Abstract

A model is proposed for the origin and emplacement of the ca. 341 Ma Aguablanca magmatic Ni-Cu-(platinum group element [PGE]) sulfide deposit (SW Iberia) integrating petrological, geochemical, structural, and geophysical data. The Aguablanca deposit occurs in an unusual geodynamic context for this ore type (an active plate margin) as an exotic , magmatic subvertical breccia located at the northern part of the coeval gabbronorite Aguablanca stock (341 ± 1.5 Ma). Structural and gravity data show that mineralized breccia occurs inside the inferred feeder zone for the stock adjacent to the Cherneca ductile shear zone, a Variscan sinistral transpressional structure. The orientation of the feeder zone corresponds to that expected for tensional fractures formed within the strain field of the adjacent Cherneca ductile shear. Two distinctive stages are established for the origin and emplacement of the deposit: (1) initially, the ore-forming processes are attributed to magma emplacement in the crust, assimilation of crustal S, and segregation and gravitational settling of sulfide melt (a scenario similar to most plutonic Ni-Cu sulfide ores), and (2) final emplacement of the Ni-Cu sulfide-bearing rocks by multiple melt injections controlled by successive opening events of tensional fractures related to the Cherneca ductile shear zone.

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