【作者】 高浮萍；

【导师】 杜杨松；

【作者基本信息】 中国地质大学（北京） ， 矿产普查与勘探， 2010， 硕士

【摘要】 桃冲铁矿地处长江中下游多金属成矿带铜陵-繁昌铁-铜矿区的东北部。矿体严格受地层控制,并与矽卡岩伴生,在本区具有典型意义。本文对不同成矿阶段和不同层位矽卡岩和矿石中的流体包裹体进行了岩相学、测温学、地球化学和同位素特征研究,初步探讨了该矿床成矿流体的演化规律和成矿机制。通过上述研究,得到以下主要认识:1.桃冲矿区流体包裹体类型多样,包括富气相包裹体、富液相包裹体、含子晶包裹体,但以富液相包裹体和含子晶包裹体为主。2.桃冲铁矿成矿流体以NaCl-H₂O体系为主,其中气相成分主要为H₂O,液相成分中阴离子为Cl^-、SO₄^2-、F^-等,阳离子为K⁺、Na⁺、Ca²⁺、Mg²⁺等,但以Na⁺和Cl^-为主。流体包裹体均一温度集中于260～460℃之间,密度集中于0.92～1.11 g/cm3之间,lgfO₂为-19.3～-10.3,pH值为3.0～6.4,反映出桃冲铁矿主要形成于中高温、弱酸性、强氧化环境中。3.从时间上看,从矽卡岩阶段到成矿阶段,再到碳酸盐阶段,富液相包裹体数量逐渐增加,温度、盐度、氧逸度逐渐降低,pH值逐渐升高,密度、压力、气相成分基本保持不变,液相成分由富Na⁺、Ca²⁺、Cl^-、SO₄^2-变为富Na⁺、Cl^-;从空间上看,由深到浅富气相包裹体和富液相包裹体含量及氧逸度稍有增高,其它特征基本保持一致。上述变化表明桃冲矿区成矿作用主要受温度、盐度、pH值和Cl-浓度等参数制约。此外,成矿早期以高温高盐度流体为主,显示出岩浆流体的特征;成矿晚期流体可分为高盐度（NaCl equiv > 30%）和低盐度（NaCl equiv≤23.8%）两种,反映出不同来源的两种流体的混合。流体氢氧同位素数据显示桃冲铁矿成矿流体由岩浆水和大气降水混合而成,但以岩浆水为主;同时,随着成矿作用的进行大气降水的含量逐渐增加。4.桃冲矿区矽卡岩为岩浆成因。桃冲铁矿是由矽卡岩冷却产生的富铁气成热液在上升过程中与大气降水混合后发生沉淀形成的;在成矿过程中,铁主要以氯的络合物的形式迁移,大气水与岩浆水混合可能是导致矿质沉淀的主要因素。更多还原

【Abstract】 The Taochong iron deposit is located in the northeast of the Tongling-Fanchang Fe-Cu district of the Middle-Lower Yangtze River metallogenic belt. The most pronounced feature of the iron deposit is that skarns associated with iron orebodies occur as tabular bodies along the bedding-slip fault between the carbonate strata of the Lower Permian Qixia and Middle Carboniferous Huanglong Formations, with occurrence of evident boundaries between the skarn bodies and strata of two sides and no outcrops of pluton. A detailed study has been carried out on the fluid inclusions in the Taochong iron deposit, with a focus on the origin of the deposit.The following are major achievements obtained in this thesis.1. The petrographical study shows that there are many kinds of fluid inclusions, but the main types are liquid-rich and daughter mineral-bearing ones.2. The geochemical study of fluid inclusions indicates that the ore-forming fluids mostlybelong to NaCl-H₂O system, with H₂O as a major component of gas facies, and Cl^- and Na⁺ as main anion and cation of liquid facies, respectively. The homogenization temperatures, densities, lgfO₂ and pH values of the ore-forming fluids are defined mainly in the ranges of 260～460℃, 0.92～1.11 g/cm3, -19.3～-10.3, and 3.0～6.4, respectively, indicating formation of the Taochong iron deposit mainly in the high temperature, weak acidic and strong oxidizing environment.3. From early to late, increasing in number of liquid-rich inclusions with decreasing in homogenization temperature, salinity, lgfO₂, increasing in pH, and no evident varying in density and pressure occurs, associated with increasing in Na⁺ and Cl^- and decreasing in Ca²⁺ and SO₄^2- in the liquid facies and no evident changing in component of the gas facies. In contrast, from deep to shallow, no evident variation in most of parameters occurs except little increasing in number of gas and liquid-rich inclusions and value of lgfO₂. The data mentioned above suggest mineralization in the Taochong iron deposit might be mainly affected by temperature, salinity, pH, and Cl-concentration. The ore-forming fluid with salinity ranging from 34～48 wt.% NaCl equiv at the stages of skarnization and early mineralization is simple in composition, indicating its origin of magmatic evolution. In contrast with this, The ore-forming fluid having two ends with high salinity （NaCl equiv > 30%） and low salinity （NaCl equiv≤23.8%） at the stage of late mineralization is complex, indicating its mixing origin of magmatic water with meteoric water. The hydrogen and oxygen isotopic analyses of the ore-forming fluids also support involving the magmatic fluid at the stages of skarnization and early mineralization and the magmatic–meteoric mixed fluid predominated by magmatic fluid at the stage of late mineralization. Evidently, the ratio of magmatic water to meteoric water in the ore-forming fluids is gradually reduced from the early stage to the later stage.4. The petrographic, microthermometric and geochimecal data of fluid inclusions presented in this thesis indicate an origin of the skarn in the Taochong iron deposit by injection and crystallization of skarn magma, and a genesis of the associated iron orebodies possibly by precipitation of the mixed fluids of magmatic water with meteoric water. Fe in the fluids was transported mainly in the form of chloride complexes and precipitated owing to the mixing of magmatic water with meteoric water.更多还原