贵州水城二叠系茅口组含锰岩系地质地球化学特征与锰矿成因分析

Geochemical Characteristics and Origin of A Manganese Deposit in the Middle Permian Maokou Formation in Shuicheng,Guizhou,China

贵州水城二叠系茅口组内发现新锰矿。通过对含锰岩系的地质地球化学研究,其富集Zn,Ni,As,Sb,Sr,Ba,Ga,Ag,V,U元素;锰含量较高层位,Th/U比值小于1,锰含量较低层位,Th/U比值往往高达4～5。Co/Ni比值小于1。含锰岩石的(Fe+Mn)/Ti均大于47,高于20,特别是含锰高的岩石,其(Fe+Mn)/Ti值在300以上。含锰岩石的Al/(Al+Fe+Mn)均远远低于0.35,一般为小于0.02。稀土配分模式与峨眉山玄武岩相似,∑REE较高,LREE/HREE值偏低等特征。根据锰岩系地球化学和区域构造特征分析,水城二叠系茅口组含锰岩系属于热水喷流沉积的产物。

A new manganese deposit in the Middle Permian Maokou Formation in Shuicheng County, Guizhou Province, China was discovered. Study on trace elements of the manganese deposit shows that Cu, Zn, Ni, Co, As, Sb, Sr, Ba, Ga, Ag, V, U is enriched in the manganese deposit. The content of manganese is higher when the ratio of Th/U is lower than 1 , and lower when the ratio of Th/U is 4 - 5. At the same time, Co/Ni values are lower than 1 in the manganese deposit. The plot of ∑Fe/Ti versus Al/（ Al ＋ Fe ＋ Mn） shows that all samples located at the hydrothermal sediment area. （Fe ＋ Mn）/Ti ratio values of the manganese deposit are high,up to 47 -300, especially, （Fe ＋ Mn）/Ti ratio values of the manganese deposit are higher, up to 300 in the higher Mn samples. The rock or manganese deposit was considered hydrothermal sedimentation when （ Fe ＋ Mn）/Ti ratio values is higher than 20, and Al/（ Al ＋ Fe ＋ Mn） ratio values are low to 0.35. Al/（Al ＋ Fe ＋ Mn） ratio values of the manganese deposit present about 0.02 in the higher Mn samples. Therefore, ratio values of （ Fe ＋ Mn）/Ti and Al/（ Al ＋ Fe ＋ Mn） show that the manganese deposit was formed under a hydrothermal sedimentary environment. Additionally, the higher ∑REE （mean 168 × 10^-6 ） , the lower ratio of LREE/HREE, negative Eu anomalies, and few remarkable positive Ce anomalies （ except y-16, y-22） is similar to those of the Emeishan basalt. The geochemical characters of the manganese deposit abovementioned suggest that manganese mineralization was affected by hydrothermal process of mantle plumes.