Mineral chemistry of In-bearing minerals in the Santa Fe mining district, Bolivia

Abstract

The Santa Fe mining district is located in the Central Andean tin belt of Bolivia and contains several Sn-Zn-Pb-Ag deposits. From the economic point of view, the most important deposits of the district are Japo, Santa Fe and Morococala. Beyond the traditional metal commodities, the Central Andean Tin Belt could become an exploration target for indium, owing to the potential of the ore-bearing paragenesis with high concentrations of this technology-critical element. In the Santa Fe mining district, the ore occurs as two main types: (a) Sn-rich cassiterite-quartz veins, and (b) Zn-Pb-Ag veins with sphalerite, galena and stannite mineral phases. The In content in igneous rocks is between 1.5 and 2.5 ppm, whereas in the ore concentrate it attains up to 200 ppm. The 1,000×In/Zn ratio in concentrate ranges from 25 up to 4,000. Exceptionally high In values were found in sakuraiite from Morococala deposit (2.03 wt%). Sakuraiite in this deposit shows evidences for a link between stannite and kësterite trend of solid solutions. There is a noteworthy exploration potential for strategic metals in this district and even in similar deposits elsewhere in the Central Andean tin belt.

Mineralogy and Distribution of Critical Elements in the Sn–W–Pb–Ag–Zn Huanuni Deposit, Bolivia

“…The ore mineralogy and paragenetic sequences in all these deposits are very similar, as already noticed in early works in the region [12][13][14]. The contents in critical elements (i.e., In, Ga, Ge) in these deposits are also variable, normally in the form of minor or trace contents in sphalerite, cassiterite, stannite-kësterite, and a number of sulphides and sulphosalts [5,6,[8][9][10], rarely as minerals in which such elements are stoichiometric constituents like petrukite, sakuraite or argyrodite. In the case of Huanuni, indium also occurs exceptionally as a constituent of a supergene carbonate with unknown mineralogical characteristics ( Figure 6F).…”

“…Beyond the relatively limited collection of variables with which it is possible to characterise a given ore deposit as part of a deposit type or family, the Bolivian tin deposits (at least those formed during the Neogene) stand collectively as a mineral system, in the sense of references [51][52][53]. Recent studies in critical element-bearing deposits of the region [4][5][6][7][8][9][10], along with this one, describe deposits whose depositional models vary between xenothermal or mesothermal (i.e., Huari Huari, Huanuni) and epithermal (i.e., Poopó), whereas others (i.e., Ánimas-Chocaya-Siete Suyos) exhibit intermediate characteristics between those. The ore mineralogy and paragenetic sequences in all these deposits are very similar, as already noticed in early works in the region [12][13][14].…”

“…The 2017 production was 8415 tonnes of tin and, despite a fall in production below 7000 tons in 2018, the tin production in Huanuni still accounts for over a half of the total production of Bolivia. These deposits belong to the Bolivian Tin (Sn-W-Ag-Sb-Bi) Belt ( Figure 1) that has significant critical metal resources (In, Ge and Ga [1][2][3][4][5][6][7][8][9][10]). Increasing international demand is envisaged for In, Ge and Ga, particularly in emerging technologies such as the production of photovoltaic cells (In and Ga), optical fibre and infrared optical technologies (Ge).…”

Indium Mineralization in the Volcanic Dome-Hosted Ánimas–Chocaya–Siete Suyos Polymetallic Deposit, Potosí, Bolivia

“…A number of polymetallic mineral deposits from the central Andes in Peru, Bolivia, and northern Argentina are listed as major In hosts [11,34,35]. Chief among them are xenothermal polymetallic-vein deposits hosted by the Andean tin belt [29,[36][37][38][39]. Whole-rock geochemical analysis of ore samples (including composites) from SW Bolivia deposits has revealed In contents as high as 5740 ppm for Potosí, 3080 ppm for Huari Huari, 2730 ppm for Bolivar, and 2510 ppm for Ánimas-Siete Suyos deposits [37].…”

“…A femto-second laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICP-MS) study combined with EPMA by Murakami and Ishihara [29] yielded concentrations of In as high as 7.89 wt.% in Fe-rich ("black") sphalerite in a sample from the Huari Huari deposit, and concentrations up to 5.08 wt.% In in a sample from the Potosí deposit; in addition, these authors determined concentrations up to 18 wt.% In in an undetermined Zn-In mineral. In the Santa Fe mining district, the contents of In in ore are up to 200 ppm and concentrations of In as high as 2.03 wt.% In were determined in sakuraiite [38]. In the Huari Huari deposit, an EPMA study that is based on a large number of ore samples distributed along the mineralized zones allowed for Torró et al [39] to determine that an early generation of sphalerite rich in Cu, and in part co-crystallized with stannite, was the main host for In, and pointed out that the highest concentrations of this metal are found in a central position of the deposit complex.…”