The Genesis Of Aqishan First Iron Deposit Of Jueluotage Tectonic Belt In The Eastern Tianshan

The East Tianshan metallogenic belt was one of the important geological prospecting areas for iron deposits in last century.The Hami district,especially,has the most abundant iron resources and the considerable prospecting potential.However,the degree of geological study for iron deposits in this area are generally low.For some typical deposits,the genesis is still controversial,such as Yamansu iron deposit and Hongyuntan iron deposit.To understand regional iron mineralization,iron metallogenic regularity and regional tectonic evolution,it is necessary to study more iron deposits in this district.Aqishan First iron deposit is hosted in the volcanic rock of the Yamansu Formation.The main ore bodies are stratiform-like,and the boundary between the main ore bodies and country rocks is distinct.The ore types can be devided into ore-magma type and hydrothermal type.The main ore bodies are mainly made up of the ore-magma iron ore.The hydrothermal low-degree ores are laminated and disseminated.The mineral crystallization sequence in hydrothermal ore is as follows: garnet ? actinolite – tremolite ? magnetite – hematite – quartz – epidote ? quartz – carbonate – chalcopyrite.According to the mineral crystallization sequence,the hydrothermal alteration can be divided into garnet phase,tremolite/actinolite – magnetite/hematite – quartz – epidote phase and quartz – carbonate – chalcopyrite phase.This sequence is consistent with the skarn mineral crystallization order of the typical skarn deposit.Fluid inclusion data shows that,Th(the homogenization temperature)peak datas of secondary fluid inclusions in the garnet are 120~160 ? and 180~220 ?;Th peak datas of fluid inclusions in the epidote are 200~240 ?,which is consistent with one of Th peaks data of fluid inclusions in the quartz.It can be regarded as the temperature of the magnetite–hematite–quartz–epidote phase;Another Th peaks data of fluid inclusions in the quartz is 120~160 ?,which can be regarded as the temperature of the quartz–carbonate–sulfide phase.In general,the Aqishan frist iron deposit appears to be the result of multiple stages of magmatic-hydrothermal processes,which can be devided into cryptovolcanic rock iron deposit.This thesis reports LA-ICP-MS zircon U-Pb age of 350 ± 2 Ma(n=30,MSWD=0.21)from dacite porphyry sample X150714-8 from the countery rock,which can be regarded as the formation age of the dacite porphyry.The forming age of the Aqishan frist iron deposit is consistent with this age,which is coeval with formation ages of different iron depisits in Jueluotage tectonic belt,such as Yamansu iron deposit,Bailingshan iron deposit,Duotoushan iron deposit and Kumtag gypsum-siderite deposit.The analyses to the geochemical data of the country rock shows that the tectonic setting of the Aqishan first iron ore was the continental arc.