Applied Mineral Exploration
Discussion and research relevant to mineral
exploration. Using decrepitation to assist in selective analysis of inclusion fluids
Chemical or isotopic analysis of fluid inclusion fluids typically
requires the release of the fluids from the inclusions. This is
done either by mechanical crushing or thermal decrepitation, but
to obtain sufficient fluid quantities, fluid from a large number
of inclusions is required and the resulting extract is an average
of all fluid trapping events in the sample. Montoya-Lopera et.al.
have used thermal decrepitation over selected temperature ranges
to determine the fluid isotope composition from potentially
different, overlapping inclusion trapping events in a single
source sample. To select the temperature ranges of interest they
used baro-acoustic decrepitation of a separate aliquot of the
sample to recognize different fluid inclusion populations.
They have published their analytical method in the Journal of
Geochemical Exploration, Vol. 277, 2025, reference 107812.
New method to sequential thermal extract of
fluid inclusion water associated with overprinted mineral
deposits
Paula Montoya-Lopera,
Gilles Levresse, Elisa Fitz-Díaz, Edith Cienfuegos-Alvarado,
Francisco Otero-Trujano, Pedro Morales-Puente
They used acoustic decrepitation to distinguish 3 different fluid
inclusion populations, based on the temperature of decrepitation,
on 3 samples from Ag and Au deposits in Mexico, and collected the
fluid released during thermal decrepitation in these 3 separate
temperate intervals. The collected fluids were used for
Oxygen and Hydrogen isotope analyses of potentially different
fluid events within the mineralisation samples. The isotope
analyses on fluids released in different temperature ranges were
different and showed the presence of multiple fluid events during
the sample formation.
This Figure from the above paper shows the use of baro-acoustic
decrepitation to select 3 different temperate ranges for use in
the subsequent selective thermal decrepitation and fluid
collection for analysis. The temperature ranges selected
were 100 - 320 °C shown with pink shading, 320 - 545 °C
shown with blue shading and >545 °C shown with green shading.
Here is the abstract of their paper:
The importance of fluid inclusions (FI) as a geological record of the fluid inventory of the earth's crust is current
widely recognized. Less accepted, however, is their reliability in providing unequivocal information on the
isotopic chemistry of the fluids. Such uncertainties are fully justified since the quantitative analysis of FI presents
several technical issues. For example, the use of a small amount of water, typically <30 μL, which could lead to
errors. Also, it is unusual to find geological materials that contain only one FI generation. The study of multiple
populations of inclusion offers an exciting insight into changes in fluid activity. The existence of multiple generations
of FI complicates bulk sample analysis methods and led to data interpretation bias. To avoid these issues,
we created a new method to identify multiple or particular hydrothermal events. We used data from a worldclass silver‑gold
multi-event (San Dimas District, Sierra Madre Occidental, Mexico) to describe this sequential
thermal extraction method, that allows: (i) estimate decrepitation temperature range for multiple or particular FI
generation, (ii) extract FI water for multiple or particular FI generations, and (iii) analyze δ18O and δ2H of
trapped water from multiple generations. Our findings demonstrate that obtained δ18O and δ2H results of FI
water of quartz crystals are reproducible and consistent with geological and geochemical contrasts on the
different paragenetic events.