deletions | additions       diff --git a/discussion_bulk isotopes.tex b/discussion_bulk isotopes.tex  index ef67b77..02168c5 100644  --- a/discussion_bulk isotopes.tex  +++ b/discussion_bulk isotopes.tex 
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\section{Discussion}  There are four, possibly five, distinct diagenetic carbonate phases in the Visean carbonates of the Peak District \citep{Walkden_1991, Hollis_2002}. The vein carbonates at Dirtlow Rake are equivalent to the zone 4 diagenetic carbonates of this scheme. Such carbonates are associated with Pb-Zn mineralization and occur as fracture and vein fill. They are ascribed to burial diagenesis as a result of the migration of tectonically derived formation waters sourced from the sedimentary basins surrounding the Derbyshire Platform. The range ranges  of $\delta$^{13}C and $\delta$^{18}O values for zone 4 calcites reported by Hollis and Walkden (2002) for the northern margin of the platform is are  coincident with those we report here. The positive $\delta$^{13}C values ($\approx$+3 to +4‰_{VPDB}) and moderately depleted $\delta$^{18}O values (-7 ($\approx$-7  to -10‰_{VSMOW}) suggest precipitation from warm formation fluids that have evolved under closed system conditions with low water to rock ratios. We develop these ideas in the discussion using data for the clumped isotope temperature to constrain the likely source of the mineralizing fluids and outline a simple two component mixing process between formation waters from the Edale Basin and groundwaters local to the site of mineralization. We identify a temperature anomaly associated with upwelling hot waters along the Dirtlow rake fault and use a simple thermal model to estimate the necessary rates of fluid migration required to sustain the temperature anomaly. Finally, we attempt a synthesis of the data in terms of a simple basin evolution model, the development of overpressure as a result of gas generation, the initiation of seismic activity and subsequent fluid flow along high permeability rupture zones i.e. a seismic valve. \subsection{Temperature}  The data for the temperature at which calcite precipitated at Dirtlow Rake are the first measurements made for the southern Pennines using the clumped isotope technique. It's pertinent to ask if these temperatures are robust and representative of the hydrothermal fluid temperatures. We see a temperature range of 40$^{\circ}$C to 100$^{\circ}$C. The most direct comparison we can make is with fluid inclusion homogenization temperatures. Several fluid inclusion studies have been completed, largely using fluorite but also with a limited number of data points for calcite. Overall there is wide variation in the reported homogenization temperatures ranging from 60$^{\circ}$C to greater than 240$^{\circ}$C. Our temperature estimates fall towards the lower end of this range and are consistent with the homogenization temperatures reported for type 2 (62$^{\circ}$-82$^{\circ}$C), type 3 (64.9$^{\circ}$-98.9$^{\circ}$C), type 4 (63.4$^{\circ}$-106$^{\circ}$C) and type 5 (66.3$^{\circ}$-68.3$^{\circ}$C) inclusions in fluorite reported by Atkinson (1983). The type 1 inclusions reported on by Atkinson (1983) have higher homogenization temperatures of 119.5$^{\circ}$ - 157$^{\circ}$C. These are higher than the maximum temperatures we have observed for this part of the orefield. A difficulty in making a comparison is that the different types of inclusions are thought to relate to different stages in the mineral paragenesis and may not directly relate to the calcite veins at Dirtlow Rake.