Speaker
Dr
Wojciech Przybylowicz
(Materials Research Department, iThemba LABS, Somerset West, South Africa)
Description
Analysis of melt and fluid inclusions in minerals is an important way to understand ore formation processes. Nuclear microprobe provides direct non-destructive methods to determine their composition. Methodology related to micro-PIXE fluid inclusion analyses has been mastered by the CSIRO-GEMOC nuclear microprobe group [1] and is now available to the users of the GeoPIXE software [2].
We performed simultaneous PIXE-PIGE analyses on multi-phase inclusions (containing glass, crystals, vapour) hosted in quartz and topaz from the Ary-Bulak complex in Mongolia, complementing Raman spectroscopy, EDS-EPMA and LA-ICP-MS analyses. Previous studies of Ary-Bulak rocks have revealed the presence of silicate glass with extremely high F contents (up to 7-8 wt.%) [3]. Given the multi-phase nature of the inclusions, the PIXE-PIGE analysis was the only method possible to analyse the entire inclusions without homogenising them, and to prevent the loss of fluid. PIXE and PIGE spectra (for the detection of F) were collected using the same HPGe detector.
PIXE of topaz-hosted inclusions indicates the presence of K, Rb, Ca, As, Cs, Fe, Mn, Cu and Zn. A combination of PIXE, Raman spectroscopy and EDS allowed the identification of cryolithionite [Na3Li3Al2F14], mica, alkali-feldspar, and an Fe-Mn mineral (possibly an oxide) as daughter phases (formed after melt entrapment), and Nb-Ta-W oxides co-trapped with the melt. The obtained results revealed that the two melts with different F contents were trapped at different stages by quartz and topaz phenocrysts, and bear important implications on the magmatic evolution of F-rich silicic magmas and the deposition of Nb-Ta-W ores.
[1] C.G. Ryan et al. Nucl. Instr. Meth. B 181 (2001) 570.
[2] C.G. Ryan. Int. J. Imag. Syst. Tech. 11 (2000) 219.
[3] I.S. Peretyazhko and E.A. Savina. Russian Geol. Geoph. 51 (2010): 1110.
Primary author
Dr
Wojciech Przybylowicz
(Materials Research Department, iThemba LABS, Somerset West, South Africa)
Co-authors
Dr
Andrea Agangi
(University of Johannesburg)
Prof.
Axel Hofmann
(Department of Geology, University of Johannesburg,)
