Edad y geoquimica isotopica Rb-Sr del yacimiento de cobre Mantos Blancos: relacion temporal con el magmatismo jurasico

Abstract

ABSTRACT. Rb-Sr isotopic age and geochemistry of The Mantos Blancos copper deposit: temporal relation of the Jurassic magmatism. The Mantos Blancos volcanic sequence, host of the stratabound Cu (-Ag) deposit of the same name, has been studied for its Rb-Sr isotope geochemistry, to provide insights into the age and genesis of this important mineral deposit. Whole rock Rb-Sr ages of rock units characterized for their alteration pattern, allow the following generalizations: a- errorcrons from the NK unit (rocks with normal K2O contents and with little sodic alteration), yield ages of ca. 175 Ma, interpreted as the age of the host Mantos Blancos volcanic sequence; b- the ages of about 150 Ma obtained for the strongly altered ANa unit (sodic alteration), are interpreted to represent the age of hydrothermal alteration responsible for sodium metasomatism and its associated copper mineralization; c. intrusives emplaced into La Negra Formation and Mantos Blancos volcanic sequence may have been responsible for the thermal event causing the hydrothermal alteration process related to the ore mineralization. The initial 87Sr/86Sr of both NK and ANa units, and in calcite, which crystallized late in the paragenetic sequence of the ores, suggests that the hydrothermal fluids could not have been purely magmatic, nor of sea water origin, but could represent meteoric waters that have partially equilibrated with the host formations, or mixtures of different fluids.