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On a plot of $\delta$^{13}C versus $\delta$^{18}O the restricted range of isotopic composition of the vein is highlighted with $\delta$^{13}C and $\delta$^{18}O values between +1.5 to +3.7‰_{VPDB} and -7 to -10‰_{VPDB} respectively, Figure 6(a). There is a degree of structure in the data but given the limited data set it is hard to determine the significance of this. For the most part $\delta$^{18}O and $\delta$^{13}C are decoupled with a horizontal band of data covering a range of $\delta$^{18}O values between -8 and -10‰_{VPDB} and little or no variation in $\delta$^{13}C at a value close to +3.5‰_{VPDB}. A subset of the data with a positive 1:1 correlation between $\delta$^{13}C and $\delta$^{18}O and an outlier of three points with relatively high $\delta$^{18}O values (-7 to -8‰_{VPDB}) and low $\delta$^{13}C values (1.5 to 2‰_{VPDB})is evident.
Whilst the lowest temperature vein calcite does have the lowest $\delta$^{13}C value (32$^{\circ}$C and 1.6‰_{VPDB} there is no overall correlation between temperature and carbon isotopic composition, Figure 6(b). In contrast there is a clear inverse covariation between T($\Delta$_{47}) and $\delta$^{18}O. A change in precipitation temperature from
30$^{\circ}$ to 100${\circ}$C 30$^{\circ}$-100$^{\circ}$C is accompanied by a near 3‰ decrease in the $\delta$^{18}O value of the vein calcite from -7 to -10‰_{VPDB}, Figure 6(c).
Using the measured
T{$\Delta$_{47}) T$\Delta$_{47}) and $\delta$^{18}O values we have calculated the composition of the fluid that is in isotopic equilibrium with the samples of vein calcite. For this we used the Kim and O'Neill (1996) calibration of the calcite-water fractionation factor. The data plotted in Figure 6(d) show a marked linear covariation with data for the two sections DLR7 and DLR7(i) being the same within measurement error. At the high temperature end the calcite is in equilibrium with water at 100-110$^{circ}$C and having an enriched $\delta$^{18}O value close to +6‰_{VSMOW}. The low temperature end
(30-40$^{circ}C$) (30-40$^{\circ}$C) is characterized by more negative values of $\delta$^{18}O between -2 and -4‰_{VSMOW}.