Compositional characteristics and geodynamic significance of late M iocene volcanic rocks associated with the C hah Z ard epithermal gold–silver deposit, southwest Y azd, I ran

Abstract

Whole‐rock geochemical and S r– N d isotopic data are presented for late M iocene volcanic rocks associated with the C hah Z ard epithermal A u– A g deposit in the U rumieh‐ D okhtar M agmatic A rc ( UDMA ), I ran, to investigate the magma source, petrogenesis and the geodynamic evolution of the study area. The C hah Z ard andesitic to rhyolitic volcanic rocks are characterized by significant L arge I on L ithophile E lement ( LILE ) and L ight R are E arth E lement ( LREE ) enrichment coupled with H igh F ield S trength E lement ( HFSE ) depletion. Our geochemical data indicate an adakitic‐like signature for the volcanic rocks (e.g. SiO 2 > 62 wt%, Al 2 O 3 > 15 wt%, MgO S r/ Y > 70, L a/ Y b > 35, Y b Y E u anomalies), distinguishing them from the other volcanic rocks of the UDMA . The C hah Z ard volcanic rocks have similar S r and N d isotopic compositions; the 87 S r/ 86 S r(i) ratios range from 0.704 902 to 0.705 093 and the ε Nd (i) values are from +2.33 to +2.70. However, the rhyolite porphyry represents the final stage of magmatism in the area and has a relatively high 87 S r/ 86 S r ratio (0.705 811). Our data suggest that the andesitic magmas are from a heterogeneous source and likely to result from partial melting of a metasomatized mantle wedge associated with a mixture of subducted oceanic crust and sediment. These melts subsequently underwent fractional crystallization along with minor amounts of crustal assimilation. Our study is consistent with the model that the volcanic host rocks to epithermal gold mineralization in the UDMA are genetically related to late M iocene N eo‐ T ethyan slab break‐off beneath C entral I ran.

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