华北石炭纪沁源一矿铝土矿形成环境研究

Study on formation environment of carboniferous Qinyuanyikuang bauxite deposit in North China Craton

中文关键词:风化  形成环境  铝土矿  沁源一矿

keywords:weathering  formation environment  Bauxite deposit  Qinyuanyikuang

中文摘要:华北克拉通是中国最重要的铝土矿成矿域，以发育大规模岩溶型铝土矿为特色。然而，对其形成环境仍存在争议，制约着对区域成矿规律的认识。文章以沁源县沁源一矿为研究对象，系统的野外和岩相学研究发现铝土矿赋存于上石炭统本溪组下段，不整合于奥陶系峰峰组古岩溶界面之上，矿物组成以一水硬铝石、锐钛矿和高岭石为主，含少量针铁矿、赤铁矿、伊利石、锆石、磷灰石和白云母；含矿岩系地球化学分析获得平均化学蚀变指数（CIA）为96，Eu异常介于0.53~0.77，表明沁源铝土矿形成于温暖、潮湿环境，且源区经历了强烈的化学风化；难溶元素分析结果显示，含矿岩系源岩为形成于陆源弧环境的长英质火山岩；氧化-还原敏感金属元素和矿物共生组合综合分析指示沁源铝土矿可能形成于碱性、次氧化-还原环境。该研究进一步表明铝土矿形成受源区风化程度和沉积环境氧化-还原状态的共同控制。

Abstract:The North China Craton (NCC) is the most significant bauxite metallogenic domain in China, characterized by large-scale karst-type bauxite deposits. However, their formation environment remains controversial, which constrains the understanding of regional metallogeny. This study focuses on the Qinyuanyikuang bauxite deposit in Qinyuan County, Shanxi Province. Systematic field and petrographic investigations reveal that the bauxite ores are hosted in the lower member of the Late Carboniferous Benxi Formation, unconformably overlying the paleo-karst surface of the Ordovician Fengfeng Formation. The mineral assemblage is predominantly composed of diaspore, anatase, and kaolinite, with minor amounts of goethite, hematite, illite, zircon, apatite, and muscovite. Geochemical analysis of the ore-bearing rock series yields an average Chemical Index of Alteration (CIA) value of 96 and Eu anomalies ranging from 0.53 to 0.77, indicating that the Qinyuan bauxite formed in a warm and humid environment where the source area underwent intense chemical weathering. Analysis of immobile elements suggests that the source rocks for the ore-bearing series are felsic volcanic rocks formed in a continental arc setting. Comprehensive analysis of redox-sensitive metal elements and the mineral paragenetic association suggests that the Qinyuan bauxite likely formed in an alkaline, suboxic-anoxic environment. This study further demonstrates that bauxite formation was governed by both the degree of source rock weathering and the redox conditions of the depositional environment.