Indium-bearing paragenesis from the Nueva Esperanza and Restauradora veins, Capillitas mine, Argentina

Abstract

The Nueva Esperanza and Restauradora are two of the twenty-three veins described at Capillitas mine, an epithermal precious-and base-metal vein deposit located in northern Argentina. Capillitas is genetically linked to other mineralizations of the Farallón Negro Volcanic Complex, which hosts several deposits. These include two world-class (La Alumbrera and Agua Rica) and some smaller (e.g., Bajo El Durazno) porphyry deposits, and a few epithermal deposits (Farallón Negro, Alto de la Blenda, Cerro Atajo and Capillitas). The main hypogene minerals found at these two veins include pyrite, sphalerite, galena, chalcopyrite, tennantite-(Zn) and tennantite-(Fe). Accessory minerals comprise hübnerite, gold, silver, stannite, stannoidite and mawsonite, and also diverse indium-and tellurium-bearing minerals. Quartz is the main gangue mineral. Indium participates in the structure of sphalerite, tennantite-(Zn), ishiharaite and an indium-bearing mineral, still under study, the former being the most abundant of these phases. The chemical composition of sphalerite shows very low concentrations of Fe and a wide range in indium contents from below the detection limit (0.03 wt. %) to values close to 22 wt. %. Atomic proportions of In and Cu correlate positively at a ratio In : Cu = 1 : 1 atoms per formula unit. Cadmium reaches up to 0.68 wt. %. Other analyzed elements (Ge, As, Se, Ag, Sn, Te, Au, Pb and Bi) are systematically below their respective detection limits. Indium-bearing tennantite-(Zn) (up to 0.24 wt. % In) is rare and restricted to the area where ishiharaite appears. Ishiharaite and the unclassified indium-bearing mineral are extremely scarce and host up to 10 and 30 wt. % In, respectively. The zoning in sphalerite and the variable indium content of the different bands could be ascribed to significant fluctuation in the composition of the fluids (possibly pulses). They are evidenced by the presence of a high f Te 2 mineral, like calaverite, and a low f Te 2 phase, such as silver, within the same stage, with local periodic increments on In and Cu that could also be associated with recurring reactivation of fractures.

Grandviewite redefinition, new formula Cu3Al2(SO4)(OH)10⋅H2O, and crystal-structure determination

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Fig. 1.Schematic geology of Capillitas, showing the location of the Restauradora vein (modified from Márquez-Zavalía et al , 2020).

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“…Twenty veins are hosted by the volcanic and granitic rocks in ENE and WNW directions (Márquez-Zavalía, 1999) and the mineralisation is very diverse with more than 120 minerals among primary and secondary species described by several authors (e.g. Márquez-Zavalía et al , 1999, 2020; Márquez-Zavalía and Craig, 2004; Márquez-Zavalía, 2006; Putz et al , 2009). It is the type locality for five minerals: putzite (Paar et al , 2004), catamarcaite (Putz et al , 2006), ishiharaite (Márquez-Zavalía et al , 2014), lislkirchnerite (Effenberger et al , 2015) and omariniite (Bindi et al , 2017).…”