Metallogenesis Of Neoproterozoic Zn-Enriched VMS Deposits In The Gebel Abu Hamamid Region Of Eastern Desert Of Egypt:Constraints From Geology And Geochemistry

The volcanogenic massive sulfide(VMS)deposits,normally containing significant amounts of sulfides minerals and precious metals,are important to understand both ancient volcanism and geological evolution.The VMS deposits generally originated through the focused discharge of fluids that were mainly seawater-derived and metal-laden solutions associated with volcanism.Hundreds of metal occurrences are found within the Arabian-Nubian Shield(ANS)that represent the Earth's largest block of juvenile Neoproterozoic crust.The exploration of VMS ore is currently underway in many districts within the shield,including Hamama deposit in Egypt,Hassai deposit in Sudan,Bisha deposit in western Eritrea,and Ash Shizm,Shayban,and Kutam deposits in Saudi Arabia.Such deposits are characterized by economic grades and volumes of Zn,Cu,Au,and Ag metals.The study area,Gebel Abu Hamamid area,forming the middle part of Shadli Metavolcanics Belt of the South Eastern Desert,Egypt,hosts several VMS deposits.Historically,the oxidized outcrops of ore zone(i.e.,iron oxides and secondary copper sulfides and carbonates)were used as prospective guides to discover these mineralizations.Three distinct occurrences of Zn-Cu-Pb mineralization(Um Samiuki,Hilgit,and Maaqal)in Neoproterozoic island arcs have been investigated in this study.The host-rock succession belongs to the first cycle of Younger Hamamid Metavolcanics(YHM)group,consisting of mafic and felsic lavas with variable volcaniclastics.It was suffering deformation,metamorphism(greenschist facies),and erosion during a polyphase orogeny.Structurally,the Abu Hamamid asymmetric syncline is the most prominent and the main fault is trend NW-SE.Although several studies have attempted to clarify the crustal evolution of the Neoproterozoic basement rocks of the South Eastern Desert,researchers have yet to develop a deep understanding of the petrogenesis,tectonic setting,and ages of the VMS host rocks in the Shadli Metavolcanics Belt.Additionally,the relationship between the mineral occurrences and host rocks remains poorly constrained and controversial.Moreover,few geochronological studies have been undertaken on these deposits.In the current study,new field observations,paragenetic data,whole-rock geochemistry,mineral chemistry,in situ U-Pb-Lu-Hf zircon dating from basaltic to rhyolitic rocks of the YHM group,and in situ sulfur isotopes for sulfide minerals are reported to(1)describe their magmatic evolution,(2)characterize the sulfide mineralization,and(3)gain insights into its genesis.Results indicate that the mafic rocks are characterized by tholeiitic affinity and arc-like geochemical signatures with significantly enriched large-ion lithophile elements(LILE)and depleted high field strength elements(HFSE).The parental magma was likely generated by partial melting(?10-15%)of a spinel-lherzolite source mantle that was metasomatized by fluids from a former subduction event,followed by magma ascent under low pressure and low oxygen fugacity conditions.The felsic lavas(-695 Ma)are characterized by subduction-related geochemical characteristics with significant enrichments in Zr,Hf,and Sm.They formed from lithosphere-derived magma enriched by melts from the ancient,subducted slab,and later experienced an assimilation-fractional crystallization(AFC)process.The YHM group was formed under extensional geodynamic conditions(back-arc basin setting)during the Mozambique Ocean closure stage of the Pan-African Orogeny.The magmatic zircons of basaltic lavas from the YHM group show negative ?Hf values from-0.5 to-10.3 and their crustal model ages(TDMC)vary between 1706 Ma and 2322 Ma,suggesting the source of these metavolcanics contain some older crustal components(pre-Neoproterozoic continental crust).In contrast,all concordant zircons from intermediate and felsic rocks of the YHM group have positive ?Hf values and show nearly unimodal distributions and plot completely above the Chondritic Uniform Reservoir(CHUR),suggesting that these studied samples were derived from a juvenile source.The magmatic and inherited zircon grains display hydrothermal overgrowth at the rims,most likely due to regional metamorphic and hydrothermal changes.This characteristic is likely the effect of hydrothermal fluids associated with the Jurassic-Cretaceous tectono-thermal event in the South Eastern Desert.Two mineralization styles have been identified in the studied deposits.The first style in the Um Samiuki deposit is characterized by two massive mineralized bodies that are often stratiform in nature.It is distinguished by sphalerite,chalcopyrite,pyrite,galena,and Ag-bearing minerals;followed by bornite and covellite in decreasing abundance.Stratiform massive sulfides are coeval with the felsic volcanism of YHM.They are accompanied by products of supergene phases such as secondary copper minerals and iron oxides.The hydrothermal alteration is characterized by sericitization,chloritization,epidotization,and silicification.The second style represents disseminated and vein-type sulfides that can be mainly encountered in Hilgit and Maaqal deposits(wall rocks).It is characterized by pyrite with minor sphalerite and chalcopyrite.The 834Sv-CDT values range from+5.44‰ to+9.08‰ with an average of+8.11‰ for massive mineralized zones and from-2.25‰ to+3.78‰ with an average of+1.06‰ for disseminated and veined sulfides imply that they were mainly derived from the thermochemical sulfate reduction(TSR)of seawater and leaching of basement lithologies in varying quantities.They are consistent with those reported from VMS deposits of back-arc basins.The negative ?34Sv-CDT values of some sulfides from the second mineralization style show direct evidence for magmatic SO2 disproportionation.Compared to the Hamama mine(currently active)on the central part of the Egyptian Eastern Desert,which is classified as a gold-rich VMS deposit,the studied YHM prospects can be classified as Zn-enriched VMS deposits that have not been entirely evaluated.They present a key opportunity to modern-day explorers and need much further geological work.