Drilling at the Escalones porphyry prospect in central Chile has encountered high-grade copper values for
Results from the first drillhole suggest the deposit has the potential to host a copper deposit.
The first 377 metres of the hole averaged 0.63% copper. Starting from the surface, the core hole intercepted alternating skarn and intrusive mineralization for 77 metres, which averaged 1.3%
copper, 0.13 gram gold, 4.1 grams silver and 15 parts per million molybdenum.
Within that interval was a 45-metre interval of 1.75% copper. The mineralization consists of chalcopyrite, chalcocite, bornite and other copper oxides in black magnetite skarn, which formed as a replacement of Jurassic-age limestone units. The units overlie the porphyry target and have a known strike length of 1,500 metres.
Farther down at a depth of 109 metres, the hole hit a 92-metre interval grading 0.62%, which included a 24-metre interval at a depth of 163 metres grading 1% copper. The mineralization here is hosted in calc-hornfels, a metasomatized calcareous siltstone composed of fine-grained garnet, pyroxene and quartz. The pyrite content of the calc-hornfels averages 3-8%, reaching as high as 20% in individual 1-metre samples, suggesting the drill hole was located in the pyrite halo of the porphyry system.
At a depth of 271 metres, the hole cut a 106.6-metre interval grading 0.54% copper.
General Minerals stopped the hole at a depth of 548 metres. The bottom 170 metres of the hole contained porphyry-style alteration and visible chalcopyrite and bornite, with grades varying from trace to 0.4% copper.
Assays for the hole were performed by Acme Analytical in Santiago, with check samples re-analyzed at Bondar-Clegg, also in Santiago.
Hole Es-1 was collared in the eastern part of the known mineralizing system at Escalones, near the top of the prospect area at an elevation of 3,900 metres. The hole was designed to test the Escalones Alto target, which consists of exposed magnetite skarn immediately adjacent to highly altered intrusive bodies.
The hole did not intercept sufficient chalcocite mineralization to suggest a secondary enrichment blanket, though the company believes the potential for this enrichment still exists, perhaps beneath the leached capping at the Meseta zone.
Prior to drilling, the extent of the mineralizing system had been indicated by trenching and road building, which exposed long intervals of copper and gold values. General Minerals plans to drill a total of five holes at Escalones, totalling 2,500 metres. The second hole was collared 600 metres south of Es-1 and will test the edge of the Meseta zone.
The results of hole Es-1 were the subject of some speculation after a group of analysts, including The Northern Miner, visited Escalones in November (T.N.M., Nov. 30/98). At that time, the company had drilled the first 40 metres of the hole, which contained visible copper oxides and chalcopyrite. As an immediate result, the price of the company’s shares climbed 25 cents to $1.70, before falling back to $1.17.
The Escalones project, situated 100 km southeast of Santiago, comprises 75 sq. km. in the Andes, along the Maipo River valley. The porphyry system at Escalones covers 6 sq. km over coincident induced-polarization anomalies and contains three main zones: Escalones Alto and Meseta, where drilling is under way, and the Escalones Bajo, which is below Meseta.
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