Nora Rubinstein, Anabel Gómez y Laura Kleiman
2 013
Rev. Asoc. Geol. Argent. vol.70 no.3 Buenos Aires set. 2013
El distrito minero El Infiernillo, localizado en el sector norte del bloque de San Rafael, comprende un depósito tipo cobre porfírico emplazado en una secuencia volcaniclástica perteneciente al ciclo magmático Choiyoi. Dicha secuencia está integrada por tres litofacies ignimbríticas de composición dacítica-traquiandesítica, un cuerpo lacolítico dacítico y un conjunto de diques andesíticos. Las características geoquímicas de las ignimbritas y el lacolito son comparables a las de volcanitas de la sección inferior del ciclo magmático Choiyoi de otras áreas con y sin mineralización del bloque de San Rafael. Estas rocas presentan características típicas de un magmatismo de arco emplazado en una corteza relativamente engrosada. Por otra parte, las características geoquímicas de los diques andesíticos son comparables a las de otros diques similares correspondientes a la sección superior del ciclo magmático Choiyoi. El depósito de cobre porfírico desarrolla un patrón de alteración concéntrico, con un núcleo de cuarzo rodeado de una zona con alteración potásica y externamente un halo fílico con vetas polimetálicas asociadas. Los cambios químicos producto de la alteración de la roca de caja permiten concluir que el proceso de alteración fílica produjo pérdidas de Ca y Na y localmente ganancias en Mg, Si, Fe y K, las cuales se ven reflejadas en la mineralogía de alteración. El control del magmatismo y la estructura sobre la mineralización permite asignarle una edad cercana al límite Pérmico inferior -Pérmico superior.
Lithofacies and geochemical characterization of the volcanic rocks from El Infiernillo mining district, Mendoza.
El Infiernillo mining district is a porphyry Cu (Mo) type deposit located in the northern part of the San Rafael Massif. It is hosted by a volcaniclastic sequence which corresponds to the Choiyoi Magmatic Cycle. This volcaniclastic sequence comprises three ignimbritic facies of dacitic-trachyandesitic composition, a dacitic laccolith and a set of andesitic dykes. The geochemical characteristics of the ignimbrites and the laccolith are similar to those of volcanic rocks belonging to the lower section of Choiyoi Magmatic Cycle from other mineralized and non mineralized areas of the San Rafael Massif. These rocks have a geochemistry typical of an arc-related magmatism over a thickened crust. Conversely, the geochemistry of the andesitic dykes is similar to the volcanics of the upper section of Choiyoi Magmatic Cycle. The ore deposit develops an alteration halo with a concentric pattern consisting of a central quartz neck surrounded by a potassic alteration zone followed by a phyllic outer halo and small polymetallic veins. The phyllic alteration affecting the ignimbrites led to losses of Na and Ca and gains of Mg, Si, Fe and K and these chemical changes are revealed by its alteration mineralogy. The geologic setting allows constraining the age of the El Infiernillo ore deposit close to the Early-Late Permian limit.
El Infiernillo mining district is a porphyry Cu (Mo) type deposit located in the northern part of the San Rafael Massif. It is hosted by a volcaniclastic sequence which corresponds to the Choiyoi Magmatic Cycle. This volcaniclastic sequence comprises three ignimbritic facies of dacitic-trachyandesitic composition, a dacitic laccolith and a set of andesitic dykes. The geochemical characteristics of the ignimbrites and the laccolith are similar to those of volcanic rocks belonging to the lower section of Choiyoi Magmatic Cycle from other mineralized and non mineralized areas of the San Rafael Massif. These rocks have a geochemistry typical of an arc-related magmatism over a thickened crust. Conversely, the geochemistry of the andesitic dykes is similar to the volcanics of the upper section of Choiyoi Magmatic Cycle. The ore deposit develops an alteration halo with a concentric pattern consisting of a central quartz neck surrounded by a potassic alteration zone followed by a phyllic outer halo and small polymetallic veins. The phyllic alteration affecting the ignimbrites led to losses of Na and Ca and gains of Mg, Si, Fe and K and these chemical changes are revealed by its alteration mineralogy. The geologic setting allows constraining the age of the El Infiernillo ore deposit close to the Early-Late Permian limit.
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