Newest Topics:

Exploration of the Mt. Boppy Au deposit, NSW

Forensic tests on soil samples

Gold at Okote, Ethiopia


Do IOCG deposits form from CO2 fluids?

How CO2 inclusions form from aqueous fluids (UPDATED)

Understanding heterogeneous fluids : why gold is not transported in CO2-only fluids

Gold-quartz deposits form from aqueous - CO2 fluids: NOT from CO2-only fluids

Discussions why H2 analysis by mass spectrometry is wrong


Kalgoorlie Au data

Sangan skarn Fe deposits, Iran

New models 205 & 216 decreptiometer

Studies of 6 Pegmatite deposits

A study of the Gejiu tin mine, China

Exploration using palaeo-hydrothermal fluids

Using opaque minerals to understand ore fluids

Understanding baro-acoustic decrepitation.

An introduction to fluid inclusions and mineral exploration applications.

 Interesting Conferences:


ECROFI 2021, Reykjavik, Iceland

SGA, Rotorua NZ, RESCHEDULED to march 28-31 2022
6th Archean, Perth, W.Aust. RESCHEDULED unknown date 2022

Comprehensive Geology Conference Calendar

All non-condensing gases give similar low temperature decrepitation peaks

Although much of the focus of Au exploration and acoustic decrepitation is on the CO2 content of fluid inclusions, other gases such as CH4 and N2 also give the same low temperature decrepitation peaks as seen on CO2 rich samples. This is a consequence of the fact that all these gases, above their critical point temperatures, behave in accordance with the gas law, namely PV=nRT. This behaviour is completely independent of the nature of the gas species and only subject to variations due to the non-ideal behaviour of some gases. However, at the temperatures and pressures used in acoustic decrepitation analyses, these variations from ideallity are very small and do not affect the results at all.

To demonstrate this, I have used the modified Redlich & Kwong equation of state to calculate the behaviour of CO2, CH4 and N2 at 2 different molar volumes using a computer program from Holloway, 1980.  The results, plotted below, show that these 3 gases behave similarly and that decrepitation of inclusions containing any of these gases, or mixtures of these gases, will all develop high internal pressures and decrepitate at low temperatures, as explained in the item: Why CO2 rich fluid inclusions decrepitate at low temperatures.   The small differences between gases due to non-ideallity are of no consequence to the acoustic decrepitation method.

 Consequently, the acoustic decrepitation method will work regardless of the presence of mixtures of these gases or other gases above their critical temperatures.  The reason for using Molar Volume (the inverse of density) in these calculations is that the gaseous components of fluid inclusions formed at the same P-T conditions will have the same molar volume, although their gas densities will differ. (This is a consequence of the fact that 1 mole of any gas at STP occupies the same volume.)

gas equation of state

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