Rapid fluid inclusion data
for exploration (decrepitation)
Fluid inclusions are trapped remnants of the fluids which formed hydrothermal mineral deposits and provide a unique insight into the chemical and physical conditions of ore forming fluids. Academic studies of ore deposit genesis have long relied on this vital fluid inclusion data to understand the genesis of ore deposits. But despite the obvious relevance of this information, the exploration community has largely failed to use this data in their routine exploration activities to target potentially economic hydrothermal systems.
Baro-acoustic decrepitation is a simplified method to obtain reproducible, non-subjective fluid inclusion data quickly and without the need for polished thin sections or microscopes. It can provide information about the source fluid environment and targeting vectors on project-scale numbers of samples, at modest price and with quick analytical turnaround. It does not provide fluid salinities or the pedantic levels of precision required in academia, but these aspects are not particularly useful in exploration and frequently just add confusion rather than resolution.
The most important
use of baro-acoustic decrepitation is in determining approximate total gas
contents of samples, as this data is frequently closely
correlated with mineralisation potential. Examples in this
documentation show this use as well as others including
the discrimination between samples which are visually
identical and in discerning
temperature zonation effects within a vein, mine or small
exploration area. It can even be used on opaque minerals where microscopy
is completely impossible, and many examples from iron oxide
minerals are shown here.
The baro-acoustic decrepitation method was wrongly discredited by early work in the 1950's in Canada at a time when the presence of gas-rich fluids in hydrothermal systems was not understood and neither was the thermodynamic behavior of such fluids within inclusions. With the benefit of our currently much improved understanding of fluid systems it is now clear that baro-acoustic decrepitation does in fact provide a very useful and practical mineral exploration technique, particularly given the ability to digitally automate the instrumentation as has been done.
decrepitation is not intended to compete with the very high
accuracy of slow and painstaking microscopic fluid inclusion
research. However, as with soil geochemical surveys, where low
cost and speed are more important than extreme accuracy,
baro-acoustic decrepitation has a valuable role to play in many
types of exploration programme. Although the method is usually
applied to quartz samples, it has been used on various minerals
including sulphides, haematite, magnetite, fluorite,
carbonates and jasperoids.
An extensive database of some 5000 analyses from numerous ore deposits worldwide is the basis for the following information.
Exploration of the Mt. Boppy Au deposit region, Cobar, NSW, Australia: by K.G. McQueen
Intrusion related gold at Okote, Southern Ethiopia: by Solomon Geda
Exploring for Au using fluid inclusions in the Tanami region, NT, Australia: by T. Mernagh
The use of fluid inclusion decrepitometry to distinguish mineralised and barren quartz veins in the Aberfoyle tin-tungsten mine area, Tasmania. (1983) (abstract) (full paper, pdf)
An instrument for fluid inclusion decrepitometry and examples of its application. (1988) (abstract) (full paper, pdf)
The recognition of variations in sample suites using fluid inclusion decrepitation - applications in mineral exploration (1988) (abstract) (full paper, pdf)
Decrepitation studies in gold exploration. A case history from the Cotan prospect, N.T., Aust. (1991) (abstract) (full paper, pdf)
Comparison of decrepitation, microthermometric and compositional characteristics of fluid inclusions in barren and auriferous mesothermal quartz veins of the Cowra Creek gold district, New South Wales, Australia By: J.A. Mavrogenes et. al., (1995) (abstract)
Acoustic Decrepitation as a means of rapidly determining CO2 (and other gas) contents in fluid inclusions and its use in exploration, with examples from gold mines in the Shandong and Hebei provinces, China (2007) (full paper, html)
A discussion to point out errors in H2 analyses of fluid inclusion volatiles by mass spectrometry. (2013)
Fluid types and their genetic meaning for the BIF-hosted iron ores, Krivoy Rog, Ukraine. By Marta Sośnicka et.al. (2015) Extract (PDF file, 3.5 Mbyte) here
Mineral geochemistry of the Sangan skarn deposit, NE Iran: Implication for the evolution of hydrothermal fluid. By Fatemeh Sepidbar et.al. (2017) Extract (PDF file, 5.8 Mbyte)
Mt Bischoff, Tasmania, Australia
East Kemptville (Mt. Pleasant), Nova Scotia, Canada
Erzgebirge tin greisens, Germany - Czech Republic
Gejiu, Yunnan, China
Kapuskasing, Ontario, Canada
Great Bear magmatic zone
Black Bull Silica
Mt. Pleasant Sn