Fluid components in accessory minerals of Pan-African granitoids in the S■r Rondane Mountains, East Antarctica

Fluids （fluorine, chlorine, and OH） in accessory minerals （apatite, titanite and allanite） of Pan-African granitoids （Group-I granitoids, Group-II granitoids and Mefjell Plutonic Complex） from the Sor Rondane Mountains, East Antarctica were precisely measured by an electronic microprobe analyzer in this study. Apatites in the granites have commonly high fluorine contents. However, fluorine contents from the Group-Ⅰ, Group-Ⅱ granitoids and Mefjell Plutonic Complex （MPC） are of important variation, which F contents （3.21-7.20 wt%） in apatite from the Group-Ⅱ granitoids are much higher than those from the Group-Ⅰ granitoids （1.22-3.60 wt%） and the MPC （3.21-4.11 wt%）. Titanite in the MPC has a low fluorine content （0.23-0.50 wt%）, being less than those in the Group-Ⅰ granitoids （2.28 wt%） and Group-Ⅱ granitoids （1.85-2.78 wt%）. Fluorine in allanite in the Group-Ⅱ granitoids seems to have much lower contents than those from the Group-Ⅰ granitoids and the MPC. Higher fluorine contents in the titanite from the Group-Ⅱ granitoids may be mainly controlled by late-magmatic fluid-rock interaction processes associated with melt, but may not be indicative of original magma contents based on its petrographic feature, Due to very lower chlorine contents from all of accessory minerals, the authors suggest that titanite and apatite with higher fluorine contents in the Group-Ⅱ granitoids have much lower H2O （OH） contents compared with those in the Group-Ⅰ granitoids according to the partition among （F, Cl, OH）. Fluorine contents in whole-rock samples show a variation from the higher in the Group-Ⅰ granitoids to the lower in the Group-Ⅱ granitoids and the MPC, which are consistent with the changes of those from the biotite and hornblende as well as fluorite occurred in the Group-Ⅰ granitoids reported previously. Based on the above study of fluorine in accessory minerals and combined with the previous fluorine contents from biotites and hornblendes, the authors suggest that apatites and titanites with higher F contents in the Group-Ⅱ granitoids and the MPC may not be an indicator of higher fluorine contents in whole-rock, which reflect fluorine contents in magma sources and/or late-thermal activity. Higher fluorine contents in apatite, titanite and allanite may be an additional evidence of A-type affinity.

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

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(Na0.95[]0.05)Y(Mg2.39Fe0.61)Z(Al5.10Mg0.90)(BO3)3T[Si6O18](OH)3[(O,OH)0.88F0.12]. 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.