Following delays caused by heavy snowfall in 1997,
The mountainous property (which means “big steps” in Spanish) is believed to represent a prospective porphyry target within a 6-sq.-km mineralizing system.
Escalones was not the only project in the region to experience weather-related delays. For example, the Refugio gold mine, held jointly by Kinross and Bema Gold, was shut down for several weeks after 5 metres of snow left many workers stranded.
Fortunately, the winter of 1998 saw relatively little snowfall in the Chilean Andes, and General Minerals was able to begin work earlier than anticipated. The first hole, which started in early November, is designed to test mineralization found in trenching at the Escalones Alto zone, 3,900 metres above sea level.
On the southwestern face of Escalones Alto, one of several roadcuts encountered 19 metres of copper-silver mineralization averaging 2.5% copper and 20 grams silver per tonne hosted in garnet skarn. About 200 metres east, in the second roadcut, the company encountered 38 metres of 1.4% copper and 0.2 gram gold in magnetite skarn. Fifty metres to the northeast, a trench encountered 26 metres of magnetite skarn grading 0.7% copper and 1.2 grams gold.
While the trenches demonstrate that high-grade skarn exists over a significant area, geologists have yet to determine the strike and full extent of this mineralization. “We expected to hit the skarn within the first few metres of the hole,” according to General Minerals President Ralph Fitch.
The Northern Miner and a group of analysts were on hand to see the first 40 metres of core coming from the first hole. Collared near the top of the mountain at Escalones Alto, hole 1 contained visible copper oxides, chalcopyrite and magnetite skarn in at least the first 40 metres of core.
The company reports that the hole intersected alternating skarn mineralization and intrusive rock down to about 70 metres. Assays are pending.
Fitch expects the first hole to be drilled to a depth of 600 metres. “We want to get down into the intrusive to get a feeling for the mineralization,” he said, adding that the company is also looking for a leached cap of this proposed porphyry system. “There is plenty of evidence of a large copper-bearing system here.”
General Minerals has found stalactites of copper sulphate in an adit high on the mountain near the first drillhole, as well as native copper, which has precipitated from the surface waters. Anomalous molybdenum values have been found in leached rocks at the property.
Before Christmas, General Minerals will drill as many as six holes of similar length to test the various areas in this large mineralizing system, and then continue with more holes after the holidays. Depending on results, these holes could test the Escalones Bajo and Meseta zones. The latter, situated at 3,700 metres, may represent the leach capping over the porphyry, Fitch said.
Escalones Bajo, which lies at a lower elevation, is the site of a coincident geophysics anomaly that is believed to represent a highly prospective zone of copper mineralization. The mineralization is hosted in siltstones covered by a younger thrust fault of folded clastic rocks. Beneath the fault is a second drill target.
Escalones Alto contains Mesozoic-age limestones which have been altered to skarns and lie over top of the intrusive porphyry. The skarn has a strike of more than 1 km and extends down the backside of the project into a steep area. General Minerals plans to drive a road there to gain access to deeper portions of the porphyry and test for additional skarn mineralization.
The Escalones project is in the Maipo River valley, which was formerly accessible only by helicopter or horseback. In the 1920s, local miners pulled high-grade copper-gold ores from the property. Access improved greatly when the Transandian gas pipeline, which passes within a few hundred metres of the Escalones base camp, connected Santiago with Argentina. General Minerals geologist Waldo Cuadra first visited the project after a 2-day trek on horseback in the 1980s. A dirt road leads up into the valley, and the governments of Chile and Argentina are considering upgrading this into a paved highway to form an alternative route from Santiago to Mendoza.
General Minerals acquired the Escalones project in early 1997, based on alteration-enhanced satellite imagery.
The company says it is encouraged by similarities which Escalones shares with the nearby El Teniente copper mine, situated 35 km to the east and operated by Chilean government-owned Corporacion Nacional Del Cobre de Chile (Codelco). Both projects are at roughly the same altitude and share intrusive rocks that are about 8 million years old.
El Teniente is the largest underground copper mine in the world, processing as much as 100,000 tonnes of ore per day. Headgrades run about 1.1% copper.
Should Escalones prove to be minable, General Minerals will consider whether to develop it as an open pit or, like El Teniente, as a bulk-tonnage, block-caving operation.
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