Copper isotopic compositions of the Zijinshan high-sulfidation epithermal Cu-Au deposit, South China: Implications for deposit origin

- Most of the Cu-bearing minerals in the Zijinshan deposit have a hypogene origin.
- High- and low-sulfidation epithermal deposits all have deep metal source.
- Cu isotopes could provide insights into metal precipitation and fluid flow.

The Zijinshan high-sulfidation epithermal Cu-Au deposit is located in the Zijinshan ore field of South China, comprising porphyry-epithermal Cu-Au-Mo-Ag ore systems. The Cu ore body is more than 1000 m thick and is characterized by an assemblage of digenite-covellite-enargite-alunite. Digenite is the dominant Cu-bearing mineral, which makes this deposit unique, although the mechanisms of digenite formation remain controversial. To elucidate the genesis of digenite, this paper presents the Cu isotopic compositions of Cu-sulfides in the Zijinshan high-sulfidation Cu-Au deposit. The Cu isotopic values (65Cu relative to NIST 976) of all samples range from −2.97‰ to +0.34‰, and most values fall in a narrow range from −0.49‰ to +0.34‰, which is similar to the Cu isotopic signature of typical porphyry systems. Copper isotope ratios of each mineral decrease with increasing depth, a trend that is also typical of porphyry deposits. The variation tendency of δ65Cu values between sulfides is consistent with the sequence of mineral formation. These observations suggest that the Cu-sulfides in the Zijinshan Cu-Au deposit have a hypogene origin.

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