Active in Argentina — Yamana samples epithermal targets

The discovery of an epithermal gold district appears to be taking shape south of here in the province of Santa Cruz.

During a site visit, The Northern Miner visited six of the 10 cateos, or claim blocks, being investigated by field crews of Yamana Resources (TSE).

Atop the flat and windy plains of Patagonia, Yamana has completed interpretation of LANDSAT (satellite) imagery which covers a large portion of the southern province. Crews are in the process of carrying out reconnaissance geological mapping and sampling to “ground truth” targets for drilling.

Speculation about the area’s potential has been running high since last year, when reports surfaced which suggested that South African gold mining giant Anglo American had outlined a 10-million-tonne deposit averaging 12 grams gold per tonne on a Cerro Vanguardia cateo. The Vanguardia deposit is hosted within a large quartz vein which is thought to remain open along strike and at depth.

Another discovery, Manatial Espeje, was made previously by Lac Minerals and is now part of Barrick Gold’s (TSE) stable of South American properties. Manatial Espeje lies 100 km west-southwest of Vanguardia, suggesting the extent of the district could be vast. Other companies, including Canadian and Australian interests, are either acquiring or seeking to acquire ground in and around these discoveries.

Yamana’s subsidiary, Compania Minera Polimet, is no newcomer to the region, having embarked on the search for gold in Santa Cruz about four years ago.

Yamana geologists think this area represents a back-arc basin environment analogous to central Nevada. It is characterized by extensional plate tectonics which have caused cracks to form in the earth’s crust. According to this model, fluids carrying gold in solution came to the surface in the form of geysers, forming hot springs and sinter deposits. Repeated injection of fluids continued to break and seal the rocks, giving them a brecciated texture. In some cases, the degree of fracturing and annealing is so extreme that Yamana geologists have resorted to describing the rocks as “extremely tortured.”

However, one major difference between Santa Cruz and Nevada is that the former has undergone little, if any, modern, systematic exploration. “If these outcrops had been found in Nevada, they would have been sampled,” said Christopher Broili, project manager for Yamana. “But here, we’re walking on virgin ground.”

The company is using LANDSAT imagery data in order to concentrate its search for gold in areas with proper structural ground preparation and epithermal alteration. A key feature of these targets is that they are silicified and resistant to erosion. As such, they are quite prominent, rising up to 75 metres above the peneplain gravels that cover the region.

During the past year, Yamana took more than 1,200 rock chip samples, the results from most of which are now available. The outcome is that at least one drill target has been identified on six of the company’s 10 cateos.

At Microonda, field crews have identified seven resistant knobs, defining an epithermal zone covering a surface area of 4 sq. km. Although 250 rock chip samples have been taken, the company anticipates taking another 1,000 before fully delineating the surface extent of the zone.

Background values for the area run in excess of 0.1 gram, and many samples have assayed between 1 and 3 grams over 1 to 3 metres. One of the more spectacular assays came from a mineralized sinter; it averaged 4.12 grams over 15 metres. More detailed sampling of the showing returned a value of 18 grams over 3 metres.

Elsewhere, on the Condor cateo, which is adjacent to Anglo’s Vanguardia cateo, a 1-km, sulphide-bearing quartz vein has been identified. The structure, which strikes on to the Vanguardia cateo, has assayed up to 4 grams across 1 metre.

Many other multiple-gram rock chip samples have been obtained, from Yamana’s Cerrito Solo, Martinetas, Goleta and Estrella cateos.

With fall approaching, Yamana is compiling all its geological and geochemical data in preparation for drilling. According to Richard Walter, vice-president of exploration, the company will “probably drill about 60 holes to a depth of about 200 to 300 metres each.” The program should begin later this year.