A dolomite body may form for the first time at the surface or in the subsurface and it may generate or lose porosity a number of times in its burial history.
Depositional settings include;sabkhas, salinas,salterns, humid subtidal mud shoals and evaporitefree schizohaline lakes. The resulting dolomites are typically fine-grained or mimetic with sedimentary structures indicative of their depositional setting.Bacterial mediation is significant in precipitating dolomite in most earth surface and some shallow
subsurface settings.
Diagenetic settings include the shallow seafloor,shallow burial marine (connate) settings, the interiors of atolls, mixing zones between waters of differing salinities, zones of brine reflux, and deep burial settings. Later formed diagenetic dolomites are coarser-grained than depositional dolomites and the geometries of the various bodies reflect the formative
subsurface hydrologies.
Dolomites with well-developed intercrystalline porosity make excellent hydrocarbon reservoirs.Many such reservoirs have an intimate association with evaporites. This reflects both the likelihood ofthe dolomite forming by brine reflux
platform,strand-zone and basin-center evaporite hydrologies.
and the ability of evaporites to form effective seals to permeable intervals. Nonevaporitic dolomite reser voirs typically formed via fracturing or karstification.Many dolomite reservoirs can be related to regional unconformities.
Late diagenetic dolomite burial and hydrother-mal. can act as an ore host. Many MVT deposits are hosted in such dolomites. Typically, the same solutions that formed the burial dolomite host were also capable of carrying metals. Where a suitable structural focus and redox system coincide, ore deposits form in a burial dolomite host. Dolomite hosts also form as skarns, mantos and during metamorphism.
In summary, dolomite is a complex mineral that evolves throughout its burial history. It does so by a series of dissolution–reprecipitation reactions that favor the retention of intergranular porosity. Hence,it is often an excellent reservoir for hydrocarbons or a host rock to base metal ores.
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