First Quantum cuts copper grades at Nkana

Infill drilling by partners First Quantum Minerals (FM-T) and Swiss-based Glencore International is attempting to replenish reserves at the Nkana copper-cobalt operation in Zambia’s copper belt.

Nkana comprises three underground mines spread across several kilometres of the northwesterly plunging Nkana synclinorium. Grades generally increase northward, in the form of chalcopyrite at the Southern orebody, chalcopyrite-bornite at the Central zone and bornite-chalcopyrite at Mindola. Cobalt occurs mainly in the form of carrollite and cobaltiferous pyrite in equal proportions.

In March 2000, when the companies acquired their 90% stake, on a 44-46 basis, reserves were pegged at 75 million tonnes grading 2.28% copper and 0.13% cobalt. Since then, the figure has been shrinking by about 250,000 tonnes monthly, owing to regular production. However, the project still carries a resource of 111 million tonnes grading 2.29% copper and 0.1% cobalt.

The campaign saw 36 holes drilled in undefined areas of the B, C and D zones, between the southern and central shafts. All represent a significant portion of the project’s overall resource (including reserves) of 111 million tonnes grading 2.29% copper and 0.1% cobalt.

The holes were collared on the 3,360 level, directly below, and lateral to, existing workings but drilled no deeper than the southern shaft’s bottom. The best results came from hole NS 24, which returned 140 metres (true width) of C material grading 3.55% copper and 0.07% cobalt, and 29 metres of B material running 2.15% copper and 0.14% cobalt.

Holes 2, 25 and 27 also returned particularly long sections of C zone:

– 120 metres at 3.15% copper and 0.08% cobalt in hole 2;

– 135 metres at 2.19% copper and 0.89% cobalt in hole 25; and

– 50 metres at 3.93% copper and 0.102% cobalt in hole 27.

A combined section of C and B material from hole 12 ran 2.41% copper and 0.14% cobalt over 74 metres.

The longest section through the B zone (alone) was 38 metres, which graded 2.21% copper and 0.16% cobalt. Another three averaged 2.21% copper and 0.16% cobalt over 38 metres, 2.4% copper and 0.08% cobalt over 20 metres, and 1.89% copper and 0.05% cobalt over 10 metres.

Only one hole pierced the D lens, cutting 3 metres at 2.69% copper and 0.25% cobalt. That interval also represents the shortest mineralized interval overall, though results are still pending for 12 holes.

The B and D zones dip subvertically as tabular bodies, whereas the C zone is an anticline with a structurally thickened crest. Drilling has now defined the three zones over a strike length of 1,000 metres and a vertical height of 200 metres.

Mineralization remains open to the north, down-plunge.

Using the new results, First Quantum is updating Nkana’s mineral inventory. The revision, which is expected shortly, should see a considerable portion of the existing resources reclassified as reserves.

A second phase of drilling, to begin shortly, will test other portions of the resource. An area west of the recent campaign will be targeted as well.

In addition to Nkana, First Quantum and Glencore share a 90% stake in the Mufulira underground operation to the northwest. At last report, reserves there were 27 million tonnes grading 3.04% copper, whereas total resources were 68 million tonnes grading 3.09% copper.

The remaining 10% interests in both mines are held by Zambia Consolidated Copper Mines (ZCCM). As part of the deal, First Quantum and Glencore must pay the state-owned miner US$23 million in five equal annual instalments, starting in 2003, as well as invest US$159 million in the mines by April 2003.

Glencore has the right to market any production from the joint venture while First Quantum manages daily operations.