Drilling by
At the Famatina gold project in Argentina, Corriente is drilling 2,000 metres to confirm that the Mejicana Ridge gold-silver-copper vein system contains 1.7 million tonnes grading 32.1 grams gold and 40 grams silver per tonne, plus 1.3% copper.
The 145-sq.-km property has a history of gold mining dating back to the Incas in the late 1400s. Modern exploration began in 1968 when local groups explored the area for porphyry-copper mineralization. By 1986, 53 drill holes had identified several precious metal zones and outlined a geological resource of 200 million tonnes grading 0.17% copper and 0.06% molybdenum at the La Estruchura prospect.
Between 1993 and 1996, CRA Exploration spent US$9 million testing the bulk-minable potential of the La Mejicana gold zone. Situated 3 km west of La Estruchura, La Mejicana comprises seven east-westerly striking veins in an area measuring 1 km by 400 metres. By 1996, CRA had drilled 52 holes on the prospect, establishing a geological resource of 23 million tonnes grading 1.54 grams gold in a broader zone of 260 million tonnes grading 0.52 gram gold. However, CRA abandoned the project after concluding that the grade and tonnage did not meet its requirements.
Early in 1999, Corriente evaluated all the previous exploration data from the property and determined that, despite 30 years of exploration activity, the Famatina systems of mineralization remain poorly understood. A reinterpretation of CRA’s drill data has induced Corriente to adopt a high-grade copper-gold-silver model for Mejicana Ridge, as opposed to the previous, bulk-tonnage model. Targeting the high-grade intercepts hit by CRA (up to 23.7 grams gold over 20 metres), Corriente believes the current drilling will confirm the economics of a high-grade copper-gold-silver deposit.
Three types of high-sulphidation veins hosted in sandstone and siltstone occur at Mejicana Ridge: early quartz-pyrite; massive enargite-pyrite; and banded enargite-pyrite.
The 25-sq.-km property hosts several other narrow, high-grade polymetallic prospects
At the eastern edge of Mejicana Ridge, the Atacama vein has been traced for 1.1 km along strike with a width ranging from 0.5 to 1.5 metres. Grab samples taken along the vein have returned up to 5.6 grams gold, 6,300 grams silver and 2.2% copper.
In the Los Bayos area, some 2.5 km southeast of Mejicana Ridge, a silver-rich vein has been traced for 1.2 km along strike, with a width averaging 1 metre. Initial silver assays returned up to 1,000 grams.
The company will perform channel-sampling and mapping on the vein systems in an effort to define drill targets.
Corriente can earn up to an 80% interest in the property from a local group by spending US$4.7 million on exploration, paying US$4.2 million over five years and producing a feasibility study in seven years.
On the copper front, London-based Billiton has signed an option agreement allowing Corriente to acquire 70% of the Rio Zamora project in southern Ecuador. The land package comprises 880 sq. km, about 340 km south of Quito.
Following an independent review by David Lowell, Corriente and Lowell Mineral Exploration of Chile have agreed to combine forces to explore Rio Zamora. Through an exploration management agreement, Lowell can earn up to a 10% interest from Corriente by managing exploration of the properties over the next three years.
Geologist David Lowell has an impressive track record for mineral discoveries in South America. He and Catherine McLeod-Seltzer co-founded junior Arequipa Resources and went on to explore the Pierina gold project in Peru. After only nine holes were drilled,
“The Rio Zamora occurrences are among the most promising copper prospects I have seen,” says Lowell, who adds that they could eventually become “world-class producers.”
Corriente will initially focus on four prospects:
- Warintza — At this prospect, anomalous copper soil samples occur over an area measuring 1.5 by 3 km. Surface chip and channel samples have returned values of up to 1.3% copper from an interpreted chalcocite blanket. The area has never been drill-tested, and the company feels it has potential to host an oxide deposit.
- San Carlos — The inferred resource here is estimated at 400 million tonnes grading 0.7% copper in a broader zone of more than 1 billion tonnes grading 0.4% copper. The resource is based on 5,900 metres of drilling in 25 holes. Corriente believes there is potential for a copper-oxide deposit, as indicated by hole 7, which hit 60 metres averaging 0.7% copper from surface.
- Panantza — This prospect has been drill-tested by 11 holes totalling 2,900 metres. Hole 2 hit 27 metres grading 1.3% copper, while hole 9 intersected 60 metres of 1.15% copper — both from surface. Here also, Corriente believes there is good potential for a copper-oxide deposit.
- Sutzu — The Sutzu prospect is defined by a large soil copper geochemical anomaly extending over 2 sq. km in a zone of porphyry-style alteration. The area has never been drill-tested.
Corriente can earn its interest by completing a feasibility study and issuing 1.8 million units to Billiton in stages extending to May 2003. Each unit consists of one share and one purchase warrant. Upon completion of a feasibility study, Billiton can retain a 70% back-in by providing production financing, maintain its 30% interest, or dilute to a 15% net profits interest.
Meanwhile, the Taca-Taca copper project in Argentina is undergoing drilling by Corriente’s partner,
Situated in Salta province, the project comprises the Taca-Taca Lower property and 27 surrounding concessions 50 km east of the Chilean border.
Rio Tinto can earn 60% interest in the Salar Arizaro area of the Corriente-owned property by spending US$2.5 million on exploration before July 2004.
Targeting the Salar prospect, where chip samples have defined two copper anomalies of up to 0.3%, Rio Tinto is searching for a possible shallow copper-oxide deposit. Earlier this year, three of the seven holes drilled by Rio Tinto outlined shallow copper-gold mineralization over a 750-by-300-metre area at the Cerro Cobre prospect. Drill hole 2 returned 0.45% copper over 78 metres from surface, including 0.58 gram gold over 66 metres. After evaluating the results, the company concluded that the mineralization is not large enough to warrant further work.
From 1996 to 1998, under an option agreement, BHP Minerals spent $2.8 million drilling the Taca-Taca Lower property. The 9,200-metre program outlined a deep-seated inferred resource of 440 million tonnes grading 0.58% copper and 0.18 gram gold. BHP withdrew from the joint venture in March 1998.
Other projects held by Corriente, such as the Tasna property in Bolivia and the Fantasma gold property in Argentina, have been assigned a lower priority.
Corriente has been evaluating the Tasna project for its gold potential since 1994. The polymetallic vein target has produced bismuth, tin, copper and tungsten since the 1880s, and recently the Bolivian government granted Corriente a 25-year lease for the claims covering its gold targets. However, Corriente has so far been unable to develop an economic model.
Frustration also prevails at Fantasma, where
acific Rim returned the property to Corriente.
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