Geochemistry Of Nagarparkar Igneous Complex And Saindak Adakites,Pakistan:Cu-Au Mineralization And Tectonic Implications

Since a couple of decades,it has been evaluated that most of the economical minerals have been discovered via different igneous rock types.These igneous rocks have been considered as a principle source for the mineralization of Cu-Au-Mo and Ag.These igneous rocks can be originated from different tectonic settings,i.e.,continet-continent collision,oceanic to continental collision,volcanic arc setting,back arc setting,or within plate tectonic settings.It is generally believed that most of the economical minerals are mineralized in the different tectonic settings;arc-related rocks are one of these tectonic settings.Arc-related rocks have much importance for the generation of ore minerals such as Cu,Au,Mo and Ag.The mineralization of ore minerals has been noticed in the arc-related tectonic environment in the world,such as Pacific arc,Pacific ring of fire,Tethyan arc,Indonesia arc,Philippine arc.From a number of arc-related rocks,Malani Igneous Suite(MIS)of Aravalli-Delhi magmatic arc system is also world famous arc suite,which is getting more attention for economical mineral resources since two decades.Along with MIS,the Nagarparkar Igneous Complex(NPIC)is being considered western most part of MIS is situated in SE Sindh,Pakistan.In this study,two areas of Pakistan have been studied.The Nagarparkar Igneous Complex(NPIC)rocks are from southeast Sindh,Pakistan and Saindak adakitic rocks are from west Balochistan,Pakistan.The NPIC igneous rocks reveal that mineralization must have been taken place in this area.In these rocks,prominent mineralization has been seen on the top and some oxidized zones are also noticed in the area.Similar mineralization also has been observed in MIS.Geochemical analyses,U-Pb age dating,and isotope investigation were conducted for the NPIC rocks in this study.LA-ICP-MS U-Pb dating of magmatic zircons yielded weighted mean 206Pb/238U ages ranging from 812.3±14.1 Ma to 810±7.4 Ma for the biotite-granites,755.3 ± 7.1 Ma to 736.3 ± 4.3 Ma for Kfs-granites,and 781 ± 23 Ma to 799 ± 23 Ma and 806± 13 Ma for gabbro rocks,representing Neoproterozoic magmatic events.These granites are distinguished into two types:i.e.,biotite-granites(Bt-granites)as peraluminous I-type and potash-granites(Kfs-granites)as A-type.For the Bt-granites,LILEs show positive anomalies,whereas HFSEs positive anomalies of Zr and Hf and negative anomalies of Nb.The Kfs-granites are high-K calc-alkaline rocks with moderately high Na and K contents.The contribution of crustal materials led to the enrichment of some incompatible trace elements,and the depletion of Sr and Ba in Kfs-granites and relatively high Sr and Ba in Bt-granites,indicating juvenile lower continental crust affinity.The ?Hf(t)values of zircons from the two types of granites are highly positive,as well as in gabbro rocks,indicating that these were derived from a juvenile upper and lower continental crust.The Bt-granites formed in the lower continental crust prior to the rifting time,whereas the Kfs-granites formed in the upper continental crust during crustal thinning caused by Rodinia rifting.Geochemical data of these two types of granites in southeast Pakistan and Western border of India indicate a same tectonic events and those ages of Barmer,Jalore,Siwana,Dhiran and Mount Abu granite rocks of Malani Igneous Suite(MIS)from ca.812 to 736 Ma,reveal that the NPIC and adjacent MIS might have been stuck together or may be considered to be the missing link of the same supercontinent Rodinia remnants.The area of western Balochistan,Pakistan is rich in porphyry Cu,Au and Mo deposits that are most important resources of the world.Young arc related large porphyry Cu-Au deposits are coupled with Early Miocene intrusive/rocks,these rocks are the segment of Tethyan belt,which have been discovered along Chagai magmatic arc Western Pakistan adjacent to southwest Iran.Saindak porphyry is a large Cu-Au deposit in the Chagai arc.This study covers the two types of intrusive rocks from Saindak porphyry area,i.e.,quartz-diorites and monzo-diorites,both type rocks are associated regional Cu-Au mineralization.LA-ICP-MSU-Pb dating of magmatic zircons yielded weighted mean 206Pb/238U ages of 22.16±0.23,22.21±0.34 and 24.25±0.54 Ma for quartz-diorites and 22.6±1.3 Ma for monzo-diorite,respectively.These intrusive rocks illustrate the slight difference in distribution patterns in trace elements enriched in LILEs and depleted in HFSEs,with no Eu negative anomalies.The quartz-diorites and monzo-diorites are calc-alkaline rocks with high Sr contents and Sr/Y ratios,intermediate to high(La/Yb)N ratios,from which they are identified as typical adakites.Quartz-diorites have been manifested with negative anomalies of Hf,Zr,while monzo-diorites have positive anomalies of Hf and Zr.The geochemical characteristics reveal that these adakitic rocks are associated with two types of series as high silica adakites(HSA)and low silica adakites(LSA).The quartz-diorites are characterized as HSA,with low to medium MgO contents and high Mg#,and low ratios of K2O/Na2O.Decoupling of Sr/Y and(La/Yb)N,and low Th/U values,exhibiting characteristics of slab-derived adakitic rocks and most likely these rocks were originated through partial melting of the Arabian oceanic crust followed by subsequent mantle interaction.In contrast,the monzo-diorites have lower silica and higher MgO than the quartz-diorites,characterized as LSA,possibly generated by partial melting of adakitic melt from the metasomatized mantle.These adakitic rocks are characterized by high radiogenic Sr(87Sr/86Sr(i)= 0.706621 to 0.707181)and Pb isotopes(206Pb/204Pb(i)= 18.866 to 18.924,207Pb/204Pb(i)= 15.682 to 15.710,208Pb/204Pb(i)= 39.079 to 39.160)with sNd(t)values ranging from-1.77 to-1.72,which mostly plot in the field of EMII.These geochemical characteristics indicate the origin of adakites is mostly from the young oceanic crust.These adakites typically coupled Au-bearing chalcopyrite and molybdenite,showing high oxygen fugacity,which is responsible for regional Cu-Au mineralization.