Abstract

Volcanogenic massive sulfide (VMS) deposits typically contain significant proportions of magma-derived chalcophile (Cu affinity) and siderophile (Fe affinity) elements such as Au, Cu, V, Zn, Mo, Bi, Sb, and As that relate to the composition of associated (host) magmatic rocks. Here, we combine new and published trace element data for lavas recovered from 15 volcanic centers along the Kermadec arc. The data show that mafic back-arc and arc-front lavas are enriched in most of the chalcophile and siderophile elements when compared with mid-ocean ridge basalts (MORB). Elevated (Cu, Zn, V, Mo, Pb)/Yb, Ba/La, As/Ce, and Sb/Pr ratios indicate that the chalcophile and siderophile elements are either transported into the mantle wedge via hydrous fluids derived from the subducting slab, or are liberated from residual mantle wedge sulfides that are oxidized by hydrous fluids. Lower ratios of (Cu, Zn, Mo, Sb, and Pb)/(MREE, HREE) in basalts from the Kermadec back arc (Havre Trough) when compared to the arc front suggests decreasing slab-related input into the mantle source away from the arc front. Unusually high contents of LILE, Ag, Sn, Mo, Th, LREE, MREE, Nb, Zr, Hf, and positive trends in (Ag, Sn)/Yb with Th/Yb, Hf/Y, (La/Sm)N, but low Sr/Y, in dacites from the Brothers volcanic center, southern Kermadec arc, indicate the additional transport of Ag and Sn via a solute-rich supercritical fluid, or via a sediment-derived melt. Magmas generated through partial melting of a sub-arc mantle metasomatized by hydrous melts thus appear to play an important role in the formation of Cu-Au-Ag−rich arc-type VMS deposits.

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