Rb-Sr and Sm-Nd isotopic compositions and Petrogenesis of ore-relatedintrusive 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 ea stern part of lutblock, 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 tomonzonite have been distinguished. monzonitic porphyries had major role in cu-au mineralization. the orebearingporphyries are i-type, metaluminous, high-k calc-alkaline to shoshonite intrusive rocks which wereformed in island arc setting. these rocks are characteri zed by average of si02> 59 wt %, ai20 } > 15 wt %,mgo< 2 wt %, na20> 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 normaladakites, including higher k20 contents and k20ina20 ratios and lower mg#, (la/ybje , (ce/ybj; and i:ndin maherabad rocks. maherabad intrusive rocks are the first k-rich adakites that can be related withsubduction zone. partial melting of mantle hybridi zed by hydrou s, silica-rich slab-deri ved melts orland inputof enriched mantle-derived ultra-potassic magmas during or prior to the formation and migration of adakiticmelts could be explain their high k20 contents and k20/na20 ratios . low mg# values and relati vely lowmgo, cr and ni contents imply limited interaction between adakite-like magma and mantle wedgeperidotite. the initial 87sr/86sr and e4 3ndj144nd)i was recalculated to an age of 39 ma (unpublished data).initial r7srl6sr ratios for hornblende monzonite porphyry arc 0.7047 -0.704 8. the (14 3nd/h 4nd)i isotopecompos ition are 0.512694-0.512713. initial end isotope values 1.45 -1.81. these values could be consideredas representative of oceanic s lab-derived magmas. source modeling indicates that high-degree of partialmelting (relatively up to 50%) of a basaltic garnet-bearing (lower than 10%) amphibolite to amphibolitelacking plagioclase as a residual or source mineral can explain most of the moderate to low y and ybcontents, low (la/ybjs, high srly ratios and lack of negative anomaly of eu in the rocks of the di strict. thegeochemical signature of the adakites within the granitoid rocks represents a charac teristic guide for furtherexploration for copper porphyry-type ore deposit in eastern iran