Indium

Indium was discovered in 1863 by Ferdinand Reich and Hieronymus Theodor Richter at the Freiberg School of Mines, Saxony, Germany while they were studying zinc ore (sphalerite ore with traces of pyrite, arsenopyrite, galena, chalcopyrite, stannite) from the local Freiberg polymetallic vein-type deposit (‘Himmelfahrt Fundgrube’) for thallium (Fig. 1.1; Reich and Richter 1863a,b). The spectroscopy of unknown coatings led to the identification of characteristic indigo blue spectral lines instead of the thallium spectrum. The new element was named indium. Reich and Richter (1863a) noted: “... Es zeigte (sich) keine Thalliumlinie, dagegen eine indigoblaue bisher unbekannte Linie. Nachdem es gelungen war, den vermutheten Stoff, wenn auch bisher nur in äusserst geringen Mengen, theils als Chlorid, theils als Oxydhydrat, theils als Metall darzustellen, erhielten wir, nach Befinden nach dem Anfeuchten mit Chlorwasserstoffsäure, im Spectroskop die blaue Linie so glänzend, scharf und ausdauernd, dass wir aus ihr auf ein bisher unbekanntes Metall, das wir Indium nennen möchten, zu schliessen nicht anstehen” (“[...] It appeared no thallium line but an unknown indigo blue line. Following the preparation of small quantities of the material as chloride, hydroxide and metal, we got, after subtle moistening with hydrochlorine acid, a glancing, sharp and persistent blue line in the spectroscope. We concluded an unknown metal which we beg to inform you we want to call indium.”). Further analytical work led to the identification of sphalerite as the general mineral host for indium (Reich and Richter 1863b). Subsequent work on zinc flue dusts from 2.15 tons of zinc from the Freiberg ore deposit yielded about one kilogram of the pure metal. An ingot of 0.5 kilogram of this material was first exhibited during the world exhibition in Paris in 1867.

The most complete data of indium concentrations in different rock-types and minerals are given by Linn and Schmitt (1974; in: Wedepohl 1974).

Indium occurs in many different types of ore deposits including volcanic-hosted and sedimentary exhalative massive base metal sulfide deposits, epithermal-style gold deposits, porphyry copper deposits, polymetallic base metal vein deposits, granite-related vein-stockwork tin-base metal deposits, and skarn deposits. A wide variety of indium-bearing ore deposits is described in the literature. Figure 3.1 and Chapter 10.2 summarize and classify the worldwide occurrences of known indium-bearing ore deposits and ore provinces.

The southwestern Hokkaido metallogenetic province hosts the Toyoha lead-zinccopper-silver-indium epithermal vein-type deposit, which belongs to the Jozankei-Chitose ore belt. Its indium content, mineralogy, and distribution has been described in detail in Chapter 3.5.1. Other indium occurrences are described from the Shakotan ore belt (Narita et al. 1965). The tin-bearing polymetallic base metal Kunitomi (Kinoshita 1965), Ohe, Inakuraishi, Tamakawa, and Taishu deposits are reported to contain elevated indium concentrations (cf., Fig. 3.18; Murao et al. 1991). Genetic relationships suggest an epithermal-style or polymetallic vein-type origin of these deposits.

Provinces of indium-bearing ore deposits can be delineated with respect to time and space. Ore deposits enriched in indium are commonly associated with oceanic or continental plate margins and orogenic belts. Within the different metallogenic provinces there have been periods of time in which the deposition of indium-bearing ore deposits was most pronounced (Figs. 5.1 and 5.2).

Indium occurs in different types of ore deposits of all ages, from the presently-forming deposits at modern, actively spreading ridges and fumarole precipitates of active volcanoes to deposits in the Archean volcanic strata of the Abitibi and Murchison greenstone belts of Canada and South Africa, respectively. Indium deposits encompass many different types of ore deposits, including volcanic- and sediment-hosted exhalative massive sulfide deposits, epithermal deposits, polymetallic base metal vein deposits, granite-related tin-base metal deposits, and skarn deposits. These deposits are commonly associated with active oceanic or continental plate margins and orogenic belts with steep geothermal gradients due to magmatic activity. Close affinities to former active subduction environments and/or collision processes are also reflected by the formation ages of indium-bearing deposits which clearly scatter around geotectonically active periods, namely the Ordovician, the Carboniferous, the Late Cretaceous, and Tertiary (cf., Figs. 5.1–5.3). Different crustal environments of indium deposition are shown schematically in Figure 6.1.

Indium is principally recovered as a by-product of zinc processing. The known resources of indium therefore are closely related to the deposits of zinc currently being exploited. The indium content of zinc ores mined in 1995 was estimated at just below 150 tons, increased to 175 tons in 1997 and significantly to 215 tons in 1999. The estimated world refinery indium production reached approximately 220 tons in the year 2000 (Brown 2001) which represents an almost fifty per cent increase over the last five years. The principal sources of zinc ores and associated indium are Canada, Australia, China, Peru, and the USA. These five countries accounted for over 60% of the total mine production of zinc in 1995 (Roskill Information Services 1996). The estimated mine production of indium in 1995 is given in Table 7.1, based on the assumption that sphalerite ores contain 67% zinc and an average of 15 ppm indium (Roskill Information Services 1996).

World reserves are reported to be sufficient to meet anticipated demand for the next decade. Canada has greater approved resources of indium than any other country. It hosts about 27% of the world reserves and 35% of the world reserve base. Reserves were estimated at 600 tons in 1994 and 700 tons in 2000. Its current reserve base is 2,000 tons of indium. Canada has become one of the world’s largest indium producing country. Most indium is recovered from lead-zinc-silver and zinc-copper ores of sediment-and volcanic-hosted exhalative origin. Corresponding amounts for the United States are 12% (300 tons) and 11% (600 tons), respectively (Brown 1996, 1997, 1999, 2001). Second largest indium reserves are located in China which accounts for current reserves of 400 tons (15%) and a reserve base of 1,000 tons (18%). Largest reserves may be expected in the base metal-rich deposits of the Dachang district.

Indium demand has grown strongly in the last few years at an average of ten per cent per year. Exceptional growth in demand has come from Japan and the Republic of Korea, which accounted for more than fifty per cent of indium consumption between 1995 and 2000 (Roskill Information Services 1996; Brown 1999). More than half of Japanese and Korean demand is consumed in applications for indium-tin oxide (ITO) and indium prices worldwide are now closely linked to the fortunes of ITO applications, as this sector has overtaken all other end-uses for indium. Flat bed display applications account for more than half of world indium demand.

The tables in this chapter summarize the characteristic features of some indium-bearing deposits for which indium grades and other substantial information are available.