Metallogenic Study Of The Two Types Of Gold Deposits Formed During The Accretionary-collisional Orogenic Process Of The Western Tianshan

The western Tianshan Orogen(WTSO)is a 2500 km long orogenic belt located in the southwest part of the Paleo-Asia domain.A large number of giant gold deposits formed along the WTSO making it one of the highest resources potential region in the world.The prophyry-skarn type gold deposits and orogenic gold deposits are the two most important metallogenic types of the western Tianshan,which formed during the accretionary-collisional orogenic process of the western Tianshan.The Muruntau,Sawayaerdun orogenic gold deposits and Makmal skarn-type gold deposit are selected to decipher the mineralization stages,mineralization age and ore-forming processes.Combined with the reference of Kalmakyr porphyry gold deposit,we try to summarize the metallogenic mechanism and ore-controlling factors of the two types of gold deposits.The following achievements have been withdrawn in this study.1.Three stages of pyrite can be subdivided in the Sawayaerdun,which include diagenetic stage pyrite(Py₀)and hydrothermal stage pyrite(Py₁ and Py₂).Except for visible gold,the“invisible gold”occurs mainly in the form of structurally bound Au⁺in pyrite and arsenopyrite.The Py₀ is interpreted to have formed contemporaneously with the ore-bearing rocks,with a maximum depositional age of 355±7.3 Ma based on U–Pb dating of detrital zircons.Re–Os isotopic analyses of four Py₁ samples yielded an isochron age of 324±4.8 Ma,and those of five Py₂ samples yielded an isochron age of 282±12 Ma.Py₁ is interpreted to have formed in the syn-tectonic stage,during the collision between the Tarim craton and the Central Tianshan terrane in Late Carboniferous,whereas Py₂ was formed in a later mineralization event,during the late-to post-tectonic stage in Early Permian.The shear zone provide conduits and space and the ore-forming fluids have been inferred to be metamorphic fluids.2.The S isotope results of ores from Muruantau suggest that the strata are the main source of sulfur and minor sulfur may be provided by magma.The Pb isotope results of ores and strata rooks indicate that Pb is mainly derived from strata.Combined with ore geology characteristics,material preparation of sedimentary strata+fluid migration drived by multistage deformation(D1–D4)+superimposition of magmatic hydrotherm are the key factors controlling the gold mineralization in the Munruntau world-class gold deposit.3.The Kalmakyr is formed in a mature island-arc setting with superposition of multistage fertile magma hydrotherm.High quality geochronology dating on host rocks suggest that the ore-related magma in the Makmal deposit emplaced at 292?303Ma and 283?290 Ma,respectively.The rocks are A2-type granite formed in post-tectonic setting.The superposition of magmatic hydrotherm and associated extensional faults are the key to mineralization.4.In conclusion,the two types of gold deposits in the western Tianshan are formed during the initiation,evolution and termination of the Paleo-Asian Ocean.The prophyry-skarn type gold deposits formed during accretionary orogenic process,the ore-controlling factors are mature arc setting,multistage superposition of magma and hydrotherm.The orogenic gold deposits formed during collisional orogenic stage,the ore-controlling factors are primary enrichment of gold in strata rocks,structural deformation and magmatic hydrothermal superposition.