MINING IN AFRICA SPECIAL — Kinross working to expand

Gold output at the Zimbabwean operations of Kinross Gold (TSE) is poised to increase, as a new tailings retreatment plant nears completion at the Blanket mine and underground exploration at the Golden Kopje mine kicks into high gear.

Kinross has been working hard to increase productivity and reduce costs at the mines since acquiring them from Falconbridge Gold in 1993. Situated in the Gwanda greenstone belt, about 560 km south of Harare, the Blanket mine is actually a conglomeration of a number of mines, including the Jethro, AR, Eroica, Lima and Blanket.

Mineralization is primarily hosted in a regionally developed, northwest-southeast trending shear zone. The shear contains lozenge-shaped remnants of undeformed basalt ranging from tens to hundreds of metres in length, around which the high-strain shears are wrapped. It is within the high-strain shear zones that disseminated sulphide orebodies are developed. The Quartz Reef deposit is an exception in that it is a quartz lode that fills a fault zone.

During the past 30 years, the Blanket deposits have yielded about 4 million tonnes of ore grading 5 grams gold per tonne, to produce about 18,000 oz. of gold annually. Production in 1994 is estimated at 21,000 oz. gold. In order to boost output, the company began construction of a new, 3,500 tonne-per-day (tpd) carbon-in-leach facility late last summer. The new plant, capable of treating 3,000 tpd of tailings and 500 tpd of fresh ore, is expected to be fully operational by mid-1995.

With the new tailings plant, and increased recoveries from the existing mill, production at the mine is expected to increase by 18,200 oz. per year. Operating costs are estimated at US$134 per oz., and payback of the $4.5 million capital investment should occur in less than one year. Once the plant is fully operational, Kinross plans to increase mine production to 1,000 tpd. To achieve this, a new US$6 million shaft will be constructed, financing for which will come from the cash flow generated by the tailings project.

Current minable reserves, including proven and probable categories and extractable pillars, are estimated at 820,000 tonnes grading 4.1 grams. At the Golden Kopje deposit, about 100 km northwest of Harare, mining originally began in 1891. The property remained dormant from 1951 until 1982, when it was reactivated by Falconbridge (TSE).

Mineralization is hosted in a banded iron formation unit and three distinct orebodies are known: the footwall, intermediate and hangingwall ore zones. Footwall orebodies occur as a string of laterally discontinuous lenses 1 to 2 metres wide, which are generally concordant with the host rocks. The lenses consist predominantly of medium-to-coarse-grained pyrite and silicification. The average grade of the footwall orebodies is about 6.3 grams gold. Hangingwall orebodies occur as long continuous tabular zones, containing disseminated pyrrhotite which is overprinted by younger pyrite mineralization. The average grade of these zones is 4.8 grams. The intermediate ore zones, which locally connect the hangingwall and footwall orebodies, probably occupy secondary (Reidel) shears. These ore bodies are characterized by dense, quartz-pyrite stringer networks and have an average grade of 5.35 grams.

Under Falconbridge, the Golden Kopje mine was operated at a rate of 65,000 to 75,000 tonnes per year, yielding 6,000-8,000 oz. annually. Last year, Golden Kopje production was estimated at 13,000 oz., and output for 1995 is forecast to be 20,000 oz.

Mining and milling methods employed are similar to those utilized at the Blanket Mine. All ore extracted to date has been mined from above the 250-metre level. The recently completed AR shaft, which has a capacity of 1,000 tpd, will allow access to the 400-metre level.

During the last half of 1993, an exploration program from surface outlined a drill-indicated resource of 3.1 million tonnes grading 7.5 grams in a parallel zone north of the present workings. In 1994, a 700-metre-long drift was driven out to the North zone on the 250-metre level to provide access for drilling and bulk sampling.

Kinross Chairman Robert Buchan recently told The Northern Miner that a 50-hole drill program is under way to further delineate the zone. “Hopefully, the drilling will justify a major expansion,” he said.

Successful delineation of the North zone could justify a further expansion of the Golden Kopje mine to a rate of between 1,000 and 1,500 tpd. At the end of 1993, fully diluted minable reserves in the Main zone stood at 477,000 tonnes grading 4.9 grams. This figure includes proven and probable reserves plus extractable pillars.