Hydraulic fracturing-induced gold remobilization: Pyrite geochemical and sulfur isotopic insights from the Liuan lode gold deposit, South China

Abstract

The coupled dissolution-reprecipitation (CDR) process is critical for gold remobilization and re-enrichment within global gold mineralization systems, and its driving mechanism warrants further investigation. The Liuan lode gold deposit in the Dayaoshan district (South China) features multiple generations of pyrite, including Py1 (pre-ore stage), Py2 (including Py2c and Py2r) and Py3 (ore stage), and Py4 (post-ore stage). Py2c is As-Cu-Pb-Ag-Au-rich (initial gold enrichment), suggestive of fluid boiling during its formation, corroborated by low δ³⁴S values (avg. −3.83‰) and hydrothermal breccias. In contrast, Py2r is depleted in these elements, indicative of non-boiling conditions, further supported by heavier δ³⁴S values (avg. −2.53‰). Several pieces of evidence, including sharp reaction fronts and As-Au contents differences between Py2c and Py3, and Py2c remnants and mineral inclusions (chalcopyrite, galena, and native gold) within Py3, indicate the CDR process, during which Au in Py2c was remobilized and reprecipitated as native gold. The CDR process is triggered by oxidation of the mineralizing fluids, consistent with the decreasing δ³⁴S values from Py2r to Py3. Combined with higher Co-Ni concentrations in Py3 (similar to Py2c) relative to Py2r, we infer that fluid oxidation is associated with hydraulic fracturing restart. Multiple sulfur isotopes (δ³⁴S: −4.92 to 0.45‰; Δ³³S: −0.05 ± 0.10‰) and low Co-Ni and high Se contents of pyrite suggest a magmatic fluid origin from a possible concealed intrusion. This study underscores magmatic-hydrothermal contributions in forming lode gold deposits in Dayaoshan, and highlights the importance of pressure-driven hydrothermal processes in initial gold precipitation, remobilization, and reprecipitation within gold deposits.