deletions | additions       diff --git a/discussion_fluids2.tex b/discussion_fluids2.tex  index 097d6a8..3b6e1f2 100644  --- a/discussion_fluids2.tex  +++ b/discussion_fluids2.tex 
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At a temperature of 100$^{\circ}$C a pore fluid in equilibrium with the shale has a $\delta$^{18}O $\delta^{18}$O  value of $\approx$5‰_{VSMOW} $\approx$5‰$_{VSMOW}$  in good agreement with the derived fluid isotope composition determined using T($\Delta$_{47}) T($\Delta_{47}$)  and the $\delta$^{18}O $\delta^{18}$O  value of the vein calcite. None of the assumptions we have made in this calculation are unreasonable. Both the clay mineral content and bulk rock isotope values for shales are close to +20‰_{VSMOW}. +20‰$_{VSMOW}$.  Using the excess He content of fluids trapped in fluid inclusions Kendrick et al. (2002) have estimated typical pore water residence times for the Edale Gulf fluids of as much as 50Ma allowing plenty of time for the pore water to come to thermal equilibrium with detrital and authigenic clay minerals. We are reassured that the derived fluid $\delta$^{18}O values are consistent with our understanding of the isotopic compositions of naturally occurring fluids and suggests that the clumped isotope temperatures are robust. For example were the calcite temperatures to have been as high as the maximum reported fluid inclusion homogenization temperatures of 240$^{\circ}$C then the derived fluid $\delta$^{18}O values would need to have been in excess of 18 - 20‰_{VSMOW}. Such values are in excess of any reported data for modern geothermal and formation waters \citep{Sheppard:1986ta}.   That mineral precipitation is from a two component fluid is confirmed in Figure 8. Here we have taken the data plotted in Figure 5(c) (T($\Delta$_{47}) (T($\Delta_{47}$)  versus $\delta$^{18}O $\delta^{18}$O  of the vein calcite) and superposed two trends. The first is for the expected composition of calcite precipitated from a mixed fluid consisting of a high temperature formation water and a meteoric groundwater. The two end members were determined from the line of best fit to the data in Figure 6(c) and assuming cold and hot end members of 30 and 100$^{\circ}$C. The second trend line describes the expected calcite oxygen isotope composition as the result of precipitation from a fluid cooling from the high temperature end member composition. The data, well described by the mixing model, are clearly inconsistent with precipitation from a cooling high temperature fluid.