María Celeste D'annunzio y Nora Rubinstein
2 013
Rev. Asoc. Geol. Argent. vol.70 no.4 Buenos Aires dic. 2013
El distrito minero Gualcamayo (68°38'26"O; 29°43'10"S) se ubica en la provincia morfoestructural de Precordillera Central, en el extremo nororiental de la provincia de San Juan. Este sector está caracterizado por rocas carbonáticas y sedimentitas clásticas de edad ordovícica y carbonífera-pérmica que fueron intruídas por cuerpos de composición dacítica-andesítica de edad miocena. El distrito incluye tres depósitos: Quebrada del Diablo Main, Amelia Inés- Magdalena y Quebrada del Diablo Lower West. Quebrada del Diablo Main es un depósito tipo Carlin y es el cuerpo sobre el cual se desarrolla la mina a cielo abierto. Amelia Inés y Magdalena son depósitos de hierro, molibdeno, cobre, zinc, plomo y oro, asociados a skarns magnesianos. Quebrada del Diablo Lower West es un cuerpo no aflorante que se encuentra entre 500 y 600 metros de profundidad. En el cuerpo Quebrada del Diablo Lower West, la mineralización de oro se encuentra principalmente asociada a brechas caracterizadas por una gran variación en la composición y abundancia relativa de clastos, matriz y cemento, así como en el tamaño de los clastos. El análisis textural de las brechas mineralizadas de Quebrada del Diablo Lower West sugiere para las mismas un origen esencialmente tectónico. La paragénesis inicial de pirita, esfalerita y oro indica condiciones de baja sulfuración y pH neutro a alcalino para los fluidos mineralizantes. La marcasita sobreimpuesta sugiere una disminución de la concentración de azufre en los fluidos mineralizantes. Las vetillas posteriores de calcita con rejalgar, oropimente y oro indican un aumento de la actividad de arsénico en el sistema.
Origin and mineralization stages of the breccias from Quebrada del Diablo Lower West, Gualcamayo mining district, San Juan Province.
Gualcamayo mining district (68°38'26"W, 29°43'10" S) is located in the Central Precordillera, in the northeast of San Juan province. This sector is characterized by carbonate and sedimentary rocks of Ordovician-Permian age. This sequence is intruded by Miocene dacites and tonalites rocks. The district includes three deposits: Quebrada del Diablo Main, Amelia Ines-Magdalena and Quebrada del Diablo Lower West. Quebrada del Diablo Main is a Carlin-type deposit which is mined as an open pit. Amelia Inés-Magdalena is an iron, molybdenum, copper, zinc, lead and gold deposit, associated to magnesian skarns. Quebrada del Diablo Lower West is a blind ore body located between 500 and 600 metres deep. In Quebrada del Diablo Lower West, the gold mineralization is hosted by breccias with an wide variation in composition and relative abundance of clasts, matrix and cement, as well as the size of the clasts. The textural analysis of the mineralized breccias from Quebrada del Diablo Lower West suggests a tectonic origin. The mineral assemblage of pyrite, sphalerite and gold indicates low-sulphidation conditions and neutral to alkaline pH. The overprinted marcasite suggests a decrease in the concentration of sulfur in the mineralizing fluids. Later calcite veins with realgar, orpiment and gold indicate an increasing arsenic activity in the hydrothermal system.
Gualcamayo mining district (68°38'26"W, 29°43'10" S) is located in the Central Precordillera, in the northeast of San Juan province. This sector is characterized by carbonate and sedimentary rocks of Ordovician-Permian age. This sequence is intruded by Miocene dacites and tonalites rocks. The district includes three deposits: Quebrada del Diablo Main, Amelia Ines-Magdalena and Quebrada del Diablo Lower West. Quebrada del Diablo Main is a Carlin-type deposit which is mined as an open pit. Amelia Inés-Magdalena is an iron, molybdenum, copper, zinc, lead and gold deposit, associated to magnesian skarns. Quebrada del Diablo Lower West is a blind ore body located between 500 and 600 metres deep. In Quebrada del Diablo Lower West, the gold mineralization is hosted by breccias with an wide variation in composition and relative abundance of clasts, matrix and cement, as well as the size of the clasts. The textural analysis of the mineralized breccias from Quebrada del Diablo Lower West suggests a tectonic origin. The mineral assemblage of pyrite, sphalerite and gold indicates low-sulphidation conditions and neutral to alkaline pH. The overprinted marcasite suggests a decrease in the concentration of sulfur in the mineralizing fluids. Later calcite veins with realgar, orpiment and gold indicate an increasing arsenic activity in the hydrothermal system.
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