1. Origins and Formation
Amorphous gold is a distinctive form of gold mineralisation characterised by the presence of nanoscale gold particles that lack a well-defined crystalline structure. These particles exist in a disordered, non-crystalline, or colloidal state, often associated with amorphous silica gels or carbon-rich phases. Amorphous gold primarily forms in orogenic (lode) gold deposits and mesothermal vein systems through hydrothermal processes occurring at mid-crustal depths, typically several kilometres below the Earth’s surface.
The formation process involves the rise of hot, metal-bearing hydrothermal fluids through crustal fractures and faults. As these fluids experience changes in temperature, pressure, and chemistry—especially due to mixing or boiling—amorphous silica precipitates suddenly as a gel, trapping gold nanoparticles co-precipitated within this gel matrix. Over time, the amorphous silica gel recrystallises into quartz, during which the amorphous gold nanoparticles coalesce and migrate along quartz grain boundaries or fractures, forming visible native gold grains. This sol-gel transition explains textures observed in high-grade gold zones.
The geological significance of amorphous gold lies in its role as a transient sol-gel phase facilitating efficient nanoscale transport and episodic concentration of gold in structurally controlled vein systems, especially within greenstone belts and volcanic-intrusive-sedimentary sequences globally.
2. Global Occurrence and Expected Grades
Amorphous gold is predominantly found in some of the world’s highest-grade orogenic gold deposits. Below is a list of notable deposits known to contain significant concentrations of amorphous gold nanoparticles, with their approximate grades in grams per tonne (g/t):
| Deposit Name | Location | Approximate Amorphous Gold Grade (g/t) |
|---|---|---|
| Beta Hunt | Australia | 40 – 100+ |
| Discovery Mine | Canada | 50 – 100+ |
| Red Lake | Canada | 25 – 80 |
| Callie | Nevada, USA | 30 – 70 |
| Sixteen to One | Nevada, USA | 30 – 60 |
| Macassa Mine | Canada | 20 – 60 |
| Fire Creek Mine | Nevada, USA | 40 – 90 |
| Kedrovka Mine | Russia | 30 – 50 |
| Edie Mine | Canada | >30 |
These deposits occur in hydrothermal quartz veins and mesothermal vein systems within greenstone belts and volcanic-intrusive rock environments. Amorphous gold grades in these deposits often exceed typical commercial thresholds, with some ‘bonanza’ zones surpassing 100 g/t, indicating exceptionally focused precipitation.
3. Identification and Characterisation
Amorphous gold, due to its nanoscale size and lack of crystallinity, requires sophisticated analytical techniques:
- Transmission Electron Microscopy (TEM) with Fast Fourier Transform (FFT) analysis: Essential to image nanoparticles and establish their amorphous nature.
- Energy Dispersive X-ray Spectroscopy (EDS): Provides elemental distribution maps of gold within amorphous silica or carbon phases.
- X-ray Absorption Spectroscopy (XANES, EXAFS): Probes the oxidation state and local bonding environment of gold.
- Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS): Enables precise, in situ elemental analysis.
- Optical microscopy is insufficient due to the fine and invisible nature of amorphous gold particles.
4. Recovery of Amorphous Gold
Traditional extraction methods, such as cyanide leaching and gravity concentration, tend to be ineffective because amorphous gold nanoparticles are encapsulated in refractory, amorphous silica or carbon-rich matrices, which prevent gold liberation.
The recovery of amorphous gold requires innovative, high-temperature processes capable of disrupting the encapsulating phases without harmful chemicals.
IPRI.Tech AG has developed the revolutionary Ultra High Temperature Pyrometallurgy™ (UHTP™) process, utilising their proprietary Plasma Accelerated Oxidation (PAO™) machine. This cutting-edge technology:
- Achieves extremely high temperatures, enabling the complete breakdown of refractory silicates and carbon matrices, thereby liberating the trapped amorphous gold nanoparticles.
- Is a chemical-free process, avoiding hazardous reagents like cyanide, promoting environmental sustainability.
- Has demonstrated the ability to recover amorphous gold commercially at scale, outperforming all other commercially available gold extraction methods.
- Significantly increases gold recovery yields from complex, refractory ores containing amorphous gold, enhancing mine profitability and resource utilisation.
No other technology currently on the market matches the efficiency and eco-friendly nature of the UHTP™ process combined with PAO™ machinery for commercial amorphous gold extraction.
5. Summary
Amorphous gold is an important but challenging mineral form found principally in very high-grade orogenic gold deposits around the world. It comprises nanoscale, non-crystalline gold particles intimately associated with amorphous silica and carbon phases, formed by hydrothermal sol-gel precipitation at mid-crustal depths.
Grades in deposits enriched with amorphous gold typically range from 25 to over 100 grams per tonne, often in bonanza pockets attaining even higher concentrations. Advanced electron microscopy and spectroscopy are required to identify and characterise this gold type.
Due to its fine dispersion and encapsulation, recovery of amorphous gold eludes conventional gold processing methods. IPRI.Tech AG’s Ultra High Temperature Pyrometallurgy™ (UHTP™) technology, employing the PAO™ machine, provides the only commercially viable, environmentally sustainable solution capable of efficiently extracting amorphous gold at scale, unlocking new value from previously refractory and uneconomical ores.
6. References
- Gold Grade
Explanation of gold grade as a measure of ore quality in mining, differences between gold grade and purity, and grades relevant to underground and open-pit mining. Includes discussion on deposit composition and profitability.
https://www.bullionbypost.co.uk/index/gold/gold-grade/ - What Does the Grade of a Gold Mine Refer To?
Overview of gold mine grade definitions, factors influencing mining viability, and how grades impact economic feasibility.
https://www.investopedia.com/ask/answers/022315/what-does-grade-gold-mine-refer.asp - Making Sense of Grams per Tonne (g/t): A Friendly Guide to the Mining Investment
A detailed guide to understanding grams per tonne as a measurement unit for gold deposits in the mining industry.
https://www.bcyukonmining.com/2024/07/05/making-sense-of-grams-per-tonne-g-t-a-friendly-guide-to-the-mining-investmentelementor-2278232/ - Exploration and Mining of Lateritic Gold Deposits (Part I)
Scientific article covering geological aspects and mining methods related to lateritic gold deposits.
https://www.sciencedirect.com/science/article/pii/S0169136824002798 - Geology & Mineralisation
Overview of geological contexts and mineralisation processes relevant to mining activities.
https://www.niuminco.com.au/geology.html - Gold Mines – an overview
Technical summary and engineering aspects of gold mines.
https://www.sciencedirect.com/topics/engineering/gold-mines - Chapter III. Gold Deposits Introduction
Government publication providing an introduction to the types and characteristics of gold deposits.
https://publications.gc.ca/collections/collection_2016/rncan-nrcan/M42-280-4-eng.pdf - Gold Mine Stripping Ratios Rise on High Prices, Grades Continue Declining
Analysis of trends in gold mine stripping ratios and grade variations amid changing market conditions.
https://www.spglobal.com/market-intelligence/en/news-insights/research/gold-mine-stripping-ratios-rise-on-high-prices-grades-continue-declining - Happy Sullivan Property- Colloidal and Amorphous Quartz
Mineral deposit summary from a government database providing technical details on a specific mining site.
https://minfile.gov.bc.ca/Summary.aspx?minfilno=104M++013 - IPRI.Tech – LinkedIn
Company profile providing professional information about IPRI.Tech and its services.
https://ch.linkedin.com/company/ipri-tech - Intelligent Polymer Research Institute – University of Wollongong
Research institute profile including information on polymer research related to innovative materials.
https://www.uow.edu.au/research/our-research/research-institutes-and-facilities/australian-institute-for-innovative-materials/ipri/ - IPRI.Tech Official Website
The main site for IPRI.Tech, detailing their technology, services, and innovation focus.
https://IPRI.Tech/ - IPRI.Tech Services Overview
Detailed descriptions of services offered by IPRI.Tech.
https://IPRI.Tech/Services/
