大吉山钨矿中钨铌锰矿与富钨铌锰矿的交生现象及其成因探讨

文章对大吉山钨锰矿矿石进行了电子探针分析 ,发现了一种主要元素为Nb、Ta、Fe、Mn、W的复杂氧化物矿物———钨铌锰矿。这种矿物与富钨铌锰矿交生 ,在成分上与后者呈渐变过渡。证实在自然界中黑钨矿与铌钽铁矿之间可能存在着广泛的W_Nb(Ta)类质同像置换现象。通过对其成分、形态和共生关系的研究 ,结合大吉山钨矿的形成期次 ,联系矿体与区域内两期花岗岩的内在关系 ,对大吉山钨矿的成因机制进行了探讨

Intergrowth of Wolframoixiolite and W-rich Manganocolumbite in Dajishan Tungsten Deposit, Jiangxi Province, South China

The Dajishan tungsten deposit in Jiangxi Province is of quartz_wolframite_vein type. The mineralized granite is an Early Yanshanian granitic complex, which consists from old to young of medium_megagrained porphyroid biotite monozonitic granite, medium_grained muscovite alkali_feldspar granite and Nb_, Ta_rich fine_grained rare element muscovite granite (69 # body). The Dajishan tungsten deposit is associated mainly with the second stage medium_to_fine grained two_mica granite. Some aggregates of Nb(Ta)_Mn(Fe)_W complex oxides were found in fractures along the borders of wolframite or scheelite. Back_scattered electron images show that the aggregates consist of two components whose brightness is different from each other. The darker one is columbite, whereas the brighter one is considered to be wolframoixiolite, a complex Nb(Ta)_Mn(Fe)_W oxide mineral. The wolframoixiolite is intimately intergrown with manganocolumbite, and changes gradually in composition into W_rich manganocolumbite. Considering their modes of occurrence and EPMA data, it is held that the intergrown W_rich manganocolumbite and wolframoixiolite are related to the third stage Nb_Ta_rich fine_grained granite. The granite was enriched in Nb_Ta_rich fluids at the late evolution stage, and such a type of fluid must have replaced the early_formed wolframite, leading to successive crystallization of wolframoixiolite and W_rich manganocolumbite. All this suggests that there probably exist a wide replacement range between wolframite and columbite in the nature.