Zn–S isotopic fractionation effect during the evolution process of ore-forming fluids: A case study of the ultra-large Huize rich Ge-bearing Pb–Zn deposit

Abstract

The fluid evolution process is a key research subject in the field of ore deposit geology. An accurate inversion of the evolution history of ore-forming fluids (OFFs) can play a crucial role in the investigation of mineralisation processes and metallogenesis. In addition, analysing the combination of Zn–S isotopes eliminates the uncertainty and unilaterality of monoisotopic tracing and provides a more accurate interpretation of the evolution of OFFs during the mineralisation process. To trace the migration direction and evolution process of OFFs, based on a collected and tested batch of Zn–S isotope compositions, the characteristics of Zn–S isotopic fractionation and the type of metallogenesis were comprehensively analysed to determine the basis for building a metallogenic model of the Ultra-large scale Huize rich Ge-bearing Pb–Zn Deposit, composed of Kuangshanchang deposit and Qilinchang deposit. Previous studies have shown that OFFs migrate upward from deep sections, whereas stratum brine and atmospheric precipitation containing reduced S migrate downward from shallow sections. Rayleigh fractionation of Zn–S isotopes occurred during the migration and evolution of OFFs, resulting in the accumulation of the heavier isotopes of Zn and S present in the fluids. For example, from shallow to deep sections, δ34S values were 5–9‰ (2400–2200 m), 8.5–17.2‰ (1900–1400 m), and 13.6–15.2‰ (1274 m), the δ66Zn values of ore minerals in Qilinchang were 0.205–0.307‰ (1832–1840 m) and 0.203–0.247‰ (1261 m), while the δ66Zn values of ore minerals in Kuangshanchang were 0.290–0.424‰ (1752 m), 0.169–0.3157‰ (1463 m), and 0.033–0.123‰ (1274 m), respectively. Consequently, the isotopic composition of sulfides exhibited an obvious spatiotemporal zoning. Heavier Zn isotopes and lighter S isotopes gradually accumulated in the sulfides at increasingly shallow depths; temporally, the sulfides gradually enriched in heavier isotopes between the early and late stages of mineralisation.