Results from 41 diamond drill holes on the TG-1 deposit at Tambo Grande, in northern Peru, have confirmed extensions to sulphide and oxide portions of the deposit and revealed a significant gold content.
Drilling by owner
TG-1, a copper-zinc deposit discovered in 1979 by Bureau de Recherches Geologique et Minieres (BRGM), has an inferred resource, based on 21 holes, of 42.3 million tonnes grading 2.04% copper, 1.47% zinc and 0.36% lead, plus 37.6 grams silver per tonne. Mineralization is near enough to surface that the deposit could be mined through an open pit at a stripping ratio of 2-to-1.
Re-assay work by Manhattan also revealed that the sulphides contain varying amounts of gold.
The resource, defined in a 700-by-350-metre gravity anomaly, is associated with a 100-million-tonne pyrite body. The bowl-shaped TG-1 deposit is covered by 25-40 metres of alluvium and a leached cap. Its bottom lies 250 metres below surface.
Drilling also confirmed that the overlying, leached oxide cap carries significant gold and silver values. Results from 20 of the new holes, combined with the re-assays of BRGM’s 21 holes, indicate that the oxide cap has an uncut, weighted average grade of 4.75 grams gold and 113.1 grams silver over a true thickness of 14 metres. The leached cap is overlain by 14.1 metres of sandy overburden.
Consultants Derry, Michener, Booth & Wahl earlier estimated the cap to contain a resource of about 5 million tonnes. According to Manhattan President Graham Clow, drilling has more than doubled that estimate. “There is a very significant gold resource sitting on top of this thing,” he says.
The overlying oxide cap is composed of a stratified gossanous sequence. Gold appears to be associated with a baritic sandstone unit interpreted as a late-stage exhalative phase that caps the underlying sulphide event. The barite is transitional with an epithermal, silica-dominated sequence. The oxide cap appears to be fault bounded on the east and west, and pinched off to the south. It remains open to the north, where a hole sunk by BRGM outside the sulphide deposit intersected 4.54 grams gold and 54 grams silver over 19 metres.
Manhattan also reported results from 27 holes that intersected the TG-1 sulphide deposit. The remaining 14 holes sunk outside the resource area were deemed economically insignificant. “We have extended the sulphide body to the south, added on a few tonnes there, and confirmed the original drilling and the grade distribution inside the sulphide deposit,” says Clow.
Stepout drilling on the southeastern flank of TG-1 extended sulphide mineralization more than 100 metres to the south. Highlights include: 16 metres of 0.6% copper, 2.5% zinc, 0.2% lead, 0.82 gram gold and 41.1 grams silver in hole 35; 54.3 metres of 0.7% copper, 2.3% zinc, 0.2% lead, 0.85 gram gold and 40.9 grams silver in hole 37; 12 metres of 0.8% copper, 4.1% zinc, 0.2% lead, 0.8 gram gold and 51.5 grams silver in hole 44; and 14.7 metres of 2.1% copper, 3% zinc, 0.1% lead, 1.18 grams gold and 58.9 grams silver in hole 46.
The three holes — 50, 51, and 53 — indicate that sulphide mineralization thins to the south. Hole 50 intersected 3.8 metres of 2.3% copper, 1.9% zinc, 0.3% lead, 1.26 grams gold and 87 grams silver, followed farther down-hole by 2.9 metres of 0.5% copper, 2.4% zinc, 0.3% lead, 0.39 gram gold and 31.7 grams silver. Hole 51 intersected 3.7 metres of 1.7% copper, 1.9% zinc, 0.2% lead, 0.83 gram gold and 53.2 grams silver, followed by 3.1 metres of 0.3% copper, 1.3% zinc, 0.2% lead, 0.21 gram gold and 14.3 grams silver. Hole 53 encountered 1.7 metres of 2.1% copper, 2.4% zinc, 0.3% lead, 0.78 gram gold and 35.5 grams silver.
Manhattan says the TG-1 sulphide body remains open to the southwest along an anomalous gravity trend connected to the TG-3 gravity anomaly, 700 metres to the south.
The company has three rigs turning on the TG-3 anomaly in an attempt to define the limits of another sulphide system. At a depth of 143.1 metres, the first hole intersected 42.3 metres grading 1% copper, 1% zinc, 0.1% lead, 1.11 grams gold and 29 grams silver. Results for 20 other holes are pending.
Clow says the company is outlining a large sulphide body at TG-3 with similarities to TG-1. Both have a pyrite core with base metals around the edges. “TG-1 was 150 million tonnes of sulphides, about a third of which is base metals. TG-3 could be a similar sort of magnitude,” says Clow.
TG-3 is one of seven gravity anomalies that have been defined within 5 km of the TG-1 deposit. Manhattan will drill-test the TG-6 and TG-7 anomalies in the next two weeks.
Manhattan has the right to earn a 75% interest in the project. The remaining 25% is held by state-owned Minero Peru.
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