Genesis of the giant Huoshaoyun non-sulfide zinc-lead deposit in Karakoram, Xinjiang: constraints from zinc isotope geochemistry

“Non-sulfide” Zn-Pb deposits are comprised of a series of non-sulfide minerals and are of crucial economic importance. Nonetheless, the metal sources for non-sulfide deposits are difficult to constrain by C-O isotopes due to possibly different sources of metals and carbon and oxygen. To evaluate zinc isotopes as a tracer of metal sources, here we study the range, cause, and result of zinc isotope fractionation in the Huoshaoyun world-class non-sulfide Zn-Pb deposit along with C-O isotope analysis. The smithsonite has higher δ 13 C VPDB (1.5‰–4.7‰) and δ 18 O VSMOW (21.0‰–24.7‰) values than cerussite (δ 13 C VPDB : −6.5‰ to −3.4‰, δ 18 O VSMOW : 10.3‰–12.2‰). The inter-mineral isotope differences are consistent with equilibrium fractionation at low temperature. Because heavier Zn isotopes prefer to incorporate into Zn-carbonate relative to fluids, most carbonate minerals have heavy Zn isotope compositions. However, smithsonite and cerussite in the Huoshaoyun deposit have the same extremely low δ 66 Zn of 0.00‰–0.11‰ (n = 41). Processes such as oxidation of sulfide minerals, equilibrium fractionation, or Rayleigh distillation alone cannot fully account for the low and homogeneous δ66Zn values. The most plausible interpretation is that Zn in the carbonate ores was supplied by an isotopically light Zn reservoir, with published MVT sphalerite datasets showing the closest isotopic match among the source reservoirs tested by Monte Carlo simulations. Our studies shed new light on the genesis of non-sulfide deposits and show that zinc isotopes can be a useful tracer of Zn sources in non-sulfide deposits and other settings.