Critical Metals Handbook

Gus Gunn, Gus Gunn

• Publisher: American Geophysical Union
• Year: 2014
• ISBN:
  9781118755211
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Mankind is using a greater variety of metals in greater quantities than ever before. As a result there is increasing global concern over the long-term availability of secure and adequate supplies of the metals needed by society. Critical metals, which are those of growing economic importance that might be susceptible to future scarcity, are a particular worry. For many of these we have little information on how they are concentrated in the Earth's crust, how to extract them from their ores, and how to use, recycle and dispose of them effectively and safely. Published with the British Geological Survey, the Critical Metals Handbook brings together a wealth of knowledge on critical metals and provides a foundation for improving the future security and sustainability of critical metal supplies. Written by international experts, it provides a unique source of authoritative information on diverse aspects of the critical metals, including geology, deposits, processing, applications, recycling, environmental issues and markets. It is aimed at a broad non-specialist audience, including professionals and academics working in the exploration and mining sectors, in mining finance and investment, and in mineral processing and manufacturing. It will also be a valuable reference for policy makers concerned with resource management, land-use planning, eco-efficiency, recycling and related fields.

1. Metal resources, use and criticality

T.E. GRAEDEL¹, GUS GUNN² AND LUIS TERCERO ESPINOZA³

¹ Center for Industrial Ecology, Yale University, New Haven, Connecticut, USA
² British Geological Survey, Keyworth, Nottingham, UK
³ Fraunhofer Institute for Systems and Innovation Research ISI, Karlsruhe, Germany

The geology and technology of metals

Key concepts

In a book such as this, which is intended for a broad audience, it is important to discuss some key concepts and terminology relating to minerals and metals which, although widely used, are seldom defined. In some cases the meaning may be obvious, while in others they are anything but obvious. To avoid confusion and misuse, and to minimise the risks of misunderstanding, we define in the first part of this chapter certain fundamental terms that will provide a foundation for the chapters which follow.

Minerals are essential for economic develop-ment, for the functioning of society, and for maintaining our quality of life. Everything we have or use is ultimately derived from the Earth, produced either by agricultural activities or by the extraction of minerals from the crust. Unlike crops, which are grown for the essential purpose of maintaining life by providing the nutrients we need to survive, mankind does not generally need the minerals themselves. Rather, minerals are extracted for the particular physical and chemical properties their constituents possess and which are utilised for specific purposes in a huge range of goods and products. Following some form of processing and purification, a mineral, often in combination with certain other minerals, is incorporated into a component which is used in a product. It is the need or desire for the products that generates a demand for minerals, rather than demand for the mineral itself. As a result, there is always the possibility of finding an alternative material to provide the required functionality. The only exceptions to this possibility are nitrogen, phosphate and potash, which are essential to life itself and cannot be substituted.

The term ‘mineral’ is used to describe any naturally occurring, but non-living, material found in, or on, the Earth’s crust for which a use can be found. ¹ Four principal groups of minerals may be distinguished according to their main uses:

1. Construction minerals – these comprise bulk minerals such as sand and gravel, crushed rock and clay, which are used for making concrete and bricks to provide foundations and strength in buildings, roads and other infrastructure. They are produced in large quantities at low cost from extensive deposits that are widely distributed at shallow depths in the Earth’s crust.

2. Industrial minerals – these are non-metallic minerals that, by virtue of specific chemical or physical properties, are used for particular applications in a wide range of industrial and consumer products. There are numerous industrial minerals but the most widely used include salt, gypsum, fluorspar, and kaolin. They tend to occur in large quantities but only at relatively few locations. They generally require specialist processing in their production and consequently they are relatively expensive.

3. Energy minerals – these are minerals such as oil, gas and coal that are used to generate energy that is captured when they are burned. They are used in the production of electricity, in fuels for transportation and heating, and also in the manufacture of plastics. Coal is relatively easy to find and cheap to extract; in contrast, oil and gas are generally difficult to find and extract and, therefore, command high prices.

4. Metals – metals are distinguished by distinctive chemical and physical properties, such as high electrical and thermal conductivity, malleability, ductility and the ability to form alloys. They are exploited for a multitude of purposes and some, such as iron, aluminium and copper, are used in huge quantities. Other metals with fewer or more specialised applications, such as platinum, indium and cobalt, are used in much smaller quantities, ranging from tens to hundreds or thousands of tonnes per year. Economic deposits of metals are rare and difficult to locate. The metal-bearing ores are expensive to mine and to process, and consequently metals command a high price.

Another term in common usage is ‘mineral commodity’ which is used to refer to any mineral raw material that can currently be extracted from the Earth for a profit.

The abundance of individual metals in the Earth’s crust varies greatly (Figure 1.1) and influences the costs involved in locating, mining and preparing the metals for use. Some of the major industrial metals, like iron, aluminium and calcium, have crustal abundances similar to the main rock-forming elements, such as oxygen, silicon and calcium, and are several orders of magnitude more abundant than many of the widely used base metals such as copper, lead and zinc. Many others, such as the precious metals gold and platinum, are considerably rarer. However, crustal abundance is only one factor that influences production costs. Some metals that are common in the crust, such as magnesium, aluminium and titanium, occur in forms that need a high input of energy to separate them from their ores, thus making them relatively expensive. It is also important to note that the localised concentrations of metals that can be exploited economically result from unusual geological processes. Consequently, the distribution of economic deposits in the Earth’s crust is highly dispersed, with some regions richly endowed in metals and others largely devoid of them. Furthermore, our knowledge of the processes that lead to the concentration of particular metals in the Earth’s crust varies widely. For metals that are used in large quantities, such as copper and zinc, we have a reasonably good idea of where and how to locate new deposits. However, for many of the scarcer metals, especially those that have been brought into wide use relatively recently, information on their occurrence, concentration and processing is generally very limited.

It is a complex and expensive process to prove economic viability once an unusual enrichment of a potentially useful mineral or assemblage of minerals, commonly referred to as a ‘mineral occurrence’, is discovered. This involves determination of the quantity of mineral present and the assessment of the optimum methods for mining and processing the ore. Apart from geological processes that determine the physical availability of a metal there are a host of other factors that influence access to the resources in the ground – cheap labour or cheap power may confer a competitive advantage to a particular country or region while, on the other hand, government regulation, fiscal and administrative requirements, or social and cultural constraints may restrict or prevent access to potentially valuable deposits.

The timescale from discovery of a mineral occurrence to mine production is generally a long one. It commonly takes more than ten years to evaluate the mineral resource in the ground, to raise the funds to build a mine, to acquire the necessary regulatory approvals and to secure the trust and cooperation of the local communities. Once these are in place, and provided that favourable economic conditions prevail, the mine and supporting infrastructure can be built and mineral extraction can commence.

Figure 1.1 The abundance of the chemical elements in the Earth’s upper continental crust as a function of atomic number. Many of the elements may be classified into partially overlapping categories. (Modified from USGS, 2002.)

Definitions and terminology

The costs involved in bringing a new mine into production today commonly amount to hundreds of millions of dollars or, in the case of a large new mine on a greenfield site, more than a billion dollars. A metal mine typically operates for a minimum period of a decade although, depending on economic and other circumstances, it may continue for more than 100 years. Given the size and duration of these investments it is essential that all parties – the mining company, investors, local communities, governments and regulators – ‘speak the same language’ and fully understand their obligations and expectations throughout the life of the mine, from construction to operation, closure and site rehabilitation. Without effective communication, based on clear unambiguous terminology, such understanding can never be attained and problems may well arise at some stage.

The first steps in determining the economic viability of a mineral deposit are the exploration and resource assessment stages which involve drilling and detailed sampling to determine the quantity of material present and its quality – or, in the case of a metallic mineral deposit, its grade, which is the percentage of metal that the rock contains. The consistent and correct use of terminology is essential for the reporting and assessment of exploration results and to underpin sound decision making. Without this, discrimination between genuinely economic deposits and those of marginal or unproven economic significance is impossible.

The assessment is, therefore, based on a system of resource classification the main objective of which is to establish the quantities of minerals likely to be available in the future. Many governments now require that resources and reserves are reported according to internationally accepted codes in countries where the company’s stock is listed. Adherence to such reporting standards ensures full and transparent disclosure of all material facts and is intended to provide all parties with reliable information on which to base investment decisions. Such codes include the Joint Ore Reserves Committee (JORC) code in Australia and the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) reporting standard which is referred to as National Instrument (NI) 43-101. Following an era of industry self-regulation, these codes were developed in response to scandals in Australia and Canada where many people were misled by speculation and rumour leading to unfounded spectacular rises in share prices and, soon after, rapid falls. In the short term these led to huge financial losses and, in the longer term and more significantly, to a prolonged loss of investor confidence in the mining industry. Accordingly these, and other codes, were developed to set minimum standards of reporting of exploration results, mineral resources and ore reserves. They provide a mandatory system of classification of tonnage and grade estimates according to geological confidence and technical/economic considerations. They require public reports to be prepared by appropriately qualified persons and provide guidance on the criteria to be used when preparing reports on exploration results, mineral resources and ore reserves.

Resources and reserves

The key elements of the reporting codes are the terms ‘resources’ and ‘reserves’, which are frequently confused and/or used incorrectly. They are, in fact, fundamental to the distinction between a mineral deposit that is currently economic (reserves) and another which may become economic in the future (resources).

A mineral ‘resource’ is a natural concentration of minerals or a body of rock that is, or may become, of potential economic interest as a basis for the extraction of a commodity. A resource has physical and/or chemical properties that makes it suitable for specific uses and is present in sufficient quantities to be of intrinsic economic interest. To provide more information about the level of assurance, resources are divided into different categories which, in the JORC code, are referred to as measured, indicated and inferred resources, reflecting decreasing level of geological knowledge and hence decreasing confidence in their existence.

It is important to note that identified resources do not represent all the mineral resources present in the Earth, a quantity that is sometimes referred to as the ‘resource base.’ In addition to identified resources, there are resources that are undiscovered or unidentified (Figure 1.2). Undiscovered resources may be divided into hypothetical and speculative categories. Hypothetical resources are those which may reasonably be expected to occur in deposits similar to those known in a particular area under similar geological conditions. Speculative resources are those which may be present either in known deposit types in areas with favourable geological settings but where no discoveries have yet been made or in new types of deposit whose economic potential has not yet been recognised.

A miner...