Using fluid inclusion data in mineral exploration
Rapid data acquisition by the baro-acoustic decrepitation methodAn overview of information and results on using fluid inclusion information in exploration
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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.
Fluid inclusion decrepitation for mineral exploration - Overviews
Gold exploration using Baro-acoustic decrepitation
The decrepitation method - what is it and why use it?
Decrepitometry application to porphyry deposits (1981 report)
The fluid inclusion technique in exploration for Au mineralisation (Old report, 1982)
Practical usage of decrepitation in exploration
Decrepigram interpretation features
Using fluid inclusions in the opaque minerals haematite and magnetite
Fluid Inclusion Studies on Opaque Minerals
Customs information for sample entry to Australia
Using 3 software packages to de-convolve decrepigrams into component populations for quantitative interpretation
Using Baro-acoustic decrepitation data in exploration at the Drake mineral field, NSW and the application of curve fitting to the decrepitation data
Theoretical understanding of decrepitation
Why CO2-rich fluid inclusions decrepitate at low temperatures
Decrepitation behavior of all non-condensing gases are similar
Inclusion abundances and controls on decrepitation
Using baro-acoustic decrepitation to semi-quantitatively measure CO2 contents
Decrepitation ONLY detects fluid inclusions, it does not detect crystallographic changes.
The Model 105 decrepitometer - a brief description
Comparison of different decrepitation Instruments
Comparison of the Russian decrepitometer and the BGS model 105 decrepitometer.
Comparison of decrepitation with mass spectrometric gas determinations during heating
Explaining the formation of CO2-only fluid inclusions
Gold deposition from heterogeneous aqueous, CO2-rich fluids: resolving the enigmatic and misleading hypothesis of deposition from CO2 only fluids.
Gas dominated inclusion assemblages may be trapped from aqueous dominant heterogeneous fluids by disproportional trapping
The extreme differences between aqueous boiling heterogeneous fluids and immiscible gas aqueous heterogeneous fluids.
Spherical inclusion morphology of CO2 only inclusions indicates heterogeneous trapping from a liquid.
Fluid inclusions in quartz cannot prove that non-aqueous fluids CO2 formed the ore.
Why don't exploration geologists use or understand fluid inclusions? The case at the Cadia Au-Cu mine, NSW, Australia.
Hydrogen contents of fluid inclusion volatiles should not be analysed by mass spectrometer.
A model for the formation of H2 from water in the electron impact ioniser of the mass spectrometer
A discussion and reply on the error of using mass spectrometry to analyse hydrogen in aqueous analytes.
Papers presented at conferences
Geochemical exploration using hydro-thermal fluids - a paper at the SGA conference, Uppsala Sweden, Aug. 2013
Fluid Inclusion Studies on Opaque Minerals - a paper presented at the ACROFI-4 conference, Brisbane QLD., August 2012
Gold exploration using Baro-acoustic decrepitation - a paper presented at the IMA, Budapest, 2010
Understanding baro-acoustic decrepitation - a paper presented at ACROFI-2, Kharagpur, 2008
Exploration for gold using fluid inclusions - a paper presented at the AAG conference, Oviedo, Spain, 2007.
An updated understanding of the baro-acoustic decrepitation method. (proposed for the ECROFI meeting, Bern, 2007)
Acoustic decrepitation as a rapid means of determining CO2 (and other gas) content of inclusion fluids and its use in exploration (Nanjing, 2006)
Fluid inclusions in mineral exploration - a paper presented at the AAG conference, Santiago, Chile, 2001. Poster presentation
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)
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)
Bibliography / References
Index by deposit style
Meguma Terrane, Nova Scotia, Canada
Orogenic / Structual gold-quartz systems
Iron oxide - Copper - Gold deposits
Great Bear magmatic zone, NWT, Canada
Tennant Creek, NT, Australia
Magnetite and haematite decrepitation data
Mengku, northern Xinjiang, China
Magnetite at Krivoy Rog, Ukraine
Magnetite from the Bergslagen region, southern Sweden
Comparing and contrasting skarn and BIF magnetites
Mt Bischoff, Tasmania, Australia
East Kemptville (Mt. Pleasant), Nova Scotia, Canada
Erzgebirge tin greisens, Germany - Czech Republic
Gejiu, Yunnan, China
Decrepitation in minerals other than quartz
Index by location
Enterprise, Pine Creek
Pine creek (COTAN project)
Ballarat University grounds
Fosterville, Bendigo, Wattle Gully, Maldon
Woods point - the Morning Star mine
Great Bear magmatic zone
Black Bull Silica
Mt. Pleasant Sn
Europe (including Turkey)
Bergslagen region, magnetite study
Krivoy Rog, magnetite in BIF