滇西老厂富银红土型锰矿次生富集机制及40Ar/39Ar年龄

This proposed research involves detail field observations and intensive investigation on the mineralogy, petrography, geochemistry, Nd-Pb isotope geochemistry, and 40Ar/39Ar geochronology to unravel the history and supergene enrichment processes of the Laochang lateritic Mn(Ag) deposits in southwestern Yunnan Plateau. 40Ar/39Ar dating of K-bearing Mn oxides will provide the timing constraints on supergene Mn-Ag mineralization in southwestern Yunnan Plateau. The mineralogical and geochemical data of Ag-bearing Mn-oxides will be used to characterize the occurrences and enrichment mechanisms of Ag and associated Pb and Zn, providing a guide for the comprehensive utilization of the silver resources. Comparisons of the geochemistry and isotopic geochemistry among the various potential source components are used to understand the processes and sources of supergene mineralization, which may provide potential information for geochemical exploration of primary sulfide deposits. These new data, in combination with the previous weathering geochronological, tectonic, paleoclimatic, and geomorphological data in Yunnan-Guizhou Plateau, will be used to discuss the history of regional chemical weathering, geomorphological evolution, and paleoclimatic changes during the late Neogene in Yunnan-Guizhou Plateau.

本项目以滇西老厂红土型富银氧化锰矿为研究对象，在详细的野外地质观察基础上综合利用各种先进测试方法开展系统的矿物学、元素-同位素地球化学和40Ar/39Ar年代学研究，精确限定滇西老厂红土型氧化锰矿床次生富集作用发生和持续的时间，为全面深入地理解滇西地区新生代大规模化学风化和矿床次生富集提供重要的年代学资料。查明老厂红土型富银氧化锰矿床中银及伴生元素铅、锌等的赋存状态和富集机制，为资源的综合回收利用提供科学依据。通过元素-同位素地球化学的对比研究揭示矿床的次生富集过程和成矿物质来源，为区域深部原生硫化矿体的找矿勘探提供理论指导。在本项目的研究基础上综合其他学科的研究成果并结合云贵高原地区其他氧化锰矿的40Ar/39Ar年龄资料探讨区域晚新生代以来的大陆化学风化历史、地貌演化和古气候条件。

本项目对滇西老厂红土型富银氧化锰矿开展了详细的野外地质观察，在此基础上对该矿床的原生硫化物体和次生银锰矿体进行了矿物学、地球化学和年代学的研究。对火山岩、原生Ag-Pb-Zn矿体和斑岩-矽卡岩矿体开展了系统的年代分析：火山岩喷发年龄为320.8 ± 2.7 Ma；斑岩中锆石U-Pb年龄为44.4 ± 0.4 Ma；Ag-Pb-Zn矿体中黄铁矿Re-Os年龄为45.7 ± 3.1 Ma；蚀变带热液榍石U-Pb年龄为43.4 ± 1.2 Ma ，表明老厂矿床为一典型的斑岩型成矿热液系统。本次研究通过对次生锰结核矿物学和地球化学研究表明银及伴生的铅锌等主要赋存于钡硬锰矿族矿物中，为资源的综合回收利用提供科学依据。通过对钡硬锰矿族矿物系统的40Ar-39Ar年代学分析精确限定滇西老厂红土型氧化锰矿床次生富集成矿时间为9.5~6.66 Ma，结合滇西地区巴夜锰矿床研究结果表明该区在晚中新世以来经历了强烈的化学风化和矿床次生富集。