Porphyry to Epithermal Transition in the Agua Rica Polymetallic Deposit, Catamarca, Argentina: An intergrated petrologic analysis of ore and alteration parageneses

FRANCHINI M. B., AIMPICINI A., LENTZ D., FRANCIRÍOS F.J., O´LEARY S., PONS M. J., SCHALAMUK I. B.

ORE GEOLOGY REVIEWS

ELSEVIER SCIENCE BV

Año: 2011 vol. 41 p. 49 - 74

0169-1368

Agua Rica (27º26?S-66º16?O) is a world class Cu-Au-Mo deposit located in Catamarca,Argentina. In the E-W 6969400 section examined, the Seca Norte and the Trampeadero porphyries that have intruded the metasediment are cut by interfingered igneous and hydrothermal heterolithic and monolithic breccias, and sandy dikes. Relic biotite and K-feldspar of the early, potassic alteration (370° to >550°C), with Cu (Mo-Au) mineralization, are locally preserved and encapsulated in a widespread, white mica + quartz + rutile or anatase halo(phyllic alteration) with pyrite + covellite that suggests fluids with temperatures ≤360°C and high f(S2). The Trampeadero porphyry and the surrounding metasediment with phyllic alteration have molybdenite in stringers and B-type quartz veinlets and the highest Mo grades (>1000ppm). Multistage advanced argillic alteration overprinted the earlier stages. Early andalusite ± pyrite ± quartz is preserved in the roots of the argillic halo rimmed by an alumina-silica material and white micas. This alteration assemblage is considered to have been formed at temperatures ≥375°C from condensed magmatic vapor. At higher levels, pyrophyllite replaces muscovite and illite in clasts of hydrothermal breccias in the center and east sector of the study section,suggesting temperatures of 280° to 360°C. Clasts of vuggy silica in the uppermost levels of the central breccia, indicates that at lower temperatures (