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《Acta Geologica Sinica》 2018-06
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The Metallogenic Age and Geodynamic Setting of the Laojiezi Pb-Ag Polymetallic Deposit,Central Yunnan Province: Evidence from Re-Os Isotope of Sulfides

JIANG Xiaojun;YAN Qinggao;LI Wenchang;LI Chao;WU Peng;GUAN Shenjin;YU Haijun;LI Jinlong;Department of Earth Sciences,Faculty of Land Resource Engineering,Kunming University of Science and Technology;Chengdu Center,China Geological Survey;National Research Center for Geoanalysis;Yunnan Geological Survey Bureau;Science and Technology Department,Coal Geological Bureau of Yunnan Province;  
The Laojiezi Pb-Ag deposit,located in the middle section of the Cenozoic Red River-Ailaoshan alkalirich porphyry belt,is the typical alkali-rich volcanic-magmatic hydrothermal deposit in central Yunnan province.A 70-m-wide syenite porphyry and molybdenite-pyrite vein with high Cu-Mo abnormal pyritization was firstly discovered in the deep part of the deposits(3# vein of 2073 level).It is believed that obvious alkali-rich porphyry and magmatic-hydrothermal Cu-Mo superimposed mineralization occurs at depth of the deposit.This study conducted Re-Os isotopic analysis for molybdenite-pyrite samples from molybdenite-pyrite veins,pyrite-galena veins and high Cu-Mo syenite porphyry from deep adits in the Laojiezi Pb-Ag deposits.An isochron age of 33.71± 0.29 Ma and a weighted average age of 33.99±0.22 Ma were obtained for molybdenite,indicating that the mineralization of the Pb-Ag polymetallic deposit took place in Oligocene,which is consistent with the diagenetic age of the syenite porphyry.The initial Os value of 0.3049~1.5549 and theγOsvalue of 140.5~1126 suggest that the metallogenic material was derived from partial melting of the crust-mantle transition layer.The metallogenic age of the Laojiezi porphyry Pb-Ag polymetallic deposit is roughly the same as that(30~40 Ma)of regional alkali-rich porphyry and magmatic hydrothermal polymetallic deposits.It shows that,after the collision between the India plate and Eurasia plate,the change of tectonic stress field resulted in large-scale strike-slip faulting system,which induced partial melting of crust-mantle transition zone within the stable cratons,forming alkali-rich intrusive rocks and metallogenic fluids,and the fluid formed alkali-rich porphyry and magmatichydrothermal polymetallic deposits along the weak structures.
【Fund】: 北京离子探针中心开放基金(DDC15-016);; 国家重点基础研究发展计划(973计划)(编号:2015CB452605);; 云南省应用基础研究计划青年(2016DF031);; 云南省科技领军人才培养计划(编号:2013HA001)等项目联合资助
【CateGory Index】: P618.2
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