San Pedro Project
The San Pedro project is located in the central part of the Deseado Massif at about 100 km to the NE of the Gobernador Gregores town. The mining rights are secured by five mineral properties that cover 7200 ha.
Fomicruz has explored the project intermittently since 2001 and has detected numerous veins located in eight areas, which were named: Mario, Francisco, Carla, Jacinto, Yanina, Emilce, Gabriel and Volcan. In most of those areas, there are several discontinuous and sub-parallel siliceous veins, which are hosted in jurassic volcanic rocks, mainly those of the Bajo Pobre Formation, although a few ones are hosted in the Chon Aike and La Matilde Formations.
A summed length of veins of more than 8000 m has been identified in this project. The veins have continuous lengths of up to 300 m, but some of them can be traced discontinuously for up to 800 m. Their more frequent thickness is of 1 to 1.5 m, with a maximum of 8.5 m. In general, their orientation varies between 310º and 345º, although a few veins have E-W, N-S or NNE orientations. Their dips are strongly variable (even in the same area) from sub-vertical up to 45º to the east or west.
The veins are composed of fine grained quartz and chalcedony bands, alternating with oxides and hydroxides of Fe and Mn, and they often show banded and colloform textures, and occasionally, breccias. They also show some geodes with coarse grained, comb quartz, and locally, pseudomorphs of silica after calcite and/or barite. The veins also include pyrolusite (polianite), cryptomelane, pyrite, hematite, limonite and barite. In addition, adularia has been identified in the Francisco and Yanina areas, in veinlets hosted by rhyolitic lavas. The Mn minerals, (mainly pyrolusite) are ubiquitous; in contrast, calcite was only detected in the Carla vein, being a late mineral in the paragenetic sequence.
The contacts between veins and host rocks are generally sharp, and the alteration is restricted around the veins. A few X-Ray analyses identified abundant kaolinite, but also illite, smectites, scarce Fe-rich chlorite, and interstratified smetite-chlorite. Preliminary interpretation of spectroscopic data from one borehole in the Yanina area, indicate the predominance of kaolinite group minerals (kaolinite +- dickite), while smectite is scarce, and illite and muscovite are very scarce. The interpretations of some fluid inclusion data suggest that at least part of the veins may have formed at temperatures below 100ºC, however, microthermometry in fluid inclusions showed homogenization temperatures of 135-184ºC, and estimated salinity of 0.88-2 % NaCl equiv. Boiling evidence was not observed in any case.
The exploration activities in this project, included geological mapping, rock-chip sampling, local topographic surveys, a localized geophysical survey, opening and sampling of some trenches, drilling, and some specific geological studies, such as petrographic studies, X-Rays diffraction, fluid inclusions, and reflectance spectroscopy.
Fomicruz collected more than 200 rock-chip samples. Their chemical assays indicate that Au and Ag contents are low, returning maximum concentrations of 0.07 g/t Au and 15.6 g/t Ag. In only few cases, base metal anomalous concentrations were detected, including 900 g/t Zn and 945 g/t Pb. There are however, high concentrations of other elements reaching up to 9% Mn, 15.36% Fe, 1.9% Ba, 960 g/t As, 1070 g/t Sb, 2.9 g/t Hg, and 73.2 g/t Tl.
