ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    湖南天明金矿区云斜煌斑岩年代学、同位素地球化学及成矿意义

    Geochronology, Isotopic Geochemistry of Diorite Porphyrite in Tianming Gold Deposit, Hunan

    • 摘要: 湖南安化天明金矿区的勘查工作中,岩芯揭露隐伏云斜煌斑岩。为探讨脉岩与成矿关系,对云斜煌斑岩开展岩石学、LA−ICP−MS锆石U−Pb年代学、全岩主微量元素和Sr−Nd同位素组成研究。结果显示,云斜煌斑岩遭受强烈的碳酸盐化蚀变;成岩时代不早于104 Ma,可能是晚燕山期华南构造–岩浆事件的响应;(418.79±1.57)Ma与(2506±14)Ma两组谐和年龄分别记录了志留纪扬子地块华夏诸岛弧陆弧碰撞以及太古宙地壳初始大规模增生,表明基底物质来源于上述2次地质事件。云斜煌斑岩属高钾钙碱性系列,轻稀土元素(LREE)富集、重稀土元素(HREE)亏损,具有明显的Eu负异常和Ce正异常;大离子亲石元素和高场强元素亏损,相容元素含量高;全岩εNd(t)=−8.28~−7.61表明壳幔混源;认为云斜煌斑岩由地幔岩浆在源区残留角闪石、钛铁矿和/或金红石,经历以斜长石为主的分离结晶,并受地壳混染,最终在近EW向断裂中侵位形成。对比湘中地区脉岩,赋矿地层,地壳Au、Sb含量,暗示脉岩与锑可能具有深部同源性,天明矿床具有锑成矿潜力。

       

      Abstract: The exploration in the Tianming Mining Area, Anhua, Hunan, has uncovered the concealed mica−plagioclase lamprophyre. In order to study the relationship between the dike and mineralization, we conducted various studies including petrographic, LA−ICP−MS zircon U−Pb chronology, whole−rock major and trace elements and Sr−Nd isotope composition analyses on the mica-plagioclase lamprophyre. The results indicate that the mica−plagioclase lamprophyre underwent significant carbonate alteration. The diagenesis age is estimated to be no earlier than 104 Ma and may be a response to the Late Yanshanian tectonic−magmatic events in South China Block. The concordant ages of (418.79±1.57) Ma and (2506±14 )Ma document the events of Silurian arc−crust collision of the Yangtze plate and the Cathaysia island arc, and Archaean crustal accretion, respectively, indicating the crystal basement material source. The mica−plagioclase lamprophyre belongs to a high−K calcium−alkaline series with an enriched light rare−earth element (LREE) and depleted heavy rare−earth element (HREE), with Eu negative anomalies and Ce positive anomalies. The rock also has large ionic lithophile and high−field strength elements depleted and high compatible element content. Whole−rock εNd(t) values ranging from −8.28 to −7.61 suggest crust−mantle mixing. Our findings suggest that the mica−plagioclase lamprophyre was formed by mantle magma in the source area with residual hornblende, ilmenite, and/or rutile. It underwent fractional crystallization dominant of plagioclase, was mixed by crust, and finally intruded in near−EW faulting tectonics. Comparison of the Au and Sb contents of dikes in central Hunan, ore−bearing formation, and crust, implies that the dikes and antimony may have deep homology. These findings suggest that the Tianming deposit has antimony mineralization potential. Overall, the study highlights the complex geological processes that lead to the formation of mineral deposits. By using a multidisciplinary approach, it is able to unravel the complex history of the mica−plagioclase lamprophyre and its association with mineralization. These findings can provide valuable insights for future exploration activities in the region.

       

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