The role of dehydration of subducted serpentinites in the genesis of gold-rich magmatic-hydrothermal ore deposits

Resumen

Here we present a geochemical study of whole-rock concentrations of gold and other noble metals (Ir, Ru, Rh, Pt and Pd) in subducted serpentinites and their dehydration products, i.e. chlorite harzburgites, from Cerro del Almirez (southern Spain). The Cerro del Almirez massif exposes the arrested front of antigorite breakdown in high-pressure subducted serpentinites (Trommsdorff et al., 1998; Padrón-Navarta et al., 2011), which is one of the most important reactions that generate fluids in subduction zones (Ulmer and Trommsdorff, 1995). Hence, the concentrations of precious metals, including gold, in these rocks constitute a unique opportunity to evaluate the impact of serpentinization, subduction metamorphism and serpentinite dehydration on the metal budget of subducted mantle, and to constrain the role of serpentinite-derived fluids in the transfer of metals to the mantle wedge. We show that gold has been significantly partitioned into fluids released by the dehydration of serpentinites, thus providing a firm natural evidence of gold endowment in the source of arc magmas that may form gold-rich deposits. Additionally, we provide a direct application of our results to explain the source of gold in epithermal deposits currently under exploitation in southern Spain.