Comparative Study On The Lamasu And Kekesala Skarn Fe-Cu Deposit In The Western Tianshan,Xinjiang Province

Lamasu copper deposit and Kekesala iron-copper deposit are two typical skarn deposits,which are located in the northern of West Tianshan,Xinjiang province,formed during the southward subduction of the North Tianshan ocean under the Yili plate in the late Paleozoic.Field investigations have revealed that a large amount of pyrrhotite was developed,and there were few magnetites,hematite and gypsum were not developed in Lamasu copper deposit.A large amount of magnetite and hematite were developed in Kesala iron-copper deposit.The oxidation-reduction property of them are quite different.In order to explore the causes of this difference,systematic studies have been carried out on the geological characteristics of the deposit,the characteristics and evolution of ore-forming fluids,mineral chemistry of skarn,the metallogenic physicochemical condition,and metallogenic mechanism through field investigations,microscopic identification of rock and ore,laser raman spectroscopy analysis and microthermometry of fluid inclusions and electron probe and LA-ICP-MS micro-area chemical analysis of skarn minerals.Studies show that garnet,diopside,wollastonite and hedenbergite are developed in the dry skarn stage,ferropargasite and a small amount of epidote and magnetite are developed in the wet skarn stage,a large number of pyrrhotite,chalcopyrite,sphalerite and pyrite are developed in the quartz-sulfide phase,in Lamasu copper deposit.In Kekesala iron-copper deposit,the garnet-diopside stage develops garnet,diopside and wollastonite,and the epidote-magnetite stage develops a large number of magnetite and epidote,hematite of the oxide Stage are developed,chalcopyrite,pyrite,bornite and no pyrrhotite are developed in the quartz-sulfide phase.The difference between the ore composition indicates that the ore-forming environment of the Lamasu copper deposit is a reductive environment,and the ore-forming environment of the Kesala iron-copper deposit is an oxidative environment.For the Lamasu copper deposit,the mineralization temperature is 183⁵50?,the salinity and density of the ore-forming fluid are respectively 9.0³9.0 wt%and0.69⁰.94 g/cm³,the metallogenic depth is 1.5⁴.1 km,and the fluid composition includes H₂O and CH₄.Its ore-forming fluid is reductive.For the Kekesala iron-copper deposit,the ore-forming temperature is 250⁵07?,the salinity and density of the ore-forming fluid are respectively 3.6³5.2 wt%and 0.46⁰.83 g/cm³,the ore-forming depth is 1.1³.8 km,and the fluid composition are mainly H₂O.Its ore-forming fluid is oxidative.The fluid boiling is the main mechanism of mineral precipitation for both deposits.The studies for mineral chemistry of skarn show that the garnets of the Lamasu copper deposit and the Kekesala iron-copper deposit are mainly garnet and grossularite.The garnets of the Lamasu copper deposit,which is formed by diffusion metasomatism and infihration metasomatism in the relatively reductive and weak acidic to weak alkaline environment.The garnets of the Kekesala iron-copper deposit is formed by infihration metasomatism in a relatively oxidative and weak alkaline to alkaline environment.The ore-forming fluid of the Lamasu copper deposit extracts the reducing components in the carbonaceous limestone,resulting in the overall reduction of the ore-forming environment,this is the renson for the difference between the two deposits.