Characteristics of tourmalines from Nanping granitic pegmatites in Fujian Province
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    Abstract:

    Tourmaline is a kind of accessory mineral widely distributed in acidic igneous rocks and metasomatites, and the most widely distributed Fe-Mg-Li tourmaline includes several end members like dravite, schorl and elbaite as well as a series of transitional minerals. In the same area, the same rock is often characterized by the development of the same type of tourmaline. Nevertheless, the end members and transitional minerals are well developed in Nanping pegmatite and altered wall rocks, except for elbaite. Such a phenomenon is very rarely observed in the same type of granitic pegmatites both in China and abroad. In Nanping, tourmalines with different components are distributed in different types of granitic pegmatites and different differentiation evolution stage of the pegmatite. The schorl (Fe tourmaline) is widely distributed in the four types of pegmatites as well as their altered wall rocks. In the rare metal mineralized pegmatite, the tourmaline can be divided into two types, i.e., the middle member of the Fe-Li series (Li-Fe tourmaline) and the members of the Mg-Fe series comprising dravite and Mg-Fe tourmaline. The two types of tourmalines are apparently different in the formation age and the paragenetic association of minerals. Based on detailed descriptions of physical-optical characteristics, chemical components, X-ray powder diffractions, infrared absorption spectra and thermal spectra of tourmalines from Nanping pegmatites, this paper discusses the evolution regularity and formation environment of these tourmalines. The schorl in Type Ⅰ pegmatite was formed under the conditions of upper hydraulic pressure, low content of rare elements and absolute domination of crystallization. In contrast, the schorl in Type Ⅱ-Ⅲ pegmatites was formed in a relatively low depth suggesting the beginning of the transformation to the open system, with rare elements concentrated in the pegmatite melt-solution in such an environment. The Li-Fe tourmaline in TypeⅣ pegmatite was formed in a relatively open system with wide metasomatism, with its formation depth apparently shallower than that of Type Ⅰ-Ⅲ pegmatites. In such a formation environment, elements such as Li, Rb, Cs, Nb, Ta and Sn are highly concentrated in the pegmatite melt-solution. The formation environment of dravite in Type Ⅳ pegmatite was no longer belonging to endogenic pegmatite mineralization, but this mineral inherited some characteristics of Li-Fe tourmalines in Type Ⅳ pegmatite in content of elements such as Li. Its modes of occurrence are very rarely seen in pegmatite areas both in China and abroad. The formation sequence of tourmalines in Nanping pegmatites and wall rocks is on the whole in order of black Fe-tourmaline→yellowish green Li-Fe tourmaline→yellowish brown Mg-Fe tourmaline→grayish blue dravite. This sequence will surely play an important indicating role in researches on the formation environment and evolution of the Nanping pegmatite .

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杨岳清,王 勇,吕庆田,赵金花,2010,福建南平花岗伟晶岩中的电气石研究[J].岩石矿物学杂志,29(3):235~242. YANG Yue_qing, WANG Yong, LV Qing_tian, ZHAO Jin_hua,2010,Characteristics of tourmalines from Nanping granitic pegmatites in Fujian Province[J]. Acta Petrologica et Mineralogica,29(3):235~242.

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