大别山北缘千鹅冲斑岩型钼矿床锆石U-Pb和辉钼矿Re-Os年代学及其地质意义  

LA-ICP-MS Zircon U-Pb and Molybdenite Re-Os Dating for Qian'echong Porphyry-type Mo Deposit in Northern Dabie,China,and Its Geological Significance

作　　者：杨梅珍[1] 曾键年[1] 覃永军[1] 李法岭[2] 万守权[2] 

机构地区：[1]中国地质大学,武汉430074 [2]河南省地质矿产勘查开发局第三地质调查队,河南信阳464000

出　　处：《地质科技情报》2010年第5期35-45,共11页Geological Science and Technology Information

基　　金：河南省国土资源厅地质科研计划项目(2882)

摘　　要：河南省光山县千鹅冲钼矿床是大别山地区近年最新发现的大型斑岩型钼矿床。采用LA-ICP-MS锆石U-Pb和ICP-MS辉钼矿Re-Os同位素精细测年技术,对与成矿相关的宝安寨钾长花岗岩、千鹅冲花岗斑岩2个锆石样品和4个细网脉型钼矿石中的辉钼矿样品进行了同位素年代学测定,分别获得(135.3±1.9),(128.8±2.6),(127.82±0.87)Ma的同位素年龄。结果表明,千鹅冲钼矿床成矿作用时间与千鹅冲花岗斑岩成岩作用时间一致,晚于大别山巨量花岗质岩浆活动近7Ma,它们为统一构造背景同期不同次岩浆作用的产物。与成矿相关岩体的地球化学研究结果显示,岩体具有低Sr(wB<400×10-6)、低Yb(wB<1.8×10-6)、中等程度Eu负异常[δ(Eu)>0.5]、轻重REE强烈分异{[w(La)/w(Yb)]N>24}等特征,其Sr-Nd同位素显示较高的[N(87Sr)/N(86Sr)]i(0.70669～0.72422,变化较大)和极低的ε(Nd)(t)(-18.01～-21.37)。综合分析表明成岩成矿作用发生在大别造山带碰撞造山后构造体制由挤压收缩向伸展的转折时期,与成矿有关的酸性侵入岩是加厚陆壳部分熔融作用的产物。千鹅冲斑岩型钼矿床与成矿带内汤家坪、大银尖、天目山、银山、东沟钼矿床在成矿时间及成矿岩体地球化学特征的显著差异,反映它们形成于造山带演化的不同历史时期和不同的构造动力学背景。Qian＇echong porphyry-type Mo deposit in the Northern Dabie mountain has been discovered from Guangshan County,Henan Province in recent years.The in situ zircon LA-ICP-MS U-Pb and molybdenite ICP-MS Re-Os highly precise dating techniques are used to study two zircon samples collected from Baoanzhai K-feldspar granite and Qian＇echong granite-porphyry related to Mo deposit.and four samples of molybdenum collected from Mo deposit.Zircon U-Pb age of（135.3±1.9）,（128.8±2.6）Ma and molybde-nite Re-Os of（127.82±0.87）Ma are obtained respectively.The results indicate that Mo mineralization concurred with the emplacement of granite porphyry,later than the large-scale granite emplacement in the Dabie Mountain by nearly 7Ma.They were formed under unified tectonic setting at the same period but in different times.The intrusions related to mineralization exhibit low Sr（400×10-6）,low Yb（1.8×10-6）,moderate Eu negative anomaly（δEu0.5）,strong differentiation of light and heavy REE[（La/ Yb）N24],and high（87Sr/86Sr）i（0.706 69—0.724 22）,extremely lowεNd（t）（-18.01—-21.37）.It is concluded that the magmatism and related mineralization happened during the tectonic system of Dabie oro-gen shifted from compression to extension,and the granitic magma related to Mo mineralization should have been derived from the thickened continental crust by partial melting.Qian＇echong Mo deposit is def-ferent in the ore-forming time and geochemistry of ore-forming rocks from other deposits including Tangjiaping,Dayinjian,Tianmushan,Yinshan,Donggou Mo deposits in metallogenic belt.This reflects that they were formed in different geological periods and in different tectonic dynamic settings.

关 键 词：锆石U-PB年龄 辉钼矿RE-OS年龄 千鹅冲斑岩型钼矿床 大别山北缘 

分 类 号：P597[天文地球—地球化学] P618.65[天文地球—地质学]