The Clarke Lake gas field, one of the largest gas fields in western Canada, is hosted in pervasively dolomitized Middle Devonian carbonates of the Slave Point Formation. The reservoir displays a highly complex paragenetic sequence. In addition to multiple phases of dolomite (matrix and saddle dolomite), late diagenetic phases included sphalerite, galena, quartz, and sparry calcite cement. A proper characterization and interpretation of dolomitization and commensurate porosity-permeability development should improve exploration success and enhance gas recovery throughout the region, and may lead to a new model for dolomitization.

Both dolomite phases have identical oxygen and Sr isotope compositions: d¹⁸O range from –16 to –13‰ VPDB, and ⁸⁷Sr/⁸⁶Sr ratios range from 0.7087 to 0.7167. Fluid inclusions contain  complex Ca-Cl brines and have T_h values between 140 and 190ºC. T_h and d¹⁸O values together indicate precipitation from evaporated seawater with d¹⁸O between -1 and +4‰ VSMOW.      

The present formation fluids bear seemingly incompatible ionic and/or isotopic characteristics.  Their composition suggests a modified seawater component that is depleted in Mg and enriched in Ca, but dD values range from –135 to –60‰ VSMOW, which is characteristic of mixing between meteoric and metamorphic/basement fluids. Furthermore, the ⁸⁷Sr/⁸⁶Sr ratios suggest a contribution of at least two distinct fluids, one that travelled through underlying clastics, and another that has interacted with basement rocks. Apparently, the fluid(s) responsible for dolomitization were flushed from the system, and the present formation fluids are of mixed origin of at least two end members.