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UBC Theses and Dissertations

Geology, alteration, mineralization and hydrothermal evolution of the La Bodega-La Mascota deposits, California-Vetas Mining District, Eastern Cordillera of Colombia, Northern Andes Rodríguez Madrid, Alfonso Luis

Abstract

La Bodega (LB) and La Mascota (LM) deposits (inferred resources in 2010 of 3.47 Moz Au, 19.2 Moz Ag and 84.4 Mlbs Cu at 2 g/t Au cut off) are located in the California-Vetas Mining District, 35 km NE of Bucaramanga, in the Eastern Cordillera of Colombia within the Santander Massif. Mineralization exhibits NE-trending, NW-dipping structural control associated with the right lateral strike-slip La Baja fault. Mineralization at LB is composed of veins networks and tectonic-hydrothermal breccias while LM mineralization is largely contained in hydrothermal breccias with adjacent narrow veining zones. Mineralization is hosted in Proterozoic Bucaramanga (gneiss) Complex and Triassic-Jurassic leucogranites. Hydrothermal alteration and mineralization occur in six stages. An early porphyry-style phase comprises stages 1 and 2. Stage 1 is characterized by propylitic alteration with epidote, chlorite, calcite, specularite veins, minor pyrite and chalcopyrite, probably associated in time with Mo-Cu mineralization (Re/Os on molybdenite ~10 Ma) and porphyritic granodiorites (U/Pb in zircon ~10-8.4 Ma) cropping out in the district. Stage 2 (⁴⁰Ar/³⁹Ar on muscovite ~3.4 Ma) is characterized by phyllic alteration (muscovite/sericite – illite, quartz, pyrite) associated with quartz+pyrite veins. Epithermal phase (stages 3-6) is related to multi-phase hydrothermal breccia development and advanced argillic (quartz-alunite) alteration which based on alunite ⁴⁰Ar/³⁹Ar geochronology took place between ~2.6 and ~1.3 Ma. Stage 3 is characterized by copper sulfide deposition. Stage 4 is characterized by wolframite deposition in veins/breccias. Stage 5 is characterized by enargite deposition. Stage 6 is characterized by minor porous quartz deposition followed by sphalerite with alunite+quartz. Pyrite is common to all these stages. Gold-silver mineralization took place in stages 2-5 associated with sulfides, sulfosalts, tellurides, as electrum and native gold. Hydrothermal events were by followed by near surface supergene alteration and fault reactivation that created intensely fractured/gouge-rich fault zones. At LM, stages 4-5 quartz primary fluid inclusions assemblages indicate boiling and they have homogenization temperatures of ~143-238°C and salinities of 0.5-5.6 wt% NaCl equiv. LM and LB pyrite exhibit light δ³⁴S signatures: -16.9‰ to –11.3‰ at LM and -8.3‰ and –6.1‰ at LB. Alunite δ¹⁸O and δD data indicate that it was precipitated largely from magmatic fluids.

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