Geochemical indicators for cobalt-rich skarn exploration: constraints from the Pusangguo granodiorite (Gangdese) on geochemistry, zircon U-Pb geochronology and Hf-Nd-Sr isotopes

The Pusangguo skarn-type copper-polymetallic deposit in the Gangdese metallogenic belt hosts economic cobalt mineralization. An integrated study of petrography, zircon U-Pb geochronology, whole-rock geochemistry, and Sr–Nd–Hf isotopes indicates the ore-forming Pusangguo granodiorite was emplaced at 15.09 ± 0.74 Ma and exhibits adakitic affinities, characterized by high Sr, low Y, and high La/Yb and Sr/Y ratios. The isotopic compositions (ε Hf(t) = −0.6 to +2.5; ε Nd(t) = −5.43 to −5.2) support a derivation from the partial melting of thickened juvenile lower crust. It is posited that a genetic association exists between cobalt-rich skarns and such adakite-like intrusions, which is not observed for cobalt-poor skarns. The high oxygen fugacity of these magmas inhibits early sulfide saturation, thereby promoting the incompatible behavior of cobalt. This enables its preconcentration in the melt and, thus, its ultimate deposition in skarns via magmatic-hydrothermal processes. Consequently, adakitic signatures in intrusions are a key indicator for targeting cobalt-rich skarn deposits in the Gangdese belt. This study aims to identify the key geochemical signatures of intrusions associated with cobalt-rich skarn deposits, and to evaluate whether adakitic affinities can serve as a reliable exploration indicator in the Gangdese belt.