『Abstract
We measured the Fe, Cu, and Zn isotopic compositions of the fluids
generated during leaching experiments with pyrite-, chalcopyrite-,
and sphalerite-rich rocks and with a sphalerite mineral separate.
Our study demonstrates that the oxidative weathering of sulfide-rich
rocks can produce substantial variations in Fe (-1.75 to +1.0‰Δ56Fesolution-pyrite rock) and Cu (0.0 to +2.0‰Δ65Cusolution-chalcopyrite rock) isotopes and small
variations in Zn isotopes (0.0 to +0.2‰Δ66Znsolution-sphalerite)
in the fluid phase relative to the rock. For the Fe and Cu systems
we suggest that isotopic fractionation is caused by electron-exchange-driven
(e.g., Fe(II)/Fe(III) and Cu)I)/Cu(II) redox) reactions at the
surfaces of the sulfide minerals that occur during air and aqueous
chemical reactions. Under acidic conditions, these reactions tend
to enrich the fluid phase in the heavier Fe and Cu isotopes. However,
under circumneutral pH conditions, the Fe isotopic composition
in solution was controlled by the precipitation of Fe(III)-oxide
phases, which enriched the solution in the lighter Fe isotopes.
This investigation provides a preliminary framework for interpreting
the impact of sulfide oxidation reactions on the distributions
of stable Fe, Cu, and Zn isotopes in natural waters.
Keywords: Cu; Fe; Zn; Isotopes; MC-ICP-MS』
1. Introduction
2. Methods
2.1. Samples and materials
2.2. Experimental setup
2.3. Elemental analyses
2.4. Isotopic analyses
3. Results
3.1. Sample characterization
3.2. Continuous batch leaching experiments
3.3. Cyclic leaching experiments
3.4. De, Cu, and Zn isotopes in rock samples
3.5. Fe isotopes in leachate
3.6. Cu isotopes in leachate
3.7. Zn isotopes in leachate
4. Discussion
4.1. Fractionation of Fe isotopes during oxidative weathering
of sulfide-rich rock
4.2. Fractionation of Cu isotopes during oxidative weathering
of sulfide-rich rock
4.3. Fractionation of Zn isotopes during oxidative weathering
of sulfide-rich rock and sphalerite
5. Conclusion and implications for natural systems
Acknowledgments
Appendix A. Supplementary data
References