European Journal of Scientific Research (ISSN: 1450 ... - EuroJournals

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© European Journal of Scientific Research, Vol 7, No 5, 2005 controlled MCA coupled with a standard electronic chain was used for the data acquisition and the storage of the energy spectra. The other details of the experimental set up for routine PIXE analysis at this laboratory have been reported [4,5]. For the analysis, the recent approach of Balzan et al [6] was adopted where every sample was bombarded twice for the lower and higher energy sections of the spectrum without damaging the samples. An 80 µm thick aluminum absorber was placed in front of the Si (Li) detector to remove X-rays with low energies, thereby enhancing the sensitivity of the heavy elements. The beam currents of between 70 and 100 nA were conveniently used here without any negative effects on the performance of the detector due to high counting rates. This produced the high energy part of the spectrum. Similarly, for the low energy section of the spectrum, a 250 um thick Mylar funny filter with 3.3 % hole was used. Here the beam currents of 5 to 20 nA were used, and the dead time was generally below 10%. The stored X-ray energy spectra were later analyzed using the computer code GUPIX [7] leading to elemental concentrations of the muscovites. RESULTS AND DISCUSSION The major element data and trace element data on the muscovites are presented in Tables 1 and 2. The results of PIXE analysis of the samples together with their corresponding standard deviations are presented in Table 2. Our results were in very good agreement with the certified values of the geological standards and hence establish the reliability of the data. Electronprobe data ( Ige unpublished Table 1) shows that the investigated white micas are phengites to nearly pure muscovites with compositions as shown by the following contents (in atoms per formula unit) Si = 6.15 - 6.18; Ti = 0.004 - 0.09; Al tot = 5.29 - 5.44; Fe tot =0.31 – 0. 32; Mg = 0.12 - 0.13, Na= 0.25-0.32, whilst K= 1.44-1.61. The approximate muscovite calculated formula (Al1.9 K0.8 Fe0.15Mg0.1 O12 Si3.1) and conforms with muscovites used as electrical insulator [7, 8]. The PIXE data on trace elements shows that concentration of elements are variable even within samples. K contents vary between 1.6 and 6.3% Ca content ranges between 97 and 510 ppm whilst V value ranges between 8 and 22ppm. Ti concentration ranges between 15 and 82ppm whilst V value generally ranges between 13 and 23 ppm. Mn ranges between 185 and 636 ppm with majority of the data falling in the 280 and 350 range. The Fe contents range between 0.78 and 1.05%. More than half of the samples showed the concentration of cobalt between 18 and 26
© European Journal of Scientific Research, Vol 7, No 5, 2005 ppm, three of the samples have the cobalt contents to be 59, 226 and 417 ppm respectively while the rest are below the detection limit. Cu values are generally less than 10ppm except two samples that contain 29 and 84ppm. The Zinc values are also variable ranging between 379 and 1690ppm. Ga content is similar in samples from the two locations with majority falling in the range 169-186 except four samples containing 136,137,153 and 233ppm.Rubidium values are quite high but generally within 3000 and 5000ppm range. Sr values are generally low with majority of the samples below detection limit. Other trace elements such as Nb (113 - 237 ppm) and Sn (250 – 736 ppm) show unsystematic variation even within samples. Yb and W were detected in only two samples having 68 and134ppm and 29 and 72ppm respectively. A significant feature of the muscovite from Ife is the presence of gold in ppm range( 21-36 ppm). The Ife pegmatites intrudes the greenstones (amphibolite) which has been suggested as the ultimate source of the placer gold in this area. The data may suggest that trace element data on muscovites may be used as tracer for gold prospecting. This is however tentative as more work is necessary to ascertain the importance of this data. CONCLUSIONS PIXE analysis provides the non-destructive qualitative and quantitative data in the industrial mineral, muscovites, from the Ife and Ijero areas of the South Western Nigeria. The elemental composition in the muscovite samples allows the better evaluation of an industrial potentials of the mineral. The trace elements are from muscovites are generally similar. However, the two series of samples can be distinguished on the basis of Au contents. This result probably suggests that muscovite from different geological environments can be distinguished on the basis of trace element composition e.g. Au. Acknowledgements The authors acknowledge the support of AS-ICTP programme for training and research in Italian laboratories (TRIL), Trieste, Italy and Obafemi Awolowo University, Ile-Ife, Nigeria. The assistance of Mr. M. Loriggiola and Mr. G. Manente in sample preparation is highly appreciated. We are also grateful to the Director of the Natural History Museum Ife for permission to publish the data. 17
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