Sulfide texture and geochemistry of the Neoarchean Hongtoushan Cu-Zn deposit (NE China): Implication for mixed-state metamorphic remobilization

Abstract

The Hongtoushan Cu-Zn deposit in the Neoarchean Qingyuan greenstone belt of the North China Craton is the oldest volcanogenic massive sulfide (VMS) deposit in China. The ore samples are classified by massive sulfide ores, disseminated sulfide ores, and sulfide-bearing quartz veins. Four types of massive sulfide ores are further identified. Type A massive ore, characterized by the granular quartz and euhedral dark mineral aggregates in the massive sulfides matrix, is interpreted as the result of partial melting of primary sulfides, and type B might record the process of partial melting and mechanical migration. Type C massive ore, formed by the recrystallization of type B massive ore, is characterized by coarse pyrite and pyrrhotite porphyroblasts. Type D massive ore undergoes deformation and upgrades by elements released during recrystallization. The relic anhydrite in type A massive ore is the preserve of the primary mineral from VMS mineralization. Most sulfide in massive ores has δ34S values closing to ∼ 0 ‰, showing magmatic sulfur characteristics. The intergrowth of pyrrhotite and magnetite with higher δ34S (5.5–8.3 ‰) is suggested to be the dissolution product of primary anhydrite. The sulfides from the tourmaline-bearing quartz veins have negative δ34S (-6.0 – −2.6 ‰) values, indicating that the sulfur was released from the desulfurization of massive pyrite. The ore remobilization is dominated by partial melting of sulfide and mechanical migration during the peak metamorphism. The fluid metasomatism is activated at the retrograde metamorphism. This mixed-state metamorphic remobilization plays a key role in the formation of metamorphosed massive sulfide ore and ore upgrading.