Distribución de las Alteraciones y Mineralizaciones en la Sección Central del

MARTA FRANCHINI; AGNES IMPICCINI; SOL OLEARY; JAVIER RÍOS; ABEL SCHALAMUK

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 2009 vol. 64 p. 211 - 228

Agua Rica is a world class Cu (Mo-Au) deposit in which the porphyry and high sulfidationepithermal stages usually distant 1 km vertically, are located at the same level of erosion. TheSeca Norte porphyry in the east side of the study section, preserves relic potassic alteration of the early, high temperature stage with Cu (Mo) mineralization encapsulated in a phyllic halo that has a distinct characteristic: the low to intermediate sulfidation chalcopyrite, pyrite and bornite of the early stage were reconstituted as high sulfidation covellite and pyrite. The high temperature advance argillic alteration paragenesis (andalusite and pyrophyllite ± diaspore), considered to have been formed from condensed magmatic vapor, are preserved in the roots of the argillic halo and in clasts of hydrothermal breccias in the center and east sector of the section, replacing the phyllic alteration. Clasts of vuggy silica in the uppermost levels of the central breccia, suggest that at lower temperatures, fluids reached very low pH. Subsequent hydrothermal brecciation -probably driven by unroofing and the mechanical energy released from the shallow magma emplacement- and fluids exsolution, precipitated intermediate temperature advance argillic paragenesis (alunite + diaspore + zunyite) as cement accompanied by abundant covellite, enargite pyrite, and native sulfur (kuramite) in deepest parts of breccias. A final stage of sphalerite, emplectite, colucite, Pb and Bi-bearing sulfides, and native sulfur with gold and silver introduction in the upper breccias level, indicates a late flux of gold-rich fluids at probably lower temperatures but still high sulfide activity, considering the absence of iron in the sphalerite composition.