Professor Barbara Dutrow, BSc, MSc, PhD

Abstract:

Minerals, the naturally occurring crystalline chemical solids, comprising planet Earth underpin many societal advances. From the beginnings of humankind, Earth’s minerals have been essential for artistic expression, scientific and technological advances, and for the well-being of society. Prior to written language, paintings made of mineral pigments decorated caves. Personal adornment exploited a wide variety of mineral gemstones that continues today. Early Homo sapiens separated different minerals based on their physical properties, advancing uses for food gathering and protection. Utilization of these minerals defines the Ages of Humankind: Stone, Bronze, Iron and Technological ages [1]. Ben Franklin used the pyroelectric and piezoelectric properties of the mineral tourmaline for supporting his theory of electricity.  Diamond, nature’s hardest substance, is not only a highly prized gemstone but has a myriad of applications such as a substrate for electronics due to the exceptional 3D heat transporting properties. Two areas underscore the criticality of minerals to the science and technological needs leading to a more sustainable future.

The chemical constituents extracted from minerals power advances in the clean energy transition. Predictions indicate that total mineral demand from clean energy technologies will double to quadruple depending on the scenario [2]. Battery storage materials (lithium, graphite, cobalt, nickel, manganese) account for nearly half of the mineral requirements. Some minerals find application essentially as the occur, e.g. graphite and copper, whereas others are refined to extract their constituents; the critical elements needed across the spectrum of existing and proposed new technologies. As examples, rare earth elements (REEs), with unique properties essential to hybrid and electric cars, high-strength magnets for wind turbines and as components in solar photovoltaic cells, are housed in unusual minerals (RE phosphates) or adsorbed onto their surfaces (e.g. clays). Uncommon geochemical environments are required to concentrate these trace elements, with an average of ~169 𝜇g/g in the continental crust [3], into deposits that can be mined profitably. A 50% increase in demand is projected in 10 years [2]. REE deposits are not uniformly distributed across Earth’s surface, creating countries with few resources and those with abundant resources. Lithium, a critical element for batteries, is extracted largely from minerals and must similarly be concentrated into an extractable ore. Lithium is rare in the bulk silicate earth (~1.39 𝜇g/g on average) but concentrated in the upper continental crust from ~21 𝜇g/g to 7,000 𝜇g/g [4]. Of the 124 known Li minerals, about 73% are silicates of which about four occur in sufficient quantities to be mined. Nearly 50% of the world’s lithium derives from minerals in one country, Australia [4]. While many countries have reserves, also in brines, over 40 times the current demand will be needed by 2040 in the scenario of rechargeable batteries [2]. From aluminum to zinc, the elements extracted from minerals form the basis for advanced materials. The global energy transition has far-reaching consequences for mineral demand over the next few decades.

Geothermal energy is a sustainable and clean source of power that harnesses heat from within the Earth, typically involving circulation of hot fluids. However, understanding the long-term evolution of high-temperature geothermal systems remains challenging. Two primary approaches are used to investigate these systems: (1) numerical modelling of geothermal processes, and (2) analyzing minerals that form within the system. Geothermal (hydrothermal) systems are modelled as a complex interplay of non-linear thermal, mechanical, and chemical feedback among fluids and minerals [5]. Certain minerals can record thermal evolution by acting as natural thermometers. One such mineral is tourmaline, a chemically complex borosilicate that incorporates the fluid-mobile element boron. Tourmaline has an exceptional ability to capture geochemical and thermal conditions during its growth. Its crystallographic sectors partition chemical elements in a way that allows sector zoning to function as a mineral thermometer [6]. When geochemical conditions change rapidly, oscillatory zoning may develop, overlaying the intersector partitioning to create a detailed record of the system's thermal history. This approach is demonstrated by sector-, and oscillatory-zoned tourmalines from the Siglo XX hydrothermal system in Bolivia. Chemical analysis by the electron microprobe indicates that temperatures during tourmaline formation occurred at about 380°C, gradually dropped to around 300°C, and later rose again to approximately 470°C when growth ceased. Such findings showcase the power of mineral-based methods to reconstruct the thermal evolution of geothermal systems and complement traditional modelling techniques for understanding the system’s lifetime. As the world strives to a sustainable future, minerals play an essential role for the new, carbon-free, advanced technologies.