Lyell Collection
Journal of the Geological Society
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by JASSIM, S. Z.
Right arrow Articles by BOTTRELL, S. H.
Right arrow Search for Related Content
Journal of the Geological Society; 1999; v. 156; issue.1; p. 25-39;
DOI: 10.1144/gsjgs.156.1.0025
© 1999 Geological Society of London

Article

Genesis of the Middle Miocene stratabound sulphur deposits of northern Iraq

S. Z. JASSIM, R. RAISWELL & S. H. BOTTRELL

Department of Earth Sciences, Leeds University, Leeds LS2 9JT, UK (email: jassim{at}earth.leeds.ac.uk)

Stratabound sulphur deposits of northern Iraq occur in folded Middle Miocene evaporites overlying Lower Miocene hydrocarbon reservoirs. Rocks hosting sulphur mainly comprise gypsum, dolomitic marl, carbonate mudstones and bioclastic dolomitized limestones, whereas the mineralized rocks are mainly composed of calcite and sulphur. Sulphur was formed by the oxidation of H2S produced from gypsum dissolution followed by sulphate reduction in the presence of hydrocarbons. Sulphate reduction occurred in a partially closed to closed system as reflected by the sulphur {delta}34S values of +7{per thousand} to +20{per thousand} (original gypsum +21{per thousand}). Host rock carbonates were calcitized by the dissolved carbonate formed by oxidation of the hydrocarbons, which produced low {delta}13C values ( – 14 to – 32{per thousand}). Periodic invasion by meteoric water and elevated temperatures produced 18O-depleted compositions for the newly-formed calcite (down to – 9{per thousand}) and dolomite (down to – 7{per thousand}), and oxidized the H2S produced during sulphate reduction.

These sulphur deposits formed through the favourable stratigraphic juxtaposition of gypsum sulphate, brines and hydrocarbons. Tectonically produced fracture permeability in carbonates allowed rising brines from the underlying hydrocarbon reservoirs to mix with laterally migrating and descending, sulphate-bearing meteoric waters and produced the oscillating redox conditions needed for the bacterial reduction of sulphate and the oxidation of sulphide.


Keywords: Iraq, sulphur, isotopes.