Genesis of the early Cretaceous porphyritic granitoid: New insights from the Hongling skarn polymetallic metallogenesis, NE China

Abstract

The Hongling skarn Fe–Pb–Zn deposit is situated in the Lindong district of eastern Inner Mongolia, southern Great Hinggan Range. Previous investigations have established that the metallogenic fluid and ore-forming material at Hongling originated from the magmatic system, with mineralization temporally coinciding with the early Cretaceous granitic emplacement (ca. 142–143  Ma). Petrogenetic studies further suggest that the Hongling granitoids share comparable magmatic origins and evolutionary pathways with regional contemporaneous intrusions. In this contribution, we integrate new zircon U-Pb geochronology, whole-rock geochemistry, and Sr-Nd-Hf-S-Pb isotopic analyses of porphyritic granitoids and associated sulfides with existing regional datasets to: (1) constrain the magmatic evolution of Hongling intrusives; (2) discriminate between mineralized and barren intrusion characteristics; and (3) elucidate metallogenic processes. In situ sulfur (δ³⁴S = −2.8 ‰ to +1.1 ‰) and lead (²⁰⁶Pb/²⁰⁴Pb = 18.292 to 18.303) isotopic signatures from ore minerals demonstrate a predominant magmatic derivation..The porphyritic granitoids exhibit transitional Sr-Nd-Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.7065–0.7091, ε_Nd(t) = −1.25 to +0.69, and ε_Hf(t) = +0.12 to +8.39), consistent with partial melting of juvenile lower crustal sources. Comparative analysis with regional coeval plutons reveals that the Lindong mineralized intrusions underwent crystal-melt segregation processes, with the Hongling porphyritic phase representing interstitial melts extracted from crystal-rich mush zones.. Subsequent reactivation of these segregated melts facilitated efficient extraction and concentration of ore-forming fluids, ultimately leading to Fe-Pb-Zn mineralization through fluid-rock interaction in skarn systems.