【作者】 丰成友；

【导师】 张德全；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学、矿床学， 2002， 博士

【摘要】 对青海东昆仑地区的构造演化及其中金矿床地质、地球化学的详细研究结果表明，东昆仑地区是一个有复杂演化历史的复合造山带，具有多岛洋／裂陷槽、软碰撞和多旋回造山等特点。这里产出的金（锑）矿床有相似的地质-地球化学特征，并与显生宙造山过程有密切的成因联系，是典型的造山型金矿床。各矿床严格受深断裂／碰撞带、大型剪切带、褶皱和断裂-裂隙三级构造系统控制，围岩普遍发生绿片岩相变质，矿石类型主要为破碎带蚀变岩型和石英脉型，硫（砷）化物类金属矿物含量介于3％～5％，黄铁绢英岩化是金矿床中最强烈、最典型的蚀变类型。伴随着矿区构造由韧性向韧-脆性、脆性演化，矿床明显经历了不同的矿化期次和成矿阶段。流体包裹体地球化学研究结果显示，本区金矿床中代表不同成矿阶段的石英含有十分丰富的流体包裹体，主要有三种类型，即富CO₂包裹体、CO₂-H₂O包裹体和H₂O包裹体，其中CO₂-H₂O包裹体十分发育，成矿流体为一套中低温（118～378℃）、低盐度（0.35～9.54wt％NaCl）的H₂O-CO₂-NaCl-CH₄±N₂体系。氢、氧同位素测定结果和水-岩交换作用研究表明，不同成矿阶段成矿流体的氢、氧同位素投点与相应温度的大气降水演化曲线比较吻合，从成矿早期到晚期，温度逐渐降低，有效W／R比值逐渐增大，反映了成矿前热液主要为变质水和地层建造水，成矿期以来大气降水不断混入并占主导地位。流体不混溶作用是流体演化和成矿流体形成的重要机制。4个金矿床的硫同位素组成均为正或负向偏离于零的不大数值，塔式分布效应明显，铅同位素组成分布集中且比值较高，为典型的放射性成因铅，在Zartman等（1981）的构造图解中，投点均集中分布于造山带演化线附近，表明硫、铅等成矿物质为少量地幔和围岩地层的混合来源，以大气降水为主的热液不断从强烈破碎变形的地层岩石中淋滤放射性成因铅是造成铅同位素组成明显偏高的主要原因。精细的同位素地质测年结果表明，金矿床主要成矿时代为印支期，另在一些矿区还存在晚加里东期的矿化作用，反映出多期次成矿和复合叠加成矿特征。晚加里东期和晚华力西—印支期的强烈俯冲及碰撞作用，不但形成了区域深断裂、大型剪切带及次一级的褶皱和断裂-裂隙控矿构造，而且还促使了成矿流体活化和成矿元素的初步富集。与俯冲和碰撞有关的热事件（包括造山花岗岩的侵位），不断提高地热梯度，驱使被加热的建造水和大气降水等热液流体沿碰撞带和大型剪切带做远距离的运移，并在途中淋取围岩的成矿元素，形成含金流体。当这些流体进入到矿床或矿体构造后，由于构造性质的转换（韧性→韧-脆性或脆性），温、压等物理化学条件亦随之改变，金、锑络合物在成矿流体中的溶解度也越来越小，于是迅速发生沉淀。成矿流体交代剪切带及其围岩，形成蚀变岩、石英脉，进而形成金（锑）等矿床。更多还原

【Abstract】 This paper did some research on tectonic evolution in the East Kunlun orogen, Qinghaiprovince and characteristics of geology and geochemistry of gold deposits in this region. Someimportant conclusions have been reached. The East Kunlun area is a multiple orogen whichunderwent a very complicated evolutionary process and is characterized by archipelagic ocean/aulacogen, soft collision and multicyclicity. Many gold deposits in this area have similarcharacteristics of both geology and geochemistry, and are correlated to orogenic processes of thisorogen in genesis. As a result, they should be typical orogenic gold deposits. Each deposit iscontrolled strictly by three-order structural systems which are profound faults and/or collisionalbelts, large-scale ductile shear belts, and folds and faults, respectively.Although the wallrocks ofthese orogenic gold deposits vary in age and petrology, all of them were deformed andmetamorphosed into greenschist facies. According to ore types, the orogenic gold deposits can bedivided into two subtypes, namely altered rock type and quartz vein type. The pyritic-phyllicalteration is the most extensive and typical alteration. With evolution of the structures in oredistricts from ductile, ductile-brittle to brittle, the gold deposits also underwent differentmineralization phases and ore-forming stages.Based on a great deal of studies on fluid inclusion petrography and microthermometry of theWulonggou, Kaihuangbei, Dachang and Dongdatan orogenic gold deposits, the quartzrepresenting different ore-forming stages contain three main types of fluid inclusions: （1）primary CO₂-rich inclusions, （2） CO₂-H₂O inclusions with variable CO₂ content, （3） aqueousinclusion. The CO₂-H₂O inclusions are very plenty and content of CO₂ is comparatively high （≥5mol%） in this kind of inclusions. The ore-forming fluid is a type of middle-low temperature（118～378℃）, low-salinity （0.35～9.54wt%NaCl） H₂O-CO₂-NaCl-CH₄±N₂ system. Thedeterminations of hydrogen and oxygen isotopes and studies on water-wallrock exchange suggestthat the distribution of hydrogen and oxygen isotopes of different stages of ore-forming fluid ineach deposit is very consistent with corresponding meteoric water evolutionary line, withtemperature reducing gradually and W/R ratio increasing correspondingly from early to late. Allabove inform us that the pre-ore fluids mainly originated from metamorphic and formationwater, but since the mineralization episode meteoric water joined and predominated gradually. Inaddition, carbon isotopic measurements of fluid inclusions also show us the meteoric water is veryimportant for mineralization. The unmixing of a homogeneous CO₂-H₂O parent fluid is the mostimportant mechanism that caused some ore-forming substance such as gold, silver and antimony, metallic minerals and quartz to be enriched and deposited. The major evidences forfluid unmixing include the CO₂-H₂O inclusions with a wide range of CO₂ content coexistingintimately in the same quartz, their similar homogenization temperatures and salinities.Isotopic geochemical studies show thatδ³⁴S values of different sulfides aren’t big and can begrouped into 1.1～6.9 per mil for Wulonggou and Kaihuangbei gold deposits and -6.3～-0.9 permil for Dachang and Dongdatan gold deposits. The pyramidal distribution is very apparent. Thelead isotopic compositions vary in a small range, but the values are very high, therefore they areradiogenic lead. In the Zartman’s （1981）tectonic diagram about lead isotope, all lead isotopic dataare put together near evolutionary line of orogen. It indicate that the ore-forming material wasderived from mixed little mantle and wall rocks. Leaching radiogenic lead from highly deformedwallrocks by predominant meteoric water is a major reason to make lead isotopic compositionbecome very high. According to field observation and isotopic dating, the main age of goldmineralizations is late Variscan-Indosinian. In addition, the mineralization of late Caledonianexisted in some deposits as well.In summary, intensive subduction and collision during late Caledonian and late Variscan-Indosinian not only formed deep faults, large-scale shear belt, and low-order folds and faults butalso make ore-forming fluid activated and mineralizing elements enriched initially. Subduction-related thermal events and episodically rising geothermal gradients drove formation water andmeteoric water migrate for long distance along collisional belts and large-scale shear belt andleached ore-forming substance from wallrocks during migration, and gold-bearing fluid wereformed. When ore-forming fluid flowed into ore-controlled structures, gold and antimony arelargely deposited as temperatures and pressures fall accompanying fluid immiscibility during themain mineralization stages.更多还原