Vapor–liquid partitioning of alkaline earth and transition metals in NaCl-dominated hydrothermal fluids: An experimental study from 360 to 465 °C, near-critical to halite saturated conditions

Abstract

Multi-phase fluid flow is a common occurrence in magmatic hydrothermal systems; and 1 extensive modeling efforts using currently established P-V-T-x properties of the NaCl-H 2 O system are 2 impending. We have therefore performed hydrothermal flow experiments (360-465 °C) to observe vapor-3 liquid partitioning of alkaline earth and first row transition metals in NaCl-dominated source solutions. 4The data allow extraction of partition coefficients related to the intrinsic changes in both chlorinity and 5 density along the two-phase solvus. The coefficients yield an overall decrease in vapor affinity in the 6 order Cu(I) > Na > Fe(II) > Zn > Ni(II) ≥ Mg ≥ Mn(II) > Co(II) > Ca > Sr > Ba, distinguished with 95% 7 confidence for vapor densities greater than ~0.2 g/cm 3 . The alkaline earth metals are limited to purely 8 electrostatic interactions with Cl ligands, resulting in an excellent linear correlation (R 2 > 0.99) between 9 their partition coefficients and respective ionic radii. Though broadly consistent with this relationship, 10 relative behavior of the transition metals is not well resolved, being likely obscured by complex bonding 11 processes and the potential participation of Na in the formation of tetra-chloro species. At lower densities 12 (at/near halite saturation) partitioning behavior of all metals becomes highly non-linear, where M/Cl ratios 13 in the vapor begin to increase despite continued decreases in chlorinity and density. We refer to this 14 phenomenon as "volatility", which is broadly associated with substantial increases in the HCl/NaCl ratio 15 (eventually to > 1) due to hydrolysis of NaCl. Some transition metals (e.g., Fe, Zn) exhibit volatility prior 16 to halite stability, suggesting a potential shift in vapor speciation relative to nearer critical regions of the 17 © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 vapor-liquid solvus. The chemistry of deep-sea hydrothermal fluids appears affected by this process 18 during magmatic events, however, our results do not support suggestions of subseafloor halite 19 precipitation recorded in currently available field data. Ca-Cl systematics in vent fluids are specifically 20 explored, revealing behavior consistent with partitioning due to phase separation. Interestingly, the effect 21 of variable chloride on dissolved Na/Ca ratios associated with plagioclase solubility (in single-phase 22 solutions) appears fundamentally similar to that of phase separation on vapor compositions such that 23 vapors evolved in hydrothermal systems may naturally remain near equilibrium with the host lithology. 24Conversely, residual liquids/brines left behind in the crust may be undersaturated with metals, enhancing 25 the rate and extent of hydrothermal alteration. 26 3 near the magma-hydrothermal interface prior to eruption (Coombs et al., 2004;le Roux et al., 2006; 49 Michael and Cornell, 1998). Such data are not only consistent with phase separation, but also phase 50...

Spatial Variations in Vent Chemistry at the Lucky Strike Hydrothermal Field, Mid‐Atlantic Ridge (37°N): Updates for Subseafloor Flow Geometry From the Newly Discovered Capelinhos Vent

“…Li and Cs distributions exhibit a negative linear trend, while Rb and Sr show a positive trend, indicating a preferential partitioning to the vapor and brine phases, respectively (Figure 4). This is in line with previous studies (Berndt & Seyfried, 1990;Foustoukos & Seyfried, 2007a;Pester et al, 2015;Pokrovski et al, 2005). This is also coherent with the LSHF study of Pester et al (2012), apart for Rb that shows less brine affinity with the extended Cl range of the present data set.…”

“…We investigate the distribution of trace element concentrations (Br, Li, Sr, Rb, and Cs) over the LSHF chlorinity range, following the methodology of Pester et al () to detect the potential occurrence of a second hydrothermal source. The elements considered are controlled by vapor/brine partition coefficients during phase separation (Berndt & Seyfried, ; Foustoukos & Seyfried, , ; Foustoukos et al, ; Pester et al, , among others). Li and Cs distributions exhibit a negative linear trend, while Rb and Sr show a positive trend, indicating a preferential partitioning to the vapor and brine phases, respectively (Figure ).…”

Organic, Gas, and Element Geochemistry of Hydrothermal Fluids of the Newly Discovered Extensive Hydrothermal Area in the Wallis and Futuna Region (SW Pacific)

“…Phase separation is of great importance in metal transportation and ore-forming processes, for example, [24,[49][50][51]. It also implies that seawater experiences dramatic changes in its physical and chemical properties as it reaches the super-or subcritical state.…”

Quartz Solubility in the Two‐Phase Region of the NaCl‐H2O System: An Experimental Study With Application to the Piccard Hydrothermal Field, Mid‐Cayman Rise

“…The reactor, heating bands, and steel cylinder are housed in a calcium-silicate furnace, and void space is filled with a ceramic fiber blanket (Pester et al, 2015). The thermocouple communicates with three external heating bands through an EZ Zone PM (Watlow Electric Manufacturing Co.) proportional-integral-derivative controller.…”

“…The heating bands attach to the outside of a steel cylinder that holds the reactor. The reactor, heating bands, and steel cylinder are housed in a calcium-silicate furnace, and void space is filled with a ceramic fiber blanket (Pester et al, 2015). The furnace is attached to a steel frame and can rotate to promote mixing (Seyfried et al, 1987).…”