【作者】 刘锋；

【导师】 李延河； 毛景文；

【作者基本信息】 中国地质科学院 ， 地球化学， 2009， 博士

【摘要】 阿尔泰金属成矿带是我国重要的成矿省。其中铁矿床主要产在阿尔泰南缘阿巴宫-蒙库一带的克兰和麦兹火山沉积盆地中。尽管前人对该区域的金属矿床做了很多工作,取得了显著成果,但大多集中于铜、铅、锌及稀有金属等矿产的研究,针对铁矿床的专项研究较少,缺乏系统性,对以蒙库铁矿为代表的一些主要铁矿床的成矿作用及成因类型的认识存在较大争议。本文以野外地质调查为根本,对典型铁矿床地质特征进行详细观察,同时对赋矿地层、花岗岩、典型矿床、蚀变围岩等的岩石学、岩石地球化学、同位素以及流体包裹体和微量稀土等进行系统研究,探讨了铁矿形成的构造环境、成矿物质来源、成矿流体性质、成矿时代等关键科学问题。在此基础上,总结了本区铁矿的成矿作用及其规律性,初步建立了区域铁矿床的成矿模型。阿巴宫-蒙库一带铁矿床主要赋存在康布铁堡组中酸性变质火山沉积岩组中,与岩浆活动有关;阿巴宫铁矿属于岩浆分异的晚期矿浆贯入充填型铁矿,蒙库、萨尔布拉克和加尔巴斯套铁矿床是与酸性侵入岩有关的矽卡岩型铁矿;铁矿空间产出位置受深大断裂附近的北西向次级断裂破碎带控制;矿物组合较为简单,围岩蚀变以矽卡岩化为主。岩石学、岩石地球化学及同位素研究表明,康布铁堡组变质火山岩、与主要铁矿床有关的花岗岩具有同源、同构造环境特征,是晚志留世-早泥盆世岩浆演化的不同相。康布铁堡组变质火山沉积岩组合原岩为一套石英角斑质岩-角斑岩-细碧岩的火山岩建造,形成于413Ma左右,是陆缘弧环境中板块俯冲作用下洋壳熔融、同化陆壳物质,并经结晶分异演化,最终形成的一套基性-中性-酸性的钙碱性火山岩组合。与铁矿成矿有关的花岗岩多在410～400Ma形成,也是陆缘弧环境中板块俯冲作用下洋壳熔融、分异的产物。少数与铁矿有关的花岗岩形成于早二叠世(287Ma),为后造山伸展环境下岩浆侵入产物。研究了各典型矿床的地球化学特征。阿巴宫铁矿磁铁矿氧同位素特征反映了成矿流体中水来源于原始岩浆水,暗示该铁矿的岩浆成因;与磁铁矿共生的磷灰石稀土和微量元素特征与Kiruna型铁矿以及宁芜玢岩铁矿中磷灰石特征非常相似,表明它们具有相同的成因机理,反映出阿巴宫铁矿为岩浆分异的晚期矿浆贯入式成因;其硫同位素特征表明成矿物质源自幔源的玄武质岩浆。蒙库铁矿床矿石和地层中黄铁矿硫同位素显示双峰特征,表明硫一部分来自地层,一部分来自花岗质岩石,反映该铁矿是酸性侵入岩与火山岩地层共同作用形成的矽卡岩型铁矿。康布铁堡组火山岩、蒙库岩体以及与萨尔布拉克矽卡岩型铁矿有直接成因关系的萨尔布拉克花岗岩体都具有幔源特征,说明成矿物质来源于俯冲掉的洋壳。综合本区典型铁矿地球化学特征认为,康布铁堡组火山岩和有关花岗岩提供了主要的成矿物质。成矿流体来源较为复杂,有的以岩浆水为主混有大气降水,也有大气降水占主导,部分受到变质流体的影响。磁铁矿的形成主要发生在中低温、低盐度、低密度的矽卡岩晚期阶段。年代学研究表明,蒙库铁矿的形成限定在400Ma左右,阿巴宫铁矿略晚于413Ma,萨尔布拉克铁矿形成于410Ma左右,加尔巴斯套铁矿形成于287Ma。由此可见,阿巴宫-蒙库一带铁矿主要形成于晚志留世-早泥盆世,少数形成于早二叠世时期。基于上述研究,建立本区铁成矿模式如下:早古生代开始的古亚洲洋板块向北俯冲到西伯利亚大陆板块的构造运动是阿尔泰南缘一带成矿作用发生的源驱动力。晚志留世-早泥盆世期间沿大陆边缘局部撕裂形成一系列拉张断陷盆地,同时引发的火山喷发作用和岩浆侵入作用是成矿作用发生的直接诱因。岩浆分异或不混溶作用形成的晚期含矿岩浆可以形成矿浆贯入型铁矿,更多的是侵入岩浆与地层发生交代反应形成的矽卡岩型铁矿。岩浆侵入作用是铁富集成矿床的主要控制因素。更多还原

【Abstract】 The metallogenetic belt of Altay is an important metallogenetic province in our country. In this belt, the main iron deposits are located in the Kelan and Mazy volcanic-sedimentary basin from Abagong to Mengku area in the southern margin of Altay. The prevenient investigation mostly focused on the mineral deposits of copper, lead, zinc and rare metal etc. in despite of a lot of works and prominent achievement on metal deposits in the area. The less special and systematical research resulted in much dispute on metallogenesis and genetic type of several iron deposits such Mengku deposit as the first. In this study, the geological features of several tipical iron deposits were surveyed detailedly on the base of the in-depth investigation in the field and the petrology, the geochemistry, the isotopic geology, the inclusion fluid and trace elements, REE were systematically studied on producting-ore stratum, granites, typical deposits and altered hostrocks. In the mean time, the key problems about tectonic setting, origin of metal, ore-forming fluid and geochronology were mainly discussed. On these basic works, we summarized the metallogenesis of the iron deposits and its regulation and primarily constructed the metallogenesis model of the area.The Abagong iron deposit is attributed to the intrusion and filling of late ore magma by magmatic differentiation and the Mengku, Serblak and Jerbast iron deposits are shared by skarn iron deposits related to the silicic plutons. The shape of ore bodies are controlled by the northwest sub-fault belts near the large regional faults. They are mainly characterized by simple mineral assemblage and skarn alteration for hostrocks.The study on petrology, geochemistry and isotope geology indicates that there are the common resource and tectonic setting for the Kangbutiebao formation with metamorphic volcanic rocks and the granite plutons related to the main iron deposits.They are different facies from magma evolvement in late Silurian-early Devonian. The protolyte for the Kangbutiebao formation with volcanic-sedimentary rocks resides in the formation with quartz ceratophyre, ceratophyre and protolyte formed at about 413Ma. They attribute to the calc-alkalic unit from basic to intermediate to silicic volcanic rocks resulted from the melting and differentiation evolvement of oceanic crust with assimilating crustal material in the continent-arc setting due to oceanic plate subduction. The granite plutons related to metallogenesis of iron mostly formed from 410Ma to 400Ma, resulted from the melt and differentiation of oceanic crust in a arc-continent setting because of subduction of plate. Only did few plutons related to iron deposits form at about early Permian(287Ma), showing post-orogenic setting.We have studied the geochemical characteristics of several typical iron deposits.The feature of oxygen isotope for magnetite from Abagong iron deposit reflects that the water in the fluid of mineralization resides in the initial magma, implying the magma genesis of mineralization. The similaritary features of REE and trace elements for coexisting apatite with magnetite in the Abagong, the Kiruna type and the Ninwu porphyrite iron deposit show their common genesis, indicating that Abagong iron deposit resulted from the intrusion of late ore magma due to the magma differentiation. The characteristic of sulfur isotope composition implies that the Abagong iron deposit resides in basaltic magma from mantle resource. The bimodal feature of sulfur isotope composition for the pyrite from ore and hostrocks indicates that sulfur in the Mengku iron deposit partly originates from stratum, partly from granitics, implying that the deposit attributes to skarn type resulted from the reaction between silicic pluton and volcanic stratum. The Kangbutiebao formation volcanics, the Mengku pluton and the Serblak granite related directly to the formation of iron deposit all take on mantle resource, indicating that iron resides in the subducted oceanic crust. Above all geochemical characteristics of typical iron deposits, we think that the Kangbutiebao formation volcanic rocks and granites-related provided the main origin of metal. The ore-forming fluids derived from more complex resources that some were mainly derived from magmatic water with some contributions from meteoric water, some prominently resulted from meteoric water and some were partly influenced by metamorphic water. The formation of magnetite arised mainly in the late stage of skarn period in which the fluid appeared in the middle-low temperature, low salt and density.The study on geochronology indicates that the age of Mengku iron deposit is defined at about 400Ma, Abagong iron deposit at later than 413Ma somewhat, Saerblak iron deposit at about 410Ma and Jerbast iron deposit at about 287Ma. The above all illustrate that the iron deposits in Abagong-Mengku area were mainly formed in the period of late Silurian-early Devonian, few in the period of early Permian.Based on the above study, the metallogenesis model of iron in this area was suggested as follow: The subduction of the Paleo-Asia ocean north-ward beneath the Siberian plate beginned in the early Paleozoic provides the resource of power driving metallogenesis in the southern margin of Altay. Because of the subduction, a series of stretched and fault-through basins formed in late Silurian to early Devonian, volcanic emission and magmatic intrusion directly urged metallogenesis. The late bearing-ore magma (ore-magma) formed by the differentiation and immiseibility of magma may form the intrusive iron body, but more iron deposits attribute to skarn type resulted from the metasomatic reaction between intrusive magma and stratum. The intrusion of magma mainly controlled the iron mineralization.更多还原