Geochemical Characteristics of Pyrite: Implications for Genesis of gold deposits in Tatun volcanic area, Taipei

Pyrite is the most abundant sulfide mineral on Earth's surface, widely distributed in various types of hydrothermal deposits and diagenetic processes. Its mineralogical and geochemical characteristics are important indicators for gold exploration. This study focuses on Sihuangziping in the Tatun volcanic area, near the Sanchungchiao gold deposit (Ba-yan), reportedly mined by the Spanish. Mineralogical evidence suggests a potential connection between this area and the Chinkuashih gold deposit, though this hypothesis remains controversial, and its economic viability has not been confirmed. Nevertheless, both areas share a hydrothermal mineralization background, indicating potential metallogenic conditions in the Tatun volcanic area. However, the pyrite formation mechanism and its relationship with gold enrichment in this area remain unclear.

In this study, we aim to establish the first comprehensive trace element database of pyrite from the Tatun volcanic area, elucidating the metallogenic processes and providing reliable indicators for geochemical exploration. Pyrite from drill core samples (depth of 775 meters) was analyzed using Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Electron Probe Microanalysis (EPMA), and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Preliminary results show that pyrite is relatively enriched at depths of 450–500 meters, occurring primarily as irregular aggregates and massive forms. Crystal habits are cubic and octahedral, with sizes ranging from 100 to 1000 micrometers (µm) and gold concentrations of 1.1–2.6 weight percent (wt%). Some samples (at 400 and 700 m) show arsenic oscillatory zonation, with individual layers containing up to 2.97 wt% arsenic and trace amounts of cobalt (0.0109 wt%), nickel (0.0078 wt%), and copper (0.0359 wt%).

Future research will focus on elemental ratios such as Fe/S, Co/Ni, S/Se, and Te/Se to interpret the metallogenic environment and fluid sources of the study area. Additionally, gold within sulfides may occur as "invisible gold," either in nanoparticle form or through lattice substitution. The Au/As ratio will be analyzed to determine the mode of gold occurrence and compared with Chinkuashih gold deposit samples to better understand the mechanisms and processes of mineralization. By integrating these findings, this study seeks to evaluate the potential for gold deposits in Sihuangziping and provide critical insights into the genetic significance of the Tatun volcanic area.