Vein quartz at Victory Au mine, Kalgoorlie
This mine is hosted in archean greenstones and has several distinct quartz vein systems. During mining it was useful to try and relate the quartz vein sets with their Au potential. This was based on vein orientation with horizontal veins considered to be mineralized and vertical veins to be sub-economic.
However, decrepitation shows that in the ore zones, veins of both horizontal and vertical orientation have intense CO2 peaks, whereas such peaks are absent on nearby barren veins of either orientation. In addition, multiple samples from a single horizontal vein in the pit wall give very different decrepigrams. This shows that the vein's orientation is not a consistent guide to the composition of its parent fluid and that the veins show strong internal zoning. The similarity of decrepitation of adjacent horizontal and vertical veins also indicates that they formed from similar fluids despite being formed in presumably different stress regimes. The relationship between mineralization and the presence of CO2 peaks on decrepigrams is more consistent than the relationship with vein orientation at the Victory mine.
complex environments a technique based on formation fluid
content rather than an indirect technique based on geological
stress fields is a better guide to mineralization.
Overview summary plot
Individual sample data plots
The barren quartz veins typically show no low-temperature decrepitation.
Note the presence of low temperature decrepitation (from CO2 rich fluid inclusions) in ore zone quartz
Chert gives only very weak decrepitation - note the major change in scale of the Y axis. This is typical of all chert samples.