Copper grades improve at Tambo Grande

Initial results from a second round of diamond drilling at the Tambo Grande project in northern Peru are mixed, reports Manhattan Minerals (MAN-T).

Although infill drilling of the TG-1 sulphide deposit encountered significant high-grade copper mineralization, stepout drilling has limited the northern extension of the overlying oxide gold zone. Manhattan had believed there was good potential to expand the oxide resource, based on hole 6, previously drilled by French government-owned Bureau de recherches geologiques et minieres (BRGM). That hole intersected 19 metres of 4.54 grams gold and 54 grams silver per tonne about 100 metres beyond the northern limits of the sulphides.

In late 1999, Manhattan drilled 16 holes in the northern extension of the oxide cap, mostly north and northeast of the BRGM hole. Only two of the holes encountered significant mineralization. Hole 68 stepped out about 60 metres immediately east of hole 6 and intersected 8.6 metres of 0.53 gold and 4.4 grams silver, starting at a depth of 20.4 metres, whereas hole 69, drilled a further 30 metres to the east, hit 10.1 metres averaging 1.74 grams gold and 7.3 grams silver at a 24-metre depth.

The company reports that drilling in the north is refining the geologic model and the importance of underlying structural controls to gold distribution in the oxide cap. Manhattan continues to test the flanks of a silica-iron domal hill zone to the north.

The near-surface zone of oxide silica-barite-gold mineralization, which overlies the TG-1 sulphides, was estimated by MRDI Canada to host an inferred resource of 8 million tonnes grading 5.2 grams gold and 48 grams silver per tonne, equivalent to 1.3 million oz. gold and 12.4 million oz. silver. MRDI based its estimate on results from 41 holes completed by Manhattan last summer and on the re-assaying of 21 previously drilled BRGM holes.

In the meantime, Manhattan has encountered oxide gold mineralization in a new area, 140 metres south of the existing resource limit, along the edge of the Piura River. Hole 112 intersected 10.6 metres grading 2.4 grams gold and 5.3 grams silver, starting at a depth of 12.4 metres. A further 50 metres to the southeast, hole 111 hit 3.4 metres of 0.73 gram gold and 1.3 grams silver at a depth of 16.5 metres.

The oxide gold cap represents a good portion of the prestripping required to mine the underlying TG-1 sulphides, which host an inferred resource of 64.2 million tonnes grading 1% copper and 1.4% zinc, plus 0.7 gram gold and 31 grams silver, based on a cutoff of grade of 1% copper-equivalent. Included in this estimate is a higher-grade copper zone of 18 million tonnes grading 2.4% copper, 0.1% zinc, 0.7 gram gold and 30 grams silver, as well as an enriched zinc zone of 34.9 million tonnes averaging 2.4% zinc, 0.9% copper, 0.8 gram gold and 36 grams silver.

In the weeks preceding Christmas 1999, Manhattan drilled 30 infill holes on the TG-1 oxide and sulphide zones, resulting in some high-grade copper intervals. Highlights include 6.8 metres grading 15.93% copper, 0.13% zinc, 0.12 gram gold and 41.4 grams silver in hole 90, and 16.9 metres of 11.18% copper, 0.13% zinc, 0.14 gram gold and 51.5 grams silver in hole 99.

The second (40,000-metre) stage of drilling at Tambo Grande will continue until April. Six rigs will concentrate on extending the oxide gold cap and upgrading the TG-1 gold and sulphides to reserve status. To date, 61 holes have been completed on TG-1, and another 150 are planned.

Additional drilling is also scheduled for TG-3, about 500 metres south of TG-1. TG-3 consists of two distinct mounds, or lobes, of mineralization. The north lobe is typically richer in zinc and contains 20 million tonnes grading 2.7% zinc and 0.9% copper, plus 0.8 gram gold and 35 grams silver, based on a cutoff grade of 1% copper-equivalent. The copper-enriched south lobe hosts 48 million tonnes grading 1.1% zinc and 1.1% copper, plus 0.9 gram gold and 25 grams silver.

A prefeasibility study of TG-1 and TG-3 is due late in the second quarter. Metallurgical tests are under way at the labs of Lakefield Research in northern Ontario.

Manhattan can earn a 75% stake in Tambo Grande, which consists of 10 concessions comprising 100 sq. km. The company also has a 100% interest in the Lancones concessions (737 sq. km) and an option to earn up to a 100% interest in the Papayo joint-venture lands (32 sq. km). The Lacones land package adjoins Tambo Grande mainly to the south and partially to the east and north, whereas the Papayo concessions are to the south. Manhattan can earn an initial 51% interest in Papayo by spending $5 million on exploration over five years and paying $250,000.

Manhattan currently has a rig at Papayo; it will test the B-3, B-5 and B-7 geophysical gravity anomalies.