Journal
GEOFLUIDS
Volume 10, Issue 3, Pages 422-437Publisher
WILEY-HINDAWI
DOI: 10.1111/j.1468-8123.2010.00295.x
Keywords
crush-leach; fluid inclusions; hydrothermal dolomite; Newfoundland
Categories
Funding
- PPSC (Pan-Atlantic Petroleum Systems Consortium)
- PRAC (Petroleum Research Atlantic Canada)
- ISPSG (Irish Shelf Petroleum Studies Group, Ireland)
- Earth Science Sector of Natural Resources Canada
- Department of Natural Resources and Mines of Newfoundland and Labrador
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Dolomite reservoirs are increasingly recognized as an important petroleum exploration target, although the application of a hydrothermal dolomite exploration model to these reservoirs remains controversial. The St. George Group of western Newfoundland consists of a sequence of dolomitised carbonates, with significant porosity development (up to 30%) and petroleum accumulations. Fluid inclusion microthermometry and bulk fluid leach analyses indicated that fluids responsible for matrix dolomitization (associated with intercrystalline porosity) and later saddle dolomitization are CaCl2 +/- MgCl2 rich, high salinity (up to 26 eq. wt% NaCl) brines. Integration of fluid inclusion data with thermal maturation histories from the St. George Group show that these dolomites formed at temperatures higher than the ambient rock temperature, and are therefore hydrothermal in origin. Bulk leach analyses show that dolomitization is associated with influxes of postevaporitic brines (+/- Cl enriched magmatic fluids) late in the diagenetic history of these carbonates. This dolomitization is possibly Devonian in age, during a period of significant magmatic activity, extensional tectonics and development of hypersaline basins. Petrographic and geochemical similarities between Paleozoic hosted hydrothermal dolomitization in western Newfoundland, eastern Canada and the northeastern United States are consistent with a regional-scale hydrothermal dolomitization event late in the diagenetic history of these carbonates. Geofluids (2010) 10, 422-437.
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