Skarn Type Lead-zinc Mineralization In Late Paleozoic Island Arc Environment,Xinjiang Tianshan

The world's major zinc and lead resources are produced in sediment-hosted Pb-Zn deposits,such as SEDEX,MVT and sandstone type.Whereas the Zn-Pb deposit developed in the Tianshan orogenic belt is featured as skarn type mineralization.To date,numerous large-superlarge skarn type zinc-lead deposits have been discovered in Tianshan,which suggests a great potential of Zn-Pb mineralization here.What kind of geological environment did these skarn Zn-Pb deposits formed? Why did those skarn type mineralization happened? How about their mineralization process? These scientific questions have attracted great attention.In this dissertation,based on detailed field geological survey and indoor micropetrography observation,we selected the Arqiale deposit from Western Tianshan and the Aqishan deposit from Eastern Tianshan,Xinjiang,China to illuminate the metallogenic environment and ore-forming process of Zn-Pb skarn deposit at late Paleozoic in Tianshan Orogenic Belt.We also established different kinds of skarn Zn-Pb mineralization model in Tianshan,i.e.,distal and proximal skarn.Furthermore,with a view to the spatial and temporal distribution,geological background,ore-hosting strata,magmatic activity and hydrothermal ore-forming process of the skarn Zn-Pb deposit in Tianshan Belt,we want to reveal several key factors that influenced its metallogeny process,matter composition and mineralization evolution.To do so,we tried to explore further skarn Zn-Pb prospecting in the Tianshan Belt.Several achievements have been draw from this study as follows:(1)The Arqiale deposit is formed at ca.340 Ma.Stable and radio isotope compositions suggest its ore forming material and fluid has a magmatic source,and part of S and metals are derived from the wall rock,i.e.,the Dahalajunshan Formation.The closed spatial and temporal relationships between Zn-Pb mineralization and regional magmatism suggests the Arqiale deposit is formed in the late Paleozoic island arc environment,and is connected with the large-scale intermediate-felsic magmatism at the Southern Yili Block which resulted from the subduction of South Tianshan Ocean.The Arqiale deposit is a distal Zn-Pb skarn,which is resulted from the infiltration metasomatic between magmatic fluid and Carboniferous carbonates along the weak contact surface in the wall rock.(2)The Aqishan deposit is formed at ca.306 Ma.Stable and radio isotope compositions suggest its ore forming material and fluid has a magmatic source,and part of S and metals are derived from the wall rock,i.e.,the Yamansu Formation.The closed spatial and temporal relationship between Zn-Pb mineralization and regional magmatism suggests that the Aqishan deposit is formed in the late Paleozoic island arc environment which is related to subduction of the South Tianshan Ocean.The Aqishan deposit is a distal Zn-Pb skarn,which is resulted from the fluid-rock reaction between magmatic fluid and lenses of calcareous sandstone and limestone in the Yamansu Formation.(3)Skarn Zn-Pb mineralization in the Tianshan Belt is mainly occurred in the late Paleozoic,it is restrained by several factors including Late Paleozoic subduction-related island arc environment,cal-alkaline magmatism,Paleozoic marine volcaniclastic and carbonate rocks,favorable hydrothermal supplying channel and proper preservation condition.(4)Based on the induction of the metallogeny epoch,geological background,ore-hosting strata,magmatic activity,mineralization and alteration of skarn Zn-Pb deposits,we proposed that there is a great potential of skarn Zn-Pb prospecting in the Tianshan Belt.The North Tianshan Island Arc Belt,southern and northern margin of the Khazakstan-Yili Plate,the Central Tianshan Block of the Eastern Tianshan in Xinjiang,China,and the southern margin of the Middle Tianshan in Uzbekistan are favorable prospecting area.