Study on Dynamic Mechanism of Magmatic Copper-Nickel Sulfide Deposits in Orogenic Belts

Previous studies have proposed various ore-forming dynamic models for magmatic Cu-Ni deposits in orogenic belts, including mantle plume overlapping orogenic belts, plate subduction and mantle plume interaction, partial melting of the lithospheric mantle, mixing of asthenospheric and lithospheric mantle during post-collision extension, and decompression melting caused by tearing of slab leading to asthenospheric mantle upwelling. However, the multiple episodes of subduction-accretion orogeny throughout the history of Earth evolution, the above dynamic processes have occurred, but Cu-Ni sulfide deposits have not been formed. Therefore, the key factors for the formation of Cu-Ni sulfide deposits in orogenic belts await further clarification. Based on the fact that the above models all point to Cu-Ni sulfide deposits in orogenic belts originating from subducted metasomatic mantle sources and forming after the peak subduction period, we propose a two-stage ore-forming dynamic model for Cu-Ni sulfide deposits in orogenic belts. Stage One: During the subduction period, interactions between mantle peridotites and silicic melts from the subducting slab lead to the release of elements such as nickel from olivine and sulfur carried by the subduction melts, thus forming a mantle source dominated by pyroxenite containing orthopyroxene and nickel sulfides. Stage Two: After the end of the subduction-collision period, the pyroxenite mantle source enriched during subduction enters the asthenospheric mantle through delamination and undergoes remelting, where the melting conditions change to near hydrous-free conditions. In this condition, these mafic magmas differentiate to form sulfur-rich, copper-affinitive sulfides crystallizing into sulfide piles or magma sulfide deposits. The large depth fault, ductile shear zones, and suture zones serve as magma conduits for the enrichment of the parent magma, with the combined action of source region and magmatic process leading to the formation of Cu-Ni sulfide deposits in orogenic belts.