Genetic correlation of metasomatized mantle source with Ni-Cu mineralization in orogenic belt
Orogenic belts normally have complex dynamic environments,subduction history and thermodynamic conditions,hence,their mantle source components,melting mechanisms and magmatic products are significantly different from those of mantle plumes and continental rift zones.For this reason,mafic/ultramafic magmatism-related Ni-Cu sulfide mineralization in orogenic belts is different from those in intra-plate environments.This article reviews the new progress in the relationship between metasomatized mantle sources and Ni-Cu mineralization in orogenic belts,focusing on the following three aspects:(1)Contributions of lithosphere and asthenosphere:Ore-forming mafic/ultramafic magmas are generated through the combination of decompression melting of asthenospheric mantle and hydrous melting of metasomatized lithospheric mantle.The metasomatized mantle,showing volatile-and carbonate-rich characteristics,was previously modified by variable proportions of slab sediments/melts(Ca-rich sediments)and fluids derived from low-temperature altered oceanic crust.The most important mineralization commonly forms in the post-subduction stage.(2)Constraints on mineralization from the redox state of mantle-derived magmas:A rapid drop in oxygen fugacity exists in the ore-forming magmas before and after sulfide saturation,leading to exponentially decrease in sulfur solubility in the magma system of the Phanerozoic orogenic belts,which may result in sulfide segregation or create low-sulfur solubility conditions for further sulfide saturation.The magma reduction process has proven to be caused by efficient assimilation of carbonaceous matter during magma emplacement.(3)Transport and concentration of sulfide droplets by volatile components:Volatiles significantly reduce the viscosity of the silicate melt,decreasing the viscous resistance to magma overpressure.The exsolution and nucleation of volatiles during magma ascent produce many low-density bubbles which combine with sulfide droplets to form compound drops.This process promotes the aggregation of sulfide droplets,increases their metal content,and facilitates the upward transport of sulfide droplets.These understandings in combination with the spatial-temporal coupling between some typical Ni-Cu metallogenic provinces and the underlying metasomatized mantle indicate that the metasomatized mantle may promote magmatic sulfide mineralization.Although significant advances have been achieved in recent years in the study of contribution of metasomatized mantle to Ni-Cu sulfide mineralization in orogenic belt,further research is needed on the effect of the redox state on the ore-forming magmas in the pre-Cambrian orogenic belt,the diversity of Ni-Cu-Co mineralization in orogenic belts,the effect of different metasomatism on the behavior of chalcophile elements during mantle melting,and the controls of volatile recycling within mantle-crust on the migration and enrichment of chalcophile elements.
Ni-Cu depositsMetasomatized mantleMagma reductionVolatilesOrogenic belt
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