湖南省沉积型锰矿床地球化学特征

Geochemical characteristics of sedimentary manganese deposits, Hunan Province

湖南省锰矿资源丰富,类型多样,沉积型锰矿是最重要的类型,主要沉积成锰期集中在早南华世大塘坡期、中奥陶世烟溪期及晚二叠世孤峰期。通过对三个主要成锰期代表性锰矿石电子探针分析显示,三个主要成锰期所成锰矿床,矿石组分类似,组成矿石的锰矿物主要为锰的碳酸盐,包括菱锰矿、钙菱锰矿、镁菱锰矿、锰白云石、锰方解石等。三个主要成锰期代表性锰矿石及地层稀土元素地球化学标准化参数与配分模式显示,各成矿期含锰地层与锰矿石之间无显著差异,暗示了它们是相似的沉积环境下形成的产物,为正常沉积与热水沉积的复合。一方面,各成矿期岩、矿石稀土元素总量中等偏高,表现为正常沉积物的稀土元素特征。另一方面,在北美页岩标准化配分曲线上,呈现出水平或重稀土相对富集的左倾配分曲线,Ce的负异常,又是典型热水沉积成因呈现出的稀土元素地球化学特征。δCe异常特征,指示了成锰作用处于波动的缺氧还原/氧化沉积环境。

Manganese resources in Hunan Province are characterized as being rich and various. As the most important manganese ore deposit type, sedimentary manganese mineralization occurred mainly in 3 periods ： Datangpo period of Early Nanhua, Yanxi period of Middle Ordovician and Gufeng period of Early Permian. A series of Electronic Probe Micro-analysis and REE geochemistry analysis of respective manganese ores from 3 dominant periods were carried out here. As can be concluded, there are no siginificant difference from 3 manganese mineralization periods in ore constitution and texture. The ore is mainly composed of manganese carbonate, including dialogite, cal-dialogite, kutnahorite, greinerite, manganocalcite etc. Both the chondrite-nomalized and North American Shale-nomalized pattern of the stratum and manganese ores are similar, which can be considered as they owning similar sedimentary condition. All in all, compound genesis of normal and hot-water sedimentation is believed. On the one hand, ∑ REE is medium to high levels, being characteristics of normal sedimentation. The North American shale normalized REE patterns, on the other hand, are enriched in HREE and negative Ce anomaly, and indicate that manganese probably formed under the fluctuant oxidation-reduction environment.