C P Broadbent (Wardell Armstrong), R Seltmann (Natural History Museum), J Drielsma (Euromines),
W Reimer (Geokompetenzzentrum Freiberg), M Cox (MMTA)
Because there is no exploration and little process technology development for metals when their by-production fully satisfies demand, by-product resources and reserves are consistently underestimated. Assessment methods that take resource or reserve estimates as inputs tend therefore to exaggerate supply risks associated with by-products. For the same reason, claims as to whether current by-products will ever be economically mined as a main product could be highly speculative(1).
DEFINITION OF RESOURCES AND RESERVES—JORC
A mineral resource is a concentration of material that has reasonable prospects of economic recovery. A mineral reserve implies technical feasibility and economic viability and ALL modifying factors have been considered (Fig. 1). To quote a resource and / or reserve, considerable work has to have been done. In the case of most by-products, they may (or may not) be known in the deposit, but rarely has any detailed metallurgical processing work (modifying factor) been done—hence, they will never appear in reserve and only occasionally in resource statements. This may limit the promotion of the reserve for investments or will indicate higher investment costs and / or requires longer to reach a break-even position.
MAJOR METALS—e.g. copper (Cu)
For major metals, resources and reserves are reasonably well described, but as some elements are produced mostly as by-products from production of a major commodity, their appearance in resource and reserve statements is much more problematic. Copper ores provide a good example. Many important elements are produced as by-products from copper production (Fig. 2). Over 80% of total world production of rhenium (Re), selenium (Se) and tellurium (Te) is produced as a by-product from primary copper production. Most, if not all, of these by-product (elements) will not have featured at all in reserve statements prepared at the relevant feasibility studies required pre-mine start up. Whilst the major metals are reasonably well known, it is a different story for minor metals. Resource, reserve and even basic production data can be scarce or not available.
The BGS and the USGS publish World Mineral Production statistics (most recently available for 2012 and 2014 respectively). However, reserves data are dynamic and will change with time. In essence reserves may be considered a working inventory of a mining company’s supply of an economically extractable mineral commodity. The USGS has now discontinued the publication of its reserve base data.(3)
Reserves will only ever be a relatively small proportion of the known resources. Future supplies of minerals will, in the very short term, be derived from reserves. In the mid to long term, however, they will be derived from currently undiscovered resources, in deposits that will be discovered in the future and material recycled from current in-use stocks, or minerals in waste disposal sites. This situation leads to seemingly anomalous results. For example, in 1970, identified and undiscovered world copper resources were estimated to contain 1.6 billion tons of copper, with reserves of about 280 million tons of copper. Between 1970 and 2011 about 400 million tons of copper have been produced worldwide, but world copper reserves in 2011 were estimated to be 690 million tons—more than double those of 1970.
Production statistics are generally more reliable than ‘reserve’ data. The BGS now publishes data on 73 commodities (Ref: World Mineral Production 2008-2012 Centenary edition(4)) compared with 39 commodities in the original data set. Many of the commodities that have been added might be termed ‘technology metals’ and are critical to new technologies, such as use in clean energy production, modern communications and computing—but it is incorrect to regard the commodities themselves as being ‘new’. The BGS data are available for some metals commonly produced as a by-product of a major metal commodity, but in some cases are absent, for example, indium data consist of refined metal production data only, and no data are given for mined ore production, and even with these data, most are presented as estimated values only.
MINOR METALS—e.g. tin (Sn), tungsten (W), indium (ln)
Given this background, it is not surprising that some of the best available data for reserves and resources are those produced by companies involved with the mining, processing or refining of these by-product elements.
Data are provided below for world deposits containing indium (Fig. 3)(5) and tin (Fig. 4)(5).
These ore data originate from Anglo Saxony Mining(5,6), and the indium resources will only represent those that are known (i.e., predominantly Sn deposits in which chemical analysis for In was carried out). They do not represent, in any way, world resources (or reserves) for indium.
Similar bubble diagrams (Figs. 5-6) are commonly presented for main commodities such as WO3(7) and Sn(8) which tend to be a major component of the ore, however, almost certainly these will also appear as by-products in other ores and will certainly be under-represented in both resource and reserve data.
Once again these bubble diagrams for WO3 and Sn were created by mining companies, based on their in-house archives and probably reflect the best available data. Metals such as indium (In) and tungsten (W) are included on the list of 20 Critical Raw Materials, and care has to be taken when evaluating the resource and reserve base for these commodities. Premier African Mineral (PAM) who produced the bubble diagram for W (Fig. 5) has not investigated the presence of co-existing by-product metals such as Sc, In, Ga, Ge, etc. at all. Indeed, these have been rarely, if at all, analysed for by PAM. Hence, there may be significant unreported inventories of these by-products associated with the deposits quoted in the diagram. A very obvious example is that of Sn and W hosting considerable by-products. The geological setting of Sn and W, in particular, means that a range of other by-product metals / elements could be present, and often these potential by-products are not included in Reserve Statements and hence cannot show in financial evaluations.
The Tellerhäuser Tin Project is located in Germany and being evaluated by Anglo Saxony Mining. A resource (Sn) estimate was prepared in 2015 by Simon Tear of H&S Consultants out of Brisbane, Australia.
It is interesting to note that the resource estimate grade / tonnage curve produced in Figure 7(5) only takes into account Sn. The economics may be significantly different, thereby allowing lower cut off grades, if by-products (especially indium) were taken into account. The resource (and subsequent reserves) will be totally different if all valuable by-products are included. However, to do this, it is likely that new processing techniques will be required, especially innovative mineral processing technologies to separate the different mineralogical (chemical) constituents of the ore. Process flow sheets for by-products must be economically viable in their own right and ‘contribute’ to mining minor metals, but not vice versa. This still requires extensive R&I work.
European R&I into mineral processing has been generally lacking in the last 20 years, due in part to the reduced size of the European mining sector and decline of mining / mineral processing taught at universities and colleges. For example, in the UK, 30 years ago mineral processing was taught at the Royal School of Mines (RSM—London Imperial College), Camborne School of Mines (CSM, Cornwall), Birmingham University, Leeds University, Nottingham University and Cardiff University. Whereas only really CSM (now as part of the University of Exeter) retains significant mineral processing teaching capability.
The EU call topic SC5-ll-2015: New Solutions for Sustainable Production for Raw Materials, Flexible Processing attempted to re-address this situation, and one of the successful projects attracting EU funding was FAME (Figs. 8-9)(9).
An objective of FAME is to help maintain skills, especially mineral processing expertise, within Europe to enable exploitation of complex ores. These skills are exactly what will be needed to enable exploitation of all valuable components (i.e., by-product recovery) from ores in a sustainable mining context.
Reasonably robust resource / reserve estimates exist for the major metals, e.g. Cu. However, many of these ‘major’ metal producers are also significant producers of minor metal by-products. Whether these by-products are shown in reserve statements is dependent upon a number of factors, especially whether they are actively explored for and whether viable process flow sheets exist so that the economically viable recovery of the minor element can be proven. If by-production fully satisfies demand, there is no active exploration, and resources and reserves are simply not discovered and reported at rates comparable to those of major metals(10). Similarly, if no viable process flow sheet exists, a reserve (and in some instances a resource) can not be quoted to an international standard such as JORC.
For ore deposits where there is no dominant major metal, the position is slightly different to that of the majors. The grade/tonnage relationship and life of mine relationship is far more complex, and it is often much more difficult to demonstrate economic viability and hence, quote reserves.
Whilst utilisation of all components in ores represents the most sustainable approach to mining, it is clear that without other incentives (for example a change in government policies), many of the minor metals (by-products) will not appear in reserve estimations, as their financial and technical viabilities are often not proven. Furthermore novel, or innovative, process flow sheets are often required to recover all the potential metals of value (i.e. enable recovery of all potential by-products). Until enhanced, flexible mineral processing options have been developed, as well as in some instances improved refining techniques (especially with respect to smelting technology), many potential sources of by-products will not be realised. Without improvements to the process at both the mineral processing (beneficiation) as well as the metal extraction (smelting and refining) stage, to ensure effective recovery, by-products are unlikely to appear in reserve estimates. This situation may become crucial in attracting investors if prices of by-product metals continue to rise, or by-product metals will become even more strategic.
There are current EU initiatives in the Horizon 2020 programme designed to address some of the (mineral) processing and metallurgical challenges but, perhaps, different financial / policy scenarios will be required before resource and reserve estimates reflect accurately the actual availability of many by-product metals. Currently estimates must therefore be treated with caution and will under-estimate resources and reserves of these metals.
1: The JORC Code 2012 Edition, Prepared by the Joint Ore Reserves Committee of the Australasian IMM, Australian Inst. of Geoscientists and Mineral Council of Australia.
2: Copper Alliance (http://sustainablecopper.org/about-copper/33-more-than-copper.html)
3: Resource Data: the Providers perspective (USGS) – J. Hammarstrom. (http://www.euromines.org/events/2015-10-14-mineral-resources-lcia-mapping-path-forward)
4: World Mineral Production 2008-2012 British Geological Survey, T.J. Brown et all. 2014.
5: Presentation by Anglo Saxony Mining (Saxore / Treliver Minerals), ITRI Conference Shanghai 2015.
6: Internal presentation by Anglo Saxony Mining
7: Premier African Minerals (www.premierafricanminerals.com)
8: Kasbah Resources Presentation, ITRI Conference Shanghai 2015
9: FAME (www.fame-project.eu)
10: Drielsma J, Russell-Vaccari A, Drnek T, Brady T, Weihed P, Mistry M, Perez Simbor L (2015) Mineral Resources in Life Cycle Impact Assessment – Defining the Path Forward. Int J Life Cycle Assess (DOI 10.1007/s11367-015-0991-7)