Indium: Understanding its Behavior in Magmatic-Hydrothermal Systems Today to Meet Tomorrow's Demand
Tuesday, 16 December 2014
Indium is integral to modern electronic devices, and is an essential component in indium-tin oxide (ITO), an electrically conductive, and optically transparent material that forms the basis for touch screens and high-end LCDs. World-wide production of indium has increased almost seven-fold from 1990 to 2012. Continued increases in production can be aided by better models for the formation of indium-bearing ores, yet little is known about the behavior of indium in magmatic-hydrothermal systems. As a first step toward solving this problem, we performed experiments to evaluate the partitioning of indium between pyrrhotite (po) and silicate melt (m). Experiments were performed at 800 °C, 100 MPa, and fO2 ≈ NNO in a po-saturated, vapor-brine-rhyolite melt system for durations of 5 to15 days. Three separate series of experiments were conducted in which each series differed by the aqueous solution added. The first series of experiments were prepared with pure water, the second series of experiments with a 1.01 M chloride solution and the third series with a 0.35 M CuCl2-bearing starting aqueous solution. These changes in starting material produced changes in the composition of the run product po and glass. The partition coefficient D(po/m) for the pure-water series experiments is on the order of ≈ 10. The addition of chloride-bearing aqueous solution leads to a decrease in the partition coefficient to ≈ 1.5. The copper-bearing experiments yield a D ≈ 3. The lower values for D in the chloride-bearing experiments may be explained by indium-chloride interactions in the melt phase. Although the D does vary depending upon the composition of the starting aqueous solution, an order of magnitude estimate for D, for general modeling purposes, can be made by assuming a value of 4. By using reasonable estimates of the mass fraction of po that crystallizes in crustal magmatic systems, the proportion of indium sequestered by po, during fractional crystallization, can be evaluated. The results indicate that po sequesters less than 0.5% indium from a crystallizing silicate melt because of the small magnitude of the D, and low modal abundances of po. Experimental and modeling results indicate that crystallization of po alone cannot limit the capacity of a magmatic-hydrothermal system to yield an indium-rich ore fluid.