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Abstract: Agua Rica (27°26′S–66°16′O) is a world class Cu (Mo–Au) deposit located in Catamarca, Argentina, in which the porphyry and high sulfidation epithermal stages usually distant 1km vertically, are located at the same level of erosion. Seventy one samples and 120 phyllosilicates were analyzed from the study section (E–W 6969400N) to determine distinctive mineralogical zones which differ not only by their hydrothermal history but also by their potential behavior during the ore processing operations via flotation. In the east side of the section, biotite K1.78–1.67 Na0.05–0.02(Al0.42–0.00Mg3.77–3.22Fe1.46–1.00Ti0.90–0.18Mn0.02–0.01) (Si5.42–4.82Al3.18–2.58)(OHF1.90–1.40Cl0.06–0.04)4 of the early, high temperature potassic alteration (>550°C to 370°C) is encapsulated in a phyllic halo dominated by illite K1.73–1.08 Na0.10–0.0(Al3.96–3.49Mg0.36–0.03Fe0.25–0.01Ti0.06–0.0) (Si6.53–6.07Al1.93–1.47) (OHF0.54–0.0Cl0.02–0.0)4 +quartz+pyrite+covellite+molybdenite+rutile. This mineral assemblage formed from fluids with temperatures≤350°C that attained high sulfur fugacity. The clasts of the hydrothermal and mineralized breccia bodies located at the center of the section and to the east contain widespread pyrophyllite K0.05–0.0(Al4.07–3.94Fe0.12–0.01)(Si7.92–7.50Al0.50–0.05)(OHF0.15–0.02Cl0.03–0.0)4 that had replaced illite at temperatures between 360°C and 280°C. Minor amounts of dickite and widespread kaolinite occur in the advanced argillic and phyllic halos, respectively, as late minerals in clots or in veinlets thus, fluids cooled enough (<270° and <200°C, respectively) for their formation. The presence of phyllosilicate minerals is a potential cause of loss in recovery of copper and molybdenite during the flotation process. Carefully planned and controlled comprehensive liberation and flotation testing should be undertaken in conjunction with mineralogical analysis to optimize and quantify recoveries, separations, grades and gangue deportment. [Copyright &y& Elsevier]

The mineralogy and chemical composition of mica-like phyllosilicates (>2 µm) and clay fraction (<2 µm) of the shallow hydrothermal alteration zones of the Quebrada de la Mina Cu-Au deposit (San Juan Province, Argentina) were constrained by petrography, XRD, electronic microprobe and IR. The results allow us to identify: (1) relict patches of quartz + K-feldspar ± rutile (potassic) alteration, (2) a peripheral clinochlore-rich propylitic halo, and (3) a central white mica (>2 µm) and illite halo associated with phyllic and tourmaline-rich phyllic assemblages. The subhorizontal, shallow level Au-rich (>0.5 ppm Au) zone at the Quebrada de la Mina deposit coincides with the phyllic halo. The distribution of Au, Ag, Zn, Pb and As forms partially overlapping haloes toward shallower levels. Weak Cu (Mo) anomalies were found in potassic patches below the Au-rich zone. High Mn and Fe contents in clinochlore from the peripheral propylitic halo suggest a distance of ∼1 km to a porphyry Cu-(Au) mineralized core at deeper levels. White micas (>2 µm) in Quebrada de la Mina show a range of compositions between muscovite and illite. In the propylitic halo and in the patches of potassic alteration, white micas (>2 µm) show the highest values of Fe + Mg + Mn (0.40–0.55 apfu) and the lowest of Al (2.40–2.55 apfu). In the phyllic alteration zone of Quebrada de la Mina, white micas (>2 µm) with Al contents between 2.45 and 2.70 apfu and Fe + Mg + Mn between 0.35 and 0.15 apfu match the areas with high gold content (>0.5 ppm Au). The lowest values of Fe + Mg + Mn (0.11–0.05 apfu) and the highest Al contents (2.80–2.85 apfu) occur in white micas from the tourmaline-rich phyllic zone. Values of the Kübler index of illite of 0.19–0.1 2θ in the clay fraction of deep samples are indicative of higher temperature and/or higher fluid/rock ratios during illite formation, compared to values of the Kübler index > 0.2 2θ recognized in shallow samples. Thus, both the compositional variations in chlorite and white micas and the illite crystallinity could be used as a guide for exploration of copper-gold mineralization in shallow levels of porphyry systems. [ABSTRACT FROM AUTHOR]