Insights on geochemical characteristics, microthermometry of hydrothermal fluids, and sulfur isotope systematics of the Daralu porphyry Cu deposit, SE Iran

Abstract

The Miocene Daralu Porphyry Copper Deposits (PCDs) is found associated with other porphyries such as Sarcheshmeh and Meiduk in the Kerman Cenozoic Magmatic Arc (KCMA), southern Iran. In this research, we provided whole-rock geochemical data, characteristics of hydrothermal fluid and sulfur isotope composition of the Daralu intrusive body, and discussed the nature, tectonic setting and fluid evolution of this deposit aiming to investigate its fertility. The Daralu porphyry shows adakites affinity, that is, high Sr/Y and La/Yb ratios and positive Eu anomalies. The REEs patterns indicate a strong fractionation ([La/Yb]n= 28.73). High La/Sm and Dy/Yb ratios suggest enrichment of amphibole and garnet as residual phases in melt source, whereas partial melting of plagioclase increases Eu and Sr in the parent magma. The presence of garnet implies a pressure equivalent to the thickness of more than 40km of crust. To elucidate the evolutionary history of fluids and the origin of the Daralu deposit, we focused on the origin and composition of the fluid through petrography, laser Raman, and microthermometry studies of fluid inclusions. The fluid inclusions have been divided into four types: vapor (type I), aqueous-vapor (type II), CO2-bearing (type III), and multiphase (type IV). The Raman shifts included 1284 and 1388 cm−1 for CO2 and 2750–3900 cm−1 for H2O. The events such as NaCl supersaturation, exhausting of CO2-rich components, high oxygen fugacity and temperature decreasing through mineralization stages were critical in controlling the fertility of the Daralu PCD. The obtained δ34S data for sulfides yielded an average of +5.5‰. Based on the observed features, it was concluded that Daralu porphyry shares formation conditions with other productive porphyries of the KMCA.