小秦岭东桐峪金矿床黄铁矿LAICPMS微量元素特征及其成矿意义
LAICPMS In Situ Trace Element Analysis of Pyrite from Dongtongyu Gold Deposit and Its Metallogenic Significance, Xiaoqinling Gold District

位于华北克拉通南缘的小秦岭地区是我国仅次于胶东的大型金矿床集中区，但金矿床的成矿物质来源及成因问题一直存在较大争议.以华北南缘小秦岭矿集区东桐峪金矿床中的黄铁矿作为研究对象，在黄铁矿显微结构研究的基础上利用LAICPMS对黄铁矿的微量元素进行原位分析，为进一步认识东桐峪金矿床及区内其他同类型矿床的成因提供新的资料和制约.东桐峪金矿床的黄铁矿从早到晚依次划分为3个世代(PyI、PyII和PyIII).PyI主要形成于粗粒黄铁矿-石英阶段，颗粒粗大且自形程度高，呈星点状或斑点状赋存于乳白色石英脉中.PyII主要形成于石英-中细粒黄铁矿阶段，呈半自形-他形结构且裂隙发育，常被晚期石英、多金属硫化物、自然金等矿物充填.PyIII主要形成于多金属硫化物阶段，常呈他形粒状结构与黄铜矿、方铅矿及闪锌矿等硫化物密切共生.LAICPMS分析结果显示，PyI中As平均含量为16.63×10-6，Au、Ag和Te含量较低且常位于检测限以下；相较而言，PyII中As含量稍低，而Au、Ag和Te含量略高(其中Au含量为0.10×10-6~0.59×10-6)；PyIII中Au、Ag和Te含量差异较大且显著升高，其中Au、Te含量最高可达35.58×10-6和79.79×10-6，而As含量较低且大部分数值低于检测限；不同世代黄铁矿的Co/Ni比值基本上都大于1， 且PyIII的Co、Ni含量和Co/Ni比值明显低于PyII和PyI.以上结果表明，东桐峪金矿床的载金矿物黄铁矿中As的含量很低，金的富集与As无关；不同世代的黄铁矿中Au、Ag和Te之间存在显著且稳定的线性正相关关系，暗示金矿化与Te关系密切.另外，第3世代黄铁矿(PyIII)中Au、Ag及Te存在显著富集，指示Te(而不是As)在金和银的迁移、搬运、富集、沉淀等过程中具有重要作用.华北克拉通南缘小秦岭地区晚中生代大规模的金成矿作用及金矿床中普遍存在TeAuAg矿物，且黄铁矿中As含量低、Te含量高等特征，暗示该区金矿床的成矿物质/成矿流体可能来自深部岩浆的脱挥发分或地幔脱气作用，而与区域变质作用的关系不大.
Situated in the southern margin of the North China craton, the Xiaoqinling district is one of the most important gold metallogenic belts and has been the second largest gold producer in China. Although most gold deposits have been extensively studied, issues related to the source of the ore materials and fluids remain debated. This paper presents a study of the distribution characteristics of trace elements in goldbearing pyrite to explore the source of oreforming materials, the precipitation mechanism and ore genesis. The Dongtongyu lode gold deposit is the important deposit in Xiaoqinling and pyrite is the predominant sulfide mineral. Three generations of pyrite were identified, broadly corresponding to the three mineralization stages, and termed as the first generation, second generation and third generation (PyI, PyII and PyIII). The first generation (PyI) is mainly present as isolations or as aggregate masses dispersed in milky quartz veins, consisting of coarsegrained, euhedral to subhedral crystals. The second generation (PyII) pyrite occurs as veins or veinlets generally associated with light gray quartz or cutting milky quartz. Many grains are porous and contain abundant microfractures that are usually filled with laterstage quartz, other sulfide minerals and free gold. The third generation (PyIII) pyrite is commonly intergrown with other sulfide minerals including chalcopyrite, sphalerite, and galena. Laser ablation inductively coupled plasma mass spectrometry (LAICPMS) results show that the average content of As in PyI is 16.63×10-6, and the contents of Au, Ag and Te are low and often below detection limit. In contrast to PyI, the c