deletions | additions       diff --git a/discussion_bulk isotopes.tex b/discussion_bulk isotopes.tex  index b5e4f33..6b764d5 100644  --- a/discussion_bulk isotopes.tex  +++ b/discussion_bulk isotopes.tex 
...
\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 fluids  sourced from the sedimentary basins surrounding the Derbyshire Platform. The range 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 coincident with those we report here. The positive $\delta$^{13}C values ($\approx$+3 to +4‰_{VPDB}) and moderately depleted $\delta$^{18}O values ($\approx$-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.