铜陵荷花山铅锌矿区闪长岩类LA-ICP-MS锆石U-Pb年代学、地球化学特征及地质意义

摘要

荷花山铅锌矿床是长江中下游成矿带铜陵矿集区内新发现的大型铅锌矿床,该矿床矿体呈似层状主要赋存于三叠系南陵湖组下段瘤状灰岩中.矿区内经钻孔揭露,有两种岩性的闪长岩类,分别为矿区西侧的闪长岩体和东侧的石英闪长岩体.锆石LA-ICP-MS U-Pb年代学分析得出这两个岩体的年龄分别为133.0±2.1Ma和130.1±1.7Ma,表明其形成时代为早白垩世.全岩地球化学分析显示,荷花山闪长岩类表现为SiO2＞56％ (56.17％ ～ 65.90％),Al2O3≥15％ (15.10％ ～17.22％),MgO＜ 3％ (0.84％ ～2.22％),Yb＜ 1.9×10-6(1.35×10-6～1.64×10-6),Y＜ 18×10-6(11.60×10-6～15.70×10-6),无明显的Eu异常等特征,具有与典型的埃达克岩相似的特征,微量元素判别图解表明荷花山矿区闪长岩类岩浆来源于幔源岩浆和加厚下地壳埃达克岩浆的混合,是铜陵地区晚期岩浆活动的代表;构造判别图解表明荷花山闪长岩类形成于相对挤压或者挤压向拉张过渡的岩石构造环境,其形成与古太平洋板块的俯冲有关,可能预示着铜陵地区存在130Ma左右的铅锌矿化事件.%Hehuashan zinc-lead deposit is located in the Tongling district,which is one of the most significant ore districts of the Middle and Lower Reaches of Yangtze River Belt.The ore bodies of Hehuashan deposit are hosted by nodular limestone of Triassic Lower Nanlinghu Formation.There are two intrusions in Hehuashan deposit,with the lithology of diorite and quartz diorite,respectively.The zircon LA-ICP-MS U-Pb dating results of the diorite and quartz diorite show that their weighted 206Pb/238U age is 133.0 ± 2.1Ma and 130.1 ± 1.7Ma,respectively,indicating that the intrusions of Hehuashan deposit intruded in the Early Cretaceous.The whole-rock geochemical analysis results show that the geochemical characteristics of the diorite of Hehuashan deposit are similar to those of typical adakites.For example,the diorites have SiO2 ＞ 56％ (56.17％ ～65.90％),Al2 O3 ≥ 15％ (15.10％ ～ 17.22％),MgO ＜3％ (0.84％ ～2.22％),Yb ＜ 1.9 × 10-6(1.35 × 10-6 ～ 1.64 × 10-6),Y ＜ 18 × 10-6(11.60 × 10-6 ～ 15.70 × 10-6) with weak negative Eu anomaly.It suggests that Hehuashan diorites maybe the joint product of partial melting of thickened lower crust and partial melting mantle wedge.The tectonic discriminant diagram shows that the Hehuashan diorites were formed in a setting of compression or transition from compression to extension,maybe related to the subduction of ancient Pacific plate.The occurring of the Hehuashan diorites maybe give implications for new mineralization in Tongling district.