favona decrepitation curve fitting

Fitting gaussian populations to the Favona area decrepitation data

The decrepitation results show the total decrepitation from all inclusion types present in the samples. Each sample usually contains several different populations of inclusions which may be the result of zonation during the host mineral deposition. Statistical methods can be used to determine a group of individual gaussian curves which sum to produce the observed decrepitation curve. For this work, I have used the scaled Levenberg-Marquardt algorithm to derive the best fit gaussian component populations. I use skewed gaussian population components as it has been found that they usually produce a better fit to the data envelope. Using the parameters of these component sub-populations it is possible to make detailed and reproducible temperature comparisons between samples and also to quantify the various populations, particularly any populations in the 200 C to 400 C range, which are typically due to the presence of CO₂ rich fluid inclusion populations.

Upper Favona vein

There were probably 6 samples collected in this area. Two sample locations are uncertain due to suspected mis-labeling. These samples represent a high grade gold zone. Samples 1881 and 1882 had 41 g/t gold. Both of these samples also show a peak near 320 C, even though the data shows considerable noise on sample 1882 because the overall decrepitation intensity was extremely low.

1881

Samples 1884 and 1885 had high gold grades of 79 g/t. These samples probably come from The upper Favona area, although they were mislabeled during sampling and their exact location is yet to be verified. Sample 1884 shows a prominent low temperature toe on the main peak, and the fit algorithm suggests a separate low temperature, highly skewed population near 320 C. On sample 1885 there is a very prominent low temperature population near 320 C

1884

Peak Temperatures - Upper Favona Samples
Sample #	No. of Peaks	Temp	Temp	Temp	Temp
1881	3	308	446	-	588
1882	3	366	-	496	592
1884	3	336	444	-	588
1885	4	344	426	482	588

Mid-depth Favona Vein

Sample 1877 was collected from deeper down in the Favona vein. Although it has very low decrepitation intensity and a rather noisy envelope, there is still a distinct low temperature peak caused by CO₂ rich fluid inclusions. This sample has only a low Au grade near 1 g/t. However, the presence of CO₂ rich fluid inclusions suggests that this fluid is closely related to the fluid which deposited the high grade Au nearby, and that this location should be regarded as potentially mineralised.

1877

Peak Temperatures - Mid-depth Favona Samples
Sample #	No. of Peaks	Temp	Temp	Temp	Temp
1877	3	286	434	482	-

Favona South Area

Sample 1886 is from the Favona South area and contains only 0.23 g/t Au. This sample showed visible inhomogeneity and so was split during preparation into 3 samples. There are significant differences between these 3 results which is typical of strongly zoned quartz. This sample had much more intense decrepitation, perhaps due to a higher liquid content in the inclusions. There is also still a weak low temperature peak, perhaps even 2 seperate peaks, caused by a high CO₂ content.

1886B

Peak Temperatures - Favona South Samples
Sample #	No. of Peaks	Temp	Temp	Temp	Temp	Temp
1886B	4	-	342	460	526	584
1886C	4	-	372	446	510	592
1886A	4	244	328	460	-	612

Moonlight Area

Sample 1880 and 1878 from the Moonlight area contained only very low Au at 0.12 g/t. One sample, 1880A, lacks the low temperature peak and it is interpreted that CO₂ is absent from this sample. However, sample 1878B does have a low temperature peak caused by CO₂ rich inclusions.

1880

Peak Temperatures - Moonlight samples
Sample #	No. of Peaks	Temp	Temp	Temp	Temp
1880A	3	-	418	540	608
1878B	3	346	438	-	580

General notes on the graphs

In all these graphs, the mathematical fit curve is shown in red. The individual component curves are also summed to generate the SUM curve, which is plotted in yellow. In all cases the SUM curve is almost identical to the mathematical fit and plots on top of the red curve, giving a brown-orange colour.