Ultramafic-hosted volcanogenic massive sulfide deposits from Cuban ophiolites

A track record of Au–Ag nanomelt generation during fluid-mineral interactions

“…These changes leading to NP melting took place at temperatures much lower (~ 375 ºC 24 ) than the theoretical melting point for 60–120 nm sized particles (similar to the bulk melting point of Ag at 961 ºC 26 ). Consequently, our observations, together with the results from the experiments by Liu et al 24 , conflict with the proposed size-dependent melting curves of Au 19 and Ag 26 , which predict that only NPs with sizes below 10 nm are able to melt within the estimated range of temperature of the studied hydrothermal system (400–500 ºC 20 ). Regarding the size reduction of the NPs during melting, Lee et al 25 argued that NPs start melting at the surface, and the formed Ag nanomelt is driven away from its site of melting due to the repulsive forces acting at the interface between the NP and its corresponding melt.…”

“…The partial dissolution and replacement of safflorite by cobaltite by hydrothermal fluids occurred at ca. 400–500 ºC and upon an increase in the f S 2 and f O 2 20 , 21 . In this scenario, some of the Au–Ag NPs originally hosted within the safflorite were partially or totally released, allowing interaction with the hydrothermal fluid.…”

“…Partial dissolution of safflorite by a hydrothermal fluid with higher f S 2 and f O 2 and at temperatures between 400 and 500 ºC 20 triggered partial to total melting of pre-existing euhedral Au–Ag NPs as they were partially to totally exposed to reactive hydrothermal fluids (Fig. 3 a, b).…”