华北克拉通南缘老里湾大型银多金属矿床成因：微区地球化学和年代学制约

The Laoliwan deposit is a newly discovered large silver-polymetallic deposit in the Xiaoshan district, southern North China Craton. The orebodies are mainly hosted in the porphyritic monzonitic granitic rocks, which is distinctly different from other sliver-polymetallic deposits in the area. Therefore, the Laoliwan deposits has been considered to be a new type of sliver deposit in the area, and may have important implications for both scientific investigation and regional exploration. Based on field investigation, petrography, ore petrography, and microthermometry study of fluid inclusions for the Laoliwan deposit, the proposed project will focus on in-situ elemental analysis of melt/fluid inclusions in quartz, H-O isotopic analysis of quartz and H2O-bearing alteration minerals, pyrite Re-Os and ore-related sericite 40Ar/39Ar isotopic dating of the sliver-polymetallic ores. These data will provide significant insights into the sources of ore-forming fluids, ore-forming mechanism and genesis of the sliver-polymetallic mineralization, and hence establish metallogenic and prospecting models for the Laoliwan deposit. In-situ lead and silver isotopic analyses will be conducted on galena and silver minerals, respectively, from Laoliwan and other types of representative sliver-polymetallic deposits in the area, to reveal the sources of silver and other metals. The proposed study will not only promote the understanding of the relationships between the Laoliwan sliver-polymetallic mineralization and magmatic-hydrothermal activity or regional metamorphism and the sources of enormous silver in the area, but also provide useful guide for mineral exploration of similar sliver-polymetallic deposits in the southern North China Craton.

老里湾矿床是华北克拉通南缘崤山地区新近发现的大型银多金属矿床，其主要矿体产于斑状二长花岗岩内，被认为可能是华北南缘新的银矿床类型，具有重要的科研价值和找矿意义。本项目拟结合野外地质、岩相学、矿相学、包裹体测温等资料，重点对老里湾矿床开展岩体和矿体石英熔融/流体包裹体原位微区成分分析、石英和蚀变含水矿物H-O同位素分析、黄铁矿Re-Os和绢云母40Ar/39Ar同位素测年等研究，查明含矿热液来源和成岩-成矿时代，探讨银多金属成矿作用机制和矿床成因，并建立正确合理的成矿模式和找矿模型。在此基础上选取华北南缘其它类型代表性银多金属矿床，分别对方铅矿和银矿物开展系统的原位微区Pb和Ag同位素分析，对比并探讨银等金属元素的来源。本项目顺利实施不仅能够深入理解老里湾银多金属成矿作用与岩浆热液活动或区域变质作用的关系，获取区内巨量银的来源信息，也将为区域上寻找更多同类型矿床提供理论指导。

老里湾矿床是华北克拉通南缘崤山地区新近发现的大型银多金属矿床，其矿体主要赋存于老里湾花岗斑岩内，是研究银多金属成矿作用与岩浆热液活动关系的理想对象。本项目重点对老里湾矿床的矿化-蚀变特征、成岩-成矿时代以及含矿热液的来源、组成和演化等方面开展综合研究，深入探讨矿床成因并建立成矿模式；在此基础上对区域多金属成矿作用进行对比研究，总结华北克拉通南缘早白垩世岩浆-热液成矿系统的特征和规律。本项目主要获得了以下五个方面的成果：（1）通过U-Pb和Re-Os同位素测年查明老里湾花岗斑岩和银多金属成矿作用均形成于130Ma左右，二者具有紧密的时间关系；（2）查明老里湾矿床成矿流体为中低温、低盐度的H2O-NaCl±CO2体系，基于H-O-C-S-Pb多元同位素示踪揭示成矿流体和成矿物质主要为岩浆热液来源；（3）提出老里湾矿床为浅成低温热液型矿床，认为赋矿的花岗斑岩与银多金属矿体为“兄弟关系”，二者受控于同一深部岩浆房的岩浆作用，基于这一认识建立了老里湾矿床的成矿模式；（4）认为老里湾矿床深部还具有寻找斑岩型钼矿体的潜力，而崤山地区断裂带和岩体交汇处是寻找银多金属矿床的有利部位；（5）在归纳总结华北克拉通南缘早白垩世主要矿床类型地质特征和时空分布的基础上，提出这些不同类型的矿床组成了巨型岩浆-热液成矿系统，受控于区域晚中生代岩石圈伸展及其诱发的大规模岩浆作用。本项目研究工作不仅丰富了华北克拉通南缘银铅锌矿床的成因类型并总结了华北克拉通南缘早白垩世多金属成矿作用规律，相关研究成果对推动区域上钼和银多金属矿床的找矿勘查工作也有一定指导价值。