【作者】 瞿泓滢；

【导师】 裴荣富； 梅燕雄；

【作者基本信息】 中国地质科学院 ， 矿产普查与勘探， 2010， 博士

【摘要】 安徽铜陵凤凰山矿田是长江中下游成矿带内具有代表性和典型性的矽卡岩型铜矿田。矿田内构造活动、岩浆作用及成矿作用复杂。大地构造演化经历了活动(基底形成阶段)—稳定(盖层)—再活动(板内变形)3个发展演化阶段。中三叠世以后,板内变形阶段引发大规模的中酸性岩浆侵入活动。本文以凤凰山铜矿床为代表,主要采用SHRIMP锆石U-Pb同位素精确定年,辉钼矿Re-Os同位素精确定年,岩体主量、微量和稀土元素分析,流体包裹体均一温度、冰点温度以及拉曼成分分析,氢、氧、碳、硫、铅等同位素组成在空间上的三维成矿流体演化趋势,结合区域成矿背景的研究,运用现代成岩成矿地质地球化学理论,探索矿田岩浆作用及岩浆演化、成岩与成矿关系、成矿流体的时空演化、成矿物理化学场与矿床矿体定位的时空祸合。论文取得了以下主要成果和创新性认识：1.凤凰山铜矿床辉铝矿Re-Os等时线年龄为141.1±1.4 Ma,形成于早白垩世,属燕山晚期中酸性岩浆与相关热液上侵定位的产物。成矿物质为壳幔混合型。矿床位于长江中下游多金属成矿带上,长江中下游Cu-Au-Fe-Mo矿床系统形成时正处于地球动力学调整期,即中生代第二期大规模成矿期,地球动力学背景为构造体制大转折,凤凰山铜矿床亦处于中生代第二期大规模成矿期内。2. SHRIMP锆石U-Pb同位素精确定年,石英二长闪长岩样品测年获得年龄数据139.4±1.2 Ma；花岗闪长岩样品测年获得年龄数据为141.04±1.1 Ma,形成于晚侏罗世,岩浆侵入活动发生在燕山晚期,和铜陵矿集区主要成矿岩体的形成时代一致。岩浆在上升过程中,由于密度等因素制约,石英二长闪长岩晚于花岗闪长岩而形成,与矽卡岩型矿床有关的成矿主岩体可能为花岗闪长岩。凤凰山矽卡岩型铜矿床与岩体为同期产物,并且在时间上存在很短的时差,成岩成矿有着密切的关系。同位素组成表明幔源岩浆分异的深部流体参与了成矿作用。岩体侵位和岩石圈整体加厚产生伸展作用,软流圈地幔与上覆地壳减压熔融产生玄武岩浆底侵作用,二者密切相关。3.凤凰山铜矿床侵入岩的岩石类型主要为石英二长闪长岩和花岗闪长岩。根据岩石化学和地球化学的研究,侵入岩以富钾钙碱性系列岩石为主。其岩浆来源属于幔壳混合型,原始岩浆来源于上地幔碱性玄武岩区,并且与地壳物质混染。岩体成岩过程以混合作用为主,外来物质可能是在地幔部分熔融过程中加入的,也可能是在岩浆上侵过程中加入的。该矿床与新屋里岩体有着密切的时空和成因联系。石英二长闪长岩和花岗闪长岩是控制区内铜矿形成的最主要因素,成矿物质主要来自岩体。铜矿体稍晚于岩浆岩侵入事件形成。矿体分布于岩体与大理岩内矽卡岩带上。成矿热液以岩浆期后热液为主,并经历了从高温矽卡岩阶段到中低温热液阶段的复合型成矿作用。4.石榴石、透辉石、石英和方解石中的流体包裹体分别集中于3个区,其流体包裹体的温度和盐度区间代表着成矿流体演化的3个不同阶段。成矿流体经历了从高温度、高盐度向低温度、低盐度的持续演化过程,与成矿作用阶段基本对应,降温、流体沸腾是导致流体中巨量铜元素卸载的主要因素。5.氢、氧同位素组成表明成矿流体以岩浆水为主,可能在成矿晚期混有少量大气降水。硫同位素值集中于1.8‰～2.9‰,具岩浆来源的特征,为幔源硫,表明硫来自地幔。铅同位素组成显示该区铅具有岩浆热液物质来源特征,表明成矿期流体中的铅来自上地幔。更多还原

【Abstract】 The Fenghuangshan ore-field is the typical skarn Copper Ore-Field of the Middle-Lower River metallogenic belt at Tongling, Anhui. The tectonic movement, the magmatism and the mineralization of the ore-field are very complicated. The geotectonic evolution has been through three periods:the movement (the basement formation period), the stability (the cover) and the reprise (the intra-plate distortion). From the Middle Triassic, the intra-plate distortion period induced the large-scale intermediated-acidic magma movement.This study takes the Fenghuangshan Copper Deposit as an example adopting SHRIMP U-Pb dating on zircon, Re-Os dating, major elements, trace elements and rare earth elements, microthermometric studies, carbon, hydrogen, oxygen, sulfur and lead isotope compositions to show the spatial three-dimension metallogenic fluid trend. Moreover, combining region metallogenic background studies and utilizing the modern geological and geochemical theories of rock forming and mineralization, this thesis demonstrates the magmatism, the magma revolution, the relationship of the rock forming and mineralization, the space-time revolution of the metallogenic fluid, the metallogenic physical and chemical fields and the space-time combining of the deposit orientation.The Re-Os isochronal age is 141.1±1.4 Ma of the Fenghuangshan Copper Deposit forming Early Cretaceous The Fenghuangshan Copper Deposit is the offspring of the Late Yanshanian intermediated-acidic magma and the correlated hydrotherm intruding and locating. The metallogenin material is the crust-mantle mixed type. This deposit lies on the he Middle-Lower River metallogenic belt. The Middle-Lower River Cu-Au-Fe-Mo deposit system formed at the geodynamical adjusting period, the second large-scale metallogenic period of Mesozoic. The geodynamical background is the tectonic system transition. The Fenghuangshan Copper Deposit lies at this period.The Fenghuangshan quartz monzodiorite and granodiorite in Tongling, Anhui Province are spatially and temporally associated with Cu mineralization. Sensitive High Resolution Ion Microprobe (SHRIMP) U-Pb zircon dating of quartz monzodiorite is from (136.0±2.0) to (143.0±2.4)Ma, and the weighted mean age is (139.4±1.2)Ma (n=15, MSWD=0.76). SHRIMP U-Pb zircon dating of granodiorite is from (136.7±2.0) to (145.3±2.4)Ma, and the weighted mean age is (141.0±1.1)Ma (n=17, MSWD=1.5). The intrusive age is the Late Jurassic, the Late Yanshanian. The molybdenite Re-Os isochronal age is the same to the intrusive age of granodiorite and elder than the age of quartz monzodiorite. The mineralization has the relationship with granodiorite. Isotope compositions indicate that the mineralization relates to deep fluids of mantle magma differentiation. The extensional process which is resulted from the pluton emplacement and the whole thickening of the lithosphere has the relationship with the basaltic magma underplating which is resulted from the aesthenosphere mantle and the upper crust decompression.The Xinwuli pluton is the Late Yanshanian high-K, calc-alkaline intrution (144 Ma, U-Pb zircons age), which is composed by quartz monzodiorite envelope and granodiorite inner. Geochemical characteristics of the Xinwuli quartz monzodiorite indicate that the original magma is upper mantle alkli basalt, which is contaminated by crust materials during intrusion. Curst material contamination could be happened during partial melting or magma moving upwards. The Cu mineralization has closed spatial, temporal and genesis relations with the Xinwuli pluton. Orebodies are hosted by both quartz monzodiorite and marble along the contact zone, and endoskarn orebodies are dominanted. Similar trace element features of ore samples and quartz monzodiotite indicate that copper comes from the monzodiorite intrusion. Fluids bimetasomatism between quartz monzodiorite and carbonate rocks cause Cu precipitation. Orebodies are jointly controlled by bimetasomatism and structural deformation on the three dimension distribution, resulting in breccia ores distributed along the contact zones. The whole mineralization history can be classified as high temperature skarn stage and middle-low temperature hydrothermal stage.This study takes the Fenghuangshan Copper Deposit as an example to examine the metallogenic mechanism, the nature and origin of ore-forming fluid using the characteristics of metallogenic fluid and C, H and O isotope analysis. The Fenghuangshan deposit contains garnet, quartz and calcite in which fluid inclusions were well developed. Most of the fluid inclusions in garnet, diopside, quartz and calcite are concentrated mainly in three zones and the temperatures and salinity ranges of fluid inclusions represent three different phases of ore-forming fluid evolution, indicating that the fluid experienced a continuous process of evolution, which was well coupled with metellogenic phases of the Fenghuangshan deposit. Temperature decreasing and fluid boiling resulted in the discharge of a large amount of copper from Cu-bearing fluid. Furthermore, H and O isotopic analysis indicates that the ore-forming fluid consisted mainly of magmatic water, with minor meteoric water at the late stage of mineralization of the Fenghuangshan deposit. The value of Isotope S is 1.8%o to 2.9%o. S comes from the mantle. Isotope Pb constitutes show that Pb has the character of the magma material sources and Pb of the metallogenic fluid comes from the upper mantle.更多还原