Publication: Estudio geoquímico prospectivo en un distrito de
Cu-Au-Hg asociado a zona de cizalla: Punitaqui, Chile
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2001
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Instituto Geológico y Minero de España
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Abstract
El distrito de Punitaqui se localiza en una zona montañosa semi árida de la Cordillera de la Costa de la región norte de Chile central. El distrito alberga una serie de mineralizaciones filonianas de Cu-Au-Hg, que se emplazan a lo largo del sector occidental de una zona de cizalla NNE de unos 200-400 m de potencia. La zona de cizalla separa a granitoides del Cretácico medio de una secuencia principalmente volcánica (andesitas y andesitas basálticas) de edad Valanginiense. Como base para la búsqueda de nuevas reservas en el distrito se realizaron estudios estructurales y geoquímicos. El estudio estructural indicó la existencia de fenómenos de superposición de una fábrica frágil sobre otra dúctil en la zona de cizalla, así como la existencia de una importante zona de transpresión. Se tomaron más de 160 muestras de suelo para el estudio geoquímico. Estas fueron recolectadas a lo largo del sector oeste de la zona de cizalla y a través de secciones perpendiculares a ésta. El estudio incluyó además 20 muestras de rocas, y 5 de minerales de mena. Las muestras se analizaron por 48 elementos, mediante extracción total. Adicionalmente, se analizaron 59 elementos por el método de extracción enzimática. Au, Cu, Ag, Hg, Sb, y As “totales”, así como el Au y el Sb “enzimáticos” probaron ser los mejores trazadores geoquímicos para la detección de cuerpos mineralizados no aflorantes. El estudio geoquímico permitió descartar sectores a lo largo de la zona de cizalla, restringiendo el interés a la parte norte (sector Culebra-Viña Vieja). Sondeos realizados en esta zona mostraron la existencia de recursos minerales (Au-Cu) del orden de los 9 Mt.
The Punitaqui district is located within a hilly semiarid region of the Coastal Cordillera of northern central Chile. The district hosts Cu-Au-Hg vein deposits emplaced along the western side of a 200-400 m wide NNE trending shear zone. The shear zone separates a Middle Cretaceous granitoid from a mainly volcanic sequence (andesites and basaltic andesites) of Valanginian age. Exploration for new reserves in the district required detailed structural and geochemical works. The structural study of the shear zone allowed recognition of brittle-on-ductile overprinting (mylonite to breccia) phenomena along the shear zone, and the existence of a major restraining (contractional) bend within the district.Over 160 soil samples were taken for the geochemical study, both along the western side of the shear zone, and along sections cross-cutting the structure. The survey also included 20 samples from rocks and 5 from ores. The samples were analyzed for 48 elements (total extraction). Additionally, 59 elements were analized in the soil samples by the enzyme leach extraction technique. Total Au, Cu, Ag, Hg, Sb, and As, as well as ‘enzymatic’ Au and Sb proved to be the best tracers for hidden orebodies. The geochemical survey allowed definition of a major target in the northern part of the district (Culebra-Viña Vieja zone). A drilling campaign (DDH) showed the existence of gold copper mineral resources (9 Mt) in that zone.
The Punitaqui district is located within a hilly semiarid region of the Coastal Cordillera of northern central Chile. The district hosts Cu-Au-Hg vein deposits emplaced along the western side of a 200-400 m wide NNE trending shear zone. The shear zone separates a Middle Cretaceous granitoid from a mainly volcanic sequence (andesites and basaltic andesites) of Valanginian age. Exploration for new reserves in the district required detailed structural and geochemical works. The structural study of the shear zone allowed recognition of brittle-on-ductile overprinting (mylonite to breccia) phenomena along the shear zone, and the existence of a major restraining (contractional) bend within the district.Over 160 soil samples were taken for the geochemical study, both along the western side of the shear zone, and along sections cross-cutting the structure. The survey also included 20 samples from rocks and 5 from ores. The samples were analyzed for 48 elements (total extraction). Additionally, 59 elements were analized in the soil samples by the enzyme leach extraction technique. Total Au, Cu, Ag, Hg, Sb, and As, as well as ‘enzymatic’ Au and Sb proved to be the best tracers for hidden orebodies. The geochemical survey allowed definition of a major target in the northern part of the district (Culebra-Viña Vieja zone). A drilling campaign (DDH) showed the existence of gold copper mineral resources (9 Mt) in that zone.