【作者】 段超；

【导师】 毛景文； 李延河；

【作者基本信息】 中国地质大学(北京) ， 矿物学、岩石学、矿床学， 2012， 博士

【摘要】 凹山铁矿床位于长江中下游多金属成矿带宁芜矿集区，是一个典型的玢岩型铁矿床，成矿过程具有多阶段的特征。本次研究工作，通过详细的野外地质调查研究和室内的实验分析研究，对矿床的成矿演化过程进行了详细的研究和探讨。凹山铁矿床主要矿石矿物磁铁矿的形成划分为4个世代，分别为浸染状磁铁矿，角砾状磁铁矿，粗粒脉状磁铁矿和伟晶状磁铁矿，它们是四个成矿阶段的产物。其中隐爆作用诱发了大规模铁沉淀，并为成矿提供了空间。各成矿阶段磁铁矿电子探针和LA-ICP-MS原位分析表明，随着成矿作用的演化，磁铁矿主量元素中Ti、Mn、V含量变化微弱，Al、Mg含量增高；微量元素中Ga、Sn及高场强元素Zr、Hf、Nd、Ta含量变化较小；从角砾状矿石到伟晶状矿石Co含量逐渐增高、Sc含量逐渐降低。在成矿过程中磁铁矿具有同源连续演化的特征，铁质来源于岩浆演化后期，受不混溶作用影响而形成富铁流体。对成矿各阶段磁铁矿、磷灰石、石英的氢氧同位素特征测试，以及伟晶状磁铁矿化阶段中磷灰石的流体包裹体形成温度的测量，并结合前人工作得出，成矿过程中流体成分不断变化，早期为岩浆水，随着成矿作用的演化大气水逐渐加入。赋矿围岩辉石闪长玢岩和穿切矿体发育的花岗闪长斑岩锆石U-Pb年代学研究得出，他们的成岩年龄分别为131.7Ma和126.1Ma。利用成岩成矿地质关系，约束凹山铁矿床的成矿年代阈值为131-126Ma，矿床形成于大王山组火山作用晚期，受区域岩石圈伸展和减薄作用的影响，处于区域拉张环境中。辉石闪长玢岩和花岗闪长斑岩的主量元素、微量元素、稀土元素、Sr-Nd同位素以及锆石微量元素和Hf同位素的研究表明，花岗闪长斑岩与赋矿围岩即辉石闪长玢岩具有相似的源区特征。岩浆岩的形成源于富集地幔并在其上升就位过程中混染了壳源物质，其中花岗闪长斑岩混染了更多的壳源物质。花岗闪长斑岩形成时代相似于区域中与铜金矿化有关的娘娘山组火山岩。锆石Ce（Ⅳ）/Ce（Ⅲ）比值大多低于100，δEu>0.4，具有部分斑岩型铜矿床赋矿岩体特征，成矿潜力需进一步研究。宁芜矿集区中矿床成矿系统研究得出，玢岩型铁矿床的成矿过程具有极大的相似性，经历浸染状矿化→角砾状矿石（或矿浆充填）→网脉状矿石（磷质逐渐沉淀形成大量的磷灰石），差别于在这个过程中受不同的成矿环境的影响，铁质在不同的成矿阶段富集并形成了不同的脉石矿物。铁矿化与其之后发育的铜金矿化存在怎样的成因联系尚未揭示，对铜金矿床的找寻仍需要深入的科学研究和地质勘探工作。更多还原

【Abstract】 Washan iron deposit is located in the Ningwu ore district, Middle-Lower YangtzeRiver polymetallic ore Belt（MLYRB）, East China. It is a typical porphyry-type irondeposit, with a multi-stage ore-forming process, and displays the iron mineralizationevolution of the Washan ore field. Based on the detailed field geological investigationand indoor experimental analysis, a detailed evolution of mineralization has beencarried out.The magnetite formation of the Washan deposit is divided into four stages,namely, disseminated magnetite, magnetite in breccia, coarse-grained vein magnetiteand pegmatitic vein magnetite. The cryptoexplosion induced large-scale ironprecipitation, and provides space for the mineralization.In situ electron microprobe and LA-ICP-MS analysis of the magnetite fromWashan iron deposit show that with the evolution of mineralization, the contents of Ti,Mn, V in magnetite are consistent; the Al and Mg contents increased; the contents ofGa, Sn and high field strength elements（Zr, Hf, Nd, Ta）change in a small range;from magnetite in breccia to pegmatitic vein magnetite, Co content graduallyincreased and Sc decreased gradually. The compositions of magnetite in variousstages indicate that the process of magnetite mineralization has a continuous evolutionwith a similar source. The iron derived from the late of magmatic evolution, and isenriched to be iron-rich fluid by the effect of immiscibility.Hydrogen and oxygen isotope characteristics of the mineralization various stagesof magnetite, apatite and quartz, and the homogenize temperature of apatite inpegmatitic vein magnetite ore indicate that during the mineralization process, the fliudcomposition was changed, combined with previous studies. The ore-forming fliud wasmainly of magmatic water, and then the meteoric water gradually added.The zircon U-Pb ages of the host rock（gabbrodiorite porphyrite）and the rockstock（granodiorite porphyry）, which cut across the ore body, are 131.7±0.7Ma and126.1±0.5Ma respectly. According to the relationship between petrogenesis andmineralization, the ages of mineralization of Washan iron deposit is in the 131.7 ~126.1Ma. It belongs to the Early Cretaceous in the Dawangshan cycle. This ironmineralization is proposed to occur in an extensional tectonic regime, possiblyinduced by lithospheric thinning. The characteristics of major elements, trace elements, rare earth elements, Sr-Ndisotopic of the gabbrodiorite porphyrite and granodiorite porphyry with their zircontrace element and Hf isotope features have shown that the two type rocks have thesimilar source. The formation of magmatic rocks derived from enriched mantle andthe crust material was involved in the magma during ascent process. The granodioriteporphyry was involved more.In the late stage of volcanic activity, hydrothermal vein-type copper and/or golddeposits occurred in part of the Ningwu ore district, which are considered to beclosely related with the Niangniangshan Formation. The ages of the granodioriteporphyry is similar to that of the volcanic rocks of the Niangniangshan cycle. The Ce（Ⅳ）/Ce（Ⅲ）ratios of zircons in granodiorite porphyry are mostly less than 100,which is different（much more lower）with the one of the pluton（>300）accosiated with copper porphyry deposit, but theδEu values（>0.4）. Therefore,further research is needed to study the possibility that granodioritic stocks are relatedto copper and/or gold mineralization.By the metallogenic system study, we infer that the porphyry iron mineralizationsin different typical deposits（i.e. Washan deposit, Meishan deposit, Gushan depositand Gaocun deposit）have a great similarity, experiencing disseminated magnetitemineralization - magnetite in breccia mineralization - coarse-grained vein magnetitemineralization - pegmatitic vein magnetite mineralization with the different of themainly mineralization in different stage be the effect of the different metallogenicenvironment. The relationship between iron and copper（gold）mineralizations isstill unrevealed. It needs further study and exploration to improve our understanding.更多还原