Abstract: Petroleum and Mississippi Valley Type Ore Deposits--Common Origin?
Alden B. Carpenter, Tom Freeman
The following facts suggest that localizations of petroleum in carbonate rocks and Mississippi Valley type ore deposits may have, in part, a common origin. (1) Sphalerite in many MV type ore deposits contains inclusions of oil, and sphalerite is common as disseminated crystals in petroleum reservoirs in carbonate rocks. (2) The mineralogy and diagenetic histories of rocks that host petroleum and MV type ore deposits are remarkably similar. (3) The chemical composition of petroleum-related brines is very much like that of fluid inclusions in sphalerite in MV type deposits. (4) Many deposits of petroleum and MV type deposits appear to be related genetically to the distribution of dolostone.
Data indicate that the brines were derived from seawater from which halite was precipitated and that these brines were modified further by reactions with calcite, feldspars, and clay minerals. The brines are believed to have been instrumental both in the delivery of metals and in the dolomitization of host rocks. Migration of the brines was, in some instances, upward (from evaporite deposits) along fractures related to diapiric structures. In other cases, brines moved downward (from evaporite deposits) along major faults.
Investigation of the chemical evolution and migration of brines associated with halite-bearing evaporites has provided new insights into the origin of Mississippi Valley type ore deposits and some petroleum localizations. This approach shows promise of becoming an important exploration tool.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC