【作者】 江思宏；

【导师】 聂凤军；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2004， 博士

【摘要】 北山地区地处西伯利亚、哈萨克斯坦和塔里木三大板块交汇部位，区内前寒武纪和古生代地层出露广泛，构造形迹复杂，岩浆岩发育和金矿床（点）星罗棋布。该区不仅是天山—阴山—兴安金属成矿带的重要组成部分，而且也是了解中亚地区古大陆地质构造演化历史的重要窗口。因此，该区基础地质和金矿床地质理论研究以及找矿勘查工作历来为国内外地质学家所关注。北山地区目前已经发现了近百处金矿床（点），根据赋矿围岩和矿床地质特征，可以将这些金矿床划分为以下五种类型，它们分别是（1）斑岩型，代表性金矿床为流沙山钼—金矿床；（2）火山岩型，代表性矿床有马庄山、新金厂、老金厂和狼娃山等；（3）与花岗岩类深成侵入岩有关的金矿床（点），代表性金矿床有南金山、金窝子、照壁山、拾金坡、金庙沟、金沟井、磨金洞、明舒井等；（4）以变质岩为容矿围岩金矿床（点），代表性金矿床有小西弓、老硐沟和交叉沟等；和（5）矽卡岩型，代表性金矿床为花牛山。上述这些矿床均不同程度地与岩浆活动关系密切。为了探讨岩浆活动与金矿床成矿作用之间的关系，本文首次对北山地区代表性花岗岩类侵入岩体开展了系统岩石学、地球化学、铅和钕同位素示踪以及⁴⁰Ar-³⁹Ar同位素年代学研究，对各代表性侵入岩体的成岩环境、形成时代和含矿特征进行了深入讨论。尽管在研究区范围内，从前寒武纪到中生代燕山期各时代的花岗岩类侵入岩均有出露，但是海西期花岗岩类以分布范围广、出露面积大和含矿性好为特点。绝大部分花岗岩类侵入岩属古大陆边缘活动带或碰撞造山环境内形成的Ⅰ型花岗岩。根据Nd同位素分析结果，在同一花岗岩体的不同部位，既可以有正ε_Nd（t）值，也可以有负ε_Nd（t）值，这可能一方面反映了整个岩体本身同位素体系并未达到均一，另一方面也反映了岩体在形成过程中，可能同化混染了大量前寒武纪基底。由于成岩物质中新生的地壳物质和古老的地壳物质组分所占比例的差别，致使岩石的ε_Nd（t）值也变化较大。由于上述划分的前四类矿床规模较大和产量较高，因此文章中分别从这前四种类型金矿床中挑选出一个典型矿床，对其成矿地质背景、矿体地质、矿石结构构造、同位素和元素地球化学特征等进行了解剖研究，并探讨了金矿床成矿作用时空演化规律和成矿元素富集过程。研究结果表明，马庄山和流沙山金矿床与海西期花岗类侵入岩具密切时空分布关系，而南金山金矿床与印支期花岗类侵入岩关系密切，都属中温热液脉型金矿床。相比之下，小西弓金矿床则是海西期花岗岩类侵入岩对前寒武纪变质岩型金矿床（或矿胚）进行叠加改造的结果，属混源型（岩浆热液和变质热液）中温热液金矿床。区域上主要金矿床（点）沿板块缝合带两侧分布，明显受板块碰撞拼合的控制。区域金矿床成矿作用研究表明，北山地区金的成矿作用主要集中在三个时期，分别是前寒武纪、海西期和印支期，其中以海西晚期金的成矿作用最为强烈，它控制了北山地区主要金矿床（点）的形成。北山地区海西期大规模的金成矿作用主要与塔里木、哈萨克斯坦和西伯利亚三大板块之间的碰撞对接所诱发的大规模岩浆侵入—喷发活动有关，金矿床的成矿作用高峰时间也与这三大板块碰撞拼合的时间相吻合，显示了碰撞造山过程对金矿床形成的控制作用，形成了许多同造山期金矿床。而由印支期构造—岩浆活动形成的金矿床具有造山后金矿床的形成特点。更多还原

【Abstract】 The Beishan Mt. spans three provinces-Gansu, Xijiang and Inner Mongolia, having an area of120 000 km². Yectonically, it transverses three different tectonic units, i.e. Siberia, Kazakhstan andTarim plates, respectively, and is composed of nine terrains with widely exposed Precambrian andPaleozoic strata, complex structures, intensive magmatic activities and widespread ore deposits. Itis not only a main part of Tianshan-Yinshan-Great Hinggan metallogenic belt in China, but also akey to understand the evolution of central-Asian orogenic system. Therefore, the studies of basicgeology, ore deposits and mineral exploration have attracted great attention from domestic andabroad geologists.At present, more than 100 gold deposits and prospects have been discovered, explored andmined. Based on the host rocks and geological features, the gold deposits in the study area can bedivided into five groups （or types）, （1） porphyry Au deposit, such as Liushashan Mo-Au deposit;（2） volcanic type Au deposit, such as Mazhuangshan, Xinjinchang, Laojinchang and Langwashandeposits; （3） plutonic intrusions-related Au deposit, such as Nanjinshan, Jinwozi, Zhaobishan,Shijinpo, Jinmiaogou, Jingoujing, Mojindong and Mingshujing deposits; （4） hosted byPrecambrian metamorphic rocks, such as Xiaoxigong, Laodonggou and Jiaochagou deposits; and（5） skarn type Au deposit, such as Huaniushan deposit. The origin of all of these gold deposits isclosely related to the magmatism.In order to discuss the relationship between the magmatism and the gold metallogeny, theresearch on petrology, geochemistry, Nd and Pb isotopes and ⁴⁰Ar-³⁹Ar age dating of the granitoidintrusions in the study area was first conducted systematically, and the emplacement setting andages of the major granitoid intrusions as well as their relations to gold deposits were discussed indetail. Although the emplacement ages of the granitoids in the Beishan Mt. area vary fromPrecambrian to Mesozoic Yanshanian, the Hercynian granitoid intrusions are predominant, and arecharacterized by wide distribution, large outcrop area and high concentration of ore-formingelements. Most granitoid intrusions belong to theⅠtype of granites intruded along the ancientcontinental margin or collision zone. According to the Nd isotopic analytical results, somegranitoid intrusions bears both positive and negativeεNd （t） values, which indicates that theisotopic system of the intrusion is not homogeneous, and in the other hand, a large amounts ofPrecambrian metamorphic rocks were assimilated by the granitoid intrusions. Due to theproportional difference of the ancient and juvenile crustal materials in the granitic intrusions, theεNd （t） value varies greatly.Four typical gold deposits, which are included in the former four types of gold deposits mentioned above, was discussed in detail in light of the ore-forming setting, ore body features, oretextures and structures, isotopic and elemental geochemistry. It has been suggested that theMazhuangshan and Liushashan deposits are spatially and temporally related to the Hercyniangranitoid intrusions, while the Nanjinshan gold deposit is associated with the Indosinianmagmatism. They all belong to the mesothermal vein type gold deposit. In contrast, theemplacement of the Hercynian granitoid intrusion into the Precambrian metamorphic rocksresulted in the formation of the Xiaoxigong deposit. It belongs to the mixed sources （magmaticand metamorphic hydrothermal） type mesothermal gold deposit.The regional gold deposits in the study area are mainly distributed along the suture zones.The studies on these deposits indicate that the gold metallogeny in the Beishan Mt. area is mainlyconcentrated in three periods, i.e. Precambrian, Hercynian and Indosinian. Among these periods, the late Hercynian gold metallogeny is the most intense ones. Most of gold deposits are formedduring this period. The gold metallogeny at this period is intimately related to the intensemagmatic activities caused by the collisions among Siberia, Kazakhstan and Tarim plates.Therefore, the gold metallogeny is controlled by the orogenic process. The gold deposits formed atthis period could be called syn-orogenic gold deposit. In contrast, the gold deposits formed duringIndosinian are characterized by post-orogenic gold deposit.更多还原