河南南沟钼矿矿床地球化学研究兼论东秦岭钼矿床成岩成矿动力学  

Ore Geochemistry,Petrogenesis and Metallogenic Dynamics of the Nangou Molybdenum District in the East Qinling Orogenic belt

作　　者：杨晓勇[1] 卢欣祥 杜小伟[1] 李文明 张正伟[3] 屈文俊[4] 

机构地区：[1]中国科学技术大学地球与空间科学学院矿产资源研究室,合肥230026 [2]河南省地质科学研究所,郑州450053 [3]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵阳550002 [4]国家地质实验测试中心,北京100037

出　　处：《地质学报》2010年第7期1049-1079,共31页Acta Geologica Sinica

基　　金：中国科学院知识创新工程重要方向项目"东秦岭钼矿成矿带深部构造制约及成矿地球化学动力学(编号KZCX2-YW-QN509)";河南省国土资源厅"秦岭钼矿找矿项目";国家自然科学基金重点项目(编号90814008)资助的成果

摘　　要：本文对东秦岭南沟钼矿床开展成矿年代学与地球化学综合研究。岩石地球化学研究表明:南沟钼矿床侵入岩为高钾钙碱性系列,高硅(71.79%～78.09%)、低钛(0.112%～0.268%)、富铝(11.69%～14.89%)、富碱(Na2O含量为2.21%～4.26%,K2O含量是4.01%～7.57%,K2O/Na2O在1.07～3.42之间)、Mg#低(16.44～42.50)、贫钙(0.2%～1.54%)。南沟矿区侵入岩稀土总量较低,轻重稀土分异明显,有弱的铕负异常,δCe有强的负异常,样品的Ce负异常可能是具有Ce负异常的沉积物俯冲重熔所致,反应了形成花岗岩的源区物质可能为俯冲的海相沉积物源的特征,且具有还原特征。稀土配分模式图解与上地壳配分模式十分相似,也指示了花岗岩的物源区有大量的上地壳物质参与。南沟钼矿区侵入岩的微量元素分析表明,具有较高浓度的大离子亲石元素(LILE、Rb、K等),具有相对低含量的高场强元素(HFSE:Zr、Hf等),过渡金属含量变化较大,明显富集Cu,Sc,Co。本区侵入岩贫Ba、Sr,富Rb、K。壳型花岗岩类Ba、Sr含量低,Rb含量高,而幔源型或壳幔同熔型花岗岩的Ba、Sr含量高,且贫Rb,指示本区含钼侵入岩多具有壳源物源的性质。岩石地球化学判别图解指示这些含钼岩体主要为同碰撞花岗岩和后碰撞花岗岩。利用锆石LA-ICP-MS法测定了东秦岭南沟钼矿区两个相对独立的白石尖和马脖壕两个矿段含矿侵入岩体的U-Pb年龄,同时采用辉钼矿Re-Os同位素方法直接测定上面两个矿段的成矿年龄。高精度的锆石LA-ICP-MS研究表明:白石尖矿段花岗岩中锆石206Pb/238U加权平均年龄为451.7±5.7Ma(MSWD=1.6),马脖壕矿段花岗岩锆石206Pb/238U加权平均年龄为109.8±4.1Ma(MSWD=1.17)。由此可见南沟钼矿区至少有两期岩浆活动:1)早古生代晚奥陶世(约451Ma)第一次岩浆活动;2)中生代早白垩世(约109Ma)第二次岩浆活动。辉钼矿的Re-Os同位素模式年龄研究表明:白石尖矿段辉钼矿Re-Os等In this paper,detailed field work and systematic study of typical ore deposit dissection was carried out on molybdenum deposit in eastern Qinling.The ages of intrusive rock in the Nangou molybdenum deposit were determined by zircon U-Pb analysis with LA-ICP-MS,while ages of Baishijian and Mabohao molybdenum deposit were determined directly by Re-Os method with molybdenite using ICP-MS.Based on the geochronological research,together with geological and geochemical investigation on both granite and molybdenum deposit,the origin of rock-forming and ore-forming materials,geodynamic background and ore-forming model are discussed.Detailed microscope observation indicates that the main rock-forming minerals in the Nangou molybdenum deposit are orthoclase,microcline,plagioclase,quartz with minor biotite,muscovite and sericite,and with tourmaline as the primary accessory mineral.The contents of alkaline feldspars are 50% c.a.,with 40% quartz,10% plagioclase and less than 1% biotite and muscovite.Nangou intrusive rocks are high potassic calc-alkaline series,with high SiO2（71.79%～78.09%）,low TiO2（11.69%～14.89%）,rich in alkali（with Na2O content between 2.21%～ 4.26%,K2O between 4.01%～7.57%,K2O/Na2O between 1.07～3.42）,low Mg#（16.44～42.50）and CaO（0.2%～1.54%）.The Nangou intrusive rocks exhibit a low amount of total rare earth elements（ΣREE）,with obvious differentiation between light rare earth elements（LREE）and heavy rare earth elements（HREE）,slightly negative Eu anomaly and strongly negative Ce anomaly.The strongly negative Ce anomaly may result from subduction of sediments with negative Ce anomaly,reflecting a reduced marine environment for the source rocks.The chondrite-normalized REE distribution patterns are similar to those of the upper crust,indicating the involvement of huge amount of upper crust materials during the formation of the granites.The trace elements analysis of Nangou intrusive rocks shows high content of large ion lithophile elements（LILEs）and low content of

关 键 词：地球化学 LA-ICP-MS测年 RE-OS同位素测年 成矿模式 东沟钼矿床 东秦岭 

分 类 号：P618.65[天文地球—矿床学] P597.3[天文地球—地质学]