UV-vis spectrophotometric measurements, potentiometric titrations, and solubility measurements were performed to evaluate the hydrolysis constants for aqueous Fe(III) and the solubility of 2-line ferrihydrite over a wide concentration range (0-3 M NaClO4 and p[H+] 1.54-11.23). From these measurements, Fe3+ was found to hydrolyze to form FeOH2+, Fe2(OH)24+, Fe(OH)2+, Fe(OH)3(0), and Fe(OH)4-. The hydrolysis and solubility constants of these species were determined together with their dependence on ionic strength. The iron (III) hydrolysis constants at infinity dilution were (logbeta(1,1) to logbeta(1,4) and logbeta(2,2))-2.19 +/- 0.02, -5.76 +/- 0.06, -14.30 +/- 0.32, -21.71 +/- 0.24, and -2.92 +/- 0.02, respectively. The solubility product for 2-line ferrihydrite was (logK(s,0)) +3.50 +/- 0.20. The results have been compared with literature values.

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The effusive six months long 2014-2015 Bárðarbunga eruption (31 August-27 February) was the largest in Iceland for more than 200 years, producing 1.6 ± 0.3 km 3 of lava. The total SO 2 emission was 11 ± 5 Mt, more than the amount emitted from Europe in 2011. The ground level concentration of SO 2 exceeded the 350 µg m −3 hourly average health limit over much of Iceland for days to weeks. Anomalously high SO 2 concentrations were also measured at several locations in Europe in September. The lowest pH of fresh snowmelt at the eruption site was 3.3, and 3.2 in precipitation 105 km away from the source. Elevated dissolved H 2 SO 4 , HCl, HF, and metal concentrations were measured in snow and precipitation. Environmental pressures from the eruption and impacts on populated areas were reduced by its remoteness, timing, and the weather. The anticipated primary environmental pressure is on the surface waters, soils, and vegetation of Iceland.

Figure 1. Phase stabilities in NaCl ؉ H 2 O fluid system, emphasizing two-phase coexistence surface (vapor ؉ brine; gridded by isopleths and isotherms; Driesner and Heinrich, 2003). Critical curve (heavy gray line at crest of two-phase surface) swings from high salinities at high pressure and temperature (P, T ) across to lower salinities at low P and T. Hot vapor-like fluid (V) of low to medium salinityoriginating from slightly above two-phase surface or coexisting with brine (B) along that surface-can be cooled and contracted to an aqueous liquid (L) without heterogeneous phase change provided that, during this stage of cooling, P remains above two-phase surface (arrows in 7% NaCl plane). Backface shows projection of critical curve (thick gray), halite saturation envelope (thin line), and one P-T path, including isobaric cooling interval (long arrow segment) modeled in Figure 2. ABSTRACTFluid-phase stability relations combined with thermodynamic modeling using fluid-inclusion analyses and new gold-solubility experiments lead to an integrated geological interpretation linking epithermal gold mineralization and porphyry-style ore formation to the cooling of hydrous magma chambers. The essential chemical requirement for gold transport to low temperatures is an initial excess of sulfide over Fe in the magmatic fluid, which is best achieved by condensing out Fe-rich brine from a buoyant, low-to medium-salinity vapor enriched in volatile S. This vapor can contract directly to an aqueous liquid, by cooling at elevated pressure above the critical curve of the salt-water fluid system. Physical and chemical conditions are matched when magmatic fluid is released through a gradually downward-retracting interface of crystallizing magma beneath a porphyry stock, predicting the consistent zoning and overprinting relations of alteration and mineralization observed in magmatic hydrothermal systems.

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River, ground, and peat water from a basaltic catchment area, Laxá in Kjó s Southwest Iceland, were sampled and analyzed for major element concentrations to define the effect of glassy versus crystalline basalt, the formation of secondary minerals, and runoff on fluxes of dissolved elements to the ocean. The proportions of the dissolved solids in the water samples derived from precipitation, air, and rock weathering were estimated. The amounts of Na, Mg, Ca, K, and S originating from precipitation were calculated from the respective solute/Cl marine ratios and the estimated aqueous Cl originated from precipitation, which was calculated using measured B content of the waters and B/Cl molal marine and rock ratios. The rock contribution from weathering ranged from 22 to 46 percent of the total dissolved solids of the waters. Iron and Al showed low mobility compared to Na. This was primarily due to consumption of these elements by ferrihydroxides, allophane, imogolite, and clay minerals. Also, Si and to a lesser degree Ca show apparent slightly lower mobility than Na. These results are in good agreement with these phases being dominant in the soils of the study area (Wada and others, 1992) and the main secondary minerals of basaltic glass in Iceland (Crovisier and others, 1992). Reaction progress calculations support these findings. According to a model interaction of basaltic glass and meteoric water Al, Fe, and Si are consumed by amorphous Fe and Al hydroxides and imogolite and allophane at low reaction progress. With increasing reaction progress, CaFe -Mg smectite became the primary secondary minerals, limiting the mobility of Ca, Fe, Mg, Si, and Al. These findings suggest that the weathering in the Laxá in the Kjó s catchment area has evolved into the beginning of the smectite weathering stage and that it is dominated by a relatively low reaction progress and a high water to rock ratio. In the present study the effect of runoff and rock crystallinity was quantified for dissolved elemental fluxes. Temperature, lithology (other than rock crystallinity), and rock age were similar in all of the catchment areas in this study. Silica, Ca, F, S, Al, K, Mg, and B had a very similar dependence on runoff. On the other hand, Na fluxes were found to be less dependent on runoff, and Fe fluxes were found to be independent of runoff. Basaltic glass dissolves faster than fully crystallized basaltic rocks (Gíslason and Eugster, 1987a). Therefore, increased glass content of the primary rocks is thought to increase the leaching and elemental fluxes at constant runoff. However, because some of the solutes, particularly Al and Fe, were highly influenced or even controlled by the formation of secondary minerals, this increasing dissolution with increasing glass content was hidden. On the other hand, basaltic glass was observed to enhance the fluxes of more mobile elements like Na, Si, Ca, F, and S by a factor of 2 to 5 at a constant runoff of 200 cm/yr, constant vegetative cover, and 0 to 100 percent glass content of the rocks. The

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