BHP, Northern Orion hit high grade in Argentina

High-grade gold and silver values have been intersected at the Agua Rica project in the northwestern Argentine province of Catamarca.

Agua Rica is a large porphyry copper-gold-silver-molybdenum deposit held 70% by BHP Copper and 30% by Northern Orion Explorations (NNO-T).

The joint venture is halfway through a $45-million program designed to bring the project to completion of a final feasibility, which is expected in 1998.

A 25,000-metre drill program is in progress.

Based on the first 103 holes completed to the end of 1996, BHP calculated a sulphide resource of 1.7 billion tonnes grading 0.44% copper and 0.19 gram gold per tonne, plus 3.01 grams silver and 0.028% molybdenum, using a 0.2% copper cutoff grade. This is equivalent to a contained resource of 16.2 billion lb. copper, 10.2 million oz. gold, 166 million oz. silver and 1.1 billion lb. moly.

At a cutoff of 0.4% copper, the sulphide resource is estimated at 802 million tonnes grading 0.61% copper and 0.24 gram gold, plus 3.17 grams silver and 0.034% moly, equivalent to 10.8 billion lb. copper, 6.2 million oz. gold, 82 million oz. silver and 601 million lb. moly.

Based on a 0.25-gram cutoff, an overlying leached cap is estimated to contain 89 million tonnes grading 0.41 gram gold, or 1.2 million contained ounces.

This gold may be amenable to heap-leach recovery methods.

The deposit extends more than 2,000 metres east to west and up to 1,200 metres north to south. It remains open in several directions.

At the end of 1996, less than 40% of a 7.5-sq.-km copper geochemical anomaly had been drilled.

The drilling program for 1997 includes 25,000 metres of infill and stepout drilling on the Mi Vida, Quebrada Minas and Trampeadero areas of mineralization, as well as exploration drilling of other prospective targets on the 5,000-acre property.

The latest hole to be released, AR-133, was drilled on the northeastern edge of the Mi Vida area, which is a high-grade enriched copper-gold zone associated with a porphyry intrusive and has a significant layer of secondary enriched copper mineralization.

The high-grade core of Mi Vida extends across 500 metres and averages 135 metres in thickness, with grades of 1.03% copper and 0.43 gram gold, plus 2.2 grams silver and 0.023% moly.

A leached cap covering the area averages 54 metres thick and grades 0.48 gram gold and 1.8 grams silver.

Hole 133 cut the leached cap, returning 25 metres of 0.47 gram gold and 3.02 grams silver, plus 0.03% copper and 0.023% moly, before averaging a grade of 0.56% copper and 0.74 gram gold, plus 5.65 grams silver and 0.017% moly over a length of 468 metres.

The highlight of hole 133 is a 44-metre intercept averaging 4.66 grams gold and 33.3 grams silver per tonne, plus 0.59% copper and 0.02% moly, (including 32 metres averaging 6.11 grams gold and 39.42 grams silver, plus 0.58% copper and 0.021% moly) at a downhole depth of 420 to 464 metres.

The hole bottomed at a 500-metre depth in 36 metres averaging 1.74% copper and 0.52 gram gold, plus 5.07 grams silver and 0.015% moly.

The high-grade mineralization is associated with sulphides and argillic altered hydrothermal breccia.

Further drilling will be carried out in an effort to determine the extent of the high-grade mineralization encountered in hole 33.

Meanwhile, an initial feasibility study is evaluating the potential of a 60,000- and a 120,000-tonne-per-day mining and milling operation.

Miramar Mining (MAE-T) has a 53.9% interest in Northern Orion.