赣南九龙脑岩体及洪水寨云英岩型钨矿年代学

Isotopic Chronology of Jiulongnao Granite and Hongshuizhai Greisens-Type Tungsten Deposit in South Jiangxi Province

通过赣南大余县九龙脑岩体及与之有密切成因关系的洪水寨云英岩型钨矿野外地质调查和系统的岩石化学、微量元素、稀土元素和成岩成矿时代研究,结合区域成岩成矿时代的最新研究成果,探讨了赣南地区钨矿的成岩成矿时代及构造环境。结果表明:九龙脑花岗岩体在化学成分上具有高Si、富碱、准铝质到弱过铝质、贫Ca、贫Mg、铁镁比值大、K2O/Na2O>1的特征;微量元素以富含Rb、K,亏损Ba、Sr等大离子亲石元素(LILE)和富含Th、U、Ce、Y、Sm、Nd、Ta、Hf,亏损Nb、P等高场强元素(HFSE)为主要特征,具强烈的Eu负异常(δEu=0.07～0.10)和较高的10 000Ga/Al特征比值(2.76～2.93),所有这些均显示铝质A型花岗岩的特征。利用锆石SHRIMP U-Pb法,获得九龙脑岩体的成岩年龄为(155.8±1.2)Ma(n=12,MSWD=0.6);利用辉钼矿Re-Os法,获得洪水寨云英岩型钨矿的成矿年龄为(156.3±1.3)Ma(n=7,MSWD=1.5),成岩成矿年龄基本一致。结合崇(义)—(大)余—(上)犹钨锡矿集区已有的年代学资料,指出本区的成岩成矿年龄主要集中在150～160Ma,属于华南中生代第二次大规模成矿作用,形成于中生代岩石圈伸展时期的侏罗纪板内拉张环境的地球动力学背景。

The age of tungsten mineralization and petrogenesis of its metallogenetic granitoids,and tectonic environment of the Jiulongnao tungsten orefield in southern Jiangxi Province are studied based on the field investigations and analysis on major-,trace-,and rare earth elements and dating.The Jiulongnao granite is characterized by high silica,alkali,metaluminous to weakly peraluminous,low Ca,Mg,and K2O/Na2O〉1.It also has relatively high LILE（Rb,K）,but low LILE（Ba,Sr）,and high HFSE（Th,U,Ce,Y,Sm,Nd,Ta,Hf）,low HFSE（Nb,P）.In addition,Jiulongnao granite shows strong negative Eu anomalies（δEu=0.07-0.10） and high ratios of 10 000Ga/Al（2.76-2.93）.Geochemical features of Jiulongnao granite indicate that it belongs to the A-type.The SHRIMP U-Pb dating of zircon from Jiulongnao granite yields an age of（155.8±1.2） Ma.Re-Os isotopic dating of molybdenite from the Hongshuizhai greisen-type tungsten deposit by ICP-MS yields a weighted mean age of（156.3±1.3） Ma,which is consistent with diagenetic age of Jiulongnao granite.Combined with chronological data of Chongyi-Dayu-Shangyou tungsten-tin polymetallic ore concentration area,we conclude that the age of both diagenesis and mineralization of this area are mainly concentrated in 150 to 160 Ma,which is corresponding to the time of the second regional large-scale mineralization in the Mesozoic and these mineralization occurred at the same geodynamic background that is Jurassic intraplate extensional environment during the large-scale extension period of lithosphere.