Modeling Solubility of Fe-Ni Sulfides in Basaltic Magmas: The Effect of Nickel

Abstract

A new model of sulfur solubility in mafic and/or ultramafic silicate magmas, which accounts for the effects of pressure, temperature, oxygen fugacity, major element, and Ni contents in the silicate melt and the coexisting sulfide liquid, is presented in this paper. The model postulates the existence of positively charged Fe-Ni sulfide complexes in the melt of a general formula (FeyNi1-y)zS 2(z-1)+ , which are formed as a result of complexation reactions between the sulfide-forming ions (Fe 2+ , Ni 2+ , S 2− ) and (Fe,Ni)S species in the silicate liquid. The new model can explain both the anomalously high S solubility in iron-enriched silicate systems and the "parabolalike" dependence of S contents in silicate melts on their Fe content. The proposed mechanism of sulfide solubility was calibrated on a dataset of 213 anhydrous experimental glasses (both Ni free and Ni bearing) and 53 S-saturated MORB glasses, and incorporated into a new version of the COMAGMAT (v. 5) magma crystallization model. The COMAGMAT-5 model can estimate sulfur concentration at sulfide saturation (SCSS) in a wide range of experimental and natural compositions, including Fe/Ni variations in silicate melts and coexisting sulfides. Despite relatively low concentrations, nickel is shown to have a pronounced effect on S solubility, causing significant variations in the onset of sulfide immiscibility in melts with otherwise similar major element compositions. An application example of the new SCSS model to "B-1 magma" proposed as parent for the Lower and Lower Critical zones of the Rustenburg Layered Suite, Bushveld Complex, is discussed.

Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

“…The sulfur concentration in a silicate melt depends on parameters (total pressure, temperature, oxidation state and melt composition) that control the sulfur speciation and solution mechanisms (see detailed review in Mungall (2014) and Ariskin et al (2013) for further information). The sulfur concentration at sulfide saturation (SCSS) depends mainly on the melt composition (particularly the Fe content), temperature, pressure and oxygen fugacity ( fO 2 ).…”

“…The sulfur concentration at sulfide saturation (SCSS) depends mainly on the melt composition (particularly the Fe content), temperature, pressure and oxygen fugacity ( fO 2 ). In addition to Fe, chalcophile elements such as and Sun (1995) Ni and Cu (Ariskin et al 2009;Ariskin et al 2013;Ariskin et al 2010;Evans et al 2008) and some of the PGE (Laurenz et al 2013) may also play a significant control on sulfur solubility in ultramafic and mafic magmas. Over the past few years, empirical (Ariskin et al 2009;Ariskin et al 2010;Li and Ripley 2009;Li and Ripley 2005) and experimental (Liu et al 2007) models have been developed to predict the sulfur concentration at sulfide saturation.…”

Simulating the behavior of volatiles belonging to the C–O–H–S system in silicate melts under magmatic conditions with the software D-Compress

“…These efforts include largely empirical models (e.g., Moore et al, 1998;Liu et al 2005), semi-empirical models (e.g., Iacono-Marziano et al, 2012;Ariskin et al, 2013;Duan, 2014), and thermodynamical models using various formalisms (e.g., Papale, 1999;Moretti et al, 2003). These models have found a wide range of applications, which includes the interpretation of melt inclusion data (Papale, 2005;Moore, 2008), the interpretation of gas measurements on active volcanoes (Aiuppa et al, 2007;Oppenheimer et al, 2011), the feedback between chemistry and physics in conduit flow models (Papale and Polacci, 1999;Burgisser et al, 2008), and the assessment of the impact of volcanic gases on the atmosphere of terrestrial planets Scaillet, 2009, 2014;Gaillard et al, 2011).…”

“…Owing to such complexity, not all of these models have been released to the volcanological community in a userfriendly format. Notable exceptions are the models VolatilCalc (Newman and Lowenstern, 2002), PELE (Boudreau, 1999), and SolEx (Witham et al, 2012), and the models of Papale et al (2006), Iacono-Marziano et al (2012), Ariskin et al (2013), and Duan (2014). Altogether, these models cover a wide range of situations of geological interest, but each of them handles a specific range of intensive parameters and volatile and melt compositions.…”

Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR)

“…Instead, a decreasing Fe content is consistent with lowering the level of sulfur concentration at sulfide saturation (SCSS; Haughton et al, 1974;O'Neill and Mavrogenes, 2002;Tsujimura and Kitakaze, 2005;Ariskin et al, 2013), and could play a major role for sulfide precipitation from percolating melt. Iron loss is likely efficient in narrow melt channels (Ciazela et al, 2017b), where Fe in melt is buffered by the exchange reaction with large amount of olivine and pyroxene on conduit walls (Dick and Natland, 1996).…”