Modelling Fluid Evolution in Ore-Forming Systems Detailed PIXE analysis, using the CSIRO-GEMOC Nuclear Microprobe, of brine fluid inclusions which trap the more primitive fluids exsolved from crystallising intrusives provides starting compositions for modelling the formation of ore deposits in the surrounding area.

Modelling of progressive cooling of the brine composition, given by PIXE analysis of brine fluid inclusions in the Yankee Lode quartz, with addition of meteoric water, predicts the sequence of ore deposition (right to left) from cassiterite, through arsenopyrite, chalcopyrite, galena and sphalerite, to pyrite in the country rock.

This trend is in general agreement with the regional distribution of Sn, As and base metal deposits away from the centre of the intrusion, and helps to explain the detailed zonation of ore deposits in the Mole Granite of the New England district of eastern Australia (Heinrich and Ryan, 1992).

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

• Heinrich, C.A., and C.G. Ryan (1992), "Mineral Paragenesis and Regional Zonation of Granite-related Sn-As-Cu-Pb-Zn Deposits: A Chemical Model for the Mole Granite District (Australia) Based on PIXE Fluid Inclusion Analysis", in Proceedings of 7th International Symposium on Water - Rock Interaction, eds. Y.K. Kharaka and A.S. Maest, (Balkema, Rotterdam, 1992) p. 1583-1587.