Applied mineral exploration methods, hydrothermal fluids, baro-acoustic decrepitation, CO2 rich fluids

How CO2 inclusions form from aqueous fluids

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

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

Inclusion shapes can prove heterogeneous FI trapping

Disproportional FI trapping from heterogeneous fluids explains gas-dominant systems

A discussion of H2 analysis by mass spectrometry

A mechanism to form H2 in the MS ioniser during analyses


Sangan skarn Fe deposits, Iran

New model 205 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:

AGCC expo, Adelaide, Aust. Oct. 14-18 2018


ECROFI, June 24-26, Budapest, Hungary

AOGS, Singapore, 28 Jul-2 Aug 2019

SGA, Glasgow Scotland, Aug. 27-30 2019

Comprehensive Geology Conference Calendar

Acoustic decrepitation as a rapid means for determining CO2 (and other gas) content of inclusion fluids. An explanation of the acoustic decrepitation behaviour of gas rich fluid inclusions.

Kingsley Burlinson

Presented at ACROFI I   Nanjing, China, May 2006

The acoustic decrepitation method heats a small monomineralic sample and counts pressure impulses as the inclusions burst when they develop high internal pressures. For aqueous fluids, the decrepitation temperature is correlated with the homogenisation temperature, but gas rich fluids give a distinct and characteristic low temperature decrepitation peak which can actually be used to identify gas rich fluid inclusions. This information is useful in exploration for Au deposits, which are frequently associated with CO2 rich and sometimes CH4 rich fluids.

This distinctive decrepitation occurs because the non-aqueous inclusion fluids expand according to the gas law and develop internal pressures high enough to burst the host mineral grain at temperatures well below their homogenisation temperatures. In contrast, aqueous fluids condense to a liquid and gas phase during post-entrapment cooling. Upon subsequent heating their internal pressures do not increase significantly until after homogenisation to a single phase occurs and hence they do not decrepitate "prematurely" as gas rich inclusions do.

This behaviour is usually regarded as an annoyance in conventional microthermometric homogenisation studies, but can readily be used as an exploration aid to find mineralisation deposited from such gas rich fluids.

Because all the non-condensing gases follow the gas law with only minor differences due to non-ideallity, decrepitation determines the total gas contents. All of the gases CH4, CO2 and N2 contribute almost equally to this and although the actual composition of the gas phase cannot be determined, this is of no detrimental effect when used in exploration to search for the gas-rich inclusions often associated with Au minearalisation

Decrepitation results on samples from Cowra, NSW, Australia, which have also been microthermometrically measured for XCO2, show that amounts of less than 5% XCO2 are easily distinguished by decrepitation and amounts as low as 1% may be determinable. Microthermometric results from one sample at the Southern pit of the Tanami goldfield, NT, Australia, shows Xgas ranged from 5% to 43% in 18 observations, but decrepitation analsis of an averaged sample shows only about 1% Xgas. In this case the inclusions containing high Xgas were restricted to a single late event in the rims of vug fill quartz crystals and are numerically insignificant and probably not part of the main Au depositional event even though they have received disproportionate attention in research of this deposit.

Not only does the decrepitation method provide a means of rapidly and reliably determining the gas content of inclusion fluids, but it also provides an averaged result which can be more useful in exploration than focusing on an individual quartz formation event, which may inadvertently not be related to the mineralisation for which one is exploring.

The full paper as html is here

Back to bibliography

Back to main Contents