辽宁青城子铅锌多金属矿田叠加成矿信息的精细厘定

Multi-stage polymetallic metallogenesis holds great complexity due to the superimposed multi-stage mineralization and various modifications. Studies devoted to distinguish those mixed mineralization information are rather limited. Qingchengzi ore field in Liaoning province is a large polymetallic ore field hosting several large Pb-Zn deposits, Au-Ag deposits and Mo deposit. Primary studies show there are at least two stages of mineralization which are related to two episodes of Mesozoic magmatic-hydrothermal activities. The combination of skarn Mo mineralization and epithermal Au-Ag mineralization in Jurassic mineralization event shows affinity with porphyry-epithermal system. The complexity of Qingchengzi ore field makes it an excellent case for studying the superimposed polymetallic system. Targeting to the different mineralization styles (Pb-Zn, Au-Ag and Mo ores), this program prepare to apply a series of new analytical technologies including CL-SEM imaging, in-suit LA-ICPMS analysis of fluid inclusion and high-resolution LA-ICPMS trace element mapping of ore minerals. Through these cutting-edge in-suit micro-analysis, this application aims to distinguish the superimposed multi-stage ore-forming information and further identify stages of Pb-Zn, Au-Ag and Mo mineralization and clarify the genetic relationships of these metals. Besides, the dynamic picture of metallogenic processes evolving from fluid exsolution to fluid transportation to the metal precipitation would be built from the integrated studies of the information pieces extracted from each mineralization stage. This program has significant scientific meaning to delicate studies of superimposed polymetallic metallogenesis and provides valuable guidance for future exploration work of similar deposits.

多期多金属成矿作用具有复杂性，存在多种成矿作用及多期叠加和改造，如何把各期次的成矿信息剥离开，尚缺少精细研究的范例。辽宁青城子矿田是一个富集铅锌矿、金银矿和钼矿的大型多金属矿田，初步研究揭示至少存在两期中生代岩浆热液成矿作用，其中侏罗纪成矿事件形成了矽卡岩型钼矿和浅成低温热液型金银矿的共生组合。青城子矿田为多金属复合成矿系统研究提供了典型案例。本申请拟针对青城子矿田的铅锌、金银以及钼矿开展脉石矿物CL-SEM图像分析、单个包裹体LA-ICPMS原位成分分析、金属矿物的原位2D扫面等高精度原位微区分析，剥离不同期次的成矿流体和成矿物质信息，厘定青城子矿田铅锌、金银及钼矿的成矿期次和共生关系。同时，对各成矿期次的各阶段信息进行整合拼图，重建成矿流体从出溶到运移，再到沉淀的演化过程。本研究旨在利用高精度原位微区分析技术深化对多金属成矿系统的精细化研究，对同类型矿床的深入勘查工作有重要借鉴意义。

通过对辽宁青城子铅锌多金属矿集区的系统工作，厘定了成矿类型、成矿流体和成矿物质来源：通过系统的野外和室内分析，识别出三种铅锌矿化类型：1顺层状矿化，2脉状矿化（开放空间充填型），3两者过渡类型（羽毛状矿化）。流体包裹体测试显示层状、脉状矿化的矿石发育相似的包裹体类型组合和相近的均一温度和盐度，成矿流体为中低温、中盐度的H2O-CO2-NaCl流体体系。钼矿成矿流体为中高温、中盐度的H2O-NaCl的盐水溶液。独立金银矿成矿流体为低温、低盐度的H2O-NaCl体系。矿石及围岩中碳酸盐C-O同位素测试显示，相比于围岩变沉积岩，矿石碳酸盐具有显著亏损的δ13C和δ18O值，暗示成矿热液可能是岩浆热液和大气水或建造水等低δ18O流体混合的结果；碳酸盐矿物LA-ICPMS分析显示矿石碳酸盐矿物相对富集的REE及正的Eu异常以及低的Y/Ho比值，指示为相对高温的热液沉淀产物，而围岩大理岩中碳酸盐的REE配分型式和高Y/Ho比值指示其为正常的海相碳酸盐沉积成因。C-O-S-Pb同位素及野外观察显示，青城子铅锌成矿并非沉积喷流成因，而是具有显著的热液改造的特征，显示为碳酸盐交代型成因特征。.精细化成矿过程：针对各个期次和类型的硫化物原位点分析显示早期的细粒黄铁矿和闪锌矿成分显著不同于晚期主成矿期的黄铁矿和闪锌矿：层状矿化中乳滴状细粒黄铁矿和细粒闪锌矿均富集Mn，V，Co，Ni，Zn，Cu等元素，这些特征与其沉积热水环境对应。而主成矿期闪锌矿更加富Cd，Ga,In元素，黄铁矿更加富Au, As, Sb, Ag,Pb等元素；不同元素的富集和替代方式指示存在不同的成矿过程，早期对应低温的热水沉积，晚期为高温的热液改造；同样硫化物LA面扫描也显示指示多期成矿作用叠加，自形黄铁矿核部富集Cu,Zn等元素，而边部呈环带状富集Au,As,Co,Ni等元素，指示黄铁矿后期受到富Au,As,Co, Ni成矿流体改造富集。Pb-Zn和Pb-Zn-Ag体的闪锌矿和黄铁矿成分都表现出显著的差别，Pb-Zn-Ag中的闪锌矿与Pb-Zn中的闪锌矿相比异常富Fe, Cd，Ga, In，黄铁矿表现出显著高的Au, As, Sb，Ag, 低的Mn, V, Co, Ni，Bi等，同时铅锌矿和金银矿成矿流体和Pb同位素存在差异，初步推断两者是不同的成矿作用的产物。