Colloidal gold transport: a key to high-grade gold mineralization?
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LETTER
Colloidal gold transport: a key to high-grade gold mineralization? Laura Petrella 1
&
Nicolas Thébaud 1 & Denis Fougerouse 2 & Katy Evans 2 & Zakaria Quadir 3 & Crystal Laflamme 1,4
Received: 25 September 2019 / Accepted: 19 February 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Introduction Experimental evidence suggests that hydrosulfide is the main ligand for gold transport in solution and the main mechanism of Au transport in aqueous crustal hydrothermal fluids (Liu et al. 2014; Pokrovski et al. 2014). In modern Au-rich systems, the maximum measured concentration of dissolved Au is 16 ppb (Hardardóttir et al. 2009; Simmons and Brown 2006; Simmons et al. 2016). At this solubility, more than 1010 l (c. 2.7 × 105 Olympic swimming pools) is required to form a world-class gold deposit
Editorial handling: H. Frimmel * Laura Petrella [email protected] Nicolas Thébaud [email protected] Denis Fougerouse [email protected] Katy Evans [email protected] Zakaria Quadir [email protected] Crystal Laflamme [email protected] 1
Centre for Exploration Targeting, University of Western Australia, Crawley 6009, Australia
2
School of Earth and Planetary Sciences, Curtin University, Bentley 6102, Australia
3
John de Laeter Centre, Faculty of Science & Engineering, Curtin University, Bentley 6102, Australia
4
Département de géologie et génie géologique, Université Laval, Québec G1V 0A6, Canada
(> 6 Moz Au) if 100% of the Au is precipitated. The formation of high-grade gold vein might results from the circulation of large volumes of hydrothermal fluids facilitated by processes such as increased fluid flow associated with repeated and protracted fault failure (Cox et al. 1995; Sibson and Scott 1998; Weatherley and Henley 2013). However, the degree of focusing required by such mechanisms is difficult to justify in high-grade deposits such as the world-class Callie deposit (Northern Territory, Australia) where gold is contained in narrow veins associated with restricted wallrock alteration (Petrella et al. 2019). As an alternative model, it has been suggested that Au may be transported as colloidal suspensions in the ore fluid (Hannington and Garbe-Schönberg 2019; Harrichhausen 2016; Herrington and Wilkinson 1993; Hough et al. 2011; Saunders 1990; Saunders and Schoenly 1995). At thermophysical conditions typical of orogenic-type gold systems, Au colloids tend to coagulate spontaneously shortly after nucleation, which prevents effective transport at elevated length and time scales in hydrothermal fluids (Frondel 1938). Gold colloids can, however, remain in suspension in the fluid if protected by Si colloids, which have been demonstrated to remain stable in solution at temperatures up to 350 °C (Frondel 1938; Liu et al. 2019). The presence of gold colloids has been documented in active hydrothermal systems (Gartman et al. 2018; Hannington and Garbe-Schönberg 2019; Hannington et al. 2016) and Phanerozoic epithermal gold systems (Harrichhausen 2016; M
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