Zn/Cd ratios and cadmium isotope evidence for the classification of lead-zinc deposits

Abstract

Lead-zinc deposits are often difficult to classify because clear criteria are lacking. In recent years, new tools, such as Cd and Zn isotopes, have been used to better understand the ore-formation processes and to classify Pb-Zn deposits. Herein, we investigate Cd concentrations, Cd isotope systematics and Zn/Cd ratios in sphalerite from nine Pb-Zn deposits divided into high-temperature systems (e.g., porphyry), low-temperature systems (e.g., Mississippi Valley type [MVT]) and exhalative systems (e.g., sedimentary exhalative [SEDEX]). Our results showed little evidence of fractionation in the high-temperature systems. In the low-temperature systems, Cd concentrations were the highest, but were also highly variable, a result consistent with the higher fractionation of Cd at low temperatures. The δ114/110Cd values in low-temperature systems were enriched in heavier isotopes (mean of 0.32 ± 0.31‰). Exhalative systems had the lowest Cd concentrations, with a mean δ114/110Cd value of 0.12 ± 0.50‰. We thus conclude that different ore-formation systems result in different characteristic Cd concentrations and fraction levels and that low-temperature processes lead to the most significant fractionation of Cd. Therefore, Cd distribution and isotopic studies can support better understanding of the geochemistry of ore-formation processes and the classification of Pb-Zn deposits.

Cadmium Isotope Ratios of Standard Solutions and Geological Reference Materials Measured by MC‐ICP‐MS

“…These minerals commonly have extremely high Zn/Cd ratios (e.g., up to 500) (Wen et al . ). A significant influence of Zn on Cd isotope ratio measurement result was previously found by Cloquet et al .…”

The Cd isotope composition of atmospheric aerosols from the Tropical Atlantic Ocean

“…For leachate subsamples, the EF crust values of the corresponding total digests are plotted. The colored bars denote the Cd isotope compositions of the upper continental crust [ Schmitt et al , ], fumes/ash from metal smelting operations [ Cloquet et al , ; Shiel et al , , Chrastńy et al , ], and ore minerals [ Wombacher et al , ; Shiel et al , ; Zhu et al , , Chrastńy et al ., , Wen et al , , ; Zhu et al , ; Martinková et al , ].…”

High‐Precision Cd Isotope Measurements of Soil and Rock Reference Materials by MC‐ICP‐MS with Double Spike Correction

“…This makes Cd isotopes useful for the study of the evolution of the solar system (Wombacher et al , ). Cadmium isotopes have also been used to investigate ore deposit formation processes (e.g., Zhu et al , Wen et al , Zhu et al ) and marine cycling of Cd (e.g., Lacan et al , Ripperger et al , Abouchami et al , Conway and John ). In recent decades, Cd mass fractions in world‐wide soils have dramatically increased due to contamination from mining, smelting, electroplating, wastewater irrigation, and use of chemical fertilisers and pesticides (e.g., Ghosh and Singh , Zhang et al , Wei et al ).…”