Genesis of the Zhangquanzhuang gold deposit in the northern margin of North China Craton: Constraints from deposit geology and ore isotope geochemistry

Abstract

The genesis of orogenic gold deposits in the northern margin of the North China Craton (NCC) is still ambiguous, and this is addressed in this case study on the Zhangquanzhuang gold deposit. This deposit shows features typical of orogenic gold deposits, including quartz vein-type mineralization controlled by shear zones, sericite-quartz-pyrite-carbonate alteration along shear zones, absence of connection to any magmatic intrusion, and occurrence of native gold and electrum. The Zhangquanzhuang gold deposit, which is hosted in Archean high-grade metamorphic rocks, was formed in Mesozoic and largely later than the regional metamorphism. In this deposit, the Pb isotope compositions of sulfides in ores have low 206Pb/204Pb ratios of 16.874–17.007, 207Pb/204Pb ratios of 15.368–15.410, and 208Pb/204Pb ratios of 37.023–37.215, and these are much less radiogenic than those of regional metamorphic and magmatic rocks. This finding precludes the possible derivation of ore fluid from regional magmatism and metamorphism. In pyrite-hosted fluid inclusions in the ores, the 3He/4He and 40Ar/36Ar ratios are 1.26–1.75 Ra and 1622–2816, respectively, showing prominent signature of mantle sources. These geochemical features, together with the large temporal discrepancy between regional metamorphism and mineralization, suggest that ore fluid and metal had a subcrustal source similar to the gold deposits in the Jiaodong gold province in the southeastern margin of the NCC. The calculated δ34SH2S values for the ore fluid are 2.31–4.48‰, which are heavier than the δ34S of depleted mantle. The δ18O of ore-related quartz mostly cluster around 11‰, implying high δ18O of subcrust-derived ore fluid. The stable O and S isotope data indicate that the subcrustal source has been metasomatized by subducted crustal sediments.