Having kicked off a 1-year, US$8.4-million work program, BHP Copper and Northern Orion Explorations (NNO-T) are well on the way to completion of final feasibility work on the Agua Rica porphyry project in Argentina’s Catamarca province.
The current program includes an extensive underground bulk-sampling program that will provide several large samples (totalling 300 tonnes) for pilot-scale metallurgical testing. These samples will be collected from adits driven into the higher-grade Mi Vida and Trampeadero areas. A total of 1,150 ft. of tunnelling is planned.
In preparation for groundwater drilling, 50 line km of transient electromagnetic surveys and 20 line km of seismic-reflection surveys will be completed. Potential water sources are situated about 20 km from the project site.
Further infill and geotechnical drilling will also be conducted.
Environmental baseline studies are continuing, as is an ongoing evaluation of potential enhancements to the initial feasibility study, released last November.
Agua Rica is a large copper-
porphyry deposit with significant credits of gold, molybdenum and silver.
Ownership is shared on a 70-30 basis between BHP Copper, a unit of Australian-based Broken Hill Proprietary (BHP-N), and Vancouver-based Northern Orion. The deposit lies 17 km north of the town of Andalgala and ranges in elevation from 3,200 to 3,500 metres above sea level.
At year-end 1997, a total of 168 holes in 65,000 metres of drilling had been completed by the joint venture. Another 20 holes have been drilled so far this year.
Based on the first 150 diamond drill holes (totalling about 58,000 metres), Agua Rica is estimated to contain a sulphide resource of 750 million tonnes grading 0.62% copper and 0.04% molybdenum, plus 0.23 gram gold and 3.2 grams silver per tonne, using a cutoff grade of 0.4% copper.
If the cutoff grade is lowered to 0.2% copper, the sulphide resource rises to 1.7 billion tonnes grading 0.43% copper, 0.03% molybdenum, 0.17 gram gold and 3 grams silver, equivalent to a contained a resource of 16.2 billion lbs. copper, 1.2 billion lbs. moly, 9.5 million oz. gold and 165 million oz.
silver.
The initial feasibility study, completed by BHP Copper in cooperation with Northern Orion and consulting firm Fluor Daniel Wright, examined the viability of a conventional open-pit mining and milling operation with a daily throughput rate of 60,000 tonnes in the first two years and 120,000 tonnes thereafter.
The 120,000-tonne-per-day model pegs the minable resource at 681 million tonnes grading 0.59% copper, 0.03% moly, 0.25 gram gold and 3.61 grams silver, equivalent to 8.9 billion lbs. copper, 496 million lbs. moly, 5.5 million oz. gold and 79.1 million oz. silver, for an overall stripping ratio of 1.8-to-1 and a mine life of 17 years.
The study was based on the 103 holes completed to the end of 1996. More recent drilling has encountered higher-grade mineralization that is expected to have a positive effect on the study results.
Production in the early years would be enhanced by the mining of near-surface, higher-grade mineralization in the Mi Vida and Trampeadero areas by way of starter pits. An overlying leached cap would have to be stripped first, and Northern Orion says there is the potential for gold recovery from the cap, which is estimated to contain 89.4 million tonnes grading 0.41 gram gold, for 1.2 million contained ounces, based on a 0.25-gram cutoff.
Crushing and grinding tests indicate the ore is relatively soft, and metallurgical flotation testwork indicates recoveries of 87% for copper, 50% for gold and 65% for moly.
Annual production for the first five years is forecast to average 539 million lbs. copper, 18 million lbs. moly, 159,000 oz. gold and 1.9 million oz. silver. For the remaining years,
six through 17, annual production would average 463 million lbs. copper, 20.4 million lbs. moly, 167,000 oz. gold and 2.6 million oz. silver.
Capital costs are estimated at US$1.1 billion, with operating costs averaging US$5.86 per tonne over the life of the mine.
The study proposes trucking the concentrate about 200 km to a rail head. The nearest paved road is 22 km away, at Andalgala.
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