Nanogeoscience in Resource Geology

Gold in many hydrothermal ore deposits occurs as “invisible gold,” structurally incorporated into arsenian pyrite or present as nanoscale particles that cannot be detected by conventional microscopy. Using atomic-resolution transmission electron microscopy (TEM), HRTEM, and SIMS, we conducted pioneering studies that directly imaged gold nanoparticles within arsenian pyrite and established the nanogeoscience framework for ore mineral research.

Our work demonstrated that gold solubility in pyrite is strongly controlled by arsenic content. When Au concentrations exceed the As-dependent solubility limit, nanoscale gold particles precipitate within As-rich domains. We also identified nanoscale “liquid-like” As–Fe–S inclusions and determined unusual trivalent arsenic speciation in specific pyrite types, revealing complex redox and structural controls during ore formation. In situ heating experiments confirmed that gold nanoparticles undergo Ostwald ripening within the geological matrix, documenting dynamic nanoscale processes during thermal evolution of ore systems.

Beyond gold, we reported a variety of trace metal nanoparticles embedded in pyrite, providing new insights into coupled geochemical behavior of Au, As, Cu, and other elements in hydrothermal systems. These findings bridged micro- and nanoscale observations and helped establish nanogeoscience as a transformative approach in resource geology.

Building on this foundation, we have initiated a new project on the Chinkuashi (Jinguashi) gold–copper deposit in northern Taiwan, one of East Asia’s historically important gold mining districts. Chinkuashi is characterized by epithermal mineralization associated with volcanic–hydrothermal activity and contains complex assemblages of Au, Ag, Cu, and As-bearing minerals. Our current research focuses on the nanoscale occurrence, chemical state, and partitioning of noble metals (Au, Ag) and toxic elements within ore minerals from this site. By integrating advanced TEM, spectroscopy, and isotopic analysis, we aim to clarify metal enrichment mechanisms and contribute to sustainable resource exploration and environmental management of legacy mining areas.