Abstract
The Huari Huari deposit, Potosí Department in SW Bolivia, hosts polymetallic stratiform and vein mineralization of Miocene age with significant concentrations of the critical metal indium (In). Vein mineralization records document early crystallization of quartz and cassiterite followed by prominent associations of sulfides and sulfosalts. The earliest sulfide was arsenopyrite, followed by pyrrhotite, and progressively giving way to pyrite as the main iron sulfide, whereas Cu–Ag–Pb sulfosalts constitute late hypogene associations. Sphalerite is the chief ore mineral, and its crystallization is extended during most of the mineralization lifespan as evidenced by its initial cocrystallization with pyrrhotine, then with pyrite, and finally with Ag–Pb sulfosalts. The composition of sphalerite varies from early to late generations with a continuous decrease in FeS that attests to a decrease in temperature, which is constrained to vary from ~450 to <200 °C, and/or an increase in f(S2), both congruent with the described paragenetic sequence. Indium concentrated mostly in the structure of Fe-rich sphalerite (up to 3.49 wt. %) and stannite (up to 2.64 wt. %) as limited solid solutions with roquesite in the (Zn,Fe)S–Cu2FeSnS4–CuInS2 pseudoternary system. In sphalerite, In shows a strong positive correlation with Cu at Cu/In = 1, suggesting its incorporation via a (Cu+ + In3+) ↔ 2Zn2+ coupled substitution, and it does not correlate with Fe. In stannite, In shows a moderate, negative correlation with Cu and Sn, and an In3+ ↔ (Cu+ + ½ Sn4+) coupled substitution is suggested. Coexisting sphalerite and stannite yielded the highest In concentrations and crystallized at temperatures between 350 and 250 °C. Copper activity probably played a major role in the accumulation of In in the structure of sphalerite since In-bearing sphalerite coexisted with the deposition of stannite, shows high concentrations of Cu (up to 0.13 atoms per formula unit (a.p.f.u.)) in its structure, and hosts exsolutions of stannite and chalcopyrite. Distribution on the district scale of In suggests an input of hydrothermal fluids richer in Cu in the central position of the mineralizing system, represented by the Antón Bravo vein.
Highlights
There is a growing concern for securing reliable, sustainable, and undistorted access to raw materials fundamental to the global economy
Indium (In), which is at the heart of our research, is among the raw materials categorized by the European Commission and the U.S Geological Survey as critical because of its high economic importance combined with a high supply risk [1,2]
Indium is an essential component in bonding, high-purity and low-temperature alloys, soldering and thin films used in the manufacture of LCDs, flat panel displays, touch screens, solar panels, etc
Summary
There is a growing concern for securing reliable, sustainable, and undistorted access to raw materials fundamental to the global economy. In order to illustrate such importance, this deposit was the main source for raw material obtained by the Indium Corporation of America between 1976 and 1978, and it provoked a global shortage of this metal upon its closure in 1978 [22] During this period, the mine was operated by Empresa Minera Caballo Blanco. Laser ablation (LA)-ICP-MS determinations performed on sulfide minerals from four Bolivian deposits have shown wide ranges of indium concentrations in sphalerite even on the single crystal scale [16] These previous studies shed light on the mineralogical expression of indium in sulfide ore and on concentration and tonnage estimates for some Bolivian deposits. Specific objectives include: (1) to determine the concentration of indium in mineral phases and to identify those that preferentially concentrate this metal in the primary ore and (2) to comprehend the spatial distribution of indium on the mineralized district scale at Huari Huari
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