应用电子探针技术研究桂西南下雷锰矿床锰钾矿的结构特征

The Application of EPMA in the Textural Characterization of Cryptomelane in the Xialei Manganese Deposit,Southwest Guangxi

八面体分子筛(OMS-2)具有2×2孔道结构,在离子交换、催化剂、能源和环境等方面具有非常重要的应用价值,然而天然OMS-2矿物材料——锰钾矿在典型结构的成分精细表征和成因研究等方面仍然缺乏。环带和核-边结构在锰氧化物矿物的结构中非常具有代表性,明确其矿物种属、探索其成分特征对于探究其成因、开拓锰氧化物的应用具有重要意义。广西锰矿资源储量占中国锰矿资源储量的23%,其中位于桂西南的下雷锰矿是中国最早发现的超大型锰矿床,氧化锰矿石平均品位30%左右。本研究主要利用电子探针(EPMA)定量分析和面扫描等手段针对下雷锰矿中的环带和核-边结构开展研究。结果表明:下雷锰矿产出具有环带结构和核-边结构的锰钾矿,具有环带结构的锰钾矿元素强度按平均强度排序从强至弱依次为Mn、K、Mg、Al、Zn、Ba、P、Fe,具有核-边结构的锰钾矿元素强度按平均强度排序从强至弱依次为Mn、K、Ca、Mg、Zn、Ba、P、Fe,这些元素从内到外的变化反映了其氧化环境的变化。从中间到边部钾含量逐渐升高(质量分数为2.31%~4.17%,单位分子式中原子数为0.38~0.62),暗示了氧化过程中钾的富集,也反映了锰氧化物逐渐趋于最稳定状态的过程。钾离子和锰离子趋势的变化是导致环带和核-边结构形成的直接原因,氧化环境的变化和锰氧化物逐渐趋于最稳定状态的趋势可能是锰钾矿环带和核-边结构形成的根本原因。

BACKGROUND: OMS-2 has shown great significance in ion exchange, catalyst, energy and environment, but the research of natural OMS-2 mineral material cryptomelane is still lacking in the detailed characterization of the composition, structure and genetic research. Annulus and core-rim structures are representative in the structure of manganese oxide minerals. It is of great significance to clarify the mineral species and explore its composition characteristics, its origin and develop the application of manganese oxides. The Mn ore resource of Guangxi account for 23% of the manganese ore resource reserves in China. The Xialei Mn deposit located in Southwest Guangxi is the earliest super-large Mn deposit discovered in China, with an average grade of about 30% for the manganese oxide ore. OBJECTIVES: To explore the annulus and core-rim texture and its composition of cryptomelane in the Xialei Mn deposit.METHODS: Quantitative analysis and element mapping of EPMA and microscopy were carried out.RESULTS: The element intensity of the cryptomelane with annulus texture was Mn, K, Mg, Al, Zn, Ba, P, Fe in order of average from strong to weak. The average element intensity of the cryptomelane with core-rim texture was Mn, K, Ca, Mg, Zn, Ba, P, Fe from strong to weak. The K content gradually increased(2.31%-4.17%, 0.38-0.62 atoms per formula unit) from the middle to the rim of the cryptomelane, indicating K enrichment during oxidization and the stable status of Mn oxides.CONCLUSIONS: The change in the trend of K and Mn ions is the direct cause of the formation of the annulus and core-rim texture, reflecting the changes of oxidation environment. Potassium content gradually increases from the inner to outer zone, which may indicate the enrichment of potassium during the oxidation process, and also reflects manganese oxide gradually tending to the most stable state.