Gartman, Amy, Hannington, Mark D., Jamieson, John William, Peterkin, Ben, Garbe-Schönberg, Dieter, Findlay, Alyssa J., Fuchs, Sebastian and Kwasnitschka, Tom (2018) Boiling-induced formation of colloidal gold in black smoker hydrothermal fluids. Geology, 46 (1). pp. 39-42. DOI 10.1130/G39492.1.

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Abstract

Gold colloids occur in black smoker fluids from the Niua South
hydrothermal vent field, Lau Basin (South Pacific Ocean), confirming
the long-standing hypothesis that gold may undergo colloidal
transport in hydrothermal fluids. Six black smoker vents, varying
in temperature from 250 °C to 325 °C, were sampled; the 325 °C
vent was boiling at the time of sampling and the 250 °C fluids were
diffusely venting. Native gold particles ranging from <50 nm to 2
μm were identified in 4 of the fluid samples and were also observed
to precipitate on the sampler during collection from the boiling vent.
Total gold concentrations (dissolved and particulate) in the fluid samples
range from 1.6 to 5.4 nM in the high-temperature, focused flow
vents. Although the gold concentrations in the focused flow fluids are
relatively high, they are lower than potential solubilities prior to boiling
and indicate that precipitation was boiling induced, with sulfide
lost upon boiling to exsolution and metal sulfide formation. Gold
concentrations reach 26.7 nM in the 250 °C diffuse flow sample, and
abundant native gold particles were also found in the fluids and associated
sulfide chimney and are interpreted to be a product of colloid
accumulation and growth following initial precipitation upon boiling.
These results indicate that colloid-driven precipitation as a result of
boiling, the persistence of colloids after boiling, and the accumulation
of colloids in diffuse flow fluids are important mechanisms for the
enrichment of gold in seafloor hydrothermal systems.

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