Structural and Chemical Characteristic of Tourmaline, and Mineralogy of Associated Micas from Tourmaline Bearing Quartzite of KombéII (Bafia Group, Central Africa Fold Belt);Implication on the Metamorphic Conditions  

作　　者：Ganwa Alembert Alexandre Klötzli Urs Tchakounté Numbem Jacqueline Klötzli Eva Ertl Andreas Djom Bernard Ganwa Alembert Alexandre;Klötzli Urs;Tchakounté Numbem Jacqueline;Klötzli Eva;Ertl Andreas;Djom Bernard(Department of Earth Sciences, University of Ngaoundéré, Ngaoundéré, Cameroon;Department of Lithospheric Research, University of Vienna, Vienna, Austria;Department of Earth Sciences, University of Yaoundé I, Yaoundé, Cameroon;Institut Für Mineralogie und Kristallographie, University of Vienna, Vienna, Austria)

机构地区：[1]Department of Earth Sciences, University of Ngaoundéré, Ngaoundéré, Cameroon [2]Department of Lithospheric Research, University of Vienna, Vienna, Austria [3]Department of Earth Sciences, University of Yaoundé I, Yaoundé, Cameroon [4]Institut Für Mineralogie und Kristallographie, University of Vienna, Vienna, Austria

出　　处：《International Journal of Geosciences》2022年第10期882-904,共23页地球科学国际期刊（英文）

摘　　要：Bafia Group is part of the southernmost portion of the Central African Fold Belt (CAFB) in Cameroon. The geological feature of the group is characterized by the presence of metamorphic rocks in which tourmaline had been recognized among accessory minerals. In the present study, attention is focus on the tourmaline bearing quartzite to the southeast of Kombé II. Structure refinement shows that tourmaline is a Fe-dravite with the formula X(Na_0.95[]_0.05)Y(Mg_2.39Fe_0.61)Z(Al_5.10Mg_0.90)(BO₃)₃T[Si₆O₁₈](OH)₃[(O,OH)_0.88F_0.12]. The Fe-dravite is hosted in a Ca-poor quartzite, which is made up, in addition to quartz and tourmaline, of biotite and muscovite. The structure of the dravites shows a low vacancy at the X site, which militates for a crystallization of the tourmaline at a high temperature > 750℃. This is in agreement with previous work which shows that the metamorphic peak in the associated biotite gneiss reaches 825℃. The R1 value of 1.24% means that the crystal structure of the tourmalines is of high quality. The genetical link between gold mineralization and tourmaline should stimulate exploration interest in the study area.Bafia Group is part of the southernmost portion of the Central African Fold Belt (CAFB) in Cameroon. The geological feature of the group is characterized by the presence of metamorphic rocks in which tourmaline had been recognized among accessory minerals. In the present study, attention is focus on the tourmaline bearing quartzite to the southeast of Kombé II. Structure refinement shows that tourmaline is a Fe-dravite with the formula X(Na_0.95[]_0.05)Y(Mg_2.39Fe_0.61)Z(Al_5.10Mg_0.90)(BO₃)₃T[Si₆O₁₈](OH)₃[(O,OH)_0.88F_0.12]. The Fe-dravite is hosted in a Ca-poor quartzite, which is made up, in addition to quartz and tourmaline, of biotite and muscovite. The structure of the dravites shows a low vacancy at the X site, which militates for a crystallization of the tourmaline at a high temperature > 750℃. This is in agreement with previous work which shows that the metamorphic peak in the associated biotite gneiss reaches 825℃. The R1 value of 1.24% means that the crystal structure of the tourmalines is of high quality. The genetical link between gold mineralization and tourmaline should stimulate exploration interest in the study area.

关 键 词：Fe-Dravite Structure Refinement Accessory Mineral Metamorphic Condition Kombé II Bafia Group Central African Fold Belt 

分 类 号：P59[天文地球—地球化学]