Werner, et al., reported in 2017 that indium has considerable technological and economic value to society due to its use in solar panels and liquid crystal displays for computers, television and mobile devices (see Part I of this study). Yet, without reliable estimates of known and potentially exploitable indium resources, our ability to sustainably manage the supply of this critical metal is limited. Here, in Part III of the authors' series of papers they present the results of a rigorous, deposit-by-deposit assessment of the global resources of indium using a new methodology developed for the assessment of critical metals outlined in Part II of this study.
The authors concluded that at least 356 kt of indium are present within 1,512 known mineral deposits of varying deposit types, including VMS, skarn, epithermal and sediment-hosted Pb-Zn deposits. A total of 101 of these deposits have reported indium contents (some 76 kt of contained In) with the remaining 1,411 deposits having mineralogical associations that indicate they are indium-bearing, yielding ~ 280 thousand tons of contained indium. An additional 219 deposits contain known indium enrichments but have currently unquantifiable contents, indicating that the authors' estimated global resource figure of 356 thousand tons of contained indium is therefore most certainly a minimum.
A limited number of case studies also indicates that a further minimum of ~ 24 thousand tons of indium is present in mine wastes, a total that is undoubtedly smaller than reality given the minimal reporting of mine waste indium concentrations and the extensive volume of historical mine wastes. These quantities are sufficient to meet demand for indium this century, assuming current and projected levels of consumption. However, given indium’s classification as a critical metal, its supply still remains a concern, and hence we have also discussed the economic viability and spatial distribution of the indium resources identified during this study to further our understanding of the geopolitical scarcity of this critical metal.
The authors suggested that the global indium supply chain is fairly adaptable, primarily as the spatial distribution of indium resources deviates significantly from the current supply chains for this metal. The authors claim that they have provided a stronger justification than previously for future studies of indium's criticality, provenance, supply chain dynamics, and stocks and flows in the fields of economic geology and industrial ecology.
While China is by far the dominant producer of refined indium at present, significant quantities of indium exist outside of the current suite of producing countries. This suggests that in the event of a supply restriction, indium capacity could be developed elsewhere, although there are numerous challenges in converting dormant resources into supply. Australia and Bolivia notably contain large indium resources and have not historically produced refined indium, although they may already supply indium-laden Zn concentrates to other countries for refined indium production. The monetary value of reported and inferred indium contents across the authors' databases were also analysed, suggesting that indium may contribute ~ 6% and ~ 10% of a deposit’s resource value in deposits where it is unreported and reported, respectively.
Global indium resources are dominantly hosted by sediment-hosted Pb-Zn deposits, which contain the equivalent of VMS, skarn, epithermal and porphyry deposits combined in their deposit databases, indicating a clear relationship between the base metals concentrated in these deposit types (e.g. Zn and to a lesser extent Cu) and indium abundances. However, the majority of these quantities are inferred, not reported, highlighting the need for better reporting of by-products/critical metals. Overall, the indium grades of many deposits appear sufficient to justify continued improvements in indium processing efficiency. Our study also indicates that robustly compiled and assessed resource estimates such as the one presented here should be the preferred basis of policy development and mineral exploration programs. The authors intend to promote a shift towards greater focus on the impacts of extraction from different resources and by extension the substitutability of indium.
Further research into the nature and adaptability of the global indium market is necessary to understand specific pricing thresholds and the ability of the global resources identified in this study to translate to supply. Ideally, this research would also further explore the potential oversupply of Zn necessary to meet future indium demand.
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