Lonnee, Jeff1, Hans G. Machel1
(1) University of Alberta, Edmonton, AB
ABSTRACT: Hydrothermal Dolomite Model - Old Concept and New Challenges
The latest dolomite bandwagon is the "Hydrothermal Dolomite model", which is based on the more general and time-honored concept of base metal mineralization from hydrothermal fluids. Hydrothermal dolomitization may occur in a variety of geologic settings, but it has been significantly overrated. Many alleged “hydrothermal dolomites” are not hydrothermal, or proof of a hydrothermal origin has not been provided.
The challenge is to provide proof of hydrothermal mineralization, which requires comparison of the temperature of mineralization with that in the surrounding strata. A mineral is hydrothermal, if it can be demonstrated to have formed at a temperature that is significantly higher (>5oC) than ambient, regardless of fluid source or drive. This definition does not carry a lower or upper temperature limit. Even a dolomite formed at 40oC could be hydrothermal. By extension, dolomites formed at temperatures lower than ambient are not hydrothermal, even if they formed at temperatures of higher than 100oC.
In the Western Canada Sedimentary Basin, almost all dolomites and dolostones have recently been (re-)interpreted as hydrothermal, based on petrographic observations alone. However, in the southern half of the basin there is no evidence of hydrothermal dolomitization, except in a few, isolated, and volumetrically insignificant locations. Conversely, large bodies of hydrothermal dolomites are known to occur in the northern part of the basin. Some of these, e.g. Slave Point at Clarke Lake, are prolific gas reservoirs. Most hydrothermal dolomites forms massive dolostones that are localized around faults, but regional or basin-wide dolomitization is not hydrothermal.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.