Fluid inclusion thermometric and stable isotope (δ18O-δD) evidence for “cryptic boiling” in the Profitis Ilias epithermal gold deposit, Milos : a potential exploration tool for epithermal gold

“Cryptic boiling” has been disclosed throughout the vertical extent of the Profitis Ilias epithermal system (~450 m) by assessing systematic variations in fluid inclusion and stable isotope (δ18O-δD) data in relation to elevation. Highest gold grades (Au: 2-57.9 g/t) are preferentially concentrated in the upper 200-250 m of the system in a “steam-dominated zone” that is separated from a lower “liquid-dominated zone” (Au < 2 g/t). This distribution of gold may be due to colloidal transport in a boiling epithermal system. The identification of the base of the “steam-dominated zone” using fluid inclusion and stable isotope data may potentially guide exploration drilling to depths with high-grade gold ore in productive epithermal systems.