Geology and geochemistry of the San Antonio area, Cajamarca, Tolima
DOI:
https://doi.org/10.32685/0120-1425/bolgeol29.2.1988.282Keywords:
Colombia, hydrothermal breccia, La Guala mountain, oxides, fault zones, silicification, sericitization
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Abstract
In the San Antonio region, municipality of Cajamarca, Tolima, anomalous gold values (0.60 ppm in rocks and 0.51 ppm in soils) are associated with hydrothermal breccia bodies located within metamorphic rocks of the Cajamarca Group. On the eastern side of the study area, several breccias are spatially related to fault zones, developing pipe-like shapes.
Towards the upper part of Cerro La Guala, the main breccia body has at the surface, a semicircular shape of 65 by 35 m and consists of angular to subrounded fragments of schistose and porphyritic rocks, embedded in a very fine matrix with abundant druses in some areas. The main effects of hydrothermal alteration, silicification, and sericitization, are most developed within this breccia body. Pyrite, the most common metallic mineral (2% volume), occurs in disseminated and filling druses. The best gold values (up to 4.30 ppm) are related to zones of druses rich in iron oxides.
Anomalous concentrations of Ag, As, Sb, Cu, Mo, W, and Ba tend to exhibit distribution patterns like Au.
It seems that the San Antonio breccias were formed during upward hydrothermal activity, genetically related to the magmatic activity that generated the dacitic-andesitic porphyries present in the area during the Upper Tertiary.
The San Antonio region presents favorable characteristics for developing a disseminated gold deposit related to hydrothermal breccias, whose true economic potential must be proven through exploratory drilling.
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