Progress further in this document and web constitutes acceptance of the terms of our copyright and disclaimer.

Fluid Inclusion Microanalysis using PIXE

Recent advances in technique now permit routine non-destructive analysis and imaging of fluid inclusion in minerals using Proton Induced X-ray Emission (PIXE) and beams of 3 MeV protons from the CSIRO-GEMOC Nuclear Microprobe.

Development is continuing to augment this capability with Proton Induced Gamma-ray Emission (PIGE) for light element detection and 3D fluid mapping using elastic recoils. Using PIGE we can now provide images of light elements such as Na and F.

Method

Energetic protons pass easily through minerals like quartz to depths of more than 80 µm, and excite X-rays from elements within trapped fluid inclusions. The X-rays are counted using a cooled germanium or lithium-drifted silicon detector. By focussing the proton beam to about 1.3 µm in diameter, and raster scanning the beam over each inclusion, individual fluid inclusions can be imaged and analyzed non-destructively.

In order to relate the detected X-rays to concentration of an element in an inclusion, a model has been developed at the CSIRO for calculating X-ray yields from specific 3D inclusion geometries (inclusion size, shape, density, orientation and depth) (Ryan et al., 1993). Now by raster-scanning the beam over a fluid inclusion to provide a uniform dose, and using the 3D model, the method permits the extraction of the concentration of all detected elements in the inclusion (Ryan et al., 1995). If there has been no loss from the inclusion, this provides the composition of the original homogeneous trapped fluid.

Imaging

The high resolution of the new CSIRO-GEMOC Nuclear Microprobe also provides a tool for imaging the internal contents of individual fluid inclusions.

Sensitivity

The sensitivity of the Proton Microprobe enables the analysis of individual fluid inclusions down to ~ 5 µm in diameter. In typical inclusions (10-15 µm) ore-related elements (such as Cu, Zn, Au and Pb) can be detected and analyzed down to concentrations of ~20 ppm.

Accuracy

Test performed using synthetic fluid inclusions in quartz have shown the method to be accurate to 10-15% for undersaturated solutions (no daughter minerals present). With the presence of daughter minerals, and due to the uncertainties associated with the positions of these minerals, uncertainties typically grow to ~30%.

Application

The PIXE technique for the non-destructive analysis of fluid inclusions is in routine use at the CSIRO for the analysis of ore-fluids associated with porphyry Cu-Au and VMS deposits worldwide.



For further information contact: Dr. Chris Ryan via email: (Chris.Ryan@csiro.au)

+61-2-9490 8673
+61-2-9490 8909

CSIRO Exploration and Mining
PO Box 136
North Ryde NSW 2113
Australia


CSIRO-GEMOC Nuclear Microprobe
CSIRO Exploration and Mining


References

Copyright © 1999-2001 CSIRO
Please direct comments about this web page to Chris Ryan
Graphics for these pages have been prepared using Amiga rendering and image processing software and the IDL graphics package.