Key points
- Realgar and orpiment are arsenic-rich minerals and significant sources of this critical mineral.
- Arsenic is used in semiconductors for high-speed electronic and metal alloys.
- They are often used as indicator minerals for gold mineralisation in modern exploration.
Realgar (As₄S₄) and orpiment (As₂S₃) are arsenic sulfide minerals known since antiquity for their vivid colours and toxic properties. Arsenic, found within these minerals, was once known as the 'King of Poisons', feared for its toxicity and association with intrigue, murder and environmental harm.
Realgar's fiery red and orpiment's golden yellow are as much warnings as they are wonders, particularly prized by painters and glassmakers for the vivid pigments they produce. In traditional Chinese medicine, these minerals were used to treat inflammation and malignancies. In Ayurvedic practices, they were believed to extend life. But not if you are a rat! Arsenic is the toxic active ingredient in many rat poisons.
But in the 21st century, arsenic's story is being rewritten. Once a villain, it is now emerging as an unsung hero in the world of critical minerals.
Arsenic: a critical mineral for tech metals
Arsenic is officially classified as a critical mineral in Australia, the United States and the European Union due to its strategic importance in high-tech industries.
Arsenic is considered a critical mineral because it plays an essential role in modern technologies. High-purity arsenic is used to make semiconductors for high-speed electronics, such as smartphones and solar cells, and to strengthen metal alloys such as copper and lead. Its unique properties help improve performance, durability and energy efficiency in these applications.
Arsenic's versatility makes it indispensable in the development of advanced materials and clean energy technologies.
While arsenic is now mostly recovered as a by-product from gold and copper processing, realgar and orpiment remain important primary sources in countries such as China, Peru and the Philippines. In Australia, due to inherent toxicity risks, arsenic mining ceased in the 1950s.
An indicator mineral for gold mineralisation
Enthusiastic mineral explorer and Chief Geologist at Everest Metals Corp. Ltd, Mr Bahman Rashidi, first became interested in realgar and orpiment during extensive exploration work across the Tethyan and Central Asian Orogenic Belts. This vast geological corridor stretches from Eastern Europe through the Middle East and Himalayas into Southeast Asia. These regions host some of the world's richest copper and gold deposits.
"Realgar and orpiment are not only beautiful mineral specimens but important indicator minerals in Carlin-type gold deposits and hydrothermal mineralisation," said Mr Rashidi.
"In these terrains, realgar and orpiment frequently appeared within significant gold mineralisation systems, often in proximity to ancient mining districts. Their presence can signal arsenic-rich ore bodies, which are often co-located with gold, silver and other valuable metals."
The occurrence of these minerals helps guide exploration strategies, acting as geochemical beacons for arsenic and gold, becoming valuable tools in modern mineral exploration.
"While realgar and orpiment have long been recognised as toxic minerals, their occurrence within gold systems provides valuable insight into the chronological sequence of mineral formation," said Mr Rashidi.
"Their shift from notorious poisons to essential exploration indicators illustrates how scientific inquiry continually reshapes our view of the natural world"
Everest Metals Corp. Ltd. has collaborated with CSIRO through the Kick-Start Program to advance geochemical and mineralogical research at its Mt Edon Critical Minerals Project in Western Australia, focusing on rubidium, lithium, and caesium. The collaboration, supported by a $50,000 voucher, aims to improve mineral recovery processes and identify high-potential exploration zones and develop a commercial rubidium extraction process.
