• journal_title：Economic Geology
• Contributor：J. M. Barker ; D. E. Cochran ; R. Semrad
• Publisher：Society of Economic Geologists
• Date：1979-
• Format：text/html
• Language：en
• Identifier：10.2113/gsecongeo.74.2.484
• journal_abbrev：Economic Geology
• issn：0361-0128
• volume：74
• issue：2
• firstpage：484
• section：Articles

The Mishraq native sulfur deposit is in northern Iraq about 40 km southeast of Mosul and 315 km north of Baghdad. This deposit is the largest known occurrence of stratiform bioepigenetic sulfur, containing at least 100 million tons of elemental sulfur. It underlies a 10 km ² portion of the southeast end of a northwest-trending, doubly plunging anticline on the west bank of the Tigris River at its confluence with the Great Zab River. The deposit is in one anticline among many in the folded portion of the Mesopotamian depression and represents part of what may be the largest reserve of elemental sulfur in the world.Small, tight, en echelon folds are superimposed on the southwest limb of the Mishraq anticline with axial trends similar to the main fold (320 degrees ). Faulting is normal and reverse with dominant northwest and subordinate northeast trends. Mining-induced subsidence of 4 to 5 m causes fractures which tend to follow these preexisting directions.The sulfur mineralization is in three main zones of vuggy and bituminous bioepigenetic limestone in the basal Lower Fars Formation of middle Miocene age and marine origin. The Lower Fars consists of intercalated bituminous marine carbonates (dolomite, limestone, marl) and anhydrite/gypsum with minor shale and sandstone interbeds. The depositional environment was of periodic marine influxes followed by evaporation in a partially barred basin with southern access to the sea.The sulfur forms by oxidation of hydrogen sulfide produced during metabolysis of petroleum and anhydrite/gypsum by anaerobic bacteria (D. desulfuricans), a conclusion supported by the ³⁴ S and ¹³ C fractionation data. Sulfur mineralization is thickest in areas of intense folding and faulting which enhance solution, movement, and mixing of reactants. Combined thickness of the three sulfur-bearing zones is from 2 to 123.9 m, with a maximum ore section of 107.9 m and a grade of 23.14 wt percent sulfur. Seven ore types have been recognized of which predominant coarse crystalline sulfur alternates with bands of secondary limestone.Hydrologic conditions at the mine are complex with subsurface drainage via karst features, fractures, faults, and vuggy porosity within the ore zones of the productive member. The productive member contains the bulk of the ground water, although up to 13 aquifers have been recognized throughout the section, and it is intersected by the Tigris River. A very steep hydraulic gradient exists with flow southeastward toward the Tigris where it is discharged from springs in and beside the river. Hydrogen sulfide-carbonate waters predominate. Recharge is mainly at the northwest portion of the anticline where the Lower Fars crops out. The ground water connection and flow to the river is important in sulfur generation as it is the pathway by which oxygen is carried into contact with hydrogen sulfide at depth yielding sulfur and water.The deposit is currently being mined by the Polish hydrodynamic (modified Frasch) process at a rate of about 600,000 tons per annum out of a total capacity of 1,000,000 tons per annum. The maximum capacity has not been reached because of infrastructural constraints related to transportation and because the mine is difficult to operate. Large injection water losses and excessive bitumen contamination are paramount. Water losses are mitigated by the installation of subsurface impermeable screens. Bentonite/sulfuric acid filtration removes the excess bitumen but at a cost of 8 to 25 percent loss of sulfur in filter cake and skim foam.Initially sulfur was vatted at the mine, crushed, and shipped via rail to the port of Um Qasr about 1,000 km south of Mishraq. Liquid sulfur is currently shipped to the port where vatting is done as necessary.