【作者】 司荣军；

【导师】 顾雪祥；

【作者基本信息】 中国科学院研究生院（地球化学研究所） ， 矿物学岩石学矿床学， 2005， 博士

【摘要】 富乐分散元素多金属矿床位于扬子地块西南缘、川滇黔多金属成矿带东南部。该矿床是一个伴生大型镉、锗、硒矿床、小型镓矿床的中型铅锌矿床。该矿床富含四种分散元素,是一个典型的分散元素矿床。矿床的研究程度很低。 矿床赋存于下二叠统茅口组中段白云岩、灰岩中,矿体呈似层状、透镜状,矿石发育角砾状构造、块状构造和粗粒结构,矿物主要为闪锌矿、方铅矿、白云石、方解石。本次工作系统研究了常量元素、微量元素、稀土元素、稳定同位素地球化学特征和成矿流体特征,主要取得以下成果: 1.查明了分散元素的分布特征:分散元素Cd、Ge、Se、Ga主要赋存在闪锌矿中,它们在闪锌矿中的平均含量为Cd 16183ppm,Se 163ppm,Ge 135ppm,Ga 86 ppm。Cd、Ge以类质同象形式代替Zn的位置,Se以类质同象形式代替S的位置,Ga在闪锌矿中有类质同象和显微吸附两种存在形式。Cd富集在深色闪锌矿中,Ge富集在浅色闪锌矿中,Ga在黄棕色闪锌矿中的含量最高,而Se在深浅不同颜色闪锌矿中的含量没有明显的变化。闪锌矿中Zn与Cd负相关,与Ge正相关,与Se相关性不明显。 2.探讨了闪锌矿颜色成因:闪锌矿晶体内部的颜色是不均匀的,裸眼观察到的闪锌矿颜色是晶体内部紫色、红色、黄色、无色的综合效应。闪锌矿颜色是Ni、Cu、Tl、Ga、Hg、Fe、Cr等多种元素共同引起的,其中最主要的元素是Ni、Cu、Ga。Ni使闪锌矿呈紫色,Cu使闪锌矿呈红色,Ga使闪锌矿呈黄色。分散元素Cd之所以在深色闪锌矿中相对富集,是因为Cd与引起闪锌矿颜色变深的Ni、Cu正相关,Ni、Cu、Cd含量越高,闪锌矿颜色也就越深。 3.查明了矿床地球化学特征:矿石稀土含量很低,（∑REE=2.66～10.19ppm）,相对富集轻稀土并显示Eu负异常。成矿流体δD=-76～-60‰,δ¹⁸O=10.8～14.7‰,δ¹³C=-19.1～-2.6‰。白云石、方解石δ¹⁸O=16.64～19.91‰,δ¹³C=1.12～3.02‰。闪锌矿δ³⁴S=12.97～14.91‰,方铅矿δ³⁴S=7.91～11.14‰。硫化物铅同位素²⁰⁶pb/²⁰⁴pb=18.470～18.586,²⁰⁷pb/²⁰⁴pb=15.542～15.707,²⁰⁸pb/²⁰⁴pb=38.283～38.643。成矿流体主要来自建造水,但有油田卤水的参与。更多还原

【Abstract】 The Fule dispersed element-polymetallic deposit is located in the southwestern margin of the Yangtze block, at the southeastern part of the Sichuan-Yunnan-Guizhou Zn-Pb polymetallic district. The deposit is a medium-scale Zn-Pb associated with large-scale Cd, Ge, Se and small-scale Ga deposit. The deposit is poorly studied.The deposit occurs in dolomite and limestone of the Lower Permian Maokou Formation. The ore bodies are typically layer- or lens-like. The ore consists of sphalerite, galena, dolomite and calcite typically shows massive or brecciated structures and coarse-grained texture. Based on systematic studies on geochemistry of major elements, trace elements, rare earth elements and stable isotopes as well as characteristics of ore-forming fluids, the following achievements have been obtained:1. The distribution characteristics of dispersed elements. Cd, Ge, Se, and Ga exist principally in sphalerite, with average contents of 16183 ppm Cd, 163 ppm Se, 135 ppm Ge and 86 ppm Ga. Cd, Ge, and Se occur in crystal lattice of sphalerite, where Cd and Ge occupy the position of Zn and Se occupies the position of S. Ga partially exists in crystal lattice of sphalerite and partially is adsorbed in lattice defect as micro-adsorption form. Cd enriches in dark color sphalerite, Ge in light color sphalerite, and Ga in yellow-brown sphalerite, while the content of Se in sphalerite does not change with color. In sphalerite Zn is negatively correlated with Cd, positively correlated with Ge, but insignificantly correlated with Se.2. The color genesis of sphalerite. The color of sphalerite is uneven internally, varying from purple, red, yellow to blank. The color seen by naked eyes is a synthetic effect of inside crystal and caused by Ni, Cu, T1, Ga, Hg, Fe, Cr, etc., of which the most important elements are Ni, Cu, Ga. Ni induces purple, Cu red and Ga yellow. Cd enriches in dark color sphalerite because itspositive correlation with Ni and Cu.3. Ore deposit geochemistry. The ores have a low total content of rare earth elements (￡REE=2.66—10.19 ppm), relatively enriched light rare earths and a negative Eu anomaly. The hydrogen, carbon and oxygen isotopic compositions of ore fluids are 5 D=-76~-60%o, 6 18O= 10.8—14.7%o and 8l3C=-19.1—-2.6%. Carbon and oxygen isotopic compositions of dolomite and calcite are 518O= 16.64-19.91% and 513C=1.12-3.02%. 6 34S values vary from 12.97 to 14.91 %o for sphalerite and from 7.91 to 11.14% for galena. The lead isotopic compositions of sulfides are 206Pb/204Pb= 18.470-18.586, 2O7Pb /204Pb = 15.542-15.707, and 208Pb/204Pb = 38.283—38.643. It was mainly derived from evolved formation water with slight amounts of oil-field brines. Sulfate reduction in the strata was the main source of sulfur for sulfide precipitation. CO2 came mainly from carbonates dissolution and partly from oxidatin of CH4.4. Discussion on ore genesis. The Mile—Shizong fracture zone may serve as an ore conductive fault, while the interlayer faults at the core of the Tuoniu-Duza anticline are favorable ore-hosting structures. The deposit contains abundant fluid inclusions. The ore-forming fluid has a medium-low temperature (160-240 °C)i a low salinity (4.5~10 wt%NaCl), and a low pressure (52.9~60.1 MPa). The ore-forming elements may have been derived from several sources, among which the sedimentary rock cover was the main source, especially the Permian Maokou Formation and the Carboniferous Baizuo Formation. The ore precipitated in a slightly alkalic and reducing environment with medium sulfur fugacity. The driving force for ore fluids was tectonic stress. This deposit belongs to the Mississippi Valley-type lead-zinc deposit and its metallogenic epoch is Yanshanian. Favorable source beds and oil-field brines were important for the deposit to enrich in dispersed elements.更多还原