Vancouver — Through an option agreement, Montreal-based
The 20-hectare Promontorio concession is near the historical mining town of Tutuaca in the Sierra Madre Occidental gold-silver belt, at an elevation of 2,000 metres.
Although the property had seen some exploration, and even production, it did not gain much attention until 1993, when Canmex, a subsidiary of
Between 1995 and 1998, Sierra Nevada drilled 57 core holes, remapped the area, and confirmed the high-grade copper zones. The company completed more than 22,000 ft. of core drilling, dewatered and rehabilitated old mine workings, and performed underground sampling.
The drilling outlined a copper-gold-silver resource within 100 metres of surface and which was open to depth. Five major mineralized structures containing high-grade copper and economic gold and silver were intersected. The main areas of mineralization include the Mina Vieja and Veta Grande zones, which contain primarily copper, and another, which contains primarily gold. One target, La Cascada, returned 18 grams gold per tonne over 7.6 metres.
The veins appear to be hosted in an intrusive dacite. Locally the rocks are argillized and pyritic, with silicification occurring near the mineralized structures. The mineralization includes massive sulphide, disseminated sulphides, and vein-hydrothermal breccias. A younger volcanic flow unit caps the dacitic unit.
The Veta Grande vein was traced over 30 metres along strike and to a depth of 130 metres in five holes. The best intersection occurred in hole 3, which returned 25 metres grading 6.2 grams gold and 105 grams silver per tonne, plus 7.33% copper. Six holes tested the Mina Vieja vein, revealing a wide zone of silicification but generally lower copper values. The best result was 24.4 metres grading 2.6% copper and 0.65 gram gold, and this intercept included a 10.7-metre section of 1 gram gold and 5.39% copper. Four holes intersected the Santiago vein, the highlight being 0.68 gram gold and 4.47% copper over 7.2 metres.
The results were used in an independent resource estimate by Reno-based Mine Development Associates in 1997. The resource was contained in a 150-by-150-metre area, and the deposit was open at depth. Although it is considered reliable, the resource is not in compliance with NI-43-101 standards; it was based on a 94-hole program that extended down to 100 metres. Indicated resources at a cutoff of 0.5% copper totalled 625,000 tonnes grading 4.04% copper, 2.61 grams gold, and 65.79 grams silver. The inferred resource was estimated at 398,000 tonnes grading 3.87% copper, 2.19 grams gold and 59.16 grams silver. Within this resource is a higher-grade component of 201,000 tonnes grading 9.06% copper, 3.82 grams gold, and 116.21 grams silver.
In 1997, a deeper test hole was drilled in the Veta Grande zone, and though the hole was not included as part of the resource, it nonetheless indicated significant potential at depth. At a down-hole depth of 159 metres, the hole intersected 4 metres grading 2.77 grams gold, 66.1 grams silver and 7.8% copper.
Several underground workings with gold, silver and copper mineralization occur on the property, and some of these were bulk-sampled in 1998. One is a 43-metre shaft with two adits in the Veta Grande vein, where some 40% of the ore is estimated to be.
The company is improving access roads and constructing drill pad for a 10,000-metre program designed to expand the resource at depth.
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