Las Mellizas
Quick Facts
Location:
Santa Cruz Province, Southern Argentina. 900m elevation.Ownership:
Andean is currently earning a 100% interest in Las Mellizas through an Option Agreement.Mineralisation:
Low-sulphidation, epithermal gold (and potentially silver) hosted within quartz veins and associated stockworks with potential bonanza type grades.
The three properties - San Augustin, La Esperanza and Las Mellizas - and all located in a regional cluster approximately 100km to the southeast from Cerro Negro, in the province of Santa Cruz.
Access to all of the properties is good, via a series of good hard-packed tracks easily navigable, in dry weather, with 4-wheel drive vehicles. All of the properties are accessible, to the south, from Ruta 39 that connects Las Heras and Bajo Caracoles, via the access entrance to the Cerro Negro property.
Early exploration by IAMGold identified the potential for both disseminated gold mineralization and high-grade precious metal mineralized structures. Geological mapping, rock-chip and lag sampling on the property defined consistent anomalous gold values associated with highly altered volcanics in the south-western part of the area. High-grade gold values were also detected within quartz vein structures hosted within andesitic rock types.
Rio Tinto plc, attracted by the potential for bulk-tonnage mineralization, acquired an option to explore. During the 2000-2001 field seasons, they focused on the disseminated gold target, firstly by trenching (1,460m) and then by drilling 6 core holes (987m). Results confirmed that gold was present, but at lower grades than hoped for, with a best intersection of 14m at 0.6g/t gold.
Two phases of reverse circulation drilling, totaling 2,486m, were then completed to investigate the quartz veins, as well as test anomalous gold geochemistry in other zones with potential for bulk-tonnage mineralization. The surface mapping, prospecting and trenching had located 7 structures over some 1,500m of strike, within a zone up to 1,000m wide. The most intensive work was focused on the T12 Structure, with 19 trenches over a strike of 900m and 16 drill tests within 500m of that strike and to a vertical depth of 150m. The drilling confirmed that, in one area, surface values can be traced to depth, with the following significant results:
- MZRC10: 5m at 22g/t Au, including 1m at 104.84g/t Au (50m depth);
- MZRC36: 5m at 189g/t Au, including 1m at 940g/t Au (150m depth).
Reconnaissance by Andean Resources has confirmed high-grade values within the T12 structure with up to 526.15g/t Au and >200g/t Ag being reported from a surface sample.
It is interpreted that these results suggest that that the vein structure pinches and swells along strike and down-dip. Five other vein structures were also drill-tested, but often by only one drill-hole each, and generally returned anomalous but not high-grade results.
Due to the focus on investigating the potential for bulk-tonnage mineralization, areas with potential for high-grade mineralised structures have not been explored in detail by the work to-date. The potential within these structures is for shoots of high-grade gold mineralization exploitable by underground methods.