AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Mississippi Valley Type (MVT) Mineralization in the Khuff "B" and "C" Reservoirs, Saudi Arabia
(1) Geological Technical Services Division, Saudi Aramco, Dhahran 31311, Saudi Arabia.
Mississippi Valley Type (MVT) mineralization consisting of small percentages of emplaced pyrite, sphalerite and galena with gangue minerals, such as saddle (baroque) dolomite, was recognized in cores of several Khuff “B” and ”C” carbonate reservoirs. In one particular case, MVT mineralization was represented by the complete replacement of some Khuff “C” carbonate beds. In this instance, MVT mineralization formed multiple thick deposits that also contained moldic porosity. X-ray diffractometry confirmed the presence of pyrite, sphalerite and galena.
In most cases where MVT mineralization was identified in Saudi Arabia, it was located within the Khuff “C” immediately above the Khuff “D” evaporite. MVT mineralization in the overlying Khuff “B” was found to have nucleated around anhydrite nodules. Major faults are thought to have been the conduit that delivered iron-, zinc- and lead-rich fluids from basement sources, red beds resting atop the basement, or from the intervening stratigraphic section. It is suspected that metal-rich fluids reacted with Khuff “D” evaporite, which provided a source of sulfur. The source of the sulfur in the Khuff “D” anhydrite or Khuff “B” evaporite nodules provided the anion necessary for the formation of MVT mineralization.
The movement of these fluids essentially created a mixing zone combining metals with sulfur as the fluids were emplaced in the Khuff during periods of deformation. Following deformation and emplacement of these minerals, ductile evaporite beds healed and formed a seal to vertical fluid flow. This seal lasted until the next deformation phase reactivated existing faults and fractures and started the process anew.