Oxygen Fugacity And Water Content Of Intrusions In Zhunuo Porphyry Cu Deposit In The Western Segment Of Gangdese Belt

The oxygen fugacity and water are crucial to the formation of porphyry copper deposits.The Zhunuo porphyry copper deposit,located in the western segment of the Gangdese in the southern Tibet,is one typical porphyry Cu deposits formed in the post-collisional setting.Magmatism in the Zhunuo ore district leads to formation of pre-ore quartz porphyry?⁵0Ma?,syn-ore complex?13¹5Ma??composed of monzogranite porphyry,monzogranite and the host enclave?,and post ore?granite porphyry??10¹2Ma?.Many methods?such as zircon,amphibole,biotite,plagioclase,magnetite-ilmenite,biotite?have been used to study the oxygen fugacity and water of the magmatic evolution stage,and compare them to those of other deposits in eastern segment of Gangdese belt.The Ce⁴⁺/Ce³⁺ ratios of enclave,monzogranite porphyry,monzogranite and diorite range from 372 to 919,142 to 364,45 to 182,3 to 195.Based on amphibole composition,the estimated magmatic oxygen fugacity of enclave is ? FMQ= +1.2⁺3.0,magmatic water 4.0⁴.3 wt%.Magmatic oxygen fugacity of monzogranite porphyry is?FMQ= +2.6⁺3.4,magmatic water is 3.2³.9 wt%.Magmatic oxygen fugacity of monzogranite is?FMQ= +2.8⁺3.7,magmatic water is 2.9³.7 wt%.Based on the plagioclase composition,the estimated magmatic water of enclave is 3.5⁴.2% wt%,magmatic water of monzogranite porphyry is 2.7³.4 wt%,magmatic water of monzogranite is 2.9³.1wt%.The oxygen fugacity and water content of enclave and monzogranite porphyry is higher than monzogranite and diorite,so the enclave and the monzogranite porphyry,monzogranite with enclave is the most beneficial to mineralization.The zircon Ce⁴⁺/Ce³⁺ ratio of the quartz porphyry before mineralization is 328⁹59,and the water content is less than 2.8 wt%,which reflects the quartz porphyry before mineralization has a higher oxygen fugacity and lower water content than the main mineralization epoch.The zircon Ce⁴⁺/Ce³⁺ ratio of the granite porphyry after mineralization is 39¹96,and the water content is less than 3.0wt%,which reflects the granite porphyry after mineralization has a lower oxygen fugacity and lower water content than the main mineralization epoch.This paper makes a systematic contrastive study of oxygen fugacity and water content in the western segment and eastern segment of the Gangdese belt.The zircon Ce⁴⁺/Ce³⁺ ratios of the intrusion in Lakang'e,Dabu,Chongjiang,Zhunuo is 492,398,263,249;The water content of the intrusion in Qulong is 3.8⁴.6wt%,the water content of Dabu is 3.5⁴.9 wt%,the water content of Zhunuo is 3.2³.9 wt%,The magmatic oxygen fugacity and water content of porphyry deposits in the western segment of the Gangdese belt is lower than the east,which could be resulted from more contaminations of Indian crust material in the west.The?Ce/Nd?/Y ratio of metallogenic rock in Qulong porphyry deposit and Jiama porphyry deposit is more than 0.01,the 1000?Eu/Eu*?/Y ratio is more than 1,the Eu/Eu* ratio is more than 0.4;The?Ce/Nd?/Y ratio of metallogenic rock in Zhunuo porphyry deposit is less than 0.01,the 1000?Eu/Eu*?/Y ratio is less than 1,the ratio of Eu/Eu* is less than 0.4.Zhunuo porphyry copper deposit in the western segment of Gangdese Porphyry Copper Belt has lower oxygen fugacity and water,suggesting the western segment of Gangdese Porphyry Copper Belt undergo the contamination by India continental crust of a greater degree..