Gold enrichment in active geothermal systems by accumulating colloidal suspensions

Formation and Aggregation of Gold (Electrum) Nanoparticles in Epithermal Ores

“…Further, boiling would also lead to increased particle velocities, which can lead to overcoming surface-charge repulsions, causing effective particle sticking by a process called orthokinetic aggregation [34]. Recently, Hannington et al [2] proposed that deeper reservoirs of solutions containing gold nanoparticles can contribute them episodically to shallow geothermal systems, and thus might be a plausible explanation for the formation of bonanza epithermal ores.…”

“…The recent discovery of gold nanoparticles in sub-aerial geothermal systems [2,26,27] and submarine hydrothermal vents [28], along with the documentation of metal-sulfide nanoparticles in the "black smoke" emanating from submarine vents, suggest that gold and other metallic nanoparticles may be important contributors to a variety of hydrothermal ores, such as volcanogenic massive sulfideor Carlin-type ores. However, the essential requirement appears to be the evolution of hydrothermal fluids to form gold-supersaturated, far-from-equilibrium conditions that are capable of forming nanoparticles.…”

“…Although we describe the role of nanoparticles in epithermal ore formation here, perhaps such particles are important in other systems. For example, gold colloids, nanoparticles, and/or nanocrystals also have been documented in "supergene" ± bacterial processes related to weathering of gold ores and gold-nugget formation [19][20][21], in volcanic fumaroles [22,23], in Carlin-type gold deposits [24,25], and also in active geothermal systems [2,[26][27][28]. Finally, metallic sulfide nanoparticles are significant components in the "black smoke" discharging from submarine hydrothermal vents [29][30][31].…”

“…Colloidal particles can be of a similar size (typically 1-1000 nm in the chemistry usage) but they have the added requirement that they must be dispersed in a stable manner in another medium composed of different materials, such as an aqueous solution. Thus, perhaps it is more fitting to retain the term colloids for hydrothermal solutions that transport these small particles, but the recent economic geology and geochemistry literature uses both terms [1,2]. Given their size, colloids, and nanoparticles have very-high surface area to volume ratios, which can impart unique chemical properties that can differ from that of the bulk materials [1].…”

Compositions of hydrothermal silicates and carbonates as indicators of physicochemical conditions in the Reykjanes geothermal system, Iceland

“…As a result of the elevated salinity of the present-day geothermal fluid, the in-situ pH (i.e., at reservoir temperatures) is about 5.5, which is lower than is typically the case in other geothermal fields in Iceland (Arnórsson, 1978;Henley and Ellis, 1983). The fluid chemistry of the Reykjanes geothermal system has been documented extensively in Arnórsson (1978Arnórsson ( , 1995, Ólafsson and Riley (1978), Lonker et al (1993), Hardardóttir et al (2009Hardardóttir et al ( , 2013, Seward (2014), Kaasalainen et al (2015), Óskarsson et al (2015), Libbey and Williams-Jones (2016-supplementary material), and Hannington et al (2016).…”