Abstract

FRANCHINI, Marta et al. Alterationand mineralization along the central section of the Agua Rica deposit(27º26'S-66º16'O), Catamarca. Rev. Asoc. Geol. Argent. [online]. 2009, vol.64, n.3, pp.391-408. ISSN 0004-4822.

Agua Rica is aworld class Cu (Mo-Au) deposit in which the porphyry and high sulfidationepithermal stages usually distant 1 km vertically, are located at the samelevel of erosion. The Seca Norte porphyry in the west side of the studysection, preserves relic potassic alteration of the early, high temperaturestage with Cu (Mo, Au) mineralization encapsulated in a phyllic halo that has adistinct characteristic: the low to intermediate sulfidation chalcopyrite,pyrite and bornite of the early stage were reconstituted as high sulfidationcovellite and pyrite. The high temperature advance argillic alterationparagenesis (andalusite and pyrophyllite ± diaspore), considered to have beenformed from condensed magmatic vapor, are preserved in the roots of the advanceargillic halo and in clasts of hydrothermal breccias in the center and eastsector of the section, replacing the phyllic alteration. Clasts of vuggy silicain the uppermost levels of the central breccia, suggest that at lowertemperatures, fluids reached very low pH. Subsequent hydrothermal brecciation,probably driven by unroofing and the mechanical energy released from theshallow magma emplacement, and fluids exsolution precipitated intermediatetemperature advance argillic paragenesis (alunite + diaspore + zunyite) ascement 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 goldand silver introduction in the upper breccias level, indicates a late flux ofgold-rich fluids at probably lower temperatures but still high sulfide activity,considering the absence of iron in the sphalerite composition.

Keywords : Porphyry Cu (Mo,Au); Epithermalhigh sulfidation; Hydrothermalbreccias; Telescoping.

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