【作者】 王力；

【导师】 孙丰月；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 华北地块为华北古板块的核心,是我国最重要的产金区,也是世界的重要金产地之一。论文运用区域成矿理论,以华北地区地球动力学演化为基础,以脉状金矿成矿作用研究为核心,以典型矿床解剖和室内样品测试分析为方法和手段,总结区内矿床地质特征、成矿条件、成矿时代及矿化的时、空分布规律,建立区域成矿模式,为进一步找矿工作奠定基础。通过对地质背景和地球动力学演化的综合研究,认为华北地块主要经历了前寒武纪结晶基底形成、中元古代到古生代稳定地块沉积和中-新生代的地块“活化”等3个演化阶段。华北地区中生代之前是一个典型的克拉通块体,自中生代以来进入强烈的构造活跃阶段,燕山期突发性地转变为造山带。中生代早中期表现为挤压造山环境,晚期表现为伸展环境。对比研究中国华北地块前寒武纪玄武岩和国外具有代表性绿岩带的地球化学特征,由于华北地块前寒武纪玄武岩中MgO含量低,熔浆中MgO含量小于20%,反映了华北地块前寒武纪时期地幔起源深度较小、热度不够、温度较低,地幔相对较冷,将导致地幔小比例熔融。这种小比例熔融机制,将导致华北地块早前寒武纪基性火山岩系在许多方面与国外典型的绿岩带存在非常明显的差异,主要表现为科马提岩不发育、变质程度较高、受后期的活化改造作用强烈。从而确定在华北地块上不存在太古代绿岩带,同时也不存在太古代绿岩带型金矿床。提出了华北地块太古代金的上地幔源区观点。由于硫化物富集金的能力比硅酸盐要高得多,在上地幔产生饱和硫的玄武岩熔体上升过程中会因液态不混溶而形成硫化物相,可把大部分金富集其中并滞留在上地幔,形成太古代金的上地幔源区。上地幔中的金具有很强的活化迁移能力,容易被幔源流体所携带并上升至地壳参与成矿。通过分析华北地块脉状金矿床和国外太古代绿岩带型金矿床的成矿作用特点,华北地块脉状金矿床与国外绿岩带型金矿床有诸多相似特点,但也表现出自己独特的一面。表现在华北地块固结时间较晚,活动性较强,其中脉状金矿床主要形成于陆块活化阶段,其总的构造背景可概括为由挤压、碰撞作用晚期或期后向伸展构造的转变时期,即由挤压向引张构造转变时期。成矿区中脉状金矿床主要分布在地块周边地带,与深断裂带、造山带、板块挤压碰撞带以及地体拼贴带相邻,这种构造环境是形成金矿带的基本条件。金矿床赋矿围岩以中深变质的镁铁质岩石和花岗岩类岩石为主；韧性-韧-脆性剪切带控制金矿田和矿带的分布,大规模金矿床一般产在韧-脆性剪切叠加的构造带中,如夹皮沟、金厂峪、乌拉山、小秦岭及胶东等地的金矿床都具有这种控矿特征。在空间上金矿化发生在韧性向脆性变形转变的地段。华北地块金矿床大多与燕山期中酸性岩浆活动有较为密切的空间关系。如小秦岭、胶东和夹皮沟等许多金矿床赋存在中酸性花岗岩中及其接触带附近。在国内首次研究使用世界上最先进的定年技术——SHRIMP热液独居石U-Pd定年法对金岭金矿床和灵山沟金矿床成矿年龄进行测定,得出成矿年龄分别为122±6.3 Ma和118±11Ma,精确厘定了胶东地区金矿床的形成时代为燕山晚期早白垩世。该方法在研究后生矿床和相关热液蚀变的演化和年龄确定方面是一个重要的进步,是金属矿床直接定年方法之一。并进一步划分出本区中生代成矿的三个重要时期,即190～160Ma和126～110Ma的金矿化以及100～80Ma的金-银多金属矿化三个成矿期,而以126～110Ma为成矿高峰期。本文尝试使用新西兰构造地质学家Sibson(1988)建立的断裂带内流体压力和深度之间存在非线性关系,结合流体包裹体C02-H20等容线相交法估算成矿压力,依据孙丰月等(2000)把Sibson的研究成果引用到热液脉状金矿成矿深度的计算公式,计算华北地块脉状金矿的成矿深度为6.45～9.8km。同时结合大量的成矿流体包裹体地球化学研究,认为华北地块主要脉状金矿床成矿流体为CO2-H2O-NaCl体系；成矿温度为234.6～386.7℃；压力为64.0～138.0MPa；流体的盐度为2.73％～11.46%NaCl;密度为0.64～1.0g/cm3;氢、氧、碳同位素表明流体主要以幔源流体为主,并伴有岩浆流体和大气降水的加入。硫、铅、氦、氩同位素研究表明,成矿物质主要来源于上地幔源区。华北地块金矿中广泛存在碲的独立矿物和煌斑岩这一普遍现象,从矿物学和岩石学角度支持幔源流体参与成矿的认识。同时指出煌斑岩中高含量的金是幔源流体从上地幔中带来金的重要证据。通过对华北地块典型矿床解剖,综合成矿地质背景、矿床地质地球化学特征、成矿物质来源、成矿流体来源、成矿作用、成矿条件和同位素年代学等特征认为,华北地区不同构造单元的脉状金矿床形成于同一种地球动力学背景,即中生代晚期的碰撞向伸展的转换体制,地壳显著伸展、造成了该区深部地幔物质-能量强烈上涌、岩石圈快速减薄、拆沉、岩石圈地幔岩浆底侵,大规模火山喷发、导致上地幔源区中成矿元素被带出,含矿热流体在脆性断裂中突发式集中卸载成矿。并建立了华北地块脉状金矿床的区域成矿模式。在确定找矿标志和大型矿田产出条件的基础上,提出7个找矿方向,为该区下一步找矿工作提供了理论依据。更多还原

【Abstract】 Located in the center of the North China ancient plate, North China block is one of the most important gold-producing area,both for our country and for the world.In this paper, on the basis of the regional metallogenic theory, geodynamic evolution of North China region, study of lode gold mineralization,and analysis of typical deposits and experimental test,the author summarized the characteristics of the region deposit, and mineralization conditions, times and space.Further more,regional metallogenic model is established, which is helpful to make further exploration wok.According to the study of geological setting and geodynamic evolution. It is suggested that the North China block had gone through three stages,which are:1.the formation of the Precambrian crystalline basement;2.the formation of sediments in the stable block from the period of Proterozoic to Paleozoic;and 3.activation of the block from the period of Mesozoic to Cenozoic.North China craton which used to be a typical block before Mesozoic changed into an tectonic active region after that,and turned into an orogenic belt during Yanshan period. During the early and middle Mesozoic,it is an compressive orogenic environment,and changed into an extended environment in the late Mesozoic.The author compared the geochemical characteristics between Precambrian basalt in North China block and the typical greenstone belt abroad. Precambrian basalt has a low content of MgO(<20%),which reflects the North China block has a small origin depth of the mantle at that time, and less heat, lower temperature,together with the relatively cold mantle,all of which caused a small percentage of mantle melting. This small-scale melting mechanism lead to great differences between the mafic volcanic rocks of the North China block in the early Precambrian and typical greenstone belt abroad. They are demonstrated as higher metamorphism,intense transformation, and lack of komatiites. It is suggested that Archean greenstone belt and related gold deposits are not exist in the North China block.The point that Archean gold deposits of North China block is mantle source is proposed in this paper. Because sulfide has the higher ability of gold concentration than the silicate, during the process of basalt lava contained saturated sulfur which derived from upper mantle move upward,the basalt lava could form immiscible sulfide phase,and case most of gold remaining in the upper mantle. Gold in the upper mantle has a high capacity of mobilization and migration,and can easily be carried upward to the crust to form gold deposits.There are many similar characteristics in mineralization between lode gold deposits in North China block and the gold deposit in Archean greenstone belt abroad, but they also demonstrated their Unique sides. The North China block has a later time of consolidation and stronger activity, and the lode gold deposits mainly formed during active period of the continental blocks.The tectonic setting can be summarized in the grounds of extrusion, collision period and extensional tectonics period.In other words,It transformed from compression to tensile period. In the mining area, lode gold deposits mainly distribute in the block edge,adjacent to the deep fault zone, orogenic belt, the plates collision zone and the terrane collage zone.Wall rocks of gold deposits are mainly mafic and granitic rocks which are medium-high grade metamorphic rocks. The distribution of gold deposits is controlled by ductile and ductile to brittle shear zones.Large gold deposits are generally located in the ductile-brittle superposition shear belt,such as Jiapigou, Jinchangyu, Ural mountains, Small Qinling and Jiaodong gold deposits. Most gold deposits in North China Block are closely related to the mediate to acid magmatic activities. Such as small Qinling, Shandong and Jiapigou and so on.In this paper, SHRIMP U-Pd dating of Monazite uesd in Jinling and Lingshangou gold deposits is first used in the domestic,and the age of ore forming is 122±6.3 Ma and 118±11Ma,determined the time of formation of Jiaodong gold deposits is in the early Cretaceous.It is an important advance in determining the age of epigenetic deposits and related hydrothermal alteration,and it is one of the direct dating methods of the metal deposit. Three ore forming periods are determined,which are gold forming period in 190-160Ma and 126～110Ma,and gold-silver forming period in 100-80Ma.The period of 126～110Ma is the main ore forming period.According to the nonlinear relationship between fluid pressure and depth in fault zone established by Sibson(1988), combined with the pressure determined by immiscible inclusion geobarometry of CO2-H2O fluid inclusions, refered to formula to calculate the depth of hydrothermal lode gold mineralization by Sun Fenyue(2000),the depth of gold deposits formed in the North China block is determined to be 6.45～9.8km. Combined with geochemistry of ore-forming fluid inclusion, fluid of lode gold deposits in the North China block is CO2-H2O-NaCl system,with the ore forming temperature of 234.6～386.7℃and pressure of 64.0～138.0Mpa.Salinity of fluid is 2.73%～11.46%NaCl, and the density of fluid is 0.64～1.0g/cm3. Hydrogen, oxygen and carbon isotope show that the ore forming fluid was mostly mantle derived fluids, mixed with magmatic fluid and meteoric water. Studies on sulfur, lead, helium and argon isotope show that ore foming minerals are mainly from the upper mantle. The phenomenon of widespread distribution of independent tellurium minerals and lamprophyres in gold deposits in the North China block,together with mineralogy and petrology evidence,help to understand the mantle derived ore forming fluids.The paper also pointed out that the high content of gold in lamprophyre is the important evidence of mantle derived gold.On the basis study of typical deposits on the North China block, combining with geological setting, deposit geological and geochemical characteristics, source of ore-forming fluids, mineralization, ore-forming conditions and characteristics of isotopic chronology, it can be concluded that lode gold deposits of different structures in North China formed in the same geodynamic setting,which is,a transition system from collision to extension condition in the late Mesozoic. At that time, crustal extended significantly, resulting in mantle material and energy upwelling, rapid thinning and delamination of the lithosphere, large-scale volcanic eruption, resulting in the mantle ore forming elements being draged out,and ore-bearing hydrothermal fluids discharged in the brittle fracture. In the paper, the regional metallogenic model of lode gold deposits in the North China block is established. Seven prospecting directions are proposed and a theoretical basis for further exploration in this area is provided.更多还原