【作者】 韩世礼；

【导师】 张术根；

【作者基本信息】 中南大学 ， 地质资源与地质工程， 2013， 博士

【摘要】 摘要：埃塞俄比亚北部位于西冈瓦纳古陆北缘,是阿拉伯-努比亚地盾西南部新元古代岛弧增生带的重要组成部分。施瑞(Shire)地区是厄立特里亚阿斯马拉(Asmara)—埃塞俄比亚施瑞VMS型铜多金属成矿带的南西延伸地段,具有优越的区域地质成矿条件和找矿前景。近年来,该成矿带发现了阿迪内弗斯(Adi Nefas)、德巴瓦(Debarwa)及英坝德芙(Emba Derho)等中大型VMS型矿床,被誉为是世界上近三十年来VMS型矿床找矿勘探方面取得的最大成就。然而,研究区的基础地质和矿产地质研究程度较低,赋存VMS型矿床的新元古界地层已广泛遭受绿片岩区域变质和强烈的构造变形,造山前、造山期及造山后花岗岩类岩浆侵入活动均较为强烈,使得该地区地质和矿化面貌比较复杂,矿床成因模式、定位机制、定位规律的把握较困难,严重影响铜多金属矿床的勘查部署及外围成矿预测,故迫切需要强化施瑞地区块状硫化物型铜多金属矿床成矿地质条件、成矿机理、控矿因素及矿化定位机制研究。通过本文研究工作,主要取得如下成果：(1)查明了埃塞俄比亚北部施瑞地区具有造山前、造山期和造山后三期花岗岩类型,各花岗岩类与铜多金属矿床不具有成因关系,不存在成矿元素的叠加作用；较完整的认识了各花岗岩类的成因类型、构造环境及地壳演化背景,为成矿带铜多金属矿的成矿环境提供了必要的基础性数据,为探讨西冈瓦纳古陆东北缘消减带的构造特征和演化机制提供了进一步的依据。(2)首次获得埃塞俄比亚北部施瑞地区造山前花岗岩全岩Sm-Nd等时线年龄(824.4Ma±15.5Ma),属新元古代的拉伸纪；源区以幔源物质为主的Ⅰ型花岗岩,构造环境处于新元古代早期沟—弧—盆演化阶段,被动大陆边缘—火山岛弧环境。(3)利用地球化学元素频数直方图、蚀变指数及构造环境等方法,查明Pvai变火山岩并不具有明显的双峰式火山岩特征,即非裂谷成因火山岩。变火山岩全岩Sm-Nd等时线年龄(830.7Ma±15.4Ma),与造山前花岗同属新元古代的拉伸纪,形成于洋壳为底的岛弧构造域的张应力较强的弧后扩张盆地。(4)首次利用地球化学数据进行小波分析处理,不仅有效划分了区域火山旋回,还有效判别了旋回中的韵律,为利用地球化学资料研究火山旋回韵律提供了一条新的途径。根据火山旋回的地质特征、地球化学及遥感解译综合分析,研究区变火山岩系共划分出6个旋回15个韵律。(5)首次利用剖面地球化学数据,通过转换计算得出绿泥石化指数、绢云母化指数、高岭土化指数和硅化指数,研究其蚀变与矿化的关系。结果表明矿体产出位置往往处于各蚀变指数的波峰位置,综合蚀变指数明显大于非赋矿围岩的蚀变指数,且上下盘围岩蚀变程度具有明显对称的特点。(6)查明了埃塞俄比亚施瑞地区铜多金属矿的成矿作用,划分出三个成矿期,即次火山热液期、区域变质期和表生氧化期,其中次火山热液期是研究区主成矿期；区域变质作用有限,未叠加新的成矿元素。(7)查明了铜多金属矿的成矿物质来源,主要来自富含挥发份铜多金属成矿元素的次火山热液,部分来自流经的先形成的中基性火山熔岩,少部分来自海水从上覆中酸性火山碎屑岩中渗滤萃取出来的成矿元素。(8)详细查明了埃塞俄比亚施瑞地区铜多金属矿的矿床成因、控矿因素和成矿规律。施瑞地区铜多金属矿是一个与陆缘岛弧海相火山活动有关的次火山热液充填交代型块状硫化物矿床。矿体主要就位在中(基)性—(中)酸性岩性转换界面附近,构造的交汇部位,火山旋回韵律的第Ⅱ旋回的第3韵律、第Ⅲ旋回的第2韵律和第Ⅳ旋回的第3韵律等。(9)提出并探讨了次火山热液充填交代型块状硫化物矿床的成矿机制及成矿理论研究,建立了施瑞地区铜多金属矿床的成矿模式,丰富了VMS型矿床成矿理论及成矿模式方面的研究。该成矿模式是在火山喷发间歇期,中酸性次火山热液(含矿热液)侵入到中基性熔岩与中酸性凝灰岩、沉凝灰岩的岩性组构界面或中酸性凝灰岩、沉凝灰岩内部的有利空间,与从上盘渗滤下来的海水(含矿)相遇,因物理化学条件的变化,形成的次火山热液充填交代型块状硫化物矿床。(10)以成矿模式、矿化定位机制和定位规律为建模指导思想,建立了研究区铜多金属多元信息成矿定位预测模型；并在施瑞地区Pvai变火山岩系中圈定了6个找矿靶区。更多还原

【Abstract】 Abstract:North of Ethiopia, located in the northern margin of west Gondwana, is an important part of Arabia-Nubian shield southwest Neoproterozoic arc accretionary zones. Shire is in the southwest extension area of VMS copper polymetallic mineralization belt in Asmara, Eritrea-Ethiopia, with superiority of regional geology and metallogenic conditions and prospecting potentials. In recent years, the metallogenic belt found a batch of Adi Nefas, Debarwa and Emba Derho medium VMS type copper zinc ore bed, was the greatest achievements in VMS deposit prospecting exploration in nearly three decades in the world. However, the research degree of the basic geology and mineral resources geology in the research area is low. The Neoproterozoic stratum with VMS type deposit has widely experienced the greenschist regional metamorphism and intense tectonic deformation. In addition, the cranite magma intrusion activities were relatively intensive during preorogenic, orogenic and postorogenic periods, making regional geological and mineralization features complex and deposit genesis model, deposit location mechanism and location law hard to grasp, seriously affecting copper polymetallic ore of the exploration deployment and the peripheral metallogenic prediction. Therefore, there is an urgent need to strengthen the research on massive sulfide copper polymetallic deposit ore-forming geological conditions, mineralization mechanism and ore-controlling factors and mineralization locating mechanism in Shire.Through the research work in this project, the main achievements were obtained as follows:(1) It was found out that there were three kinds of granitoids of periods of preorogenic, orogenic and postorogenic in Shire in northern Ethiopia, granitoids and copper polymetallic deposit were not genetic relationship, there is no superimposition of ore-forming elements. For different granitoids, the differences of petrology characteristics, rare earth microelements and major elements were obvious. And the genetic types, tectonic environment and the background of crust evolution were completely understood. These findings provided the necessary basic data for the metallogenic environment of copper polymetallic metallogenic belt and offered a further basis for exploring tectonic characteristics and the evolution mechanism of subduction zone in the northeast of west Gondwana.(2) Sm-Nd isochron age (824.4Ma±15.5Ma) of total rock of the granitoids of the preorogenic period in Shire in northern Ethiopia, was gained for the first time, which belonged to Tonian of the Neoproterozoic; the I type granite in source area mainly consisted of mantle-derived materials, and its tectonic environment was the passive continental margin-volcanic island arc environment in the trench-arc-basin evolution stage of early Neoproterozoic.(3) Methods of geochemical element frequency histogram, alteration index and tectonic environment were used in the research, and it was found out that Pvai metavolcanic rock did not have obvious characteristics of bimodal volcanic rock, indicating that it was non-rift valley origin volcanic rock. Sm-Nd isochron age (830.7Ma±15.4Ma) of total rock of the metavolcanic rocks and granitoids of the preorogenic period belonged to Tonian of the Neoproterozoic, and were formed on the site of back-arc spreading basin with strong tensile stress in island arc tectonic domain, where oceanic crust was the bottom.(4) It was the first time to use the geochemical data to make wavelet analysis and processing. Not only the volcanic cycle was effectively divided, but also the rhythm of the cycle was discriminated effectively, which provided a new way for studying volcanic cycle rhythm with the geochemical data. According to comprehensive analysis of the geologic features of volcanic cycle, geochemistry and remote sensing interpretation, metavolcanic series in the study area were divided into6cycles and15rhythms.(5) It was the first time that the profile geochemical data was used and calculated conversional to get the chloritization index, and sericitization index, kaolinization and silicification index to study the relationship between alteration and mineralization. The results showed that the orebody locality was always right in the crest of the alteration index, the comprehensive alteration index was significantly greater than that of non-enriched ore surrounding rock, and the feature of symmetry of wall rock alteration was obvious.(6) The copper polymetallic mineralization in Shire was found out. Mineralization was divided into subvolcanic hydrothermal period, regional metamorphism reform period and supergene oxidation period, among which the subvolcanic hydrothermal period was the main metallogenic period in the study. Superposition of regional metamorphism is limited, there were not the new ore-forming elements.(7) We found out the copper polymetallic metallogenic material source. The main part was from subvolcanic hydrothermal solution with rich volatile copper polymetallic ore-forming elements, with a small part from the flowing formed basic lava, and some from the ore-forming elements infiltrated and extracted by sea water from overlying intermediate-acid volcanic clastic rock.(8) We found out copper polymetallic ore deposit genesis and ore-controlling factors and metallogenic regularity in Shire in Ethiopia in detail. The genesis of ore deposit of copper polymetallic in Shire was a subvolcanic hydrothermal filling and metasomatic type copper polymetallic massive sulfide deposit related to the epicontinental island arc marine volcanic activities. The main orebody was near the basic-(mid) acidic lithology transition interface, intersection parts of the structure and the3rd rhythm in the II volcanic cycle, the2nd rhythm in the III cycle, the3rd rhythm in the IV cycle, etc.(9) Metallogenic mechanism of the subvolcanic hydrothermal filling and metasomatic type massive sulfide deposits and the study of metallogenic theories were proposed and deeply discussed, massive sulfide copper polymetallic deposit metallogenic pattern in Shire was established, and the VMS deposit metallogenic theory and model research was enriched. It was considered that massive sulfide orebody was a kind of subvolcanic hydrothermal filling metasomatic type deposit formed in the intermittent period of volcanic eruption due to the change of physical and chemical conditions, when the mid-acidic subvolcanic hydrothermal (ore-bearing hydrothermal) invaded into the lithologic fabric interface of the basic lava and mid-acidic tuff, tuffite or the internal space of mid-acidic tuff and tuffite, then met with the infiltrated seawater (ore-bearing) from hanging wall.(10) Based on the modeling guiding ideology of "metallogenic model, mineralization locating mechanism and locating rule", the model of copper polymetallic multivariate information mineralization locating prediction in the study area was established; and six prospecting target areas were framed in Pvai metavolcanic series in Shire.更多还原