Alkaline sulphate fluids produced in a magmatic hydrothermal system

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Fig. 3: Histogram of δ 34 S values of spring sulphate and native sulphur samples from Savo. Fig. 4: δD H2O vs. δ 18 O H2O for springs and wells. Error bars represent one standard deviation from mean value for samples analysed in triplicate; most are within symbol size. Arrows indicate enrichment trends produced by evaporation, particularly important for acid sulphate springs and alkaline sulphate outliers (the two samples to the right of the main cluster of alkaline sulphate data); mixing with a magmatic fluid; equilibration with host rocks; and boiling. Magmatic mixing trend uses fluid composition of δ18O = 6‰ (typical value for host rocks; Smith, 2009), δD = −20‰ ("andesitic water"; Giggenbach, 1992). 34
Fig. 5: 87 Sr/ 86 Sr versus δ 34 S SO4 for hot springs and seawater (this study). Range of whole rock 87 Sr/ 86 Sr for local unaltered rocks also shown (Smith et al., 2009). Fig. 6: Na–Mg–K ternary diagram, after Giggenbach (1988). Full equilibrium line plotted by intersection of Na/K and K/Mg isotherms (plotted at 20°C intervals as fine dotted and dashed lines respectively, 100° and 260°C intersections marked). Rock dissolution field shows fluid compositions expected by isochemical dissolution of unaltered host rock (trachytes and mugearites; Petterson et al., 2003; Smith et al., 2009). Hot spring waters from Savo plot as immature waters, but define a chord trending back towards 260–300°C equilibrium. 35
Page 1 and 2: Alkaline sulphate fluids produced i
Page 3 and 4: low-chloride fluids which precipita
Page 5 and 6: timescales of a few minutes, and in
Page 7 and 8: 3 Sampling and Analytical Methods 3
Page 9 and 10: Comparison of SO 2− 4 as determin
Page 11 and 12: isotopes were measured relative to
Page 13 and 14: enrichment of both 18 O and D, and
Page 15 and 16: average meteoric water composition
Page 17 and 18: The thermometer discrepancies indic
Page 19 and 20: same process. Evidence of mixing in
Page 21 and 22: the addition of magmatic volatiles
Page 23 and 24: The Black Pool in the crater of El
Page 25 and 26: Dilution is the key process whereby
Page 27 and 28: Coleman, M.L. and Moore, M.P., 1978
Page 29 and 30: Petterson, M.G., Cronin, S.J., Tayl
Page 31 and 32: 9 Tables Table 1: Data for Crater W
Page 33: temperature >30°C) are shaded; the
Page 37 and 38: Fig. 8: Plots showing effects of mi

Alkaline sulphate fluids produced in a magmatic hydrothermal system

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