Surface rock sampling at the Luicho gold project in southern Peru has enabled
The new discovery is in the Luicho fault zone, north of the structural corridor that comprises the Northeast, Central and South prospects. The zone was identified by 235 continuous chip samples along a sinuous, 322-metre path; the samples returned an average of 1.1 grams gold per tonne.
The zone is mineralized over a minimum width of 50 metres, with gold mineralization occuring some 150 metres below the shale contact in a sandstone package that is stratigraphically lower than the sandstone unit being sampled in the Main zone.
Pacific Rim’s chief executive officer, Thomas Shrake, says the discovery proves that the Luicho system extends for a significant vertical depth. “Luicho continues to provide pleasant surprises,” he says. “In addition to confirming the size and grade of the structural corridor with the latest results, we have added another significant target area that lies outside of the corridor.”
At the main prospect, which measures 1,850 by 250 metres, Pacific Rim continues to expand and infill the Northeast, Central and South prospects. The target is a 250-metre-wide, north-to-northeasterly trending structural corridor of mineralization that extends over a strike length of 1,850 metres. Crews have collected 2,539 samples, the average grade of which is 2.25 grams gold.
The corridor is related to a complex series of converging north-southerly and northeast-southwesterly trending right-lateral slip faults. The faults have produced a large fractured and brecciated zone.
At the Northeast zone, 559 chip samples, collected over a 700-by-400-metre area, returned 1.41 grams gold. Of these, 67% exceeded 0.31 gram with an average grade of 2.04 grams.
A total of 1,400 chip samples, collected over the 550-by-250 metre Central zone, returned an average of 3.07 grams gold. Of these, 73% exceeded the 0.31-gram gold mark, the average being 4.14 grams. Pacific Rim is especially encouraged by the higher grades encountered immediately north of the Central zone, where a 52-metre interval returned 8.42 grams gold.
At the South zone, 580 chip samples, collected over a 650-by-250-metre area, returned 1.08 grams gold. Of these, 52% exceeded 0.31 gram gold, the average being 1.94 grams gold.
Situated 540 km southeast of Lima, the 10-sq.-km property represents a low-sulphidation epithermal prospect. Hosted in sandstone, the mineralization occurs as stockwork quartz veining below an impermeable shale unit.
Company geologists believe gold mineralization at Luicho is defined by two dominant controls: the degree of fracturing and brecciation, and the competency of the rock (that is, the inherent ability of the rocks to hold those fractures open).
The key structural feature at Luicho is the north-south Luicho fault zone, which influences the overall shape of the corridor. The southern portion of the corridor trends north-south and is bound on the west by the Luicho fault. At the point where a series of northeasterly trending faults intersects the Luicho fault zone, the corridor bends towards the northeast and is bound by northeasterly trending faults.
The Luicho region comprises a thick sequence of Tertiary-aged volcanics that unconformably overlie Paleozoic-to-Mesozoic-aged sediments. Rocks in the vicinity of the property consist of Jurassic-aged sandstones and shales overlain by a 250-metre-thick, Cretaceous, quartz-sandstone unit. Most of the known mineralization is hosted in these sandstones. A series of thinly bedded shales overlies the sandstones and remains preserved at the northern end of the property, as well as at the southern end of the main target area.
Pacific Rim agreed to acquire the property in October 1999. It must spend US$1.4 million by October 2001 and pay US$24.2 million in cash by October 2002. At production, a maximum 3% royalty will be payable to the vendor, a private Peruvian company.
Surface sampling will continue over the next several months, following which 12,000 metres of reverse-circulation drilling will be performed.
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