and was being prepared for drill access. Drilling from this level was expected to start once the Serie Recurrente programme was completed. This drill access would facilitate detailed confirmatory and exploratory deep drilling of the Big Zinc, and of down-plunge unmined extensions to the copper-rich northern portion of the historical Kipushi deposit.

Also on the Cascade side, a water dam was being built on the 1 112 m level to reduce pumping requirements. Fabrication of a new ventilation fan for Shaft No 4 was complete and the fan would be commissioned later this month.

Refurbishment of the No 5 shaft was ongoing, with the hoist ropes being replaced. Soon after resuming operations, the main pump station would be refurbished at the bottom of the shaft, improving the efficiency of pumping operations, and delivering mechanised underground equipment to the active part of the mine.

In the Kipushi mine’s 70 years of operation, 60-million tonnes of material was extracted at a grade of 6.78% copper and 11.03% zinc. In addition, 400 000 t of lead, 45 000 t of cadmium and 120 t of germanium were extracted through the existing processing plant.

Kipushi currently has a historic measured and indicated resource – stated only to the 1 500 m level – of 16.92-million tonnes, grading 2.32% copper and 16.76% zinc.

Ivanhoe Mines, formerly known as Ivanplats, also owns the high-grade Kamoa copper deposit in the DRC, as well as the Platreef polymetals project, in South Africa.