Rb–Sr and Sm–Nd isotopic compositions and Petrogenesis of ore-related intrusive rocks of gold-rich porphyry copper Maherabad prospect area (North of Hanich), east of Iran

The Maherabad gold-rich porphyry copper prospect area is located in the eastern part of Lut block, east of Iran. This is the first porphyry Cu-Au prospecting area which is discovered in eastern Iran. Fifteen mineralization-related intrusive rocks range (Middle Eocene 39 Ma) in composition from diorite to monzonite have been distinguished. Monzonitic porphyries had major role in Cu-Au mineralization. The ore-bearing porphyries are I-type, metaluminous, high-K calc-alkaline to shoshonite intrusive rocks which were formed in island arc setting. These rocks are characterized by average of SiO2> 59 wt %, Al2O3 > 15 wt %, MgO< 2 wt %, Na2O> 3 wt %, Sr> 870 ppm, Y< 18 ppm, Yb< 1.90 ppm, Sr/Y> 55, moderate LREE, relatively low HREE and enrichment LILE (Sr, Cs, Rb, K and Ba) relative to HFSE (Nb, Ta, Ti, Hf and Zr). They are chemically similar to some adakites, but their chemical signatures differ in some ways from normal adakites, including higher K2O contents and K2O/Na2O ratios and lower Mg#, (La/Yb)N, (Ce/Yb)N and εNd in Maherabad rocks. Maherabad intrusive rocks are the first K-rich adakites that can be related with subduction zone. Partial melting of mantle hybridized by hydrous, silica-rich slab-derived melts or/and input of enriched mantle-derived ultra-potassic magmas during or prior to the formation and migration of adakitic melts could be explain their high K2O contents and K2O/Na2O ratios. Low Mg# values and relatively low MgO, Cr and Ni contents imply limited interaction between adakite-like magma and mantle wedge peridotite. The initial 87Sr/86Sr and (143Nd/144Nd)i was recalculated to an age of 39 Ma (unpublished data). Initial 87Sr/86Sr ratios for hornblende monzonite porphyry are 0.7047-0.7048. The (143Nd/144Nd)i isotope composition are 0.512694-0.512713. Initial εNd isotope values 1.45-1.81. These values could be considered as representative of oceanic slab-derived magmas. Source modeling indicates that high-degree of partial melting (relatively up to 50%) of a basaltic garnet-bearing (lower than 10%) amphibolite to amphibolite lacking plagioclase as a residual or source mineral can explain most of the moderate to low Y and Yb contents, low (La/Yb)N, high Sr/Y ratios and lack of negative anomaly of Eu in the rocks of the district. The geochemical signature of the adakites within the granitoid rocks represents a characteristic guide for further exploration for copper porphyry-type ore deposit in Eastern Iran.