New method to sequential thermal extract of fluid inclusion water associated with overprinted mineral deposits

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 world-class 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.