A review of high-purity quartz for silicon production in Australia

Abstract

High-purity quartz (HPQ) is the only naturally occurring and economically viable source for the production of silicon. Silicon is a critical mineral, and a key component in modern technologies such as semiconductors and photovoltaic cells. Critical minerals support the move towards a greater reliance on electrification, renewable energy sources and economic security. The global transition to net zero carbon emissions means there is a growing need for new discoveries of HPQ to supply the silicon production chain. HPQ deposits are identified in a multitude of geological settings, including pegmatites, hydrothermal veins, sedimentary accumulations and quartzite; however, deposits of sufficient volume and quality are rare. Quartz is abundant throughout Australia, but the exploration and discovery of HPQ occurrences are notably under-reported, making assessment of the HPQ potential in Australia extremely difficult. This paper presents a much-needed summary of the state of the HPQ industry, exploration and deposit styles in Australia.

KEY POINTS

1. High-purity quartz (HPQ) is a key material for the manufacture of photovoltaic cells, semiconductors and other high-technology applications.

2. HPQ can be recovered from a variety of different source rocks in a range of geological settings.

3. Currently, the HPQ industry in Australia is under-utilised for high-technology applications, and historical exploration and mining records are under-reported and opaque.

4. This review presents an outline of the characteristics, processing requirements and end uses of HPQ, and a summary of the operations, deposits, exploration targets and known occurrences of HPQ in Australia.

Keywords:

• high-purity quartz
• silicon
• Australia
• critical minerals
• mineral systems
• photovoltaics
• semiconductor
• renewable energy
• net zero

Introduction

The global transition to clean technologies, including renewable energy and household electrification, is driving an ever-increasing demand for critical minerals (Department of Industry, Science and Resources, 2022, 2023). This demand is rapidly evolving owing to the phasing out of, for example, traditional machinery and manufacturing processes reliant on hydrocarbon resources (Ali et al., 2017; Bruce et al., 2021; International Energy Agency, 2021, 2023; Skirrow et al., 2013). The diversity of critical minerals needed for the global energy transition is promoting a focus on the efficient exploration of new styles of mineralisation across the globe and is also resulting in a re-examination of existing minerals systems knowledge.

In this context, one mineral that has gained significant attention is high-purity quartz (HPQ). HPQ is the principal raw material for the production of silicon, which has recently been classified as a critical mineral in Australia (Department of Industry, Science and Resources, 2022, 2023), and elsewhere across the globe including in the European Union (Grohol & Veeh, 2023), United Kingdom (Department for Business, Energy and Industrial Strategy, 2022), Japan (Nakano, 2021), India (Ministry of Mines, 2023) and South Korea (Australian Trade and Investment Commission, 2023). HPQ has been identified in a variety of silica-rich hard rock sources globally, including pegmatites (Ibrahim et al., 2015; Larsen et al., 2000; Müller et al., 2015; Swanson & Veal, 2010), hydrothermal quartz (Afahnwie et al., 2022; Wang et al., 2022; Xia et al., 2023), sedimentary sources (Abeysinghe, 2003; Davies et al., 2015; Phillips & Hughes, 1996) and quartzite (Fedorov et al., 2019; Hancock, 2022; Müller et al., 2007; Wanvik, 2019). Both HPQ and its refined product, silicon, have a variety of high-technology applications. Processing and refining requirements dictate the minimum standards required of HPQ feedstock for silicon production are (i) a very low level of impurities, (ii) application-dependent particle size and (iii) melting behaviour that is acceptable for downstream manufacturers (PricewaterhouseCoopers [PwC], 2022). The refining of HPQ to produce silicon requires gravel to cobble-sized feedstock (30–100 mm). Silica sand is currently unsuitable for the production of silicon, as the particle size is too small for the silicon smelting process (PwC, 2022); however, it can be used for other HPQ applications providing it meets the requisite purity, for example, glass sand (including flat, colourless, coloured, and fibre glass), foundry and moulding sand, and industrial uses (including water filtration, construction, ceramics and refractories). Given that silica sand is not suitable for silicon production, its discussion falls beyond the scope of this paper.

High-purity quartz exploration and mining in Australia have historically been under-reported—quartz is categorised as an industrial commodity, and production is not required to be publicly reported, making the status of the current resource and reserve potential in Australia difficult to accurately assess. A lack of transparency surrounding appropriate methods to characterise HPQ resources further confounds this issue. An additional reason for the lack of knowledge surrounding the HPQ industry may be due to predominance of exploration being undertaken by companies that are privately owned and operated, and therefore not required to release public statements about potential resources, reserves or grade on the Australian Securities Exchange (ASX). However, with growing interest in renewable energy and the associated demand for critical minerals in Australia and globally, HPQ exploration and discoveries are increasingly being reported in public forums (such as the ASX or company websites).

At present, the main suppliers of HPQ globally are the United States of America, Canada, Norway, Brazil, Russia and India (Pan et al., 2022). In Australia, despite the increased exploration and discovery of potentially significant HPQ occurrences, Simcoa Operations Pty Ltd (herein, Simcoa; Figure 1) represents the only operator currently mining HPQ, and also the only Australian-based manufacturer of high-purity silicon (Simcoa, 2020). Accordingly, Australia is well positioned to incentivise the supply of raw materials, and expand onshore silicon production capacity (PwC, 2022). This could contribute significantly to meeting the global demand for HPQ required for high-technology applications.

Figure 1. Map of Australia highlighting known high-purity quartz (HPQ) operations, deposits, exploration targets and occurrences. Note that the HPQ information shown on the map is not exhaustive, and new deposits, exploration targets and occurrences are being discovered. Refer to Table 1 for further detail.

The purpose of this paper is to provide a snapshot of the current state of the HPQ industry in Australia. This present contribution details the first collated dataset (Figure 1; Table 1) on the operations, deposits, exploration targets and known occurrences of HPQ in Australia.

Table 1. Known Australian HPQ operating mines, deposits, exploration targets and occurrences.

Deposit	Company	State	Status	Deposit type	Resource/purity	Source
Granitic
Rockley		NSW	Deposit	Hydrothermal	464 kt up to 99.9 wt% SiO2	Stuart (2015)
Clear Creek		NSW	Occurrence	Hydrothermal	99.5 wt% SiO2	McClatchie (1995)
Dingo Hole	Verdant Minerals Ltd	NT	Occurrence	Hydrothermal	>99.94 wt% SiO2	Verdant Minerals (formerly Rum Jungle Resources) (2015)
Lighthouse^a	Hunter Bay Silica	Qld	Deposit	Hydrothermal	6 Mt @ 99.98 wt% SiO2	Queensland Government (2015)
HJ Reef	Cloncurry Industrial Minerals Pty Ltd	Qld	Deposit	Hydrothermal	6 Mt @ 99.5 wt% SiO2 inferred feedstock	Lava Blue (2024)
Sugarbag Hill	Ultra HPQ Ltd	Qld	Deposit	Hydrothermal	Strike length of 800 m > 2 Mt @ 99 wt% SiO2 with a JORC reserve of 1.2 Mt	Ultra HPQ (2024)
Douglas Range Project	Australian Silica Quartz Group Ltd	Qld	Exploration target	Hydrothermal	99.99 wt% SiO2 after beneficiation	Australian Silica Quartz (ASQ) (2021)
Mount Eliza	Australian Silica Quartz Group Ltd	Qld	Exploration target	Hydrothermal	Rock chips up to 99.98 wt% SiO2	Australian Silica Quartz (ASQ) (2021)
Quartz Hill	Australian Silica Quartz Group Ltd	Qld	Deposit	Hydrothermal	Resource of 17 Mt total at 99.04 wt% SiO2, of which 7.6 Mt indicated at 99.09 wt% SiO2 (per JORC 2012)	Australian Silica Quartz (ASQ) (2023)
Mt Grey	SolQuartz	Qld	Exploration target	Hydrothermal	Purity unknown	SolQuartz (2024)
White Ridge	SolQuartz	Qld	Exploration target	Hydrothermal	Purity unknown	SolQuartz (2024)
May Downs^a	Greentech Minerals Ltd	Qld	Deposit	Hydrothermal	JORC total measured, indicated and inferred resource of 388 kt @ 99.96 wt% SiO2	Greentech Minerals website 2024
Pandanus Creek Project	Australian Silica Quartz Group Ltd	Qld	Exploration target	Pegmatite	Rock chips up to 99.98 wt% SiO2. White Springs exposed outcrop of 4000 m^2—quartz core of zoned pegmatite	Australian Silica Quartz (ASQ) (2021)
Cromer ‘C’		SA	Occurrence	Hydrothermal	99.7 wt% SiO2	Keeling (1984)
Raven Hill South		SA	Occurrence	Hydrothermal	99.6 wt% SiO2	Keeling (1984)
Maldorky Hill		SA	Occurrence	Hydrothermal	Further assaying required	Keeling (1984)
White Hill		WA	Deposit	Hydrothermal	172 Kt @ 99.9 wt% SiO2	McNab (1991)
Lake Seabrook	Australian Silica Quartz Group Ltd	WA	Exploration target	Hydrothermal	Rock chip purity up to 99.98 wt% SiO2 after beneficiation. Vein 5 km strike length	Australian Silica Quartz (ASQ) (2022)
Warrawanda	VRX Silica	WA	Occurrence	Hydrothermal	99.95 wt% SiO2 rock chip sample	VRX Silica (2019)
Bonnie Rock SW	Corella Resources	WA	Exploration target	Hydrothermal	99.4 wt% SiO2 rock chip sample	Corella Resources (2021)
Karratha Project	Industrial Minerals	WA	Exploration target	Hydrothermal	Purity unknown. Awaiting results	Industrial Minerals ASX announcement 22/3/23
Pippingarra	Industrial Minerals	WA	Exploration target	Pegmatite	Potential resource of 1.5–3 Mt at 97–99 wt% SiO2, initial testing returned 99.994 wt%	Industrial Minerals ASX announcement 24/4/24
Potts Road	Australian Silica Quartz Group Ltd	WA	Occurrence	Pegmatite	HPQ within 15–20 m of surface	Abeysinghe (2003); Australian Silica Quartz (ASQ) (2024)
Karloning		WA	Exploration target	Pegmatite	99.7–99.8 wt% SiO2	Abeysinghe (2003)
Mukinbudin		WA	Exploration target	Pegmatite	391 Kt @ 98.8 wt% SiO2. Up 99.5 wt% SiO2	Abeysinghe (2003)
Calcaling		WA	Occurrence	Pegmatite	Historical assay results indicate HPQ	Abeysinghe (2003)
Metamorphic
Weld River		TAS	Occurrence	Quartzite	Estimated resource of >100 Mt at 99.3 wt% SiO2 (more testing needed)	Forster (1973)
Sedimentary
Moora	Simcoa Operations Pty Ltd	WA	Operating Mine	Chert	>2 Mt @ 99.4 wt% SiO2	Simcoa website 2020; Szymkowski and Bultitude-Paull (1992)
Kiaka Hills	Simcoa Operations Pty Ltd	WA	Deposit	Chert	Estimated resource of 2.34 Mt LoM >99 wt% SiO2	GHD (2022)
Alluvial
Creswick^a	Creswick Quartz Ltd	VIC	Deposit	Aggregate	99.99 wt% SiO2	Jeffries (2010)
Glenella^a	Glenella Quarry Pty Ltd	NSW	Deposit	Aggregate	99.8 wt% SiO2	Border (2000)

^aSelected deposits discussed in the paper owing to available information.

HPQ composition, impurities and processing

Silicon, one of the most abundant elements in the Earth’s crust, does not occur naturally in its elemental form. It is found in various silicate minerals, and in oxide form (silica; SiO₂), which serves as the sole source of silicon. The SiO₂ system is diverse, with several polymorphs known to occur (Table 2; Götze, 2012; Götze et al., 2021). The chemical and physical properties of silica are affected by mineral structure (Götze, 2012). The most common silica mineral, and the most important for industrial applications, is α-quartz (hereafter referred to as quartz). Quartz occurs as a common constituent of magmatic, metamorphic and sedimentary rocks, and can also form through secondary metamorphic and diagenetic processes. Defects and micro-inclusions can be incorporated into quartz during crystallisation and subsequent alteration (Götze, 2012; Götze et al., 2021). Conditions of formation therefore play an important role in the physical and chemical properties of quartz.

Table 2. Common polymorphs of the SiO₂ system, including minerals and mineraloids (modified after Götze, 2012).

	Form	Crystal symmetry
Atmospheric and low pressure	Low (α) quartz	Trigonal
	High (β) quartz	Hexagonal
	Tridymite	Monoclinic
	Cristobalite	Tetragonal
High and ultra-high pressure	Coesite	Monoclinic
	Stishovite	Tetragonal
Amorphous	Opal	H2O-bearing, solid SiO2 gel

Trace elements in quartz

Not all quartz deposits have the requisite characteristics to be classified as HPQ. Economically viable deposits of HPQ are very rare in nature (Müller et al., 2012), and need to meet specific requirements (Müller et al., 2007, 2012; Pan et al., 2022). For the processing and refinement of quartz to be energy- and cost-efficient, the raw material must be at a very high level of purity, with naturally occurring quartz feedstock attaining a target grade of >98.5–99 wt% SiO₂ (Harben, 2002).

The type, size and concentration of impurities can impact the suitability for processing significantly. Elevated concentrations of trace elements in quartz are commonly related to fluid (Na, Cl, K, Rb, Ca, Mg, Sr) and mineral (Ti, Al, Fe, Mn, Mg, K, Zr, U, Th, Hf) micro-inclusions (Götze et al., 2017; Müller et al., 2012). Fluid inclusions can be removed by thermal treatment and calcination (Müller et al., 2012). Mineral inclusions in quartz are common and are a major source of contamination; they may be deleterious to the beneficiation process, as they are difficult to remove if completely encased in quartz (Müller et al., 2012). In quartz of igneous origin, melt inclusions may also represent a source of contaminants. These are less common than fluid inclusions but can be a significant source of trace elements such as Si, Al, Fe, Ca, Na and K. In pegmatitic quartz, melt inclusions may also be a source of F, Cl, B, P, Li, Cs and Rb contaminants (Müller et al., 2012).

While beneficiation can effectively remove certain impurities, such as fluid and mineral inclusions, contaminants that are bound to the crystal lattice present a more complex challenge. Quartz allows only minimal incorporation of other elements into its structure; however, small concentrations of foreign ions can be incorporated into the atomic lattice. These are referred to as lattice-bound impurities (Flem & Müller, 2012; Götze, 2012). Substitution of Si⁴⁺ by Al³⁺ is the most common lattice-bound impurity in quartz. This substitution incorporates an additional charge compensating cation (H⁺, Li⁺, Na⁺) in the interstitial position. Other trace-element substitutions noted to occur in quartz include Ti, Ge and Fe (Götze, 2012).

There is no definitive consensus within the industry on the definition of HPQ with regard to impurity profiles; however, a commonly accepted definition in the literature is that the sum of impurities (Na, K, Li, Al, Ca, Fe, Ti, B and P) analysed on single quartz grains should be <50 ppm, where the concentration of each element is Al <30 ppm, Ti <10 ppm, Na <8 ppm, K < 8 ppm, Li <5 ppm, Ca <5 ppm^, Fe <3 ppm, P < 2 ppm and B < 1 ppm (Harben, 2002; Müller et al., 2012). It should be noted that although HPQ is widely regarded as being the primary feedstock for silicon production, quartz of moderate purity (i.e. >98 wt% SiO₂; Williams, 2000) is commonly employed. In order to meet stringent purity conditions, it is generally necessary to process the quartz ore to remove many of the impurities. Understanding trace-element deportment in quartz is therefore imperative for determining appropriate processing methods.

Downstream processing

Several steps are required to process and prepare raw quartz for use in the production of silicon. Once extracted, quartz is passed through a comminution circuit (crushing and grinding) to reduce grainsize (Pan et al., 2022). Various beneficiation methods can be applied depending on the characteristics of the impurities within the quartz ore. Flotation, magnetic separation and gravity separation can be utilised to remove accessory mineral phases; high-temperature calcination and microwave heating can treat fluid inclusions, and chlorination, calcination, pressure leaching and acid leaching are employed to remove lattice-bound impurities (Buttress et al., 2019; Larsen & Kleiv, 2016; Lin et al., 2018; Pan et al., 2022). The current production methods for high-purity silicon are material- and energy-intensive (Figure 2), which presents a challenge for manufacturers with the transition to net zero carbon emissions (Hallam et al., 2022). Using existing methods of processing and refining, approximately 15 kg of quartz feedstock is required to produce 1 kg of silicon (Vatalis et al., 2015) and 11–13 kWh of electricity (Takla et al., 2013). The purification process of metallurgical grade silicon to form polysilicon for photovoltaics is six times more energy-intensive than aluminium processing, and eight times more than the initial process of extracting silicon from quartz (PwC, 2022). There are continuous improvements to the downstream processing of silicon. Canada-based producer HPQ Silicon has developed a patented reactor-based method to manufacture high-purity silicon (99.92 wt% SiO₂) for high-end technologies from lower-grade (∼98 wt% SiO₂) quartz feedstock. The method is purported to use 25% less feedstock per Mt of silicon produced (HPQ Silicon, 2023a, 2023b).

Figure 2. Simplified production chain showing high-purity quartz applications, including feedstock for silicon production: carbothermic reduction of silica to metallurgical grade silicon (Si_MG); refinement of Si_MG by Siemens or Fluidised Bed Reactor (FBR) producing polycrystalline silicon; and conversion into a single crystal ingot using the Czochralski (CZ) process resulting in monocrystalline silicon. End applications of silica products are shown in purple. Note this process flow represents the most common methods used in the production of high-purity silicon and is not an exhaustive list of all processes and refinement techniques available.

The carbothermic reduction method is the process of converting SiO₂ to metallurgical-grade silicon (Si_MG) in a submerged-electrode electric arc furnace (Brown et al., 2002; Dal Martello et al., 2011). Within the furnace, the feedstock SiO₂ is combined with a carbon source (e.g. coal, charcoal and/or wood chips) or a combination of carbon sources, and is heated to ∼1800 °C. This process involves the Si being separated from O, as demonstrated in Equation (1)(1) $${\text{SiO}}_{2(\mathrm{s})}+{\text{2C}}_{(\mathrm{s})}\to {\text{Si}}_{(\mathrm{l})}+{\text{2CO}}_{(\mathrm{g})}$$(1) (Brown et al., 2002; where, s = solid, l = liquid, g = gas). The process is complex with multiple intermediary reactions occurring in various parts of the furnace, with the generalised reaction as follows: (1) $${\text{SiO}}_{2(\mathrm{s})}+{\text{2C}}_{(\mathrm{s})}\to {\text{Si}}_{(\mathrm{l})}+{\text{2CO}}_{(\mathrm{g})}$$(1)

While there are only two main chemical inputs into the production of Si_MG, the purity of both the feedstock SiO₂ and the source of carbon (e.g. coke produced from coal or specifically selected species of timber for woodchips) is important, as contaminants introduced by these require removal further down the process chain (Dal Martello et al., 2011).

The chemistry of the silicon that is used in photovoltaics and semiconductors is highly important, with small concentrations of contaminants (<1 ppm) of some elements resulting in significant penalties to efficacy or simply a non-functional product (Safarian et al., 2012). The purity of ultra-refined silicon is commonly denoted by the number of nines in its percentage. For example, a purity of 99.99% is referred to as 4 N. Purities exceeding 6 N are necessary for various high-technology applications (Johnston et al., 2012; Safarian et al., 2012). In order to achieve these purity levels, Si_MG undergoes multiple stages of refinement to remove contaminants (Figure 2). First, polycrystalline silicon is produced through the decomposition silicon-bearing gas, using the traditional Siemens process or newer technology known as the Fluidised Bed Reactor deposition process (Maurits, 2014). Polycrystalline silicon cannot be used as semiconductor material owing to inherent grain boundaries (Maurits, 2014). For high-technology applications, polycrystalline silicon must be converted into a single crystal ingot known as monocrystalline silicon. The most common method by which to achieve this is the Czochralski process (Haus et al., 2012; Vatalis et al., 2015).

Industrial applications of HPQ

Silica has a wide range of uses; it is used widely in the construction industry in cement and ceramics, in the manufacture of silicone compounds, silicon carbide and glass (Figure 2). Historically, quartz has been a mineral of industrial significance owing to its piezoelectric properties (Vatalis et al., 2015). More recently, technological advances have increased demand for highly pure quartz for use in high-technology applications.

Metallurgical grade silicon

Crude silicon (∼99% purity) produced from the carbothermic reduction of silica (Safarian et al., 2012; Figure 2) is predominantly used in the production of aluminium alloys and within the chemical industry, largely in the manufacture of silicone compounds (United States Geological Survey, 2023). In the automotive industry, aluminium-silicon alloys are replacing vehicle parts that have traditionally been manufactured with steel or iron. The alloy helps improve fuel efficiency by reducing the weight of the vehicle (Mehdi, 2015). Aluminium–silicon alloys are also utilised in aviation, specifically in the manufacture of aircraft, owing to their light weight and corrosion-resistant properties (Asmatulu, 2012).

Metallurgical-grade silicon is also the foundation for further refinement of silicon for use in high-technology applications, such as photovoltaics and semiconductors (Figure 2).

Photovoltaics

Polycrystalline and monocrystalline silicon are common materials used in the production of photovoltaic cells (Figure 2), which are components of solar modules for the generation of electricity from sunlight (Haus et al., 2012). Solar-grade silicon requires a minimum of 6 N purity (Johnston et al., 2012; Safarian et al., 2012). Approximately 15 kg of HPQ is required to produce 1 kg of silicon suitable for use in photovoltaic cell manufacturing (Vatalis et al., 2015; Figure 2). Despite making up only 3–4% of the mass of a photovoltaic cell, silicon accounts for approximately 35–50% of the total cost of a photovoltaic module (International Energy Agency, 2022). Solar is one of the leading renewable-energy sources in global decarbonisation and is a key driver in the renewable energy generation in Australia, with global transition to renewable-energy sources leading to a rapid increase in demand for photovoltaics (International Energy Agency, 2022).

Semiconductors

Semiconductor manufacture uses monocrystalline silicon to produce silicon wafers (Vatalis et al., 2015; Figure 2). This requires highly refined silicon, with a minimum purity for semiconductor applications of 9 N (Johnston et al., 2012; Safarian et al., 2012). Semiconductor production also necessitates the use of HPQ ware, such as quartz crucibles (Haus et al., 2012), to minimise contamination. Pure silicon exhibits semiconductor properties, with electrical conductivity increasing with temperature (Vatalis et al., 2015). The electrical conductivity and properties of silicon can be improved by adding small amounts of impurities, known as dopants, to the material during the manufacturing phase (Australian Nuclear Science and Technology Organisation, 2023; Jones, 1991). Semiconductors are used in a range of applications, such as smart phones, satellites and quantum computers (National Institute of Standards and Technology, 2023).

Other applications

Aside from refinement to produce silicon, HPQ has numerous other uses (Figure 2). Silica glass is used for optical fibres and optoelectronic telecommunication devices, in excimer laser optics and in microelectronic components (Haus et al., 2012; Vatalis et al., 2015; Figure 2). The high transmission characteristics, high thermal shock resistance and thermal stability of HPQ are ideal for use in the manufacture of high-performance, high-temperature lamps such as halogen, xenon and mercury bulbs, UV lamps and high-intensity discharge lamps (Haus et al., 2012). Additionally, HPQ is used in the production of fused quartz glassware and crucibles necessary for the production of monocrystalline silicon (Haus et al., 2012; Warden et al., 2023).

Global silicon production and demand

The estimated global production of silicon in 2022 was ∼8800 kt (United States Geological Survey, 2023), which includes high-technology industries highlighted in this paper and other industrial uses. Australia produced 50 kt of silicon in 2022, with all domestic silicon production undertaken by Simcoa, which operates a silicon refinery in Kemerton, Western Australia (Simcoa, 2020; United States Geological Survey, 2023).

Pegmatite deposits are currently the world’s largest source of HPQ, with the Spruce Pine deposit in the United States of America supplying ∼70% of the global supply (VRX Silica, 2023). During the 1960s, the main economic minerals at Spruce Pine were feldspar and mica, while quartz mining was considered unviable owing to the economic cost of extracting and transporting the resource (Brobst, 1962).

With the price and demand for HPQ increasing in the 2000s, Sibelco and The Quartz Corp reassessed the economic viability of extracting the quartz alongside other commodities and have been able to obtain HPQ successfully and consistently from the various pegmatite occurrences (Sibelco, 2023; The Quartz Corp, 2023). The history of mining at Spruce Pine suggests there may be pegmatite bodies in Australia with potential for HPQ, which have been traditionally exploited for other commodities.

The market price of HPQ is determined by the purity of the raw, unprocessed quartz. In 2022, the HPQ market was valued at nearly US $894.6 million and is estimated to grow to US $1.5 billion by 2031 (Transparency Market Research, 2022). Given the importance of HPQ in high-technology applications, its strategic value may outweigh its economic significance. The demand for HPQ is forecast to increase, primarily driven by the semiconductor and photovoltaics industries. The Australian Silicon Action Plan (PwC, 2022) highlights that in order to meet solar energy requirements, the global demand for raw quartz feedstock will increase by nearly a factor of 40 by 2050. However, as is the case with other critical minerals, the supply chain is volatile owing to the geopolitics of global trade, economic factors and availability of alternative materials (Ali et al., 2017; Bruce et al., 2021). As of 2022, China manufactured over 80% of key elements for solar panels, including polysilicon and wafers (International Energy Agency, 2022). There is a clear need for diversification throughout the entire silicon supply chain, from mining to manufacturing.

Geological context of Australian HPQ resources

Quartz is common in igneous, metamorphic and sedimentary rocks; however, economic deposits of HPQ have only been actualised and developed for a few specific geological settings: granite-related sources (i.e. pegmatites), hydrothermal quartz veins, sedimentary accumulations of quartz (such as gravel or chert) and quartzites formed from the metamorphism of silica-rich protoliths. Regolith accumulations (e.g. silcretes) may also be a potential source for HPQ; however, further investigation is required, and no economic deposits are known. We have catalogued known Australian deposits in Table 1 and Figure 1. However, not all of these deposits are discussed within the main text of this paper owing to the limited information available on certain deposits.

Pegmatites

Pegmatites are coarse-textured igneous rocks that can be enriched in a variety of critical minerals including Li, Ta, Nb, Y and rare earth elements (REE) (Dill, 2015; Müller et al., 2023). Granitic pegmatites have been purported to provide the best source of HPQ (Götze et al., 2021 and references within), with well-known deposits at Spruce Pine, United States of America, and Drag, Norway.

The trace-element chemistry of quartz in pegmatites is a function of the physicochemical conditions of formation, and as such, quartz chemistry can provide petrogenetic information regarding the pressure–temperature conditions during crystallisation (Keyser et al., 2023). Melt source is considered to be a major control of quartz chemistry, although trace-element concentrations are also affected by temperature and pressure (i.e. Ti), and the degree of fractionation of the melt (e.g. Ge, Rb, B and Be; Müller et al., 2021). Additionally, deformation and recrystallisation may result in purification of quartz (e.g. Morteani et al., 2012).

A common classification scheme for pegmatites identifies abyssal, muscovite, rare-element and miarolitic classes, with rare-element pegmatites subdivided into niobium–yttrium–fluorine (NYF) and lithium–caesium–tantalum (LCT) endmembers (Černý, 1991; Černý & Ercit, 2005). Müller et al. (2012) suggested that NYF-type pegmatites can generate HPQ directly from melt. Conversely, quartz in LCT-type pegmatites can exhibit Al and Li enrichments of >100 ppm Al and 30 ppm Li (Keyser et al., 2023; Müller et al., 2021), which places it outside the criteria of HPQ (<30 ppm Al, <5 ppm Li; Müller et al., 2012). However, it is important to note that the scope of these studies is limited, which leaves uncertainty around the broader applicability of these findings. To our knowledge, there is no comprehensive review of quartz chemistry across various types of pegmatites, and as such it is unknown which pegmatite varieties are most prospective for HPQ.

In Australia, the Proterozoic Karloning deposit located in the southwest of the Yilgarn Craton (Western Australia; Figure 1) was historically mined for quartz and feldspar (Abeysinghe, 2003). The Karloning NYF-type zoned pegmatite system is approximately 1.5 km in length and up to 200 m wide (Codrus Minerals, 2022). The pegmatites intrude an Archean granite along the margin of a large quartz outcrop. Sampling and testing by the Geological Survey of Western Australia (GSWA) determined that the quartz is of relatively high purity (99.7–99.8 wt% SiO₂), with an estimated resource size of ∼100 kt (Abeysinghe, 2003).

Hydrothermal quartz

Hydrothermal quartz forms when hot, silica-rich aqueous fluids migrate along structures or discontinuities such as faults and fractures. Upon cooling, with a decrease in pressure and/or a change in the chemical conditions of the fluids and possible interaction with host rocks, this process can trigger the precipitation of large accumulations of quartz, with or without other commodities of economic interest (e.g. Au and Ag; White & Hedenquist, 1990). Quartz precipitation and vein formation can take place across a range of temperature and pressure conditions (e.g. Oliver & Bons, 2001; Vearncombe, 1993). Fluid chemistry, precipitation rate, crystal orientation, oxygen fugacity, and crystallisation pressure and temperature can all affect trace-element concentrations in hydrothermal quartz (Müller et al., 2012; Shah et al., 2022). Hydrothermal quartz is typically zoned and exhibits discontinuous internal fabrics, reflecting dynamic conditions that affect trace-element incorporation (Shah et al., 2022). These conditions, which also drive the precipitation of quartz-dominated veins, can lead to significant variability in chemical composition, both within a single vein and between different veins in the same area.

Despite the abundance of hydrothermal quartz associated with mineral deposits, the presence of sulfides and other contaminants can, in some cases, compromise these as suitable sources of HPQ. Accordingly, large non-mineralised hydrothermal quartz veins are interpreted to represent a more likely source of HPQ and are therefore receiving the most attention from Australian exploration companies in the pursuit of HPQ deposits. These hydrothermal veins are exposed at the surface commonly forming the dominant landscape feature; they can be tens of metres wide and have strike lengths of several kilometres and are therefore easily explored for and exploited by mining companies. Recently, numerous Australian companies have been reporting promising results for high purity grades of quartz from their exploration activities (Table 1).

HPQ explorer Greentech Minerals Ltd has developed a JORC resource of 388 kt at a purity of 99.96%, from mapping and sampling hydrothermal veins and blows at their May Downs tenement near Mount Isa, in far north Queensland (Figure 1). These intrude the Paleoproterozoic–Mesoproterozoic Sybella Granite, May Downs Gneiss and Alpha Centauri Metamorphics (Greentech Minerals, 2023). Some of the hydrothermal veins are reported to be up to 3 km in strike length and rise 1.5–36 m above ground, and the larger reef systems are 10–20 m wide (Greentech Minerals, 2023).

The Lighthouse deposit, located in northeast Queensland (Figure 1), is reported to be made up of two ∼38 m-wide quartz blows that extend over at least 500 m (Calcifer Industrial Minerals, 2007). Quartz scree and smaller quartz veins are also found in the surrounding area. The Lighthouse deposit has an estimated resource of 6 Mt at 99 wt% SiO₂ (Solar Silicon Resources Group, 2014). The host intrusion is part of the Paleoproterozoic–Mesoproterozoic Einasleigh Metamorphics, which form the basement to the Forsayth Subprovince. The Einasleigh Metamorphics, which are also characterised by Paleoproterozoic–Mesoproterozoic leucogranitic veins and dyke swarms found throughout, may be genetically related to the hydrothermal HPQ deposit and are all likely to be of similar age (Paleoproterozoic–Mesoproterozoic). Other quartz veins contained within the Einasleigh Metamorphics range in size from thin veins (centimetre scale) to large outcrops (tens of metres scale) and may be a potential source of HPQ in the region (Solar Silicon Resources Group, 2012). To our knowledge, outside the Lighthouse deposit, the Einasleigh Metamorphics area is underexplored for HPQ.

Other examples of hydrothermal HPQ include Rockley (NSW), HJ Reef (QLD), Quartz Hill (QLD), Sugarbag Hill (QLD), White Hill (WA) and a significant number of exploration targets and minimally documented occurrences (Table 1; Figure 1).

Quartzite

Few quartzites have been identified internationally as having purity suitable for the production of HPQ (e.g. Moberly, Canada, and Tana, Norway) (Hancock, 2022; Wanvik, 2019). The process of metamorphism triggers recrystallisation of the small, un- to semi-consolidated grains of quartz that make up the sandstone protolith to a fused, intergranular and commonly coarser grained rock (quartzite), containing high SiO₂ content. These deposits are typically large volume but of low quality (Haus et al., 2012).

To our knowledge, there are no known HPQ-bearing quartzite occurrences in Australia. However, there are quartzite occurrences with HPQ potential identified at Weld River, Tasmania (99.3 wt% SiO₂), and near the town of Kauring, Western Australia with promising initial assay results showing up to 99 wt% SiO₂ (Abeysinghe, 2003). More work is needed to determine their potential as an HPQ feedstock.

Sedimentary and alluvial

Chert

Chert is a fine-grained sedimentary rock that is highly siliceous in composition, originating from biochemical or diagenetic processes. Silicon manufacturer Simcoa sources its HPQ feedstock from the Neoproterozoic Noondine Chert at Australia’s only HPQ mining operation in Moora, Western Australia (Figure 1). The Noondine Chert is a metamorphosed unit that is formally identified as a chert (Geological Survey of Western Australia, 1982; Geoscience Australia, 2023), but locally it is referred to as a quartzite (Abeysinghe, 2003). Mining operations began at Moora in 1989 and have continued on an annual campaign basis. This HPQ feedstock is used to feed its processing plant in Kemerton, Western Australia, the only continuously operating silicon refinery in Australia (Simcoa, 2020).

Alluvial

Currently there are two known HPQ aggregate resources in Australia (Figure 1). Creswick Quartz have identified high-purity feedstock within process tailings from historic gold mining north of Ballarat, Victoria (Jeffries, 2010). The deposit was originally mined for deeply buried alluvial gold during the Victorian gold rush between 1851 and 1914, with gold hosted in alluvial gravel that consists of iron sulfide cemented quartz boulders in a quartz silt or clay matrix (Davies et al., 2015; Phillips & Hughes, 1996). Textural evidence suggests that the quartz gravels are derived from hydrothermal quartz (Hughes et al., 2004). Creswick Quartz has reported that the quartz is of high purity (>99.99 wt% SiO₂) and requires only washing with water to make it suitable for use in the production of silicon (Jeffries, 2010).

The second HPQ aggregate resource is at Glenella Quarry, located at Cowra in central west New South Wales (Figure 1; New South Wales Government, 2015). This deposit is likely to have been derived from the erosion of hydrothermal quartz veins and subsequent transportation by a river system during the early Cenozoic (New South Wales Government, 2015). Glenella Quarry has produced quartz pebble (known as Cowra White or Western White River Pebble) with a purity of 99.5 wt% SiO₂ (Border, 2000). Glenella Quarry has an estimated resource of 6.9 Mt from the quartz pebble horizon, with a further potential 4.6 Mt within the project area (Border, 2000).

Regolith accumulations

Historically, regolith accumulations (e.g. silcretes) have been used in construction and other industries for road base and aggregate. In Australia, silica-rich silcretes (e.g. Monaro Region, Shoalhaven Region and Broken Hill in New South Wales; Eromanga Basin, central and northern Australia) are abundant (see, for example, Taylor & Eggleton, 2017). However, they have not been assessed for suitability for HPQ feedstock for silicon production. Furthermore, the status of silcrete or other silica-rich regolith deposits being explored as a source for HPQ is currently unknown.

International overview of significant HPQ deposits and exploration

This section provides an international overview of significant HPQ deposits and exploration. It is important to note that this is intended to serve as a general overview and does not constitute a comprehensive review of all global deposits. The intention is also to highlight the diversity of international HPQ deposit types, which may be relevant to the Australian context, and serve as an opportunity to understand, re-examine and explore mineral systems most prospective for HPQ in Australia.

Americas

The United States of America hosts the world’s largest HPQ deposit, Spruce Pine, North Carolina, which has been mined mainly for feldspar and mica for over a century (Swanson & Veal, 2010). The Spruce Pine pegmatite complex is approximately 40 km long and 16 km wide (Brobst, 1962). HPQ from Spruce Pine is associated with near-source anatectic pegmatites that locally intrude surrounding host rock and granodiorite plutons (Swanson & Veal, 2010).

Vitreo Minerals Ltd sources HPQ from a stockpile associated with the Moberly mine operation (British Columbia, Canada). The quartzite (>99 wt% SiO₂) originates from the Ordovician Mount Wilson Quartzite, which is up to 300 m thick near the mine (Hancock, 2022). Similarly, Sinova Global Inc. also extracts HPQ from the Mount Wilson Quartzite at the Horse Creek quartz mine (Hancock, 2022). HPQ producer PAL Quartz mines HPQ (99.5 wt% SiO₂) from its Baie Johan-Beetz hydrothermal deposit located in Quebec, Canada. Currently the deposit is estimated to be ∼6 Mt in size above sea-level with an unknown tonnage below sea-level. PAL Quartz estimates the deposit longevity to be approximately 35 years (PAL Quartz, 2023).

The majority of the quartz mines in South America are located in Brazil within the states of Para, Minas Gerais, Santa Catarina and Bahia. Brazil has one of the largest quartz reserves globally and, until 1974, was a major exporter of HPQ (Haus et al., 2012). However, the Brazilian government imposed an embargo on the export of lump quartz in 1974, which resulted in the country losing its place in the global HPQ supply market (Haus et al., 2012).

Europe

Norway has several well-documented quartz deposits and mines, with HPQ being sourced from hydrothermal veins (Svanvik, Nesodden), quartzite (Tana, Mårnes) and pegmatites (Drag, Setesdal), making it the leader in Europe for HPQ production (Müller et al., 2007, 2023; Wanvik, 2019). Kyanite-rich quartzites are also being considered as potential resources for HPQ (Müller et al., 2007); however, grainsize inhibits processing for high-technology applications (Wanvik, 2019).

European silicon producer Imerys Société Anonyme sources and processes HPQ lump feedstock from mines in Sweden (hydrothermal vein) and France (aggregate; Imerys, 2023). The purity is reported to be 99.8 wt% SiO₂ (Imerys, 2023).

The Southern Urals region of Russia hosts several HPQ deposits from a range of geological settings; these include quartzite, pegmatites and unmetamorphosed and metamorphosed veins (i.e. have undergone deformation and partial recrystallisation during fluid-present metamorphism). These deposits are particularly favourable, as reports have noted ultra-low (<50 ppm) trace-element impurities in the quartz feedstock (Götze et al., 2017). The largest HPQ producer in Russia is Russian Quartz, based in Kyshtym, Southern Urals, where quartz ore is sourced from a hydrothermal vein deposit (Russian Quartz, 2023).

Australian explorer Eclipse Metals Ltd has full ownership of the Ivigtût project in Greenland, which has traditionally been a source of cryolite (Na₃AlF₆); however, the company has identified HPQ potential below the open-cut pit floor, with reported bulk sample analysis confirming 99.9 wt% purity grades from historical records (Eclipse Metals, 2022; Proactive Investors UK, 2022).

Asia

China is the leader in the silicon manufacturing industry in Asia International Energy Agency (2022) and, as a country, is actively exploring for HPQ, with hydrothermal and pegmatite deposits discovered in areas including Qinling, Anhui and Hubei provinces (Wang et al., 2022; Zhang et al., 2022, 2023; Zhou & Yang, 2018). Reports also exist of deposits in nearby Mongolia; however, there are limited proximal processing capabilities available to efficiently utilise these quartz sources (Zhou & Yang, 2018). Other countries in Asia supplying HPQ to the global market include India (Ministry of Mines, 2021) and Sri Lanka (Pathirage, 2018).

Africa and Middle East

There are several countries in Africa (e.g. Cameroon, Mauritania, Angola, Madagascar and Nambia) with potential HPQ deposits in the form of pegmatites, hydrothermal veins and quartzites. However, there is little to no production owing to geopolitical instability or an absence of infrastructure, particularly HPQ refineries, and lack of government interest (Haus et al., 2012). In the Middle East, the Arabian Shield in Saudi Arabia has been identified as an area of HPQ potential (Nehlig et al., 1999), with some explorers discovering deposits in the form of hydrothermal quartz veins (United Mining Investments Co, 2023).

Summary

HPQ is a key material for the manufacture of photovoltaic cells and other high-technology applications, with demand projected to increase globally. Australia is well placed to be a global supplier of HPQ owing to the endowment of numerous deposits from a range of geological settings and source rocks, including pegmatites, hydrothermal quartz veins, sedimentary accumulations and quartzite.

It is important to reiterate that not all quartz deposits have the requisite characteristics to be classified as HPQ. Although outside the scope of this study, geochemical characterisation of HPQ deposits, inclusive of their components (i.e. mineral assemblages and host rocks), is required to understand the physical and chemical properties needed to form highly pure quartz; this in turn will generate increased knowledge of mineral systems most prospective for HPQ in Australia. It is also imperative to acknowledge that understanding and early adoption of knowledge related to downstream processing (geometallurgy) are fundamental to the success of silicon production.

This review has presented an overview of the chemical, physical and processing requirements of HPQ, and a summary of the current HPQ industry in Australia and globally. Although the HPQ industry in Australia is in its infancy compared with other global suppliers, the ongoing global shift towards clean technologies and high-technology innovation presents a significant opportunity. This transition could incentivise the supply of raw materials and stimulate the expansion of onshore silicon production capacity. With further investment and exploration into HPQ, as well as increased potential for processing and refining silicon domestically, Australia is staged to become a world leader in supply and production.

Author contributions

Conceptualisation: A.J., A.S. and P.M.; methodology: A.J., A.S. and P.M.; investigation: A.J. and A.S.; data curation: A.J., and A.S.; writing—original draft preparation: A.J. and A.S.; writing—review and editing: A.J., A.S., K.G., J.W. and P.M. All authors have read and agreed to the final version of the manuscript.

Acknowledgements

Geoscience Australia acknowledges the Traditional Owners and Custodians of Country throughout Australia and their continuing connection to land, waters and community. We pay our respects to the people, the cultures and the Elders past and present. The authors would like to thank Dr Simon Richards, Anthony Schofield and Marina Costelloe for their valued scientific expertise and guidance. We are grateful for the design expertise of the Geoscience Australia cartography and creative production teams for the development of the HPQ map and silicon chain diagram. We acknowledge the detailed and constructive reviews from Dr Dominique Tanner (University of Wollongong) and Dr Nicholas Tailby (University of New England). Dr Chris Yeats is thanked for editorial handling of the manuscript.

Disclosure statement

The authors declare that they have no competing financial interests or personal relationships that could have influenced the work reported in this paper.

Data availability statement

All associated data in this manuscript are made available in the main text.

Additional information

Funding

This work has been supported by the Australian Critical Minerals Research and Development Hub whose activities are funded by the Australian Government. This work is published with the permission of the CEO, Geoscience Australia.